Cutting Tool Applications

Cutting

Tool

Applications

Cutting Tool Applications

By George Schneider, Jr. CMfgE

2 Tooling & Production/Chapter 1 www.toolingandproduction.com

1.1 IntroductionMany types of tool materials, ranging from high carbon steel to ceramics and dia-monds, are used as cutting tools in today’s metalworking industry. It is importantto be aware that differences do exist among tool materials, what these differencesare, and the correct application for each type of material.

The various tool manufacturers assign many names and numbers to their prod-ucts. While many of these names and numbers may appear to be similar, the appli-cations of these tool materials may be entirely different. In most cases the tool man-ufacturers will provide tools made of the proper material for each given application.In some particular applications, a premium or higher priced material will be justi-fied.

This does not mean that the most expensive tool is always the best tool. Cuttingtool users cannot afford to ignore the constant changes and advancements that arebeing made in the field of tool material technology. When a tool change is neededor anticipated, a performance comparison should be made before selecting the toolfor the job. The optimum tool is not necessarily the least expensive or the mostexpensive, and it is not always the same tool that was used for the job last time.The best tool is the one that has been carefully chosen to get the job done quickly,efficiently and economically.

Author’s NoteI wish to express my sincere appreciation to Prentice Hall and to Stephen Helba

in particular, for giving me permission to use some of the information, graphs andphotos recently published in Applied Manufacturing Process Planning authored byDonald H. Nelson and George Schneider, Jr.

The author also wishes to thank over 40 companies who have provided technicalinformation and photo exhibits...their contributions have made this reference textpossible.

And finally, I would like to express my appreciation to Tooling & Production’sStan Modic and Joe McKenna for giving me the opportunity to make this informa-tion available to the general public.

George Schneider, Jr.

Chapter 1

Cutting-Tool

Materials

George Schneider, Jr. CMfgEProfessor Emeritus

Engineering TechnologyLawrence Technological University

Former ChairmanDetroit Chapter ONE Society of Manufacturing Engineers

Former PresidentInternational Excutive BoardSociety of Carbide & Tool Engineers

Lawrence Tech. Univ.: www.ltu.edu

Prentice Hall: www.prenhall.com

Upcoming Chapters

Metal RemovalCutting-Tool Materials

Metal Removal MethodsMachinability of Metals

Single Point MachiningTurning Tools and Operations

Turning Methods and MachinesGrooving and Threading

Shaping and Planing

Hole Making ProcessesDrills and Drilling Operations

Drilling Methods and MachinesBoring Operations and Machines

Reaming and Tapping

Multi Point MachiningMilling Cutters and OperationsMilling Methods and Machines

Broaches and BroachingSaws and Sawing

Abrasive ProcessesGrinding Wheels and OperationsGrinding Methods and Machines

Lapping and Honing

A cutting tool must have the follow-ing characteristics in order to producegood quality and economical parts:

Hardness: Hardness and strength ofthe cutting tool must be maintained atelevated temperatures also called HotHardness

Toughness: Toughness of cuttingtools is needed so that tools don’t chipor fracture, especially during interrupt-ed cutting operations.

Wear Resistance: Wear resistancemeans the attainment of acceptable toollife before tools need to be replaced.

The materials from which cutting

tools are made are all characteristicallyhard and strong. There is a wide rangeof tool materials available for machin-ing operations, and the general classifi-cation and use of these materials are ofinterest here.

1.2 Tool Steels and Cast AlloysPlain carbon tool steel is the oldest ofthe tool materials dating back hundredsof years. In simple terms it is a highcarbon steel (steel which contains about1.05% carbon). This high carbon con-tent allows the steel to be hardened,offering greater resistance to abrasivewear. Plain high carbon steel served itspurpose well for many years. However,because it is quickly over tempered(softened) at relatively low cutting tem-peratures, (300 to 500 degrees F), it isnow rarely used as cutting tool materialexcept in files, saw blades, chisels, etc.The use of plain high carbon steel islimited to low heat applications.

High Speed Tool Steel: The need fortool materials which could withstandincreased cutting speeds and tempera-

Chap. 1: Cutting-Tool Materials

www.toolingandproduction.com Chapter 1/Tooling & Production 3

tures, led to the development of highspeed tool steels (HSS). The major dif-ference between high speed tool steeland plain high carbon steel is the addi-tion of alloying elements to harden andstrengthen the steel and make it moreresistant to heat (hot hardness).

Some of the most commonly usedalloying elements are: manganese,chromium, tungsten, vanadium, molyb-denum, cobalt, and niobium (columbi-um). While each of these elements willadd certain specific desirable character-istics, it can be generally stated that theyadd deep hardening capability, high hot

hardness, resistance to abrasive wear,and strength, to high speed tool steel.These characteristics allow relativelyhigher machining speeds and improvedperformance over plain high carbonsteel.

The most common high speed steelsused primarily as cutting tools are divid-ed into the M and T series. The M seriesrepresents tool steels of the molybde-num type and the T series representsthose of the tungsten type. Althoughthere seems to be a great deal of simi-larity among these high speed steels,each one serves a specific purpose andoffers significant benefits in its specialapplication.

An important point to remember isthat none of the alloying elements foreither series of high speed tool steels isin abundant supply and the cost of theseelements is skyrocketing. In addition,U.S. manufacturers must rely on foreigncountries for supply of these veryimportant elements.

Some of the high speed steels arenow available in a powdered metal

(PM) form. The difference betweenpowdered and conventional metals is inthe method by which they are made.The majority of conventional highspeed steel is poured into an ingot andthen, either hot or cold, worked to thedesired shape. Powdered metal isexactly as its name indicates. Basicallythe same elements that are used in con-ventional high speed steel are preparedin a very fine powdered form. Thesepowdered elements are carefully blend-ed together, pressed into a die underextremely high pressure, and then sin-tered in an atmospherically controlledfurnace. The PM method of manufac-turing cutting tools is explained inSection 1.3.1 Manufacture of CarbideProducts.

HSS Surface Treatment: Many sur-face treatments have been developed inan attempt to extend tool life, reducepower consumption, and to controlother factors which affect operatingconditions and costs. Some of thesetreatments have been used for manyyears and have proven to have somevalue. For example, the black oxidecoatings which commonly appear ondrills and taps are of value as a deterrentto build-up on the tool. The black oxideis basically a ‘dirty’ surface which dis-courages the build-up of work material.

One of the more recent developmentsin coatings for high speed steel is titani-um nitride by the physical vapor deposi-tion (PVD) method. Titanium nitride isdeposited on the tool surface in one ofseveral different types of furnace at rel-atively low temperature, which does notsignificantly affect the heat treatment(hardness) of the tool being coated.This coating is known to extend the lifeof a cutting tool significantly or to allowthe tool to be used at higher operatingspeeds. Tool life can be extended by asmuch as three times, or operatingspeeds can be increased up to fifty per-cent.

Cast Alloys: The alloying elementsin high speed steel, principally cobalt,chromium and tungsten, improve thecutting properties sufficiently, that met-allurgical researchers developed the castalloys, a family of these materials with-out iron.

A typical composition for this class oftool material was 45 percent cobalt, 32percent chromium, 21 percent tungsten,and 2 percent carbon. The purpose ofsuch alloying was to obtain a cuttingtool with hot hardness superior to high

Ceramics

Cast alloys

2000 400 600 800 1000 1200 1400

60

55

65

70

75

80

25

30

35

40

45

50

55

60

65

70

20

85

90

95100 300

Carbides

Carbontool

steels High-speedsteels

500 700

Temperature (˚F)

Temperature (C˚)

Har

dnes

s (H

-Ra)

Har

dnes

s (H

-Rc)

(a)

Diamond, CBN

Aluminum oxide (HIP)Silicon nitride

CermetsCoated carbides

Carbides

Strength and toughness

(b)

HSS

Hot

har

dnes

s an

d w

ear

resi

stan

ce

Figure 1.1. (a) Hardness of various cutting-tool materials as a function of temperature. (b)Ranges of properties of various groups of materials.


4 Tooling & Production/Chapter 1 2001 www.toolingandproduction.com

speed steel.When applying cast alloy tools, their

brittleness should be kept in mind andsufficient support should be provided atall times. Cast alloys provide high abra-sion resistance and are thus useful forcutting scaly materials or those withhard inclusions.

1.3 Cemented Tungsten CarbideTungsten carbide was discovered byHenri Moissan in 1893 during a searchfor a method of making artificial dia-monds. Charging sugar and tungstenoxide, he melted tungsten sub-carbidein an arc furnace. The carbonized sugarreduced the oxide and carburized thetungsten. Moissan recorded that thetungsten carbide was extremely hard,approaching the hardness of diamondand exceeding that of sapphire. It wasmore than 16 times as heavy as water.The material proved to be extremelybrittle and seriously limited its industri-al use.

Commercial tungsten carbide with 6percent cobalt binder was first producedand marketed in Germany in 1926.Production of the same carbide began inthe United States in 1928 and in Canadain 1930.

At this time, hard carbides consistedof the basic tungsten carbide systemwith cobalt binders. These carbidesexhibited superior performance in themachining of cast iron, nonferrous, andnon metallic materials, but were disap-pointing when used for the machiningof steel.

Most of the subsequent developmentsin the hard carbides have been modifi-

cations of the original patents, princi-pally involving replacement of part orall of the tungsten carbide with othercarbides, especially titanium carbideand/or tantalum carbide. This led to thedevelopment of the modern multi-car-bide cutting tool materials permittingthe high speed machining of steel.

A new phenomenon was introducedwith the development of the cementedcarbides, again making higher speedspossible. Previous cutting tool materi-als, products of molten metallurgy,depended largely upon heat treatmentfor their properties and these propertiescould, in turn, be destroyed by furtherheat treatment. At high speeds, andconsequently high temperatures, theseproducts of molten metallurgy failed.

A different set of conditions existswith the cemented carbides. The hard-ness of the carbide is greater than that ofmost other tool materials at room tem-perature and it has the ability to retain ithardness at elevated temperatures to agreater degree, so that greater speedscan be adequately supported.

1.3.1 Manufacture of Carbide Products

The term “tungsten carbide” describes acomprehensive family of hard carbidecompositions used for metal cuttingtools, dies of various types, and wearparts. In general, these materials arecomposed of the carbides of tungsten,titanium, tantalum or some combinationof these, sintered or cemented in amatrix binder, usually cobalt.

Blending: The first operation afterreduction of the tungsten compounds totungsten metal powder is the milling oftungsten and carbon prior to the carbur-izing operation. Here, 94 parts byweight of tungsten and 6 parts byweight of carbon, usually added in theform of lamp black, are blended togeth-er in a rotating mixer or ball mill. Thisoperation must be performed undercarefully controlled conditions in orderto insure optimum dispersion of the car-bon in the tungsten. Carbide BlendingEquipment, better known as a Ball Mill,is shown in Figure 1.2.

In order to provide the necessarystrength, a binding agent, usually cobalt(Co) is added to the tungsten (WC) inpowder form and these two are ballmilled together for a period of severaldays, to form a very intimate mixture.Careful control of conditions, including

time, must be exercised to obtain a uni-form, homogeneous product. BlendedTungsten Carbide Powder is shown inFigure 1.3.

Compacting: The most commoncompacting method for grade powdersinvolves the use of a die, made to theshape of the eventual product desired.The size of the die must be greater thanthe final product size to allow fordimensional shrinkage which takesplace in the final sintering operation.These dies are expensive, and usuallymade with tungsten carbide liners.Therefore sufficient number of the finalproduct (compacts) are required, to jus-tify the expense involved in manufac-turing a special die. Carbide

Figure 1.2. Carbide blending equipment,better known as ball mill is used to ensureoptimum dispersion of the carbon withinthe tungsten. (Courtesy American NationalCarbide Co)

Figure 1.3. Blended tungsten carbide pow-der is produced by mixing tungsten carbide(WC) with a cobalt (Co) binder in a ballmilling process. (Courtesy AmericanNational Carbide Co)

Figure 1.4. Carbide compacting equipment,better known as a pill press, is used to pro-duce carbide products in various shapes.(Courtesy American National Carbide Co)



Compacting Equipment, better knownas a Pill Press, is shown in Figure 1.4.Various pill pressed carbide parts areshown in Figure 1.5.

If the quantities are not high, a largerbriquette, or billet may be pressed. Thisbillet may then be cut up (usually afterpre-sintering) into smaller units andshaped or preformed to the requiredconfiguration, and again, allowancemust be made to provide for shrinkage.Ordinarily pressures used in these coldcompacting operations are in the neigh-borhood of 30,000 PSI. Various carbidepreformed parts are shown in Figure1.6.

A second compacting method is thehot pressing of grade powders ingraphite dies at the sintering tempera-ture. After cooling, the part has attained

full hardness. Because the graphite diesare expendable, this system is generallyused only when the part to be producedis too large for cold pressing and sinter-ing.

A third compacting method, usuallyused for large pieces, is isostatic press-ing. Powders are placed into a closed,flexible container which is then sus-pended in a liquid in a closed pressurevessel. Pressure in the liquid is built upto the point where the powders becomeproperly compacted. This system isadvantageous for pressing large pieces,because the pressure acting on the pow-ders operates equally from all direc-tions, resulting in a compact of uniformpressed density.

Sintering: Sintering of tungsten -cobalt (WC-Co) compacts is performedwith the cobalt binder in liquid phase.The compact is heated in hydrogenatmosphere or vacuum furnaces to tem-peratures ranging from 2500 to 2900degrees Fahrenheit, depending on thecomposition. Both time and tempera-ture must be carefully adjusted in com-bination, to effect optimum control overproperties and geometry. The compactwill shrink approximately 16 percent onlinear dimensions, or 40 percent in vol-ume. The exact amount of shrinkagedepends on several factors includingparticle size of the powders and thecomposition of the grade. Control ofsize and shape is most important and isleast predictable during the coolingcycle. This is particularly true with

those grades of cemented carbides withhigher cobalt contents.

With cobalt having a lesser densitythan tungsten, it occupies a greater partof the volume than would be indicatedby the rated cobalt content of the grade;and because cobalt contents are general-ly a much higher percentage of the massin liquid phase, extreme care is requiredto control and predict with accuracy themagnitude and direction of shrinkage.Figure 1.7 shows carbide parts beingloaded into a Sintering Furnace.

Figure 1.5. Various carbide compacts,which are produced with special diesmounted into pill presses. (CourtesyAmerican National Carbide Co)

Figure 1.6. If quantities are not high, presin-tered billets are shaped or preformed intorequired shapes. (Courtesy DurametCorporation)

Figure 1.7. Carbide parts are loaded into asintering furnace, where they are heated totemperatures ranging from 2500° to2900°F. (Courtesy American NationalCarbide Co)

Figure 1.8. Schematic diagram of the cemented tungsten carbide manufacturing process.



A more detailed schematic diagramof the cemented tungsten carbide manu-facturing process is shown in Figure1.8.

1.3.2 Classification of Carbide ToolsCemented carbide products are classi-fied into three major grades:

Wear Grades: Used primarily indies, machine and tool guides, and insuch everyday items as the line guideson fishing rods and reels; anywheregood wear resistance is required.

Impact Grades: Also used for dies,particularly for stamping and forming,and in tools such as mining drill heads.

Cutting Tool Grades: The cuttingtool grades of cemented carbides aredivided into two groups depending ontheir primary application. If the carbideis intended for use on cast iron which isa nonductile material, it is graded as acast iron carbide. If it is to be used tocut steel, a ductile material, it is gradedas a steel grade carbide.

Cast iron carbides must be moreresistant to abrasive wear. Steel car-bides require more resistance to crater-ing and heat. The tool wear characteris-tics of various metals are different,thereby requiring different tool proper-ties. The high abrasiveness of cast ironcauses mainly edge wear to the tool.The long chip of steel, which flowsacross the tool at normally higher cut-ting speeds, causes mainly cratering andheat deformation to the tool. Tool wearcharacteristics and chip formation willbe discussed in Chapter 2.

It is important to choose and use thecorrect carbide grade for each job appli-cation. There are several factors thatmake one carbide grade different fromanother and therefore more suitable fora specific application. The carbidegrades may appear to be similar, but thedifference between the right and wrongcarbide for the job, can mean the differ-ence between success and failure.

Figure 1.8 illustrates how carbide ismanufactured, using pure tungsten car-bide with a cobalt binder. The puretungsten carbide makes up the basic car-bide tool and is often used as such, par-ticularly when machining cast iron.This is because pure tungsten carbide isextremely hard and offers the best resis-tance to abrasive wear.

Large amounts of tungsten carbideare present in all of the grades in the twocutting groups and cobalt is always usedas the binder. The more common alloy-

ing additions to the basictungsten/cobalt material are: tantalumcarbide, and titanium carbide.

While some of these alloys may bepresent in cast iron grades of cuttingtools, they are primarily added to steelgrades. Pure tungsten carbide is themost abrasive-resistant and will workmost effectively with the abrasivenature of cast iron. The addition of thealloying materials such as tantalum car-bide and titanium carbide offers manybenefits:

• The most significant benefit of tita-nium carbide is that it reduces cra-tering of the tool by reducing the ten-dency of the long steel chips to erodethe surface of the tool.• The most significant contribution oftantalum carbide is that it increasesthe hot hardness of the tool which, inturn, reduces thermal deformation.Varying the amount of cobalt binder

in the tool material largely affects boththe cast iron and steel grades in threeways. Cobalt is far more sensitive toheat than the carbide around it. Cobaltis also more sensitive to abrasion andchip welding. Therefore, the morecobalt present, the softer the tool is,making it more sensitive to heat defor-mation, abrasive wear, and chip welding

and leaching which causes cratering.On the other hand, cobalt is strongerthan carbide. Therefore more cobaltimproves the tool strength and resis-tance to shock. The strength of a car-bide tool is expressed in terms of‘Transverse Rupture Strength’ (TRS).Figure 1.9 shows how TransverseRupture Strength is measured.

The third difference between the castiron and steel grade cutting tools, is car-bide grain size. The carbide grain sizeis controlled by the ball mill process.There are some exceptions, such asmicro-grain carbides, but generally thesmaller the carbide grains, the harderthe tool. Conversely, the larger the car-bide grain, the stronger the tool.Carbide grain sizes at 1500x magnifica-tion are shown in Exhibits 1.10 and1.11.

In the C- classification method(Figure 1.12), grades C-1 through C-4are for cast iron and grades C-5 throughC-8 for steel. The higher the C- numberin each group, the harder the grade, thelower the C- number, the stronger thegrade. The harder grades are used forfinish cut applications; the strongergrades are used for rough cut applica-tions.

Many manufacturers produce and

Figure 1.9. The method used to measure Transverse Rupture Strength (TRS) is shown aswell as the relationship of TRS to cobalt (Co) content.

Figure 1.10. Carbide grain size (0.8micron WC @ 1500×) consisting of 90%WC and 10% Co.

Figure 1.11. Carbide grain size (7 micronsWC @ 1500×) consisting of 90% WC and10% Co.



distribute charts showing a comparisonof their carbide grades with those ofother manufacturers. These are notequivalency charts, even though theymay imply that one manufacturer’s car-bide is equivalent to that of anothermanufacturer. Each manufacturerknows his carbide best and only themanufacturer of that specific carbidecan accurately place that carbide on theC- chart. Many manufacturers, espe-cially those outside the U. S., do not usethe C- classification system for car-bides. The placement of these carbideson a C- chart by a competing companyis based upon similarity of applicationand is, at best an ‘educated guess’.Tests have shown a marked differencein performance among carbide gradesthat manufacturers using the C- classifi-cation system have listed in the samecategory.

1.3.3 Coated Carbide ToolsWhile coated carbides have been inexistence since the late 1960’s, they didnot reach their full potential until themid 1970’s. The first coated carbideswere nothing more than standard car-bide grades which were subjected to acoating process. As the manufacturersgained experience in producing coatedcarbides, they began to realize that thecoating was only as good as the basecarbide under the coating (known as thesubstrate).

It is advisable to consider coated car-bides for most applications. When the

proper coated carbide, with the rightedge preparation is used in the rightapplication, it will generally outperformany uncoated grade. The microstructureof a coated carbide insert at 1500x mag-nification is shown in Figure 1.13.

Numerous types of coating materialsare used, each for a specific application.It is important to observe the do’s anddont’s in the application of coated car-bides. The most common coating mate-rials are:

• Titanium Carbide• Titanium Nitride• Ceramic Coating• Diamond Coating• Titanium Carbo-NitrideIn addition, multi-layered combina-

tions of these coating materials are

used. The microstructure of a multi-layered coated carbide insert at 1500xmagnification is shown in Figure 1.14.

In general the coating process isaccomplished by chemical vapordeposition (CVD). The substrate isplaced in an environmentally con-trolled chamber having an elevatedtemperature. The coating material isthen introduced into the chamber as achemical vapor. The coating materialis drawn to and deposited on the sub-strate by a magnetic field around thesubstrate. It takes many hours in thechamber to achieve a coating of0.0002 to 0.0003 inch on the substrate.Another process is Physical VaporDeposition (PVD).

Titanium Carbide Coating: Of allthe coatings, titanium carbide is themost widely used. Titanium carbide isused on many different substrate mate-rials for cutting various materialsunder varying conditions. Titanium

carbide coatings allow the use of highercutting speeds because of their greaterresistance to abrasive wear and crater-ing and higher heat resistance.

Titanium Nitride Coating - GoldColor: Titanium nitride is used onmany different substrate materials. Theprimary advantage of titanium nitride isits resistance to cratering. Titaniumnitride also offers some increased abra-sive wear resistance and a significantincrease in heat resistance permittinghigher cutting speeds. It is also said thattitanium nitride is more slippery, allow-ing chips to pass over it, at the cuttinginterface, with less friction.

Ceramic Coating - Black Color:Because aluminum oxide (ceramic) isextremely hard and brittle, it is not opti-

ClassificationNumber

Materials tobe Machined

Cast iron,nonferrousmetals, andnonmetallic

materialsrequiringabrasion

resistance

C-1

C-2

C-3

C-4

Steels and steel-alloys requiring

crater anddeformationresistance

C-5

C-6

C-7

C-8

MachiningOperation

Roughingcuts

Generalpurpose

Finishing

Precisionboring and

fine finishing

Roughingcuts

Generalpurpose

Finishing

Precisionboring and

fine finishing

Type ofCarbide

Wear-resistantgrades;

generallystraightWC–Co

with varyinggrain sizes

Crater-resistantgrades;various

WWC–Cocompositions

with TICand/or TaC

alloys

Cut

Increasingcutting speed

Increasingfeed rate

Characteristics Of

Carbide

Typical Properties

HardnessH-Ra

TransverseRuptureStrength(MPa)

89.0 2,400

92.0 1,725

92.5 1,400

93.5 1,200

91.0 2,070

92.0 1,725

93.0 1,380

94.0 1,035

Increasingcutting speed

Increasingfeed rate

Increasinghardness and

wear resistance

Increasingstrength and

binder content

Increasinghardness and

wear resistance

Increasingstrength and

binder content

Figure 1.12. Classification, application, characteristics, and typical properties of metal-cut-ting carbide grades.

Figure 1.13. Microstructure of a coatedcarbide insert at 1500× magnification.(Courtesy of Kennamental Inc.)

Figure 1.14. Microstructure of a multilay-ered coated carbide insert at 1500× magni-fication. (Courtesy of Kennamental Inc.)



mal for interrupted cuts, scaly cuts, andhard spots in the workpiece. This is notto say that it will never work underthese conditions, but it may be moresubject to failure by chipping. Evenwith these limitations, aluminum oxideis probably the greatest contributor tothe coated carbides. Aluminum oxideceramic allows much higher cuttingspeeds than other coated carbidesbecause of its outstanding resistance toabrasive wear and its resistance to heatand chemical interaction.

Diamond Coating: A recent devel-opment concerns the use of diamondpolycrystalline as coating for tungstencarbide cutting tools. Problems existregarding adherence of the diamondfilm to the substrate and the differencein thermal expansion between diamondand substrate materials. Thin-film dia-mond coated inserts are now availableusing either PVD (Physical VaporDeposition) or CVD (Chemical VaporDeposition) coating methods. Diamondcoated tools are effective in machiningabrasive materials, such as aluminumalloys containing silicon, fiber rein-forced materials, and graphite.Improvements in tool life of as much astenfold have been obtained over othercoated tools.

Titanium Carbo-Nitride - BlackColor Multilayered Coatings:Titanium carbo-nitride normallyappears as the intermediate layer of twoor three phase coatings. The role of tita-nium carbo-nitride is one of neutrality,helping the other coating layers to bondinto a sandwich-like structure (Figure 1-14). Other multi-layer coating combi-nations are being developed to effec-tively machine stainless steels and aero-space alloys. Chromium-based coatings such aschromium carbide have beenfound to be effective inmachining softer metals suchas aluminum, copper, andtitanium.

There are a few importantpoints to remember aboutusing coated carbides.Coated carbides will notalways out-perform uncoatedgrades but because of thebenefits offered by coatedcarbides, they should alwaysbe a first consideration whenselecting cutting tools.

When comparing the costbetween coated and uncoated

carbides there will be little differencewhen the benefits of coated carbides areconsidered. Because coated carbidesare more resistant to abrasive wear, cra-tering, and heat, and because they aremore resistant to work material build-upat lower cutting speeds, tool life isextended, reducing tool replacementcosts. Coated carbides permit operationat higher speeds, reducing productioncosts.

All coated carbides have an edgehone to prevent coating build-up duringthe coating process. This is because thecoating will generally seek sharp edges.The edge hone is usually very slight andactually extends tool life. However, acoated insert should never be regroundor honed. If a special edge preparationis required the coated carbides must beordered that way. The only time theedge hone may be of any disadvantageis when making a very light finishingcut. Carbide insert edge preparationswill be discussed in Chapter 2.

1.4 Ceramic and Cermet ToolsCeramic Aluminum Oxide (Al2O3)material for cutting tools was firstdeveloped in Germany sometimearound 1940. While ceramics wereslow to develop as tool materials,advancements made since the mid1970’s have greatly improved their use-fulness. Cermets are basically a combi-nation of ceramic and titanium carbide.The word cermet is derived from thewords ‘ceramic’ and ‘metal’.

Ceramic Cutting Tools: Ceramicsare non-metallic materials. This putsthem in an entirely different categorythan HSS and carbide tool materials.The use of ceramics as cutting tool

material has distinct advantages anddisadvantages. The application ofceramic cutting tools is limited becauseof their extreme brittleness. The trans-verse rupture strength (TRS) is verylow. This means that they will fracturemore easily when making heavy orinterrupted cuts. However, the strengthof ceramics under compression is muchhigher than HSS and carbide tools.

There are two basic types of ceramicmaterial; hot pressed and cold pressed.In hot pressed ceramics, usually blackor gray in color, the aluminum oxidegrains are pressed together underextremely high pressure and at a veryhigh temperature to form a billet. Thebillet is then cut to insert size. Withcold pressed ceramics, usually white incolor, the aluminum oxide grains arepressed together, again under extremelyhigh pressure but at a lower tempera-ture. The billets are then sintered toachieve bonding. This procedure issimilar to carbide manufacture, exceptno metallic binder material is used.While both hot and cold pressed ceram-ics are similar in hardness, the coldpressed ceramic is slightly harder. Thehot pressed ceramic has greater trans-verse rupture strength. Various shapesof both hot and cold pressed ceramicinserts are shown in Figure 1.15.

The brittleness, or relative strength,of ceramic materials is their greatestdisadvantage when they are comparedto HSS or carbide tools. Proper toolgeometry and edge preparation play animportant role in the application ofceramic tools and help to overcometheir weakness. Some of the advantagesof ceramic tools are:

• High strength for light cuts on veryhard work materials.• Extremely high resistanceto abrasive wear and cra-tering.• Capability of running atspeeds in excess of 2000SFPM.• Extremely high hot hard-ness.• Low thermal conductivi-ty.

While ceramics may notbe the all-around tool forthe average shop, they canbe useful in certain appli-cations. Ceramic toolshave been alloyed with zir-conium (about 15%) toincrease their strength.

Figure 1.15. Various sizes and shapes of hot- and cold-pressed ceramicinserts. (Courtesy Greenleaf Corp.)



Many ceramic tool manufacturers arerecommending the use of ceramic toolsfor both rough cutting and finishingoperations. Practical shop experienceindicates that these recommendationsare somewhat optimistic. To use ceram-ic tools successfully, insert shape, workmaterial condition, machine tool capa-bility, set-up, and general machiningconditions must all be correct. Highrigidity of the machine tool and set-up isalso important for the application ofceramic tools. Ceramics are beingdeveloped to have greater strength(higher TRS). Some manufacturers areoffering ceramic inserts with positivegeometry and even formed chip breakergrooves.

Cermet Cutting Tools: The manu-facturing process for cermets is similarto the process used for hot pressedceramics. The materials, approximately70 percent ceramic and 30 percent tita-nium carbide, are pressed into billetsunder extremely high pressure and tem-perature. After sintering, the billets aresliced to the desired tool shapes.Subsequent grinding operations forfinal size and edge preparation, com-plete the manufacturing process.

The strength of cermets is greaterthan that of hot pressed ceramics.Therefore, cermets perform better oninterrupted cuts. However, when com-pared to solid ceramics, the presence ofthe 30 percent titanium carbide in cer-mets decreases the hot hardness andresistance to abrasive wear. The hothardness and resistance to abrasive wearof cermets are high when compared toHSS and carbide tools. The greaterstrength of cermets allows them to beavailable in a significantly larger selec-tion of geometries, and to be used instandard insert holders for a greatervariety of applications. The geometriesinclude many positive/negative, andchip breaker configurations.

Silicon-Nitride Base Ceramics:Developed in the 1970’s, silicon-nitride(SIN) base ceramic tool materials con-sist of silicon nitride with various addi-

tions of aluminum oxide,yttrium oxide, and titaniumcarbide. These tools havehigh toughness, hot hard-ness and good thermalshock resistance. Sialonfor example is recommend-ed for machining cast ironsand nickel base superalloysat intermediate cuttingspeeds.

1.5 Diamond, CBN and Whisker-Reinforced Tools

The materials describedhere are not commonlyfound in a heavy metalworking environment.They are most commonlyused in high speed auto-matic production systemsfor light finishing of precision surfaces.To complete the inventory of tool mate-rials, it is important to note the charac-teristics and general applications ofthese specialty materials.

Diamond: The two types of dia-monds being used as cutting tools areindustrial grade natural diamonds, andsynthetic polycrystalline diamonds.Because diamonds are pure carbon, theyhave an affinity for the carbon of fer-rous metals. Therefore, they can onlybe used on non-ferrous metals.

Some diamond cutting tools are madeof a diamond crystal compaction (manysmall crystals pressed together) bondedto a carbide base (Fig. 1.16). These dia-mond cutting tools should only be usedfor light finishing cuts of precision sur-faces. Feeds should be very light andspeeds are usually in excess of 5000surface feet per minute (SFPM).Rigidity in the machine tool and the set-up is very critical because of theextreme hardness and brittleness of dia-mond.

Cubic Boron Nitride: Cubic boronnitride (CBN) is similar to diamond inits polycrystalline structure and is alsobonded to a carbide base. With the

exception of titanium, or titaniumalloyed materials, CBN will work effec-tively as a cutting tool on most commonwork materials. However, the use ofCBN should be reserved for very hardand difficult-to-machine materials.CBN will run at lower speeds, around600 SFPM, and will take heavier cutswith higher lead angles than diamond.Still, CBN should mainly be consideredas a finishing tool material because ofits extreme hardness and brittleness.Machine tool and set-up rigidity forCBN as with diamond, is critical.

Whisker-Reinforced Materials: Inorder to further improve the perfor-mance and wear resistance of cuttingtools to machine new work materialsand composites, whisker-reinforcedcomposite cutting tool materials havebeen developed. Whisker-reinforcedmaterials include silicon-nitride basetools and aluminum-oxide base tools,reinforced with silicon-carbide (SiC)whiskers. Such tools are effective inmachining composites and nonferrousmaterials, but are not suitable formachining irons and steels.

Figure 1.16. Polycrystalline diamond material bonded to acarbide base of various sizes and shapes. (Courtesy ofSandvik Coromant Co.)


2.1 InroductionThe process of metal removal, a process inwhich a wedge-shaped tool engages aworkpiece to remove a layer of material inthe form of a chip, goes back many years.Even with all of the sophisticated equip-ment and techniques used in today’s mod-ern industry, the basic mechanics of form-ing a chip remain the same. As the cuttingtool engages the workpiece, the materialdirectly ahead of the tool is sheared anddeformed under tremendous pressure. Thedeformed material then seeks to relieve itsstressed condition by fracturing and flow-ing into the space above the tool in theform of a chip. A turning tool holder gen-erating a chip is shown in Figure 2.1.

2.2 Cutting Tool ForcesThe deformation of a work material meansthat enough force has been exerted by thetool to permanently reshape or fracture thework material. If a material is reshaped, itis said to have exceeded its plastic limit. Achip is a combination of reshaping andfracturing. The deformed chip is separat-ed from the parent material by fracture.The cutting action and the chip formationcan be more easily analyzed if the edge ofthe tool is set perpendicular to the relativemotion of the material, as shown in Figure2.2. Here the undeformed chip thicknesst1 is the value of the depth of cut, while t2is the thickness of the deformed chip afterleaving the workpiece. The major defor-mation starts at the shear zone and diame-ter determines the angle of shear.

A general discussion of the forces act-ing in metal cutting is presented by usingthe example of a typical turning operation.When a solid bar is turned, there are three

Chip thicknessafter cutting

(t2)

Rakeangle(α)

Shearangle (φ)

Undeformedchip thickness

(t1)

Tool

FIGURE 2.1 A turning toolholder insert gener-ating a chip. (Courtesy Kennametal Inc.)

FIGURE 2.2 Chip formation showing the defor-mation of the material being machined.

Chapter 2

Metal Removal

Methods

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing





Lawrence Tech. Univ.: http://www.ltu.edu

Prentice Hall: http://www.prenhall.com

forces acting on the cutting tool (Fig.2.3):

Tangential Force: This acts in adirection tangential to the revolvingworkpiece and represents the resistanceto the rotation of the workpiece. In anormal operation, tangential force is thehighest of the three forces and accountsfor about 98 percent of the total powerrequired by the operation.

Longitudinal Force: Longitudinalforce acts in the direction parallel to theaxis of the work and represents theresistance to the longitudinal feed of thetool. Longitudinal force is usuallyabout 50 percent as great as tangentialforce. Since feed velocity is usuallyvery low in relation to the velocity ofthe rotating workpiece, longitudinalforce accounts for only about 1 percentof total power required.

Radial Force: Radial force acts in aradial direction from the center line ofthe workpiece. The radial force is gen-erally the smallest of the three, oftenabout 50 percent as large as longitudinalforce. Its effect on power requirementsis very small because velocity in theradial direction is negligible.

2.3 Chip Formation and Tool WearRegardless of the tool being used or themetal being cut, the chip formingprocess occurs by a mechanism calledplastic deformation. This deformationcan be visualized as shearing. That iswhen a metal is subjected to a loadexceeding its elastic limit. The crystalsof the metal elongate through an actionof slipping or shearing, which takesplace within the crystals and betweenadjacent crystals. This action, shown inFigure 2.4 is similar to the action thattakes place when a deck of cards is

Chap. 2: Metal Removal Methods


given a push and sliding orshearing occurs between theindividual cards.

Metals are composed ofmany crystals and each crys-tal in turn is composed ofatoms arranged into somedefinite pattern. Withoutgetting into a complicateddiscussion on the atomicmakeup and characteristicsof metals, it should be noted,that the slipping of the crys-tals takes place along a planeof greatest ionic density.

Most practical cuttingoperations, such as turningand milling, involve two ormore cutting edges inclinedat various angles to thedirection of the cut.However, the basic mecha-nism of cutting can beexplained by analyzing cut-ting done with a single cut-ting edge.

Chip formation is sim-plest when a continuous chipis formed in orthogonal cut-ting (Fig. 2.5a). Here thecutting edge of the tool isperpendicular to the line oftool travel, tangential, longi-tudinal, and radial forces are in the sameplane, and only a single, straight cuttingedge is active. In oblique cutting, ( Fig.2.5b), a single, straight cutting edge isinclined in the direction of tool travel.This inclination causes changes in thedirection of chip flow up the face of thetool. When the cutting edge is inclined,the chip flows across the tool face witha sideways movement that produces ahelical form of chip.

2.3.1 Chip FormationMetal cutting chips have been classified

into three basic types:• discontinuous or segmented• continuous• continuous with a built-up edge.

All three types of chips are shown inFigure 2.6 a,b,and c.

Discontinuous Chip - Type 1:Discontinuous or segmented chips areproduced when brittle metal such as castiron and hard bronze are cut or whensome ductile metals are cut under poorcutting conditions. As the point of thecutting tool contacts the metal, somecompression occurs, and the chip begins

FIGURE 2.3Typical turning operationshowing the forces acting on the cuttingtool.

FIGURE 2.6 Types of chip formations: (a) discontinuous, (b) continuous, (c) continuouswith built-up edge (BUE).

FIGURE 2.4 Chip formation compared to a slidingdeck of cards.

FIGURE 2.5 Chip formation showing both (a) orthogo-nal cutting and (b) oblique cutting.

Tangentialforce

Longitudinalforce

Radial force

101112131415 9 8 76

54

32

1

Tool

Workpiece

Workpiece

(a)

Workpiece

(b)

90¡

Tool Tool

ChipChip

Built-upedge

Tool

(a) (b) (c)

Tool

Roughworkplacesurface

Chip

Primarydeformationzone Tool



flowing along the chip-tool interface.As more stress is applied to brittle metalby the cutting action, the metal com-presses until it reaches a point whererupture occurs and the chip separatesfrom the unmachined portion. Thiscycle is repeated indefinitely during thecutting operation, with the rupture ofeach segment occurring on the shearangle or plane. Generally, as a result ofthese successive ruptures, a poor sur-face is produced on the workpiece.

Continuous Chip - Type 2: TheType 2 chip is a continuous ribbon pro-duced when the flow of metal next tothe tool face is not greatly restricted bya built-up edge or friction at the chiptool interface. The continuous ribbonchip is considered ideal for efficient cut-ting action because it results in betterfinishes.

Unlike the Type 1 chip, fractures orruptures do not occur here, because ofthe ductile nature of the metal. Thecrystal structure of the ductile metal iselongated when it is compressed by theaction of the cutting tool and as the chipseparates from the metal. The processof chip formation occurs in a singleplane, extending from the cutting tool tothe unmachined work surface. The areawhere plastic deformation of the crystalstructure and shear occurs, is called theshear zone. The angle on which thechip separates from the metal is calledthe shear angle, as shown in Figure 2.2.

Continuous Chip with a Built-upEdge (BUE)- Type 3: The metal aheadof the cutting tool is compressed andforms a chip which begins to flow alongthe chip-tool interface. As a result ofthe high temperature, the high pressure,and the high frictional resistance againstthe flow of the chip along the chip-toolinterface, small particles of metal beginadhering to the edge of the cutting toolwhile the chip shears away. As the cut-ting process continues, more particlesadhere to the cutting tool and a largerbuild-up results, which affects the cut-ting action. The built-up edge increasesin size and becomes more unstable.Eventually a point is reached wherefragments are torn off. Portions of thesefragments which break off, stick to boththe chip and the workpiece. The build-up and breakdown of the built-up edgeoccur rapidly during a cutting actionand cover the machined surface with amultitude of built-up fragments. Thesefragments adhere to and score the

machined surface,resulting in a poorsurface finish.

Shear Angle:Certain characteris-tics of continuouschips are determinedby the shear angle.The shear angle isthe plane where slipoccurs, to begin chipformation (Figure2.2). In Figure 2.7the distortion of thework material grainsin the chip, as com-pared to the parentmaterial, is visible.Each fracture line inthe chip as it moves upwardover the tool surface can beseen, as well as the distortedsurface grains where the toolhas already passed. In certainwork materials, these distortedsurface grains account for workhardening.

Regardless of the shearangle, the compressive defor-mation caused by the tool forceagainst the chip, will cause thechip to be thicker and shorterthan the layer of workpiecematerial removed. The work orenergy required to deform thematerial usually accounts forthe largest portion of forces andpower involved in a metalremoving operation. For alayer of work material of givendimensions, the thicker the chip, thegreater the force required to produce it.

Heat in Metal Cutting: The mechan-ical energy consumed in the cutting areais converted into heat. The main sourcesof heat are, the shear zone, the interfacebetween the tool and the chip where thefriction force generates heat, and thelower portion of the tool tip which rubsagainst the machined surface. Theinteraction of these heat sources, com-bined with the geometry of the cuttingarea, results in a complex temperaturedistribution, as shown in Figure 2.8.

The temperature generated in theshear plane is a function of the shearenergy and the specific heat of the mate-rial. Temperature increase on the toolface depends on the friction conditionsat the interface. A low coefficient offriction is, of course, desirable.

Temperature distribution will be a func-tion of, among other factors, the thermalconductivities of the workpiece and thetool materials, the specific heat, cuttingspeed, depth of cut, and the use of a cut-ting fluid. As cutting speed increases,there is little time for the heat to be dis-sipated away from the cutting area andso the proportion of the heat carriedaway by the chip increases.

In Chapter 3 - Machinability ofMetals - this topic is discussed in moredetail.

2.3.2 Cutting Tool WearCutting tool life is one of the mostimportant economic considerations inmetal cutting. In roughing operations,the tool material, the various toolangles, cutting speeds, and feed rates,are usually chosen to give an economi-

Rakeangle

ToolReliefangle

Distortedsurfacegrains

Parent material

Cut depth

Shear plane

Slip lines

Chip segment

Grainfragments

Workpiece

Chip Tool675

750

850 93

0

930

1100

1100

1100…F

1300

1200

1200

1300

FIGURE 2.7 Distribution of work material during chip forma-tion.

FIGURE 2.8 Typical temperature distribution in thecutting zone.



cal tool life. Conditions giving a veryshort tool life will not be economicalbecause tool-grinding, indexing, andtool replacement costs will be high. Onthe other hand, the use of very lowspeeds and feeds to give long tool lifewill not be economical because of thelow production rate. Clearly any tool orwork material improvements thatincrease tool life without causing unac-ceptable drops in production, will bebeneficial. In order to form a basis forsuch improvements, efforts have beenmade to understand the behavior of thetool, how it physically wears, the wearmechanisms, and forms of tool failure.

While the tool is engaged in thecutting operation, wear may devel-op in one or more areas on and nearthe cutting edge:

Crater Wear: Typically, crater-ing occurs on the top face of thetool. It is essentially the erosion ofan area parallel to the cutting edge.This erosion process takes place asthe chip being cut, rubs the top faceof the tool. Under very high-speedcutting conditions and whenmachining tough materials, craterwear can be the factor which deter-mines the life of the tool. Typicalcrater wear patterns are shown inFigures 2.9 and 2.10a. However, whentools are used under economical condi-tions, the edge wear and not the craterwear is more commonly the controllingfactor in the life of the tool

Edge Wear: Edge wear occurs onthe clearance face of the tool and ismainly caused by the rubbing of thenewly machined workpiece surface onthe contact area of the tool edge. Thistype of wear occurs on all tools whilecutting any type of work material. Edgewear begins along the lead cutting edgeand generally moves downward, awayfrom the cutting edge. Typical edgewear patterns are shown in Figures 2.9and 2.10b. The edge wear is also com-monly known as the wearland.

Nose Wear: Usually observed after aconsiderable cutting time, nose wearappears when the tool has alreadyexhibited land and/or crater wear. Wearon the nose of the cutting edge usuallyaffects the quality of the surface finishon the workpiece.

Cutting tool material in general, andcarbide tools in particular, exhibit dif-ferent types of wear and/or failure:

Plastic Deformation: Edge depres-

sion and body bulging appear, due toexcessive heat. The tool loses strengthand consequently flows plastically.

Mechanical Breakage: Excessiveforce may cause immediate failure.Alternatively, the mechanical failure(chipping) may result from a fatigue-type failure. Thermal shock also causesmechanical failure.

Gradual Wear: The tool assumes aform of stability wear due to interactionbetween tool and work, resulting incrater wear. Four basic wear mecha-nisms affecting tool material have beencategorized as:

Abrasion: Because hard inclusionsin the workpiece microstructure plowinto the tool face and flank surfaces,abrasion wear predominates at relative-ly low cutting temperatures. The abra-sion resistance of a tool material is pro-portional to its hardness.

Adhesion: Caused by formation andsubsequent destruction of minute weld-ed junctions, adhesion wear is common-ly observed as built-up edge (BUE) onthe top face of the tool. This BUE mayeventually disengage from the tool,causing a crater like wear. Adhesion

can also occur when minute particles ofthe tool surface are instantaneouslywelded to the chip surface at the tool-chip interface and carried away with thechip.

Diffusion: Because of high tempera-tures and pressures in diffusion wear,microtransfer on an atomic scale takesplace. The rate of diffusion increasesexponentially with increases in temper-ature.

Oxidation: At elevated temperature,the oxidation of the tool material cancause high tool wear rates. The oxidesthat are formed are easily carried away,leading to increased wear.

The different wear mechanisms aswell as the different phenomena con-tributing to the attritious wear of thecutting tool, are dependent on the multi-tude of cutting conditions and especial-ly on the cutting speeds and cutting flu-ids.

Aside from the sudden prematurebreakage of the cutting edge (tool fail-ure), there are several indicators of theprogression of physical wear. Themachine operator can observe these fac-tors prior to total rupture of the edge.

FIGURE 2.9 Carbide insert wear patterns: (a) crater wear, (b) edge wear.

FIGURE 2.10 Carbide insert wear patterns: (a) crater wear, (b) edge wear. (CourtesyKennametal Inc.)

Noseradius

R

Flank face

Depth-of-cut lineEdge wear

Rake faceCraterwear

Depth-of-cut line

(a) (b)

(a) (b)



The indicators are:• Increase in the flank wear size above apredetermined value.• Increase in the crater depth, width orother parameter of the crater, in the rakeface.• Increase in the power consumption, orcutting forces required to perform thecut.• Failure to maintain the dimensionalquality of the machined part within aspecified tolerance limit.• Significant increase in the surfaceroughness of the machined part.• Change in the chip formation due toincreased crater wear or excessive heatgeneration.

2.4 Single Point Cutting ToolsThe metal cutting tool separates chipsfrom the workpiece in order to cut thepart to the desired shape and size. Thereis a great variety of metal cutting tools,each of which is designed to perform aparticular job or a group of metal cut-ting operations in an efficient manner.For example, a twist drill is designed todrill a hole of a particular size, while aturning tool might be used to turn a vari-ety of cylindrical shapes.

2.4.1 Cutting Tool GeometryThe shape and position of the tool, rela-tive to the workpiece, have an importanteffect on metal cutting. The mostimportant geometric elements, relativeto chip formation, are the location of thecutting edge and the orientation of thetool face with respect to the workpieceand the direction of cut. Other shapeconsiderations are concerned primarilywith relief or clearance, i.e., taperapplied to tool surfaces to prevent rub-bing or dragging against the work.

Terminology used to designate thesurfaces, angles and radii of single pointtools, is shown in Figure 2.11. The toolshown here is a brazed-tip type, but thesame definitions apply to indexabletools.

T & P TO PLACE FIG. 2.11 HEREThe Rake Angle: The basic tool

geometry is determined by the rakeangle of the tool as shown in Figure2.12. The rake angle is always at the topside of the tool. With the tool tip at thecenter line of the workpiece, the rakeangle is determined by the angle of thetool as it goes away from the workpiececenter line location. The neutral, posi-

tive, and negative rakes are seen in (a),(b), and (c) in Figure 2.12. The anglefor these geometries is set by the posi-tion of the insert pocket in the tool hold-er. The positive/negative (d) and doublepositive (e) rake angles are set by acombination of the insert pocket in thetool holder and the insert shape itself.

There are two rake angles: back rakeas shown in Figure 2.12, and side rakeas shown in Figure 2.13. In most turningand boring operations, it is the side rakethat is the most influential. This isbecause the side rake is in the directionof the cut.

Rake angle has two major effects dur-ing the metal cutting process. One

major effect of rake angle is its influ-ence on tool strength. An insert withnegative rake will withstand far moreloading than an insert with positiverake. The cutting force and heat areabsorbed by a greater mass of tool mate-rial, and the compressive strength ofcarbide is about two and one half timesgreater than its transverse rupturestrength.

The other major effect of rake angleis its influence on cutting pressure. Aninsert with a positive rake angle reducescutting forces by allowing the chips toflow more freely across the rake sur-face.

Negative Rake: Negative rake tools

Side relief angle

Side rake

Side clearance angle

Nose radius

End-cutting edge angle

Side-cutting edge angle

Positive back rake

End relief

End clearance

Negative back rake

(a)

(b)

(c)

(d)

(e)

FIGURE 2.11 Terminology used to designate the surfaces, angles, and radii of single-point tools.

FIGURE 2.12 With the cutting tool on center, various back rake angles are shown: (a)neutral, (b) positive, (c) negative, (d) positive/negative, (e) double positive.



should be selected whenever workpieceand machine tool stiffness and rigidityallow. Negative rake, because of itsstrength, offers greater advantage dur-ing roughing, interrupted, scaly, andhard-spot cuts. Negative rake also offersmore cutting edges for economy andoften eliminates the need for a chipbreaker. Negative rakes are recom-mended on insert grades which do notpossess good toughness (low transverserupture strength)

Negative rake is not, however, with-out some disadvantages. Negative rakerequires more horsepower and maxi-mum machine rigidity. It is more diffi-cult to achieve good surface finisheswith negative rake. Negative rake forcesthe chip into the workpiece, generatesmore heat into the tool and workpiece,and is generally limited to boring onlarger diameters because of chip jam-ming.

Positive Rake: Positive rake toolsshould be selected only when negativerake tools can’t get the job done. Someareas of cutting where positive rake mayprove more effective are, when cuttingtough, alloyed materials that tend to‘work-harden’, such as certain stainlesssteels, when cutting soft or gummy met-als, or when low rigidity of workpiece,tooling, machine tool, or fixture allowschatter to occur. The shearing actionand free cutting of positive rake toolswill often eliminate problems in theseareas.

One exception that should be notedwhen experiencing chatter with a posi-tive rake is, that at times the preloadeffect of the higher cutting forces of anegative rake tool will often dampen outchatter in a marginal situation. Thismay be especially true during lightercuts when tooling is extended or whenthe machine tool has excessive back-lash.

Neutral Rake: Neutral rake tools are

seldom used or encountered. When anegative rake insert is used in a neutralrake position, the end relief (betweentool and workpiece) is usually inade-quate. On the other hand, when a posi-tive insert is used at a neutral rake, thetip of the insert is less supported, mak-ing the insert extremely vulnerable tobreakage.

Positive/Negative Rake: The posi-tive/negative rake is generally appliedusing the same guidelines as a positiverake. The major advantages of a posi-tive/negative insert are that it can beused in a negative holder, it offersgreater strength than a positive rake,and it doubles the number of cuttingedges when using a two-sided insert.

The positive/negative insert has a tendegree positive rake. It is mounted inthe normal five degree negative pocketwhich gives it an effective five degreepositive rake when cutting. The posi-tive/negative rake still maintains a cut-ting attitude which keeps the carbideunder compression and offers moremass for heat dissipation. The posi-tive/negative insert also aids in chip

breaking on many occasions, as it tendsto curl the chip.

Double Positive Rake: The doublepositive insert is the weakest of allinserts. It is free cutting, and generallyused only when delicate, light cuts arerequired which exert minimum forceagainst the workpiece, as in the case ofthin wall tubing, for example. Otheruses of double positive inserts are forvery soft or gummy work materials,such as low carbon steel and for boringsmall diameter holes when maximumclearance is needed.

Side Rake Angles: In addition to theback rake angles there are side rakeangles as shown in Figure 2.13. Theseangles are normally determined by thetool manufacturers. Each manufactur-er’s tools may vary slightly, but usuallyan insert from one manufacturer can beused in the tool holder from another.The same advantage of positive andnegative geometry that was discussedfor back rake, applies to side rake.When back rake is positive so is siderake and when back rake is negative sois side rake.

Side and End Relief Angles: Reliefangles are for the purpose of helping toeliminate tool breakage and to increasetool life. The included angle under thecutting edge must be made as large aspractical. If the relief angle is too large,the cutting tool may chip or break. Ifthe angle is too small, the tool will rubagainst the workpiece and generateexcessive heat, and this will in turn,cause premature dulling of the cuttingtool.

Small relief angles are essential when

FIGURE 2.13 Side-rake-angle variations: (a) negative, (b) positive.

FIGURE 2.14 Lead-angle variations: (a) negative, (b) neutral, (c) positive.

Rotation

Feed

(a)

Rotation

Feed

(b)

Feed

Feed

Negative leadangle

Positive leadangle

Feed

Neutral leadangle

(a) (b)

(c)



machining hard and strong materials,and they should be increased for theweaker and softer materials. A smallerangle should be used for interruptedcuts or heavy feeds, and a larger anglefor semi-finish and finish cuts.

Lead Angle: Lead angle (Fig. 2.14)is determined by the tool holder whichmust be chosen for each particular job.The insert itself can be used in anyappropriate holder, for that particularinsert shape, regardless of lead angle.

Lead angle is an important considera-tion when choosing a tool holder. Apositive lead angle is the most common-ly used and should be the choice for themajority of applications. Positive leadangle performs two main functions:• It thins the chip• It protects the insert

The undeformed chip thicknessdecreases when using a positive leadangle.

Positive lead angles vary, but themost common lead angles available onstandard holders are 10, 15, 30 and 45degrees. As seen in Figure 2.15, thevolume of chip material is about thesame in each case but the positive leadangle distributes the cutting force over agreater area of the tool’s edge. Thisallows a substantial increase in feed ratewithout reducing the tool life because ofexcessive loading. The greater the leadangle, the more the feed rate can beincreased.

Positive lead angle also reduces thelongitudinal force (direction of feed) onthe workpiece. But positive lead angleincreases the radial force because thecutting force is always approximatelyperpendicular to the cutting edge (Fig.2.16). This may become a problemwhen machining a workpiece that is notwell supported. Care must be taken incases where an end support, such as atail stock center is not used.

A heavy positivelead angle also has atendency to inducechatter because of agreater tool contactarea. This chatter is anamplification of tool orworkpiece deflectionresulting from theincreased contact. Inthis situation it isappropriate to decreasethe positive lead angle.

A positive lead angleprotects the tool and promoteslonger tool life. As shown inFigure 2.17 the tool comes in con-tact with the workpiece well awayfrom the tool tip, which is theweakest point of the tool. As thetool progresses into the cut, theload against the tool graduallyincreases, rather than occurring asa sudden shock to the cuttingedge. The positive lead anglealso reduces the wear on the cut-ting edge caused by a layer ofhardened material or scale, bythinning the layer and spreading itover a greater area. These advan-tages are extremely beneficial duringinterrupted cuts. Another way that pos-itive lead angle helps to extend tool lifeis by allowing intense heat build-up todissipate more rapidly, since more ofthe tool is in contact with the work-piece.

Neutral and negative lead angle toolsalso have some benefits. A neutralangle offers the least amount of toolcontact, which will sometimes reducethe tendency to chatter, and lowers lon-gitudinal forces. This is important onless stable workpieces or set-ups.Negative lead angles permit machiningto a shoulder or a corner and are usefulfor facing. Cutting forces tend to pullthe insert out of the seat, leading toerratic size control. Therefore, negativelead angles should be avoided if at allpossible.

2.4.2 Edge PreparationEdge preparation is a step taken to pro-long tool life or to enhance tool perfor-mance. There are four basic approach-es to edge preparation:• Edge hone• Edge “L” land• Edge chamfer• Combinations of the above

Many inserts, including carbide,ceramic, etc., are purchased with a stan-dard edge preparation, normally an edgehone. The primary purpose of edgepreparation is to increase the insert’sresistance to chipping, breaking, andwear. Figure 2.18 illustrates the basicedge preparations.

Tool materials such as carbide andceramic are very hard and brittle.Therefore, a lead sharp cutting edge oninserts made of these materials isextremely prone to chipping and break-ing. Once a cutting edge is chipped, thewear rate is greatly accelerated orbreakage occurs. A prepared edge elim-inates the sharp edge and provides otherbenefits such as redistributing cuttingforces.

Edge Hone: The edge hone is by farthe most commonly used edge prepara-tion. Many inserts are automaticallyprovided with an edge hone at the timeof purchase, especially larger insertsthat will be exposed to heavy cutting.An edge hone on a ground or precisioninsert must usually be specially request-ed. A standard light hone in the UnitedStates usually has a radius of 0.001 to0.003 inch; A standard heavy hone hasa radius of 0.004 to 0.007 inch. Heavier

Feed (IPR)


Feed (IPR)


FIGURE 2.15 Lead angle vs. chip thick-ness. A positive lead angle thins the chipand protects the insert.

FIGURE 2.16 Lead angles and their effects on longitudinaland radial cutting cutting-tool feed forces.

FIGURE 2.17 Gradual feed/workpiece contactprotects the cutting tool by slowing increasing theload.

Radialdirection

Feed force

Feedforce

Longitudinaldirection

(a) (b)

Work piece

Feed

Initial contactpoint



hones are available on request. Theheavier the hone, the more resistance anedge has to chipping and breaking,especially in heavy roughing cuts, inter-rupted cuts, hard spot cuts, and scalycuts.

It is standard practice of all manufac-turers to hone inserts that are to be coat-ed before the inserts are subjected to thecoating process. The reason for this isthat during the coating process, thecoating material tends to build up onsharp edges. Therefore it is necessary tohone those edges to prevent build-up.

‘L’ Land: The ‘L’ land edge prepara-tion adds strength to the cutting edge ofan insert. Essentially, the ‘L’ landamplifies the advantages of negativerake by diverting a greater amount ofcutting force into the body of the insert.The ‘L’ land amplifies this conditionbecause the included angle at theinsert’s edges is 110 degrees as opposedto 90 degrees. The ‘L’ land is particu-larly beneficial when engaging severescale, interruptions, and roughing.

The ‘L’ land configuration is normal-ly 20 degrees by two thirds of the fee-drate. The feedrate should exceed theland width by about one third. This isnot a hard and fast rule, but it does serveas a good starting point. If the landwidth is greater than the feedrate, severejamming of the chips, excessive highpressures, and high heat will likelyoccur, resulting in rapid tool failure.

Something other than a 20 degreeland angle may be considered, withvarying land width. Some experimenta-tion may prove beneficial, however, ifthe land angle is varied from 20 degreesit should probably be less rather thanmore than 20 degrees to keep from jam-ming the chips.

An ‘L’ land is normally used only onnegative, flat top inserts placed at a neg-ative rake angle. To use an ‘L’ land ona positive or a positive/negative insert

would defeat the purpose of positivecutting action.

Chamfer: A chamfer is a compro-mise between a heavy hone and an ‘L’land. A chamfer will also increase aninsert’s resistance to chipping andbreaking. In a shop situation a chamferis easier and quicker to apply than aheavy hone, because it can be appliedwith a grinder rather than a hand hone.When a chamfer is applied it should bevery slight, 45 degrees by 0.005 to0.030 inch.

Normally a chamfer presents a nega-tive cutting situation which can result insome problems. The area of applicationfor chamfers is limited and caution mustbe exercised. A slight chamfer is oftenused on a hard and brittle tool for mak-ing a very light finishing cut on hardwork material. In this instance, thechamfer will strengthen the cuttingedge.

Combinations: Any time that a sharpedge can be eliminated the life of aninsert will likely be extended. When an‘L’ land or chamfer is put on an insert, itwill make a dramatic improvement inperformance, but the ‘L’ land or cham-fer will leave some semi-sharp corners.To get the maximum benefit from an ‘L’land or chamfer, it will help to add aslight hone to each semi-sharp corner.This will be of significant value inextending tool life, particularly when alarge ‘L’ land is used.

Nose Radius: The nose radius of aninsert has a great influence in the metalcutting process. The primary functionof the nose radius is to provide strengthto the tip of the tool. Most of the otherfunctions and the size of the nose radiusare just as important. The choice ofnose radius will affect the results of thecutting operation; however, inserts areprovided with various standard radiiand, in most cases, one of these willmeet each specific cutting need.

The larger the radius, thestronger the tool tip will be.However, a large radius causesmore contact with the work surfaceand can cause chatter. The cuttingforces will increase with a largeradius for the same reason,increased contact with the worksurface. When taking a shallowcut, a depth approximately equal tothe radius or less, the radius acts asa positive lead angle, thinning thechip. A large radius will allow the

cutting heat to dissipate more quicklyinto the insert body, reducing the tem-perature build-up at the cutting edge.

One of the most important influencesof a large radius is that of surface finish.The larger the radius, the better the sur-face finish will be at an equal feedrate.A larger radius will allow a faster fee-drate and yet obtain a satisfactory fin-ish. During a finishing cut, the feedrateshould not exceed the radius if a reason-able surface finish is required.

2.4.3 Chip BreakersBreaking the chip effectively whenmachining with carbide tools is of theutmost importance, not only from theproduction viewpoint, but also from thesafety viewpoint. When machiningsteel at efficient carbide cutting speeds,a continuous chip flows away from thework at high speed.

If this chip is allowed to continue, itmay wrap around the toolpost, theworkpiece, the chuck, and perhapsaround the operator’s arm. Not only isthe operator in danger of receiving anasty laceration, but if the chip windsaround the workpiece and the machine,he must spend considerable time inremoving it. A loss of production willbe encountered. Therefore it is impera-tive that this chip be controlled and bro-ken in some manner.

With the advent of numerial control(NC) machining and automatic chiphandling systems, the control of chips isbecoming more important than ever.The control of chips on any machinetool, old or new, helps to avoid jam-upswith tooling and reduces safety hazardsfrom flying chips. There is a great dealof research and development being con-ducted in chip control, much of whichhas been very successful.

There are two basic types of chipcontrol being used with indexable inserttooling: the mechanical chip breaker,

FIGURE 2.18 The three basic edge preparations are (a) edge hone, (b) L land, (c) edge cham-fer.

X X

Y Y

(a) (b) (c)

R



Figure 2.19, and the sintered chip break-er, Figure 2.20. Mechanical chip break-ers are not as commonly used as sin-tered chip breakers. There are moreparts involved with the mechanical chipbreaker, which increases the cost, andthe chip breaker hampers changing andindexing the insert. However, mechan-ical chip breakers are extremely effec-tive in controlling chips during heavymetal removing operations.

There are two groups of mechanicalchip breakers, solid and adjustable asshown in Figure 2.21. Solid chip break-ers are available in various lengths andangles, to suit each metal cutting appli-cation. The adjustable chip breaker caneliminate the need for stocking varioussizes of solid chip breakers.

Sintered chip breakers are availablein many different configurations, somedesigned for light feeds, some for heavyfeeds, and still others for handling bothlight and heavy feeds. Figure 2.22shows examples of the various sinteredchip breaker configurations availablefrom a single manufacturer. There aresingle sided and double sided designs ofsintered chip breaker inserts.

Many of the designs will significant-ly reduce cutting forces as well as con-trol chips. Normally it would be moreeconomical to use a double sided insert

because of the addition-al cutting edges avail-able. However, this isnot always true. Whilea double sided insert ismore economical undermoderate and finish cut-ting conditions becauseof its additional cuttingedges, a single sideddesign will justify itself,from a cost standpoint,through more effective chip control andreduced cutting forces in certain situa-tions. Figure 2.23 shows five common

insert styles with sintered chip breakers.Figure 2.22 illustrates that a single

sided insert is flat on the bottom as com-

FIGURE 2.19 Mechanical chip breaker.

FIGURE 2.21 Solid and adjustable chip breaker.

FIGURE 2.22 Various sintered chipbreaker configurations, with application

recommendations.

FIGURE 2.20 Sintered chip breaker.

Double-Sided General-Purpose Groove Geometries

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use at lowfeed rates.

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use atmedium feed rates

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use at highfeed rates

Single-Side Low Force Groove Geometries

Offers lower cutting forces than general-purpose grooves in medium feed rangeapplications. Insert has 11¡ clearanceangle for use in positive rake tool holder.

Generates about 25% less cutting forcethan general-purpose chip grooves. De-signed for medium-feed applicationswhere force reduction, particularly inthe radial direction, is important.

Double-Sided Low Feed Groove Geometries

Offers excellent chip control at ultra-lowfeed rates. Positive/negative design providessome force reducing advantages. Lowcost per cutting edge.

Positive/negative design provides lowercutting forces than general-purposegrooves in low- to medium-feed range.Offers low cost per cutting edge thanother force-reducing geometries.

Generates about 25% less cutting forcethan general-purpose chip grooves. De-signed for ultra-high-feed applicationswhere force reduction is important.

.004—.020 ipr

feedrange

.005—.065 ipr

feedrange

.012—.070 ipr

feedrange

.005—.045 ipr

feedrange

.006—.050 ipr

feedrange

.012—.078 ipr

feedrange

.003—.024 ipr

feedrange

.004—.032 ipr

feedrange



pared to a double sided insert. This flatbottom provides a single sided insertwith better support under the cuttingedge in a severe cutting situation. Thesingle sided insert, because of its addedsupport, has the ability to remove largeramounts of material with greater easeand efficiency, making it more econom-ical to use. Another reason the singlesided insert may be more economical isthat, under heavy machining conditions,it is rare that all of the cutting edges ofa double sided insert can be used. Theintense thermal and mechanical shockto the insert will normally damage it tothe point where the opposite cuttingedge is not usable and in a sense, wast-ed. Figure 2.24 a,b shows two squareinserts with special purpose chip break-ers.

Statistics have proven that undersevere conditions a single sided insert ismore often the most economical choicebecause its higher efficiency willremove more metal in less time.

Additionally, if half of the availablecutting edges of a double sided insertare unusable, for reasons stated before,then the more efficient single sidedinsert, having essentially the same num-

ber of usable cutting edges, is themost economical insert to use.

There are many other configura-tions of chip breaker designs thanthe ones shown in Figure 2.22.Each manufacturer has its own.The recommended applicationareas are generally listed in eachmanufacturer’s catalog. However,for specific recommendations andspecial applications, it is best toconsult the manufacturer.

Figure 2.25 shows the varioustypes of chips that are encounteredevery day. Examining the chipsthat are coming off a workpiecewill give a lot of information as to

how well the job is going, how toolwear is progressing, and why prematuretool failure or short tool life is occur-ring.

Straight Chips: Straight chips areusually the most troublesome. Theystring out all over the machine tool, theyget snarled in the tool, workpiece, andfixturing, they cause tooling to break,they jam up chip handling equipment,they are difficult to remove, and theyare dangerous, especially when theybegin to whip around. Soft gummy lowcarbon and tough steels usually causethis type of chip. One of the quickestways to eliminate the straight chip, is toincrease the feedrate, because a thickerchip breaks more easily. Other ways toeliminate straight chips are to decreasethe lead angle, which would also thick-en the chip, increase the speed, use anegative rake tool, or use a chip breakerinsert.

Snarling Chips: Snarling chips arecontinuous chips much the same asstraight chips. They are generallycaused by the same conditions asstraight chips and create the same prob-lems. It stands to reason, therefore, thatto correct a snarling chip situation, the

same methods would beused as with straightchips. In addition, cool-ing the chips with aflood or mist coolant asthey come off the tool,will frequently help tobreak them.

Infinite Helix Chips:Infinite helix chips arechips that are near thebreaking point. Theproblems this type ofchip creates are similar

to those created by straight chips.Infinite helix chips are common whenmachining very ductile material, such asleaded or resulfurized steels, and othersoft materials. They will most oftenoccur when making light cuts with pos-itive rake tools. Using a sintered chipbreaker insert, that will force the natur-al chip flow direction to change, is ofteneffective in breaking the infinite helixchip. An increase in feed or speed willalso help break the chip.

Full Turn Chips: Full turn chips arenot usually a problem so long as theyare consistent and without occasionalstringers. A consistent full turn chip isnear the ideal half turn chip.

Half Turn Chip: If there is such athing as a perfect chip, it is the half turnor ‘6’ shape chip. This is the chip shapethat the machinist strives for in his cut-ting operation. The half turn chip isknown as the classic chip form. The‘Half turn’ or just about perfect chip isshown in Figure 2.26.

Tight Chips: Tight chips do not pre-sent a problem from a handling or inter-

FIGURE 2.23 Five common insert shapes withvarious sintered chip-breaker configurations.(Courtesy American National Carbide Co.)

FIGURE 2.25 Various types of chip for-mations.

FIGURE 2.24 Two square inserts with one-sided special-purpose chip breakers. (Courtesy Iscar Metals, Inc.)

FIGURE 2.26 Half-turn chip or “perfect”chip. (Courtesy Kennametal Inc.)

Straight chips

Snarling chips

Infinite helix chips

Full turns

Half turns

Tight chips



facing point of view, but these tightchips are a sign that poor tool life orpremature tool failure may occur. Thetight chip is formed by very high pres-sure and causes intense heat, deflectionof the tool and workpiece, and rapidtool failure. A tight chip is a jammedchip, meaning that its flow path is over-ly restricted. Causes include; too high afeed rate, too negative a rake angle,improper chip breaker selection or set-ting, or a worn insert.

Many times a straight, snarled or infi-nite helix chip will be generated at thestart of a cutting operation, when theinsert is new. As the insert begins towear, the chip gradually becomes wellshaped and properly broken. It mayeven progress into a tight chip and even-tually cause catastrophic tool failure.This is caused by a type of insert wearknown as cratering.( see Figures 2.9aand 2.10a) In cratering, a groove isworn into the insert causing a false chipbreaker groove to be formed. This is adefinite sign of a problem, such as theinsert is not of the correct carbide grade,is not the correct geometry, or that thecutting speed may be too fast.

2.5 Indexable Type ToolingOne of the more recent developments incutting tool design is the indexableinsert which is mechanically held in atoolholder. Inserts are available in sev-eral thicknesses and a variety of sizesand shapes. The round, square, triangle,and diamond account for the greatestpercentage. Many other shapes, includ-ing the parallelogram, hexagon, andpentagon, are used to meet specificmachining requirements. Each shapehas its advantages and limitations sincethe operational, as well as the economi-cal factors must be considered in toolingselection. The most common insertshapes were shown in Figure 2.23.

2.5.1 Indexable Insert ShapesIndexable inserts have certainly estab-lished their position and potential in themetal working industry. The elimina-tion of regrinding, accuracy of toolgeometry, reduced inventory tool costs,and down time for tool changes, aresome of the advantages resulting fromthe use of this tooling.

There are four basic shapes and avariety of special shapes. Becauseapproximately 95 percent of all machin-ing is done with the four basic shapes,

these are the ones of inter-est here. The four basicshapes are:• square• triangle• diamond• round

These shapes are avail-able in many different con-figurations for almost anyjob. Each shape can beobtained for positive, nega-tive, or positive/negativerake, with or without chip breakergrooves, with or without holes, withvarious edge preparations, in varioustolerances, and in various radii andsizes. A variety of insert shapes andconfigurations are shown in Figure 2.27

Choosing a particular shape or insertrequires a great deal of planning andthought. The choice of insert shapemust be based on such factors as theworkpiece configuration and tolerance,workpiece material, amount of materialto be removed, machine tool capability,and economics.

The insert shape also has an influenceon insert strength. As shown in Figure2.28, the greater the included angle atthe insert tip, the greater the strength.The round insert and the 100 degreecorner of the first diamond shaped insertare shown as the strongest. Because ofthe higher cutting forces and the possi-bility of chatter, these inserts are morelimited in use than the square shape.Therefore, for practical purposes, thesquare insert is the strongest for generaluse. Triangle and diamond insertsshould only be used when a square can-not be used, such as when machining toa corner or a shoulder.

The Round Insert: Round or buttoninserts give a good finish at heavyfeeds, and they are also ideal for form-ing inside corner radii. Their shape pro-vides the greatest geometric strength,and they offer the maximum number ofindexes when light cuts are being taken.The solid button type which isheld in place by means of a clamp,generally has edges at 90 degreesto the surfaces for use in negativerake holders, thereby providingcutting edges on both sides of theinsert. The CDH button type ismade in larger sizes and has acounterbored hole. This buttonhas clearance and is normally heldin the toolholder with neutral

rake. A typical application is for tracingor contouring, where the tool must gen-erate forms which require a large por-tion of the cutting edge to be in the cut.

Round inserts have their limitations,however, since the large nose radiusthins the chips and increases the forcesbetween the tool and workpiece for agiven size cut. Very high radial forcesare usually incurred as compared withnormal cutting, particularly at normalfeed rates. Chatter and deflection oftenresult, especially when machining long-chip materials. For this reason, buttoninserts are applied with greater successon cast iron and the other short-chip,low-strength materials, although heavyfeed rates will often improve the cuttingaction on ductile materials.

The Square Insert: Square insertsprovide four or eight cutting edges,depending on the design of the tool-holder. Positive rakes mean that reliefangles must be ground on the insert,thereby eliminating the use of one side.

Square inserts are preferred for mostmachining jobs, where the workpieceand tool design relationships allow theiruse. Their shape provides strength closeto that of the round insert, but with theeconomy of four or eight cutting edges,and also permits a reduction in the sidecutting edge angle and the problemrelated to the chip-thinning action of theround. Economical tool application dic-tates the use of an insert shape whichgives the maximum number of cutting

FIGURE 2.27 Various insert shapes, with and withoutholes, with and without chip breakers. (CourtesyAmerican National Carbide Co.)

FIGURE 2.28 Various insert shapes as related tostrength.

Round

3555608090100120

Strength increasing

Chap. 2: Metall Removal Methods


edges and is compatible with themachining operation. If the operationrequires machining to a square shoulder,the square insert would be eliminatedbecause of the design of an ‘A’ styletool. Since end cutting edge angle(ECEA) is required so that the tool willclear the machined surface, somethingless than a 90 degree included anglebetween the side and end of the tool ismandatory.

The Triangular Insert: Owing todesign and application requirements,one of which has just been pointed out,the triangular insert has assumed animportant place in indexable tooling.The triangle provides three or six cut-ting edges, depending on whether reliefangles are required on the insert for usein a positive rake holder. The 60 degreeincluded angle is not as strong as the 90degree of the square, or the radius of thebutton, yet many machining operationsare performed satisfactorily with trian-gular inserts. Turning to a shoulder,plunging and contouring, and numerousother operations require a generous endcutting edge angle which the trianglecan provide. The 60 degree includedangle is also suitable for threading oper-ations.

Because of its fewer cutting edgesand lower strength, the triangular insertand holder should only be used whenother geometric shapes will not meet thejob requirements.

The Pentagon Insert: A pentagon orfive-sided insert is a means of providingone or two more cutting edges perinsert, and the extra edges are the mainreason for this design. There is, ofcourse, a strength advantage over thesquare and triangle in the 108 degreeincluded angle. As in the case of thesquare, the pentagonal shape sets upcertain design and application limita-tions. The tool must always cut with aside cutting edge angle (SCEA), whichthins the chip and improves tool life.However, SCEA cannot always be usedowing to the requirements of the fin-ished part’s shape or because theincreased radial forces cause chatter anddeflection of the workpiece. The mini-mum SCE angle which can be used is24 degrees. This then leaves 6 degreesend cutting edge (ECE) angle. AnSCEA of 33 degrees results in 15degrees of ECEA which is the same asthat used on standard ‘B’ style tools andis quite adequate.

The Diamond Insert: The trend inlathe design is toward machines whichgenerate the form on the workpiece.This is accomplished by guiding thetool so it faces, plunges, turns, andforms radii, chamfers, and machinesother configurations. In order for a toolto satisfy the requirements of thesecomplex maneuvers, it must meet cer-tain design standards. Since the tooloften plunges along an angle, a greatamount of ECEA is needed. Back fac-ing is also a common operation on suchsetups, and this requires negativeSCEA.

The diamond insert was developedspecifically for tracing operations. Theindustry’s standard marking systemincludes designations for diamondinserts with included angles of 86, 8055, and 35 degrees. By far the mostpopular size is the 55 degree includedangle diamond. This geometry appar-ently meets the requirements of mosttracing operations. When the insert ispositioned in the toolholder and toolblock so that it cuts with 3 degree nega-tive SCEA, it will back face with depthsof cut up to 0.020 inch and in most tool-holders will be able to plunge at anangle of 20 degrees with adequate clear-ance.

Holding the insert securely in theholder so that duplication of workpiecesize to tolerances specified is achieved,has been a problem. The tendency forthe insert to twist in the pocket on turn-ing and plunging operations, and to bepulled out of the pocket on back facingoperations, has resulted in designchanges by some manufacturers.Diamond tracer inserts are made in reg-ular and elongated shapes. The elon-gated diamond provides greater resis-tance to the twisting action set up by thecutting forces.

Further developments are still beingmade in tracer inserts and holders sothat they will meet the exacting require-ments of tracing operations better. Insome designs the diamond shapedinsert, either regular or elongated, islocked into the pocket with an eccentricpin. This gives a positive holding actionand locates the insert against the backwalls of the pocket, minimizing thechances for movement during the con-touring operations.

The selection of a tool for a tracingoperation should begin with an analysisof the requirements of the contouring

operations. The tool selected should bethe one which provides the strongestgeometric shape and still meets the con-touring requirements. Many tracingjobs can be done satisfactorily with atriangular insert. If no back facing isincluded in the operations, no negativeSCEA is needed and a standard ‘A’ styletool can be used. In some cases it ispossible to use a tool designed to cutwith SCEA. Generally, better tool lifewill be realized with lower cost per cut-ting edge, when tools without negativeSCEA can be used.

The Parallelogram Insert: The par-allelogram-shaped insert provides someadvantages which make its use justifiedin certain applications. When a longside cutting edge is needed, it is some-times more economical and advanta-geous from a machining standpoint, touse a parallelogram rather than a squareor triangle.

The parallelogram also permits theconstruction of an ‘A’ style tool withgreater geometric strength than is possi-ble with a triangular insert. A limitationof the parallelogram design is the num-ber of usable cutting edges. A negativerake insert can be used on two cornersin a right or left-hand holder. To use theremaining two cutting edges, the oppo-site hand holder is required. Unless allfour corners can be used, the use of theparallelogram insert may not be eco-nomically justifiable.

The Hexagonal Insert: A versatiletool makes use of a hexagonal shapedinsert. Turning, facing, and chamferingcan all be done from a number of posi-tions. Its shape provides strong cuttingedges as in the case of the pentagon, butalso necessitates cutting with consider-able SCEA. The number of usable cut-ting edges in this design makes it a mosteconomical insert where it can beapplied.

The On-Edge Insert: The on-edgeinsert concept (Fig. 2.29), has only beenin use for a short time, but is becomingmore common. The on-edge insert wasfirst developed for milling operations.The main reason for its developmentwas to provide the strength needed towithstand the constant interruption ofmilling cuts. The on-edge concept isnow becoming more popular for turninginserts as well.

The main use of the on-edge insert isfor rough cutting when cutting forcesare high and the interruptions are often



severe. The extra thickness of the on-edge

insert offers more protection from heatand shock damage to the opposite sidecutting edge during heavy roughing,than is common with standard inserts.A milling cutter section with on-edgeinserts is shown in Figure 2.30.

2.5.2 Indexable Inserts - Classes and Sizes

Inserts are commercially available withvarious degrees of dimensional toler-ances, such as the inscribed circle of atriangle, the measurement across theflats of a square or elongated diamond,thickness, nose radii, and tangency. Allthese dimensions, and several other fac-tors, contribute to the ability of an insertto be accurately indexed and to machinea given material to a specific size. Theneed for inserts with different tolerancesdepends not so much on the dimension-al size of the finished part, but more onhow the insert is to be used in themachining operation.

Unground Inserts: Throughimproved manufacturing techniques,many carbide producers can supplyinserts that are to the required specifica-

tions, thus elimi-nating the grind-ing operation.Cutting edgesproduced by thismethod are notonly metallurgi-cally sound instructure, but arealso honed togive them geo-metric increase instrength.

U t i l i t yInserts: Thistype of insert isground on the topand bottom facesonly.

P r e c i s i o nInserts: These are ground all over andto close tolerances.

Honed Inserts: The development ofproduction honing techniques forinserts has made standard inserts avail-able to the machining industry in theprehoned condition. These inserts havethe advantage of not only having thecracked crystal layer removed from thecutting edge area, but also from the cut-ting tool surfaces. Lighter finishingcuts taken with finishing grades of car-bide should have small amounts of hon-ing performed on the cutting edge.Roughing grades should, conversely, behoned heavily. Carbide Insert HoningEquipment is shown in Figure 2.31.

Insert Size: The size of an insert isdetermined by its inscribed circle (I.C.).Every insert has an I.C. regardless of theinsert shape (Fig. 2.32). The I.C. is des-ignated in fractions of an inch in theUnited States, normally in 1/8 inchincrements. The thickness of the insertis designated by its actual thickness inincrements of 1/16 inch, and the noseradius is designated in increments of1/64 inch.

The thickness of the insert is usuallystandard to a particular I.C. Sometimeshowever, a choice of thickness will beavailable. In these situations, the thick-ness that is appropriate to the amount ofcutting force that will be applied is theoptimum choice. If a thin insert is cho-sen, a thicker shim should be used tokeep the cutting edge at the workpiececenterline.

2.5.3 Indexable Insert Identification System

A standard marking system, proposedby the Cemented Carbide ProducersAssociation and approved by theAmerican National Standards Institute(ANSI), has been adopted by thecemented carbide manufacturers. Anew identification and numbering sys-tem became necessary, due to the addi-tion of an expanded range of types andsizes of inserts incorporating a widevariety of detail. Under this new sys-tem, the insert number, with the manu-facturer’s grade of carbide, is all that isneeded to describe the insert. (See Fig.2.33). The eight sequences of markingindexable inserts are:• Shape • Size• Thickness • Clearance

Angle• Cutting Point • Class• Other Conditions • Type

Insert Economics: The cost of car-bide and other tool materials as well as

Cuttingforce

Cuttingedge Feed

FIGURE 2.29 On-edge turning tooldesign.

FIGURE 2.32 The size of an insert isdetermined by its inscribed circle (I.C.).

FIGURE 2.31 Carbide-insert honing equipment. (CourtesyAmerican National Carbide Co.)

FIGURE 2.30 On-edge milling cutter sec-tion. (Courtesy Ingersoll Cutting Tool Co.)

I.C.I.C.

I.C.I.C.



the cost of preparing these materialsinto cutting tools is relatively high andcontinuing to increase. Therefore, it ismost important to choose tool insertswisely. Here are some important thingsto consider when making the choice:• Chose a shape that offers the most cut-ting edges.

Examples:A negative insert has twice as many

cutting edges as a positive insert.A square insert has 25 percent more

cutting edges than a triangle insert. A double sided chip breaker insert has

twice as many cutting edges as asingle sided insert.

• Choose an I.C. appropriate to theamount of material to be removed.

Examples:A 1 inch I.C. square insert for a 1/4

inch depth of cut would be wasteful,because a large piece of expensivecarbide would be used where asmaller piece would achieve thesame result.

• Choose an insert tolerance that isappropriate to the job being done. Inmost cases an unground utility gradewill do the job. The closer the toler-ance, the higher the cost. Tight insert

FIGURE 2.33 Standard Identification System for indexable inserts. (Courtesy Cemented Carbide Producers Association)

Insert Shape Tolerance Class (1)

A — B — C — D — E — H — K — L — M — O — P — R — S — T — V — W —

(B) Cutting Pt. (A) I.C. (T) Thickness

(2)A= 0.001B = 0.0002C = 0.0005D = 0.0005E = 0.001G = 0.001

(3)M = 0.002-0.010(3)U = 0.005-0.012

0.0010.0010.0010.0010.0010.001

0.002-0.0040.005-0.010

0.0010.0050.0010.0050.0010.0050.0050.005

R = Blank with grind stock on all surfacesS = Blank with grind stock on top and

bottom surfaces only

Tolerance given are plus and minus from nominalThese tolerances normally apply to indexable insertswith facets (secondary cutting edges)The tolerance depends on the size and shape of the insertand should be as shown in the standards for thecorresponding shapes and sizes (See ANSI 894-25).

Cutting PointConfiguration

0 — 1 — 2 —3 —4 —6 —8 —A —D —E —F —K —

L —

M —N —P —

Sharp Corner (.003 or less)1/64 inch Radius1/32 inch Radius3/64 inch Radius1/16 inch Radius3/32 inch Radius1/8 inch RadiusSquare insert 45¡ ChamferSquare insert 30¡ ChamferSquare insert 15¡ ChamferSquare insert 3¡ ChamferSquare insert 30¡ DoubleChamferSquare insert 15¡ DoubleChamferSquare insert 3¡ DoubleChamferTruncated Triangle InsertFlatted Corner Triangle

Clearance

N — 0¡A — 3¡B — 5¡C — 7¡P — 11¡D — 15¡E — 20¡F — 25¡

G — 30¡H — 0¡ — 11¡J — 0¡ — 14¡K — 0¡ — 17¡L — 0¡ — 20¡M — 11¡ — 14¡R — 11¡ — 17¡S — 11¡ — 20¡

Secondary facet angle may vary by — 12

Insert Style

A —B —C —D —E —F —

G —

H —

J —

M —

P —

R —

Z —

X —

With holeWith hole and one countersinkWith hole and two countersinksSmaller than 1/4 I.C. with holeSmaller than 1/4 I.C. without holeClamp-on type with chipbreaker-no holeWith hole and chipbreaker topand bottomWith hole, one countersink andchipbreaker top onlyWith hole, two countersinks andchipbreaker — top and bottomWith hole andchipbreaker — top only10¡ positive land with hole andchipbreaker top and bottomWith hole and extra widechipbreaker top and bottomHigh positive land with hole andchipbreaker top and bottomWith hole, chipbreakers top andbottom with negative land angle

Thickness

Regular Polygons and Dia-monds Number 1/16thsof an inch in thickness for ICat 1/4 inch and over. For lessthan 1/4 inch I.C. the numberof 1/32nds inch.Rectangles and Parrallelo-grams. Use width dimensionin place of I.C.

Cutting Edge

F — SharpE — HonedT — K-LandS — K-Land

w/Hone

Size I.C.

Regular Polygons and Dia-monds Number 1/16thsof an inch in I.C. when I.C. is1/4 inch & over. For I.C. of less than 1/4 inch the num-ber of 1/32nd in I.C. Rectan-gles & Parallelograms. Use 2digits to size.1st Digit - Number of inchesin width2nd Digit - Number of inches in length.

Parallelogram 85¡Parallelogram 82¡Diamond 80¡Diamond 55¡Diamond 75¡HexagonParallelogram 55¡RectangleDiamond 86¡OctagonPentagonRoundSquareTriangleDiamond 35¡Trigon 80¡

TNMG — 432E



tolerances are normally required onlywhen the indexability of an insert is crit-ical.

Example:A ‘C’ tolerance insert used for finishing

to a workpiece tolerance of plus orminus 0.010 inch would not be neces-sary. An ‘M’ or even a ‘U’ toleranceinsert would be satisfactory.

• Choose a single sided insert when con-ditions make its efficiency more eco-nomical.

Example:A heavy roughing cut has made the sec-

ond side of a less efficient doublesided insert unusable because of heatand shock damage.

2.5.4 Mechanical Tool HoldersThe revolution of the indexable inserthas resulted in the availability of a widerange and variety of tool holders. Anumber of tool holders with inserts areshown in Figure 2.34.

To select or recommend the bestholder for every machining applicationwould be a formidable task. The prac-tice in many manufacturing plants is tostandardize on one or two designs, sothat a minimum of repair parts andaccessories need to be carried in inven-tory. There are basic designs and con-struction elements common to all hold-ers.• The Shank• The Seat• The Clamp or Locking Device

Turning toolholders have been stan-dardized as shown in Figure 2.35.

The Shank: The shank is the basicelement of the toolholder and its pur-pose is to hold and present the cuttingedge to the workpiece. It usually hasdrilled and tapped holes, slots andcutouts, and it must provide a firm sup-port for the carbide cutting edge.Generally shanks are made of high-car-bon or low-alloy steel, heat treated togive physical properties that will resistthread damage, chip erosion and defor-mation under the tool-block clamping

FIGURE 2.34 Four toolholders with various insert styles and sizes (CourtesyKennametal Inc.)

1HoldingMethod

S — Screw onlyM — Clamp and

Locking PinC — Clamp onlyP — Locking Pin

Only

A — Straight Shankwith 0¡ side cuttingedge angleB — Straight Shankwith 15¡ sidecutting edge angleC — Straight Shankwith 0¡ end cuttingedge angleD — Straight Shankwith 45¡ side cut-ting angleE — Straight Shankwith 30¡ side cut-ting angleF — Offset Shankwith 0¡ end cut-ting edge angleG — Offset Shankwith 0¡ side cut-ting edge angle

H — Threading andShallow GroovingI.D.J — Offset Shankwith Negative 3¡side cutting edgeangleK — Offset Shankwith 15 end cut-ting edge angleL — Offset shankwith negative 5¡side or end cuttingedge angleM — Straight Shankwith 40¡ side cut-ting edge angleP — Straight Shankwith 27 1/2¡ side cutting edge angle

R — Offset Shankwith 15¡ side cut-ting edge angleS — Offset Shankwith 45¡ side cut-ting edge angleT — Offset Shankwith 30¡ side cut-ting edge angleV — Threading andshallow groovingO.D.W — Offset Shankwith 10¡ side cut-ting edge angleZ — Offset Threadingand grooving O.D.

4 Holder Rake

N — NegativeO — NeutralP — PositiveA — Hi-Positive

5 Handof Tool

L — LeftN — NeutralR — Right

7 InsertSize I.C.

Number of 1/8thson 1/4 IC andover.Number of 1/32ndson 1/4 1 C andunder.

6ToolholderShank Size

This position is asignificant numberwhich indicates theholder cross sec-tion. For squareshants this num-ber represents thenumber of six-teenths of widthand height.For rectangularholders the firstdigit represents thenumber of eights ofwidth and the sec-ond digit the num-ber of quarters ofheights except thefollowing toolhold-ers 11/4 x 11/2which is given thenumber 91.

2Insert

GeometryC — 80¡ DiamondD — 55¡ Diamond V — 35¡ DiamondT — TriangleS — SquareR — Round*Q — Deep

GroovingCutoff andTracing

3 Toolholder Style

MTFNR — 16 — 4

FIGURE 2.35 Standard identification system for turning toolholders. (Courtesy Cemented Carbide Producers Association)



screws. Some designs and sizes whichdo not make use of a carbide seat aremade of high alloy steel to resist defor-mation under the insert.

The machined area for the seat andinsert is one of the most critical areasand must be flat to provide the propersupport for the carbide seat and insert.Common practice is to relieve the insidecorner for seat and insert clearance. Theintersections of the sides and bottom ofthe pocket usually have a small radius,since sharp corners may be the source ofcracks during heat treatment. A toolshank with basic components is shownin Figure 2.36.

The Seat: Most toolholders forindexable inserts use a carbide seat orpad as support for the insert. Cementedtungsten carbide has a high compressivestrength, is hard, and can be ground to asmooth flat surface. While hardenedsteel has been used, and still is in somedesigns, a strong preference for carbideseats prevails.

The seats shown in Figure 2.37 aretypical and will serve to illustrate thebasic design. The periphery is cham-fered at one face to clear any radius inthe steel shank pocket area. If the seator pad is held in place by a screw, thehole will be deeply countersunk so thatthe head of the screw will be well belowthe surface. If the screw head projectsabove the seat surface and the insert isclamped down on it, breakage of the lat-ter could result.

The seat is attached to the shank onlyfor convenience and to prevent its losswhen inserts are removed and replaced,or if the holder is used vertically as in avertical turret lathe or upside down as inthe rear tool post of a turret lathe.

Seat flatness is one of the most criti-cal requirements of tool holders.Application tests have shown that anout-of-flatness condition, of as little as0.001 inch, can result in insert breakage.Regardless of the design of the tool-holder selected, the pocket and seat flat-ness specifications should be carefullyexamined and the highest standards

insisted upon.The Clamp or Locking Device: Many

clamping and locking arrangementshave been developed for holding theinsert in a toolholder and there is proba-bly no one best method or design, sincespecific application requirements varyso greatly. There are a number of fea-tures and construction elements, howev-er, which warrant consideration andshould influence the selection of a tool-holder (Fig. 2.38).

The main function of the clampingmechanism is to hold the insert securelyin position and many methods of doing

FIGURE 2.36 Tool shank with basic com-ponents. (Courtesy Kennametal Inc.)

FIGURE 2.37 Schematic drawing of various insert-locking positions.

FIGURE 2.38 Various pin-type holder-locking options.

Chip breaker

Insert

SeatInsert

Seat

Insert

Seat

Type 1

Retainer clip

Insert

Shim seat

Pin Lock screwWedge

Shank

Type 2

Shim lock

Shim

Insert

Pin Lock screwShank

Spring(compressed)

Type 3

Shim lock

Shim

Insert

Lock screwLock

Holder body

Type 4

HolderLock pin

Insert

Shim

Lock cup



so are in use. On normal turning andfacing operations, the insert in moststyles of toolholders is held in the pock-

et by the cutting pressures,and the load on the clamp isvery light except as affectedby the chip. Tracing andthreading operationschange the direction andamount of the load appliedto the insert, and there ismore tendency to twist orpull the insert out of thepocket. The ability of theclamping mechanism, toperform satisfactorily undersuch conditions, should becarefully evaluated. Theuse of a pin or lever mecha-nism has been incorporatedin some designs to give amore positive holdingaction against the insert.

The suitability of the clamp design tothe machine toolholding blocks and tothe workpiece configuration should be

considered. Bulky club heads, highclamps on clamping screws, or intricateadjusting mechanisms may be in theway, especially when tools must beganged up, or when machine and work-piece clearances are small. A toolhold-er which is not easily accessible andmust be removed from the machine sothe insert can be indexed or the chipbreaker adjusted, should not be consid-ered suitable for the application. Anumber of tool holders are shown inFigure 2.39 where indexable inserts arebeing held by both pins and clamps.

Tools which are positioned upsidedown should have a wrench socket inthe lower end of the clamping screw sothat it can be easily reached. Chip-breaker plates and clamp parts shouldbe secured so that they will not bedropped in the chip pan when loosenedfor insert changing.

FIGURE 2.39 Three toolholders in which inserts areheld by both pins and clamps. (Courtesy SandvikCoromant Corp.)


3.1 IntroductionThe condition and physical properties of the work material have a direct influence on themachinability of a work material. The various conditions and characteristics described as‘condition of work material’, individually and in combinations, directly influence anddetermine the machinability. Operating conditions, tool material and geometry, and work-piece requirements exercise indirect effects on machinability and can often be used toovercome difficult conditions presented by the work material. On the other hand, theycan create situations that increase machining difficulty if they are ignored. A thoroughunderstanding of all of the factors affecting machinability and machining will help inselecting material and workpiece designs to achieve the optimum machining combina-tions critical to maximum productivity.

3.2 Condition of Work MaterialThe following eight factors determine the condition of the work material: microstructure,grain size, heat treatment, chemical composition, fabrication, hardness, yield strength,and tensile strength.

Microstructure: The microstructure of a metal refers to its crystal or grain structureas shown through examination of etched and polished surfaces under a microscope.Metals whose microstructures are similar have like machining properties. But there canbe variations in the microstructure of the same workpiece, that will affect machinability.

Grain Size: Grain size and structure of a metal serve as general indicators of itsmachinability. A metal with small undistorted grains tends to cut easily and finish easi-ly. Such a metal is ductile, but it is also ‘gummy’. Metals of an intermediate grain sizerepresent a compromise that permits both cutting and finishing machinability. Hardnessof a metal must be correlated with grain size and it is generally used as an indicator ofmachinability.

Heat Treatment: To provide desired properties in metals, they are sometimes putthrough a series of heating and cooling operations when in the solid state. A material maybe treated to reduce brittleness, remove stress, to obtain ductility or toughness, to increasestrength, to obtain a definite microstructure, to change hardness, or to make other changesthat affect machinability.

Chemical Composition: Chemical composition of a metal is a major factor in deter-mining its machinability. The effects of composition though, are not always clear,because the elements that make up an alloy metal, work both singly and collectively.Certain generalizations about chemical composition of steels in relation to machinabilitycan be made, but non-ferrous alloys are too numerous and varied to permit such general-izations.

Fabrication: Whether a metal has been hot rolled, cold rolled, cold drawn, cast, orforged will affect its grain size, ductility, strength, hardness, structure - and therefore - itsmachinability.

The term ‘wrought’ refers to the hammering or forming of materials into premanfac-

Chapter 3

Machinability of

Metals

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing







tured shapes which are readily alteredinto components or products using tra-ditional manufacturing techniques.Wrought metals are defined as thatgroup of materials which are mechani-cally shaped into bars, billets, rolls,sheets, plates or tubing.

Casting involves pouring moltenmetal into a mold to arrive at a nearcomponent shape which requires mini-mal, or in some cases no machining.Molds for these operations are madefrom sand, plaster, metals and a varietyof other materials.

Hardness: The textbook definitionof hardness is the tendency for a mater-ial to resist deformation. Hardness isoften measured using either the Brinellor Rockwell scale. The method used tomeasure hardness involves embedding aspecific size and shaped indentor intothe surface of the test material, using apredetermined load or weight. The dis-tance the indentor penetrates the mater-ial surface will correspond to a specificBrinell or Rockwell hardness reading.The greater the indentor surface pene-tration, the lower the ultimate Brinell orRockwell number, and thus the lowerthe corresponding hardness level.Therefore, high Brinell or Rockwellnumbers or readings represent a mini-mal amount of indentor penetration intothe workpiece and thus, by definition,are an indication of an extremely hardpart. Figure 3.1 shows how hardness ismeasured.

The Brinell hardness test involvesembedding a steel ball of a specificdiameter, using a kilogram load, in thesurface of a test piece. The BrinellHardness Number (BHN) is determinedby dividing the kilogram load by thearea (in square millimeters) of the circlecreated at the rim of the dimple orimpression left in the workpiece sur-face. This standardized approach pro-vides a consistent method to make com-


parative tests between a variety ofworkpiece materials or a single materialwhich has undergone various hardeningprocesses.

The Rockwell test can be performedwith various indentor sizes and loads.Several different scales exist for theRockwell method or hardness testing.The three most popular are outlinedbelow in terms of the actual applicationthe test is designed to address:

Rockwell Testing Scale Application

A For tungsten carbide and other extremely hard materials & thin, hard sheets.

B For medium hardness low and medium carbon steels in the annealed condition.

C For materials > than Rockwell ‘B’ 100.

In terms of general machining prac-tice, low material hardness enhancesproductivity, since cutting speed is oftenselected based on material hardness(the lower the hardness, the higher thespeed). Tool life is adversely affected byan increase in workpiece hardness,since the cutting loads and tempera-tures rise for a specific cutting speedwith part hardness, thereby reducing

tool life. In drilling and turning, theadded cutting temperature is detrimen-tal to tool life, since it produces excessheat causing accelerated edge wear. Inmilling, increased material hardnessproduces higher impact loads as insertsenter the cut, which often leads to a pre-mature breakdown of the cutting edge.

Yield Strength: Tensile test work isused as a means of comparison of metalmaterial conditions. These tests can

establish the yield strength, tensilestrength and many other conditions of amaterial based on its heat treatment. Inaddition, these tests are used to comparedifferent workpiece materials. The ten-sile test involves taking a cylindrical rodor shaft and pulling it from oppositeends with a progressively larger force ina hydraulic machine. Prior to the startof the test, two marks either two or eightinches apart are made on the rod orshaft. As the rod is systematically sub-jected to increased loads, the marksbegin to move farther apart. A materialis in the so-called ‘elastic zone’ whenthe load can be removed from the rodand the marks return to their initial dis-tance apart of either two or eight inches.If the test is allowed to progress, a pointis reached where, when the load isremoved the marks will not return totheir initial distance apart. At this point,permanent set or deformation of the testspecimen has taken place. Figure 3.2shows how yield strength is measured.

Yield strength is measured just priorto the point before permanent deforma-tion takes place. Yield strength is statedin pounds per square inch (PSI) and isdetermined by dividing the load justprior to permanent deformation by thecross sectional area of the test speci-men. This material property has beenreferred to as a condition, since it can bealtered during heat treatment. Increasedpart hardness produces an increase inyield strength and therefore, as a partbecomes harder, it takes a larger force toproduce permanent deformation of thepart. Yield strength should not be con-fused with fracture strength, cracking orthe actual breaking of the material intopieces, since these properties are quitedifferent and unrelated to the currentsubject.

By definition, a material with highyield strength (force required per unit ofarea to create permanent deformation)requires a high level of force to initiatechip formation in a machining opera-tion. This implies that as a material’syield strength increases, stronger insertshapes as well as less positive cuttinggeometries are necessary to combat theadditional load encountered in the cut-ting zone. Material hardness and yieldstrength increase simultaneously duringheat treatment. Therefore, materialswith relatively high yield strengths willbe more difficult to machine and willreduce tool life when compared to mate-

Chap. 3: Machinability of Metals

Load 500 kg

Large indentation Small indentation

Soft part

Load500 kg

Hard partt

Figure 3.1 Hardness is measured by depth of indentations made.



rials with more moderate strengths.Tensile Strength: The tensile

strength of a material increases alongwith yield strength as it is heat treated togreater hardness levels. This materialcondition is also established using a ten-sile test. Tensile strength (or ultimatestrength) is defined as the maximumload that results during the tensile test,divided by the cross-sectional area ofthe test specimen. Therefore, tensilestrength, like yield strength, isexpressed in PSI. This value is referredto as a material condition rather than aproperty, since its level just like yieldstrength and hardness, can be altered byheat treatment. Therefore, based on thematerial selected, distinct tensile andyield strength levels exist for each hard-ness reading.

Just as increased yield strengthimplied higher cutting forces duringmachining operations, the same couldbe said for increased tensile strength.Again, as the workpiece tensile strengthis elevated, stronger cutting edgegeometries are required for productivemachining and acceptable tool life.

3.3 Physical Properties of Work Materials

Physical properties will include thosecharacteristics included in the individ-ual material groups, such as the modu-lus of elasticity, thermal conductivity,thermal expansion and work hardening.

Modulus of Elasticity: The modulusof elasticity can be determined during atensile test in the same manner as thepreviously mentioned conditions.However, unlike hardness, yield or ten-sile strength, the modulus of elasticity isa fixed material property and , therefore,is unaffected by heat treatment. Thisparticular property is an indicator of therate at which a material will deflectwhen subjected to an external force.This property is stated in PSI and typi-cal values are several million PSI for

metals. A 2” x 4” x 8 ft. wood beamsupported on either end, with a 200pound weight hanging in the middle,will sag 17 times more than a beam ofthe same dimensions made out of steeland subjected to the same load. The dif-ference is not because steel is harder orstronger, but because steel has a modu-lus of elasticity which is 17 timesgreater than wood.

General manufacturing practice dic-tates that productive machining of aworkpiece material with a relativelymoderate modulus of elasticity normal-ly requires positive or highly positiveraked cutting geometries. Positive cut-ting geometries produce lower cuttingforces and, therefore chip formation isenhanced on elastic material usingthese types of tools. Sharp positive cut-ting edges tend to bite and promoteshearing of a material, while blunt neg-ative geometries have a tendency to cre-ate large cutting forces which impedechip formation by severely pushing ordeflecting the part as the tool enters thecut.

Thermal Conductivity: Materialsare frequently labeled as being eitherheat conductors or insulators.Conductors tend to transfer heat from ahot or cold object at a high rate, whileinsulators impede the flow of heat.Thermal conductivity is a measure ofhow efficiently a material transfers heat.Therefore, a material which has a rela-tively high thermal conductivity wouldbe considered a conductor, while onewith a relatively low level would beregarded as an insulator.

Metals which exhibit low thermalconductivities will not dissipate heatfreely and therefore, during the machin-ing of these materials, the cutting tooland workpiece become extremely hot.This excess heat accelerates wear at thecutting edge and reduces tool life. Theproper application of sufficient amountsof coolant directly in the cutting zone

(between the cutting edge and work-piece) is essential to improving tool lifein metals with low thermal conductivi-ties.

Thermal Expansion: Many materi-als, especially metals, tend to increasein dimensional size as their temperaturerises. This physical property is referredto as thermal expansion. The rate atwhich metals expand varies, dependingon the type or alloy of material underconsideration. The rate at which metalexpands can be determined using thematerial’s expansion coefficient. Thegreater the value of this coefficient, themore a material will expand when sub-jected to a temperature rise or contractwhen subjected to a temperature reduc-tion. For example, a 100 inch bar ofsteel which encounters a 100 degreeFahrenheit rise in temperature wouldmeasure 100.065 inches. A bar of alu-minum exposed to the same set of testconditions would measure 100.125inches. In this case, the change in thealuminum bar length was nearly twicethat of the steel bar. This is a clear indi-cation of the significant difference inthermal expansion coefficients betweenthese materials.

In terms of general machining prac-tice, those materials with large thermalexpansion coefficients will make hold-ing close finish tolerances extremelydifficult, since a small rise in workpiecetemperature will result in dimensionalchange. The machining of these typesof materials requires adequate coolantsupplies for thermal and dimensionalstability. In addition, the use of positivecutting geometries on these materialswill also reduce machining tempera-tures.

Work Hardening: Many metalsexhibit a physical characteristic whichproduces dramatic increases in hard-ness due to cold work. Cold workinvolves changing the shape of a metalobject by bending, shaping, rolling orforming. As the metal is shaped, inter-nal stresses develop which act to hardenthe part. The rate and magnitude of thisinternal hardening varies widely fromone material to another. Heat also playsan important role in the work hardeningof a material. When materials whichexhibit work hardening tendencies aresubjected to increased temperature, itacts like a catalyst to produce higherhardness levels in the workpiece.

The machining of workpiece materi-

Test Specimen

2.000”

Force = 0 lbsForce = 0 lbs

Figure 3.2 Yield strength is measured by pulling a test specimen as shown.



als with work hardening propertiesshould be undertaken with a generousamount of coolant. In addition, cuttingspeeds should correlate specifically tothe material machined and should notbe recklessly altered to meet a produc-tion rate. The excess heat created byunusually high cutting speeds could beextremely detrimental to the machiningprocess by promoting work hardeningof the workpiece. Low chip thicknessesshould be avoided on these materials,since this type of inefficient machiningpractice creates heat due to friction,which produces the same type of effectmentioned earlier. Positive low forcecutting geometries at moderate speedsand feeds are normally very effective onthese materials.

3.4 Metal MachiningThe term ‘machinability’ is a relativemeasure of how easily a material can bemachined when compared to 160Brinell AISI B1112 free machining lowcarbon steel. The American Iron andSteel Institute (AISI) ran turning tests ofthis material at 180 surface feet andcompared their results for B1112against several other materials. IfB1112 represents a 100% rating, thenmaterials with a rating less than thislevel would be decidedly more difficultto machine, while those that exceed100% would be easier to machine.

The machinability rating of a metaltakes the normal cutting speed, surfacefinish and tool life attained into consid-eration. These factors are weighted andcombined to arrive at a final machin-

ability rating. The following chartshows a variety of materials and theirspecific machinability ratings:

3.4.1 Cast IronAll metals which contain iron (Fe) areknown as ferrous materials. The word‘ferrous’ is by definition, ‘relating to orcontaining iron’. Ferrous materialsinclude cast iron, pig iron, wrought iron,and low carbon and alloy steels. Theextensive use of cast iron and steelworkpiece materials, can be attributedto the fact that iron is one of the mostfrequently occurring elements in nature.

When iron ore and carbon are metal-lurgically mixed, a wide variety ofworkpiece materials result with a fairlyunique set of physical properties.Carbon contents are altered in cast ironsand steels to provide changes in hard-ness, yield and tensile strengths. Thephysical properties of cast irons andsteels can be modified by changing theamount of the iron-carbon mixtures inthese materials as well as their manu-facturing process.

Pig iron is created after iron ore ismixed with carbon in a series of fur-naces. This material can be changedfurther into cast iron, steel or wroughtiron depending on the selected manu-facturing process.

Cast iron is an iron carbon mixturewhich is generally used to pour sandcastings, as opposed to making billets orbar stock. It has excellent flow proper-ties and therefore, when it is heated toextreme temperatures, is an ideal mate-rial for complex cast shapes and intri-cate molds. This material is often usedfor automotive engine blocks, cylinderheads, valve bodies, manifolds, heavyequipment oil pans and machine bases.

Gray Cast Iron: Gray cast iron is anextremely versatile, very machinablerelatively low strength cast iron used forpipe, automotive engine blocks, farmimplements and fittings. This materialreceives its dark gray color from theexcess carbon in the form of graphiteflakes which give it its name.

Gray cast iron workpieces have rela-tively low hardness and strength levels.However, double negative or negative(axial) positive (radial) rake anglegeometries are used to machine thesematerials because of their tendency toproduce short discontinuous chips.When this type of chip is produced dur-ing the machining of these workpieces,

the entire cutting force is concentratedon a very narrow area of the cuttingedge and therefore, double positive raketools normally chip prematurely onthese types of materials due to theirlower edge strength.

White Cast Iron: White cast ironoccurs when all of the carbon in thecasting is combined with iron to formcementite. This is an extremely hardsubstance which results from the rapidcooling of the casting after it is poured.Since the carbon in this material istransformed into cementite, the result-ing color of the material when chippedor fractured is a silvery white. Thus thename white cast iron. However, whitecast iron has almost no ductility, andtherefore when it is subjected to anytype of bending or twisting loads, itfractures. The hard brittle white castiron surface is desirable in thoseinstances where a material with extremeabrasion resistance is required.Applications of this material wouldinclude plate rolls in a mill or rockcrushers.

Due to the extreme hardness of whitecast iron, it is very difficult to machine.Double negative insert geometries arealmost exclusively required for thesematerials, since their normal hardnessis 450 - 600 Brinell. As stated earlierwith gray iron, this class of cast materi-al subjects the cutting edge to extremelyconcentrated loads, thus requiringadded edge strength.

Malleable Cast Iron: When whitecast iron castings are annealed (softenedby heating to a controlled temperaturefor a specific length of time), malleableiron castings are formed. Malleableiron castings result when hard, brittlecementite in white iron castings is trans-formed into tempered carbon orgraphite in the form of rounded nodulesor aggregate. The resulting material is astrong, ductile, tough and very machin-able product which is used on a broadscope of applications.

Malleable cast irons are relativelyeasy to machine when compared towhite iron castings. However, doublenegative or negative (axial)positive(radial) rake angle geometriesare also used to machine these materi-als as with gray iron, because of theirtendency to produce short discontinu-ous chips.

Nodular Cast Iron: Nodular or‘ductile’ iron is used to manufacture a

MaterialHardnessMachinability

Rating

6061-TAluminum —190%7075-TAluminum —120%B1112 Steel 160 BHN100%416 Stainless Steel 200 BHN90%1120 Steel160 BHN80%1020 Steel148 BHN



wide range of automotive engine com-ponents including cam shafts, crankshafts, bearing caps and cylinder heads.This materials is also frequently usedfor heavy equipment cast parts as wellas heavy machinery face plates andguides. Nodular iron is strong, ductile,tough and extremely shock resistant.

Although nodular iron castings arevery machinable when compared withgray iron castings of the same hardness,high strength nodular iron castings canhave relatively low machinability rat-ings. The cutting geometry selected fornodular iron castings is also dependenton the grade to be machined. However,double negative or positive (radial) andnegative (axial) rake angles are nor-mally used.

3.4.2 SteelSteel materials are comprised mainly ofiron and carbon, often with a modestmixture of alloying elements. Thebiggest difference between cast ironmaterials and steel is the carbon con-tent. Cast iron materials are composi-tions of iron and carbon, with a mini-mum of 1.7 percent carbon to 4.5 per-cent carbon. Steel has a typical carboncontent of .05 percent to 1.5 percent.

The commercial production of a sig-nificant number of steel grades is fur-ther evidence of the demand for thisversatile material. Very soft steels areused in drawing applications for auto-mobile fenders, hoods and oil pans,while premium grade high strengthsteels are used for cutting tools. Steelsare often selected for their electricalproperties or resistance to corrosion. Inother applications, non magnetic steelsare selected for wrist watches andminesweepers.

Plain Carbon Steel: This category ofsteels includes those materials whichare a combination of iron and carbonwith no alloying elements. As the car-bon content in these materials isincreased, the ductility (ability to stretchor elongate without breaking) of thematerial is reduced. Plain carbon steelsare numbered in a four digit codeaccording to the AISI or SAE system(i.e. 10XX). The last two digits of thecode indicate the carbon content of thematerial in hundredths of a percentagepoint. For example, a 1018 steel has a.18% carbon content.

The machinability of plain carbonsteels is primarily dependent on the car-

bon content of the material and its heattreatment. Those materials in the lowcarbon category are extremely ductile,which creates problems in chip break-ing on turning and drilling operations.As the carbon content of the materialrises above .30%, reliable chip controlis often attainable. These materialsshould be milled with a positive (radial)and negative (axial) rake angle geome-try. In turning and drilling operationson these materials, negative or neutralgeometries should be used wheneverpossible. The plain carbon steels as agroup are relatively easy to machine;they only present machining problemswhen their carbon content is very low(chip breaking or built up edge), orwhen they have been heat treated to anextreme (wear, insert breakage or depthof cut notching).

Alloy Steels: Plain carbon steels aremade up primarily of iron and carbon,while alloy steels include these sameelements with many other elementaladditions. The purpose of alloying steelis either to enhance the material’s phys-ical properties or its ultimate manufac-turability. The physical propertyenhancements include improved tough-ness, tensile strength, hardenability, (therelative ease with which a higher hard-ness level can be attained), ductility andwear resistance. The use of alloyingelements can alter the final grain size ofa heat treated steel, which often resultsin a lower machinability rating of thefinal product. The primary types ofalloyed steel are: nickel, chromium,manganese, vanadium, molybdenum,chrome-nickel, chrome-vanadium,chrome-molybdenum, and nickel-molybdenum. The following sum-maries detail some of the differences inthese alloys in terms of their physical aswell as mechanical properties foralloyed carbon steels:• Nickel - This element is used to

increase the hardness and ultimatestrength of the steel without sacrific-ing ductility.

• Chromium - Chromium will extendthe hardness and strength gainswhich can be realized with nickel.However, these gains are offset by areduction in ductility.

• Manganese - This category of alloyedsteels possesses a greater strengthlevel than nickel alloyed steels andimproved toughness when comparedto chromium alloyed steels.

• Vanadium - Vanadium alloyed steelsare stronger, harder and tougher thantheir manganese counterparts. Thisgroup of materials however, loses asignificant amount of its ductilitywhen compared to the manganesegroup to benefit from these otherphysical properties.

• Molybdenum - This group of alloyedsteels benefit from increased strengthand hardness without adverselyaffecting ductility. These steels areoften considered very tough, with animpact strength which approaches thevanadium steels.

• Chrome-Nickel - The alloying ele-ments present in the chrome nickelsteels produce a very ductile, tough,fine grain, wear resistant material.However, they are relatively unstablewhen heat treated and tend to distort,especially as their chromium andnickel content is increased.

• Chrome-Vanadium - This combina-tion of alloying elements produceshardness, impact strength and tough-ness properties which exceed those ofthe chrome-nickel steels. Thisalloyed steel has a very fine grainstructure and, therefore, improvedwear resistance.

• Chrome-Molybdenum - This alloyedsteel has slightly different propertiesthan a straight molybdenum alloy dueto the chromium content of the alloy.The final hardness and wear resis-tance of this alloy exceeds that of anormal molybdenum alloy steel.

• Nickel-Molybdenum - The propertiesof this material are similar to chrome-molydenum alloyed steels except forone, its increased toughness.The machinability of alloy steels

varies widely, depending on their hard-ness and chemical compositions. Thecorrect geometry selection for thesematerials is often totally dependent onthe hardness of the part. Double posi-tive milling or turning geometriesshould be selected for these materialsonly when either the workpiece,machine or fixturing lacks the neces-sary rigidity to use stronger higherforce generating geometries. In milling,positive (radial) negative (axial)geometries are preferred on alloyedsteels due to their strength and tough-ness. In turning operations, doublenegative or neutral geometries shouldbe used on softer alloy steels. Leadangled tools should be used on these



materials whenever possible to mini-mize the shock associated with cutterentry into the cut.

Tool Steels: This group of highstrength steels is often used in the man-ufacture of cutting tools for metals,wood and other workpiece materials. Inaddition, these high strength materialsare used as die and punch materials dueto their extreme hardness and wearresistance after heat treatment. The keyto achieving the hardness, strength andwear resistance desired for any toolsteel is normally through careful heattreatment. These materials are availablein a wide variety of grades with a sub-stantial number of chemical composi-tions designed to satisfy specific as wellas general application criteria.

Tool steels are highly alloyed andtherefore, quite tough; However, theycan often be readily machined prior toheat treatment. Negative cuttinggeometries will extend tool life whenmachining these materials, provided thesystem (machine, part and fixturing) isable to withstand the additional toolforce.

Stainless Steels: As the nameimplies, this group of materials isdesigned to resist oxidation and otherforms of corrosion, in addition to heat insome instances. These materials tend tohave significantly greater corrosionresistance than their plain or alloy steelcounterparts due to the substantial addi-tions of chromium as an alloying ele-ment. Stainless steels are used exten-sively in the food processing, chemicaland petroleum industries to transfer cor-rosive liquids between processing andstorage facilities. Stainless steels can becold formed, forged, machined, weldedor extruded. This group of materialscan attain relatively high strength levelswhen compared to plain carbon andalloy steels. Stainless steels are avail-able in up to 150 different chemicalcompositions. The wide selection ofthese materials is designed to satisfy thebroad range of physical propertiesrequired by potential customers andindustries.

Stainless steels fall into four distinctmetallurgical categories. These cate-gories include: austenitic, ferritic,martensitic, and precipitation harden-ing. Austenitic (300 series) steels aregenerally difficult to machine. Chattercould be a problem, thus requiringmachine tools with high stiffness.

However, ferritic stainless steels (also300 series) have good machinability.Martensitic (400 series) steels are abra-sive and tend to form built-up edge, andrequire tool materials with high hothardness and crater-wear resistance.Precipitation-hardening stainless steelsare strong and abrasive, requiring hardand abrasion-resistant tool materials.

3.4.3 Nonferrous Metals and AlloysNonferrous metals and alloys cover awide range of materials from the morecommon metals such as aluminum, cop-per, and magnesium, to high-strengthhigh-temperature alloys such as tung-sten, tantalum, and molybdenum.Although more expensive than ferrousmetals, nonferrous metals and alloyshave important applications because oftheir numerous properties, such as cor-rosion resistance, high thermal and elec-trical conductivity, low density, andease of fabrication.

Aluminum: The relatively extensiveuse of aluminum as an industrial as wellas consumer based material revolvesaround its many unique properties. Forexample, aluminum is a very light-weight metal (1/3 the density whencompared to steel), yet it possessesgreat strength for its weight. Therefore,aluminum has been an excellent materi-al for framing structures in military andcommercial aircraft. The corrosiveresistance of aluminum has made it apopular material selection for the softdrink industry (cans) and the residentialbuilding industry (windows and siding).In addition, most grades of aluminumare easily machined and yield greatertool life and productivity than manyother metals.

Aluminum is a soft, machinable metaland the limitations on speeds are gov-erned by the capacity of the machineand good safe practices. Chips are ofthe continuous type and frequently theyare a limiting safety factor because theytend to bunch up. Aluminum has beenmachined at such high speeds that thechip becomes an oxide powder. Toincrease its strength and hardness, alu-minum is alloyed with silicon, iron,manganese, nickel, chromium, andother metals. These materials should bemachined with positive cutting geome-tries.

Copper: Copper is a very popularmaterial which is widely used for itssuperior electrical conductivity, corro-

sion resistance and ease in formability.In addition, when alloyed properly, cop-per alloys can exhibit a vast array ofstrength levels and unique mechanicalproperties.

Several copper alloys are now inwidespread commercial use including:copper nickels, brasses. bronzes, cop-per-nickel-zinc alloys, leaded copperand many special alloys. Brass andbronze are the most popular copperalloys in use.

The machinability of copper and itsalloys varies widely. Pure copper andhigh copper alloys are very tough, abra-sive, and prone to tearing. To limit andprevent tearing, these materials shouldbe machined with positive cuttinggeometries. Positive geometries shouldalso be used on bronze and bronzealloys due to their toughness and duc-tility. Negative axial and positive radi-al rake angle geometries should be usedon brass alloys, since they have greaterlevels of machinability and in a caststate their chip formation is similar tocast iron.

Nickel: Nickel is often used as analloying element to improve corrosionand heat resistance and the strength ofmany materials. When nickel is alloyedor combined with copper (Monels),chromium (Inconels and Hastelloys) orchromium and cobalt (Waspalloys), itprovides a vast array of alloys whichexhibit a wide range of physical proper-ties. Other important alloys belongingto this group of materials include: Rene,Astroloy, Udimet, Incoloys, and severalHaynes alloys. The machinability ofnickel based alloys is generally quitelow.

Most nickel based alloys should bemachined using positive cutting geome-tries. Since these materials aremachined with carbide at 120 SFPM orless, positive rake angle geometries arerequired to minimize cutting forces andheat generation. In the machining ofmost materials, increased temperatureenhances chip flow and reduces thephysical force on the cutting edge.Adequate clearance angles must be uti-lized on these materials, since many ofthem are very ductile and prone to workhardening. When a tool is stopped andleft to rub on the workpiece, hardeningof the workpiece surface will oftenoccur. To avoid this condition, careshould be taken to insure that as long asthe cutting edge and part are touching,



the tool is always feeding.Titanium and Titanium alloys:

Titanium is one of the earth’s mostabundant metals. Thus, its applicationis fairly widespread from a cutting toolmaterial to the struts and framing mem-bers on jet aircraft. Titanium and itsalloys are often selected to be used inaerospace applications due to their highstrength to weight ratio and ductility.

The machining of titanium and itsalloys involves the careful selection ofcutting geometry and speed. Positiverake tools are often preferred on thesematerials to minimize part deflectionand to reduce cutting temperatures inthe cutting zone. The generous use ofcoolants on titanium and its alloys isstrongly advised to maintain thermalstability and thus avoid the disastrouseffects of accelerated heat and tempera-ture buildup which leads to workpiecegalling or tool breakage (drilling) andrapid edge wear. Type machinabilityrating for titanium and its alloys isapproximately 30% or less.

Refractory Alloys: The group ofmaterials designated as refractory alloysincludes those metals which containhigh concentrations of either tungsten(W), tantalum (Ta), molybdenum (Mo)or columbium (Co). This group ofmaterials is known for its heat resis-tance properties which allows them tooperate in extreme thermal environ-ments without permanent damage. Inaddition, these materials are known fortheir extremely high melting points andabrasiveness. Most of these materialsare quite brittle, thus, they possess verylow machinability ratings when alsoconsidering their heat resistance andextreme melting properties. Themachining of this group of materials ischaracterized by extremely low cuttingspeeds and feed rates when utilizingcarbide cutting tools.

Cast molybdenum has a machinabili-ty rating of approximately 30 percentwhile pure tungsten has a rating of only5 percent. The machinability of tanta-lum and columbium is at a more moder-ate level and thus falls between thesetwo figures. Generally speaking, thesematerials should be machined at mod-erate to low speeds at light depths of cutusing positive rake tools.

3.5 Judging MachinabilityThe factors affecting machinabilityhave been explained; four methods

used to judge machinability are dis-cussed below:

Tool Life: Metals which can be cutwithout rapid tool wear are generallythought of as being quite machinable,and vice versa. A workpiece materialwith many small hard inclusions mayappear to have the same mechanicalproperties as a less abrasive metal. Itmay require no greater power consump-tion during cutting. Yet, the machin-ability of this material would be lowerbecause its abrasive properties areresponsible for rapid wear on the tool,resulting in higher machining costs.

One problem arising from the use oftool life as a machinability index is itssensitivity to the other machining vari-ables. Of particular importance is theeffect of tool material. Machinabilityratings based on tool life cannot becompared if a high speed steel tool isused in one case and a sintered carbidetool in another. The superior life of thecarbide tool would cause the machin-ability of the metal cut with the steeltool to appear unfavorable. Even ifidentical types of tool materials are usedin evaluating the workpiece materials,meaningless ratings may still result.For example, cast iron cutting grades ofcarbide will not hold up when cuttingsteel because of excessive cratering, andsteel cutting grades of carbide are nothard enough to give sufficient abrasionresistance when cutting cast iron.

Tool life may be defined as the peri-od of time that the cutting tool performsefficiently. Many variables such asmaterial to be machined, cutting toolmaterial, cutting tool geometry,machine condition, cutting tool clamp-ing, cutting speed, feed, and depth ofcut, make cutting tool life determinationvery difficult.

The first comprehensive tool life datawere reported by F.W. Taylor in 1907,and his work has been the basis for laterstudies. Taylor showed that the rela-tionship between cutting speed and toollife can be expressed empirically by:

VTn = Cwhere: V = cutting speed, in feet

per minuteT = tool life, in minutesC = a constant depending on

work material, tool material, and other machine variables. Numerically it is the

cutting speed which would give 1 minute of tool life.

n = a constant depending on work and tool material.

This equation predicts that whenplotted on log-log scales, there is a lin-ear relationship between tool life andcutting speed. The exponent n has val-ues ranging from 0.125 for high speedsteel (HSS) tools, to 0.70 for ceramictools.

Tool Forces and PowerConsumption: The use of tool forcesor power consumption as a criterion ofmachinability of the workpiece materialcomes about for two reasons. First, theconcept of machinability as the easewith which a metal is cut, implies that ametal through which a tool is easilypushed should have a good machinabil-ity rating. Second, the more practicalconcept of machinability in terms ofminimum cost per part machined,relates to forces and power consump-tion, and the overhead cost of a machineof proper capacity.

When using tool forces as a machin-ability rating, either the cutting force orthe thrust force (feeding force) may beused. The cutting force is the more pop-ular of the two since it is the force thatpushes the tool through the workpieceand determines the power consumed.Although machinability ratings couldbe listed according to the cutting forcesunder a set of standard machining con-ditions, the data are usually presented interms of specific energy. Workpiecematerials having a high specific energyof metal removal are said to be lessmachinable than those with a lower spe-cific energy.

The use of net power consumptionduring machining as an index of themachinability of the workpiece is simi-lar to the use of cutting force. Again,the data are most useful in terms of spe-cific energy. One advantage of usingspecific energy of metal removal as anindication of machinability, is that it ismainly a property of the workpiecematerial itself and is quite insensitive totool material. By contrast, tool life isstrongly dependent on tool material.

The metal removal factor is the reci-procal of the specific energy and can beused directly as a machinability rating ifforces or power consumption are usedto define machinability. That is, metals



with a high metal removal factor couldbe said to have high machinability.

Cutting tool forces were discussed inChapter 2. Tool force and power con-sumption formulas and calculations arebeyond the scope of this article; theyare discussed in books which are moretheoretical in their approach to dis-cussing machinability of metals.

Surface Finish: The quality of thesurface finish left on the workpiece dur-ing a cutting operation is sometimesuseful in determining the machinability

rating of a metal. Some workpieces willnot ‘take a good finish’ as well as oth-ers. The fundamental reason for surfaceroughness is the formation and slough-ing off of parts of the built-up edge onthe tool. Soft, ductile materials tend toform a built-up edge rather easily.Stainless steels, gas turbine alloy, andother metals with high strain hardeningability, also tend to machine with built-up edges. Materials which machinewith high shear zone angles tend to min-imize built-up edge effects. These

include the aluminum alloys, coldworked steels, free-machining steels,brass, and titanium alloys. If surfacefinish alone is the chosen index ofmachinability, these latter metals wouldrate higher than those in the first group.

In many cases, surface finish is ameaningless criterion of workpiecemachinability. In roughing cuts, forexample, no attention to finish isrequired. In many finishing cuts, theconditions producing the desireddimension on the part will inherently

Figure 3.3 Ideal chips developed from a variety of common materials. (Courtesy Valenite Inc.)

Steel

Stainless Steel

Cast Iron

1018 Steel 1045 Steel 4340 Steel Tool Steel

316 Stainless 17-4 PH Stainles Inconel 718 Ti-6AI-4V

Gray Iron 80-55-06 Nodular Iron A356 Aluminium Brass



provide a good finish within the engi-neering specification.

Machinability figures based on sur-face finish measurements do not alwaysagree with figures obtained by force ortool life determinations. Stainless steelswould have a low rating by any of thesestandards, while aluminum alloyswould be rated high. Titanium alloyswould have a high rating by finish mea-surements, low by tool life tests, andintermediate by force readings.

The machinability rating of variousmaterials by surface finish are easilydetermined. Surface finish readings aretaken with an appropriate instrumentafter standard workpieces of variousmaterials are machined under controlledcutting conditions. The machinabilityrating varies inversely with the instru-ment reading. A low reading meansgood finish, and thus high machinabili-

ty. Relative ratings may be obtained bycomparing the observed value of sur-face finish with that of a material cho-sen as the reference.

Chip Form: There have beenmachinability ratings based on the typeof chip that is formed during themachining operation. The machinabili-ty might be judged by the ease of han-dling and disposing of chips. A materi-al that produces long stringy chipswould receive a low rating, as wouldone which produces fine powdery chips.Materials which inherently form nicelybroken chips, a half or full turn of thenormal chip helix, would receive toprating. Chip handling and disposal canbe quite expensive. Stringy chips are amenace to the operator and to the finishon the freshly machined surface.However, chip formation is a functionof the machine variables as well as the

workpiece material, and the ratingsobtained by this method could bechanged by provision of a suitable chipbreaker.

Ratings based on the ease of chip dis-posal are basically qualitative, andwould be judged by an individual whomight assign letter gradings of somekind. Wide use is not made of thismethod of interpreting machinability. Itfinds some application in drilling,where good chip formation action isnecessary to keep the chips running upthe flutes. However, the whippingaction of long coils once they are clearof the hole is undesirable. Chip forma-tion and tool wear were discussed inChapter 2; Figure 3.3 shows ideal chipsdeveloped from a variety of commonmaterials.


4.1 IntroductionTurning is a metal cutting process used for the generation of cylindrical surfaces.Normally the workpiece is rotated on a spindle and the tool is fed into it radially, axially,or both ways simultaneously, to give the required surface. The term ‘turning’, in the gen-eral sense, refers to the generation of any cylindrical surface with a single point tool.More specifically it is often applied just to the generation of external cylindrical surfacesoriented primarily parallel to the workpiece axis. The generation of surfaces oriented pri-marily perpendicular to the workpiece axis are called ‘facing’. In turning the direction ofthe feeding motion is predominantly axial with respect to the machine spindle. In facinga radial feed is dominant. Tapered and contoured surfaces require both modes of tool feedat the same time often referred to as ‘profiling’.

Turning facing and profiling operations are shown in Figure 4.1The cutting characteristics of most turning

applications are similar. For a given surfaceonly one cutting tool is used. This tool mustoverhang its holder to some extent to enable theholder to clear the rotating workpiece. Once thecut starts, the tool and the workpiece are usual-ly in contact until the surface is completely gen-erated. During this time the cutting speed andcut dimensions will be constant when a cylin-drical surface is being turned. In the case of fac-ing operations the cutting speed is proportionalto the work diameter, the speed decreasing asthe center of the piece is approached.Sometimes a spindle speed changing mecha-nism is provided to increase the rotating speedof the workpiece as the tool moves to the center of the part.

In general, turning is characterized by steady conditions of metal cutting. Except at thebeginning and end of the cut, the forces on the cutting tool and the tool tip temperatureare essentially constant. For the special case of facing, the varying cutting speed willaffect the tool tip temperature. Higher temperatures will be encountered at the largerdiameters on the workpiece. However, since cutting speed has only a small effect on cut-ting forces, the forces acting on a facing tool may be expected to remain almost constantduring the cut.

4.2 Related Turning OperationsA variety of other machining operations can be performed on a lathe in addition to turn-ing and facing. These include the following, as shown in Figure 4.2a through 4.2f.

Single point tools are used in most operations performed on a lathe. A short descriptionof six additional lathe operations are given below:

Chapter 4

Turning Tools

& Operations

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing







ProfilingTurning Facing

FIGURE 4.1: Diagram of the most com-mon lathe operations: facing, turning, andprofiling.

Chamfering: The tool is used to cut anangle on the corner of a cylinder.

Parting: The tool is fed radially intorotating work at a specific locationalong its length to cut off the end of apart.

Threading: A pointed tool is fed linear-ly across the outside or inside surfaceof rotating parts to produce externalor internal threads.

Boring: Enlarging a hole made by aprevious process. A single point toolis fed linearly and parallel to the axis


of rotation.Drilling: Producing a hole by feeding

the drill into the rotating work alongits axis. Drilling can be followed byreaming or boring to improve accura-cy and surface finish.

Knurling: Metal forming operationused to produce a regular cross-hatched pattern in work surfaces.Chamfering and profiling operations

are shown in Figures 4.3a and 4.3brespectively.

4.3 Turning Tool HoldersMechanical Tool Holders and the ANSIIdentification System for Turning ToolHolders and indexable inserts wereintroduced in Chapter 2. A moredetailed discussion of Toolholder Stylesand their application will be presentedhere.

4.3.1 Toolholder StylesThe ANSI numbering system for turn-ing toolholders has assigned letters tospecific geometries in terms of leadangle and end cutting edge angle. Theprimary lathe machining operations ofturning, facing, grooving, threading andcutoff are covered by one of the sevenbasic tool styles outlined by the ANSIsystem. The designations for the sevenprimary tool styles are A, B, C, D, E, F,and G.A STYLE - Straight shank with 0

degree side cutting edge angle, forturning operations.

B STYLE - Straight shank with 15degree side cutting edge angle, forturning operations.

C STYLE - Straight shank with 0degree end cutting edge angle, forcutoff and grooving operations.

D STYLE - Straight shank with 45degree side cutting edge angle, forturning operations.

E STYLE - Straight shank with 30degree side cutting edge angle, forthreading operations.

F STYLE - Offset shank with 0 degreeend cutting edge angle, for facingoperations.

G STYLE - Offset shank with 0 degreeside cutting edge angle; this tool is an‘A’ style tool with additional clear-ance built in for turning operationsclose to the lathe chuck.There are many other styles of turn-

ing tools available in addition to thoseshown here, as detailed by the ANSInumbering system (see Figure 2.35).The seven basic tools are shown inoperation in Figure 4.4

Right and Left Hand Toolholders The toolholder styles discussed hereand shown above represent a fraction ofthose standard styles available frommost indexable cutting tool manufactur-ers. ANSI standard turning tools can bepurchased in either right or left handstyles. The problem of identifying aright hand tool from a left hand tool canbe resolved by remembering that when

Chap. 4: Turning Tools & Operations

Alternativefeeds possible

(a)

(f)

Feed

(b)

Feed

(c)

(d)

Feed Feed

(e)

FIGURE 4.2: Related turning operations: (a) chamfering, (b) parting, (c) threading, (d)boring, (e) drilling, (f) knurling.

FIGURE 4.3: Chamfering (a) and profiling (b) operations, typically performed on alathe or a machining center. (Courtesy Valenite Inc.)

(a) (b)



holding the shank of a right hand tool asshown in Figure 4.5 (insert facingupward), will cut from left to right.

4.3.2 Turning Insert ShapesIndexable turning inserts are manufac-tured in a variety of shapes, sizes, andthicknesses, with straight holes, withcountersunk holes, without holes, withchipbreakers on one side, with chip-breakers on two sides or without chip-breakers. The selection of the appropri-ate turning toolholder geometry accom-panied by the correct insert shape andchip breaker geometry, will ultimatelyhave a significant impact on the produc-tivity and tool life of a specific turningoperation.

Insert strength is one important factorin selecting the correct geometry for aworkpiece material or hardness range.Triangle inserts are the most popularshaped inserts primarily because of theirwide application range. A triangularinsert can be utilized in any of the sevenbasic turning holders mentioned earlier.Diamond shaped inserts are used forprofile turning operations while squaresare often used on lead angle tools. Thegeneral rule for rating an insert’sstrength based on its shape is: ‘the larg-er the included angle on the insert cor-ner, the greater the insert strength’.

The following list describes the dif-ferent insert shapes from strongest toweakest. The relationship betweeninsert shapes and insert strength wasshown in Chapter 2. (see Fig. 2.28)

Insert Insert InsertLetter Description IncludedDesignation AngleR Round N/AO Octagon 135H Hexagon 120P Pentagon 108S Square 90C Diamond 80T Triangle 60D Diamond 55V Diamond 35

Six common turning tool holders areshown in Figure 4.6a and five commonindexable insert shapes with moldedchip breakers are shown in Figure 4.6b.

4.4 Operating ConditionsOperating conditions control threeimportant metal cutting variables:metal removal rate, tool life, and surface

finish. Correct operating condi-tions must be selected to balancethese three variables and toachieve the minimum machiningcost per piece, the maximumproduction rate, and/or the bestsurface finish whichever is desir-able for a particular operation.

The success of any machiningoperation is dependent on theset-up of the workpiece and thecutting tool. Set-up becomesespecially important when theworkpiece is not stiff or rigid andwhen the tooling or machine toolcomponents must be extended toreach the area to be machined.

Deflection of the workpiece,the cutting tool, and themachine, is always present andcan never be eliminated totally.This deflection is usually sominimal that it has no influenceon an operation, and often goesunnoticed. The deflection onlybecomes a problem when itresults in chatter, vibration, ordistortion. It is therefore, veryimportant to take the necessarytime and effort to ensure that theset-up is as rigid as possible forthe type of operation to be per-formed. This is especially importantwhen making heavy or interruptedcuts.

Balancing should be consideredwhen machining odd-shaped work-pieces, especially those workpiecesthat have uneven weight distributionand those which are loaded off-center.An unbalanced situation can be a safe-ty hazard and can cause work inaccu-racies, chatter, and damage to themachine tool. While unbalance prob-lems may not be apparent, they mayexist at low speed operations and willbecome increasingly severe as thespeed is increased. Unbalance condi-

AB C DE F

G

Left-Hand Tool Right-Hand Tool

Cuts left to right Cuts right to left

FIGURE 4.4: The primary lathe machining operations of turning, facing, grooving,threading and cut-off are performed with one of seven basic toolholder styles.

FIGURE 4.5: Identification method for right- andleft-hand turning toolholders.

FIGURE 4.6: Common turning toolholders(a) and common indexable insert shapes (b)with molded chipbreakers are shown.(Courtesy Valenite Inc.)

(a)

(b)



tions most often occur when usingturntables and lathe face plates.

As material is removed from theworkpiece, the balance may change. If aseries of roughing cuts causes the work-piece to become unbalanced, the prob-lem will be compounded when thespeed is increased to take finishing cuts.As a result, the reasons for problems inachieving the required accuracy andsurface finish may not be apparent untilthe machining operation has progressedto the finishing stage. Operating condi-tions become very important whenmachining very large parts as shown inFigure 4.7.

4.4.1 Work Holding MethodsIn lathe work the three most commonwork holding methods are:• Held in a chuck

• Held betweencenters• Held in a collet

Many of thevarious workholding devicesused on a latheare shown inFigure 4.8.

Chucks: Themost commonmethod of workholding, thechuck, has eitherthree or four jaws(Fig. 4.9) and ismounted on theend of the main

spindle. A three jaw chuck is used forgripping cylindrical workpieces whenthe operations to be performed are suchthat the machined surface is concentricwith the work surfaces.

The jaws have a series of teeth thatmesh with spiral grooves on a circularplate within the chuck. This plate can berotated by the key inserted in the squaresocket, resulting in simultaneous radialmotion of the jaws. Since the jawsmaintain an equal distance from thechuck axis, cylindrical workpieces areautomatically centered when gripped.

Three jaw chucks, as shown in Figure4.10, are often used to automaticallyclamp cylindrical parts using eitherelectric or hydraulic power.

With the four jaw chuck, each jawcan be adjusted independently by rota-tion of the radially mounted threaded

screws. Although accuratemounting of a workpiece canbe time consuming, a four jawchuck is often necessary fornon-cylindrical workpieces.Both three and four jawchucks are shown in Figure4.8.

Between Centers: Foraccurate turning operations orin cases where the work sur-face is not truly cylindrical,the workpiece can be turnedbetween centers. This form ofwork holding is illustrated inFig. 4.11. Initially the work-piece has a conical centerhole drilled at each end toprovide location for the lathecenters. Before supportingthe workpiece between thecenters (one in the headstock

and one in the tailstock) a clampingdevice called a ‘dog’ is secured to theworkpiece. The dog is arranged so thatthe tip is inserted into a slot in the driveplate mounted on the main spindle,ensuring that the workpiece will rotatewith the spindle.

Lathe centers support the workpiecebetween the headstock and the tailstock.The center used in the headstock spindleis called the ‘live’ center. It rotates withthe headstock spindle. The ‘dead’ centeris located in the tailstock spindle. Thiscenter usually does not rotate and mustbe hardened and lubricated to withstandthe wear of the revolving work. Shownin figure 4.12 are three kinds of deadFIGURE 4.7: Operating conditions become very important when

machining very large parts. (Courtesy Sandvik Coromant Corp.)

FIGURE 4.8: Many of the various work-holdingdevices used on a lathe for turning operations.(Courtesy Kitagawa Div. Sumikin Bussan InternationalCorp.)

FIGURE 4.9: The most common methodof work holding, the chuck, has eitherthree jaws (a) or four jaws (b). (CourtesyKitagawa Div. Sumikin BussanInternational Corp.)

(a)

(b)



centers.As shown in Figure 4.13, some man-

ufacturers are making a roller-bearingor ball-bearing center in which the cen-ter revolves.

The hole in the spindle into which thecenter fits, is usually of a Morse stan-dard taper. It is important that the holein the spindle be kept free of dirt andalso that the taper of the center beclean and free of chips or burrs. If thetaper of the live center has particlesof dirt or a burr on it, it will not runtrue. The centers play a very impor-tant part in lathe operation. Sincethey give support to the workpiece,they must be properly ground and inperfect alignment with each other.The workpiece must have perfectlydrilled and countersunk holes toreceive the centers. The center musthave a 60 degree point.

Collets: Collets are used whensmooth bar stock, or workpieces thathave been machined to a givendiameter, must be held more accu-

rately than nor-mally can beachieved in aregular three orfour jaw chuck.Collets are rela-tively thin tubu-lar steel bush-ings that aresplit into threel o n g i t u d i n a lsegments overabout two thirdsof their length(See Fig.4.14a). Thesmooth internalsurface of the

split end is shaped to fit the piece ofstock that is to be held. The external sur-face at the split end is a taper that fitswithin an internal taper of a colletsleeve placed in the spindle hole. Whenthe collet is pulled inward into the spin-dle, by means of the draw bar thatengages threads on the inner end of thecollet, the action of the two mating

tapers squeezes the collet segmentstogether, causing them to grip the work-piece (Fig. 4.14b).

Collets are made to fit a variety ofsymmetrical shapes. If the stock surfaceis smooth and accurate, collets will pro-vide accurate centering; maximumrunout should be less than 0.0005 inch.However, the work should be no morethan 0.002 inch larger or 0.005 inchsmaller than the nominal size of the col-let. Consequently, collets are used onlyon drill rod, cold drawn, extruded, orpreviously machined material.

Another type of collet has a sizerange of about 1/8 inch. Thin strips ofhardened steel are bonded together ontheir sides by synthetic rubber to form atruncated cone with a central hole. Thecollet fits into a tapered spindle sleeveso that the outer edges of the metalstrips are in contact with the inner taperof the sleeve. The inner edges bearagainst the workpiece. Puling the colletinto the adapter sleeve causes the stripsto grip the work. Because of theirgreater size range, fewer of these collets

Headstock

Drive plate

Dog Center

Tailstock

Center Workpiece

FIGURE 4.11: For accurate machining, cylindrical parts can beturned between centers.

FIGURE 4.10: Three-jaw chucks are often used in automatedmachining systems pneumatically or hydraulically clamp cylindricalparts. (Courtesy Royal Products)

FIGURE 4.12: Hardened “dead” centers are mounted in thetailstock; they do not rotate with the workpiece and must belubricated. (Courtesy Stark Industrial, Inc.)

FIGURE 4.13: Hardened “live” centers are mounted in the tailstock; they rotate with theworkpiece and do not need lubrication. (Courtesy Royal Products)



are required than with the ordinarytype.

4.4.2 Tool Holding DevicesThe simplest form of tool holderor post is illustrated in Figure4.15a and is suitable for holdingone single-point tool. Immediatelybelow the tool is a curved blockresting on a concave spherical sur-face. This method of support pro-vides an easy way of inclining thetool so that its corner is at the cor-rect height for the machining oper-ation. In Figure 4.15a the tool postis shown mounted on a compoundrest. The rest is a small slidewaythat can be clamped in any angularposition in the horizontal planeand is mounted on the cross slideof the lathe. The compound rest allowsthe tool to be hand fed at an obliqueangle to the lathe bed and is required inoperations like screw-threading and themachining of short tapers or chamfers.

Another common form of tool post,the square turret, is shown in Figure4.15b. It also is mounted on the com-pound rest. As its name suggests, thisfour-way tool post can accommodate asmany as four cutting tools. Any cuttingtool can be quickly brought into posi-tion by unlocking the tool post with thelever provided, rotating the tool post,and then reclamping with the lever.

All standard tool holders aredesigned to cut with the cutting pointlocated on the centerline of the machineand workpiece. If the cutting point isnot on the centerline, as shown inFigure 4.16a, the clearance anglebetween the tool holders and the work-piece will be reduced. The lack of clear-ance will lead to poor tool life and poorsurface finish. It will also force theworkpiece away from the tool whenworking with small diameters.

On the other hand, if the cutting edgeis positioned below the centerline, asshown in Figure 4.16b, the rake anglebecomes more negative. Very high cut-ting forces will be generated and thechip will be directed into a tight curl.Insert fracture can very easily occur anda small diameter workpiece can evenclimb over the top of the tool and betorn from the machine.

Occasionally, however, moving thecutting point off centerline can solve aproblem. An example is in situationswhen machining flimsy parts or whend e e pg r o o v i n gchatter is ac o n s t a n tt h r e a t ,even whena positiverake tool isu s e d .Moving thetool slight-ly abovecenterl ine

(2% to 4% of the workpiece diameter)will change the rake angle slightly, andthis in turn, will reduce cutting forcesand make chatter less of a danger.

Interrupted cuts present special prob-lems, particularly when machining largediameter workpieces. It is best to posi-tion the cutting point slightly below thecenterline to present the insert in astronger cutting position. A lead angleshould also be used whenever possible.Moving the cutting point slightly belowthe centerline and using a lead angle,allows the workpiece to contact the tool

Spindle nose cap

Spring collet

Collet sleeveHeadstockspindle sleeve

(b)

FIGURE 4.15: A toolpost for single-point tools (a) and a quick change indexing square turret,which can hold up to four tools (b). (Courtesy Dorian Tool)

FIGURE 4.14: A collet (a) and a colletmounting assembly (b) are shown here.(Courtesy Lyndex Corp.)

FIGURE 4.16: Cutting edge above workpiece centerline (a) and cuttingedge below workpiece centerline (b). Both conditions result in poor per-formance.

(a) (b)

(a)

(a) (b)



on a stronger part of the insert, behindthe nose.

4.5 Cutting ConditionsAfter deciding on the machine tool andcutting tool, the following main cuttingconditions have to be considered:• Cutting speed• Depth of cut• Feed rate

The choice of these cutting condi-tions will affect the productivity of themachining operation in general, and thefollowing factors in particular: the lifeof the cutting tool; the surface finish ofthe workpiece; the heat generated in thecutting operation (which in turn affectsthe life of the tool and the surfaceintegrity of the machined parts); and thepower consumption.

Cutting Speed: Cutting speed refersto the relative surface speed betweentool and work, expressed in surface feetper minute. Either the work, the tool, orboth, can move during cutting. Becausethe machine tool is built to operate inrevolutions per minute, some meansmust then be available for convertingsurface speeds into revolutions perminute (RPM). The common formulafor conversion is:

where D is the diameter (in inches) ofthe workpiece or the rotating tool, Piequals the constant 3.1416, and RPM isa function of the speed of the machinetool in revolutions per minute. Forexample:

If a lathe is set to run at 250 RPM andthe diameter of the workpiece is 5 inch-es, then:

The RPM can be calculated whenanother cutting speed is desired. Forexample, to use 350 SFPM with a work-piece which is 4 inches in diameter.

All tool materials are meant to run ata certain SFM when machining variouswork materials. The SFPM range rec-ommendations for tool and work mate-rials are given in many reference publi-cations.

Depth of Cut: The depth of cutrelates to the depth the tool cutting edgeengages the work. The depth of cutdetermines one linear dimension of thearea of cut. For example: to reduce theoutside diameter (OD) of a workpieceby .500 inches, the depth of cut wouldbe .250 inches.

Feed Rate: The feed rate for latheturning is the axial advance of the toolalong the work for each revolution ofthe work expressed as inches per revo-lution (IPR). The feed is also expressedas a distance traveled in a single minuteor IPM (inches per minute). The follow-ing formula is used to calculate the feedin IPM:

IPM = IPR × RPM

Feed, speed, and depth of cut have adirect effect on productivity, tool life,and machine requirements. Thereforethese elements must be carefully chosenfor each operation. Whether the objec-tive is rough cutting or finishing willhave a great influence on the cuttingconditions selected.

Roughing Cuts: When roughing, thegoal is usually maximum stock removalin minimum time with minor considera-tion given to tool life and surface finish.There are several important points tokeep in mind when rough cutting.

The first is to use a heavy feedbecause this makes the most efficientuse of power and, with less tool contact,tends to create less chatter. There aresome exceptions where a deeper cut ismore advantageous than a heavy feed,especially where longer tool life isneeded. Increasing the depth of cut willincrease tool life over an increase infeed rate. But, as long as it is practicaland chip formation is satisfactory, it isbetter to choose a heavy feed rate.

A heavy feed or deeper cut is usuallypreferable to higher speed, because themachine is less efficient at high speed.When machining common materials,the unit horsepower (HP) factor isreduced in the cut itself, as the cuttingspeed increases up to a certain criticalvalue. But the machine inefficiencieswill overcome any advantage when

machining heavy workpieces.Even more important, tool life is

greatly reduced at high cutting speedsunless coated carbide or other moderntool materials are used, and these alsohave practical speed limits. Tool life isdecreased most at high speeds, althoughsome decrease in tool life occurs whenfeed or depth of cut is increased. Thisstands to reason, because more materialwill be removed in less time. It becomesa choice then, between longer tool lifeor increased stock removal. Since pro-ductivity generally outweighs toolcosts, the most practical cutting condi-tions are usually those which first, aremost productive, and second, willachieve reasonable tool life.

Finishing Cuts: When taking finish-ing cuts, feed rate and depth of cut areof minor concern. The feed rate cannotexceed that which is necessary toachieve the required surface finish andthe depth of cut will be light. However,the rule about speed will still apply. Thespeeds will generally be higher for fin-ish cuts, but they must still be within theoperating speed of the tool material.

Tool life is of greater concern for fin-ish cuts. It is often better to strive forgreater tool life at the expense of mate-rial removed per minute. If tool wearcan be minimized, especially on a longcut, greater accuracy can be achieved,and matching cuts which result fromtool changes, can be avoided.

One way to minimize tool wear dur-ing finishing cuts is to use the maximumfeed rate that will still produce therequired surface finish. The less timethe tool spends on the cut, the less toolwear can occur. Another way to mini-mize tool wear during a long finishingcut is to reduce the speed slightly.Coolant, spray mist, or air flow, willalso extend tool life because it reducesthe heat of the tool.

4.6 Hard TurningAs the hardness of the workpieceincreases, its machinability decreasesaccordingly and tool wear and fracture,as well as surface finish and integrity,can become a significant problem.There are several other mechanicalprocesses and nonmechanical methodsof removing material economicallyfrom hard or hardened metals.However, it is still possible to apply tra-ditional cutting processes to hard metalsand alloys by selecting an appropriate

D × × (RPM)SFPM =

12

3.1416 × 5 × 250SFPM =

12=

392712

Answer = 327.25 or 327 SFPM

Answer = 334.13 or 334 RPM

12 × SFPMRPM =

× D

RPM =12 × 350

3.1416 × 4=

420012.57



tool material and machine tools withhigh stiffness and high speed spindles.

One common example is finishmachining of heat-treated steel machineand automotive components using poly-crystalline cubic boron nitride (PCBN)cutting tools. This process producesmachined parts with good dimensionalaccuracy, surface finish, and surfaceintegrity. It can compete successfullywith grinding the same components,from both technical and economicaspects. According to some calculationsgrinding is over ten times more costlythan hard turning.

Advanced cutting tool materials suchas polycrystalline cubic boron nitride(PCBN) and ceramics (discussed inChapter 1 - Cutting Tool Materials),have made the turning of hardened steela cost effective alternative to grinding.Many machine shops have retired theircylindrical grinders in favor of lessexpensive and more versatile CNC lath-es.

Compared to grinding, hard turning:• permits faster metal removal rates,which means shorter cycle times.• eliminates the need for coolant (dry vs.wet machining will be discussed later).• shortens set up time and permits mul-tiple operations to be performed in onechucking.

Today’s sophisticated CNC lathesoffer accuracy and surface finishescomparable to what grinders provide.

Hard turning requires much less ener-gy than grinding, thermal and otherdamage to the workpiece is less likely tooccur, cutting fluids may not be neces-sary and the machine tools are less

expensive. In addition, finishing thepart while still chucked in the latheeliminates the need for material han-dling and setting the part in the grinder.However, work holding devices forlarge and slender workpieces for hardturning can present problems, since thecutting forces are higher than in grind-ing.

Furthermore, tool wear and its con-trol can be a significant problem ascompared to the automatic dressing ofgrinding wheels. It is thus evident thatthe competitive position of hard turningversus grinding must be elevated indi-vidually for each application and interms of product surface integrity, qual-ity, and overall economics.

4.6.1 Dry vs. Wet MachiningJust two decades ago, cutting fluidsaccounted for less than 3 percent of thecost of most machining processes.Fluids were so cheap that few machineshops gave them much thought. Timeshave changed.

Today, cutting fluids account for upto 15 percent of a shop’s productioncosts, and machine shop owners con-stantly worry about fluids.

Cutting fluids, especially those con-taining oil, have become a huge liabili-ty. Not only does the EnvironmentalProtection Agency (EPA) regulate thedisposal of such mixtures, but manystates and localities also have classifiedthem as hazardous wastes, and imposeeven stricter controls if they contain oiland certain alloys.

Because many high-speed machiningoperations and fluid nozzles create air-

borne mists, governmental bodies alsolimit the amount of cutting fluid mistallowed into the air. The EPA has pro-posed even stricter standards for con-trolling such airborne particulate. andthe Occupational Safety and HealthAdministration (OSHA) is consideringand advisory committee’s recommenda-tion to lower the permissible exposurelimit to fluid mist.

The cost of maintenance, recordkeeping and compliance with currentand proposed regulations is rapidly rais-ing the price of cutting fluids.Consequently, many machine shops areconsidering eliminating the costs andheadaches associated with cutting fluidsaltogether by cutting dry.

The decision to cut wet or dry mustbe made on a case-by-case basis. Alubricious fluid often will prove benefi-cial in low-speed jobs, hard-to-machinematerials, difficult applications, andwhen surface finish requirements aredemanding. A fluid with high coolingcapacity can enhance performance inhigh-speed jobs, easy-to-machine mate-rials, simple operations, and jobs proneto edge-buildup problems or havingtight dimensional tolerances.

Many tough times though, the extraperformance capabilities that a cuttingfluid offers is not worth the extraexpense incurred, and in a growingnumber of applications, cutting fluidsare simply unnecessary or downrightdetrimental. Modern cutting tools canrun hotter than their predecessors andsometimes compressed air can be usedto carry hot chips away from the cuttingzone.


5.1 IntroductionThe basic engine lathe, which is one of the most widely used machine tools, is very ver-satile when used by a skilled machinist. However, it is not particularly efficient whenmany identical parts must be machined as rapidly as possible. As far back as 1850 therewere efforts to develop variations of an engine lathe that could be operated by a relativelyunskilled person for mass producing machined parts. The cutting tools were preset, or“set up” by a skilled machinist, and usually several cutting tools were in operation at thesame time, reducing the time spent in machining each part. This is still the basic concepton which mass- production type lathes are based.

The turret lathe and automatic screw machine in their various forms have been devel-oped and improved with the objectives of producing machined parts more rapidly andaccurately at lower cost. On most machines of this type, the power available at the spin-dle has been greatly increased to take advantage of better cutting tool material.Mechanical power, in electrical, hydraulic, or pneumatic form, has replaced human mus-cle power for such functions as feeding tools, operating chucks or collets, and feeding barstock in the machine.

5.2 Lathes and Lathe ComponentsOf the many standard and special types of turning machines that have been built, the mostimportant, most versatile, and most widely recognized is the engine lathe. The standardengine lathe is not a high production machine, but it can be readily tooled up for manyone-piece or short-run jobs. It is also possible to modify the basic machine for many high-er production applications. The modern engine lathe provides a wide range of speeds andfeeds which allow optimum settings for almost any operation. There have been advancesin headstock design to provide greater strength and rigidity. This allows the use of high-horsepower motors so that heavy cuts with carbide tools are practical. To utilize this highpower without losing accuracy, new lathes incorporate heavier beds, wider hardenedways, and deeper-sectioned carriages.

A schematic illustration of the components of an engine lathe is shown and describedin Figure 5.1.

Headstock: The headstock is the powered end and is always at the operator’s left.This contains the speed changing gears and the revolving, driving spindle, to which anyone of several types of work holders is attached. The center of the spindle is hollow sothat long bars may be put through it for machining.

Tailstock: The tailstock is non-rotating but on hardened ways, it can be moved, to theleft or right, to adjust to the length of the work. It can also be offset for cutting small-angle tapers.

Carriage: The carriage can be moved left or right either by handwheel or power feed.This provides the motion along the Z-axis. During this travel turning cuts are made.

Apron: The apron attached to the front of the carriage, holds most of the controllevers. These include the levers which engage and reverse the feed lengthwise (Z-axis)

Chapter 5

Turning Methods

& Machines

Upcoming Chapters





Shaping and Planing



Reaming and Tapping



Finishing ProcessesGrinding Wheels and OperationsGrinding Methods and Machines

Lapping and Honing







or crosswise (X-axis) and the leverwhich engages the threading gears.

Cross Slide: The cross slide ismounted on the carriage and can bemoved in and out (X-axis) perpendicu-lar to the carriage motion. This is thepart that moves when facing cuts aremade with power feed, or at any time acut must be made ‘square’ with the Z-axis. This, or the compound, is alsoused to set the depth of cut when turn-


ing. The cross slide can be moved by itshandwheel or by power feed.

Compound Rest: The compoundrest, or compound for short, is mountedon the carriage. It can be moved in andout by its handwheel for facing or forsetting the depth of cut. It can also berotated 360 degrees and fed by its hand-wheel at any angle. The compounddoes not have any power feed but italways moves longitudinally with the

cross slide and the car-riage.

Tool Post: The toolpost is mounted on thecompound rest. This canbe any of several varietiesbut in its simplest form is

merely a slotted cylinder which can bemoved left or right in the T-slot in thecompound and clamped in place. It canalso be rotated so as to present the cut-ter to the work at whatever angle is bestfor the job.

Bed: The bed of the lathe is its‘backbone’. It must be rigid enough toresist deflection in any direction underload. The bed is made of cast iron or asteel weldment, in a box or I-beamshape, and is supported on legs, a cabi-net, or a bench.

Ways: The ways of the lathe are theflat or V-shaped surfaces on which thecarriage and the tailstock are moved leftand right. Each has its separate pair ofways, often one flat surface, for stabili-ty, and one V-way for guidance in a per-fectly straight line. These ways arehardened and scraped or ground to closetolerances. The basic accuracy ofmovement of the carriage depends onthe ways. A typical Toolroom EngineLathe is shown in Figure 5.2.

Size: The size of a lathe is specifiedby two or three dimensions:• The largest diameter workpiece whichwill clear the bed of the lathe. The cen-ter is the headstock spindle center.• The largest diameter workpiece whichwill clear the cross slide is sometimesalso specified.• The longest workpiece which can beheld on centers between the headstockand the tailstock.

A larger, more sophisticated lathe isshown in Figure 5.3.

A large 40” lathe with a steady rest isshown in Figure 5.4.

5.3 Turret LatheThe standard engine lathe is versatile,

Spindlespeed

selector

Headstock

Feed changegear box

Compound rest

Spindle

Ways

Tool postCross slide

Carriage

Center

Tailstock quill

Tailstock

Apron Bed

Lead screw

Feed rod

FIGURE 5.1: Schematic illustration of the components of a standard engine lathe.

FIGURE 5.2: A typical toolroom engine lathe with faceplate, square turrent, follower, and steady rest. (CourtesySummit Machine Tool Manufacturing Corp.)

FIGURE 5.3: A more sophisticated 18-inch variable speed engine lathepermits optimal cutting speed selection. (Courtesy Clausing Industries,Inc.)

Chap. 5: Turning Methods & Machines



but it is not a high production machine.When production requirements arehigh, more automated turning machinesmust be used.

The turret lathe represents the firststep from the engine lathe toward thehigh production turning machines. Theturret lathe is similar to the engine latheexcept that tool-holding turrets replacethe tailstock and the tool post compoundassembly. These machines possess spe-cial features that adapt them to produc-tion. The ‘skill of the worker’ is builtinto these machines, making it possiblefor inexperienced operators to repro-duce identical parts. In contrast, theengine lathe requires a skilled operatorand requires more time to produce partsthat are dimensionally the same.

The principal characteristic of turretlathes is that the tools for consecutiveoperations are set up for use in the prop-er sequence. Although skill is requiredto set and adjust the tools prop-erly, once they are correct, lessskill is required to operate theturret lathe. Many parts can beproduced before adjustments arenecessary. These machines arenormally used for small to medi-um sized production runs wherethe engine lathe is too slow butthe additional production ratedesired does not warrant a spe-cial machine.

A schematic illustration of thecomponents of a turret lathe isshown in Figure 5.5.

Square and Hex Turrets: Asquare turret is mounted on thetop of the cross slide and is capa-ble of holding four tools. If sev-eral different tools are required,they are set up in sequence andcan be quickly indexed andlocked in correct working posi-tion. So that cuts can be dupli-cated, the slide is provided with

positive stops or feed trips. Likewise,the longitudinal position of the entireassembly may be controlled by positivestops on the left side of the apron. Cutsmay be taken with square turret toolsand with tools mounted on the hexagonturret simultaneously.

An outstanding feature is the turret inplace of the tailstock. This turretmounted on either the sliding ram or thesaddle, or on the back of the structure,carries anywhere from 4 to 18 tool sta-tions. The tools are preset for the vari-ous operations. The tools are mountedin proper sequence on the various facesof the turret so that as the turret indexesbetween machining operations, theproper tools are engaged into position.For each tool there is a stop screw orelectric/electronic transducer, whichcontrols the distance the tool will feedand cut. When this distance is reached,an automatic trip lever stops further

movement of the tool by disengag-ing the drive clutch.

Like the engine lathe, the mod-ern turret lathe provides fast spin-dle speeds, wide speed and feedranges, high power, and great rigid-ity. The machine is operated in thehigh end of its speed range morethan the engine lathe is, partlybecause the tools placed in the tur-ret often work on small diameterson the workpiece, but also becausethe operator is more production

conscious.5.3.1 Horizontal Turret Lathes:

Horizontal turret lathes are made in twogeneral designs and are known as theram and saddle types. The ram-type tur-ret lathe shown in Figure 5.6a has theturret mounted on a slide or ram whichmoves back and forth on a saddleclamped to the lathe bed. The saddle-type turret lathe shown in Figure 5.6bhas the turret mounted directly on a sad-dle which moves back and forth withthe turret.

5.3.2 Vertical Turret Lathes: A ver-tical turret lathe resembles a verticalboring mill, but it has the characteristicturret arrangement for holding the tools.It consists of a rotating chuck or table inthe horizontal position with the turretmounted above on a cross rail. In addi-tion, there is at least one side head pro-vided with a square turret for holdingtools. All tools mounted on the turret or

Spindlespeed selector

Forward andreverse

Stop rod

Feedshaft

Longitudinalfeed lever Carriage

handwheel

Cross-slidehandwheel

Cross-feedlever

Feed selectorsTurnstile

Squareturret Hexagon

turretRam

Turretstops

FIGURE 5.4: 40 inch lathe with steady rest is used to machine large cylindrical parts.(CourtesySummit Machine Tool Manufacturing Corporation)

FIGURE 5.5: Schematic illustration of the components of a turret lathe.



side head have their respectivestops set so that the length of cutscan be the same in successivemachining cycles. It is, in effect,the same as a turret lathe standingon the headstock end, and it has allthe features necessary for the pro-duction of duplicate parts. Thismachine was developed to facilitatemounting, holding, and machiningof large diameter heavy parts. Onlychucking work is done on this kindof machine.

A vertical turret lathe, shown inFigure 5.7, is provided with two cutterheads: the swiveling main turret headand the side head. The turret and sideheads function in the same manner asthe hexagonal and square turrets on ahorizontal lathe. To provide for anglecuts both the ram and turret heads maybe swiveled 30 degrees right or left ofcenter.

The machine can be provided with acontrol that permits automatic operationof each head including rate and direc-tion of feed, change in spindle feed,indexing of turret, starting, and stop-ping. Once a cycle of operations is pre-set and tools are properly adjusted, theoperator need only load, unload, andstart the machine. Production rate isincreased over those manually operatedmachines, because they operate almostcontinuously and make changes fromone operation to another without hesita-tion or fatigue. By reducing the han-dling time, and making the cycle auto-matic, an operator can attend more thanone machine.

The turret lathe normally has a jawedchuck to hold the workpiece; however, acollet may be more suitable when pro-ducing parts from bar stock. A turningmachine equipped with a collet and aturret is called a screw machine, but it isactually a special turret lathe. The spe-cial features of screw machines areaimed primarily at reducing idle time onthe parts being machined, therebyincreasing productivity.

In Figure 5.8 a vertical turning centeris shown machining a heavy part.

5.3.3 Advantages of Turret Lathes:The difference between the engine andturret lathes is that the turret lathe isadapted to quantity production work,whereas the engine lathe is used primar-ily for miscellaneous jobbing, toolroom,or single-operation work. The featuresof a turret lathe that make it a quantityproduction machine are:• Tools may be set up in the turret in theproper sequence for the operation.• Each station is provided with a feedstop or feed trip so that each cut of atool is the same as its previous cut.• Multiple cuts can be taken from thesame station at the same time, such astwo or more turning and/or boring cuts.• Combined cuts can be made; tools onthe cross slide can be used at the sametime that tools on the turret are cutting.• Rigidity in holding work and tools is

FIGURE 5.6a: Ram-type horizontal turret lathe has the turret mounted on a slide orram. (Courtesy: National Acme Co., Div. DeVlieg-Bullard Inc.)

FIGURE 5.6b: Saddle-type turret lathe has the turret mounted directly on the saddle.(Courtesy National Acme Co., Div. DeVlieg-Bullard Inc.)

FIGURE 5.7: Vertical turning lathesare used for machining large-diame-ter and heavy parts.

Ram

Turret

Workpiece

Cross rail

Column

Base

Cross slide



built into the machine to permit multipleand combined cuts.• Turret lathes can also have attach-ments for taper turning, thread chasingand duplicating, and can be tape con-trolled.

5.4 Automated EquipmentThere are turning machines which allowautomatic chucking, indexing, feeding,spindle speed changes, and other workthat has to be done by the operator onthe engine lathe. These automatic lath-es represent a refinement of the turretlathe, and they are particularly suitablefor long run, mass production applica-tions.

Automatic lathes may be made up assingle-spindle or multiple-spindlemachines. Generally, single-spindlemachines provide for turning the work-piece, which is held in a collet orchucked on the headstock. Multiple-spindle automatic lathes usually providemeans for indexing the workpiece totools mounted on the various spindles.These tools might include drills, coun-tersinks, boring bars, and other rotatingcutters. Both single- and multiple-spin-dle automatics may be made up withvertical as well as horizontal spindlealignment.

As far as the machining processes onan automatic lathe are concerned, thefundamental considerations are the highspeeds desired for good productivity,the economics of the cutting process,and the balancing of speeds on variousphases of the operation to obtain thedesired rate of wear on each cuttingtool.

5.4.1 Single-Spindle Automatic Lathes

The majority of single-spindle automat-ic lathes are designed to machine work-pieces that are located between two cen-ters. Some, however, hold the work-piece in a chuck, collet, or speciallydesigned fixture. Most have horizontalspindles. A conventional single-spindleautomatic lathe has six major compo-nents: base, bed, and ways; headstock;work spindle; front tool slide; rear toolslide.

The feed rates of the tool slides arecontrolled by cams, hydraulics, or leadscrews. Spindle speeds are changed tosuit workpiece diameter/materialrequirements by means of change gearsin the headstock.

A single-spindleautomatic lathe isshown in Figure 5.9.

Tooling: Any of theseveral available work-piece holders that aresuitable for the particu-lar application may beused, including chucks,faceplate drives, collets,and specially designedfixtures. Chucks,where used, should bepower operated to avoidthe time lost to manual-ly actuate chucks.

Toolholders are nor-mally designed withslots to locate, andclamps to hold individ-ual cutting tools in theirrequired locations. Theassembled toolholders are, in turn,keyed and clamped in a specific loca-tion on the front and rear tool slides.

It is good practice to provide sparetoolholders wherein a set of sharpenedtools can be preset and clamped, readyto exchange for a set of dull tools.Setup time can also be saved by havingspare toolholders preset with the toolsrequired for the next part to be run.

DeVlieg tooling for a single- or mul-tiple-spindle automatic lathe is shownin Figure 5.10.

Applications: Axle and transmissionshafts, gear blanks, pump drives, and pin-ions are all particularly well suited formachining on single-spindle automaticlathes. In fact, almost any machinablemetal part falling within its size capacitythat can be chucked, fixtured, or runbetween centers is a potential candidatefor this machine. Single-spindle auto-matic lathes perform turning, facing,chamfering, grooving, and forming oper-ations, and are usually used for parts withmoderate production rates.

FIGURE 5.9: Single-spindle automatic lathe (Courtesy: National Acme Co., Div.DeVlieg-Bullard Inc.)

FIGURE 5.8: A vertical turning center machining a heavy part. (Courtesy Giddings & Lewis, LLC)



5.4.2 Single-Spindle Automatic Screw Machines

Automatic screw machines are the pre-sent-day developments of earliermachines whose only function was theproduction of screws. Modern machinesnot only retain thread-cutting capabili-ties but are also capable of performingall turning operations. These machinesproduce a wide range of parts from barstock fed through a hollow work spin-dle. Some machines are arranged toproduce parts from coil stock.

Single-spindle automatic screwmachines have horizontal hollow spin-dles aligned with stock feeding tubes.Most are cam controlled but camlessversions, sometimes NC or CNC con-trolled, are more flexible and quicklyset up, making them more suitable forshorter production runs. Machines areavailable in several sizes and have sixmajor components: base, headstock,hollow work spindle, front tool slide,rear tool slide, and turret, as shown inFigure 5.11. A conventional single spin-dle automatic screw machine is shownin Figure 5.11

The feed rates an motion of toolslides are controlled by cams orhydraulics. Spindle speeds are changedto suit workpiece diameter/material bymeans of change gears in the machinebase. Bar stock is fed automatically toa swing stop, or a turret stop, after eachpart is completed and cut off. The col-let is automatically released duringstock advances.

Tooling: Round, square, hex, andother standard-shape collets are avail-able in sizes to suit commercial barstock sizes. Specials are also made tosuit.

Many special tools and toolholdersare designed and made for certain appli-cations, but a significant savings of timeand money can be realized by the use ofthe standard tools and holders available.A large selection of standard tools areavailable from stock.

Applications: Single-spindle auto-matic screw machines are used to pro-duce an extremely wide range of smallparts including shafts, pins, knobs,screws, bolts, and so on, from anymachinable metal. Flats and slots can bemilled and cross holes drilled, It is nor-mal for one operator to operate severalmachines, the number depending on thefrequency required for reloading barstock and adjusting or changing tools.

5.4.3 Multiple-Spindle Automatic Bar and Chucking Machines

Conventional multiple-spindle automat-ic bar and chucking machines have twomajor advantages over single-spindleautomatics - both of which reduce thetime required to produce a part: • The multiple-spindle machine per-forms work on each of its working sta-tions concurrently; it is also possible tocomplete a different operation on a partat each position within the same time. • The maximum time required to com-plete one piece is the time required forthe longest cut, plus index time, and incertain instances the longest cut can be

broken up into increments. For exam-ple, a drilled hole that is the longest cutof a certain part may be completed inthree or more positions.

Part sizes and complexity of designcan be accommodated equally well onmulti-spindle or single-spindlemachines. Shorter changeover timefavors single-spindle machines for shortproduction runs, but the shorter machin-ing time per piece of the multi-spindlemachine makes it more economical forlong runs.

A schematic diagram of s six-spindleautomatic bar machine is shown inFigure 5.12

FIGURE 5.10: DeVlieg tooling for single- or multi-spindle automatic lathe (Courtesy:National Acme Co., Div. DeVlieg-Bullard Inc.)

FIGURE 5.11: Conventional single-spindle automatic screw machine. (CourtesyCourtesy National Acme Co., Div. DeVlieg-Bullard Inc.)



5.4.4 Multiple-Spindle Vertical Automatic Chucking Machines

Multiple-spindle vertical automatic

chucking machines are manufacturedby several machine tool builders in sev-eral sizes and models ranging from 4 to

8 spindles. One maker sup-plies a 16-spindle machinethat is, in reality doublespindles for each positionof an 8-spindle machine.

These machines use lessfloor space than an equiva-lent horizontal model and

are more flexible in applica-tion. They do not, however,accept bar stock. Some otheradvantages are that they areconvenient to load, operate,and adjust or change tooling.

The machine illustrated inFigure 5.13 has three majorcomponents: base and centercolumn, carrier and workspindles, and machiningheads. The machine isdesigned to permit each spin-dle to operate independently,having independent speedsand feeds. In effect, themachine illustrated can oper-ate as seven individualmachines all loaded andunloaded at a common sta-tion.

Machines with dual spin-dles and multiple-toolmachining heads are avail-able, permitting duplicatesetups, or first and second

chucking work to be performed (bothends). Double indexing is available andis used with dual-spindle setups. A mul-tiple-spindle vertical automatic chuck-ing machine is shown in Figure 5.13.

5.5 Computer Controlled LathesIn the most advanced lathes, movementand control of the machine and its com-ponents are actuated by computernumerical controls (CNC). These lath-

FIGURE 5.12: Schematic diagram of a six-spindle automatic bar machine (Courtesy National AcmeCo., Div. DeVlieg-Bullard Inc.)

FIGURE 5.13: Multiple-spindle vertical automaticchucking machine. (Courtesy National Acme Co., Div.DeVlieg-Bullard Inc.)

FIGURE 5.14: Multi-station tool holder with four-plus-four tools(Courtesy: Dorian Tool)



es are usually equipped with one ormore turrets. Each turret is equippedwith a variety of tools and performs sev-eral operations on different surfaces ofthe workpiece. A multi-station toolholder is shown in Figure 5.14.

These machines are highly automat-ed, the operations are repetitive andmaintain the desired accuracy. They aresuitable for low to medium volumes ofproduction. A high precision CNC latheis shown in Figures 5.15.

More sophisticated machining sys-tems, including boring and millingoperations, will be discussed in a laterchapter.

FIGURE 5.15: A high production computer controlled Swiss type lathe (Courtesy:Hardinge, Inc.)


6.1 IntroductionGrooving and threading are both single point machining operations performed on lathes,automatic lathes, or machining centers. Outside diameter (OD) and face grooving oper-ations are shown in Figures 6.1a and 6.1b respectively. Internal threading or tapping willbe discussed in a later chapter.

6.2 Grooving or Recessing OperationsGrooving or recessing operations, sometimes also called necking operations, are oftendone on workpiece shoulders to ensure the correct fit for mating parts (Fig. 6.2a) Whena thread is required to run the full length of the part to a shoulder, a groove is usuallymachined to allow full travel of the nut. (Fig. 6.2b) Grooving the workpiece prior to cylin-drical grinding operations allows the grinding wheel to completely grind the workpiecewithout touching the shoulder.(Fig. 6.2c)

Chapter 6

Grooving

& Threading

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing






Prentice Hall: http://www.prenhall.comFIGURE 6.1b: Face Grooving operation(Courtesy: Valenite Inc.)

FIGURE 6.1a: Outside diameter (OD) grooving operation (Courtesy: Valenite Inc.)

6.2.1 Face GroovingWith face grooving operations the toolis fed axially rather than radiallytowards the end surface of the work-piece. The tool must be adapted to theradial curve of the groove and the bladeis therefore curved. When the machinespindle rotates in a counter-clockwisedirection, a right-hand version of thetool is used and a left-hand version isused when the machine spindle rotatesclockwise. A face grooving operation isshown in Figure 6.1b.

So that both insert and toolholder fitinto the groove, both the outer and innerdiameters of the groove must be consid-ered. The diameter measured to the out-side of the blade determines the limit forthe smallest possible diameter which


can be machined, and the diameter mea-sured to the inside of the blade deter-mines the limit for the largest possiblegroove diameter.

6.2.2 Internal GroovingThe main problem with internal groov-ing is chip evacuation. There is a veryhigh risk of chip jamming which canresult in tool breakage, especially whenmachining small diameters. The chipshave to be removed from the groovethen change direction 90 degrees andpass the side of the toolholder to finallybe removed from the hole. Introducingintermittent feed into the program is thebest way to obtain short chips. An inter-nal grooving holder with insert is shownin Figure 6.3.Vibration is another common problemassociated with internal grooving.Stability is related to the overhang, orhow far into the workpiece the groove isto be machined. The risk of vibration isreduced by using the largest toolholderpossible. The overhang should notexceed 2 - 2.5 × the diameter. Internalgrooving is a critical operation and it isimportant to choose a tool which opti-mizes chip evacuation with vibration-free machining.

Grooving tools are usually ground tothe dimensions and shape required for aparticular job. Most grooving tools aresimilar in appearance to the cutoff tool,except that the corners are carefullyrounded because they reduce the possi-bility of cracks in the part, especially if

the part is to be heat treated.

6.3 Parting or Cut Off OperationsIn parting operations the workpiecerotates while the tool carries out a radi-al feed movement. As with face turn-ing, the tool is fed from the periphery ofthe workpiece towards the center andthe cutting speed is reduced to zero - buthere the similarities end. A typical part-ing operation is shown in Figure 6.4.

As the cutting tool progressestowards the center, another factor takeseffect. As the diameter of the workpieceis reduced, the radial cutting force willcause the material to break before theinsert has cut through it. This results ina pip or burr being formed in the centerof the workpiece. This pip will alwaysbe there after parting, but its size can bereduced by choosing the correct insertgeometry, feed rate, and support for thesagging workpiece.

In a parting operation, there is mater-ial on both sides of the insert. Thismeans that the tools used are narrowand that the length of the toolholderincreases with an increased diameter.Therefore, stability becomes a criticalfactor.

Since the size of the tool and tool-holder must be optimized to meetrequirements, only a small surface ispresent for drawing off heat, and there-

Groove formating parts

(a)

Groove to allowfull travel of nut

(b)

Nut

Thread

Groove forgrinding relief

(c)

Grindingwheel

FIGURE 6.2: Grooving operations to provide clearance for a) mating parts; b) full travel of nut; c) grinding relief.

FIGURE 6.4: Parting or cut-off operation(Courtesy: Iscar Metals, Inc.)

FIGURE 6.3: Internal grooving holderwith insert (Courtesy: Valenite Inc.)

Chap. 6: Grooving & Threading



fore cutting fluid becomes important.Unfortunately, because of the spacerestrictions, the supply of cutting fluidis obstructed by the chips. Since chipevacuation is difficult and there is noth-ing against which to break the chips, theside surfaces can easily be damagedduring the operation.

6.3.1 Insert GeometryAt the beginning of a cut the insert willwork at a relatively high cuttingspeed,and must be able to resist plasticdeformation. The speed reduces as thetool approaches the center, at whichpoint it becomes zero.

Modern machines can be pro-grammed so that the spindle speed isautomatically increased towards thecenter, so that the cutting speed is keptconstant. But the maximum spindlespeed of the machine will be reachedbefore the tool reaches the center, andthis could result in insert edge build-up.Therefore a tough tool material will beneeded to resist edge build-up as thetool gets closer to the center.

Advanced insert geometries are nec-essary for performing parting andgrooving operations in a satisfactoryway. A positive rake insert gives lowercutting forces and thus lower pressureon the workpiece, and this will reducethe size of the pip. However, a largepositive rake angle means a weaker cut-ting edge.

The insert can have various leadangles. On straight or neutral inserts thelead angle is zero. This design providesa stronger cutting edge and a better sur-face finish, while maintaining closertolerances with respect to perpendicularalignment. With an increased leadangle the axial cutting force increases,

causing theinsert todeflect.

With largelead angles thedeflection canbe so strongthat a roundingof the end sur-faces occursand results in aconvex or aconcave endsurface. Areduced leadangle produceslarger radial

cutting forces but this can cause vibra-tion problems especially when smalldiameters are machined. In groovingoperations a radial displacement of theinsert results in an inaccurate groovedepth.

6.3.2 Chip ControlWith parting and grooving operations,the insert has machined surfaces on bothsides of the feed direction. Thereforethe chips must be formed in such a waythat they are narrower than the groove,otherwise the surfaces can be damaged.In addition, the chips must be formed insuch a way that they can be evacuatedfrom the groove without disrupting themachining with long, unwieldy chipcoils. Therefore the chips are formed intwo directions: bent across their widthand rolled together longitudinally toform a spiral spring-shaped chip.Figure 6.5 shows three chip controlinserts.

In order to produce this ideal chipshape the insert is usually provided witha chip former as shown in Figure 6.5,which takes into account both themachining conditions and the work-piece material. It is shaped in such away as to form a bank which the chipscan climb against during machining.After a number of revolutions the chipswill break automatically. The diameterof the spiral spring chips is influencedby the width of the insert, the height ofthe bank, the feed, and the workpiecematerial.

6.3.3 Tool PositioningAs with conventional turning, it isimportant that the cutting edge be posi-tioned on the same level as the centerline. In order to achieve satisfactory

results, a maximum deviation in posi-tioning of only ±.004 inch from the cen-ter line is acceptable.

As the cutting edge deviates from thecenter line, the rake angle and the clear-ance angle will be changed. Thischange is due to the radius of the work-piece. A clearance angle that is toosmall may cause the cutting edge to rubagainst the workpiece. If the cuttingedge is positioned too low, the tool willleave material in the center and a pipwill be formed.

6.3.4 Operational StabilityWith conventional external turning thetool overhang is not affected by thelength of the workpiece. The size of thetoolholder can be chosen so that it with-stands the stresses which arise duringthe operation. However, with partingand grooving operations, considerationmust be given to the depth of insertionand the width of the groove, whichmeans that stability must often be com-promised to meet specifications.

To obtain the best possible stability,the overhang should be as small as pos-sible, so a holder for the shortest possi-ble insertion depth should be chosen.Wider inserts can be used in order toimprove the stability, but more materialis wasted in the form of chips. This canbe expensive with large batches andwhen machining expensive materials.

Vibration can also arise as a result ofthe deflection of the workpiece. Thecloser the chuck is to the parting posi-tion, the lower the effect of the stressesand the deflection of the workpiece willbe. Therefore, if a workpiece has a ten-dency to vibrate, the machining shouldbe done as close to the chuck as possi-ble.

The risk of vibration must be kept toa minimum in order to obtain acceptableresults in quality and tool life. In addi-tion to choosing the best tool and moststable set up, the cutting data must beadapted to minimize the tendency of thetool and workpiece to vibrate.

6.3.5 Toolholder and Insert Selection

Modern parting and grooving cuttingtools consist of a toolholder and anindexable insert developed specificallyfor a particular operation. The majorityof inserts produced over the last decadewere designed to work with the SELF-GRIP concept. This clamping method

FIGURE 6.5: Chip control grooving and parting inserts (Courtesy:Iscar Metals, Inc.)



incorporates no external screws orlevers to hold the insert in place asshown in Figure 6.6. Instead, it relieson the rotation of the part and tool pres-sure to keep the insert seated in awedge-style pocket. The insertsdesigned for this type of holder are usu-ally single ended and their geometrypermits unlimited depth of cut.

With double-ended inserts, alsoknown as “dogbones”, the depth of cutis limited by the second cutting edge asshown in Figure 6.7. Dogbone insertstraditionally can only cut as deep as theoverall length of the insert. Once thedepth is reached, the trailing edge willbegin to rub inside the groove that thetool is creating. In addition, dogboneinserts usually are secured by a screw-top clamp, which also limits the depthof cut as again shown in Figure 6.7.

Coatings for grooving and partinginserts vary from supplier to supplier.But titanium carbon nitride applied bythe PVD process has practically becomethe industry standard for lower cuttingspeeds and tougher applications. And

when conditions arestable and highercutting speeds arerequired, the choicenarrows to titanium-aluminum-nitridecoatings applied bythe PVD process, orthe newer medium-temperature CVDprocess. The reasonis because TiAlNacts as a good heatbarrier for the car-bide substrate and

can handle elevated temperatures.Figure 6.8 shows a variety or groovingand parting tool holders with coatedindexable inserts..

6.4 Grooving and Parting Recommendations

The ability to efficiently cut off work-pieces and blanks in lathes has alwaysbeen important in getting the job com-pleted. Even in special purpose cutoffmachines, a good parting tool is at theheart of the operation. Today’s modernindexable insert parting and groovingtools provide the same productivity lev-els as modern turning tools.

In parting operations, the objective isto separate one part of the workpiecefrom the other as efficiently and reliablyas possible. In grooving operations, theprinciple is the same, although theseoperations are less sensitive because thegrooves are usually not as deep. Ingrooving, the shape, accuracy and sur-face finish arethe mainrequirements

that must be met.Some important hints for applying

grooving and parting tools:• always use plenty of cutting fluid.• set the center-height of the cuttingedge accurately• make sure toolholder/blade is accu-rately positioned at 90 degrees to theworkpiece axis.• use toolholder with the shortest possi-ble length of insertion for the operationin question. • select the largest shank/bar for the tool• adapt the cutting speed to avoid vibra-tions• reduce the feed rate for the final partwhen parting-off bar material/compo-nents.• for axial grooving, make the firstplunging cut at the largest diameter, far-thest out on the face, to minimize therisk of chip jamming• use the smallest possible lead angle foravoiding pips/burrs in parting-off• when possible, use a toolholder with astrengthening radius between shank andblade.

6.5 Screw Threads and Threading The screw thread dates back to 250 B.C,when it was invented by Archimedes.For centuries wooden screws, hand-made by skilled craftsmen, were usedfor wine presses and carpenters’ clampsthroughout Europe and Asia. Precisionin screw and thread manufacture did notcome into being until the screwcuttinglathe was invented by Henry Maudslayin 1797.

FIGURE 6.8: Various OD and ID grooving holders. (Courtesy:Iscar Metals, Inc.)

FIGURE 6.6: Self-grip tool holders use no external screw tohold the insert ( Courtesy: Iscar Metals, Inc.)

FIGURE 6.7: Dogbone insert tool holders have limited depthof cut (Courtesy: Iscar Metals, Inc.)



In the early 1800’s, Maudslay alsobegan to study the production of uni-form and accurate screw threads. Untilthen no two screws were alike; manu-facturers made as many threads per inchon bolts and nuts as suited their ownneeds. For example, one manufacturermade 10 threads per inch in 1/2 -in. -diameter threaded parts, whereas anoth-er made 12 threads, and so forth.During this period the need for threadstandards became acute.

Despite many attempts at standard-ization, it was not until World War I thatthread standards were developed. Thethread profile was designated theAmerican National thread form andwas the principal type of thread manu-factured in the United States until WorldWar II.

During World War II the UnitedStates manufactured military equipmentthat used the American National threadform, which presented interchangeabili-ty problems with machinery made inCanada and Great Britain. Not untilafter World War II in 1948, did thesecountries agree upon a Unified threadform to provide interchangeability ofthreaded parts.The Unified thread formis essentially the same as the oldAmerican National, except that it has arounded root and either a rounded or flatcrest. The Unified thread form ismechanically interchangeable with theformer American National threads ofthe same diameter and pitch. Today it isthe principal thread form manufacturedand used by the United States.

6.5.1 Screw Thread NomenclatureScrew threads have many dimensions.It is important in modern manufacturingto have a working knowledge of screwthread terminology to identify and cal-

culate the dimen-sions correctly.Screw set nomen-clature is shown inFigure 6.9.

The majordiameter is thelargest diameter ofthe screw thread.On an externalthread it is the out-side diameter; onan internal thread itis the diameter atthe bottom or rootof the thread.

The minor diameter is the smallestdiameter of a screw thread. On an exter-nal thread, the minor diameter is at thebottom of the thread; on an internalthread the minor diameter is the diame-ter located at the crest.

The pitch diameter is an imaginarydiameter that passes through the threadsat the point where the widths of thegroove and the thread are equal. Thepitch diameter is the most importantdimension on a screw thread; it is thebasis from which all thread measure-ments are taken.

The root is the bottom surface con-necting two sides of a thread. The crestis the top surface connecting two sidesof a thread. Pitch is the linear distancefrom corresponding points on adjacentthreads. The pitch is equal to 1 dividedby the total number of threads per inch(P=1/[no.threads/in.]). A screw having asingle lead with 16 threads per inch hasa pitch equal to 1/16 in., commonlyreferred to as a “16-pitch thread”.

The lead is the axial distance athreaded part advances in one completerotation. On a single lead threaded part,the lead is equal to the pitch.

The depth is the distance, measuredradially, between the crest and the rootof a thread. This distance is often calledthe depth of thread.

The flank is the side of the thread.Thread angle is the angle between theflanks of the thread. For example,Unified and Metric screw threads have athread angle of 60 degrees. Helix is thecurved groove formed around a cylinderor inside a hole.

A right-handed thread is a screwthread that requires right-hand or clock-wise rotation to tighten it. A left-hand-ed thread is a screw thread that requiresleft-hand or counterclockwise rotation

to tighten it. Thread fit is the range oftightness or looseness between externaland internal mating threads. Threadseries are groups of diameter and pitchcombinations that are distinguishedfrom each other by the number ofthreads per inch applied to a specificdiameter. The two common threadseries used in industry are the coarseand fine series. specified as UNC andUNF.

6.5.2 Unified Thread FormThe Unified screw thread has a 60degree thread angle with a rounded rootand a crest that is flat or rounded. Asmentioned earlier, this is the principalthread form used for screw thread fas-teners used in the United States. TheUnified screw thread system includessix main thread series:1. Unified Coarse (UNC)2. Unified Fine (UNF)3. Unified Extra-Fine (UNEF)4. Unified 8-Pitch (8 UN)5. Unified 12-Pitch (12 UN)6. Unified 16-Pitch (16 UN)

The coarse-thread series (UNC) isone of the more commonly used serieson nuts, bolts, and screws. It is usedwhen lower-tensile-strength materials(aluminum, cast iron, brass, plastics,etc.) require threaded parts. Coarsethreads have a greater depth of threadand are required on these types of mate-rials to prevent stripping the internalthreads.

The fine-thread series (UNF) is usedon higher-tensile-strength materialswhere coarse threads are not required.Because they have more threads perinch, they are also used where maxi-mum length of engagement between theexternal and internal threads is needed.

The extra-fine thread series(UNEF) is used when even greaterlengths of engagement are required inthinner materials. Eight, 12 and 16-pitch threads are used on larger-diame-ter threads for special applications. The8-pitch is generally regarded as a coarsethread for larger diameters, 12 pitch isthe fine series, and 16 is the extra-finethread used on the larger-diameterthreads.

The relationship between the pitchdiameter or major diameter deter-mines the helix angle of that thread. Forexample, a 12-pitch (12 UN) threadwith a 1.250-in. major diameter willhave a greater helix angle than a 12-

FIGURE 6.9: Screw Thread Nomenclature.

Thread angle Crest

Root

FlanksPitch

Helix angle

Single Depth

Major Diameter

Pitch Diameter

Minor Diameter



pitch thread with a 2.0-in. major diame-ter. Generally speaking, the lower thehelix angle, the greater the tensile stressapplied to the bolt for a given torqueapplied to the nut. The fastener with alower helix angle will also resist vibra-tion and loosening more effectively.

A grooving and threading holder isshown in Figure 6.10 and variousgrooving and threading inserts areshown in Figure 6.11

6.5.3 Acme Screw ThreadsAcme screw threads are manufacturedfor assemblies that require the carryingof heavy loads. They are used for trans-mitting motion in all types of machinetools, jacks, large C-clamps, and vises.The Acme thread form has a 29 degreethread angle and a large flat at the crestand root (see Fig. 6.12).

Acme screw threads were designed toreplace the Square thread, which is dif-ficult to manufacture.

There are three classes of Acmethreads (2G, 3G, and 4G), each having

clearance on all diameters toprovide for free movement.Class 2G threads are used on

most assemblies. Classes 3G and 4Gare used when less backlash or loose-ness is permissible, such as on the leadscrew of a lathe or the table screw of amilling machine.

6.5.4 Tapered Pipe ThreadsPipe threads, usually designated

NPT (National Pipe Taper) are taperedthreads used for sealing threaded jointssuch as water and air pipes. Most pipethreads have a slight taper (3/4-in./ft)and are cut using special pipe taps anddies. Pipe threads can also be machinedusing the taper attachment on an enginelathe.

6.6 Thread TurningDevelopment of threading tools hascome a long way since the days ofhigh speed tool-bits and tips ground toshape, which were then slowly fedalong by the lathe lead screw. Most oftoday’s threading is performed byindexable insert tools as part of a veryrapid CNC process. What used to be a

relatively difficult and time-consuming part of machining isnow standard procedure as withany other operation. A typicalpart that requires a thread isroutinely machined with fixedcycles of numerical control anda variety of other machinemechanisms and using toolswhich have the right threadshape. An ID and OD threadingoperation with coated indexableinserts is shown in Figure 6.13.

The principle of single pointthread cutting is the feed move-ment of the tool in relation to

the workpiece rotation. The point gen-erates the typical spiral groove thatmakes up the screw thread with a cer-tain pitch. Basically, threading is awell-coordinated turning operation witha form-tool. During the feed passes, thetool is moved longitudinally along theworkpiece and then withdrawn andmoved back to the starting position forthe next pass along the same threadgroove.

The feed rate is a key factor that hasto coincide with the pitch of the thread.The coordination is obtained by variousmeans, depending on the type ofmachine; lead screw, cam or numericalcontrol (usually handled as a sub-rou-tine in CNC). The shape of the grooveproduced is determined by the shape of

FIGURE 6.11: Various grooving and threading inserts (Courtesy: ValeniteInc.)

FIGURE 6.10: Grooving and threading tool holders(Courtesy: Valenite Inc.)

FIGURE 6.12: General purpose Acme screwthread

FIGURE 6.13: OD and ID threadingOperation (Courtesy: Sandvik CoromantCorp.)

Flat(root)

Depth29°

Pitch

Flat(crest)



the insert point, and the feed rate is con-siderably higher than for ordinary turn-ing operations.

The relatively small 60 percent pointangle of the tool makes the cutting edgesusceptible to the forces and stresses ofmetal cutting. To counter this, a longestablished method has been to use thethread depth to determine the cuttingdepth, and to avoid machining in onepass. Instead, the depth is machined inseveral passes. The cutting tool opensup the thread groove by cutting deeperand deeper, usually by making 5 to 16passes, depending on the thread pitch.As each pass is made, more and morematerial is removed per cut as a largerpart of the edge is engaged. For thisreason, the depth of cut is reduced suc-cessively as the passes are made.

It is best to have radial in-feeds whichdecrease successively as the passes areperformed. The number of in-feed pass-es must be balanced to provide the edgewith sufficient but not excessive cut intothe workpiece. Too much cutting forcewith insufficient cutting depth leads topremature tool wear.

6.6.1 Left and Right-Hand ThreadsThe difference in direction between leftand right-hand threads does not affectthe thread profile; it does, however,have some effect on the choice andcombination of tools. The method ofcutting the thread depends on the work-piece design. Working towards thechuck is the most common method,even though working away from thechuck is in many cases also satisfactory.

The advantage in using right-handtools for right-hand threads and left-hand tools for left-hand threads, is thatthe holder is designed to give maximumsupport to the insert. But under normal

cutting conditions this order is not criti-cal. It is vital, however, that insertsalways be used with holders of the samehand.

6.6.2 Toolholders and Insert Selection

Compared to conventional turning, thetool and machining parameters ofthreading are not so flexible. This ismainly because the feed is related to thepitch, the cutting depth is divided intopasses, and the cutting speed is limitedbecause of the pointed cutting edge.

Indexable inserts are available forexternal and internal threading. Theinserts for internal threadingare mirror images of the cor-responding external inserts.Both external and internalinserts are available in rightand left-hand versions. Sincetolerances and cutting geome-tries differ between externaland internal inserts, it isimportant that they should notbe confused.

6.6.3 Coated Threading Inserts

The development withinthread turning tools has beenconsiderable during the pastthirty years, since the intro-duction of the first flat insertswith a loose chip formerclamped on top of the inserts.Today’s modern inserts havedone away with most of thepossible problems that canarise with conventionalthreading inserts. This hasmade threading more closelyresemble a turning operation.

The multi-purpose PVD

coated inserts allow a wider range ofcutting speeds between the area charac-terized by built-up edge formation atlower speeds and plastic deformation athigher speeds. Threading involvesmany short cutting sequences and oftenrelatively low cutting speeds throughoutmachining. Of major importance inthreading is the ability of the cuttingtool to keep the built-up edge tendencyto an absolute minimum, or prevent itentirely, depending upon the workpiecematerial. A built-up edge will causepoor surface finish and eventually leadto edge breakdown and tool failure.

6.7 Thread MillingThread milling has been an establishedmethod of manufacturing accuratescrew threads for many years. Longscrews, such as lead screws on lathesand multiple start threads, are oftenmanufactured by milling.

Milling a screw thread is done witheither a single- or multiple-lead millingcutter. The rotating cutter is fed into thework to the required depth. The work isthen rotated and fed longitudinally at arate that will produce the proper lead onthe part (Fig. 6.14). Any class of fit orthread form can be manufactured by thethread milling process.

FIGURE 6.14: External thread milling with: a) single-row and b) multiple-row tooth cutter

(a)

Cutter Feed direction

(b)

Part

FIGURE 6.15: Shown are: a) single and b) multiplerib thread grinding wheels

Single-rib wheel

(a)

Multi-rib wheel

(b)



6.8 Thread GrindingGrinding a screw thread generally isdone when the hardness of the materialmakes cutting a thread with a die or sin-gle point tool impractical. Grindingthreads also results in greater accuracyand in superior surface finishes com-pared to what can be achieved withother thread-cutting operations. Taps,thread chasers, thread gages, andmicrometer spindles all use groundthreads.

Ground threads are produced bythread-grinding machines. A thread-grinding machine closely resembles acylindrical grinder in appearance. Itincorporates a precision lead screw toproduce the correct pitch or lead on thethreaded part. Thread-grindingmachines also have a means of dressingor truing the cutting periphery of thegrinding wheel so it will produce a pre-cise thread form on the part. Grindingwheels used in producing ground

threads are single-or multiple-rib. (Fig.6.15) Single-rib types are used forgrinding longer threads and feed longi-tudinally for the required length ofthread. The multiple-rib type of grind-ing wheel is generally used for formingshort threads. This type of wheel is“plunged” into the workpiece to pro-duce the thread.

Internal threading or tapping will bediscussed in a later chapter as part ofhole-making processes.


7.1 IntroductionBoth the shaper and the planer are single point tools and cut only in straight lines. Theyboth make the same types of cuts.

The shaper handles relatively small work. The planer handles work weighing up toseveral tons. The cutting stroke of the shaper is made by moving the tool bit attached tothe ram. The cutting stroke of the planer is achieved by moving the work past a station-ary tool bit.

The types of cuts which can be made with either machine are shown in Figure 7.1.Both the shaper andthe planer usually cutonly in one direction,so that the returnstroke is lost time.However, the returnstroke is made at upto twice the speed ofthe cutting stroke.

7.2 The ShaperThe shaper is a rela-tively simplemachine. It is usedfairly often in thetoolroom or formachining one ortwo pieces for proto-type work. Toolingis simple, andshapers do notalways require opera-tor attention whilecutting. The horizon-tal shaper is the mostcommon type, and itsprincipal componentsare shown in Figure7.2, and described asfollows:

Chapter 7

Shaping

& Planing

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing







FIGURE 7.1: Typical cuts made by both shapers and planers.

Chap. 7: Shaping & Planing


Ram: The ram slides back and forthin dovetail or square ways to transmitpower to the cutter. The starting pointand the length of the stroke can beadjusted.

Toolhead: The toolhead is fastenedto the ram on a circular plate so that itcan be rotated for making angular cuts.The toolhead can also be moved up ordown by its hand crank for precisedepth adjustments.

Attached to the toolhead is the tool-holding section. This has a tool postvery similar to that used on the enginelathe. The block holding the tool postcan be rotated a few degrees so that thecutter may be properly positioned in thecut.

Clapper Box: The clapper box isneeded because the cutter drags over thework on the return stroke. The clapperbox is hinged so that the cutting toolwill not dig in. Often this clapper box isautomatically raised by mechanical, air,or hydraulic action.

Table: The table is moved left andright, usually by hand, to position thework under the cutter when setting up.Then, either by hand or more oftenautomatically, the table is moved side-ways to feed the work under the cutterat the end or beginning of each stroke.

Saddle: The saddle moves up anddown (Y axis), usually manually, to set

the rough position of the depth of cut.Final depth can be set by the hand crankon the tool head.

Column: The column supports theram and the rails for the saddle. Themechanism for moving the ram andtable is housed inside the column.

Toolholders: Toolholders are thesame as the ones used on an enginelathe, though often larger in size. Thecutter is sharpened with rake and clear-ance angles similar to lathe tools,though the angles are smaller becausethe work surface is usually flat. Thesecutters are fastened into the toolholder,just as in the lathe, but in a verticalplane.

Work Holding: Work holding is fre-quently done in a vise. The vise is spe-cially designed for use in shapers andhas long ways which allow the jaws toopen up to 14 inches or more, thereforequite large work pieces can be held.The vise may also have a swivel base sothat cuts may be made at an angle.Work which, due to size or shape, can-not be held in the vise, is clampeddirectly to the shaper table in much thesame way as parts are secured onmilling machine tables.

Shaper Size: The size of a shaper isthe maximum length of stroke which itcan take. Horizontal shapers are mostoften made with strokes from 16 to 24

inches long, though some smaller andlarger sizes are available. These shapersuse from 2 to 5 HP motors to drive thehead and the automatic feed.

Shaper Width: The maximum widthwhich can be cut depends on the avail-able movement of the table. Mostshapers have a width capacity equal toor greater than the length of the stroke.The maximum vertical height availableis about 12 to 15 inches.

7.2.1 Drive MechanismsShapers are available with eithermechanical or hydraulic drive mecha-nisms. Figures 7.3a and 7.3b show dia-grams of both shaper drive mechanisms.

Mechanical DriveThe less expensive shaper, the one mostoften purchased, uses a mechanicaldrive. This drive uses a crank mecha-nism (Fig. 7.3a). The bull gear is drivenby a pinion which is connected to themotor shaft through a gear box withfour, eight or more speeds available.The RPM of the bull gear becomes thestrokes per minute (sometimes abbrevi-ated SPM) of the shaper.

Cutting Speed: The cutting speed ofthe tool across the work will vary duringthe stroke as shown by the velocity dia-gram in Figure 7.3a. The maximum isat the center of the stroke. However, ifthe cutting speed chosen is somewhaton the slow side, the average speed maybe used, and computations are greatlysimplified.

Although the ratio varies some-what,several shapers have a linkageusing 220 degrees of the cycle for thecutting stroke and 140 degrees for thereturn stroke. This is close to a 3:2ratio.

In setting up a mechanically operatedshaper, the length of cut (in inches) isknown, and the cutting speed (in feetper minute) is selected according to thekind of metal being cut. It is then nec-essary to compute the strokes perminute since that is how the shaperspeed is controlled. Such calculationsare beyond the scope of this text.

The stroke per minute available on ashaper will vary according to the size ofthe shaper. The larger shapers will havelower speeds. A 16 inch shaper mayhave speeds of 27 to 150 strokes perminute, while a 24 inch shaper will have10 to 90 strokes per minute speedsavailable.

FIGURE 7.2: The horizontal shaper is the most common type; its princpal componentsare shown here (Courtesy: Cincinnati Machine)



Cutting Feed: Feed per stroke on ashaper is comparable to the feed perrevolution on a lathe. Coarse feeds forroughing range up to 0.100 inch perstroke (sometimes abbreviated as IPS),and finish cuts from 0.005 to 0.015 inchper stroke. Finish would also depend onthe nose radius of the cutting tool.

Hydraulic DriveThe hydraulic shaper (Fig. 7.3b) has thesame major parts as the mechanical one,however, the ram is driven by ahydraulic cylinder as shown in the sim-plified sketch. These shapers use 5 to10 HP motors.

Cutting Speed and Feed: The cut-ting speed of the hydraulic shaper isinfinitely variable by means of

hydraulic controls, as is thecross feed. The reversestroke is made faster thanthe power stroke because ofthe smaller area in the returnside of the cylinder, if a con-stant volume pump is used.Another method is to havethe rate of fluid flowincreased to speed up thereturn stroke.

Speed and feed on ahydraulic shaper are oftencontrolled by simple dials.Speed is read directly in feetper minute and feed is readdirectly in decimal inches.The cutting speed remainsnearly constant through thefull stroke.

7.2.2 Vertical Shapers

The vertical shaper,sometimes called aslotter, has a verti-cal ram, with tableand saddle similarto the horizontalshaper. If a rotarytable is mounted onthe regular table, anumber of slots canbe made at quiteaccurately spacedintervals. Thismachine can workeither outside orinside a part, pro-vided that the inte-rior opening is larg-er than the tool

head. A schematic illustrationof a vertical shaper is shown inFigure 7.4.

7.3 The PlanerA planer makes the same typesof cuts as a shaper. However,it is a production-type machinefor certain types of work. Itcan machine any flat or angu-lar surface, including groovesand slots, in medium and largesized workpieces (see Fig.7.1). Typical work would bemachine beds and columns,marine diesel engine blocks,and bending plates for sheetmetal work. These parts areusually large iron castings or

steel weldments and may weigh a fewhundred pounds or several tons.

The most frequently used type ofplaner is the double-housing planer,shown in Figure 7.5, with the followingcomponents:

Frame: The frame is basically twoheavy columns fastened together at thetop with a large bracing section and fas-tened at the bottom to the machine bed.This creates a very strong, rigid struc-ture which will handle heavy loadswithout deflection.

Crossrail: The crossrail is also aheavy box, or similar construction. Itslides up and down on V- or flat ways,controlled by hand or by power-operat-ed screws. These crossrails are soheavy that they are counterweighted,

Ram connection

Max. forwardposition

Rocker arm

Bull gearsliding block

Adjustingscrew

Crank pin

Pivot bearing

(a)

Max. rearposition

Bevel gears(strokeadjustment)

Bull gear

Cut

Stroke length

Velocity diagram

Vel

ocity

40°

Cuttingstroke220°

140°Returnstroke

1.0

1.6 Return

Velocity diagram

Forward cutting speed

Return speed (b)

Vel

ocity

Returnstroke(faster)

Shaper ram

Cuttingstroke

4-wayvalve

Pump

Tank

Motor

Base

Ram with annularadjustment

Drive gearbox

Longitudinal feed

Tool holder

Rotating table

Table rotation

Transversefeed

FIGURE 7.3: Shapers are available with either (a)mechanical drive mechanisms or (b) hydraulic drivemechanisms.

FIGURE 7.4: Schematic illustration of a verticalshaper, also called a slotter.

Clapper box

Crossrail

Top brace Rail head

Bed

Drive motor

Column or housing

Side head

TableBedVee ways

FIGURE 7.5: Schematic illustration of a double-housing planer.



with either cast iron weights orhydraulic cylinders, in order that theymay be moved easily and positionedaccurately. After being positioned, theyare clamped in place.

Railheads: The two railheads can bemoved left or right across the crossrail,each controlled by a separate leadscrew, which can be turned by hand butusually by power feed. The railhead canbe rotated, and vertically adjusted fordepth of cut, the same as the shaperheads. They also have a clapper box(often with power lift) like the shaper.

Sideheads: The sideheads are inde-pendently moved up or down by hand orby power feed and can also be rotatedand moved in or out for depth of cut.

Table: The table is a heavy castingwhich carries the work past the cuttingheads. It runs on V- or flat ways. Thetable is driven either by a very longhydraulic cylinder or by a pinion geardriving a rack which is fastened underthe center of the table. The motor dri-ving the pinion gear is the reversibletype with variable speed.

Bed: The bed of the planer must be aweldment or casting twice as long as thetable. Thus a 12-ft table requires a 24-ft bed. The gearing of hydraulic cylin-ders for driving the table is housedunder the bed.

Toolholders: Planers use high speedsteel or carbide tipped cutting tools sim-ilar to those used on shapers. However,since planers make heavy cuts, theirtools are much larger. Rake reliefangles are similar to those used on lath-es for cutting cast iron or steel, althoughrelief angles are often only 3 to 5degrees, because all cuts are on flat sur-faces.

Work Holding: Holding the workwhile machining such heavy cuts at 60to 100 feet per minute requires consid-erable force; therefore, the workpiecesmust be solidly fastened to the table.Because the reversal of direction occursquite rapidly, the work must be espe-cially well braced at the ends. The table

has T-slots, both lengthwise and across,in which heavy bolts and clamps may beused. Sometimes holes are drilled in thetable so that large pins can be used toprevent the workpiece from going offthe table when the machine reverses.

Planer Size: The size of planers isoften referred to as a 30 inch planer or a60 inch planer. This specifies theapproximate width of the table whichranges from 30 to 72 inches. A morecomplete specification is:

Width of table x height under rail x length of table

(For example: 48 inches x 48 inches x 14 feet)

The width and height are usually, butnot always, the same. Table length isoften made to order and may be as shortas 8 feet, or as long as 20 feet or more.The drive may be 15 HP on the smallerplaners, and 100 HP or more on thelarger models.

Mechanical and hydraulic power canbe used for planers. Uniform cuttingspeed is attained throughout the cuttingstroke. Acceleration and deceleration ofthe table takes place in a short distanceof travel and does not influence the timeto machine.

Double-housing Planers: Double-housing planers consist of a long heavybase on which the table reciprocates.The upright housing near the center onthe side of the base, supports the cross-rail on which the tools are fed across thework. Figure 7.5 illustrates how thetools are supported both above and onthe sides, and their adjustment for anglecuts. They are fed by power in either avertical or a crosswise direction.

Open-sided Planers: Open-sidedplaners have the housing on one sideonly. The open side permits machiningwider workpieces. Most planers haveone flat and one double V-way, whichallows for unequal bed and platenexpansions. Adjustable dogs at the sideof the bed control the stroke length ofthe platen.

Planers are often converted to planer-

mills, for more efficient machining.

7.3.1 Comparison of Shapers and Planers

Although both the planer and the shaperare able to machine flat surfaces, thereis little overlapping in their application.They differ greatly in construction andin the method of operation. The planeris especially adapted to large work: theshaper can do only small work. On theplaner the work is moved against a sta-tionary tool: on the shaper the toolmoves across the work, which is sta-tionary. On the planer the tool is fedinto the work; on the shaper the work isusually fed across the tool. The drive onthe planer table is either by gears or byhydraulic means. The shaper ram alsocan be driven in this manner, but manytimes a quick-return link mechanism isused.

Most planers differ from shapers inthat they approach more constant-veloc-ity cutting speeds. Tools used in shaperand planer work are single point as usedon a lathe, but are heavier in construc-tion. The holder is designed to securethe tool bit near the centerline of theholder or the pivot point rather than atan angle as is customary with lathe tool-holders.

Cutting tools for the planer operationare usually tipped with high-speed steel,cast alloy, or carbide inserts. Highspeed steel or cast alloys are commonlyused in heavy roughing cuts and car-bides for secondary roughing and fin-ishing.

Cutting angles for tools depend onthe tool used and the workpiece materi-al. They are similar to angles used onother single-point tools, but the endclearance does not exceed 4 degrees.Cutting speeds are affected by the rigid-ity of the machine, how the work isheld, tool, material, and the number oftools in operation. Worktables on plan-ers and shapers are constructed with T-slots to hold and clamp parts that are tobe machined.


8.1 IntroductionDrilling is the process most commonly associatedwith producing machined holes. Although manyother processes contribute to the production ofholes, including boring, reaming, broaching, andinternal grinding, drilling accounts for the major-ity of holes produced in the machine shop. Thisis because drilling is a simple, quick, and eco-nomical method of hole production. The othermethods are used principally for more accurate,smoother, larger holes. They are often used aftera drill has already made the pilot hole.

Drilling is one of the most complex machiningprocesses. The chief characteristic that distin-guishes it from other machining operations is thecombined cutting and extrusion of metal at thechisel edge in the center of the drill. The highthrust force caused by the feeding motion firstextrudes metal under the chisel edge. Then ittends to shear under the action of a negative rakeangle tool. Drilling of a single hole is shown inFigure 8.1 and high production drilling of a platecomponent is shown in Figure 8.2.

Chapter 8

Drills & Drilling

Operations

Upcoming Chapters





Shaping and Planing



Reaming and Tapping



Finishing ProcessesGrinding Wheels and OperationsGrinding Methods and Machines

Lapping and Honing






Prentice Hall: http://www.prenhall.comFIGURE 8.2: Holes can be drilled individually as shown in Figure 8.1, or many holes can bedrilled at the same time as shown here. (Courtesy Sandvik Coromant Co.)

FIGURE 8.1: Drilling accounts for themajority of holes produced in industrytoday. (Courtesy Valenite Inc.)

Chap. 8: Drills & Drilling Operations


The cutting action along the lips ofthe drill is not unlike that in othermachining processes. Due to variablerake angle and inclination, however,there are differences in the cuttingaction at various radii on the cuttingedges. This is complicated by the con-straint of the whole chip on the chipflow at any single point along the lip.Still, the metal removing action is truecutting, and the problems of variablegeometry and constraint are present, butbecause it is such a small portion of thetotal drilling operation, it is not a distin-guishing characteristic of the process.Many of the drills discussed in thischapter are shown in Figures 8.3.

The machine settings used in drillingreveal some important features of thishole producing operation. Depth of cut,a fundamental dimension in other cut-ting processes, corresponds most close-ly to the drill radius. The undeformedchip width is equivalent to the length ofthe drill lip, which depends on the pointangle as well as the drill size. For agiven set-up, the undeformed chipwidth is constant in drilling. The feeddimension specified for drilling is thefeed per revolution of the spindle. Amore fundamental quantity is the feedper lip. For the common two-flute drill,it is half the feed per revolution. Theundeformed chip thickness differs fromthe feed per lip depending on the pointangle.

The spindle speed is constant for anyone operation, while the cutting speedvaries all along the cutting edge.Cutting speed is normally computed forthe outside diameter. At the center of

the chisel edge the cutting speed is zero;at any point on the lip it is proportionalto the radius of that point. This varia-tion in cutting speed along the cuttingedges is an important characteristic ofdrilling.

Once the drill engages the workpiece,the contact is continuous until the drillbreaks through the bottom of the part oris withdrawn from the hole. In thisrespect, drilling resembles turning andis unlike milling. Continuous cuttingmeans that steady forces and tempera-tures may be expected shortly after con-tact between the drill and the work-piece.

8.2 Drill NomenclatureThe most important type of drill is thetwist drill. The important nomenclaturelisted below and illustrated in Figure 8.4applies specifically to these tools.

Drill: A drill is an end-cutting toolfor producing holes. It has one or morecutting edges, and flutes to allow fluidsto enter and chips to be ejected. Thedrill is composed of a shank, body, and

point.Shank: The shank is the

part of the drill that is heldand driven. It may be straightor tapered. Smaller diameterdrills normally have straightshanks. Larger drills haveshanks ground with a taperand a tang to insure accuratealignment and positive drive.

Tang: The tang is a flat-tened portion at the end of theshank that fits into a drivingslot of the drill holder on thespindle of the machine.

Body: The body of thedrill extends from the shankto the point, and contains theflutes. During sharpening, itis the body of the drill that is

partially ground away.Point: The point is the cutting end of

the drill.Flutes: Flutes are grooves that are

cut or formed in the body of the drill toallow fluids to reach the point and chipsto reach the workpiece surface.Although straight flutes are used insome cases, they are normally helical.

Land: The land is the remainder ofthe outside of the drill body after theflutes are cut. The land is cut backsomewhat from the outside drill diame-ter in order to provide clearance.

Margin: The margin is a short por-tion of the land not cut away for clear-ance. It preserves the full drill diameter.

Web: The web is the central portionof the drill body that connects the lands.

Chisel Edge: The edge ground onthe tool point along the web is called thechisel edge. It connects the cutting lips.

Lips: The lips are the primary cut-ting edges of the drill. They extendfrom the chisel point to the periphery ofthe drill.

Axis: The axis of the drill is the cen-terline of the tool. It runs through the weband is perpendicular to the diameter.

Neck: Some drills are made with arelieved portion between the body andthe shank. This is called the drill neck.

In addition to the above terms thatdefine the various parts of the drill,there are a number of terms that apply tothe dimensions of the drill, includingthe important drill angles. Among theseterms are the following:

Length: Along with its outsidediameter, the axial length of a drill islisted when the drill size is given. Inaddition, shank length, flute length, andneck length are often used.(see Fig. 8.4)

Body Diameter Clearance: Theheight of the step from the margin to theland is called the body diameter clear-ance.

FIGURE 8.3: Many of the drills used in industry areshown here and described in this chapter. (CourtesyCleveland Twist Drill Greenfield Industries)

FIGURE 8.4: Nomenclature of a twist drill shown with taper and tang drives.

Taper shank

TangTang drive

Neck

Shankdiameter

AxisStraightshank

Land width

Point angle

Lip relief angle

Helix angle

Drill diameterClearance Diameter

Body Diameter Clearance

Chisel Edge Angle

Shank length

Overall length

Flutes

Flute length

MarginLip

WebChisel edge

Land

Body



Web Thickness: The web thicknessis the smallest dimension across theweb. It is measured at the point unlessotherwise noted. Web thickness willoften increase in going up the bodyaway from the point, and it may have tobe ground down during sharpening toreduce the size of the chisel edge. Thisprocess is called ‘web thinning’. Webthinning is shown in Figure 8.13.

Helix Angle: The angle that the lead-ing edge of the land makes with the drillaxis is called the helix angle. Drillswith various helix angles are availablefor different operational requirements.

Point Angle: The included anglebetween the drill lips is called the pointangle. It is varied for different work-piece materials.

Lip Relief Angle: Corresponding tothe usual relief angles found on othertools is the lip relief angle. It is mea-sured at the periphery.

Chisel Edge Angle: The chisel edgeangle is the angle between the lip andthe chisel edge, as seen from the end ofthe drill.

It is apparent from these partial listsof terms that many different drillgeometries are possible.

8.3 Classes of DrillsThere are different classes of drills fordifferent types of operations.Workpiece materials may also influencethe class of drill used, but it usuallydetermines the point geometry ratherthan the general type of drill best suited

for the job. It has already been notedthat the twist drill is the most importantclass. Within the general class of twistdrills there are a number of drill typesmade for different kinds of operations.Many of the special drills discussedbelow are shown in Figure 8.5.

High Helix Drills: This drill has ahigh helix angle, which improves cut-ting efficiency but weakens the drillbody. It is used for cutting softer metalsand other low strength materials.

Low Helix Drills: A lower than nor-mal helix angle is sometimes useful toprevent the tool from ‘running ahead’ or‘grabbing’ when drilling brass and sim-ilar materials.

Heavy-duty Drills: Drills subject tosevere stresses can be made stronger bysuch methods as increasing the webthickness.

Left Hand Drills: Standard twistdrills can be made as left hand tools.These are used in multiple drill headswhere the head design is simplified byallowing the spindle to rotate in differ-ent directions.

Straight Flute Drills: Straight flutedrills are an extreme case of low helixdrills. They are used for drilling brassand sheet metal.

Crankshaft Drills: Drills that areespecially designed for crankshaft workhave been found to be useful formachining deep holes in tough materi-als. They have a heavy web and helixangle that is somewhat higher than nor-mal. The heavy web prompted the use

of a specially notched chisel edge thathas proven useful on other jobs as well.The crankshaft drill is an example of aspecial drill that has found wider appli-cation than originally anticipated andhas become standard.

Extension Drills: The extensiondrill has a long, tempered shank toallow drilling in surfaces that are nor-mally inaccessible.

Extra-length Drills: For deep holes,the standard long drill may not suffice,and a longer bodied drill is required.

Step Drill: Two or more diametersmay be ground on a twist drill to pro-duce a hole with stepped diameters.

Subland Drill: The subland ormulti-cut drill does the same job as thestep drill. It has separate lands runningthe full body length for each diameter,whereas the step drill uses one land. Asubland drill looks like two drills twist-ed together.

Solid Carbide Drills: For drillingsmall holes in light alloys and non-metallic materials, solid carbide rodsmay be ground to standard drill geome-try. Light cuts without shock must betaken because carbide is quite brittle.

Carbide Tipped Drills: Carbide tipsmay be used on twist drills to make theedges more wear resistant at higherspeeds. Smaller helix angles and thick-er webs are often used to improve therigidity of these drills, which helps topreserve the carbide. Carbide tippeddrills are widely used for hard, abrasivenon-metallic materials such as masonry.

Oil Hole Drills: Small holes throughthe lands, or small tubes in slots milledin the lands, can be used to force oilunder pressure to the tool point. Thesedrills are especially useful for drillingdeep holes in tough materials.

Flat Drills: Flat bars may be groundwith a conventional drill point at theend. This gives very large chip spaces,but no helix. Their major application isfor drilling railroad track.

Three and Four Fluted Drills:There are drills with three or four fluteswhich resemble standard twist drillsexcept that they have no chisel edge.They are used for enlarging holes thathave been previously drilled orpunched. These drills are used becausethey give better productivity, accuracy,and surface finish than a standard drillwould provide on the same job.

Drill and Countersink: A combina-tion drill and countersink is a useful tool

FIGURE 8.5: Special drills are used for some drilling operations.

(a) Jobber s drill

(b) Low-helix drill

(c) High-helix drill

(d) Straight-shank oil-hole drill

(e) Screw-machine drill

(f) Three-flute core drill

(g) Left-hand drill

(h) Straight-flute drill

(i) Step drill

(j) Subland drill



for machining ‘center holes’ on bars tobe turned or ground between centers.The end of this tool resembles a stan-dard drill. The countersink starts a shortdistance back on the body.

A double-ended combination drilland countersink, also called a centerdrill, is shown in Figure 8.6.

8.4 Related Drilling OperationsSeveral operations are related todrilling. In the following list, most ofthe operations follow drilling except forcentering and spotfacing which precededrilling. A hole must be made first bydrilling and then the hole is modified byone of the other operations. Some ofthese operations are described here andillustrated in Figure 8.7

Reaming: A reamer is used toenlarge a previously drilled hole, to pro-vide a higher tolerance and to improve

the surface finish of the hole.Tapping: A tap is used to provide

internal threads on a previously drilledhole.

Reaming and tapping are moreinvolved and complicated thancounterboring, countersinking,centering, and spot facing, andare therefore discussed inChapter 11.

Counterboring: Counterboringproduces a larger step in a hole toallow a bolt head to be seated

below the part surface.Countersinking: Countersinking is

similar to counterboring except that thestep is angular to allow flat-head screwsto be seated below the surface.

Counterboring tools are shown inFigure 8.8a, and a countersinking toolwith two machined holes is shown inFigure 8.8b.

Centering: Center drilling is usedfor accurately locating a hole to bedrilled afterwards.

Spotfacing: Spotfacing is used toprovide a flat-machined surface on apart.

8.5 Operating ConditionsThe varying conditions, under whichdrills are used, make it difficult togive set rules for speeds and feeds. Drillmanufacturers and a variety of referencetexts provide recommendations forproper speeds and feeds for drilling avariety of materials. General drillingspeeds and feeds will be discussed hereand some examples will be given.

Drilling Speed: Cutting speed maybe referred to as the rate that a point ona circumference of a drill will travel in 1minute. It is expressed in surface feetper minute (SFPM). Cutting speed isone of the most important factors thatdetermine the life of a drill. If the cut-ting speed is too slow, the drill mightchip or break. A cutting speed that istoo fast rapidly dulls the cutting lips.Cutting speeds depend on the followingseven variables:• The type of material being drilled.

The harder the material, the slowerthe cutting speed.

• The cutting tool material and diame-

FIGURE 8.6: A double-ended combination drilland countersink, also called a center drill.(Courtesy Morse Cutting Tools)

FIGURE 8.7: Related drilling operations: (a) reaming, (b) tapping, (c) counterboring,(d) countersinking, (e) centering, (f) spotfacing.

(a) (b)FIGURE 8.8: Counterboring tools (a) and countersinking operation (b) are shown here.(Courtesy The Weldon Tool Co.)

(a) (b) (c)

(d) (e) (f)



ter. The harder the cutting tool materi-al, the faster it can machine the materi-al. The larger the drill, the slower thedrill must revolve.• The types and use of cutting fluids

allow an increase in cutting speed.• The rigidity of the drill press.• The rigidity of the drill (the shorter

the drill, the better).• The rigidity of the work setup.• The quality of the hole to be drilled.

Each variable should be consideredprior to drilling a hole. Each variable isimportant, but the work material and itscutting speed are the most importantfactors. To calculate the revolutions perminute (RPM) rate of a drill, the diame-ter of the drill and the cutting speed ofthe material must be considered.

The formula normally used to calcu-late cutting speed is as follows:

SFPM = (Drill Circumference) x (RPM)

Where:SFPM = surface feet per minute, or

the distance traveled by a point on the drill periphery in feet each minute.

Drill Circumference = the distance around the drill periphery in feet.

RPM = revolutions per minute

In the case of a drill, the circumfer-ence is:Drill Circumference =

Pi/12 x (d) = .262 x d

Where:Drill Circumference = the distance

around the drill periphery in feet.Pi = is a constant of 3.1416d = the drill diameter in inches.

By substituting for the drill circum-ference, the cutting speed can now bewritten as:

SFPM = .262 x d x RPM

This formula can be used to deter-mine the cutting speed at the peripheryof any rotating drill.

For example: Given a .25 inch drill,what is the cutting speed (SFPM)drilling cast iron at 5000 RPM?

SFPM = .262 x d x RPMSFPM = .262 x .25 x 5000Answer = 327.5 or 327 SFPM

RPM can be calculated as follows: Given a .75 inch drill, what is the

RPM drilling low carbon steel at 400SFPM?

SFPM 400 400RPM = ________ = ________ = ____.262 x d .262 x .75 .1965

Answer = 2035.62 or 2036 RPM

Drilling Feed: Once the cuttingspeed has been selected for a particularworkpiece material and condition, theappropriate feed rate must be estab-lished. Drilling feed rates are selectedto maximize productivity while main-taining chip control. Feed in drillingoperations is expressed in inches perrevolution, or IPR, which is the distancethe drill moves in inches for each revo-lution of the drill. The feed may also beexpressed as the distance traveled by thedrill in a single minute, or IPM (inchesper minute), which is the product of theRPM and IPR of the drill. It can be cal-culated as follows:

IPM = IPR x RPM

Where:IPM = inches per minuteIPR = inches per revolutionRPM = revolutions per minute.

For example: To maintain a .015 IPRfeed rate on the .75 inch drill discussedabove, what would the IPM feed ratebe?

IPM = PR x RPMIPM = .015 x 2036Answer = 30.54 or 31 IPM

The selection of drilling speed(SFPM) and drilling feed (IPR) for var-ious materials to be machined oftenstarts with recommendations in the

form of application tables from manu-facturers or by consulting referencebooks.

8.5.1 Twist Drill WearDrills wear starts as soon as cuttingbegins and instead of progressing at aconstant rate, the wear accelerates con-tinuously. Wear starts at the sharp cor-ners of the cutting edges and, at thesame time, works its way along the cut-ting edges to the chisel edge and up thedrill margins. As wear progresses,clearance is reduced. The resulting rub-bing causes more heat, which in turncauses faster wear.

Wear lands behind the cutting edgesare not the best indicators of wear, sincethey depend on the lip relief angle. Thewear on the drill margins actually deter-mines the degree of wear and is notnearly as obvious as wear lands. Whenthe corners of the drill are rounded off,the drill has been damaged more than isreadily apparent. Quite possibly thedrill appeared to be working properlyeven while it was wearing. The marginscould be worn in a taper as far back asan inch from the point. To restore thetool to new condition, the worn areamust be removed. Because of theaccelerating nature of wear, the numberof holes per inch of drill can sometimesbe doubled by reducing, by 25 percent,the number of holes drilled per grind.

8.5.2 Drill Point GrindingIt has been estimated that about 90 per-cent of drilling troubles are due toimproper grinding of the drill point.Therefore, it is important that care betaken when resharpening drills. A gooddrill point will have: both lips at thesame angle to the axis of the drill; bothlips the same length; correct clearanceangle; and correct thickness of web.

(a) (b)FIGURE 8.9: The included lip angle varies between 90 and 135 degrees (a): two drillpoints are shown in (b). (Courtesy Cleveland Twist Drill Greenfield Industries)

C2

C

C

2



Lip Angle and Lip Length: Whengrinding the two cutting edges theyshould be equal in length and have thesame angle with the axis of the drill asshown in Figure 8.9a. Figure 8.9bshows two ground drill points.

For drilling hard or alloy steels, angleC (Fig. 8.9a) should be 135 degrees.For soft materials and for general pur-poses, angle C should be 118 degrees.For aluminum, angle C should be 90degrees.

If lips are not ground at the sameangle with the axis, the drill will be sub-jected to an abnormal strain, becauseonly one lip comes in contact with thework. This will result in unnecessarybreakage and also cause the drill to dullquickly. A drill so sharpened will drillan oversized hole. When the point isground with equal angles, but has lips ofdifferent lengths, a condition as shownin Figure 8.10a is produced.

A drill having cutting lips of differentangles, and of unequal lengths, will belaboring under the severe conditionsshown in Figure 8.10b.

Lip Clearance Angle: The clearanceangle, or ‘backing-off’ of the point, is

the next importantthing to consider.When drilling steelthis angle A (Fig.8.11a) should befrom 6 to 9 degrees.For soft cast ironand other soft mate-rials, angle A maybe increased to 12degrees (or even 15degrees in somecases)

This clearanceangle shouldincrease gradually

as the center of the drill isapproached. The amount ofclearance at the center of thedrill determines the chiselpoint angle B (Fig. 8.11b).

The correct com-bination of clearanceand chisel pointangles should be asfollows: When angleA is made to be 12degrees for softmaterials, angle Bshould be madeapproximately 135degrees; when angleA is 6 to 9 degreesfor harder materials,angle B should be115 to 125 degrees.

While insufficientclearance at the cen-ter is the cause ofdrills splitting up the web, too muchclearance at this point will cause thecutting edges to chip.

In order to maintain the necessaryaccuracy of point angles, lip lengths, lipclearance angle, and chisel edge angle,

the use of machine point grinding is rec-ommended. There are many commer-cial drill point grinders available today,which will make the accurate repointingof drills much easier. Tool and cuttergrinders such as the one shown inFigure 8.12 are often used.

Twist Drill Web Thinning: Thetapered web drill is the most commontype manufactured. The web thicknessincreases as this type of drill is resharp-ened. This requires an operation calledweb thinning to restore the tool’s origi-nal web thickness. Without the webthinning process, more thrust would berequired to drill, resulting in additionalgenerated heat and reduced tool life.Figure 8.13 illustrates a standard drillbefore and after the web thinningprocess. Thinning is accomplished witha radiused wheel and should be done sothe thinned section tapers gradually

(a) (b)

(a) (b)

A B

Roll type Dub type Notch type

Originalchisel edge

Chisel edgeafter drillhas been

shortened

FIGURE 8.10: Drill with equal lip angle but unequallip length (a), and drill with unequal lip angle andunequal lip length (b).

FIGURE 8.12: Tool and cutter grinders, are used toproperly sharpen drills and other cutting tools.(Courtesy K. O. Lee Co.)

FIGURE 8.13: Web thinning restores proper web thickness aftersharpening twist drills; three methods are shown.

FIGURE 8.11: Drill lip clearance angle (a) and drill chisel point angle (b).



from the point. This prevents a bluntwedge from being formed that would bedetrimental to chip flow. Thinning canbe done by hand, but since point cen-trality is important, thinning by machineis recommended.

8.6 Spade DrillsThe tool generally consists of a cuttingblade secured in a fluted holder (SeeFigure 8.14). Spade drills can machinemuch larger holes (up to 15 in. in diam-eter) than twist drills. Spade drills usu-ally are not available in diameterssmaller than 0.75 inch. The drillingdepth capacity of spade drills, withlength-to-diameter ratios over 100 to 1possible, far exceeds that of twist drills.At the same time, because of their muchgreater feed capability, the penetrationrates for spade drills exceed those oftwist drills by 60 to 100 percent.However, hole finish generally suffersbecause of this. Compared to twistdrills, spade drills are much more resis-tant to chatter under heavy feeds oncethey are fully engaged with the work-piece. Hole straightness is generallyimproved (with comparable size capa-bility) by using a spade drill. However,these advantages can only be gained byusing drilling machines of suitablecapability and power.

The spade drill is also a very eco-nomical drill due to its diameter flexi-bility. A single holder will accommo-date many blade diameters as shown in

Figure 8.14. Therefore, whena diameter change isrequired, only the bladeneeds to be purchased whichis far less expensive thanbuying an entire drill.

8.6.1 Spade Drill BladesThe design of spade drillblades varies with the manu-facturer and the intendedapplication. The most com-mon design is shown in Figure8.15. The locator length isground to a precision dimen-sion that, in conjunction withthe ground thickness of theblade, precisely locates the blade in itsholder. When the seating pads properlycontact the holder, the holes in the bladeand holder are aligned and the assemblycan be secured with a screw.

The blade itself as shown in Figure8.15, possesses all the cutting geometrynecessary. The point angle is normally130 degrees but may vary for specialapplications. In twist drill designs, thehelix angle generally determines thecutting rake angle but since spade drillshave no helix, the rake surface must beground into the blade at the cutting edgeangle that produces the proper webthickness. The cutting edge clearanceangle is a constant type of relief, gener-ally 6 to 8 degrees. After this clearanceis ground, the chip breakers are ground,about 0.025 inch deep, in the cutting

edge.These chip breakers are nec-

essary on spade drill blades andnot optional as with twist drills.These notches make the chipsnarrow enough to flush aroundthe holder. Depending on thefeed rate, the grooves can alsocause a rib to form in the chip.The rib stiffens the chip andcauses it to fracture or breakmore easily which results inshorter, more easily removedchips. Margins on the blade actas bearing surfaces once thetool is in a bushing or in thehole being drilled. The widthof the margins will vary from1/16 to 3/16 inches, dependingon the tool size. A slight backtaper of 0.004 to 0.006 inch isnormally provided and outsidediameter clearance angles aregenerally 10 degrees.

8.6.2 Spade Drill Blade HoldersThe blade holder makes up the majorpart of the spade drill. The blade hold-er is made of heat-treated alloy steel andis designed to hold a variety of blades ina certain size range as shown in Figure8.14. Two straight chip channels orflutes are provided for chip ejection.

The holder shank designs are avail-able in straight, Morse taper, and vari-ous other designs to fit the machinespindles. The holders are generally sup-plied with internal coolant passages toensure that coolant reaches the cuttingedges and to aid chip ejection.

When hole position is extremely crit-ical and requires the use of a startingbushing, holders with guide strips areavailable. These strips are ground to fitclosely with the starting bushing to sup-port the tool until it is fully engaged inthe workpiece. The strips may also beground to just below the drill diameterto support the tool in the hole when theset-up lacks rigidity.

8.6.3 Spade Drill Feeds and SpeedsThe cutting speed for spade drills isgenerally 20 percent less than for twistdrills. However, the spade drill feedcapacity can be twice that of twist drills.The manufacturers of spade drills andother reference book publishers provideexcellent recommendations for machin-ing rates in a large variety of metals.These published rates should generallybe observed. Spade drills work bestunder moderate speed and heavy feed.Feeding too lightly will result in eitherlong, stringy chips or chips reducedalmost to a powder. The drill cuttingedges will chip and burn because of theabsence of the thick, heat absorbing, C-shaped chips. Chips can possibly jam

FIGURE 8.14: Spade drills with various cuttingblades. (Courtesy Kennametal Inc.)

FIGURE 8.15: Spade drill cutting blades shows geometry specifications.

Seating pads

Rake surface

Chipbreakers

MarginBladethickness

Chiseledge

Web

Back taper Point angle O.D. Clearance

Locatorlength



and pack, which can break the tool orthe workpiece. If the machine cannotsupply the required thrust to maintainthe proper feed without severe deflec-tion, a change in tool or machine maybe necessary.

8.7 Indexable Carbide DrillsIndexable drilling has become so effi-cient and cost effective that in manycases it is less expensive to drill the holerather than to cast or forge it. Basically,the indexable drill is a two fluted, centercutting tool with indexable carbide

inserts. Indexable drills wereintroduced using square inserts(see Fig. 8.16). Shown in Figure8.17a are indexable drills usingthe more popular Trigon Insert(see Fig. 8.17b). In most casestwo inserts are used, but as sizeincreases, more inserts are addedwith as many as eight inserts invery large tools. Figure 8.18shows six inserts being used.

Indexable drills have the prob-lem of zero cutting speed at thecenter even though speeds canexceed 1000 SFPM at the outer-most inserts. Because speed gen-erally replaces feed to somedegree, thrust forces are usually25 to 30 percent of those requiredby conventional tools of the samesize. Indexable drills have ashank, body, and multi-edgedpoint. The shank designs gener-ally available are straight, taperedand number 50 V-flange.

The bodies have two flutes that arenormally straight but may be helical.Because no margins are present to pro-vide bearing support, the tools must relyon their inherent stiffness and on thebalance in the cutting forces to maintainaccurate hole size and straightness.Therefore, these tools are usually limit-ed to length-to-diameter ratios ofapproximately 4 to 1.

The drill point is made of pocketedcarbide inserts. These inserts are usual-ly specially designed. The cutting rakecan be negative, neutral, or positive,

depending on holder and insert design.Coated and uncoated carbide grades areavailable for drilling a wide variety ofwork materials. Drills are sometimescombined with indexable or replaceableinserts to perform more than one opera-tion, such as drilling, counterboring,and countersinking.

As shown in Figure 8.19a and Figure8.19b, body mounted insert tooling canperform multiple operations. Moreexamples will be shown and discussedin Chapter 10: Boring Operations andMachines.

The overall geometry of the cuttingedges is important tothe performance ofindexable drills. Asmentioned earlier,there are no support-ing margins to keepthese tools on line, sothe forces required tomove the cuttingedges through thework material must bebalanced to minimizetool deflection, partic-ularly on starting, andto maintain hole size.

While they areprincipally designedfor drilling, someindexable drills, asshown in Figure 8.20,can perform facing,and boring in lathe

FIGURE 8.18: Indexable drill using sixTrigon inserts for drilling large holes.(Courtesy Kennametal Inc.)FIGURE 8.16: Indexing drills were introduced

using square inserts; three sizes are shown here.(Courtesy Kennametal Inc.)

12¡

84¡156¡

(b)

FIGURE 8.17: (a) Indexable drills using Trigon inserts. (b) A Trigon insert and holder. (Courtesy Komet ofAmerica, Inc.)

(a)



applications. How well these tools per-form in these applications depends ontheir size, rigidity, and design.

8.7.1 Indexable Carbide Drill Operation

When used under the proper conditions,the performance of indexable drills isimpressive. However, the manufactur-er’s recommendations must be carefullyfollowed for successful applications.

Set-up accuracy and rigidity is mostimportant to tool life and performance.Chatter will destroy drilling inserts just asit destroys turning or milling inserts. Ifthe inserts fail when the tool is rotating inthe hole at high speed, the holder andworkpiece will be damaged. Even if lackof rigidity has only a minor effect on toollife, hole size and finish will be poor. Themachine must be powerful, rigid and

capable of high speed. Radial drill press-es do not generally meet the rigidityrequirements. Heavier lathes, horizontalboring mills, and N/C machining centersare usually suitable.

When installing the tool in themachine, the same good practice fol-lowed for other drill types should beobserved for indexable drills. Theshanks must be clean and free fromburrs to ensure good holding and tominimize runout. Runout in indexabledrilling is dramatically amplifiedbecause of the high operating speedsand high penetration rates.

When indexing the inserts is neces-sary, make sure that the pockets areclean and undamaged. A small speck ofdirt or chip, or a burr will cause stress inthe carbide insert and result in a micro-scopic crack, which in turn, will lead toearly insert failure.

8.7.2 Indexable Drill Feeds and Speeds

Indexable drills are very sensitive tomachining rates and work materials.The feed and speed ranges for variousmaterials, as recommended by somemanufacturers of these tools, can bevery broad and vague, but can be usedas starting points in determining exactfeed and speed rates. Choosing the cor-rect feed and speed rates, as well asselecting the proper insert style andgrade, requires some experimentation.Chip formation is a critical factor andmust be correct.

In general, soft low carbon steel callsfor high speed (650 SFPM or more),and low feed (0.004/0.006 IPR).Medium and high carbon steels, as wellas cast iron, usually react best to lowerspeed and higher feed. The exact speedand feed settings must be consistentwith machine and set-up conditions,hole size and finish requirements, andchip formation for the particular job.

8.8 TrepanningIn trepanning the cutting tool produces ahole by removing a disk shaped piecealso called slug or core, usually fromflat plates. A hole is produced withoutreducing all the material removed tochips, as is the case in drilling. Thetrepanning process can be used to makedisks up to 6 in. in diameter from flatsheet or plate. A trepanning tool alsocalled a “Rotabroach” with a core orslug is shown in Figure 8.21a and anend view of a Rotabroach is shown inFigure 8.21 b.

Trepanning can be done on lathes,drill presses, and milling machines, aswell as other machines using singlepoint or multi point tools. Figure 8.22shows a Rotabroach cutter machiningholes through both sides of a rectangu-lar tube on a vertical milling machine.

Rotabroach drills provide greater toollife because they have more teeth thanconventional drilling tools. Since moreteeth are engaged in the workpiece, thematerial cut per hole is distributed overa greater number of cutting edges.Each cutting edge cuts less material fora given hole. This extends tool life sig-nificantly.

Conventional drills must contendwith a dead center area that is prone tochip, thus reducing tool life. In the chis-el-edge region of a conventional drillthe cutting speed approaches zero. This

FIGURE 8.19: Body-mounted insert tool-ing can perform multiple operations.

(Courtesy Komet of America, Inc.)

FIGURE 8.20: In addition to drilling, indexable drills can perform boring and facingoperations.

(b)

To diameter Larger than Diameter

Boring Facing

(a)



is quite different from the speed at thedrill O.D. Likewise, thrust forces arehigh due to the point geometry.Rotabroach drills cut in the region fromthe slug O.D. to the drill O.D. Sinceonly a small kerf is machined, cuttingspeeds are not so different across theface of a tooth. This feature extendstool life and provides uniform machin-

a b i l i t y .Figure 8.23shows drillingholes with conventional drills and holebroaching drills.

8.8.1 Trepanning OperationsTrepanning is a roughing operation.Finishing work requires a secondaryoperation using reamers or boring barsto get a specified size and finish. Of themany types of hole-making operations,it competes with indexable carbide cut-ters and spade drilling.

Several types of tools are used to trepan.The most basic is a single or double pointcutter (Fig. 8.24). It orbits the spindle cen-terline cutting the periphery of the hole.Usually, a pilot drill centers the tool anddrives the orbiting cutter like a compassinscribing a circle on paper. Single/doublepoint trepanning tools are often adjustablewithin their working diameter. They areefficient and versatile, but do begin to haverigidity problems when cutting large holes- 6 1/2 inches in diameter is about the max-imum.

A hole saw is another tool thattrepans holes. It is metalcutting’s ver-sion of the familiar doorknob hole cut-ter used in wood. Hole saws have moreteeth and therefore cut faster than sin-gle, or double-point tools. Both hole

saws and single-pointtools curl up a chip inthe space, or gullet,between the teeth, andcarry it with them inthe cut.

Hole broachingtools are hybridtrepanners. (Fig. 8.21aand 8.21b) They com-bine spiral flutes like adrill with a broach-like progressive toolgeometry that splitsthe chip so it exits thecut along the flutes.With this design, the

larger number of cuttingedges and chip evacuation,combine to reduce the chipload per tooth so this drillcan cut at higher feed ratesthan trepanning tools andhole saws. Like the holesaw, a hole broaching toolhas a fixed diameter. Onesize fits one hole.

8.8.2 Cutting Tool Material Selection

M2 High Speed Steel (HSS)is the standard Rotabroach cutting toolmaterial. M2 has the broadest applica-tion range and is the most economicaltool material. It can be used on ferrousand non-ferrous materials and is gener-ally recommended for cutting materialsup to 275 BHN. M2 can be applied toharder materials, but tool life is dramat-ically decreased.

TiN coated M2 HSS Rotabroach drillsare for higher speeds, more endurance,harder materials or freer cutting action toreduce power consumption. The TiNcoating reduces friction and operates atcooler temperatures while presenting aharder cutting edge surface. Increasedcutting speeds of 15 to 25 % are recom-mended to obtain the benefits of this sur-face treatment. The reduction in frictionand resistance to edge build-up are keybenefits. The ability to run at higherspeeds at less power is helpful for appli-cations where the machine tool is slightlyunderpowered and TiN coated tools arerecommended for these applications.TiN coated tools are recommended forapplications on materials to 325 BHN.

Carbide cutting tool materials are

FIGURE 8.21: Trepanning tool also called Rotabroach withcore or slug. (Courtesy Hougen Manufacturing, Inc.)

FIGURE 8.23: Drilling holes with conventional drill and holebroaching drill. Surface speed increases with distance fromcenter.

FIGURE 8.24: Traditional trepanning toolorbits around a center drill.

FIGURE 8.22: Rotabroach machining set-up on a milling machine. (CourtesyHougen Manufacturing, Inc.)

Velocity Approaches "Zero" at Center Point

Velocity of Cutting Edge (SFPM)

Kerf

Hole Broaching DrillConventional Drill

(a)

(b)



also available as a special option onRotabroach drills. Carbide offers cer-tain advantages over high-speed steel.Applications are limited and need to bediscussed with a manufacturer’s repre-sentative.

8.8.3 Rigidity and Hole Size Tolerance

Rotabroach drills were originallydesigned as roughing tools to competewith twist drills and provide similar holetolerances. Many users have successful-ly applied Rotabroach drills in semi-fin-ishing applications, reducing the numberof passes from two or more to just one. Arigid machine tool and set-up are requiredto produce holes to these specifications.Tolerances will vary with the applicationand are impossible to pin point.

Spindle rigidity or “tightness” andworkpiece rigidity are more crucial thanwith a twist drill. Even if a twist drill runsout slightly at first, the conical point tendsto center itself before the O.D. of the toolengages the workpiece. The higher thrustof a twist drill also tends to “ preload” thespindle and fixture. The trepanning cut-ter relies more on the rigidity of the sys-tem (workpiece, holder, and spindle). Ifexcessive spindle runout or, worse yet,spindle play exists, the cutter may chatteron entry. At best this will cause a bell-mouthed hole with poor finish, but it caneasily lead to drill breakage.

Hole tolerances are dependent onmuch more than the accuracy of any tooland its grind. The machine tool, work-piece, fixture, selection of speeds andfeeds, projection and type of applicationalso play an important part in determiningoverall results.

8.8.4 Chip ControlIn material such as aluminum, tool steelsand cast iron, proper selection of feedsand speeds usually causes the chips tobreak up and allows them to be flushedout of the cut by the cutting fluid. Inmany other materials, such as mild andalloy steels, the chips tend to be long andfrequently wrap themselves around thedrill to form a “bird’s nest”. In most man-ual operations this is an annoyance that isoutweighed by the other benefits of themethod. In automated operations, howev-er, the build-up of chips around the drillcannot be tolerated. Besides the obviousproblems that this can cause, the nest ofchips impedes the flow of additionalchips trying to escape from the flutes.

This in turncan cause theflutes to packand mayresult in drillbreakage.

There areseveral meth-ods that canbe used tobreak up thechips if thiscannot be accomplished by adjusting thefeeds and speeds. One method is to usean interrupted feed cycle. It is recom-mended that the drill not be retracted aswith a “peck” cycle, because chips maybecome lodged under the cutting edges.Instead employ an extremely short dwellapproximately every two revolutions.This will produce a chip that is usuallyshort enough not to wrap around the tool.A programmed dwell may not be neces-sary since some hesitation is probablyinherent between successive feed com-mands in an NC system

8.8.5 Advantages of Trepanning Tools

The twist drill has a center point, which isnot really a point at all - it’s the intersect-ing line where two cutting edge anglesmeet at the web of the drill. This point isthe so-called “dead zone” of a twist drill.

It’s called a dead zone because the sur-face speed of the cutting edges (a factorof revolutions per minute and diameter ofthe drill) approaches zero as the corre-sponding diameter nears zero. Slowersurface speed reduces cutting efficiencyand requires increased feed pressure forthe cutting edges to bite into the material.In effect, the center of the drill does notcut - it pushes its way through thematerial. The amount of thrustrequired to overcome the resis-tance of the workpiece often caus-es the stock to deform or dimplearound the hole, and creates a sec-ond problem - burrs or flakingaround the hole’s breakthroughside. As material at the bottom ofthe hole becomes thinner and thin-ner, if the feed is not eased off, thedrill will push through, typicallyleaving two jagged remnants ofstock attached.

Trepanning tools produceholes faster than more conven-tional tooling as shown in Figure8.25. From left to right are shown

a 1 1/2 inch hole drilled into a 2 inchthick 1018 steel plate with: a spade drill,with a twist drill, with an indexable car-bide drill, and with a Rotabroach. Withapproximately 50% to 80% fasterdrilling time, the cost per hole can besubstantially lower.

An indirect yet significant source ofsavings attributable to trepanning tool-ing is the solid slug it provides.Separating chips from coolant and oilsis increasingly called for by scraphaulers, In one application, while sig-nificant gains in productivity weremade with hole-broaching tools, thesavings in going from chips to a solidslug was enough to justify the change inprocess.

In Figure 8.26 the workpiece is a tubeholder for an industrial heat exchanger.When this workpiece is finished, betterthan 60 per cent of the plate has beenreduced to scrap.

Sixty percent of this heat exchangerplate was converted into chips by thesheer number of holes drilled. Besidesincreasing production, trepanning tool-ing’s solid core by-product increasedscrap value from $0.17 per pound ofchips, to $0.37 per pound for the coremetal.

FIGURE 8.25: Trepanning produces holes faster than more convention-al tooling. (Courtesy Hougen Manufacturing, Inc.)

FIGURE 8.26: Sixty percent of this heat exchang-er plate was converted to chips. (Courtesy HougenManufacturing, Inc.)


9.1 IntroductionOne of the most important and essential tools in any metalworking shop is the drillingmachine or drill press. Although the drilling machine is used primarily for drilling holes,it is often used for reaming, boring, tapping, counterboring, countersinking, and spotfac-ing.

All drilling machines operate on the same basic principle. The spindle turns the cut-ting tool, which is advanced either by hand or automatically into a workpiece that ismounted on the table or held in a drill press vise. Successful operation of any drillingmachine requires a good knowledge of the machine, proper set-up of the work, correctspeed and feed, and proper use of cutting fluids applied to the cutting tool and work.

9.2 Types of Drill PressesMany types and sizes of drilling machines are used in manufacturing. They range in sizefrom a simple bench mounted sensitive drill press to the large multiple-spindle machinesable to drive many drills at the same time.

Figure 9.1 shows a schematic diagram of a standard vertical drill press as well as aschematic diagram of a turret-drilling machine. Described below are these and othertypes of drill presses such as sensitive and radial drills.

Chapter 9

Drilling Methods

& Machines

Upcoming Chapters





Shaping and Planing



Reaming and Tapping




Lapping and Honing






Prentice Hall: http://www.prenhall.comFIGURE 9.1: Schematic illustration of (a) vertical drill press, (b) CNC turret drilling machine.

(a)

Fixed head(power head)

Spindle

Adjustable head

Spindle

Chuck

Table

Base

(b)

Column

Turret

Base

Table

Column

Handwheel

Chap. 9: Drilling Methods & Machines


9.2.1 Simple Drill PressA simple drill press (Fig.9.2) may befloor mounted as shown, or have ashorter main post and be mounted on abench. The motions of this machine arevery simple. The table on a floor modelcan be raised or lowered and rotatedaround the machine column. The spin-dle rotates and can be raised and low-ered, with a stroke of 4 to 8 inches.Stops can be set to limit and regulate thedepth.

9.2.2 Sensitive Drill PressThe name ‘sensitive’ is used to indicatethat the feed is hand operated and thatthe spindle and drilling head are coun-terbalanced so that the operator can‘feel’ the pressure needed for efficientcutting. A table mounted sensitive drillpress is shown in Figure 9.3.

The drill press has the same motionsas the previous one plus a telescopingscrew for raising and lowering the tableand a sliding ‘drill head’. These twofeatures allow easier handling of partsof varying heights.

9.2.3 Radial DrillFor handling medium to very large size

castings, weldments, or forgings, radialdrills are ideal. The length of the armalong which the spindle housing ridesspecifies their size. This arm can befrom 3 to 12 feet long. The column thatholds the arm may be from 10 to 30inches in diameter. A radial drill isshown in Figure 9.4.

For very large work, the arm may berotated 180 degrees and work placed onthe shop floor. Speeds and feeds aredialed in by the machine operator andare the same as for other drill presses.Drilling is either hand or power feed.

9.3 Drilling Machine ComponentsRigid and accurate construction ofdrilling machines is important to obtainproper results with the various cuttingtools used. The sensitive drillingmachine construction features are dis-cussed in this section because its fea-tures are common to most other drillingmachines.

Base: The base is the main support-ing member of the machine. It is heavygray iron or ductile iron casting withslots to support and hold work that istoo large for the table

Column: The round column may bemade of gray cast iron or ductile iron forlarger machines, or steel tubing forsmaller bench drill presses. It supportsthe table and the head of the drillingmachine. The outer surface is machinedto function as a precision way of align-ing the spindle with the table.

Table: The table can be adjusted upor down the column to the properheight. It can also be swiveled aroundthe column to the desired working posi-tion. Most worktables have slots andholes for mounting vises and otherwork-holding accessories. Some tablesare semi universal, meaning that theycan be swiveled about the horizontalaxis.

Head: The head houses the spindle,quill, pulleys, motor, and feed mecha-nism. The V-belt from the motor drivesa pulley in the front part of the head,which in turn drives the spindle. Thespindle turns the drill. Two head assem-blies are shown in Figure 9.2 b and c.Speeds on a stepped V pulley drive arechanged by changing the position of theV-belt (Fig. 9.2b) Speeds on a variable-speed drive mechanism are changed bya hand wheel on the head. (Fig. 9.2c)The spindle must be revolving whenthis is done.

Quill assembly: The spindle rotateswithin the Quill (Fig. 9.5) on bearings.

FIGURE 9.2: a) a sensitive drill press is used for drilling holes; b) speeds on a stepped Vpulley drive are changed by hanging the position of the V belt; c) speeds on a variable-speed drive mechanism are changed by the handwheel on the head. (Courtesy ClausingIndustries, Inc.)

FIGURE 9.3: A table mounted sensitivedrill used for drilling small holes.(Courtesy Clausing Industries, Inc.)



The quill moves vertically by means ofa rack and pinion. The quill assemblymakes it possible to feed or withdrawthe cutting tool from the work. Locatedon the lower end of the spindle is eithera Morse tapered hole or a threaded stubwhere the drill chuck is mounted. Fordrilling larger holes, the drill chuck isremoved and Morse tapered cuttingtools are mounted.

Size Classification: The size (capac-ity) of a drilling machine is determinedby all the following features:• Twice the distance from the center of

the spindle to the innerface of the column• The maximum lengthof quill travel• The size of the Morsetaper in the spindle• The horsepower of themotor.

9.4 Drilling SystemsDrilling systems areusually automated andcomputer controlled.Speeds, feeds, anddepth of cut are oftenpre-set. Such systemscombine drilling opera-tions with reaming, tap-ping, countersinking, etc.Figure 9.6 shows a 3-axisCNC drilling machine.

9.4.1 Multi Spindle Drilling

This type of drilling can be done on drillpresses by using special attachments.The spindle locations are adjustable,and the number of spindles may be fromtwo to eight. Drills, reamers, counter-sinks, etc., can be used in the spindles.The RPM and feed rate of all spindles inone drill head are the same, and thehorsepower needed is the sum of thepower for all cutting tools used. In thistype of machine, a large number ofholes may be drilled at one time.Several different diameters of drills maybe used at the same time.

9.4.2 Gang DrillingAn economical way to perform severaldifferent operations on one piece is bygang drilling as shown in Figure 9.7.This might include drilling two or moresizes of holes, reaming, tapping, andcountersinking. The work is held in avise or special fixture and is easilymoved along the steel table from onespindle to the next.

The drill presses usually run continu-ously so the operator merely lowerseach spindle to its preset stop to performthe required machining operation.

9.4.3 Turret DrillTurret drills (Fig. 9.1b) with either sixor eight spindles enable the operator touse a wide variety of cutters and yet

move the workpieceonly a few inches,according to the holespacing. The turret canbe rotated (indexed) ineither direction, andthen lowered, by handor automatically, tomake the cut.

Some turret drillshave automatic,hydraulically con-trolled spindles.Speeds, feeds, anddepths of cut can bepreset for fast produc-tion. Figure 9.1bshows an automaticmachine. Thesemachines are also madewith the entire opera-tion computer con-trolled, (CNC turret

FIGURE 9.4: Radial drills are used to machine large cast-ings, weldments or forgings. (Courtesy Summit MachineTool Manufacturing Corp.)

FIGURE 9.7: Gang drilling machines permiteconomical ways to perform several differentoperations. (Courtesy Clausing Industries,Inc.)

FIGURE 9.6: Shown is a 3-axis CNC drillingMachine (Courtesy: TechniDrill Systems, Inc.)

FIGURE 9.5: The spindle rotates within the quill.The quill moves vertically by means of a rack andpinion. (Courtesy: Clausing Industries, Inc.)



drill), so that the operator merely has toload and unload the parts. A numerical-ly controlled turret drill is shown inFigure 9.8.

9.5 Operation Set-upIn drilling operations the three most com-mon work holding methods are:• Vises• Angle Plate• Drill Jigs

Vises: Vises are widely used forholding work of regular size and shape,such as flat, square, and rectangularpieces. Parallels are generally used tosupport the work and protect the visefrom being drilled. Figure 9.9 shows atypical vise. Vises should be clamped tothe table of the drill press to preventthem from spinning during operation.Angular vises tilt the workpiece andprovide a means of drilling a hole at anangle without tilting the table. An angu-lar vise is shown in Figure 9.10.

Angle Plates: An angle plate sup-ports work on its edge. Angle plates

accurately alignthe work perpen-dicular to thetable surface, andthey generallyhave holes andslots to permitclamping to thetable and holdingof the workpiece.

Drill Jigs: Adrill jig is a pro-duction tool usedwhen a hole, orseveral holes,must be drilled ina large number ofidentical parts.Figure 9.11 showsa diagram of a typical drill jig. The drilljig has several functions. First, it is awork holding device, clamping the workfirmly. Second, it locates work in the cor-rect position for drilling. The third func-tion of the drill jig is to guide the drillstraight into the work. This is accom-

plished by use of drill bushings.

9.5.1 Tool Holding DevicesSome cutting tools used in drillingcan be held directly in the spindlehole of the machine. Others mustbe held with a drill chuck, collet,sleeve, socket, or one of the manytool-holding devices shown inFigure 9.12.

Drill Chucks: Cutting tools withstraight shanks are generally held ina drill chuck. The most commondrill chuck uses a key to lock the

cutting tool. Drill chucks, both with keyand keyless, are shown in Figures 9.13.

Sleeves: Cutting tools with taperedshanks are available in many differentsizes. When a cutting tool that has asmaller taper than the spindle taperused, a sleeve must be fitted to theshank of the cutting tool.

Sockets: If the cutting tool has atapered shank larger than the spindletaper, a socket is used to reduce it to thecorrect size. Figure 9.14 shows varioussize keyless drill chucks with onestraight and two tapered shank mount-ings.

9.6 Deep-hole DrillingThe term ‘deep holes’ originallyreferred to hole depths of over 5 x thediameter. Today, deep-hole drilling is acollective name for methods for the

FIGURE 9.9: Vises should be clamped to thetable of drill presses to prevent them from spin-ning. (Courtesy Kurt Manufacturing Co.)

FIGURE 9.11: Drill jigs locate and clamp workpieces, and guide thedrill through a drill bushing.

FIGURE 9.10: The angle vise tilts the workpiece and pro-vides a means of drilling a hole at an angle. (Courtesy:Palmgren Steel Products, Inc.)

FIGURE 9.8: Numerically controlled turret drill automaticallypositions the worktable. (Courtesy: Kanematsu USA, Inc.)

Drill bushings

Thumb screw

Locating pins

Bottom View

Workpiece



machining of both short and deep holes.Deep-hole drilling is the preferred

method for drilling hole depths of morethan 10 x the diameter, but because ofthe method’s high metal-removal capac-

ity and precision, it is alsocompetitive for smallholes down to 2 x thediameter.

During drilling, it isimportant that the chipsbe broken and that theycan be transported awaywithout jamming andaffecting the drilled sur-face. In deep-holedrilling, cutting fluid sup-ply and chip transporthave been provided for bythe development of threedifferent systems that per-mit trouble-free machin-ing of hole depths ofmore than 100 x thediameter. The three sys-tems are called: the GunDrilling System, the

Ejector System (two-tube system) andthe Single Tube System (STS).

Some of the tools used in deep-holedrilling are shown in Figure 9.15.Hyper Tool manufactured the gun drills,and Sandvik manufactured the index-able tools.

9.6.1 Gun Drilling SystemsThe gun drill system uses the oldestprinciple for cutting fluid supply. Thecutting fluid is supplied through a ductinside the drill and delivers coolant tothe cutting edge, after which it removesthe chips through a V-shaped chip flutealong the outside of the drill. Due to theV-groove, the cross section of the tubeoccupies 3/4 of its circumference.Figure 9.16 shows a gun drilling systemand its component parts.

Gun DrillsGun drills belong to the pressurized

coolant family of hole making tools.

They are outstanding for fast, precisionmachining regardless of hole depth. Asa rule, a gun drill can hold hole straight-ness within 0.001 inch per inch (IPI) ofpenetration, even when the tool is rea-sonably dull. For most jobs a gun drillcan be used to cut from 500 to 1000inches in alloy steel before re-sharpen-ing is necessary. In aluminum, it mightbe 15,000 inches, while in cast iron it isusually around 2000 inches. Figure9.17a shows a gun drilling tool andFigure 9.17b shows the gun drillingprocess.

Depending on the tool’s diameter, agun drill is seldom run at feed ratesexceeding 0.003 inches per revolution(IPR). This is extremely light comparedto twist drill feeds, which typicallyrange from 0.005 IPR to 0.010 IPR. Butgun drilling does use a relatively high

FIGURE 9.12: Various tool-holding devices such aschucks, collets, sleeves, and sockets are shown. (CourtesyLyndex Corp.)

FIGURE 9.13: Key and keyless chucksare used to hold drills for holemakingoperations. (Courtesy Bridgeport Machine,Inc.)

FIGURE 9.14: Various size drill chucksare shown. (Courtesy: Royal Products)

FIGURE 9.15: Deep-hole drilling tools;the gun drills were manufactured byHyper Tool and the indexable tools weremanufactured by Sandvik. (CourtesyTechniDrill Systems, Inc.)

FIGURE 9.16: Schematic diagram of a gun drilling system with major components.(Courtesy Sandvik Coromant Co.)



speed compared to high speed steel(HSS) twist drilling. This accounts forthe high metal-removal rates associatedwith the process. In aluminum, speedsmay be 600 surface feet per minute(SFPM), in steels from 400 SFPM to450 SFPM.

Speeds and feeds for gun drilling arebased on the workpiece material andshop floor conditions. Published chartsonly provide starting points. On-the-floor experimentation is critical todetermine the right combination formaximum tool life.

Gun Drill BodyThe body of a gun drill is typically

constructed from 4120 aircraft qualitysteel tubing that is heat treated tobetween 35 to 40 Rc. A 4140 steel dri-ver is brazed to one end of the tube anda carbide tool tip is brazed to the otherend. Figure 9.18 shows five differenttool tip geometries with various coolanthole placements.

There are two body styles for multi-ple flute tools; milled and crimped. Theformer is a thick wall tubular shaft withthe flutes milled into the body. The lat-ter is a thin wall tubular shaft that has

the flutes swaged into it. The number offlutes depends on the material being cut.When drilling in a material that breakseasily into small chips, such as cast iron,a two flute tool is the choice. On theother hand, for a material such as D2tool steel, a single flute design is pre-ferred. In this case, chips tend to bestringy and a single flute tool will mini-mize the chance of jamming as they areremoved from the hole.

Figure 9.19 shows both a crimp stylegun drill body with two flutes producedby swaging and a conventional milledstyle gun drill. The coolant holes in thecrimped body have an irregular shapethat permits carrying a much larger vol-ume of coolant than comparable holesin a conventional equivalent diametertool body. Also, the flutes that areformed are much deeper than milledtools because allowance does not haveto be made for wall thickness betweenflute and coolant hole. These deeperflutes improve the chip removal effi-ciency of the tool.

Gun Drill TipA conventional gun drill has a hole in

its carbide tip underneath the cutting

edge. Pressurized cuttingfluid is pumped through thetool’s body and out the hole(see Figure 9.18). Thefluid serves a three-foldpurpose: it lubricates andcools the cutting edge; itforces the chips back alongthe flute in the tool body;and it helps to stiffen theshank of the tool.

A new design has onehole in the top of the tooltip that effectively directs

fluid at the cutting edge. The other holethat is in the conventional location helpsto provide the chip ejection function.Total flow of cutting fluid is doubledwith this two-hole arrangement. Moreimportantly, the design produces chipsabout half the size of a conventional gundrill of the same diameter using thesame speed and feed rate, so that pack-ing of chips along the tool’s shank isavoided in most materials.

The most common tool tip material isC2 carbide, which is one of the hardergrades and is generally associated withcast iron applications. Because exces-sive tool wear is a major problem whencutting steel, a hard grade such as C2 isrecommended, even though C5 carbideis labeled as the steel machining gradein most text books. C5 carbide is ashock resistant grade, not a wear-resis-tant grade, so that it is not as suitable fora gun drill tool tip. C3 carbide is hard-er than C2, and is used for certain appli-cations; however, greater care must betaken when re-sharpening this materialbecause it is easier to heat check the cut-ting edge.

Recently, coatings such as titaniumnitride are being applied to gun drill tipsto extend tool life. Physical VaporDeposition (PVD) is the only practicalprocess for depositing coatings on pre-cision tools such as gun drills, but theresults have not been encouraging.Unlike coating high-speed steel tools,PVD coating of a carbide gun drill tipdoes not seem to form a good metallur-gical bond. The coating wipes off dur-ing the metal cutting process. UsingChemical Vapor Deposition (CVD) willform a metallurgical bond between thecoating and carbide substrate, but thehigh heat required by the process dis-torts the tool. Hopefully these problemswill be resolved in the near future.

(b)

FIGURE 9.17: (a) Gun drilling head. (b) A drawing of a gun drilling process. (Courtesy Star CutterCo.)

FIGURE 9.18: Shown are five different tool tip geometries with various coolanthole placements (Courtesy: Star Cutter Co.)

(a)



9.6.2 The Ejector SystemThe Ejector System consists of drillhead, outer tube, inner tube, connector,collet and sealing sleeve. The drill headis screwed to the drill tube by means ofa four-start square thread. The innertube is longer than the outer tube. Thedrill tube and the inner tube are attached

to the connector by means of a colletand a sealing sleeve. The collet andsealing sleeve must be changed for dif-ferent diameter ranges. Figure 9.20shows the Ejector System and its com-ponents.

9.6.3 The Single Tube System (STS)The Single Tube System is based on

external cutting fluid supply and inter-nal chip transport. As a rule, the drillhead is screwed onto the drill tube. Thecutting fluid is supplied via the spacebetween the drill tube and the drilledhole. The cutting fluid is then removedalong with the chips through the drilltube. The velocity of the cutting fluid isso high that chip transport takes placethrough the tube without disturbances.Since chip evacuation is internal, nochip flute is required in the shank, so tipcross-section can be made completelyround, which provides much higherrigidity than the gun drill system.Figure 9.21 shows the Single TubeSystem and its components.

9.6.4 Comparison of STS and Ejector Systems

Both the Single Tube System and theEjector System have wide ranges ofapplication, but there are times whenone system is preferable to the other.

STS is preferable in materials withpoor chip formation properties such asstainless steel, low carbon steel, andmaterials with an uneven structure,when chip breaking problems exist.STS is also more advantageous for longproduction runs, uniform and extremelylong workpieces and for hole diametersgreater than 7.875 inches.

The Ejector System requires no sealbetween the workpiece and the drillbushing. The system can therefore beadapted easily to existing machines andis preferable in NC lathes, turning cen-ters, universal machines and machiningcenters. Since the cutting fluid is sup-plied between the outer and inner tubes,no space is required between the drilltube and the hole wall as in the case ofSTS drilling. The Ejector System istherefore often used for machining inworkpieces where sealing problems canarise. The Ejector System can be usedto advantage when it is possible to use apredrilled hole instead of a drill bushingfor guidance, for example in machiningcenters.

9.6.5 Operational RequirementsMachining with high cutting speeds andhigh demands on surface finishes andtolerances requires a machine tool thatis both very rigid and very powerful. Itis possible to use conventionalmachines with sufficient power andrigidity.

Machine Requirements: The high

Milled-Style Bullnose Grind

Double-Crimp Fishtail Grind

FIGURE 9.21: The single-tube system (STS) and its major components. (CourtesySandvik Coromant Co.)

FIGURE 9.20: The ejector system and its major components. (Courtesy SandvikCoromant Co.)

FIGURE 9.19: There are two body styles of multifluted gun drills: milled style and dou-ble-crimp style.



feed speeds thatcharacterize deephole drillingimpose highdemands on avail-able power. Inorder to achievegood precision, themachine must berigid and the spin-dle bearings free ofplay. Good chipbreaking oftenrequires high feedand the feed mustbe constant, other-wise the chipbreaking may vary,leading to chipjamming. The bestpossible chipbreaking can beobtained with infinitely adjustable feed.

It is important that the machine beequipped with safety devices to protectthe machine, the tool and the workpiece.The purpose of the safety device is tostop the machine automatically in theevent of overloading. The machinespindle should not be able to start untilthe pressure of the cutting fluid hasreached a preset minimum. The tem-perature and quantity of the cutting fluidshould also reach a correct level beforethe machine starts.

Best are overload protections that areconnected to the feed pressure. It isextremely important that the overloadlimits be set no more than 10 - 13 per-cent above the actual drill pressure foreach drill diameter and feed. The feedwill then be able to stop before the drillis damaged.

Machine Types: The design of deephole drilling machines varies. Thelengths of the machines are adapted tothe special diameter ranges and lengthsof the workpiece. A special very longmachine is shown in Figure 9.22

Deep hole drilling machines are oftendesigned to permit a choice between arotating workpiece, a rotating tool orboth rotating workpiece and rotatingtool. In the machining of asymmetricworkpieces, the machine works with arotating drill and a non-rotating work-piece, since the workpiece cannot rotateat sufficient speed. In the machining oflong, slender workpieces, a non-rotatingdrill is fed into a rotating workpiece.When the hole must meet high straight-

ness requirements, both the drill and theworkpiece rotate. The direction of rota-tion of the drill is then opposite to thatof the workpiece.

The Single Tube System is difficult toadapt to standard machines, whileEjector drilling and, in some cases, gundrilling, can be done relatively simplyin conventional machines. The largestextra costs are then for the cutting fluidsystem, chip removal arrangement, fil-

ter tank and pump. Figure 9.23 shows aspecial gun-drilling machine to drill sixcamshafts simultaneously. Thismachine includes auto loading andunloading of parts.

Chip Breaking: Of primary impor-tance in drilling operations is transport-ing the chips away from the cuttingedges of the drill. Excessively long andlarge chips can get stuck in the chipducts. A suitable chip is as long as it iswide. However, the chips should not bebroken harder than necessary, since chipbreaking is power consuming and theheat that is generated increases wear onthe cutting edges. Chips with a length 3- 4 times their width can be acceptable,provided that they can pass through thechip duct and drill tube without difficul-ties. Chip formation is affected by thework material, chip breaker geometry,cutting speed, feed and choice of cuttingfluid.

Coolant System: The purposes ofthe coolant in a drilling system are:• Support and lubrication of the pads• Improvement of the tool life• Dissipation of heat• Flushing of chips

The coolant system has to provide anadequate supply of clean coolant to thetool at the correct pressure and temper-ature.

FIGURE 9.22: The length of a deep-hole drilling machinedepends on the diameter and the length of the workpiece.(Courtesy Sandvik Coromant Co.)

FIGURE 9.23: Special gun drilling machine is shown drilling six camshafts simultane-ously. This machine includes automatic loading and unloading of parts. (CourtesyTechniDrill Systems, Inc.)

Chapter 10

Boring Operations

& Machines

Upcoming Chapters

Metal Removal

Cutting-Tool MaterialsMetal Removal MethodsMachinability of Metals

Single Point Machining

Turning Tools and OperationsTurning Methods and Machines

Grooving and ThreadingShaping and Planing

Hole Making Processes

Drills and Drilling OperationsDrilling Methods and Machines

Boring Operations and MachinesReaming and Tapping

Multi Point Machining

Milling Cutters and OperationsMilling Methods and Machines


Abrasive Processes

Grinding Wheels and OperationsGrinding Methods and Machines

Lapping and Honing



Former ChairmanDetroit Chapter ONESociety of Manufacturing Engineers




10.1 IntroductionBoring, also called Internal Turning, is used to increase the inside diameter of a hole.The original hole is made with a drill, or it may be a cored hole in a casting. Boringachieves three things:

Sizing: Boring bringsthe hole to the propersize and finish. A drillor reamer can only beused if the desired sizeis ‘standard’ or if specialtools are ground. Theboring tool can work toany diameter and it willgive the required finishby adjusting speed, feedand nose radius. Preci-sion holes can be boredusing micro adjustableboring bars (Fig. 10.1)

Straightness: Boringwill straighten the original drilled or cast hole. Drills, especially the longer ones,may wander off- center and cut at a slight angle because of eccentric forces onthe drill, occasional hard spots in the material, or uneven sharpening of the drill(see Fig. 8.10). Cored holes in castings are almost never completely straight.The boring tool being moved straight along the ways with the carriage feed willcorrect these errors.

Concentricity: Boring will make the hole concentric with the outside diameterwithin the limits of the accuracy of the chuck or holding device. For bestconcentricity, the turning of the outside diameter and the boring of the insidediameter is done in one set-up, that is, without moving the work betweenoperations. The basics discussed in Chapters 4 and 5, the Turning Chapters, alsoapply to boring. However, with boring there are a number of limitations that mustbe taken into account in order to reach a high stock removal rate combined withsatisfactory accuracy, surface finish and tool life. Therefore, in this chapter thelimitations that distinguish internal turning from external turning will be discussedin greater detail. A typical boring operation is shown in Figure 10.2.

FIGURE 10.1: Adjustable boring bar for precision holes.(Courtesy: National Acme Co. Div. DeVlieg-Bullard, Inc.)


Chap. 10: Boring Operations & Machines


10.2 Boring OperationsMost of the turning operations thatoccur with external turning are also tobe found in boring. With externalturning, the length of the workpiecedoes not affect the tool overhang andthe size of the tool holder can be chosenso that it withstands the forces andstresses that arise during the operation.However, with internal turning, or bor-ing, the choice of tool is very muchrestricted by the work piece’s hole di-ameter and length.

A general rule, which applies toall machining, is to minimize thetool overhang in order to obtain thebest possible stability and therebyaccuracy. With boring the depth ofthe hole determines the overhang.The stability is increased when alarger tool diameter is used, but eventhen the possibilities are limitedsince the space allowed by thediameter of the hole in theworkpiece must be taken into consid-eration for chip evacuation and radialmovements.

The limitations with regards tostability in boring mean that extracare must be taken with productionplanning and preparation. By under-standing how cutting forces areaffected by the tool geometry andthe cutting data chosen, and alsounderstanding how various types ofboring bars and tool clamping willaffect the stability, deflection andvibration can be kept to a minimum.

10.3 Cutting ForcesOn engagement, the tangential forceand the radial cutting force will at-tempt to push the tool away from the

w o r k p i e c e ,which resultsin the deflec-tions.

The tan-gential forcewill try toforce thetool down-wards andaway fromt h ec e n t e r l i n e .Due to thecurving ofthe internalhole diam-eter thec l e a r a n c e

angle will also be reduced. Thereforewith small diameter holes it isparticularly important that the clear-ance angle of the insert be sufficientin order to avoid contact betweenthe tool and the wall of the hole.

The radial deflection will reducethe cutting depth. In addition to thediametrical accuracy being affected,the chip thickness will change withthe varying size of the cuttingforces. This causes vibration, whichis transferred from the cutting edgeto the tool holder. The stability ofthe tool and clamping will be thefactor that determines the magnitudeof the vibration and whether it isamplified or dampened.

Insert Geometry: The geometryof the insert has a decisive influenceon the cutting process. A positiveinsert has a positive rake angle. Theinsert’s edge angle and clearanceangle together will equal less than90 degrees. A positive rake anglemeans a lower tangential cuttingforce. However, a positive rakeangle is obtained at the cost of theclearance angle or the edge angle.If the clearance angle is small thereis a risk of abrasion between thetool and workpiece and the frictioncan give rise to vibration. In thosec a s e swhere therake angleis largeand theedge angleis small, as h a r p e rc u t t i n gedge is

obtained. The sharp cutting edgepenetrates the material more easilybut it is also more easily changed ordamaged by edge or other unevenwear.

Edge wear means that the geom-etry of the insert is changed,resulting in a reduction in theclearance angle. Therefore, withfinish machining it is the requiredsurface finish of the workpiece thatdetermines when the insert must bechanged. Generally, the edge wearshould be between .004 and .012inches for finishing and between.012 and .040 inches for roughmachining.

Lead Angle: The lead angleaffects the axial and radial directionsof the cutting forces. A small leadangle produces a large axial cuttingforce component while a large leadangle results in a larger cutting forcein the radial direction. The axialcutting force has a minimal negativeeffect on the operation since theforce is directed along the boringbar. To avoid vibrations, it isconsequently advantageous to choosea small lead angle but, since thelead angle also affects other factorssuch as the chip thickness and thedirection of the chip flow, a compro-mise often has to be made.

The main disadvantage of a smalllead angle is that the cutting forcesare distributed over a shorter sectionof the cutting edge than with a largelead angle. Furthermore, the cuttingedge is exposed to abrupt loadingand unloading when the edge entersand leaves the workpiece. Sinceboring is done in most cases, in apre-machined hole and is designatedas light machining, small lead anglesgenerally do not cause a problem.Lead angles of 15 degrees or lessare normally recommended. How-ever, at a lead angle of 15 degreesthe radial cutting force will bevirtually double that of the cuttingforce with a 0 degree lead angle. A

FIGURE 10.2: Typical horizontal boring operation. (Courtesy SandvikCoromant Co.)

FIGURE 10.3: Typical indexable insert boring bar with 0 deg lead angle.



typical indexable insert boring barwith a 0 degree lead angle is shownin Figure 10.3.

Nose Radius: The nose radius ofthe insert also affects the distributionof cutting forces. The greater thenose radius, the greater the radialand tangential cutting forces, and theemergence of vibration. However,this is not the case with radialcutting forces. The deflection of thetool in a radial direction is insteadaffected by the relationship betweenthe cutting depth and the size of thenose radius. If the cutting depth issmaller than the nose radius, theradial cutting forces will increasewith increased cutting depth. If thecutting depth is equal to or greaterthan the size of the nose radius, theradial deflection will be determinedby the lead angle. Therefore, it’s agood idea to choose a nose radiuswhich is somewhat smaller than thecutting depth. In this way the radialcutting forces can be kept to aminimum, while utilizing the advan-tages of the largest possible noseradius, leading to a stronger cuttingedge, better surface finish and moreeven pressure on the cutting edge.

10.4 Chip Breaking and EvacuationObtaining relatively short, spiralshaped chips is the goal in internalturning. These are easy to evacuateand do not place such large stresses onthe cutting edge when chip breakingoccurs. Hard breaking of the chips, i.e.when short chips are obtained, de-mands power and can increase vibra-tion in the boring bar. However, this ispreferred over having long chips,which can make chip evacuation moredifficult. Chip breaking is affected by anumber of factors such as the insertgeometry, nose radius, lead angle, cut-ting depth, feed and cutting speed.Generally, reduced feed and/or in-creased cutting speed results in longerchips. The shape of the chip breakeraffects the radius of the chip, whereany built-up edge or crater wear canalso act as chip breaker. The directionin which the chips flow and the waythat they turn in the spiral, is affectedby the lead angle or the combination ofcutting depth and nose radius.

The parameters that affect chipcontrol also affect the direction andsize of the cutting force. Therefore,it is necessary to choose a grade and

insert ge-o m e t r ythat, to-gether withthe selectedmachin ingparameters,fulfill ther e q u i r e -ments forgood chipcontrol. Atthe sametime, them a c h i n e ,boring barand toolc l a m p i n gmust pro-vide suffi-cient stabil-ity in orderto resist thec u t t i n gforces thatarise.

During boring operations the chipflow can be critical, particularlywhen deep holes are being ma-chined. The centrifugal forcepresses the chips outwards. Withboring, this means that the chipsremain in the workpiece. Theremaining chips could get pressedinto the machined surface or getjammed and damage the tool.Therefore, as with internal turning,tools with an internal cutting fluidsupply are recommended. The chipswill then be flushed out of the holeeffectively. Compressed air can beused instead of cutting fluid andwith trough holes; the chips can beblown through the spindle andcollected in a container.

10.5 Boring RigidityPart geometries can have external turn-ing operations as well as internal op-erations. Internal single point turningis referred to as boring, and can beutilized for either a roughing or finish-ing operation. Single point boringtools consist of a round shaft with oneinsert pocket designed to reach into apart hole or cavity to remove internalstock in one or several machine passes.Figure 10.4 shows various sizes andstyles of boring bars.

The key to productivity in boringoperations is the tool’s rigidity.Boring bars are often required to

reach long distances into parts toremove stock (see Fig. 10.5).Hence, the rigidity of the machiningoperation is compromised becausethe diameter of the tool is restrictedby the hole size and the need foradded clearance to evacuate chips.The practical overhang limits forsteel boring bars is four times theirshank diameter. When the tooloverhang exceeds this limit, themetal removal rate of the boringoperation is compromised signifi-cantly due to lack of rigidity and theincreased possibility of vibration.

Boring Bar Deflection: The sizeof the boring bar’s deflection isdependent on the bar material, thediameter, the overhang and size ofthe radial and tangential cuttingforces. Boring bar deflection can becalculated, but such calculations arebeyond the scope of this book.

Increasing the diameter of the toolto create an increased moment ofinertia can counteract this deflection.Choosing a boring bar made of amaterial that has a higher coefficientof elasticity can also counteractdeflection. Since steel has a lowercoefficient of elasticity than ce-mented carbide. Cemented carbideboring bars are better for largeoverhangs.

Compensating for Deflection:Even with the best tool clamping,

FIGURE 10.4: Various sizes and styles of boring bars. (Courtesy DorianTool)

FIGURE 10.5: Boring bars are often required to reach long distancesinto parts to remove stock. (Courtesy Sandvik Coromant Co.)



some vibration tendency will occurin boring. Radial deflection affectsthe machined diameter. Tangentialdeflection means that the insert tip ismoved in a downward directionaway from the centerline. In bothcases the size and direction of thecutting forces are affected bychanges in the relationship betweenthe chip thicknesses and insertgeometry.

If the exact size of the deflectionof the insert tip is known inadvance, then the problem can beavoided. By positioning the inserttip distance above the centerline, theinsert under the effect of thetangential force, will take up thecorrect position during machining.In the same way, setting the machineat a cutting depth that is greater thanthe desired cutting depth compen-sates for the radial deflection. Whencutting begins, the radial cuttingforce reduces the cutting depth.

Even if the approximate deflectioncan be calculated, the practicaloutcome will be somewhat differentbecause the clamping is never abso-lutely rigid and because it isimpossible to calculate the cuttingforce exactly.

Boring Bar Clamping: The slight-est amount of mobility in the fixedend of the boring bar will lead todeflection of the tool. The beststability is obtained with a holderthat completely encases the bar.This type of holder is available intwo styles: a rigid (Fig. 10.6a) orflange mounted bar, or a dividedblock (Fig. 10.6b) that clamps whentightened. With a rigidly mountedbar, the bar is either preshrunk intothe holder and/or welded in. Withflange mounting, a flange with athrough hole is normally used. Theflange is usually glued onto the

shank of the bar at a distancethat gives the required over-hang. The bar is then fed intothe holder and clamped bymeans of a screw connection orby being held in the turret.

Less efficient are those tool-clamping methods where thescrew clamps onto the bar.This form generally results invibration and is not recom-mended. Above all, thismethod must not be used forthe clamping of cemented car-bide bars. Cemented carbide ismore brittle than steel andcracks will occur as a result ofvibration, which in turn mayresult in breakage.

10.6 Boring BarsBoring bars are made in a widevariety of styles as shown in Fig-ure 10.4. Single-point boringbars (Fig. 10.7) are easily groundbut difficult to adjust when theyare used in turret and automaticlathes and machining centers, un-less they are held in an adjustableholder (Fig. 10.8).

More expensive boring barsare provided with easily adjust-able inserts. These bars aremade in standard sizes, with arange of 1/4 to 1/2 inch onthe diameter. A fine adjustmentis included in increments of0.001 inch or in some cases0.0001 inch. They are standardup to about 6 inches in diam-eter. A boring bar withadjustments is shown in Figure10.9. A different style ofadjustable boring bar with twoindexable inserts is shown inFigure 10.10.

Standard boring bars withinterchangeable heads to permit

various internal op-erations such asturning, profiling,grooving, andthreading are shownin Figure 10.11.

Many times itmay be economicalto order specialbars with two ormore preset diam-eters, set at theproper distanceapart. These spe-

(a)

(b)

FIGURE 10.6: Two proper boring bar clamping methods.

FIGURE 10.7: Single-point boring bar.(Courtesy Morse Cutting Tools)

FIGURE 10.8: Adjustable boring head forsingle-point boring tools. (CourtesyKennametal Inc.)

FIGURE 10.9: Adjustable boring bar with fine-tuning adjustment. (Courtesy Valenite Inc.)

FIGURE 10.10: Adjustable boring bar with twoindexable inserts. (Courtesy Kennametal Inc.)

FIGURE 10.11: Standard boring bar withinterchangeable heads for various internaloperations such as turning, profiling, grooving,and threading. (Courtesy Valenite Inc.)



cial bars cost more and are generallyonly used when large quantitiesmake their use economical. Some-times this may be the only way tohold the required tolerances andconcentricity. Such a special boringbar is shown in Figure 10.12.

Other special boring bars,sometimes called boringheads, are designed with re-placeable cartridges. A twincutter adjustable boring tool isshown in Figure 10.13. Vari-ous replaceable cartridges forspecial boring heads areshown in Figure 10.14.

Boring Bar Types: Boringbars are available in steel,solid carbide, and carbide-reinforced steel. The capacityto resist deflection increasesas the coefficient of elasticityincreases. Since the elasticitycoefficient of carbide is three

times larger than that of steel,carbide bars are preferred for largeoverhangs. The disadvantage ofcarbide is its poor ability to with-stand tensile stresses. For carbide-reinforced bars, the carbide sleevesare pre-stressed to prevent tensile

stresses.Boring bars can be equipped

with ducts for internal cooling,which is preferred for internalturning. An internal coolantsupply provides efficient coolingof the cutting edge, plus betterchip breaking and chip evacua-tion. In this way a longer toollife is obtained and qualityproblems, which often arise dueto chip jamming, are avoided.

Boring Bar Choice: Whenplanning production, it is veryimportant to minimize cuttingforces and to create conditionswhere the greatest possible sta-bility is achieved so that the

tool can withstand the stresses thatalways arise. The length anddiameter of the boring bar will be ofgreat significance to the stability ofthe tool. Since the appearance ofthe workpiece is the decisive factorwhen selecting the minimum over-hang and maximum tool diameterthat can be used, it is important tochoose the tool, tool clamping andcutting data which minimize, asmuch as possible, the cutting forceswhich arise during the operation.The following recommendationsshould be followed in order toobtain the best possible stability:• Choose the largest possible bar diam-eter, but at the same time ensure thatthere is enough room for chip evacua-tion.

• Choose the smallest possible over-hang but, at the same time, ensure thatthe length of the bar allows the recom-mended clamping lengths to beachieved.• A 0 degree lead angle should be used.The lead angle should, under no cir-cumstances be more than 15 degrees.• The indexable inserts should be posi-tive rake that results in lower cuttingforces.• The carbide grade should be tougherthan for external turning in order towithstand the stresses to which theinsert is exposed when chip jammingand vibration occur.• Choose a nose radius that is smallerthan the cutting depth.

Modern boring bars are designed totake into account the demands thatmust apply because the operation isperformed internally and the dimen-sions of the tool are determined by thehole depth and the hole diameter.With a positive rake insert geometry,less material deformation and lowcutting forces are obtained. The toolshould offer good stability to resist thecutting forces that arise and also toreduce deflection and vibration asmuch as possible. Due to spacerequirements, satisfactory chip controland good accessibility are also proper-ties of greater importance than withexternal turning.

10.7 Boring MachinesBoring operations can be performed onother than boring machines, such aslathes, milling machines, and machin-

FIGURE 10.12: Special multi-operation boringbar. (Courtesy: National Acme Co. Div. Devlieg-Bullard, Inc.)

FIGURE 10.13: A twin-cutter adjustable boringhead with indexable Trigon inserts. (CourtesyKomet of America, Inc.)

FIGURE 10.14: Various indexablereplaceable cartridges used in specialboring heads. (Courtesy Valenite Inc.)

FIGURE 10.15: A typical boringoperation performed on a lathe; a steadyrest is being used to provide support forthe part being machined. (CourtesySandvik Coromant Co.)



ing centers. A typical boring operationperformed on a lathe is shown in Fig-ure 10.15. A steady rest is being usedto provide support for the part beingmachined.

Boring machines, like most othermachine tools, can be classified ashorizontal or vertical:

10.7.1 Horizontal Boring

Machines (HBM)The HBM is made tohandle medium to verylarge-sized parts, butthese parts are usuallysomewhat rectangularin shape, though theymay be asymmetrical orirregular. The availablecutting tools only limitthe size of cut, the ri-gidity of the spindle,and the available horse-power. There are twotypes of Horizontal Bor-ing Machines:Table-type HorizontalBoring Machines(HBM)

The table-typeHBM shown in Figure10.16 is built on thesame principles as theh o r i z o n t a l - s p i n d l emilling machines.

The base and column are fastenedtogether, and the column does notmove. The tables are heavy, ribbedcastings which may hold loads up to20,000 pounds. Figure 10.17 showsa large part being machined on atable-type horizontal boring machine.

Size of HBM: The basic size of

an HBM is the diameter of thespindle. Table-type machines usu-ally have spindles from 3 to 6inches diameter. The larger sizeswill transmit more power and,equally important, the spindle willnot sag or deflect as much whenusing a heavy cutting tool whileextended. The size is furtherspecified by the size of the table.Although each machine has a ‘stan-dard’ size table, special sizes may beordered. The principal parts of thehorizontal boring machine are shownin Figure 10.18.

Work Holding: Work holding iswith clamps, bolts, or fixtures, thesame as with other machines. Ro-tary tables allow machining of allfour faces of a rectangular part orvarious angle cuts on any shape ofpart. Rotary tables up to 72 inchessquare or round are used for largework. If large, rather flat work is tobe machined, an angle plate is used.The workpiece is bolted or clampedonto the angle plate so that the ‘flat’face is toward the spindle. Figure10.19 shows a five-axis ram-stylemachining center. Parts can beclamped to the table and numerically(NC or CNC) positioned to performa boring operation.

Cutting Tools: Cutting tools areheld in the rotating spindle by atapered hole and a drawbar. Tospeed up the process of tool chang-ing, either or both of two things aredone:• The drawbar (which pulls the taperedtool holder tightly into the spindle

FIGURE 10.16: Table-type horizontal boring machine (HBM) (Courtesy SummitMachine Tool Manufacturing Corp.)

FIGURE 10.17: Large part being machined on a table-typehorizontal boring machine. (Courtesy WMW Machinery Co.,Inc.)

Column

Ways

Ways

Headstock

Cross-slidingcolumn

Column base

RunwayTable

Spindle

ZW

Y

X

FIGURE 10.18: Principal parts of a floor-type horizontal boring machine (HBM).



hole) can be power operated. Thus, theholder is pulled tight or ejected veryquickly.• Quick-change tooling is used. Abasic holder is secured in the spindle.It has a taper into which tools may besecured by a quarter to half turn of thelocking collar. Thus, the operator canchange preset tools in 10 to 30 seconds.

Tool holders and quick-changetool holders in particular will bediscussed in the milling chapters.

Speeds and Feeds: Speeds andfeeds cover a wide range because ofthe wide variety of cutters that maybe used on the HBM. Speeds from15 to 1500 RPM and feed rates from

0.1 to 40 IPM are com-monly used.

Floor Type HorizontalBoring Machine (HBM)

The floor type HBM(Fig. 10.18) is used forespecially tall or longworkpieces. The ‘stan-dard’ 72-inch runway canbe made almost anylength required for spe-cial jobs. Lengths of 20feet are in use today.The height of the column,which is usually 60 to 72inches, can be made toorder up to twice thisheight if the work re-quires it. Figure 10.20shows a large floor-typehorizontal boring ma-chine.

HBM Table: The tableis separate from the bor-ing machine though it is,of course, fastened to thefloor. It may be boltedto the runway.

The entire column and columnbase move left and right (the X axis)along special ways on the runway(Fig. 10.18). The runway must becarefully aligned and leveled when itis first installed, and then checked atintervals as the machine is used.

HBM Headstock: The headstockcan be moved accurately up anddown the column (the Y axis). The6 to 10 inch diameter spindle rotatesto do the machining. It is moved in

and out (the Zaxis) up to 48inches for boringcut, drilling, settingthe depth of mill-ing cuts, etc. Asin the table-typeHBM, the spindlediameter and tablesize specify themachine size.

Cutting Tools:Cutting tools arethe same as thoseused on the table-type machine.Work holding isalso the same, andangle plates are fre-quently used.

10.7.2 Vertical Boring Machines (VBM)A general description of a vertical bor-ing machine would be that it is a latheturned on end with the headstock rest-ing on the floor. This machine isneeded because even the largest enginelathes cannot handle work much over24 inches in diameter. A vertical bor-ing machine is shown in Figure 10.21.

Today’s VBMs are often listed asturning and boring machines. Iffacing is added to that name, itpretty well describes the principaluses of this machine. Just like anylathe, these machines can make onlyround cuts plus facing and contour-ing cuts.

Figure 10.22 shows the generalconstruction and the motions avail-able on the VBM. The constructionis the same as that of the double-housing planer, except that a roundtable has been substituted for thelong reciprocating table, and thetoolholders are different since theVBM does not need clapper boxes.

The size of a vertical boringmachine is the diameter of therevolving worktable. The double-housing VBM is most often madewith table diameters from 48 inchesto 144 inches. Larger machines

FIGURE 10.19: Five-axis ram-stylemachining center. (Courtesy Giddingsand Lewis, LLC)

FIGURE 10.20: Large floor-type horizontal boring machine.(Courtesy WMW Machinery Co., Inc.)

FIGURE 10.21: Vertical boring machine (VBM).(Courtesy Summit Machine Tool Manufacturing Corp.)



Swivel ram headTurret head

Turret head

Crossrail

Crossrail

Column

Column

Sidehead

Column

Table BaseBase

Front View Side View

have been made for special work. A rather large VBMis shown in Figure 10.23.

10.7.3 Jig BorersJig borers are vertical boring machines with high preci-sion bearings. They are available in various sizes andused mainly in tool rooms for machining jigs and fixtures.More versatile numerically controlled machines are nowreplacing many jig borers.

FIGURE 10.22: General construction, components andmotions of a vertical boring machine (VBM).

FIGURE 10.23: Large Vertical Boring Machine (Courtesy: WMWMachinery Co., Inc.)






Lawrence Tech.- www.ltu.edu

Prentice Hall- www.prenhall.com

CHAPTER 11Reaming andTapping





Shaping and Planing



Reaming and Tapping




Lapping and Honing

Upcoming Chapters

11.2 ReamingReaming has been defined as a ma-chining process that uses a multi-edged fluted cutting tool to smooth,enlarge, or accurately size an existinghole. Reaming is performed using thesame types of machines as drilling.

A reamer is a rotary cutting toolwith one or more cutting elementsused for enlarging to size and contoura previously formed hole. Its principalsupport during the cutting action isobtained from the workpiece. A typicalreaming operation is shown in Figure11.1.

11.2.1 Reamer NomenclatureThe basic construction and nomencla-ture of reamers is shown in Figure

11.1 IntroductionTwist drills do not make accurately sized or good finish holes; a reamer of sometype is often used to cut the final size and finish. A reamer will not make theoriginal hole; it will only enlarge a previously drilled or bored hole. It will cut towithin +0.0005 inch of tool size and give finishes to 32 micro inches (u in).

Reamers are usually made of HSS although solid carbide and carbide tippedreamers are made in many sizes and styles. Regular chucking reamers are madein number and letter sizes, in fractional inch sizes, and in millimeter sizes. Theycan be purchased ground to any desired diameter.

Screw threads are used for a variety of purposes and applications in themachine tool industry. They are used to hold or fasten parts together (screws,bolts, and nuts), and to transmit motion (the lead screw moves the carriage on anengine lathe). Screw threads are also used to control or provide accuratemovement (the spindle on a micrometer), and to provide a mechanical advantage(a screw jack raises heavy loads).

When defining a screw thread, one must consider separate definitions for anexternal thread (screw or bolt) and an internal thread (nut).

An external thread is a cylindrical piece of material that has a uniform helicalgroove cut or formed around it. An internal thread is defined as a piece ofmaterial that has a helical groove around the interior of a cylindrical hole. Thischapter will discuss internal threads and tapping, the operation that producessuch threads.

0.004 to 0.032 in.

Cutting

11.2. This shows the most frequentlyused style for holes up to 1 inch, calleda chucking reamer.

Solid reamers do almost all theircutting with the 45 degree chamfered

FIGURE 11.1: A typical reaming opera-tion removes 0.004 to 0.032 in. of stock.


Chap. 11: Reaming and TappingChap. 11: Reaming and Tapping

front end. The flutes guide the reamerand slightly improve the finish. There-fore, reamers should not be used for

heavy stock removal.Axis: The axis is the imaginary

straight line which forms the longitu-dinal centerline of a reamer, usuallyestablished by rotating the reamer be-tween centers.

Back Taper: The back taper is aslight decrease in diameter, from frontto back in the flute length of reamers.

Body: The body is: 1) The flutedfull diameter portion of a reamer, in-clusive of the chamfer, starting taperand bevel. 2) The principal supportingmember for a set of reamer blades,usually including the shank.

Chamfer: The chamfer is the angu-lar cutting portion at the entering endof a reamer.

Chamfer Length: The chamferlength is the length of the chamfermeasured parallel to the axis at thecutting edge.

Chamfer Relief Angle: The cham-fer relief angle is the axial relief angleat the outer corner of the chamfer. It ismeasured by projection into a planetangent to the periphery at the outercorner of the chamfer.

Clearance: Clearance is the spacecreated by the relief behind the cuttingedge or margin of a reamer.

Cutting Edge: The cutting edge isthe leading edge of the land in thedirection of rotation for cutting.

Flutes: The flutes are longitudechannels formed in the body of thereamer to provide cutting edges, per-

mit passage of chips, and allow cuttingfluid to reach the cutting edges.

Flute Length: Flute length is thelength of theflutes not includ-ing the cuttersweep.

Land: Theland is the sec-tion of thereamer betweenadjacent flutes.

Margin: Themargin is the un-relieved part ofthe periphery ofthe land adjacentto the cuttingedge.

Neck: Theneck is a sectionof reduced diam-eter connecting

shank to body, or connecting otherportions of the reamer.

Overall Length: The overall lengthis the extreme length of the completereamer from end to end, but not includ-ing external centers or expansionscrews.

Shank: The shank is the portion ofthe reamer by which it is held anddriven.

Straight Shank: A straight shank isa cylindrical shank.

Taper Shank: A taper shank is ashank made to fit a specified (conical)taper socket.

11.2.2 Types of ReamersReamers are made with three shapes offlutes and all are standard.

Straight Flute: Straight flute ream-ers are satisfactory for most work andthe least expensive, but should not beused if a keyway or other interruptionis in the hole.

Right-hand Spiral: Right-hand spi-ral fluted reamers givefreer cutting action andtend to lift the chips outof the hole. They shouldnot be used on copper orsoft aluminum becausethese reamers tend to pulldown into the hole.

Left-hand Spiral: Left-hand spiralfluted reamers require slightly morepressure to feed but give a smooth cutand can be used on soft, gummy mate-

rials, since they tend to be pushed outof the hole as they advance. It is notwise to use these in blind holes, be-cause they push the chips down intothe hole.

All reamers are used to producesmooth and accurate holes. Some areturned by hand, and others use ma-chine power. The method used to iden-tify left hand and right hand reamers isshown in Figure 11.3.Machine Reamers

Machine reamers are used on both

drilling machines and lathes for rough-ing and finishing operations. Machinereamers are available with tapered orstraight shanks, and with straight orhelical flutes. Tapered shank reamers(see Fig. 11.4) fit directly into thespindle, and the straight shank reamer,generally called the chucking reamer,fits into a drill chuck.

Rose Reamers: Rose reamers aremachine reamers that cut only on a 45-degree chamfer (bevel) located on theend. The body of the rose reamertapers slightly (about 0.001 inch perinch of length) to prevent binding dur-ing operation. This reamer does notcut a smooth hole and is generally usedto bring a hole to a few thousands

undersize. Because the rose reamermachines a hole 0.001 to 0.005 inchesunder a nominal size, a hand reamer isused to finish the hole to size. All

Overall length (OAL)Shank length

Shank

Straight or taper

Flute length

Cutting edge

FlutesChamferangle 45°

116

*

*

Chamferlength

Actualdiameter

Chamferrelief

*Most reamers are made to these dimensions

Actualsize

Cutting edge

Zero rake

Heel

Flute

Land widthMargin

Reliefangle

Radialrake angle

Zero rake right-hand cut Positive rake right-hand cut

Slopesto left

Slopesto right

Left-hand helix,right-hand cut

Right-hand helix,right-hand cut

FIGURE 11.2: Construction and nomenclature of a straight-flutedmachining reamer.

FIGURE 11.3: Method of identifyingleft-hand and right-hand reamers.

FIGURE 11.4: Carbide-tipped straight-fluted tapered-shank reamer. (Courtesy: Morse Cutting Tools)



hand reamers have a square shank andcannot be used and operated with ma-chine power.

Fluted Reamers: Fluted reamersare machine reamers used to finishdrilled holes. This type of reamerremoves smaller portions of metalcompared to the rose reamer. Flutedreamers have more cutting edges thanrose reamers and therefore cut asmoother hole. Fluted reamers cut onthe chamfered end as well as the sides.They are also available in solid carbideor have carbide inserts for cuttingteeth.

Shell Reamers: Shell reamers (Fig.11.5) are made in two parts: thereamer head and the arbor. In use, thereamer head is mounted on the arbor.The reamer head is available with ei-ther a rose or flute type, with straightor helical flutes. The arbor is availablewith either straight or tapered shank.The shell reamer is considered eco-nomical, because only the reamer isreplaced when it becomes worn ordamaged.Hand Reamers

Hand reamers are finishing reamersdistinguished by the square on theirshanks (see Fig. 11.6). They are turned

by hand with a tap wrench that fitsover this square (see Fig. 11.7) thistype of reamer cuts only on the outercutting edges. The end of the handreamer is tapered slightly to permiteasy alignment in the drilled hole. The

length of taper is usu-ally equal to thereamer’s diameter.

Hand reamers mustnever be turned by ma-chine power, and mustbe started true andstraight. They shouldnever remove morethan 0.001 to 0.005 inches of material.Hand reamers are available from 1/8 toover 2 inches in diameter and aregenerally made of carbon steel or high-speed steel.

Taper Hand Reamers: Taper handreamers are hand reamers made toream all standard size tapers. They aremade for both roughing and finishingtapered holes. Similar to the straighthand reamer, this taper should be usedcarefully, and never with machinepower.

Adjustable Reamers: (Fig. 11.8a)Adjustable reamers are used to pro-duce any size hole within the range ofthe reamer. Their size is adjusted bysliding the cutting blades to and fromthe shank. The two adjusting nutslocated at each end of the blades movethese blades. Adjustable hand reamersare available in sizes from 1/4 to over 3

inches diam-eters. Eachreamer has ap-proximately 1/64-inch adjust-ment above andbelow its nomi-nal diameter.

E x p a n s i o nHand Ream-ers: (Fig.11.8b)Expansion handreamers are like

the adjustable reamers, but have a lim-ited range of approximately 0.010 inchadjustment. Expansion reamers havean adjusting screw at the end of thereamer. When turned, this adjustingscrew forces a tapered plug inside thebody of the reamer, expanding its di-ameter. Expansion reamers are also

available as machine reamers.Care of Reamers: Because reamers

are precision finishing tools, theyshould be used with care;

* Reamers should be stored in sepa-rate containers or spaced in the toolingcabinet to prevent damage to the cut-ting edges.

* Cutting fluids must always be usedduring reaming operations, exceptwith cast iron.

* A reamer must never be turnedbackward or the cutting edges will bedulled.

* Any burrs or nicks on the cuttingedges must be removed with an oil-stone to prevent cutting oversize holes.

11.2.3 Operating ConditionsIn reaming speed and feed are im-

portant; stock removal and alignmentmust be considered in order to producechatter free holes.

Reaming Speeds: Speeds for ma-chine reaming may vary considerablydepending in part on the material to bereamed, type of machine, and requiredfinish and accuracy. In general mostmachine reaming is done at about 2/3the speed used for drilling the samematerial.

Reaming Feeds: Feeds for reamingare usually much higher than thoseused for drilling, often running 200 to300 percent of drill feeds. Too low afeed may result in excessive reamerwear. At all times it is necessary thatthe feed be high enough to permit thereamer to cut rather than to rub orburnish. Too high a feed may tend toreduce the accuracy of the hole andmay also lower the quality of the fin-ish. The basic idea is to use as high a

FIGURE 11.5: Shell reamer arbor with two reamer heads, oneHSS and the other carbide tipped. (Courtesy: Morse CuttingTools)

FIGURE 11.6: Left-hand-helix handreamer, square-shanked hand ream-ers cannot be power driven. (Courte-sy: Cleveland Twist Drill GreenfieldIndustries)

FIGURE 11.7: Tap wrenches are also used to hold hand reamers to finish drilledholes. (Courtesy: Cleveland Twist Drill Greenfield Industries)

FIGURE 11.8: (a) Adjustable hand reamer. (b) A square-shanked expansion reamer. (Courtesy: Morse CuttingTools)



feed as possible and still produce therequired finish and accuracy.

Stock to be Removed: For the samereason, insufficient stock for reamingmay result in a burnishing rather than acutting action. It is difficult to gener-alize on this phase as it is tied inclosely with type of material, feed,finish required, depth of hole, and chipcapacity of the reamer. For machinereaming, .010 inch on a 1/4-inch hole,.015 inch on a 1/2 inch hole, up to .025inch on a 1-1/2 inch hole seems a goodstarting point. For hand reaming,stock allowances are much smaller,partly because of the difficulty in forc-ing the reamer through greater stock.A common allowance is .001 inch to.003 inch.

Alignment: In the ideal reamingjob, the spindle, reamer, bushing, andhole to be machined are all in perfectalignment. Any variation from thistends to increase reamer wear and de-tracts from the accuracy of the hole.Tapered, oversize, or bell-mouthedholes should call for a check of align-ment. Sometimes the bad effects ofmisalignment can be reduced throughthe use of floating or adjustable hold-ers. Quite often if the user will grind aslight back taper on the reamer it willalso be of help in overcoming theeffects of misalignment.

Chatter: The presence of chatterwhile reaming has a very bad effect onreamer life and on the finish in the hole.Chatter may be the result of one ofseveral causes, some of which are listed:

* Excessive speed.* Too much clearance on reamer.* Lack of rigidity in jig or machine.* Insecure holding of work.* Excessive overhand of reamer or

spindle.* Too light a feed.Correcting the cause can materially

increase both reamer life and the qual-ity of the reamed holes.

In reaming the emphasis is usuallyon finish, and a coolant is normallychosen for this purpose rather than forcooling.

11.2.4 Reaming OperationsReaming operations can be per-

formed on lathes, drills, and machin-ing centers.

Lathe Reaming: Reaming on alathe can only be done by holding the

reamer in the tail stock positioneither in a drill chuck for straightshank reamers, or directly in thetail stock quill for tapered shankreamers ( see Fig. 11.4). Work tobe reamed can either be held in achuck or mounted onto the face-plate. In case of a turret lathe, thereamer can only be used in thehex turret.

Sometimes reamers are held in‘floating’ holders in the tailstock.These holders allow the reamer tocenter itself on the previouslydrilled hole. Deep holes (overthree times the diameter of thedrill) tend to ‘run out’. Thereamer will not correct this condi-tion and the hole must be bored ifalignment is important.

Drill Press Reaming: Reaming ona drill press also requires the reamer tobe held in the spindle with a drillchuck for straight shank machiningreamers, or directly in the spindle fortapered shank reamers (see Fig. 11.4).The work to be reamed is usually heldin a vise and centered on the drilltable.

Reaming on a lathe is performed byrotating the work with a stationaryreamer, while reaming on a drill pressis performed with a rotating reamerand a stationary workpiece. ‘Floating’heads can be used on drill presses aswell as lathes.

Machining Center Reaming:Reaming on a machining center iscommon. Reamers are usually held inthe hex turret or in an automatic toolmagazine. Set-ups are usually morecomplicated while speeds and feedsare preprogrammed.

11.3 TappingTapping has been defined as: A pro-

cess for producing internal threads us-ing a tool (tap) that has teeth on itsperiphery to cut threads in a predrilledhole. A combined rotary and axialrelative motion between tap andworkpiece forms threads. A typical

Shank diameter

Size ofsquare

Shank length Thread length

AxisLength

of square

Overall length

Chamfer

90º Thread lead angle

Pointdiameter

Core diameter

FluteExternal center

Internal center

Chamferrelief

Angle of thread

Base of thread

Basic root

Flank

Basic pitch diameter

Basic minor diameter

Basicheight of

thread

Pitch

Basic crestTap crest

Basicmajor

diameter

Min. tapmajor

diameter

Max. tapmajor

diameter

FIGURE 11.9: A typical automated tappingoperation with self-reversing unit. (Courtesy:Tapmatic Corp.)

FIGURE 11.10: Tap and thread nomenclature.


Chap. 11: Reaming and TappingChap. 15: Saws and Sawing

Lead of Thread: The lead of threadis the distance a screw thread advancesaxially in one complete turn. On asingle start tap the lead and pitch areidentical. On a multiple start tap thelead is the multiple of the pitch.

Major Diameter: This is the diam-eter of the major cylinder or cone, at agiven position on the axis that boundsthe crests of an external thread or theroots of an internal thread.

Minor Diameter: Minor diameteris the diameter of the minor cylinder orcone, at a given position on the axisthat bounds the roots of an externalthread or the crests of an internalthread.

Pitch Diameter: Pitch diameter isthe diameter of an imaginary cylinderor cone, at a given point on the axis ofsuch a diameter and location of itsaxis, that its surface would passthrough the thread in a manner such asto make the thread ridge and the threadgroove equal and, as such, is locatedequidistant between the sharp majorand minor cylinders or cones of agiven thread form. On a theoreticallyperfect thread, these widths are equalto one half of the basic pitch (mea-sured parallel to the axis).

Spiral Point: A spiral point is theangular fluting in the cutting face ofthe land at the chamfered end. It isformed at an angle with respect to thetap axis of opposite hand to that of

automated tapping operation is shownin Figure 11.9.

11.3.1 Tap NomenclatureScrew threads have many dimen-

sions. It is important in modern manu-facturing to have a working knowledgeof screw thread terminology. A ‘right-hand thread’ is a screw thread thatrequires right-hand or clockwise rota-tion to tighten it. A ‘left-hand thread’is a screw thread that requires left-hand or counterclockwise rotation totighten it. ‘Thread fit’ is the range oftightness or looseness between exter-nal and internal mating threads.‘Thread series’ are groups of diameterand pitch combinations that are distin-guished from each other by the numberof threads per inch applied to a spe-cific diameter. The two commonthread series used in industry are thecoarse and fine series, specified asUNC and UNF. Tap nomenclature isshown in Figure 11.10.

Chamfer: Chamfer is the taperingof the threads at the front end of eachland of a chaser, tap, or die by cuttingaway and relieving the crest of the firstfew teeth to distribute the cutting ac-tion over several teeth.

Crest: Crest is the surface of thethread which joins the flanks of thethread and is farthest from the cylinderor cone from which the thread projects.

Flank: Flank is the part of a helicalthread surface whichconnects the crest andthe root, and which istheoretically a straightline in an axial planesection.

Flute: Flute is thelongitudinal channelformed in a tap to createcutting edges on thethread profile and toprovide chip spaces andcutting fluid passage.

Hook Angle: Thehook angle is the angleof inclination of a con-cave face, usually speci-fied either as ‘chordalhook’ or ‘tangentialhook’.

Land: The land isone of the threaded sec-tions between the flutesof a tap.

rotation. Its length is usually greaterthan the chamfer length and its anglewith respect to the tap axis is usuallymade great enough to direct the chipsahead of the tap. The tap may or maynot have longitudinal flutes.

Square: Square is the four drivingflats parallel to the axis on a tap shankforming a square or square with roundcorners.

11.3.2 Types of TapsTaps are manufactured in many

sizes, styles and types. Figure 11.11shows some of the taps discussed be-low.

Hand Taps: Today the hand tap isused both by hand and in machines ofall types. This is the basic tap design:four straight flutes, in taper, plug, orbottoming types. The small, numberedmachine screw sizes are standard intwo and three flutes depending on thesize.

If soft and stringy metals are beingtapped, or if horizontal holes are beingmade, either two- or three-flute tapscan be used in the larger sizes. Theflute spaces are larger, but the taps areweaker. The two-flute especially has avery small cross section.

The chips formed by these taps can-not get out; thus, they accumulate inthe flute spaces. This causes addedfriction and is a major cause of brokentaps.

Spiral Point Tap: Thespiral point or ‘gun’ tap(Fig. 11.12a) is made thesame as the standard handtap (see Fig. 11.10) exceptat the point. A slash isground in each flute at thepoint of the tap. This ac-complishes several things:

* The gun tap has fewerflutes (usually three), andthey are shallower. Thismeans a stronger tap.

* The chips are forcedout ahead of the tap insteadof accumulating in theflutes, as they will with aplug tap.

* Because of these twofactors, the spiral point tapcan often be run fasterthan the hand tap, and tapbreakage is greatly re-duced.

FIGURE 11.11: Some of the many styles and shapes of taps. (Courtesy:Greenfield Industries)


Chap. 11: Reaming and TappingChap. 15: Saws and Sawing

The gun tap has, in many cases,replaced the ‘standard’ style in indus-try, especially for open-ended troughholes in mild steel and aluminum.Both regular and spiral-point taps aremade in all sizes including metric.

Spiral Flute Tap: The spiral flute-bottoming tap (Fig. 11.12b) is made inregular and fast spirals, that is, withsmall or large helix angle. They aresometimes called ‘helical-fluted’ taps.The use of these taps has been increas-ing since they pull the chip up out ofthe hole and produce good threads insoft metals (such as aluminum, zinc,and copper), yet also work well inMonel metal, stainless steel and cast

steel. They are made in all sizes up to1-1/2 inches and in metric sizes up to 12mm.

While the ‘standard’ taps will effi-ciently do most work, if a great deal ofaluminum, brass, cast iron, or stainlesssteel is being tapped, the manufacturercan supply ‘standard’ specials that willdo a better job.

Pipe Taps: General Purpose Pipe

economical for medium and high pro-duction work.

11.3.3 Operating OptionsSome threads, both external and in-

ternal, can be cut with a single-pointtool as previously shown. However,most frequently a die or tap of sometype is used because it is faster andgenerally more accurate.

Taps are made in many styles, but afew styles do 90 percent of the work.Figure 11.10 shows the general termsused to describe taps. The cutting endof the tap is made in three differenttapers.

The ‘taper tap’ is not often usedtoday. Occasionally, it is used first as astarter if the metal is difficult to tap.The end is tapered about 5 degrees perside, which makes eight partial

FIGURE 11.12: (a) Spiral-point taps have replaced ‘stan-dard’ taps in many cases. (b) A spiral-fluted bottoming tap.(Courtesy: Morse Cutting Tools)

FIGURE 11.13: Straight and spiral-fluted pipe taps and a T-handle tapwrench. (Courtesy: Morse Cutting Tools)

Taps are used for threading a widerange of materials both ferrous andnon-ferrous. All pipe taps are suppliedwith 2-1/2 to 3-1/2 thread chamfer.The nominal size of a pipe tap is thatof the pipe fitting to be tapped, not theactual size of the tap.

Ground Thread Pipe Taps are stan-dard in American Standard Pipe Form(NPT) and American Standard DrysealPipe Form (NPTF). NPT threads re-quire the use of a ‘sealer’ like Teflontape or pipe compound. Dryseal tapsare used to tap fittings that will give apressure tight joint without the use of a‘sealer’. Figure 11.13 shows straightand spiral and spiral fluted pipe taps as

well as a ‘T’ handletap wrench.

Fluteless Taps:Fluteless taps (Fig.11.14) do not looklike taps, except forthe spiral ‘threads’.These taps are notround. They areshaped so that they‘cold form’ the metalout of the wall of the

hole into the thread form with nochips. The fluteless tap was originallydesigned for use in aluminum, brass,and zinc alloys. However, it is beingsuccessfully used in mild steel andsome stainless steels. Thus, it is worthchecking for use where BHN is under180. They are available in most sizes,including metric threads.

These taps are very strong and canoften be run up to twice as fast as otherstyles, however, the size of the holedrilled before tapping must be nolarger than the pitch diameter of thethread. The cold-formed thread oftenhas a better finish and is stronger thana cut thread. A cutting oil must beused, and the two ends of the holeshould be countersunk because the tapraises the metal at all ends.

Collapsing Taps: Collapsing taps(Fig. 11.15) collapse to a smaller di-ameter at the end of the cut. Thus,when used on lathes of any kind, theycan be pulled back rapidly. They aremade in sizes from about 1 inch up, inboth machine and pipe threads. Theyuse three to six separate ‘chasers’which must be ground as a set. The tapholder and special dies make this as-sembly moderately expensive, but it is

FIGURE 11.14: Fluteless taps are usedto ‘cold form’ threads. (Courtesy: TheWeldon Tool Co.)

FIGURE 11.15: Collapsing tap assem-blies are more expensive, but economicalfor medium- and high-production runs.(Courtesy: Greenfield Industries)


Chap. 11: Reaming and Tapping

threads.The ‘plug tap’ is the style used

probably 90 percent of the time. Withthe proper geometry of the cuttingedge and a good lubricant, a plug tapwill do most of the work needed. Theend is tapered 8 degrees per side,which makes four or five incompletethreads.

The ‘bottoming tap’ (see Fig.

11.12b) is used only for blind holeswhere the thread must go close to thebottom of the hole. It has only 1-1/2 to3 incomplete threads. If the hole canbe drilled deeper, a bottoming tap maynot be needed. The plug tap must beused first, followed by the bottomingtap.

All three types of end tapers aremade from identical taps. Size, length,and all measurements except the endtaper are the same.

Material used for taps is usuallyhigh-speed steel in the M1, M2, M7,and sometimes the M40 series cobalthigh-speed steels. A few taps are madeof solid tungsten carbide.

Most taps today have groundthreads. The grinding is done afterhardening and makes much more accu-rate cutting tools. ‘Cut thread’ taps areavailable at a somewhat lower cost insome styles and sizes.

11.3.4 Tapping OperationsJust like reaming operations, tap-

ping can be performedon lathes, drills, andmachining centers amulti hole tapping op-eration on a roundpart is shown in Fig-ure 11.16.

Tap Drills: It isquite obvious that the taps shown herecannot cut their own opening. Thus, a

hole of the proper size must be madebefore the tap can be used. Usuallythis hole is drilled. A tap drill is not aspecial kind of drill. A tap drill ismerely a conve-nient way to referto the proper sizedrill to be used be-fore using a tap.Tap drill sizesbased on 75 per-cent of thread aregiven in referencetables. The trendtoday in many fac-tories, in order tosave taps, time andrejects, is to use 60to 65 percent ofthread to deter-mine tap drillsizes. Drills anddrilling operationswere discussed inChapter 9. A com-bination drill and

tap is shown in Figure 11.17 and usedto drill and tap in one pass.

The deeper the hole is threaded, thelonger it takes to drill and tap and themore likely it is that the tap will break.Yet if there are too few threads holdingthe bolt, the threads will strip. Some-where in between there is a depth ofthread engagement that is the mini-mum that will hold enough so that thebolt will break before the threads letgo. This is called the optimum depth.

Tap drilling must be deep enough inblind holes to allow for the two to fivetapered threads on the tap plus chipclearance, plus the drill point.

Toolholders: Toolholders for handtapping are called ‘tap wrenches’.They are the same for taps and forreamers (see Fig. 11.7 and Fig. 11.13),because most taps have a square shank.Tap wrenches are adjustable and canbe used on several sizes of taps.

When taps are used in drill pressesor machining centers, a special headwith a reversing, slip-type clutch isused. These tapping heads (Fig. 11.18)can be set so that if a hard spot is metin the metal, the clutch slips and thetap will not break. They are con-

FIGURE 11.17: Combination drill and tap tools are usedfor one-pass drilling and tapping (Courtesy: Morse CuttingTools)

FIGURE 11.16: An automated multihold tapping operation on a round part. (Cour-tesy: Tapmatic Corp.)

FIGURE 11.18: Various special tap heads with reversing, slip-typeclutches are used in drill pressed and machining centers. (CourtesyTapmatic Corp.)


Chap. 11: Reaming and Tapping

structed so that when the hand-feedlever or the automatic numerical con-trol machine cycle starts upward, therotation reverses (and often goesfaster) to bring the tap safely out of thehole.

Workholding: Workholding fortapping is the same as for any drillpress or lathe work: clamps, vises,fixtures, etc. as needed. It is neces-sary to locate the tap centrally andstraight in the hole. This is difficult inhand tapping but relatively easy in

FIGURE 11.19: Thread ‘chasing,’ orthe manufacturing of outside threads,is performed with dies and self-open-ing die stocks. (Courtesy: GreenfieldIndustries) FIGURE 11.20: Multihold tapping operation with automatic

coolant/lubrication system. (Courtesy: Tapmatic Corp.)

machine tapping.Numerical control

is especially effi-cient, as it will locateover a hole, regard-less of when it wasdrilled, if it wasdrilled from the sametape and on the samesetup.

Single point thread-ing was discussed inChapter 6. Thread‘chasing’ or the manu-facturing of outsidethreads is also per-formed with dies andself-opening diestocks. Figure 11.19shows a number of dieheads and die chasers used in the manu-facturing of threads.

Lubrication: The cutting edges onboth taps and dies are buried in thematerial, so lubrication is quite neces-sary. For aluminum, light lard oil isused; other metals require a sulfur-based oil, sometimes chlorinated also.Figure 11.20 shows a tapping opera-tion with an automated fluid dispens-ing system for machining centers. The‘Automiser’ unit shown here dispenses

a lubricant/coolant through the tappinghead automatically, while the head isin the machine spindle.

Copper alloys are stained by sulfur,so mineral oils or soluble oil must beused. Cast iron is often threaded with-out any lubricant.

There are several synthetic tappingfluids on the market today. They aresomewhat more expensive but maysave their cost in better threads andfewer broken tips.


CHAPTER 12Milling Cuttersand OperationsMetal Removal

Cutting-Tool MaterialsMetal Removal MethodsMachinability of Metals



Shaping and Planing



Reaming and Tapping




Lapping and Honing







12.1 IntroductionThe two basic cutting tool types used in the metal working industry are of thesingle point and multi-point design, although they may differ in appearance andin their methods of application. Fundamentally, they are similar in that theaction of metal cutting is the same regardless of the type of operation. Bygrouping a number of single point tools in a circular holder, the familiar millingcutter is created.

Milling is a process of generating machined surfaces by progressively remov-ing a predetermined amount of material or stock from the workpiece witch isadvanced at a relatively slow rate of movement or feed to a milling cutter rotatingat a comparatively high speed. The characteristic feature of the milling process isthat each milling cutter tooth removes its share of the stock in the form of smallindividual chips. A typical face milling operation is shown in Figure 12.1.

12.2 Types of Milling CuttersThe variety of milling cutters available for all types of milling machines helpsmake milling a very versatile machining process. Cutters are made in a largerange of sizes and of several different cutting tool materials. Milling cutters aremade from High Speed Steel (HSS), others are carbide tipped and many arereplaceable or indexable inserts. The three basic milling operations are shown inFigure 12.2. Peripheral and end milling cutters will be discussed below. Face

FIGURE 12.1: A typical milling operation; the on-edge insert design is being used.(Courtesy Ingersoll Cutting Tool Co.)

Chap. 12: Milling Cutters & Operations


milling cutters are usually indexableand will be discussed later in thischapter.

A high speed steel (HSS) shellend milling cutter is shown in Fig-ure 12.3 and other common HSScutters are shown in Figure 12.4and briefly described below:

12.2.1 Periphery Milling CuttersPeriphery milling cutters are usu-ally arbor mounted to performvarious operations.

Light Duty Plain Mill: Thiscutter is a general purpose cutterfor peripheral milling operations.Narrow cutters have straight teeth,while wide ones have helical teeth(Fig. 12.4c).

Heavy Duty Plain Mill: Aheavy duty plain mill is similar tothe light duty mill except that it is

used for higher rates of metal removal.To aid it in this function, the teeth aremore widely spaced and the helix angle

is increased to about 45degrees.

Side Milling Cutter:The side milling cutterhas a cutting edge on thesides as well as on theperiphery. This allows thecutter to mill slots (Fig.12.4b).

Half-Side Milling Cut-ter: This tool is the sameas the one previously de-scribed except that cuttingedges are provided on asingle side. It is used for

milling shoulders. Two cutters of thistype are often mounted on a singlearbor for straddle milling.

Stagger-tooth Side Mill: This cut-ter is the same as the side millingcutter except that the teeth are stag-gered so that every other tooth cuts ona given side of the slot. This allowsdeep, heavy-duty cuts to be taken(12.4a).

Angle Cutters: On angle cutters,the peripheral cutting edges lie on acone rather than on a cylinder. Asingle or double angle may be provided(Fig. 12.4d and Fig. 12.4e).

Shell End Mill: The shell end millhas peripheral cutting edges plus facecutting edges on one end. It has a holethrough it for a bolt to secure it to thespindle (Fig. 12.3).

Form Mill: A form mill is a periph-eral cutter whose edge is shaped toproduce a special configuration on thesurface. One example of his class oftool is the gear tooth cutter. The exactcontour of the cutting edge of a formmill is reproduced on the surface of theworkpiece (Fig.12.4f, Fig.12.4g, andFig.12.4h).

12.2.2 End Milling CuttersEnd mills can be used on vertical andhorizontal milling machines for a vari-ety of facing, slotting, and profilingoperations. Solid end mills are madefrom high speed steel or sintered car-bide. Other types, such as shell endmills and fly cutters, consist of cuttingtools that are bolted or otherwise fas-tened to adapters.

Solid End Mills: Solid end millshave two, three, four, or more flutesand cutting edges on the end and theperiphery. Two flute end mills can befed directly along their longitudinalaxis into solid material because thecutting faces on the end meet. Three

Arbor

End mill

Spindle

ShankSpindle

Millingcutter

(a) (b) (c)

FIGURE 12.2: The three basic milling operations: (a) milling, (b) face milling, (c) end milling

FIGURE 12.3: High-speed steel (HSS) shellend milling cutter. (Courtesy Morse CuttingTools)

(a) (b) (c) (d)

(e) (f) (g) (h)

FIGURE 12.4: Common HSS milling cutters: (a) staggered-tooth cutter, (b) sidemilling cutter, (c) plain milling cutter, (d) single-angle milling cutter, (e) double-angle milling cutter, (f) convex milling cutter, (g) concave milling cutter, (h) cornerrounded milling cutter.



and four fluted cutters with oneend cutting edge that extends pastthe center of the cutter can also befed directly into solid material.

Solid end mills are double orsingle ended, with straight or ta-pered shanks. The end mill can be

of the stub type, with short cut-ting flutes, or of the extra longtype for reaching into deep cavi-ties. On end mills designed foreffective cutting of aluminum,the helix angle is increased forimproved shearing action andchip removal, and the flutes maybe polished. Various single anddouble-ended end mills areshown in Figure 12.5a. Varioustapered end mills are shown inFigure 12.5b.

Special End Mills: Ball endmills (Fig. 12.6a) are availablein diameters ranging from 1/32to 2 1/2 inches in single anddouble ended types. Single pur-pose end mills such as Woodruffkey-seat cutters, corner roundingcutters, and dovetail cutters

(Fig.12.6b) are usedon both vertical andhorizontal millingmachines. They areusually made of highspeed steel and mayhave straight or ta-pered shanks.

12.3 MillingCutter NomenclatureAs far as metalcutting action isconcerned, the per-tinent angles onthe tooth are thosethat define the con-figuration of thecutting edge, the

orientation of the tooth face, and therelief to prevent rubbing on the land.

The terms defined below and illus-trated in Figures 12.7a and 12.7b areimportant and fundamental to millingcutter configuration.

Outside Diameter: The outside di-ameter of a milling cutter is the diam-eter of a circle passing through theperipheral cutting edges. It is thedimension used in conjunction with thespindle speed to find the cutting speed(SFPM).

Root Diameter: This diameter ismeasured on a circle passing throughthe bottom of the fillets of the teeth.

Tooth: The tooth is the part of thecutter starting at the body and endingwith the peripheral cutting edge. Re-placeable teeth are also called inserts.

Tooth Face: The tooth face is thesurface of the tooth between the filletand the cutting edge, where the chipslides during its formation.

Land: The area behind the cuttingedge on the tooth that is relieved toavoid interference is called the land.

Flute: The flute is the space pro-vided for chip flow between the teeth.

Gash Angle: The gash angle ismeasured between the tooth face andthe back of the tooth immediatelyahead.

Fillet: The fillet is the radius at thebottom of the flute, provided to allowchip flow and chip curling.

The terms defined above apply pri-marily to milling cutters, particularlyto plain milling cutters. In definingthe configuration of the teeth on thecutter, the following terms are impor-tant.

Peripheral Cutting Edge: The cut-ting edge aligned principally in thedirection of the cutter axis is called theperipheral cutting edge. In peripheralmilling, it is this edge that removes themetal.

FIGURE 12.5a: Various single- and double-ended HSS end mills. (Courtesy The WeldonTool Co.)

FIGURE 12.5b: Various tapered HSS end mills.(Courtesy The Weldon Tool Co.)

(a) (b)

FIGURE 12.6: (a) Ball-nose end-milling cutters areavailable in diameter ranging from 1/32 to 2 ½inches. (Courtesy The Weldon Tool Co.) (b) HSSdovetail cutters can be used on both vertical andhorizontal milling machines. (Courtesy MorseCutting Tools)

ToothTooth face

Gash angle

LandFlute

Fillet

Outside d

iamete

r

Root diameterRadial

rake angle

Peripheralcutting edge

Secondary clearance

Primary clearance

(a)(b)

Relief

FIGURE 12.7: Milling cutter configuration: (a) plain milling cutternomenclature; (b) plain milling cutter tooth geometry.



Face Cutting Edge: The face cut-ting edge is the metal removing edgealigned primarily in a radial direction.In side milling and face milling, thisedge actually forms the new surface,although the peripheral cutting edgemay still be removing most of themetal. It corresponds to the end cut-ting edge on single point tools.

Relief Angle: This angle is mea-sured between the land and a tangentto the cutting edge at the periphery.

Clearance Angle: The clearanceangle is provided to make room forchips, thus forming the flute. Nor-mally two clearance angles are pro-vided to maintain the strength of thetooth and still provide sufficient chipspace.

Radial Rake Angle: The radialrake angle is the angle between thetooth face and a cutter radius, mea-sured in a plane normal to the cutter

axis.Axial Rake Angle: The axial rake

angle is measured between the periph-eral cutting edge and the axis of thecutter, when looking radially at thepoint of intersection.

Blade Setting Angle: When a slotis provided in the cutter body for ablade, the angle between the base of theslot and the cutter axis is called theblade setting angle.

12.4 Indexable Milling CuttersThe three basic types of milling opera-tions were introduced earlier. Figure12.8 shows a variety of indexable mill-ing cutters used in all three of the basictypes of milling operations (Fig. 12.2).

There are a variety of clamping sys-tems for indexable inserts in millingcutter bodies. The examples showncover the most popular methods now inuse:

12.4.1 Wedge ClampingMilling inserts havebeen clamped usingwedges for many yearsin the cutting tool in-dustry. This principleis generally applied inone of the followingways: either the wedgeis designed and ori-ented to support the in-sert as it is clamped, orthe wedge clamps onthe cutting face of theinsert, forcing the insertagainst the millingbody. When the wedge

is used to support the insert, the wedgemust absorb all of the force generatedduring the cut. This is why wedgeclamping on the cutting face of theinsert is preferred, since this methodtransfers the loads generated by the cutthrough the insert and into the cutterbody. Both of the wedges clampingmethods are shown in Figure 12.9.

The wedge clamp system however,has two distinct disadvantages. First,the wedge covers almost half of theinsert cutting face, thus obstructingnormal chip flow while producing pre-mature cutter body wear, and secondly,high clamping forces causing clamp-ing element and cutter body deforma-tion can and often will result. Theexcessive clamping forces can causeenough cutter body distortion that insome cases when loading inserts into amilling body, the last insert slot willhave narrowed to a point where the lastinsert will not fit into the body. Whenthis occurs, several of the other insertsalready loaded in the milling cutter areremoved an reset. Wedge clampingcan be used to clamp individual inserts(Fig. 12.10a) or indexable and replace-able milling cutter cartridges as shownin Figure 25.10b.

12.4.2 Screw ClampingThis method of clamping is used inconjunction with an insert that has apressed countersink or counterbore. Atorque screw is often used to eccentri-cally mount and force the insertagainst the insert pocket walls. Thisclamping action is a result of eitheroffsetting the centerline of the screwtoward the back walls of the insert

FIGURE 12.8: A variety of indexablemilling cutters. (Courtesy IngersollCutting Tool Co.)

Insert

Support andclamping

wedge

Clampingwedge

FIGURE 12.9: Two methods of wedge clamping indexablemilling cutter inserts.

(a) (b)

FIGURE 12.10: (a) Face milling cutter with wedge clamped indexable inserts.(Courtesy Iscar Metals, Inc.) (b) Face milling cutters with indexable inserts andwedge clamped milling cartridges. (Courtesy Greenleaf Corp.)



pocket, or by drilling and tapping themounting hole at a slight angle,thereby bending the screw to attain thesame type of clamping action.

The Screw clamping method forindexable inserts is shown in Figure12.11.

Screw clamping is excellent forsmall diameter end mills where spaceis at a premium. It also provides anopen unhampered path for chips toflow free of wedges or any other ob-structive hardware. Screw clampingproduces lower clamping forces thanthose attained with the wedge clamp-ing system. However, when the cuttingedge temperature rises significantly,the insert frequently expands and

c a u s e san unde-s i r a b l er e t i gh t -ening ef-fect, in-creasingthe torque required to unlock the insertscrew. The screw clamping method canbe used on indexable ball milling cut-ters (Fig. 12.12a) or on indexable in-sert slotting and face milling cutters asshown in Figure 12.12b.

12.5 Milling Cutter GeometryThere are three industry standard mill-ing cutter geometries: double negative,double positive, and positive/negative.Each cutter geometry type has certainadvantages and disadvantages thatmust be considered when selecting theright milling cutter for the job. Posi-tive rake and negative rake milling

cutter geometries are shown in Figure12.13.

Double Negative Geometry: Adouble negative milling cutter usesonly negative inserts held in a negativepocket. This provides cutting edgestrength for roughing and severe inter-rupted cuts. When choosing a cuttergeometry it is important to rememberthat a negative insert tends to push thecutter away, exerting considerableforce against the workpiece. Thiscould be a problem when machiningflimsy or lightly held workpieces, orwhen using light machines. However,this tendency to push the work down,or push the cutter away from the

workpiece may be benefi-cial in some cases becausethe force tends to ‘load’the system, which often re-duces chatter.

Double Positive Geom-etry: Double positive cut-ters use positive insertsheld in positive pockets.This is to provide theproper clearance for cut-ting. Double positive cut-ter geometry provides forlow force cutting, but theinserts contact theworkpiece at their weakestpoint, the cutting edge. Inpositive rake milling, the

cutting forces tend to lift theworkpiece or pull the cutterinto the work. The greatestadvantage of double posi-

Insert

Insertscrew

FIGURE 12.11: Screw clamping method forindexable inserts.

FIGURE 12.12: (a) Indexable-insert ball-nosed milling cutters using the screw clamping method.(Courtesy Ingersoll Cutting Tool Co.) (b) Slotting cutters and face milling with screw-on-typeindexable inserts. (Courtesy Duramet Corp.)

(b)(a)

Lead angle or corner angle orperipheral cutting edge angle

Face or endcutting edgeangle

Effective diameter

Side View

2-45°

Axial relief angle

Chamferor radius

Axial rakeangle (positive)

FCEA2-4° Effective diameter

Side View

Lead angle2-4°

Axial relief angle

Chamfer 45°

Axial rakeangle (negative)

Wedge lock

Radial rakeangle (positive)

Bottom View

Peripheral orradial relief angle Wedge lock

Radial rakeangle (positive)

Bottom View

Peripheralrelief angle

FIGURE 12.13: Positive-rake and negative-rake face milling cutternomenclature.



tive milling is free cutting. Less forceis exerted against the workpiece, soless power is required. This can beespecially helpful with machining ma-terials that tend to work harden.

Positive / Negative Geometry:Positive/negative cutter geometry com-bines positive inserts held in negativepockets. This provides a positive axialrake and a negative radial rake and aswith double positive inserts, this pro-vides the proper clearance for cutting.In the case of positive/negative cutters,the workpiece is contacted away fromthe cutting edge in the radial directionand on the cutting edge in the axialdirection. The positive/negative cuttercan be considered a low force cutterbecause it uses a free cutting positiveinsert. On the other hand, the positive/negative cutter provides contact awayfrom the cutting edge in the radialdirection, the feed direction of a facemill.

In positive/negative milling, some ofthe advantages of both positive andnegative milling are available. Posi-tive/negative milling combines the freecutting or shearing away of the chip ofa positive cutter with some of the edgestrength of a negative cutter.

Lead Angle: The lead angle (Fig.12.14) is the angle between the insertand the axis of the cutter. Severalfactors must be considered to deter-mine which lead angle is best for aspecific operation. First, the lead anglemust be small enough to cover thedepth of cut. The greater the leadangle, the less the depth of cut that canbe taken for a given size insert. Inaddition, the part being machined mayrequire a small lead angle in order toclear a portion or form a certain shapeon the part. As the lead angle in-creases, the forces change toward thedirection of the workpiece. This couldcause deflections when machining thin

sections of thepart.

The lead anglealso determinesthe thickness ofthe chip. Thegreater the leadangle for the samefeed rate or chipload per tooth, thethinner the chipbecomes. As insingle point tool-ing, the depth of cut is distributed overa longer surface of contact. Therefore,lead angle cutters are recommendedwhen maximum material removal isthe objective. Thinning the chip al-lows the feed rate to be increased ormaximized.

Lead angles can range from zero to85 degrees. The most common leadangles available on standard cutters are0, 15, 30 and 45 degrees. Lead angleslarger than 45 degrees are usually con-sidered special, and are used for veryshallow cuts for fine finishing, or forcutting very hard work materials.

Milling cutters with large leadangles also have greater heat dissipat-ing capacity. Extremely high tempera-tures are generated at the insert cuttingedge while the insert is in the cut.Carbide, as well as other tool materi-als, often softens when heated, andwhen a cutting edge is softened it willwear away more easily. However, ifmore of the tool can be employed in thecut, as in the case of larger lead angles,the tool’s heat dissipating capacity willbe improved which, in turn, improvestool life. In addition, as lead angle isincreased, axial force is increased andradial force is reduced, an importantfactor in controlling chatter.

T h euse ofl a r g e

lead angle cutters is especially benefi-cial when machining materials withscaly or work hardened surfaces. Witha large lead angle, the surface is spreadover a larger area of the cutting edge.This reduces the detrimental effect onthe inserts, extending tool life. Largelead angles will also reduce burringand breakout at the workpiece edge.

The most obvious limitation on leadangle cutters is part configuration. If asquare shoulder must be machined on apart, a zero degree lead angle is re-quired. It is impossible to produce azero degree lead angle milling cutterwith square inserts because of the needto provide face clearance. Often a nearsquare shoulder is permissible. In thiscase a three degree lead angle cuttermay be used.

12.5.1 Milling Insert CornerGeometryIndexable insert shape and size werediscussed in Chapter 2. Selecting theproper corner geometry is probably themost complex element of insert selec-tion. A wide variety of corner stylesare available. The corner style chosenwill have a major effect on surfacefinish and insert cost. Figure 12.15ashows various sizes and shapes of

indexable millingcutter inserts.

Nose Radius: Aninsert with a nose ra-dius is generally lessexpensive than asimilar insert withany other corner ge-ometry. A nose ra-dius is also the stron-gest possible cornergeometry because ithas no sharp cornerswhere two flats cometogether, as in thecase of a chamferedcorner. For these two

Lead angle

FIGURE 12.14: Drawing of a positive lead angle on anindexable-insert face milling cutter.

Cutter Cutter

Chipflowdirection

A

Chipflowdirection

(b)

Workpiece Workpiece

FIGURE 12.15: (a) Various sizes and shapes of indexable milling cutter inserts. (Courtesy AmericanNational Carbide Co.) (b) indexable milling cutter insert chip flow directions are shown.

(a) (b)



reasons alone, a nose radius insertshould be the first choice for any appli-cation where it can be used.

Inserts with nose radii can offer toollife improvement when they are usedin 0 to 15 degree lead angle cutters, asshown in Figure 12.15b. When achamfer is used, as in the left drawing,the section of the chip formed aboveand below point A, will converge atpoint A, generating a large amount ofheat at that point, which will promotefaster than normal tool wear. When aradius insert is used, as shown in theright drawing, the chip is still com-pressed, but the heat is spread moreevenly along the cutting edge, result-ing in longer tool life.

The major disadvantage of an insertwith a nose radius is that the surfacefinish it produces is generally not asgood as other common corner geom-etries. For this reason, inserts withnose radii are generally limited toroughing applications and applicationswhere a sweep wiper insert is used forthe surface. A sweep wiper is an insertwith a very wide flat edge or a verylarge radiused edge that appears to beflat. There is usually only one wiperblade used in a cutter and this bladegets its name from its sweeping actionthat blends the workpiece surface to avery smooth finish.

Inserts with nose radii are not avail-able on many double positive and posi-tive/negative cutters because the clear-ance required under the nose radius isdifferent from that needed under theedge. This clearance difference wouldrequire expensive grinding proceduresthat would more than offset the otheradvantages of nose radius inserts.

Chamfer: There are two basic waysin which inserts with a corner chamfer

can be applied. Depending both on thechamfer angle and the lead angle of thecutter body in which the insert is used,the land of the chamfer will be eitherparallel or angular (tilted) to the direc-tion of feed, as shown in Figure12.16a.

Inserts that are applied with thechamfer angular to the direction offeed normally have only a single cham-fer. These inserts are generally not asstrong and the cost is usually higherthan inserts that have a large noseradius. Angular-land chamfer insertsare frequently used for general purposemachining with double negative cut-ters.

Inserts designed to be used with thechamfer parallel to the direction offeed may have a single chamfer, asingle chamfer and corner break, adouble chamfer, or a double chamferand corner break. The larger lands arereferred to as primary facets and thesmaller lands as secondary facets. Thecost of chamfers, in relation to othertypes of corner geometries, dependsupon the number of facets. A singlefacet insert is the least expensive,while multiple facet inserts cost morebecause of the additional grinding ex-pense. Figure 12.16b shows two preci-sion ground indexable milling cutterinserts. A face milling cutter with sixsquare precision ground indexablemilling cutter inserts was shown inFigure 12.10a.

The greatest advantage of using in-serts with the land parallel to the direc-tion of feed is that, when used cor-rectly, they generate an excellent sur-face finish. When the land width isgreater than the advance per revolu-tion, one insert forms the surface. Thismeans that an excellent surface finish

normally will be produced regardlessof the insert face runout. Parallel-landinserts also make excellent roughingand general purpose inserts for posi-tive/negative and double positive cut-ters. When a parallel land chamferinsert is used for roughing, the landwidth should be as small as possible toreduce friction.

Sweep Wipers: Sweep wipers areunique in both appearance and applica-tion. These inserts have only one ortwo very long wiping lands. A singlesweep wiper is used in a cutter bodyfilled with other inserts (usually rough-ing inserts) and is set approximately0.003 to 0.005 inches higher than theother inserts, so that the sweep wiperalone forms the finished surface.

The finish obtained with a sweepwiper is even better than the excellentfinish attained with a parallel landchamfer insert. In addition, since theedge of the sweep wiper insert is excep-tionally long, a greater advance perrevolution may be used. The sweepwiper also offers the same easy set-upas the parallel-land insert.

Sweep wiper inserts are availablewith both flat and crowned wipingsurfaces. The crowned cutting edge isground to a very large radius, usuallyfrom three to ten inches. The crownedcutting edges eliminate the possibilityof saw-tooth profiles being producedon the machined surface because theland is not exactly parallel to the direc-tion of feed, a condition normallycaused by spindle tilt. On the otherhand, sweep wipers with flat cuttingedges produce a somewhat better finishif the land is perfectly aligned with thedirection of feed.

Cutter Cutter

(a)

Workpiece Workpiece

Parallel-landchamber

Angular-landchamber

(b) (c)FIGURE 12.16: (a) indexable milling cutter inserts with angular-land chamfer and parallel-land chamfer. (b and c) Twoprecision ground indexable milling cutter inserts. (Courtesy Iscar Metals, Inc.)



12.6 Basic Milling OperationsBefore any milling job is attempted,several decisions must be made. Inaddition to selecting the best means ofholding the work and the most appro-priate cutters to be used, the cuttingspeed and feed rate must be establishedto provide good balance between rapidmetal removal and long tool life.

Proper determination of a cuttingspeed and feed rate can be made onlywhen the following six factors areknown:• Type of material to be machined• Rigidity of the set-up• Physical strength of the cutter• Cutting tool material• Power available at the spindle• Type of finish desired

Several of these factors affect cuttingspeed only, and some affect both cut-ting speed and the feed rate. The tablesin reference handbooks provide ap-proximate figures that can be used asstarting points. After the cutting speedis chosen, the spindle speed must becomputed and the machine adjusted.

Cutting Speed: Cutting speed isdefined as the distance in feet that istraveled by a point on the cutter pe-riphery in one minute. Since a cutter’speriphery is its circumference:

Circumference = Pi × d

in case of a cutter, thecircumference is:

Cutter circumference = Pi/12 × d = .262 × d

Since cutting speed is expressed insurface feet per minute (SFPM)

SFPM = Cutter circumference × RPM

by substituting for the cutter circum-ference, the cutting speed can be ex-pressed as:

SFPM = .262 × d × RPM

The concept of cutting speed(SFPM) was introduced in Chapter 4(Turning Tools and Operations) andexplained again in Chapter 8 (Drillsand Drilling Operations). It has againbeen reviewed here without giving ad-ditional examples. However, sincemilling is a multi-point operation, feedneeds to be explained in more detailthan in previous chapters.

Feed Rate: Once the cutting speedis established for a particularworkpiece material, the appropriatefeed rate must be selected. Feed rate isdefined in metal cutting as the lineardistance the tool moves at a constantrate relative to the workpiece in aspecified amount of time. Feed rate isnormally measured in units of inchesper minute or IPM. In turning anddrilling operations the feed rate is ex-pressed in IPR or inches per revolu-tion.

When establishing the feed rates formilling cutters, the goal is to attain thefastest feed per insert possible, toachieve an optimum level of productiv-ity and tool life, consistent with effi-cient manufacturing practices. Theultimate feed rate is a function of thecutting edge strength and the rigidityof the workpiece, machine andfixturing. To calculate the appropriatefeed rate for a specific milling applica-tion, the RPM, number of effectiveinserts (N) and feed per insert in inches(IPT or apt) should be supplied.

The milling cutter shown in Figure12.17 on the left (one insert cutter) willadvance .006 inches at the cuttercenterline every time it rotates one fullrevolution. In this case, the cutter issaid to have a feed per insert or an IPT(inches per tooth), apt (advance pertooth) and an apr (advance per revolu-tion) of .006 inches. The same style ofcutter with 4 inserts is shown in theright hand drawing. However, tomaintain an equal load on each insert,the milling cutter will now advance.024 inches at he centerline every timeit rotates one full revolution. Themilling cutter on the right is said tohave and IPT and apt of .006 inches,but and apr (advance per revolution) of.024 inches (.006 inch for each insert).

These concepts are used to deter-

mine the actual feed rate of a millingcutter in IPM (inches per minute) us-ing one of the following formulas:

IPM = (IPT) × (N) × (RPM)or

IPM = (apt) × (N) × (RPM)

where:IPM = inches per minuteN = number of effective insertsIPT = inches per toothapt = advance per toothRPM = revolutions per minute

For Example: When milling automo-tive gray cast iron using a 4 inchdiameter face mill with 8 inserts at 400SFPM and 30.5 IPM, what apr and aptwould this be?

Answer: = .080 in. apr= .010 in. apt

When milling a 300M steel landinggear with a 6 inch diameter 45 degreelead face mill (containing 10 inserts)at 380 SFPM and a .006 inch advanceper tooth, what feed rate should be runin IPM?

Answer: = 14.5 IPMThe following basic list of formulas

can be used to determine IPM, RPM,apt, apr, or N depending on what

++

FeedFeed

apr = .024πapr = apt = .006π apt = .006π

FIGURE 12.17: Drawing of a milling cutter showing the difference between advanceper revolution (apr) and advance per tooth (apt).

SFPM 400.262 × d .262 × 4RPM = = = 382

IPM 30.5 RPM 382apr = = = .080 in.

apr .080 N 8apt = = = .010 in.

SFPM 380.262 × d .262 × 6RPM = = = 242

IPM=apt×N×RPM = .006×10×242=14.5



information is supplied for a specificmilling application:

IPM = inches per minuteN = number of effective insertsapr = inches of cutter advance every revolutionapt = inches of cutter advance

for each effective insert every revolution

RPM = revolutions per minute

Find Given Using

IPM apr, RPM IPM = apr × RPM

IPM RPM, N, apt IPM =apt × N × RPM

apr IPM, RPM apr = IPM/RPM

RPM IPM, apr RPM = IPM/apr

RPM IPM, N, apt RPM = IPM N × apt

N IPM, RPM, apt N = IPM RPM × apt

apt IPM, N, RPM apt = IPM RPM × N

Note: In the formulas shown above IPTcan be substituted for apt and IPR canbe substituted for apr.

Horsepower Requirements: Inmetal cutting, the horsepower con-sumed is directly proportional to thevolume (Q) of material machined perunit of time (cubic inches / minute).Metals have distinct unit power factorsthat indicate the average amount ofhorsepower required to remove onecubic inch of material in a minute.The power factor (k*) can be usedeither to determine the machine size interms of horsepower required to makea specific machining pass or the feedrate that can be attained once a depthand width of cut are established on aparticular part feature. To determinethe metal removal rate (Q) use thefollowing:

Q = D.O.C. × W.O.C × IPMwhere:

D.O.C. = depth of cut in inchesW.O.C. = width of cut in inchesIPM = feed rate, in inches/minute

The average spindle horsepower re-quired for machining metal workpiecesis as follows:

HP = Q × k*where:

HP = horsepower required at themachine spindle

Q = the metal removal rate incubic inches/minute

k* = the unit power factor inHP/cubic inch/minute

*k factors are available from refer-ence books

For example: What feed should beselected to mill a 2 inch wide by .25inch depth of cut on aircraft aluminum,utilizing all the available horsepoweron a 20 HP machine using a 3 inchdiameter face mill?

HP = Q × k*k* = .25 H.P./in.3/min. for aluminum

The maximum possible metal re-moval rate (Q), for a 20 H.P. machinerunning an aluminum part is:

Answer: Q = 80 in.3/min.

To remove 80 in3/min., what feed ratewill be needed?

Answer:= 160 IPM

12.6.1 Direction of Milling FeedThe application of the milling tool interms of its machining direction iscritical to the performance and tool life

of the entire operation. The two op-tions in milling direction are describedas either conventional or climb mill-ing. Conventional and climb millingalso affects chip formation and tool lifeas explained below. Figure 12.18shows drawings of both conventionaland climb milling.

Conventional Milling: The termoften associated with this milling tech-nique is ‘up-cut’ milling. The cutterrotates against the direction of feed asthe workpiece advances toward it fromthe side where the teeth are movingupward. The separating forces pro-duced between cutter and workpieceoppose the motion of the work. Thethickness of the chip at the beginningof the cut is at a minimum, graduallyincreasing in thickness to a maximumat the end of the cut.

Climb Milling: The term oftenassociated with this milling techniqueis ‘down-cut’ milling. The cutter ro-tates in the direction of the feed and theworkpiece, therefore advances towardsthe cutter from the side where the teethare moving downward. As the cutterteeth begin to cut, forces of consider-able intensity are produced which favorthe motion of the workpiece and tendto pull the work under the cutter. Thechip is at a maximum thickness at thebeginning of the cut, reducing to aminimum at the exit. Generally climbmilling is recommended wherever pos-sible. With climb milling a betterfinish is produced and longer cutter lifeis obtained. As each tooth enters thework, it immediately takes a cut and isnot dulled while building up pressureto dig into the work.

Advantages and Disadvantages: Ifthe workpiece has a highly abrasivesurface, conventional milling will usu-

noitatoR

Workpiece

Cutter

Feedup-cut milling

noitatoR

Workpiece

Cutter

Feeddown-cut milling

FIGURE 12.18: Conventional or up-milling as compared to climb or down-milling.

Q = (D.O.C.) × (W.O.C.) × IPMQ 80

(D.O.C.)×(W.O.C.) .25×2IPM= = =160

Q = = = 80 in3/min.HP 20k .25



ally produce better cutter life since thecutting edge engages the work belowthe abrasive surface. Conventionalmilling also protects the edge by chip-ping off the surface ahead of the cut-ting edge.

Limitations on the use of climb mill-ing are mainly affected by the condi-tion of the machine and the rigiditywith which the work is clamped andsupported. Since there is a tendency

for the cutter to climb up on the work,the milling machine arbor and arborsupport must be rigid enough to over-come this tendency. The feed must beuniform and if the machine does nothave a backlash eliminator drive, thetable gibs should be tightened to pre-vent the workpiece from being pulledinto the cutter. Most present-day ma-chines are built rigidly enough. Oldermachines can usually be tightened to

permit use of climb milling.The downward pressure caused by

climb milling has an inherent advan-tage in that it tends to hold the workand fixture against the table, and thetable against the ways. In conventionalmilling, the reverse is true and theworkpiece tends to be lifted from thetable.






Shaping and Planing



Reaming and Tapping




Lapping and Honing







CHAPTER 13Milling Methodsand Machines13.1 IntroductionModern milling machines look muchthe same as they did 25 years ago.However, they now must cut superalloys, titanium, and high tensile steelsto closer tolerances and at faster ratesthen previously. To handle these re-quirements, the new milling machinesprovide higher horsepower, greaterstiffness, and wider speed and feedranges than before. In addition, moreaccurate lead screws, closer alignment,numerical control (NC) and computernumerical control (CNC) all result infaster work with better finishes andgreater accuracy than ever before at-tained. A modern CNC vertical mill-ing machine is shown in Figure 13.1

13.2 Types of Milling MachinesThe many types of milling machinesused in manufacturing have been

grouped into three general classes.• Column and Knee Machines• Bed Type Milling Machines• Special Purpose Machines

The common subtypes are also iden-tified and discussed.

13.2.1 Column and Knee MachinesColumn and knee milling machinesare made in both vertical and horizon-tal types. The schematic diagrams(Fig. 13.2a and Fig.13.2b) show bothtypes of machines. Versatility is a ma-jor feature of knee and column millingmachines. On a basic machine of thistype, the table, saddle, and knee can bemoved. Many accessories such as uni-versal vises, rotary tables, and dividingheads, further increase the versatilityof this type of machine.

Regardless of whether the machineis of the vertical or horizontal type,several components on all column andknee milling machines are similar, ex-cept for size and minor variations be-cause of manufacturer’s preference.These similarities are described interms of general shape, geometric rela-tionship to the rest of the machine,function, and the material from whichthe components are made. Figure13.3a shows a standard vertical millingmachine and Figure 13.3b shows a 3axis CNC vertical milling machine

A universal Horizontal Column andKnee milling machine is shown inFigure 13.4.

Column: The column, which isusually combined with the base as asingle casting, is cast gray iron orductile iron. The column houses thespindle, bearings, and the necessarygears, clutches, shafts, pumps, andshifting mechanisms for transmitting

FIGURE 13.1: Modern CNC verticalmilling machine (Courtesy IngersollMilling Machine Co.)

Chap. 13: Milling Methods & Machines


power from the electric motor to thespindle at the selected speed. Thegears usually run in oil and are made ofcarburized alloy steel for long life.Some of the necessary controls areusually mounted on the side of thecolumn.

The base is usually hollow, and inmany cases serves as a sump for thecutting fluid. A pump and filtrationsystem can be installed in the base.The hole in the center of the basehouses the support for the screw thatraises and lowers the knee.

The machined vertical slide on thefront of the column may be of thesquare or dovetail type. The kneemoves up and down on this slide. Theslide must be machined at a 90 degree

angle to the face of the column in boththe lateral and vertical planes. Thetolerances are very close and are usu-ally expressed in minutes or seconds ofarc. The large hole in the face of thecolumn casting is for the spindle. Thehole is very accurately bored perpen-dicular to the front slide in two planesand parallel to the upper slide.

Spindle: On a horizontal millingmachine, the spindle is one of the mostcritical parts. It is usually machinedfrom an alloy steel forging and is heattreated to resist wear, vibration, thrust,and bending loads. The spindle isusually supported by a combination ofball and straight roller bearings, or bytapered roller bearings that absorb bothradial loads and end thrust loads.

Spindles are hollow so that a drawbarcan be used to hold arbors securely inplace.

The front of the spindle is machinedto accept standard arbors. The twokeys that fit into corresponding slots inthe arbor do the actual driving of thearbor. The internal taper, which isaccurately ground so that it is concen-tric with the spindle, locates the arbor.

Knee: The knee is a casting that ismoved up or down the slide on thefront of the column by the elevatingscrew. Two dovetail or square slidesare machined at 90 degrees to eachother. The vertical slide mates with theslide on the front of the column, andthe horizontal slide carries the saddle.It contains the necessary gears, screws,and other mechanisms to providepower feeds in all directions. Theoperator can select various feed rateswith the controls mounted on the knee.

Saddle: The saddle for a plainmilling machine is a casting with twoslides machined at an exact 90 degreeangle to each other. The lower slidefits the slide on the top of the knee, andthe upper slide accepts the slide on thebottom of the table. The surfaces of theslides that make contact with the kneeand the table are parallel to each other.Locks for both the cross slide and tableis fitted to the saddle, along with thenuts that engage with the cross feedand table feed screws.

On a universal milling machine thesaddle is made in two pieces and ismore complex because it must allowthe table to swivel through a limitedarc. The lower part has a dovetail slide

OverarmMotor

Quill

Table

Saddle

Knee

Column

Base

Elevatingscrew

Spindle

Z ′

Y ′

Y

X

Z

OverarmArbor

Outboard bearingand arbor support

Table(X axis)

Saddle(Z axis)

Knee(Y axis)

Base

Elevating screw

Spindlenose

Column

Y

Z ′

Z

X

(a) (b)

FIGURE 13.2: Schematic illustration of the motions and components (a) of avertical-spindle column and knee type milling machine and (b) of a horizontal-spindle column and knee type of machine.

FIGURE 13.3: (a) Stand vertical-spindle column and knee type milling machine.(Courtesy Bridgeport Machinery, Inc.) (b) Three-axis CNC vertical-spindle columnand knee type milling machine. (Courtesy Chevalier Machinery, Inc.)

FIGURE 13.4: A universal horizontal-spindle column and knee type millingmachine. (Courtesy Summit MachineTool Manufacturing Corp.)

(b)(a)



that fits the top of the knee and acircular slide above it is graduated indegrees for a small portion of its pe-riphery. The upper portion of thesaddle consists of a circular face thatfits against the lower circular slide, acentral pivot point, and a dovetail slidethat accepts the table. Locking boltsmoving in a circular T-slot are pro-vided so that the two parts of the saddlecan be locked in any position.

Table: Milling machine tables varygreatly in size, but generally they havethe same physical characteristics. Thebottom of the table has a dovetail slidethat fits in the slide on top of thesaddle. It also has bearings at each endto carry the table feed screw. The topof the table is machined parallel withthe slide on the bottom and has severalfull length T-slots for mounting visesor other work holding fixtures.

A dial graduated in thousandths ofan inch is provided to allow for accu-rate table movement and placement.The table feed screw usually has an

Acme thread.Milling machines with

vertical spindles (see Fig.13.3a), are available in alarge variety of types andsizes. The head, whichhouses the spindle, motor,and feed controls, is fullyuniversal and can be placedat a compound angle to thesurface of the table. Theram, to which the head isattached, can be moved for-ward and back and locked inany position. A turret on topof the column allows thehead and ram assembly toswing laterally, increasing

the reach of the head of the machine.Some ram-type milling machines

can be used for both vertical and hori-zontal milling. On ram-type verticalmills that have the motorin the column, power istransmitted to the spindleby gears and splined shafts.Some heavy duty verticalmills have a spindle andhead assembly that can bemoved only vertically byeither a power feed mecha-nism or manually. Theseare generally known asover arm-type verticalmilling machines.

13.2.2 Bed-Type Milling MachinesHigh production calls forheavy cuts, and the rigidityof a knee and column typeof milling machine maynot be sufficient to take thehigh forces. A bed-type

milling machine is often ideal for thiskind of work. In this machine the tableis supported directly on a heavy bed,while the column is placed behind thebed. A CNC bed-type milling machineis shown in Figure 13.5. and an opera-tional set-up with three spindles isshown in Figure 13.6.

There are several advantages of thebed-type machine, particularly for pro-duction runs. Hydraulic table feeds arepossible; the hydraulic components be-ing housed in the bed casting. Thisallows very high feed forces; variablefeed rates during any given cut, andautomatic table cycling. The spindlemay be raised or lowered by a cam andtemplate arrangement to produce spe-cial contours. The basically heavierconstruction allows more power to besupplied to the spindle, which giveshigher productivity through fastermetal removal. Duplex bed-type mill-ing machines have two columns andspindles for milling two surfaces on apart simultaneously. A large 5-axisCNC bed-type milling machine isshown in Figure 13.7.

The chief disadvantage of a bed-typemilling machine compared to one ofthe knee and column type is that it isless versatile for machining smallparts. Its advantages lie in its higherproductivity, its adaptability to largesized machines, and its ease of modifi-cation to special applications.

13.2.3 Special Purpose Milling MachinesAs industrial products have become

FIGURE 13.5: CNC bed type milling machine. (Courtesy WMW Machinery Co.,Inc.)

FIGURE 13.6: Machining operation showing a bed-type milling machine with three heads (Courtesy:Cincinnati Machine)

FIGURE 13.7: Large 5-axis CNC bed type millingmachine. (Courtesy Ingersoll Milling Machine Co.)



more complex, new and unusual varia-tions of the more common millingmachines have been developed. Theobjectives are to accommodate largerwork, make many duplicate parts, lo-cate holes and surfaces precisely, or todo other unusual machining jobs.

Planer-Type Milling Machines:The general arrangement of these typesof machines is similar to that for plan-ers (Chapter 7), except that in place ofindividual tool bits, milling heads areinstalled. The table of the machinecarries the work past the rotating cutterheads, which are individually poweredand can be run at different speeds ifnecessary. As many as four cutterheads can be used, with two mountedon the cross rail and two on the verticalpillars. An illustration of a planer typemilling machine is shown in Figure13.8a. A part being machined on a

planer-type milling machine is shownin Figure 13.8b.

Planer-type machines are usedmostly for machining parts like thebedways for large machine tools, andother long workpieces that require ac-curate flat and angular surfaces orgrooves.

Profile Milling Machines: Twodimensional profiling can be done byusing a template, or with a numericallycontrolled vertical milling machine.Some profilers have several spindles,and a number of duplicate parts can beproduced in each cycle. Hydraulic-typeprofilers have a stylus that is broughtinto contact with the template to startthe operation. The operator thenmoves the stylus along the template,causing hydraulic fluid under pressureto flow to the proper actuating cylin-ders. The table moves the work past

the cutter, duplicat-ing the shape of thetemplate. A profilemilling operation isshown, using a ball-nosed milling cutter,in Figure 13.9a. A 5axis, multi-spindleprofile milling ma-chine is shown inFigure 13.9b.

Die sinking andother processes in-volving the machin-ing of cavities canbe done on three-di-mensional profilers.An accurate patternof the cavity is made

of wood, plaster, or soft metal. Thestylus follows the contour of the pat-tern guiding the cutter as it machinesout the cavity. Numerically controlledmilling machines are also used for thistype of work.

13.3 Computer Controlled Machining SystemsSeveral of the standard machines dis-cussed in previous chapters of this textare capable of performing multiple op-erations. A lathe for example is ca-pable of turning, facing, drilling,threading, etc. A drilling machine iscapable of drilling, reaming, counter-sinking, tapping, and so on.

However, when increased produc-tion rates require the purchase of addi-tional machining capability, it is al-most always more economical and fea-sible to purchase multifunctional ma-

FIGURE 13.8: (a) Illustration of a planer-type milling machine. (Courtesy Kennametal

Inc.) (b) Part being machined on a planer-type milling machine. (Courtesy Ingersoll

Milling Machine Co.)

(a)

(b)

FIGURE 13.9a: Profile milling operation is shown,using a ball-nosed end milling cutter. (CourtesyIngersoll Milling Machine Co.)

FIGURE 13.9b: A large 5-axis multispindle profile millingmachine. (Courtesy Cincinnati Machine)



chines capable of quickchanges, simultaneousmachining, and automaticprocessing.

The term “Automation”was coined in the 1950’sand applied to devicesthat automatically loadand unload parts. Theterm is now accepted to cover, in addi-tion to loading and unloading, func-tions such as processing, measuringworkpiece size, adjusting a machine tomaintain size, and repeating ofworkpiece cycles.

Computer Controlled Manufactur-ing Systems discussed here will beMachining Centers and Flexible Ma-chining Systems.

13.3.1 Machining CentersMachining centers are designed andbuilt to provide for flexible manufac-turing. They can be used to machinejust a few parts or large productionruns. Programming can be relativelysimple and the use of ‘canned’ cyclesprovides a great deal of versatility. AnNC machining center by definition isable to perform milling, drilling, andboring cuts and has either indexing

turret tool holders or provides for auto-matic tool change. A tool holdermagazine is shown in Figure 13.10

Machining centers are built in eitherhorizontal or vertical configuration.

The relative merits of each will bediscussed briefly.

Horizontal Machines: Horizontalmachines tend to be advantageous forheavy box-shaped parts, such as gearhousings, which have many featuresthat need to be machined on the sidefaces. The horizontal machine easilysupports heavy workpieces of this type.If a rotary indexing worktable is added,four sides of the workpiece can bemachined without re-fixturing.

Pallet systems used to shuttle piecesin and out of the workstation tend to beeasier to design for horizontal ma-chines, where everything in front of themain column is open and accessible. Ahorizontal machining center with apallet shuttling system is shown inFigure 13.11.

Vertical Machines: Vertical ma-chining centers are often preferred forflat parts that must have through holes.Fixtures for these parts are more easilydesigned and built for a verticalspindle. Also, the thrust of the cutdeveloped in drilling or in millingpockets can be absorbed directly by thebed of the machine. The motions of a 3and 5-axis CNC vertical machiningcenter are shown in Figure 13.12.

The vertical machine is preferredwhere three-axis work is done on asingle face as in mold and die work.The weight of the head of a verticalmachine as it extends away from thecolumn, particularly on large ma-chines, can be a factor in maintainingaccuracy, as there may be some ten-dency for it to drop and lose accuracyand cause chatter. A vertical machin-ing center is shown in Figure 13.13and a machining center with an adjust-able head, tool change magazine and apallet system is shown in Figure 13.14

FIGURE 13.10: Preset machining center tools are stored in a toolholder magazine.(Courtesy Kennametal Inc.)

FIGURE 13.11:Horizontal machining

center with pallet shuttlingsystem. (Courtesy

Cincinnati Machine)

(a) (b)FIGURE 13.12: The motions of (a) a 3-axis CNC vertical machining center and (b)a 5-axis CNC vertical machining center. (Courtesy Kennametal Inc.)



13.3.2 Flexible Machining SystemsFlexible machining systems employone or more machining centers, usu-ally along with other equipment, toproduce medium-volume workpieces.A workpiece-handling system is re-quired, and a central computer typi-cally controls the entire arrangement.A flexible machining system is shownin Figure 13.15.

Material Handling: Parts aremoved from storage and between ma-chine elements by means of one ofseveral different types of systems. Thematerial-handling system selectedmust be capable of routing any part toany machine in any order and also toprovide a bank of parts ahead of eachmachine to realize maximum produc-tivity. Parts are normally loaded andunloaded manually.

The various types of material-han-dling systems used include: automatedguided vehicles, towline systems, rollerconveyer systems, overhead conveyer

systems, monorails, cranes and robots.An FMS material-handling system isshown in Figure 13.16.

Control Systems: The computercontrols of flexible machining systemshave three functional levels

Master Control – The master controlmonitors and controls the entire sys-tem, including routing workpieces toappropriate machines, schedulingwork, and monitoring machine func-tions.

Direct Numerical Control – A DNCcomputer distributes appropriate pro-grams to individual CNC machinesand supervises and monitors their op-erations.

Element Control – The third andlowest level of control is

computer control of the machining

cycles of individual machines.

13.4 Milling Machine Attachments and AccessoriesMany accessories have been developedfor milling machines. Some are spe-cialized and can be used for only a fewoperations. Others, such as vises, ar-bors, and collets, are used in almost allmilling operations.

13.4.1 Special Milling HeadsSeveral types of special heads havebeen developed for use on horizontal orvertical milling machines. These ac-cessories increase the versatility of themachine. For example, a vertical headcan be attached to a conventional hori-zontal column and knee milling ma-

FIGURE 13.13: Transparent rendition of a verticalmachining center. (Courtesy Monarch Machine Tool)

FIGURE 13.14: Machining center with adjustable head, toolmagazine and pallet system (Courtesy Cincinnati Machine)

FIGURE 13.15: Flexible machiningsystem. (Courtesy Sandvik CoromantCo.)

FIGURE 13.16: FMS material-handling system. (Courtesy Giddings +Lewis LLC)



chine, greatly increasing its usefulness,especially in small shops with a limitednumber of machines.

Vertical Heads: Vertical heads aregenerally attached to the face of thecolumn or to the overarm of a horizon-tal milling machine. The head is asemi-universal type, which pivots onlyon the axis parallel to the centerline ofthe spindle, or it is fully universal.Fully universal heads can be set to cutcompound angles. Both types of headsare powered by the spindle of the mill-ing machine and accept standard ar-bors and collets. A universal millinghead attachment is shown in Figure13.17a.Figure 13.17b shows a univer-sal milling head attachment being usedon a horizontal milling machine.

Rack-Milling Attachment: Therack-milling attachment bolts to thespindle housing of the milling ma-chine. Its spindle is at a right angle tothe main spindle of the machine. Bothspur and helical racks can be milledwith this attachment, and it can also beused to mill worms. Some rack-mill-ing attachments have an outboard sup-port for the spindle, which makes itpossible to take heavier cuts.

Slotting Attachment: This attach-ment that is bolted to the column of ahorizontal milling machine can beswiveled 90 degrees in either directionfrom the vertical position. It is usedprimarily in toolmaking and prototypework for cutting keyways, internalsplines, and square or rectangular cavi-ties. The crank that actuates the recip-rocating slide is driven directly by thespindle, and the stroke is adjustable.

High Speed Attachment: Whenspindle speeds beyond the operating

range of the machine are necessary,high speed attachments can be placedon both horizontal and vertical millingmachines. A gear train is generallyused to step up the speed as much as 6to 1, which allows more efficient use ofsmall cutters.

13.4.2 Vises and FixturesIn all milling operations, the work isheld by fixtures, vises, or clampingarrangements. In most cases the workis held stationary in relation to thetable while it is being machined, butwork held in indexing heads and rotarytables can be moved in two planeswhile machining operations are inprogress.

Plain Vise: Plain milling vises (Fig.13.18a) are actuated by an Acmethreaded screw, and the movable jawmoves on either a dovetail or rectangu-lar slide. The vises are usually cast ofhigh grade gray cast iron or ductileiron and can be heat treated. Steel keysare attached in slots machined into thebottom of the vise, parallel with andperpendicular to, the fixed jaw to allowaccurate placement on the millingtable. The jaw inserts are usually heattreated alloy steel and are attached bycap screws. The jaw width and maxi-

mum opening classify vises of thistype. Cam-operated plain milling visesare widely used in production workbecause of the savings in time andeffort and the uniform clamping pres-sure that can be achieved.

Swivel-Base Vise: A swivel-basevise is more convenient to use than theplain vise, although it is somewhat lessrigid in construction. The base, whichis graduated in degrees, is slotted forkeys that align it with the T-slots in thetable. The upper part of the vise is heldto the base by T-bolts that engage acircular T-slot. The swivel-base vise,when used on a milling machine with asemi-universal head, makes it possibleto mill compound angles on aworkpiece.

Universal Vise: A universal vise(Fig. 13.18b) is used mostly intoolroom diemaking, and prototypework. The base of the vise is graduatedin degrees and held to the table by T-bolts. The intermediate part of the visehas a horizontal pivot upon which thevise itself can rotate 90 degrees. Be-cause there are several joints and piv-

FIGURE 13.17: (a) Universal millinghead attachment. (b) A universal millinghead attachment being used on ahorizontal milling machine. (CourtesyWMW Machinery Co., Inc.)

(a)

(b)

(a)

(b)

FIGURE 13.18: (a) A plain vise. (b) Auniversal vise, which is generally usedin a toolroom diemaking and protypework. (Courtesy Palmgren SteelProducts, Inc.)



ots in the vise assembly, the universalvise is usually the least rigid of thevarious types of milling machine vises.

Angle Plates: Several types ofangle plates can be used to hold workor work holding fixtures for milling(Fig. 13.19). Plain angle plates areavailable in T-slotted or blank formand are usually strong iron castings.Adjustable angle plates may tilt in onedirection only or have a swivel base.They are very useful for millingworkpieces that are irregular in shape

and cannot be held easily in avise.

Holding fixtures, that are acombination of a simpleangle plate and a collet, aresometimes used to holdround or hexagonal work formilling. The collet-holdingfixture may be manually orair operated. Both fixturescan be bolted to the millingtable in the vertical or hori-zontal position or attached toan adjustable angle plate forholding workpieces at simpleor compound angles to thetable or other reference sur-face.

Indexing Heads: The in-dexing head, also known asthe dividing head (Fig.13.20), can be used on verti-cal and horizontal millingmachines to space the cutsfor such operations as mak-ing splines, gears, wormwheels, and many other partsrequiring accurate division.It can also be geared to thetable screw for helical mill-ing operations such as cutting

flutes in twist drills and making helicalgears.

Indexing heads are of the plain oruniversal type. Plain heads cannot betilted; universal heads can be tilted tothe vertical or any intermediate posi-tion. The spindle of the indexing headcan be fitted with a chuck, or withother work holding devices, includingcollets or a center. A cross-sectionalview of an indexing head is shown inFigure 13.21.

Most indexing heads have a worm

and wheel reduction ratio of 40:1, re-quiring 40 turns of the hand crank tomake the spindle revolve once. Whenthe necessary index plates are avail-able, all divisions up to and including50 can be achieved by plain indexing.For some numbers above 50, differen-tial indexing is necessary.

In recent years, programmable pre-cision indexers have become fairlycommon in shops doing work that re-quires accurate spacing of complexhole patterns on surfaces. The indexermay be mounted with the axis of thechuck vertical or horizontal, and insome cases the chuck may be replacedwith a specially made holding fixtureor a faceplate. If necessary, a tailstockmay be used to support the end of theworkpiece. The controller is capable ofstoring a series of programs, each ofwhich may incorporate as many as 100operational steps or positions.

Rotary Table: Rotary tables (Fig.13.22) are available in a wide range ofsizes and can be used on both verticaland horizontal milling machines.Most can also be clamped with the faceat a 90 degree angle to the surface ofthe milling machine table. The face ofthe rotary table has four or more T-slots and an accurately bored hole inthe center, which is concentric with theaxis about which the table rotates.

The base of the rotary table, which

FIGURE 13.19: Adjustable-angle tables can be tiltedin one or more directions to machine irregularlyshaped parts. (Courtesy Palmgren Steel Products,Inc.)

FIGURE 13.20: Indexing heads, also called dividingheads, can be used on vertical and horizontalmilling machines. (Courtesy Cincinnati Machine)

FIGURE 13.21:Cross-sectional

view of indexinghead. (Courtesy

CincinnatiMachine)

(a)

(b)FIGURE 13.22: (a) Rotary tables can beused on both vertical and horizontalmilling machines. (b) A rotary table,that can also be tilted. (CourtesyPalmgren Steel Products, Inc.)



houses the worm drive mechanism, isgraduated in degrees, and thehandwheel can be graduated in incre-ments as small as 5 minutes or 1/12 of1 degree. On some rotary tables anindex plate may be attached to thebase.

Rotary tables can also be geared tothe table feed screw. When set up inthis manner, the rotary table can beused to make plate cams and to gener-ate a number of other irregular shapes.

13.4.3 Arbors, Collets, and Tool HoldersSeveral basic types of arbors andcollets are used to hold milling cuttersand to transmit power from the spindleto the cutter. Regardless of type, theyare usually precisely made of alloysteel and heat treated for wear resis-tance and strength.

Arbors: Arbors for horizontal mill-ing machines (Fig. 13.23) are availablein three basic types: style A, style B,and style C. A draw bolt, that goesthrough the spindle of the machine,screws into the small end of the taperand draws the arbor tightly into thetapered hole in the milling machinespindle. Power is transmitted from thespindle to the arbor by two short keysthat engage with the slots on the flange

of the arbor.Style A arbors consist of the tapered

portion that fits the spindle, the shafton which the cutter or cutters fit, thespacers, and the nut. The shaft has akeyway along its entire length. Theoutboard end of the arbor has a pilotthat fits into a bronze bushing in theoutboard support of the milling ma-chine overarm (Fig. 13.2b). One ormore cutters can be mounted on thearbor, either adjacent to each other orseparated by spacers and shims. StyleA arbors are used primarily for lightand medium duty milling jobs.

Style B arbors are used for heavymilling operations, especially where itis necessary to provide support close toa milling cutter, such as in a straddlemilling operation. One or more bear-ing sleeves may be placed on the arboras near to the cutters as possible. Anoutboard bearing support is used foreach bearing sleeve on the arbor.

Style C arbors are used to hold anddrive shell end mills (Fig. 25.25b) andsome types of face milling cutters andrequire no outboard support. In somecases, they can also be fitted withadapters for mounting other types ofcutters.

Collets: On some vertical millingmachines the spindle is bored to accept

a collet that has a partly straight andpartly tapered shank. The collet issecured by a drawbar that is screwedinto a tapped hole in the back of thecollet and tightened from the top of thespindle. Some milling machine manu-facturers offer collet arrangements thatdo not need a drawbar. Collets of thistype can be closed with a lever-oper-ated cam or with a large locking nut.Figure 13.24a shows various sizecollets and Figure 13.24b shows anumber of tool holders includingcollets and a set-up fixture.

Toolholders: Standard tool holdersare available for end mills and shellmills as shown in Figures 13.25a and13.25b respectively. For some opera-tions that require the use of tools withnon-standard shank sizes, chucks canbe used to hold the tool. These chucksare available with Morse taper orstraight shanks. Either type can beused in milling machines when theproper adapters or collets are available.

Offset boring heads (Fig. 13.26) are

Machine frame

Drawbar Arbor

SpindlenoseBearings

Detail of Arbor Mounting

FIGURE 13.23:Schematic

drawing of anarbor mounting

with drawboltused in

horizontalmilling

machines.

FIGURE 13.24: (a) Collets of various sizes. (Courtesy Lyndex Corp.) (b) Varioustoolholders with collets and a setup fixture. (Courtesy Valenite Inc.)

(a) (b)

(a)

(b)FIGURE 13.25: (a) End milling cuttertoolholders. (b) Shell end milling cuttertoolholders. (Courtesy Lyndex Corp.)



often used in vertical milling machinesfor boring, facing, chamfering, andoutside diameter turning operations.They are available with straight, Morsetaper, or standard milling machinetaper shanks and usually have threemounting holes for boring bars. Twoof the holes are usually parallel withthe centerline of the tool, and one isperpendicular to the centerline. Someboring heads have two adjustingmechanisms, and the movable slidecan be adjusted accurately in incre-ments of 0.0001 inch.

Flycutters can be used for facingoperations. The tools in cutters of thistype are adjusted so that both a rough-ing and finishing cut are taken in onepass.

13.5 Types of Milling OperationsMilling cutters are used either indi-vidually or in combinations to machinevarious surfaces as described belowand shown in Figure 13.27.

Plain Milling: Plain milling is theprocess of milling a surface that isparallel to the axis of the cutter andbasically flat. It is done on plain oruniversal horizontal milling machineswith cutters of varying widths thathave teeth only on the periphery.

Side Milling: For side milling, a

cutter that has teeth on the periphery,and on one or both sides, is used.When a single cutter is being used, theteeth on both the periphery and sidesmay be cutting. The machined sur-faces are usually either perpendicularor parallel to the spindle. Angle cut-ters can be used to produce surfacesthat are at an angle to the spindle forsuch operations as making externaldovetails or flutes in reamers.

Straddle Milling: In a typicalstraddle milling set-up (Fig. 13.27)two-side milling cutters are used. Astraddle milling operation is shown inFigure 13.28. The cutters are half-sideor plain side milling cutters, and havestraight or helical teeth. Stagger-toothside milling cutters can also be used.

The cutters cut on the inner sidesonly, or on the inner sides and theperiphery. If the straddle milling op-eration involves side and peripheral

cuts, the diameter of the two cuttersmust be exactly the same. When cut-ters with helical teeth are used, thehelix angles must be opposite.

Since straddle milled surfaces mustbe parallel to each other and are usu-ally held to close tolerances in terms ofwidth, the condition and size of thecollars and shims that separate thecutters are important. The arbor mustalso turn as true as possible to avoidcutting the workpiece undersize.

Usually, a combination of collarsand steel shims can be assembled toprovide the correct spacing betweencutters. For some production opera-tions, a special collar can be made fromalloy or medium-carbon steel, heattreated, and surface ground to length.The faces must be perpendicular to thebore and parallel to each other. Thecutters should be keyed to the arbor,and the outboard bearing supportsmust be placed as close to the cutters aspossible.

Gang Milling: In gang milling,three or more cutters are mounted onthe arbor, and several horizontal, verti-cal, or angular surfaces are machinedin one pass (Fig. 13.29). When mak-ing a gang milling set-up, several dif-ferent types of cutters can be used,depending on the job to be done. Cut-ters used for producing vertical or an-gular surfaces must be of the side-

FIGURE 13.26: Offset boring heads areoften used in milling machines forboring, facing, and chamferingoperations. (Courtesy BridgeportMachine, Inc.)

(a) Straddle milling (b) Form milling (c) Slotting (d) Slitting

FIGURE 13.27: Drawing of a milling cutter showing the difference between advanceper revolution (apr) and advance per tooth (apt).

FIGURE13.28:Conventionalor up-millingas compared oclimb or down-milling.

FIGURE 13.29:In gang milling

operations,horizontal,vertical, or

angularsurfaces aremachined in

one path.(Courtesy

SandvikCoromant Co.)



cutting type; plain milling cutters ofthe proper width can be used for hori-zontal surfaces. In some cases facemills with the teeth facing inward canbe used at one or both ends of the gangmilling set-up.

When only one wide plain helicalmilling cutter is used as part of a gangmilling set-up, the side thrust causedby that cutter should be directed towardthe spindle of the machine. If possible,interlocking cutters with opposite helixangles should be used to eliminate sidethrust and reduce the possibility ofchatter.

Because of the time and effort in-volved in setting up the milling ma-chine for gang milling, the process isused mainly for production work.Since all or almost all of the workpieceis being machined at one time, powerand rigidity are very desirable featuresin the machine being used. Everyeffort should be made to control vibra-tion, including the use of support barsthat are bolted to both the knee and theoutboard bearing support.

Form Milling: The number of par-allel surfaces and angular relationships

that can be machined by peripheralmilling is limited almost only by cutterdesign. Form cutters are expensive,but often there is no other satisfactorymeans of producing complex contoursas shown in Figure 13.27.

Slotting and Slitting Operations:Milling cutters of either the plain orside-cutting type are used for slottingand slitting operations (Fig.13.30a and13.30b). Slotting and Slitting are usu-ally done on horizontal milling ma-chines, but can also be done on verticalmills by using the proper adaptors andaccessories. Metal slitting cutters ofvarious diameters and widths are alsoused to cut slots. A number of identi-cal cutters can also be mounted on thesame arbor for cutting fins. When thethickness of the fins must be held to

close tolerances, spacers are usuallymachined and surface ground to pro-vide the necessary accuracy.

Face Milling: Face milling (Fig.13.31) can be done on vertical andhorizontal milling machines. It pro-duces a flat surface that is perpendicu-lar to the spindle on which the cutter ismounted. The cutter ranges in size andcomplexity from a simple, single-toolflycutter to an inserted-tooth cutterwith many cutting edges. Large facemills are usually mounted rigidly to thenose of the spindle. They are veryeffective for removing large amounts ofmetal, and the workpiece must be se-curely held on the milling table.

End Milling: (Fig. 13.32) Endmilling is probably the most versatilemilling operation. Many types of endmills can be used on both vertical and

(a)

(b)FIGURE 13.30: (a) Slotting operationused in the manufacturing of rotors.(Courtesy Iscar Metals, Inc.) (b) Slittingoperation to separate cast automotiveparts. (Courtesy Sandvik Coromant Co.)

FIGURE 13.31: Face milling operation.(Courtesy Valenite Inc.)

FIGURE 13.32: End milling operation.(Courtesy Valenite Inc.)

(a)

(b)FIGURE 13.33: Milling operations: (a)side and face milling cutters used tomachine various slots, (b) variousindexable milling cutters used tomachine an automotive engine block.(Courtesy Sandvik Coromant Co.)

FIGURE 13.34: Two turn milling operations. (Courtesy Sandvik Coromant Co.)

(a) (b)



horizontal milling machines. Endmills are available in sizes rangingfrom 1/32 to 6 inches (for shell endmills) and in almost any shape needed.

Milling cutters can be used individu-ally or in pairs to machine various slots(Fig. 13.33a). Many milling cutterscan also be mounted onto an arbor toperform in a gang milling operation ofautomotive engine blocks as shown inFigure 25.33b

13.6 Turn MillingTurn milling consists of a number of

different machining methods where amilling cutter machines a rotatingworkpiece. These methods are prima-rily used for machining various eccen-trically shaped parts; planes, taperedand cylindrical surfaces; grooves andinside holes.

Turn milling requires a machine toolwith certain functions and a number ofaxes. Machining centers, turning cen-ters, specially adapted lathes, millingmachines, boring mills and special-purpose machines are used. Whenother operations of turning and milling

are combined in the machines, singleset-up machining leads to advantagesof fast through-put times and flexibilityof production. Two turn milling opera-tions are shown in Figure 13.34a andFigure 13.34b.

Advantages associated with turnmilling are: capability of machininglarge and unbalanced parts which can-not be rotated at high speeds; complexsurface shapes, eccentric parts andcomponents with additional elementsthat protrude; log, unstable shafts orthin-walled parts.






Shaping and Planing



Reaming and Tapping




Lapping and Honing







Broachesand Broaching14.1 IntroductionThe broaching operation is similar toshaping with multiple teeth and is usedto machine internal and external sur-faces such as holes of circular, square,or irregular shapes, keyways, and teethof internal gears. A broach is a longmultitooth cutting tool with succes-sively deeper cuts. Each tooth removesa predetermined amount of material ina predetermined location. The totaldepth of material removed in one pathis the sum of the depth of cut of eachtooth. Broaching is an important pro-

duction process and can produce partswith very good surface finish and di-mensional accuracy. Broaching com-petes favorably with other processessuch as boring, milling, shaping andreaming. Although broaches tend to beexpensive, the cost is justified becauseof their use for high production runs.A two station broaching operation isshown in Figure 14.1.

14.2 BroachingTooling is the heart of any broachingprocess. The broaching tool is basedon a concept unique to the process -

CHAPTER 14

FIGURE 14.1: Typical broaching operation of an internal spline. (Courtesy DetroitBroach & Machine Co.)

Chap. 14: Broaches & Broaching


rough, semi-finish, and finish cuttingteeth combined in one tool or string oftools. A broach tool frequently canfinish machine a rough surface in asingle stroke. A large broach is shownin Figure 14.2

For exterior surface broaching, thebroach tool may be pulled or pushedacross a workpiece surface, or the sur-face may move across the tool. Inter-nal broaching requires a starting holeor opening in the workpiece so thebroaching tool can be inserted. Thetool or the workpiece is then pushed orpulled to force the tool through thestarter hole. Almost any irregularcross-section can be broached as longas all surfaces of the section remainparallel to the direction of broachtravel. A couple of small broachedparts are shown in Figure 14.3

14.2.1 Broaching ToolsA broach is like a single point tool withmany ‘points’ each of which cuts like aflat-ended shaper tool, although somebroaches have teeth set diagonally,called sheer cutting. The principalparts of an internal broach are shownin Figure 14.4

14.3 Broach NomenclatureFront Pilot: When an internal pullbroach is used, the pull end and frontpilot are passed through the startinghole. Then the pull end is locked to thepull head of the broaching machine.The front pilot assures correct axialalignment of the tool with the startinghole, and serves as a check on thestarting hole size.

Length: The length of a broach toolor string of tools, is determined by theamount of stock to be removed, andlimited by the machine stroke.

Rear Pilot: The rear pilot main-tains tool alignment as the final finishteeth pass through the workpiece hole.On round tools the diameter of the rearpilot is slightly less than the diameterof the finish teeth.

Broach tooth nomenclature and ter-minology are shown in Figure 14.5a.

Cutting Teeth: Broach teeth areusually divided into three separate sec-tions along the length of the tool: theroughing teeth, semi-finishing teeth,and finishing teeth (Fig. 14.4). Thefirst roughing tooth is proportionatelythe smallest tooth on the tool. Thesubsequent teeth progressively increasein size up to and including the first

FIGURE 14.2: A large broach is shown (Courtesy Detroit Broach &Machine Co.)

FIGURE 14.3: A couple of small broached parts are shown. (CourtesyDetroit Broach & Machine Co.)

Roughingteeth

Shank length

Length tofirst tooth

Cutting teeth

Front pilot Semifinishingteeth

Finishingteeth

Rear pilot

Follow rest

Pull end

FIGURE 14.4: Principal parts of a round internal-pull broach.



finishing tooth. The difference inheight between each tooth, or the toothrise, is usually greater along the rough-ing section and less along the semi-finishing section. All finishing teethare the same size. The face is groundwith a hook or face angle that is deter-mined by the workpiece material. Forinstance, soft steel workpieces usuallyrequire greater hook angles; hard orbrittle steel pieces require smaller hookangles.

Tooth Land: The land supports thecutting edge against stresses. A slightclearance or backoff angle is groundonto the lands to reduce friction. Onroughing and semi-finishing teeth, theentire land is relieved with a backoffangle. On finishing teeth, part of theland immediately behind the cuttingedge is often left straight, so that re-peated sharpening (by grinding theface of the tooth) will not alter thetooth size.

Tooth Pitch: The distance betweenteeth, or pitch, is determined by thelength of cut and influenced by type ofworkpiece material. A relatively largepitch may be required for roughingteeth to accommodate a greater chipload. Tooth pitch may be smaller onsemi-finishing teeth to reduce the over-all length of the broach tool. Pitch iscalculated so that preferably, two or

more teeth cut simultaneously. Thisprevents the tool from drifting or chat-tering.

Tooth Gullet: The depth of thetooth gullet is related to the tooth rise,pitch, and workpiece material. Thetooth root radius is usually designed sothat chips curl tightly within them-selves, occupying as little space aspossible. (Fig. 14.5b)

When designing broaches, attentionmust also be given to chip load,chipbreakers, shear angles and siderelief.

Chip Load: As each tooth entersthe workpiece, it cuts a fixed thicknessof material. The fixed chip length andthickness produced by broaching createa chip load that is determined by thedesign of the broach tool and the pre-determined feed rate.

This chip load feed rate cannot bealtered by the machine operator as itcan in most other machining opera-tions. The entire chip produced by acomplete pass of each broach toothmust be freely contained within thepreceding tooth gullet (Fig. 14.5b).The size of the tooth gullet is a func-tion of the chip load and the type ofchips produced. However the form thateach chip takes depends on theworkpiece material and hook. Brittlematerials produce flakes. Ductile or

malleable materials produce spiralchips.

Chipbreakers: Notches, calledchipbreakers, are used on broach toolsto eliminate chip packing and to facili-tate chip removal. The chipbreakersare ground into the roughing and semi-finishing teeth of the broach, parallelto the tool axis. Chipbreakers on alter-nate teeth are staggered so that one setof chipbreakers is followed by a cuttingedge. The finishing teeth complete thejob. Chipbreakers are vital on roundbroaching tools. Without thechipbreakers, the tools would machinering-shaped chips that would wedgeinto the tooth gullets and eventuallycause the tool to break.

Shear Angle: Broach designersmay place broach teeth at a shear angleto improve surface finish and reducetool chatter. When two adjacent sur-faces are cut simultaneously, the shearangle is an important factor in movingchips away from the intersecting cor-ner to prevent crowding of chips in theintersection of the cutting teeth.

Another method of placing teeth at ashear angle on broaches is by using aherringbone pattern. An advantage ofthis design is that it eliminates thetendency for parts to move sideways inthe workholding fixtures duringbroaching.

Side Relief: When broaching slots,the tool becomes enclosed by the slotduring cutting and must carry the chipsproduced through the entire length ofthe workpiece. Sides of the broachteeth will rub the sides of the slot andcause rapid tool wear unless clearanceis provided. Grinding a single reliefangle on both sides of each tooth doesthis. Thus only a small portion of thetooth near the cutting edge, called theside land, is allowed to rub against theslot. The same approach is used forone sided corner cuts and splinebroaches.

14.4 Types of BroachesTwo major types of broaches are thepush broach and the pull broach. Asecond division is internal and externalbroaches.

Push and Pull Broaches: A pushbroach must be relatively short since itis a column in compression and willbuckle and break under too heavy aload. Push broaches are often usedwith a simple arbor press if quantitiesof work are low. For medium to high

Cut per tooth(feed/tooth)

Tooth depth

Face or hook angle

Pitch

Land, or tooth width

Backoff orrake angle

(a)

Radius Gullet orchip space

(b)

FIGURE 14.5: (a)Broach tooth

nomenclature andterminology. (b)

Illustration ofhow a chip fills

the gullet duringa broaching

operation.



volume production they are used inbroaching machines.

Pull broaches (Fig. 14.4) are pulledeither up, down, or horizontallythrough or across the workpiece, al-ways by a machine. Flat or nearly flatbroaches may be pull type, or thebroach may be rigidly mounted, withthe workpiece then pulled across thebroaching teeth. Automobile cylinderblocks and heads are often faced flat bythis method. Figure 14.6 shows vari-ous broach configurations both roundand flat types.

Figure 14.1 shows a vertical splinebroaching operation; Figure 14.7shows a large spline broaching opera-tion using a horizontal broaching ma-chine.

14.4.1 Internal BroachesInternal broaches are either pulled or

pushed through a starter hole. Themachines can range from fully auto-mated multi stationed verticals, tohorizontal pull types, to simplepresses. Figure 14.8 shows a variety offorms that can be produced by internalbroaches.

Keyway Broach: Almost all key-ways in machine tools and parts are cutby a keyway broach - a narrow, flat barwith cutting teeth spaced along onesurface. Both external and internalkeyways can be cut with thesebroaches. Internal keyways usuallyrequire a slotted bushing or horn to fitthe hole, with the keyway broachpulled through the horn, guided by theslot.

If a number of parts, all of the samediameter and keyway size, are to bemachined, an internal keyway broachcan be designed to fit into the hole tosupport the cutting teeth. Only thecutting teeth extend beyond the holediameter to cut the keyway. Bushingsor horns are not required.

Burnishers: Burnishers are broach-ing tools designed to polish rather thancut a hole. The total change in diam-eter produced by a burnishing opera-tion may be no more than 0.0005 to0.001 inch. Burnishing tools, usedwhen surface finish and accuracy arecritical, are relatively short and aregenerally designed as push broaches.

Burnishing buttons sometimes areincluded behind the finishing toothsection of a conventional broachingtool. The burnishing section may beadded as a special attachment or easilyreplaced shell. These replacementshells are commonly used to reducetooling costs when high wear or toolbreakage is expected. They are alsoused to improve surface finish.

Shell Broaches: Shell broaches can beused on the roughing, semi-finishing andfinishing sections of a broach tool. Theprincipal advantage of a shell broach isthat worn sections can be removed andre-sharpened or replaced, at far less costthan a conventional single piece tool.When shells are used for the finishingteeth of long broaches, the teeth of the

FIGURE 14.6:Various broachconfigurations,both round and

flat types.

FIGURE 14.7: A large spline broaching operation using a horizontal broachingmachine. (Courtesy US Broach & Machine Co.)

Keyway

Spline

Square

Triangle

Hexagon Double D

Special shapes

FIGURE 14.8: Avariety of forms thatcan be producedwith an internalbroach.



shell can be ground to far greater accu-racy than those of a long conventionalbroach tool and the tool can continue tobe used by replacing the shell. Shellbroaches are similar to shell millingcutters that were discussed in Chapter12.

14.4.2 Surface BroachesThe broaches used to remove materialfrom an external surface are commonlyknown as surface broaches. Suchbroaches are passed over the workpiecesurface to be cut, or the workpiecepasses over the tool on horizontal, ver-tical, or chain machines to produce flator contoured surfaces.

While some surface broaches are ofsolid construction, most are of built-updesign, with sections, inserts, orindexable tool bits that are assembledend-to-end in a broach holder or subholder. The holder fits on the machineslide and provides rigid alignment andsupport. A surface broach assembly isshown in Figure 14.9a.

Sectional Broaches: Sectionalbroaches are used to broach unusual ordifficult shapes, often in a single pass.The sectional broach may be round orflat, internal or external. The principlebehind this tool is similar to that of theshell broach, but straight sections ofteeth are bolted along the long axis ofthe broach rather than being mountedon an arbor. A complex broaching tool

can be built up from a group of fairlysimple tooth sections to produce a cutof considerable complexity.

Carbide Broach Inserts: Broach-ing tools with brazed carbide broachinserts are frequently used to machinecast iron parts. Present practice, suchas machining automotive engineblocks, has moved heavily to the use ofindexable inserts (Fig. 14.9b) and thishas drastically cut tooling costs inmany applications.

Slab Broaches: Slab broaches,simple tools for producing flat sur-faces, come closest to being truly gen-eral purpose broaches. A single slabbroach can be used to produce flatsurfaces having different widths anddepths on any workpiece by makingminor adjustments to the broach, fix-ture and/or machine.

Slot Broaches: Slot broaches arefor cutting slots, but are not as generalpurpose in function as slab broaches.Adjustments can easily be made toproduce different slot depths, but slotwidths are a function of the broachwidth. When sufficient productionvolume is required however, slotbroaches are often faster and moreeconomical than milling cutters. Inbroaching, two or more slots can oftenbe cut simultaneously.

14.5 Types of Broaching MachinesThe type of broach cutting tool re-

quired for a given job is the single mostimportant factor in determining thetype of broaching machine to be used.Second in importance is the productionrequirement. Taken together, thesefactors usually determine the specifictype of machine for the job.

The type of broach tool (internal orsurface) immediately narrows downthe kinds of machines that could beused. The number of pieces requiredper hour, or over the entire productionrun, will further narrow the field.

For internal broaching, the length ofa broach in relation to its diameter maydetermine whether it must be pulledrather than pushed through theworkpiece, for a broach tool is strongerin tension than in compression. Thisin turn, helps determine the type ofmachine for the job.

The type of drive, hydraulic or elec-tromechanical, is another importantfactor in machine selection. So areconvertibility and automation. Somemachine designs allow for conversionfrom internal to surface work. Somedesigns are fully automated; others arelimited in scope and operate only withclose operator supervision.

14.5.1 Vertical Broaching MachinesAbout 60 percent of the total numbersof broaching machines in existence arevertical, almost equally divided be-tween vertical internals and verticalsurface or combination machines. Ver-tical broaching machines, used in ev-ery major area of metalworking, arealmost all hydraulically driven. Figure14.1 shows a vertical broaching opera-tion.

One of the essential features thatpromoted their development however,is beginning to turn into a limitation.Cutting strokes now in use often ex-ceed existing factory ceiling clear-ances. When machines reach heightsof 20 feet or more, expensive pits mustbe dug for the machine, so that theoperator can work at the factory floorlevel. A large vertical broaching ma-chine is shown in Figure 14.10a.

Vertical internal broaching ma-chines are table-up, pull-up, pull-down, or push-down, depending ontheir mode of operation.

Vertical Table-up: Today table-upmachines are demanded to meet thecell concept (flexible) manufacturing,where short runs of specialized compo-

(a) (b)FIGURE 14.9: (a) A surface broach assembly. (Courtesy Detroit Broach & MachineCo.) (b) A surface broach assembly with indexable carbide inserts. (CourtesyIngersoll Cutting Tools)



nents are required. Upon completionof short runs (1 - 2 years) the machinescan be re-tooled and moved to anotherarea of the plant without the problemof what to do with pits in shop floors.With this type of machine the part sitson a table that moves up while thebroach is stationary. Stroke lengthsfrom 30 to 90 inches and capacitiesfrom 5 to 30 tons are the limits for thismachine.

Vertical Internal Pull-up: Thepull-up type, in which the workpiece isplaced below the worktable, was thefirst to be introduced. Its principal useis in broaching round and irregularshaped holes. Pull-up machines arenow furnished with pulling capacitiesof 6 to 50 tons, strokes up to 72 inches,and broaching speeds of 30 FPM.Larger machines are available; somehave electro-mechanical drives forgreater broaching speed and higherproductivity.

Vertical Internal Pull-down: Themore sophisticated pull-down ma-chines, in which the work is placed ontop of the table, were developed laterthan the pull-up type. These pull-down machines are capable of holdinginternal shapes to closer tolerances bymeans of locating fixtures on top of thework table. Machines come with pull-ing capacities of 2 to 75 tons, 30 to 110inch strokes, and speeds of up to 80FPM.

Vertical Internal Push-down: Ver-tical push down machines are oftennothing more than general-purpose hy-draulic presses with special fixtures.They are available with capacities of 2to 25 tons, strokes up to 36 inches, andspeeds as high as 40 FPM. In somecases, universal machines have beendesigned which combine as many asthree different broaching operations,such as push, pull, and surface, simplythrough the addition of special fix-tures.

A special multi-station verticalbroaching machine fixture is shown inFigure 14.10b.

A vertical broaching machine withloading and unloading conveyers isshown in Figure 14.11

14.5.2 Horizontal Broaching MachinesThe favorite configuration for broach-ing machines seems now to have comefull circle. The original gear or screwdriven machines were designed ashorizontal units. Gradually, the verti-cal machines evolved as it becameapparent that floor space could bemuch more efficiently used with verti-cal units. Now the horizontal ma-chine, both hydraulically and mechani-cally driven, is again finding increas-ing favor among users because of itsvery long strokes and the limitationthat ceiling height places on verticalmachines. About 40 percent of allbroaching machines are now horizon-tals. For some types of work such as

(b)

(a)

FIGURE 14.10: (a)A large verticalbroaching machine.(b) Special multi-station verticalbroaching machinefixture. (CourtesyUS Broach &Machine Co.)

FIGURE 14.11: Vertical broaching machine with loading and unloadingconveyers. (Courtesy Detroit Broach & Machine Co.)



roughing and finishing automotive en-gine blocks, they are used exclusively.A two station internal horizontalbroaching machine is shown in Figure14.12a

Horizontal Internal BroachingMachines: By far the greatest amountof horizontal internal broaching isdone on hydraulic pull type machinesfor which configurations have becomesomewhat standardized over the years.Fully one third of the broaching ma-chines in existence are this type, and ofthese nearly one fourth are over twentyyears old. They find their heaviestapplication in the production of gen-eral industrial equipment but can befound in nearly every type of industry.

Hydraulically driven horizontal in-ternal machines are built with pullingcapacities ranging from 2 1/2 to 75

tons, the former representing machinesonly about 8 feet long the latter ma-chines over 35 feet long. Strokes up to120 inches are available, with cuttingspeeds generally limited to less than 40FPM.

Horizontal Surface BroachingMachines: This type accounts for onlyabout 10 percent of existing broachingmachines, but this is not indicative ofthe percentage of the total investmentthey represent or of the volume of workthey produce. Horizontal surfacebroaching machines belong in a classby themselves in terms of size andproductivity. Only the large continu-ous horizontal units can match or ex-ceed them in productivity. Horizontalsurface units are manufactured in bothhydraulically and electro-mechanicallydriven models, with the latter now

becoming dominant.A gear broaching operation is shown

in Figure 14.12b.The older hydraulically driven hori-

zontal surface machines now are pro-duced with capacities up to 40 tons,strokes up to 180 inches, and normalcutting speeds of 100 FPM. Thesemachines, a major factor in the auto-motive industry for many years, turnout a great variety of cast iron parts.They use standard carbide cutting toolsand have some of the highest cuttingspeeds used in broaching.

But electro-mechanically drivenhorizontal surface machines are takingover at an ever-increasing rate forsome applications, despite their gener-ally higher cost. Because of theirsmooth ram motion and the resultantimprovements in surface finish and

(a)

(b)

FIGURE 14.12: (a) Two-station internal horizontalbroaching machine. (b) Gear broaching operation.(Courtesy Detroit Broach & Machine Co.)

Workpiece

Work holder

Load manualor automatic

Unload

Work backupplate

Linked chain

Chips

Chip conveyorFloor

Broach

Broach backup plate

(b)

FIGURE 14.13: (a) Continuous chain broaching operation. (Courtesy US Broach & Machine Co.) (b) Schematic illustration of acontinuous chain broaching machine.

(a)



part tolerances, these machines havebecome the largest class of horizontalsurface broaching units built. They areavailable with pulling capacities in ex-cess of 100 tons, strokes up to 30 feet,and cutting speeds, in some instances,of over 300 FPM.

14.5.3 Chain Broaching Machines These have been the most popular typeof machine produced for high-produc-tion surface broaching. The key to theproductivity of a continuous horizontalbroaching machine is elimination ofthe return stroke by mounting theworkpieces, or the tools, on a continu-ous chain (Fig. 14.13a)

Most frequently, the tools remain sta-tionary, mounted in a tunnel in the tophalf of the machine, and the chainmounted workpieces pass underneaththem. A schematic of a chain-broachingmachine is shown in Figure 14.13b.

14.6 Turn-BroachingTurn-broaching is an efficient methodfor machining steel and nodular castiron crankshafts. Special turn-broach-ing machines are available for linear,circular and spiral operating methods.The peripheral type cutter assembliesare built in segments as shown inFigure 14.14b.

The turn-broaching systems basi-cally use similar standardized compo-nents for roughing and finishing. Thetype of machine determines the tooldesign: linear, circular or spiral. Thenumber of segments and roughing in-serts in the tool depend on the stockremoval rate required. The finishingsegments are fitted with inserts in ad-justable cartridges that can be set toclose tolerances. The segment forroughing has fixed insert pockets. Aturn-broaching operation of a crank-shaft is shown in Figure 14.14a.

(b)

(a)

Tool segments are computer de-signed and manufactured for each ma-chine to suit the required form andtolerance of each crankshaft. Thenumber of inserts and positions of eachsegment are designed to give low cut-ting forces. The roughing segmentshave hardened, fixed insert seats andbig chip pockets. Inserts are tangen-tially mounted and locked in positionby a center screw. A turn-broach cutterassembly is shown in Figure 14.14b.

Long tool life results due to the shortengagement of the individual cuttingedges. High machine utilization isobtained because the finishing cuttersneed only be changed once per shiftand the roughing cutters about onceevery third shift.

FIGURE 14.14: (a)Turn-broaching

operation of acrankshaft. (b) Turn-

broach cutter assembly.(Courtesy Sandvik

Coromant Co.)

2 Tooling & Production/April 2002 www.toolingandproduction.com







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15.2 SawingSawing is a process where a nar-

row slit is cut into the workpiece by atool consisting of a series of nar-rowly spaced teeth called a sawblade. Sawing is normally used toseparate work parts into two or morepieces or to cut off an unwantedsection of a part. These processes areoften called cut-off operations andsince many manufacturing projectsrequire cut-off operations at somepoint of the production sequence,sawing is an important manufactur-ing process.

Sawing is basically a simple pro-cess. As the blade moves past the work,each tooth takes a cut. Depending onthe thickness or diameter of the work,the number of teeth cutting at one timevaries from 2 to 10 or more. Saws maybe of the continuous cutting (band orrotary) or reciprocating type. A typicalsawing operation is shown in Figure15.1.

The cutting speeds and characteris-tics of the materials must be under-stood before the proper blades andoperating conditions can be selected.Saws are an effective and efficient

category of machine tools found inalmost every type of machine shop.

15.3 Saw BladesAll saw blades have certain common

characteristics and terminology. Someof these terms are shown in Figure15.2, and others are explained below.

Rake Angles: Rake angles are 0degrees or neutral rake on most sawblades. Some have a positive rakeangle as shown in Figure 15.2a.

Width: The width of a saw blade isits total width including the teeth.

Set: The set of a saw blade meansthe offsetting of some teeth so that the





Shaping and Planing



Reaming and Tapping




Lapping and Honing

Upcoming Chapters

FIGURE 15.1: Typical sawing operation.(Courtesy: Clausing Industries, Inc.

15.1 IntroductionOnce sawing was considered a secondary machining process and saws were usedmostly for cutting bar stock in preparation for other machining operations. Inrecent years, the development of new types of saws and better blade materialshave made metal sawing a much more effective, versatile and economicalprocess. In many cases bandsaws are now being used as the primary means ofshaping certain types of metal parts.

When the proper sawing machines and blades are used, sawing is one of themost economical means of cutting metal. The saw cut (kerf) is narrow, andrelatively few chips are produced in making a cut. When a bandsaw is used forcutting the contours of complex shapes, only a small portion of the metal isremoved in the form of chips. Therefore, the power used in removing largeamounts of waste metal is at a minimum.



Chap. 15: Saws and SawingChap. 15: Saws and Sawing

back of the blade clears the cut. The‘raker’ set is most frequently used andis furnished with all hacksaws andband saws unless otherwise specified.(See Fig. 15.2b)

Kerf: The kerf is the width of thecut made by the saw blade or thematerial cut away. The thickness of theblade is called the gage.

Pitch: The pitch of a saw blade isthe distance between the tops of twoadjacent teeth. This is specified inteeth per inch.

15.3.1 Saw Blade MaterialSaw blades are made from various

materials as explained below:Carbon Steel: General utility for

small lot, low speed work. The leastexpensive blade, these may have a hard‘back’ for greater wear.

High Speed Steel: This costs two tothree times as much as carbon steel,but it is much longer wearing and is anecessity for the ‘difficult-to-machine’metals.

High Speed Edge: This is a carbonsteel blade, which has a narrow stripwith HSS teeth welded on. This is atough blade, intermediately priced, andwidely used for most materials.

Tungsten Carbide Tipped Blades:Available in a few sizes. Used only onlarge, very rigid sawing machines forhigh production sawing of difficultmaterials.

15.3.2 Saw Blade SelectionThe process of choosing the best

bandsaw blade for a particular jobmust start with an evaluation of thematerial to be cut. Such factors ashardness, machinability, cross-sec-tional shape and area must be consid-ered.

After the material to be cut has beenproperly identified, the selector on themachine can be used to help select the

proper bladeand cuttingspeed, Tablesand selectorsare helpful,but the opera-tor often mustmake choicesthat affect thethree variablespresent in ev-ery sawing op-

eration: cutting rate, tool life, and ac-curacy. Generally, increasing any onevariable results in a decrease in one orboth of the others. For example, anincrease in cutting rate always reducestool life and may affect accuracy,

15.3.3 Saw Blade WeldingPractically all vertical metal-cutting

band-saws have an attachment forelectrically butt-welding blades. It isusually set on the column of the ma-chine at the operator‘s left and consistof a blade cutter, a small grindingwheel, and the butt welding machine.The blade welding attachment can beused for making saw bands from bulksaw-blade stock or for welding bandsthat have been cut and inserted into ahole in a workpiece that is to be band-sawed internally.

The importance of making goodwelds in saw blades couldn’t be over-emphasized. Breakage caused by poorwelding, improper joint finishing, or

improper heat treatment is time con-suming and potentially dangerous.

Butt Welder: The resistance-typebutt welders found on almost all verti-cal bandsaws operate by causing elec-trical current to flow through the endsof the bandsaw blade while pressure isbeing applied. The high resistancewhere the blade ends meet causes themetal to become white-hot momen-tarily, and the blade ends fuse. Provi-sion is made for annealing (softening)the welded joint. As the operatorpresses the anneal button for a veryshort time, current flows through thecompleted joint until the joint heats toa dull red. The joint then anneals as itcools slowly.

15.4 Sawing EquipmentIn most sawing operations, the work

is held stationary and the saw blade ismoved relative to it. As shown in Fig-ure 15.3, there are three basic types ofsawing operations, according to thesaw blade motion involved:

15.4.1 HacksawingHacksawing involves a linear recip-

rocating motion of the saw against theworkpiece. This method of sawing isoften used in cut-off operations. Cut-ting only takes place on the forwardstroke of the saw blade. Due to thisintermittent cutting action,hacksawing is less efficient than othersawing methods. Hacksawing can be

Tooth backclearance angle

Toothback(flank)

Toothface Tooth rake

angle (positive)

Gullet depth

Back edge

Width

Toothspacing

Straight tooth

Raker tooth

Wave tooth

Toothset

(a) (b)

Hydraulic or gravity pressure

Workvise

Cutting Direction

Cutting direction

Reciprocating Blade Hacksaw

Eccentricdrive

Hydraulic orgravity pressure

Work vise

Continuous Band Cutoff Saw

Blade guides

Hinge point

(a)

(c)

Blade guide

Work table

Resistanceblade welder

Drive wheel

(b)

FIGURE 15.2: Saw blade characteristics and terminology.

FIGURE 15.3: Three basic types of sawing operations: (a) hacksawing, (b) verticalbandsawing, (c) horizontal bandsawing.


Chap. 15: Saws and Sawing

done manually or with a power hack-saw. A power hacksaw provides a drivemechanism to operate the saw blade ata desired speed and feed rate. (Fig.15.3a)

Power Hacksaw: The power hack-saw is the original and least expensivesaw for the work. As shown in Figure15.4a, these saws work the same as ahand hacksaw: They cut on the forwardstroke and then lift slightly so that theblade does not drag on the returnstroke.

The size of a power hacksaw is thecross section of the largest piece ofstock that it can cut. Typical sizes are 6x 6 inches to 24 x 24 inches. Themotors used will vary from 1 to 10horsepower.

The speed of these saws is in strokesper minute. This may be from 30strokes per minute for large cuts withheavy saws on difficult materials, up to165 strokes per minute on carbon

steels and nonferrousmaterials. The hacksawusually has four to sixdifferent speeds avail-able.

Feed may be a posi-tive advance per strokeor may be gaged by afriction or pressuredrive. The smallerpower hacksaws feedabout 0.006 inches perstroke and the largerones 0.012 to 0.030inches per stroke. Feedpressures will be 450 to750 pounds on theblades. Work is held ina built-in vise, which

may be hand or power operated.Automatic power hacksaws (Fig.

15.4b) will feed the stock a presetlength, clamp the vise, cut off, andraise the saw for the next cut, all withpreset gages and limit switches. Thesewill cut accurate lengths to within0.010 inches or less. They are, ofcourse, expensive and so they would beused only if a large amount of work isto be done.

15.4.2 BandsawingBandsawing involves a linear con-

tinuous motion, using a bandsaw blademade in the form of an endless loop.The band saw provides a pulley-likedrive mechanism to continuously moveand guide the bandsaw blade past thework. Bandsaws are classified as verti-cal or horizontal. This designation re-fers to the direction of saw blade mo-tion during cutting. Vertical bandsawsare used for cut-off and other opera-tions such as contouring and slotting.Horizontal bandsaws are normallyused for cut-off operations as alterna-tives to power hacksaws. (Fig. 15.3band Fig. 15.3c)

Vertical Bandsaws: All verticalbandsaws, regardless of whether theyare light, mediums, or heavy-duty ma-chines, are made up of certain basiccomponents. Although these majorparts of the machine may be made bydifferent methods, depending on themanufacturer, their function is essen-tially the same. A typical verticalbandsaw is shown in Figure 15.5a.

Vertical bandsaws are available insizes and configurations ranging from

light-duty hand-fed machines toheavy-duty machines with power feedtables. The light-duty machines usu-ally have two wheels and are driventhrough a variable speed belt drive, Vbelts and step pulleys, or some othertype of speed change mechanism.Blades ranging from 3/16 inch to 5/8inch in width can be used on light-dutymachines.

Table Types: The table of the verti-cal metal cutting bandsaw is usuallymade of cast iron and fitted with atilting mechanism so that simple or

compound angle cuts can be made. Onfixed-table machines, the table does notmove with the work, but can be tilted 45degrees to the right and 10 degrees tothe left on most machines. The workcan be fed and guided manually, or aweight operated feed mechanism can beused to supply the feed pressure.

FIGURE 15.5a: Typical vertical band-saw. (Courtesy: Clausing Industries,Inc.)


FIGURE 15.5b: High-production auto-mated vertical bandsaw table machine.(Courtesy: Armstrong-Blum Mfg. Co.)

FIGURE 15.4a: Semiautomatic power hacksaw.

FIGURE 15.4b: Automatic power hack-saw used in high-production sawing.(Courtesy: Kasto-Racine, Inc.)



Vertical bandsaws with power tablesare generally heavy-duty machines.The feed pressure is provided by themechanism that moves the table; theoperator can vary the feed rate.

There is usually enough power avail-able to make effective use of high-speed steel or tungsten carbide sawblades rather than the high carbon steelblades used on light-duty machines.Coolant systems are also widely usedon power table machines, thus allow-ing higher cutting speeds and higherfeed rates along with longer blade life.Many types of fixtures can be used onpower table machines, particularlywhen they are used for repetitive op-erations. A high production automatedtable machine is shown in Figure15.5b.

Accessories: Most bandsaws that donot have a coolant system have an airpump that directs a stream of air at thepoint where the blade is cutting theworkpiece. This removes the chips,letting the operator see the layout linesclearly, and provides some cooling.

If the machine has a fluid coolantsystem, the tank and pump are usuallylocated in the base. A separate switchcontrols the pump. Coolant systemsare usually found on medium andheavy duty vertical bandsaws.

Blade welding attachments, whichare a specialized form of electricbutt-welding machines, are a stan-dard accessory on almost allbandsaws. The blade welder usuallyconsists of cast copper or bronzeblade clamps, a grinder, a saw thick-ness gage, and the necessaryswitches and operating levers.

Weight operated feed devices can beused on bandsaws not fitted withpower feed attachments. This reducesoperator fatigue and generally results

in more uniformfeed rates andlonger blade life.

Other attach-ments such as fix-tures for cuttingarcs and circles,ripping fences, andmiters, are used ex-tensively onbandsaws. Specialfixtures for holdingspecific types ofworkpieces are of-ten designed for usein mass productionapplications.

Horizontal Bandsaws: Becausehorizontal bandsaws are used primarilyfor cutting bar stock and structuralshapes, they are also known as cut-offsaws. The band-type cut-off saw iswidely used because it is easy to set upand takes a narrow saw cut, thus re-quiring less power to operate and wast-ing less material. The cutting action iscontinuous and rapid. The blade issupported close to either side of thematerial being cut, so the cut is accu-rate if the machine is properly adjustedand the blade is in good condition. Atypical horizontal bandsaw is shown inFigure 15.6a.

Horizontal bandsaws range in ca-pacity from small, fractional horse-power machines, (Fig. 15.6a), to largeheavy-duty industrial saws, as shownin Figure 15.6b.

The saw guides are an importantfactor in accurate cut-off operations.The saw blade has to twist as it leavesthe idler pulley and the guides makethe blade travel perpendicular to thematerial being cut. Tungsten carbideinserts help minimize wear. Figure15.7 shows a more advanced horizon-

FIGURE 15.6a: Typical horizontalbandsaw. (Courtesy: Clausing Indus-tries, Inc.)

FIGURE 15.5b: Large, heavy-duty industrialhorizontal bandsaw. (Courtesy: Armstrong-Blum Mfg. Co.)

FIGURE 15.7: Horizontal Band Saw with automated tablestock feeding system (Courtesy: Kasto-Racine, Inc.)

tal band saw with an automated tablestock feeding system.

Controls and Accessories: On lightduty saws, the controls are simple,consisting mainly of an off-on switch,a means for changing blade speed, andpossibly a control for feed pressure. Onthe larger machines a control panel isusually mounted on the saw head. Itconsists of the necessary switches,valves, and instruments that indicateblade speed in feet per minute, feedrate in inches per minute, and otherfactors, such as blade tension. Somemachines used for production work arecapable of fully automatic operationand can be preset to cut a given num-ber of pieces of work. A counter isusually part of the instrumentation onsemiautomatic and automatic ma-chines.

There are coolant systems on almostall medium and heavy duty horizontalbandsaws. The coolant extends bladelife and allows higher cutting speedsand metal removal rates. The operatorcontrols the rate of coolant flow. Solidlubricants such as wax or grease canalso be used. Wax in stick form is

usually applied manually to theblade on light-duty machines.

15.4.3 Comparison ofHacksaws and Band Saws

The decision as to which typeof cut-off saw to buy is ofteninfluenced by custom or habit.However, there are definite fac-tors that can be considered.

Cost: A hacksaw is much lessexpensive, often about half thecost of a band saw of equal sizeand power.




Saw blades: The hacksaw bladesmay cost one-half to one-quarter thecost of a band-saw blade. However, thehacksaw will become dull in one-halfto one-quarter the number of cuts thatthe band saw will make.

The hacksaw blade is almost un-breakable and is somewhat less likelyto have its teeth stripped off by hardspots in the material being cut.

Kerf: The band-saw blade is thinnerthan the hacksaw blade, especially forthe larger sizes. Thus less metal iswasted in the cut. However, this ‘sav-ing’ is often lost because of the 2 to 6inch long ‘stub end’, which is throwninto the scrap, bin when the bar ofstock is used up.

Speed: The band saw will cut offstock up to twice as fast as the hack-saw. However, it does take more careand more time to change blades, adjustsaw guides, and regulate feeds. Thus,the plain hacksaw can be used by lessexperienced operators.

15.5 Band Sawing OperationsThe types of work described here

accounts for most of the band sawingoperations used in metalworking.

15.5.1 Cut-off SawingAlthough cut-off sawing can be

done on any type of vertical or hori-zontal bandsaw, the majority of cut-off

sawing is done onpowerful horizontalmachines. A varietyof work-holdingdevices and fix-tures can be used tohold tubing, angleiron, and othershapes.

Blade selectionis important interms of economyand the finish onthe material beingcut. The precisiontooth type blade isused extensivelywith the recommended pitch rangingfrom 10 teeth per inch for sections upto 3/8 in. thickness to 4 teeth per inchfor material over 3 in. thick. Manufac-turers’ manuals should be consultedwhen heavy cuts are being attempted.The claw tooth type of blade is usedwhen cutting some tough steels be-cause the tooth penetrates the surfaceof the work more easily.

Stock feeders are often used on cut-off machines, along with an indexingmechanism that allows the operator toautomatically repeat cuts of pre-se-lected lengths. Almost all cut-off op-erations are done with a liquid coolantdelivered to the saw cut by a pump.

15.5.2 Contour SawingContour sawing, both internal and

external, is one of the most versatileoperations that can be done with abandsaw. It may range from simpleshapes cut on a fractional horsepowermachine to complex internal cutsmade with tilting table machines.Blade selection is important when cut-ting complex contours, especiallywhen small radii or corners are in-volved. Select the widest blade thatwill allow turns of the proper radius.

For internal work, a hole must bedrilled so that the blade can be passedthrough it and re-welded. For plaincontouring, the hole is drilled perpen-dicular to the face of the workpiece.When the internal shape has corners,holes must be drilled at the corners sothat the blade can be turned and the cutstarted in another direction.

15.5.3. Friction SawingFriction sawing is a unique process.

A bandsaw blade with dull teeth travel-ing at very high speed, 6000 to 15000SFPM (surface feet per minute), isused to cut both hard and soft ferrousmetals. Friction sawing works particu-larly well on metals that have poor heatconductivity because the heat-affectedzone remains very small. It is thefastest method of cutting ferrous met-als less than 1 in. thick.

As the blade contacts the work, themetal at the point of contact immedi-ately becomes white hot and is carriedout by the teeth. The blade itself re-mains relatively cool because duringits operating cycle it is in contact withhot metal for only a short time.

FIGURE 15.8: Semi-automatic CircularSaw (Courtesy: Clausing Industries, Inc.)

FIGURE 15.9: Automated Band Saw with computer-controlledfunctions (Courtesy: Kasto-Racine. Inc.)

FIGURE 15.10: Typical cold saw.(Courtesy: Clausing Industries, Inc.)




15.6 Circular SawingCircular sawing uses a rotating saw

blade to provide a continuous motionof the tool past the work. Circularsawing is often used to cut long barsand tubes to specific lengths. The cut-ting action is similar to slot milling,except that the saw blade is thinner andcontains more cutting teeth. Circularsawing machines have power spindlesto rotate the saw blade and a feedingmechanism to drive the rotating bladeinto the work. Figure 15.8 shows asemi-automatic circular saw.

Band as well as circular saws haveadvanced to be highly automated andmany of their functions are computercontrolled as shown in Figure 15.9.

15.7 Cold Sawing: Most cold saws, regardless of size,

consist of a base; drive mechanism,blade arbor, vise, feed mechanism, andnecessary guards and switches. Onsome small saws the blade is fed intothe work by hand (Fig. 15.10).

On larger machines the feed mecha-nism is pneumatically or hydraulicallyoperated. The operator controls therate of feed. (Fig. 15.11).

The base of the machine or the visecan be swiveled to make angular cuts.In some cases two machines can be setup on a single work stand for produc-tion operations.

15.7.1 Cold SawBlades

Blades smallerthan 18 inches in di-ameter are cut di-rectly in the rim ofthe saw disk. For cut-ting soft materials,the teeth are spacedfarther apart, as inthe case of bandsawand power hacksawblades, so that thegullet (the space be-tween the teeth) willbe large enough toaccommodate largechips. When cuttingthin tubing or otherthin materials usesaw blades withclosely spaced teethto avoid chatteringand tooth breakage.Cold saw blades withteeth cut directly onthe periphery of the disk may be madeof high carbon or high-speed steel.

Larger blades usually have seg-mented teeth. The body of the blade ismade of rough, resilient alloy steel,and the inserted teeth are made ofhigh-speed steel or tungsten carbide.The individual teeth or segments ofthree or four teeth are wedged or riv-eted to the blade and can be easilyreplaced if a tooth is damaged or bro-ken. Larger cold saw blades can cut akerf as wide as 1/4 inch and removemetal rapidly.

15.8 Abrasive Cut-Off MachinesAbrasive cut-off machines are used

in many shops to cut metallic andnonmetallic materials. Because anabrasive - usually aluminum oxide - isused as the cutting tool, hardened steelcan be cut without being annealed. Thecutting action here is faster than onother types of cut-off machines.

Abrasive cut-off machines may be of

FIGURE 15.11: Large, heavy-dutyindustrial cold saw. (Courtesy: Claus-ing Industries, Inc.)

FIGURE 15.12: Abrasive cut-off operation (Courtesy:Norton Company)


the wet or dry type. The flow of cool-ant, usually water and an antirustchemical of some type are controlledby the operator. The coolant tank isseparate or built into the base of themachine.

Some larger cut-off machines havepower feed mechanisms and oscilla-tors. The oscillator moves the abrasivedisk back and forth in the cut as feedpressure is applied. This reduces theamount of blade in contact with thework at any given time and reduces thepower input required to cut solid barstock of a given cross-sectional area.An abrasive cut-off operation is shownin Figure 15.12.

The abrasive disks usually have aresinoid bonding agent, although rub-ber can be used on smaller wheels.Glass fiber is sometimes impregnatedin the disk to increase its strength.Abrasive disks work efficiently at sur-face speeds of 12,000 to 15,000 sur-face feet per minute.








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Shaping and Planing



Reaming and Tapping




Lapping and Honing

Upcoming Chapters

16.2 Grinding WheelsGrinding wheels are composed of

thousands of small abrasive grains heldtogether by a bonding material. Sometypical grinding products are shown inFigure 16.2. Each abrasive grain is acutting edge. As the grain passes overthe workpiece it cuts a small chip,leaving a smooth, accurate surface. Aseach abrasive grain becomes dull, itbreaks away from the bonding materialbecause of machining forces and ex-poses new, sharp grains.

16.2.1 Types ofAbrasives

Two types of abra-sives are used in grind-ing wheels: natural andmanufactured. Exceptfor diamonds, manu-factured abrasiveshave almost totally re-placed natural abrasivematerials. Even naturaldiamonds have beenreplaced in some casesby synthetic diamonds.

The manufacturedabrasives most com-monly used in grindingwheels are aluminum

oxide, silicon carbide, cubic boron ni-tride, and diamond.

Aluminum Oxide: Refining bauxiteore in an electric furnace makes Alu-minum oxide. The bauxite ore is firstheated to eliminate any moisture, thenmixed with coke and iron to form afurnace charge. The mixture is thenfused and cooled. The fused mixtureresembles a rocklike mass. It iswashed, crushed, and screened to sepa-rate the various grain sizes.

Aluminum oxide wheels are manu-

16.1 IntroductionGrinding, or abrasive machining, is the process of removing metal in the form ofminute chips by the action of irregularly shaped abrasive particles. Theseparticles may be in bonded wheels, coated belts, or simply loose. The abrasivegrains usually cut with a zero to negative rake angle and produce a large numberof short, small, curly or wavy chips. The way an abrasive grain cuts material isshown in Fig. 16.1

Negativerake

Work

Grinding wheel

FIGURE 16.1: Abrasive grains cutting material during agrinding operation.


Chap. 16: Grinding Wheels and OperationsChap. 16: Grinding Wheels and Operations

factured with abrasives of differentdegrees of purity to give them certaincharacteristics for different grindingoperations and applications. The colorand toughness of the wheel are influ-enced by the degree of purity.

General purpose aluminum oxidewheels, usually gray and 95 percentpure are the most popular abrasivesused. They are used for grinding moststeels and other ferrous alloys. Whitealuminum oxide wheels are nearlypure and are very friable (able to breakaway from the bonding material eas-ily). They are used for grinding highstrength, heat sensitive steels.

Silicon Carbide: Silicon carbidegrinding wheels are made by mixingpure white quartz, petroleum coke, andsmall amounts of sawdust and salt, and

firing the mixture in anelectric furnace. This pro-cess is called synthesizingthe coke and sand. As inthe making of aluminumoxide abrasive, the result-ing crystalline mass iscrushed and graded byparticle size.

Silicon carbide wheelsare harder and morebrittle than aluminum ox-ide wheels. There are twoprincipal types of siliconcarbide wheels: black andgreen. Black wheels areused for grinding castirons, non-ferrous metalslike copper, brass, alumi-num, and magnesium, andnonmetallics such as ce-ramics and gem stones.

Green silicon carbide wheels are morefriable than the black wheels and usedfor tool and cutter grinding of ce-mented carbide.

Cubic Boron Nitride: Cubic boronnitride (CBN) is an extremely hard,sharp, and cool cutting abrasive. It isone of the newest manufactured abra-sives and 2 1/2 times harder than alu-minum oxide. It can withstand tem-peratures up to 2500 degrees Fahren-heit. CBN is produced by high tem-perature, high pressure processes simi-lar to those used to produce manufac-tured diamond and is nearly as hard asdiamond.

CBN is used for grinding super hardhigh-speed steels, tool and die steels,hardened cast irons, and stainless steels.Two types of cubic boron nitride wheels

are used in industry today. One type ismetal coated to promote good bondadhesion and used in general purposegrinding. The second type is an un-coated abrasive for use in electroplatedmetal and vitrified bond systems.

Diamond: Two types of diamond areused in the production of grindingwheels: natural and manufactured.Natural diamond is a crystalline formof carbon and very expensive. In theform of bonded wheels, natural dia-monds are used for grinding very hardmaterials such as cemented carbides,marble, granite, and stone.

Recent developments in the produc-tion of manufactured diamonds havebrought their cost down and led toexpanded use in grinding applications.Manufactured diamonds are now usedfor grinding tough and very hardsteels, cemented carbide, and alumi-num oxide cutting tools.

The synthetic diamond crystalsshown in Figure 16.3a can be manufac-tured into polycrystalline tool blanksshown in Figure 16.3b and discussed inchapter 1, section 1.5 or pressed intodiamond wheels shown in Figure 16.7.

16.2.2 Types of BondsAbrasive grains are held together in

a grinding wheel by a bonding mate-rial. The bonding material does not cutduring a grinding operation. Its mainfunction is to hold the grains togetherwith varying degrees of strength. Stan-dard grinding wheel bonds are vitri-fied, resinoid, sillicate, shellac, rubber,and metal.

Vitrified Bond: Vitrified bonds areused on more than 75 percent of all

FIGURE 16.2: Typical grinding products. (Courtesy:Norton Company)

FIGURE 16.3: a) Synthetic diamond crystals; b) Polycrystalline tool blanks (Courtesy: Norton Company)

a. b.


Chap. 16: Grinding Wheels and Operations

grinding wheels. Vitrified bond materialis comprised of finely ground clay andfluxes with which the abrasive is thor-oughly mixed. The mixture of bondingagent and abrasive in the form of a wheelis then heated to 2400 degrees Fahren-heit to fuse the materials.

Vitrified wheels are strong andrigid. They retain high strength at el-evated temperatures and are practicallyunaffected by water, oils, or acids. Onedisadvantage of vitrified bond wheels

is that they ex-hibit poor shockr e s i s t a n c e .Therefore, theirapplication islimited whereimpact and largetemperature dif-ferentials occur.

R e s i n o i dBond: Resinoidbonded grindingwheels are sec-ond in popular-ity to vitrifiedwheels. Phe-nolic resin inpowdered or liq-uid form ismixed with theabrasive grainsin a form and

cured at about 360 degrees Fahrenheit.Resinoid wheels are used for grindingspeeds up to 16,500 SFPM. Their mainuse is in rough grinding and cut-offoperations. Care must be taken withresinoid bonded wheels since they willsoften if they are exposed to water forextended periods of time.

Silicate Bond: This bonding mate-rial is used when heat generated bygrinding must be kept to a minimum.Silicate bonding material releases the

FIGURE 16.4: Comparison of three different grain sizes.

FIGURE 16.5: Comparison of three different grain structures.

FIGURE 16.6: ANSI standard marking system for abrasive grinding wheels. (United abrasives manu-facturers’ association.)

abrasive grains more readily than othertypes of bonding agents. Speed is lim-ited to below 4500 SFPM.

Shellac Bond: Shellac is an organicbond used for grinding wheels thatproduce very smooth finishes on partssuch as rolls, cutlery, camshafts, andcrankpins. They are not generally usedon heavy duty grinding operations.

Rubber Bond: Rubber bondedwheels are extremely tough and strong.Their principal uses are as thin cut-offwheels and driving wheels incenterless grinding machines. They arealso used when extremely fine finishesare required on bearing surfaces.

Metal Bond: Metal bonds are usedprimarily as bonding agents for dia-mond abrasives. They are also used inelectrolytic grinding, where the bondmust be electrically conductive.

16.2.3 Abrasive Grain SizeThe size of an abrasive grain is

important because it influences stockremoval rate, chip clearance in thewheel, and surface finish obtained.

Abrasive grain size is determined bythe size of the screen opening throughwhich the abrasive grits pass. The num-ber of the nominal size indicates thenumber of the openings per inch in thescreen. For example, a 60 grit-sizedgrain will pass through a screen with 55

openings per inch,but it will not passthrough a screen sizeof 65. A low grainsize number indi-cates large grit, and ahigh number indi-cates a small grain.

Grain sizes varyfrom 6 (very coarse)to 1000 (very fine).Grain sizes arebroadly defined ascoarse (6 to 24), me-dium (30 to 60), fine(70 to 180), and veryfine (220 to 1000).Figure 16.4 shows acomparison of threedifferent grain sizesand the screens usedfor sizing. Very finegrits are used for pol-ishing and lappingoperations, finegrains for fine finish



and small diameter grinding operations.Medium grain sizes are used in highstock removal operations where somecontrol of surface finish is required.Coarse grain sizes are used for billetconditioning and snagging operationsin steel mills and foundries, wherestock removal rates are important, andthere is little concern about surfacefinish.

16.2.4 Grinding Wheel GradeThe grade of a grinding wheel is a

measure of the strength of the bondingmaterial holding the individual grainsin the wheel. It is used to indicate therelative hardness of a grinding wheel.Grade or hardness refers to the amountof bonding material used in the wheel,not to the hardness of the abrasive. Asoft wheel has less bonding materialthan a hard wheel.

The range used to indicate grade is Ato Z, with A representing maximumsoftness and Z maximum hardness. Theselection of the proper grade of wheel isvery important. Wheels that are too softtend to release grains too rapidly andwheel wear is great. Wheels that are toohard do not release the abrasive grainsfast enough and the dull grains remainbonded to the wheel causing a conditionknown as ‘glazing’.

16.2.5 Grinding Wheel StructureThe structure of a grinding wheel

refers to the relative spacing of theabrasive grains; it is the wheel’s density.There are fewer abrasive grains in anopen-structure wheel than in a close-structure wheel. Figure 16.5 shows a

16.3.2 Grinding Wheel Shapes andFaces

Most grinding wheel manufacturershave adopted eight standard wheelshapes and 12 standard wheel faces forgeneral use. Figure 16.9 shows the mostcommon standard wheel shapes used onall types of grinders. Figure 16.10 illus-trates the standard wheel faces used onmost grinding wheel shapes.

16.4 Electroplated Grinding WheelsOf the several methods now used

for fixing super abrasive particles ofdiamond or CBN to the working sur-face of an abrasive tool, electroplat-ing is the fastest growing. More andmore production operations involvecombinations of hard-to-grind materi-als and complex wheel shapes thatvirtually dictate the use of electro-plated super abrasive tools.

Characteristically, such tools con-sist of a precision tool form or man-drel with super abrasive particles de-posited on the working surface andlocked in place by electrodepositon ofa bonding matrix, most frequentlynickel. The particles so locked ontothe tool surface may vary in size anddispersion to suit the purpose of thetool, but they should lie in a singlelayer.

Figure 16.11a shows a close-upview of a electroplated wheel; Figure16.11b shows various size and shapesof electroplated wheels.

16.5 Wheel Balancing, Dressingand Truing

All grinding wheels are breakable,and some are extremely fragile. Greatcare should be taken in handlinggrinding wheels. New wheels should

comparison ofd i f f e r e n ts t r u c t u r e sused in ag r i n d i n gwheel.

A numberfrom 1 to 15designates thestructure of awheel. Thehigher thenumber, themore openthe structure;the lower thenumber, themore densethe structure.

16.3 Grinding Wheel SpecificationsGrinding wheel manufacturers have

agreed to a standardization system todescribe wheel composition as well aswheel shapes and faces.

16.3.1 Grinding Wheel MarkingsAbrasive grinding wheels have a dif-

ferent marking system than CBN anddiamond wheels as discussed andshown below.

Abrasive Grinding Wheels: Thismarking system is used to describe thewheel composition as to type of abra-sive, grain size, grade, structure, andbond type. Figure 16.6 illustrates thisstandard marking system.

CBN and Diamond Wheels: Thesame standardization is applicable toCBN and diamond wheels. Some typi-cal CBN and diamond wheels areshown in Figure 16.7. Wheel markingsare a combination of letters and num-bers as shown in Figure 16.8.

FIGURE 16.7: Typical Cubic Boron Nitride (CBN) and diamondgrinding wheels. (Courtesy Norton Company)

FIGURE 16.8: Standard marking system for Cubic Boron Nitride (CBN) anddiamond grinding wheels.



be closely inspected immediately afterreceipt to make sure they were notdamaged during transit. Grindingwheels should also be inspected priorto being mounted on a machine.

To test for damage, suspend the wheelwith a finger and gently tap the side witha screwdriver handle for small wheels,and a wooden mallet for larger wheels.An undamaged wheel will produce aclear ringing sound; a cracked wheel willnot ring at all.

16.5.1 Wheel Balancing It is important to balance wheels

over 10 inches before they are mountedon a machine. The larger the grindingwheel, the more critical balancing be-comes. Grinding wheel balance alsobecomes more critical as speed is in-creased. Out-of-balance wheelscause excessive vibration, producefaster wheel wear, and chatter,poor finishes, damage to spindlebearings, and can be dangerous.

The proper procedure for bal-ancing wheels is to first staticallybalance the wheel. Next, mountthe wheel on the grinding ma-chine and dress. Then remove thewheel and rebalance it. Remountthe wheel and dress slightly asecond time.

Shifting weights on the wheelmount does balancing of wheels.The wheel is installed on a bal-ancing arbor and placed on abalancing fixture. The weights

are then shifted in a posi-tion to remove all heavypoints on the wheel as-sembly.

16.5.2 Dressing and Truing Dressing is a process used to clean

and restore a dulled or loaded grindingwheel-cutting surface to its originalsharpness. In dressing, swarf is re-moved, as well as dulled abrasivegrains and excess bonding material. Inaddition, dressing is used to customizea wheel face, so that it will give de-sired grinding results.

Truing is the process of removingmaterial from the face of the wheel sothat the resultant cutting surface runsabsolutely true. This is very importantin precision grinding, because an outof truth wheel will produce objection-able chatter marks on the workpiece. Anew wheel should always be trued be-fore being put to work. Also it is agood idea to true the wheel if it is

90˚ 65˚ 45˚

18

1v8

18

18

T

R

T

60˚ 60˚ 60˚

45˚ 45˚

EDC

JG

R = T2

R = T8

R = T8

R = 3T10

65˚ 65˚ 80˚ 80˚ 60˚ 23˚ 23˚ 60˚

R RR

RT

B

T T

A F

R

H

T

IT

S

K L

R

FIGURE 16.10: Twelve standard grinding wheel face contours.

FIGURE 16.9: Eight standard grinding wheel shapes.

being remounted on a machine.Dressing and truing conventional

grinding wheels are two separate anddistinct operations, although they maysometimes be done with the same tool.The tools used for conventional grindingwheel dressing include the following:

Mechanical dressers - commonlycalled star dressers, are held againstthe wheel while it is running. Thepicking action of the points of the starshaped wheels in the tool remove dullgrains, bond and other bits of swarf.Star dressers are used for relativelycoarse-grained conventional wheels,generally in off-hand grinding jobs,where grinding accuracy is not themain consideration.

Dressing sticks - are used for off-hand dressing of smaller conventionalwheels, especially cup and saucershapes. Some of these sticks are madeof an extremely hard abrasive calledboron carbide. In use, a boron carbidestick is held against the wheel face to

FIGURE 16.11: a) Close-up view of electroplated wheel b) Various sizes and shapes ofelectroplated wheels (Courtesy: Universal Superabrasives)



shear the dull abrasive grains and re-move excess bond. Other dressingsticks contain coarse Crystolon orAlundum grains in a hard vitrifiedbond. Various dressing sticks areshown in Figure 16.12.

Diamond dressing tools - utilize theunsurpassed hardness of a diamondpoint to clean and restore the wheelgrinding face. Although single pointdiamond tools were once the onlyproducts available for this kind ofdressing, the increasing scarcity of dia-monds has led to the development ofmulti-point diamond tools.

Multi-point diamond dressing toolsuse a number of small diamonds heldin a matrix. In use, the tool is heldsecurely in the tool holder and held flatagainst the face of the running wheel.As it dresses, the tool is traversedacross the wheel face until the job isdone. As diamonds on the surface ofthe tool wear away, fresh new diamondpoints are exposed to offer extendedlife and use. This type of tool producesa very consistent wheel face fromdress to dress.

Multi-point diamond dressing toolsare available in a wide range of shankdiameters and face shapes, to meet therequirements of a broad variety of

FIGURE 16.12: Various dressing sticks are shown.(Courtesy Norton Company)

FIGURE 16.13: Single- and multipointdiamond dressing tools. (Courtesy NortonCompany)

also important. Close grain spacing,hard wheels, and small grain sizes areused when the area of contact is small,On the other hand, open structures,softer wheels, and larger grain sizesare recommended when the area ofcontact is large.

Condition of the Machine: Vibrationinfluences the finish obtained on the partas well as wheel performance. Vibrationis generally due to loose or worn spindlebearings, worn parts, out-of-balance

wheels, or insecure foundations.Grinding Wheel Speed: Wheel

speed affects the bond and grade se-lected for a given wheel. Wheel speedsare measured in surface feet perminute (SFPM). Vitrified bonds arecommonly used to 6,500 SFPM or inselected operations up to 12,000SFPM. Resinoid-bonded wheels maybe used for speeds up to 16,500 SFPM.

Grinding Pressure: Grinding pres-sure is the rate of in-feed used during agrinding operation; it affects the gradeof wheel. A general rule to follow isthat as grinding pressures increase,harder wheels must be used.

grinding machines. Typical diamondtools used to dress grinding wheels areshown in Figure 16.13.

16.6 Grinding Wheel SelectionBefore attempting to select a grind-

ing wheel for a particular operation,the operator should consider the fol-lowing six factors for maximum pro-ductivity and safe results:

Material to Be Ground: If the ma-terial to be ground is carbon steel oralloy steel, aluminum oxide wheelsare usually selected. Extremelyhard steels and exotic alloys shouldbe ground with cubic boron nitride(CBN) or diamond. Nonferrousmetals, most cast irons,nonmetallics, and cemented car-bides require a silicon carbidewheel. A general rule on grain sizeis to use a fine grain wheel for hardmaterials, and a coarse grain wheelfor soft and ductile materials.Close grain spacing and softwheels should be used on hardermaterials, while open structure andharder wheels are preferable onsoft materials.

Nature of the Grinding Operation:Finish required, accuracy, and amountof metal to be removed must be con-

sidered when selecting awheel. Fine and accuratefinishes are best obtainedwith small grain size andgrinding wheels with res-inoid, rubber, or shellacbonds. Heavy metal re-moval is obtained withcoarse wheels with vitri-fied bonds.

Area of Contact: Thearea of contact between thewheel and workpiece is








CHAPTER 17Grinding Methodsand Machines





Shaping and Planing



Reaming and Tapping




Lapping and Honing

Upcoming Chapters

17.2 Grinding ProcessesGrinding machines have ad-

vanced in design, construction, ri-gidity, and application far more inthe last decade than any otherstandard machine tool in themanufacturing industry. Grindingmachines fall into five categories:

* Surface grinders* Cylindrical grinders* Centerless grinders* Internal grinders* Special types

of grinders.

17.2.1 SurfaceGrinding

Surface grind-ers are used toproduce flat, an-gular, and irregu-lar surfaces. Atypical hand op-erated surfacegrinder is shownin Figure 17.2a.In the surface

17.1 IntroductionGrinding, or abrasive machining, is one of the most rapidly growing metal

removal processes in manufacturing. Many machining operations previouslydone on conventional milling machines, lathes and shapers, are now beingperformed on various types of grinding machines. Computer Numerical Control(CNC) resulting in greater produc-tivity, improved accuracy, reliabil-ity, and rigid construction charac-terize today’s industrial grindingmachines. A typical internalgrinding operation is shown inFigure 17.1.

FIG. 17.1: Typical internal grinding operation.(Courtesy Kellenberger, A Hardinge Co.)

grinding process, the grinding wheelrevolves on a spindle and the work-piece, mounted on either a reciprocat-ing or rotary table, is brought into

FIG. 17.2: (a) Typical standard surface grinder. (Courtesy Bridge-port Machine, Inc.) (b) Schematic illustration of the basic compo-nents and motions of a surface grinder.


Chap. 17: Grinding Methods and Machines

contact with the grinding wheel (Fig.17.2b).

A typical surface grinding operationis shown in Figure 17.3. Four types ofsurface grinders are commonly used inindustry (Fig. 17.4).

Horizontal Spindle/ReciprocatingTable: This surface grinder is the mostcommonly used type in industry. Amanual surface grinder was shown inFigure 17.2a. A more sophisticated andautomated surface grinder is shown inFigure 17.5. It is available in varioussizes to accommodate large or smallworkpieces. With this type of surfacegrinder, the work moves back and forth

under the grinding wheel.The grinding wheel ismounted on a horizontalspindle and cuts on its pe-riphery as it contacts theworkpiece. The worktableis mounted on a saddle thatprovides cross feed move-ment of the workpiece.The wheelhead assem-bly moves vertically ona column to control thedepth of cut required.

Horizontal Spindle/Rotary Table: This sur-face grinder also has a

horizontally mounted grindingwheel that cuts on its periphery.The workpiece rotates 360 degreeson a rotary table underneath thewheelhead. The wheelhead movesacross the workpiece to provide thenecessary cross feed movements.The metal removal rate is con-trolled by the amount of down-feedof the wheelhead assembly.

Vertical Spindle/ ReciprocatingTable: This type of grinding ma-chine is particularly suited forgrinding long and narrow castings likethe bedways of an engine lathe. Itremoves metal with the face of the

grinder wheel while the work recipro-cates under the wheel. The wheelheadassembly, as on most other types ofsurface grinders, moves vertically tocontrol the depth of cut. The tablemoving laterally accomplishes crossfeed. The table is mounted on a saddleunit.

Vertical Spindle/ Rotary Table:This type of grinding machine (Fig.17.6) is capable of heavy cuts and highmetal removal rates. Vertical spindlemachines use cup, cylinder, or seg-mented wheels. Many are equippedwith multiple spindles to successivelyrough, semifinish, and finish largecastings, forgings, and welded fabrica-tions. These grinding machines areavailable in various sizes and have upto 225-HP motors to drive the spindle.

Work Holding Devices: Almost anywork holding device used on a millingmachine or drill press can be used onsurface grinders. Vises, rotary tables,index centers, and other fixtures areused for special set-ups. However, themost common work holding device onsurface grinders is the magnetic chuck.

Magnetic chucks hold the workpieceby exerting a magnetic attraction onthe part. Only magnetic materials suchas iron and steel may be mounteddirectly on the chuck. Two types ofmagnetic chucks are available for sur-face grinders: The permanent magnetand the electromagnetic chucks. Threetypes of magnetic chucks are shown inFigure 17.7.

On permanent magnet chucks, the

FIG. 17.3: Typical surface grinding operation. (Cour-tesy Norton Company)

FIG. 17.4: Four types of surface grinders commonly used in industry: (a) horizon-tal spindle/reciprocating table, (b) horizontal spindle/rotary table, (c) vertical spin-dle/reciprocating table, (d) vertical spindle/rotary table.

Infeed

Infeed

Infeed

Infeed

Wheel speed

Wheel speed

Wheel speed

Wheel speed

Crossfeed

Crossfeed

Workspeed

Workspeed

Workspeed

Workspeed

(a) (b)

(c) (d)

FIG. 17.5: Automated surface grinder withcoolant system. (Courtesy Chevalier Machin-ery, Inc.)



holding power comes from permanentmagnets. The work is placed onto thechuck and a hand lever is moved toenergize the magnets. The electromag-netic chuck operates on 110 or 220volts and is energized by a switch. Thistype of chuck has two advantages.First, the holding power may be ad-justed to suit the area of contact of theworkpiece; small amounts of currentare used with smaller parts, largeamounts with larger parts. A second

advantage is the demagnetizer switch.It reverses the current flow momen-tarily and neutralizes the residual mag-netism from the chuck and workpiece.

17.2.2 Cylindrical GrindingCylindrical grinding is the process

of grinding the outside surfaces of acylinder. These surfaces may bestraight, tapered or contoured. Cylin-drical grinding operations resemblelathe turning operations. They replacethe lathe when the workpiece is hard-ened or when extreme accuracy andsuperior finish are required. Figure17.8 illustrates the basic motion of thecylindrical grinding machine. As theworkpiece revolves, the grindingwheel, rotating much faster in the op-posite direction, is brought into con-

tact with the part. Theworkpiece and table re-ciprocate while incontact with the grind-ing wheel to removematerial.

A CNC cylindricalgrinder with a coolantsystem is shown in Fig-ure 17.9; a very largeroll grinder is shown inFigure 17.10.

Work Holding De-vices: Work holdingdevices and accessoriesused on center-type cy-lindrical grinders aresimilar to those used onengine lathes.

The primary methodof holding work is be-tween centers as shownin Figure 17.9. Thepoints on these centersmay be high-speedsteel or tungsten car-bide (Fig. 4.12). A lu-bricant is used with either type and isapplied between the point of the centerand the center hole in the work.

Independent, uni-versal and colletchucks can be used oncylindrical grinderswhen the work is odd-shaped or contains nocenter hole. They areused also for internalgrinding operations.

17.2.3 Centerless GrindingCenterless grinding machines elimi-

nate the need to have center holes forthe work or to use work-holding de-vices. In centerless grinding, the work-piece rests on a workrest blade and is

backed up by a second wheel, calledthe regulating wheel (Fig. 17.11). Therotation of the grinding wheel pushesthe workpiece down on the workrestblade and against the regulating wheel.The regulating wheel, usually made ofa rubber bonded abrasive, rotates inthe same direction as the grindingwheel and controls the longitudinalfeed of the work when set at a slightangle. By changing this angle and thespeed of the wheel, the workpiece feedrate can be changed. The diameter ofthe workpiece is controlled by twofactors: The distance between thegrinding wheel and regulating wheel,and by changing the height of theworkrest blade.

A typical centerless grinding opera-

FIG. 17.6: Vertical-spindle grinder withrotary table. (Courtesy WMW Machin-ery Co. Inc.)

FIG. 17.7: Three magnetic chucks: (a) electromagneticchuck, (b) permanent magnet chuck, (c) rotary electro-magnetic chuck.

FIG.17.8: Schematic illustration of the basic components and motions of a cylin-drical grinder.

FIG. 17.9: CNC cylindrical grinder with coolant system.(Courtesy K. O. Lee Co.)

FIG. 17.10: Very large computer controlled roll grinder(Courtesy: WMW Machinery Co. Inc.)



tion is shown in Figure 17.12 andcenterless grinder is shown in Figure17.13.

17.2.4 Internal GrindingInternal grinders are used to accu-

rately finish straight, tapered, orformed holes. The most popular inter-nal grinder is similar in operation to aboring operation in a lathe. The work-piece is held by a work holding device,usually a chuck or collet, and revolvedby a motorized headstock. A separatemotor head in the same direction as theworkpiece revolves the grindingwheel. It can be fed in and out of thework and also adjusted for depth ofcut. An internal grinding operationwith a steady rest is shown in Figure17.14.

17.2.5 Special Grinding ProcessesSpecial types of grinders are grind-

ing machines made for specific typesof work and operations. A brief de-

scription of the more com-monly used special typesfollows:

Tool and Cutter Grinders: A tooland cutter grinder was introduced inChapter 8 - Drilling Operations (Fig.8.12). These grinding machines aredesigned to sharpen milling cutters,reamers, taps, and other machine toolcutters. A tabletop tool and cuttergrinder is shown in Figure 17.15 and a5-axis CNC cutter grinder is shown inFigure 17.16.

The general purpose cutter grinderis the most popular and versatile toolgrinding machine. Various attachmentsare available for sharpening most typesof cutting tools. Sharpening of a tap isshown in Fig. 17.17a and grinding of amilling cutter is shown in Fig. 17.17b.Figure 17.18 shows sharpening of acarbide millingcutter with a dia-mond cup-grind-ing wheel.

FIG. 17.12: Typical centerless grinding operation. (Cour-tesy Cincinnati Machine)

Jig Grinding Machines: Jig grind-ers were developed to locate and accu-rately grind tapered or straight holes.Jig grinders are equipped with a highspeed vertical spindle for holding anddriving the grinding wheel. They uti-lize the same precision locating systemas do jig borers. A 5-axis continuouspath jig grinder is shown in Figure17.19.

Thread Grinding Machines: Theseare special grinders that resemble thecylindrical grinder. They must have aprecision lead screw to produce thecorrect pitch, or lead, on a threadedpart. Thread grinding machines alsohave a means of dressing or truing thecutting periphery of the grinding

FIG. 17.14: Internal grinding operation; the work-piece is held by a collet and supported in a steady-rest. (Courtesy kellenberger, A Hardinge Co.)

FIG. 17.13: A Centerless Grinder is shownCourtesy: Cincinnati Machine)

FIG. 17.11: Operating principle of a centerless grinder.

Grindingwheel

Workpiece

Regulatingwheel

Workrestblade



wheel so that it will produce a precisethread form on the part. Figure 17.20shows a CNC thread grinder with arobotic loading system and menu-driven software programs.

17.3 Creep-Feed GrindingGrinding has traditionally been asso-

ciated with small rates of metal removaland fine finishing operations. However,grinding can also be used for large-scalemetal removal operations similar to mill-ing, broaching, and planning. In creep-feed grinding, developed in the late1950’s, the wheel depth of cut is as muchas 0.25 in., and the workpiece speed islow. The wheels are mostly softer grade

resin bonded with openstructures to keep tempera-tures low and improve sur-face finish. The machinesused for creep-feed grind-ing have special features,such as high power – up to300hp – high stiffness,high damping capacity,variable spindle and work-table speeds, and amplecapacity for grinding flu-ids.

Its overall competitiveposition with other mate-rial-removal processes in-dicate that creep-feedgrinding can be economi-cal for specific applica-tions, such as in grindingshaped punches, twist-drill flutes, and variouscomplex super alloy

parts. The wheel is dressed to theshape of the workpiece to be produced.Consequently, the workpiece does not

have to be previouslymilled, shaped, orbroached. Thus near-netshape castings andforgings are suitableparts for creep-feedgrinding. Although gen-erally one pass is suffi-cient, a second pass maybe necessary for im-proved surface finish.

17.4 Grinding WheelWear

The wear of a grindingwheel can be caused bythree actions:

* Attrition or wearingdown

* Shattering of the

grains* Breaking of the bondIn most grinding processes, all three

mechanisms are active to some extent.Attritions war is not desirable becausethe dulled grains reduce the efficiencyof the process, resulting in increasedpower consumption, higher surfacetemperatures, and surface damage.However, attrition must go on to some

extent, with the forces on the gritbeing increased until they are highenough to shatter the grit or break thebond posts holding the dulled grit. Theaction of particles breaking away fromthe grains serves to keep the wheelsharp without excessive wear. How-ever, the grains must eventuallybreak from the bond or the wheelwill have to be dressed. Rupturingthe bond post that holds the gritallows dull grains to be sloughed off,exposing new sharp edges. If thisoccurs too readily, the wheel diam-eter wears down too fast. This raiseswheel costs and prohibits closesizing on consecutive parts.

G-ratio: The G-ratio is the ratio ofthe amount of stock removed versesthe amount of wear on the wheel,measured in cubic inches per minute.This ratio will vary from 1.0 to 5.0 invery rough grinding and up to 25.0 to

FIG. 17.17: Tool and cutter grinder setups: (a) sharpening of a tap, (b) sharpeningof a milling cutter. (Courtesy K. O. Lee Co.)

FIG. 17.16: 5-axis CNC cutter grinder. (Courtesy: StarCutter Co.)

FIG. 17.18 Sharpening of a carbidemilling cutter with a diamond cupgrinding wheel. (Courtesy NortonCompany)

FIG. 17.15: Table top tool and cutter grinder is shownsharpening an end milling cutter. (Courtesy ChevalierMachinery, Inc.)



50.0 in finish grinding.Even though grinding

wheels are fairly expensive, ahigh G-ratio is not necessarilyeconomical, as this may meana slower rate of stock removal.It often takes some experiment-ing to find the wheel-metalcombination, which is mosteconomical for a job.

17.4.1 Attritions Wear Attritions wear is respon-

sible for the so-called ‘glazed’wheel, which occurs when flatareas are worn on the abrasivegrains but the forces are nothigh enough to break the dullgrains out of the wheel face.Effective grinding ceases witha glazed wheel when the radialforce becomes so high that thegrit can no longer penetratethe workpiece surface to formchips. Attritions wear of the wheeloccurs most often when fine cuts aretaken on hard abrasive materials. Tak-ing heavier cuts or using a softer wheelthat will allow the grains to break outcan often avoid it.

17.4.2 Grain Fracture The forces that cause the grain to

shatter may arise from the cuttingforces acting on the wheel, thermalconditions, shock loading, welding ac-tion between the grit and the chip, orcombinations of these factors. In finishgrinding, this type of wheel wear isdesirable, because it keepssharp edges exposed, andstill results in a low rate ofwheel wear. In time, thewheel may become‘loaded’ and noisy, and re-quire dressing. A loadedwheel should be dressed bytaking a few deep cuts withthe diamond so that themetal charged layer is re-moved, and the chips arenot just pushed further intothe wheel. Then it shouldbe finish dressed accordingto the application require-ments.

17.4.3 Bond Fracture It is desirable to have

worn grit break out of the

wheel so that new cutting edges willbe exposed. This breaking down ofthe bond should progress fast enoughso that heat generation is sufficientlylow to avoid surface damage. On theother hand, bond breakdown shouldbe slow enough so that wheel costsare not prohibitive. Normally, thismeans choosing the proper wheelgrade for the job. Certain bond hard-ness is required to hold the grain inplace. Softer wheels crumble toofast, while harder wheels hold thedull grit too long.

FIG. 17.19: Continuous path 5-axis jig grinder. (CourtesyMoore Tool Co., Inc.)

17.5 Coated AbrasivesTypical examples of coated

abrasives are sandpaper andemery cloth. The grains usedin coated abrasives are morepointed than those used forgrinding wheels. The grainsare electrostatically depositedon flexible backing material,such as paper or cloth. Thematrix or coating is made ofresin.

Coated abrasives are avail-able as sheets, belts, and disksand usually have a much moreopen structure than the abra-sives on grinding wheels.Coated abrasives are used ex-tensively in finishing flat orcurved surfaces of metallic ornonmetallic parts, and inwoodworking. The surface fin-ishes obtained depend prima-rily on the grain sizes.

17.5.1 Abrasive Belt MachiningCoated abrasives are also used as

belts for high-rate material removal.Belt grinding has become an importantproduction process, in some cases re-placing conventional grinding opera-tions such as the grinding of cam-shafts. Belt speeds are usually in therange of 2500 to 6000 ft/min. Ma-chines for abrasive-belt operations re-quire proper belt support and rigidconstruction to minimize vibration.Figure 17.21 shows a multi-axis CNCdouble-station belt-grinding machine

with menu-driven cannedsoftware programs.

17.6 GrindabilityGrindability, in a like

manner as machinability,may be thought of as theease with which materialcan be removed from theworkpiece by the action ofthe grinding wheel. Surfacefinish, power consumption,and tool (wheel) life can beconsidered as fundamentalcriteria of the grindabilityof metals. In addition, thereare the important factors ofchip formation and suscep-tibility to damage of theworkpiece. Chip formation,which leads to a ‘loaded’

FIG. 17.20: CNC Thread Grinder with a robotic loading system(Courtesy: Drake Manufacturing Services)



FIG.17.21 CNC double-station Belt Grinding Machine(Courtesy: Drake Manufacturing Services)

wheel, is detrimental.The most important

machine setting affectingmachinability, the cuttingspeed, is not as importantan influence ongrindability becausegrinding is done at moreor less constant speed. In-stead, the important fac-tor becomes the nature ofthe grinding wheel. Thetype of grit, grit size,bond material, hardness,and structure of thewheel, all influence thegrindability of the work-piece. The problems oftool material and con-figuration variables were discussed inconnection with machinability.

In grinding operations like snaggingand cut-off work, the surface finish,and even the metallurgical damage tothe workpiece, may become relativelyunimportant. Wheel life and the rate ofcut obtainable then become the criteriaof grindability.

The best way to determinegrindability is to start with the selec-tion of the proper wheel. Beginningwith the manufacturer’s recommendedgrade for the conditions of the job, andthen trying wheels on each side of thisgrade do this. Any improvement ordeterioration in the grinding action, asevidenced by wheel wear, surface fin-ish, or damage to the workpiece, can

be noted. After the proper wheel hasbeen chosen, wheel life data may beobtained. Usually, this can be doneduring a production run.

Some of the factors to consider inestablishing grindability ratings arediscussed in the following examples ofthe grinding performance of metals:

Cemented Carbide: This materialcannot be ground with aluminum oxidegrit wheels. Although cemented carbidecan be ground with pure silicon carbidewheels, the grinding ratio is very lowand the material is easily damaged.Carbide is easily ground with diamondwheels if light cuts are taken to preventdamage to the workpiece material.However, diamond grit wheels are quiteexpensive. The overall grindability ofthis material is very low.

High Speed Steel: Hard-ened high speed steel can beground quite successfullywith aluminum oxide gritwheels. The grinding ratio islow, the relative power con-sumption high, and the pos-sibility of damage to theworkpiece is always present.Overall grindability is quitelow.

Hardened Steel: Mediumhard alloy or plain carbonsteels are easily ground withaluminum oxide wheels.The grinding ratio is good,and damage to the work-piece is not a serious prob-lem. Relative power con-

sumption is moderate. The grindabilityrating is good.

Soft Steel: Annealed plain carbonsteels grind with relatively low powerconsumption. Aluminum oxide wheelsare satisfactory. The grinding ratio isquite high, but surface damage may beencountered. As a group, these materi-als are rated as having goodgrindability.

Aluminum Alloys: These soft alloysgrind with quite low power consump-tion, but they tend to load the wheelquickly. Wheels with a very openstructure are needed. Grinding ratiosare good. Silicon carbide grit workswell, and belt grinding outperformswheel grinding in many cases.








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Shaping and Planing



Reaming and Tapping




Lapping and Honing

Upcoming Chapters

FIGURE 28.1: Typical lapping machine.(Courtesy Engis Corp.)

18.1 IntroductionLapping is a final abrasive finishing operation that produces extremedimensional accuracy, corrects minor imperfections of shape, refinessurface finish, and produces close fit between mating surfaces. Mostlapping is done with a tooling plate or wheel (the lap), and fine-grainedloose abrasive particles suspended in a viscous or liquid vehicle such assoluble oil, mineral oil, or grease. A typical lapping operation is shown inFigure 18.1.

Honing is a low velocityabrading process. Materialremoval is accomplished atlower cutting speeds than ingrinding. Therefore, heatand pressure are minimized,resulting in excellent sizeand geometry control. Themost common application ofhoning is on internal cylin-drical surfaces. The cuttingaction is obtained usingabrasive sticks mounted on ametal mandrel. Since thework is fixed in such a wayas to allow floating, and noclamping or chucking, thereis no distortion.

18.2 Lapping ProcessesThe principal use of the lapping

process is to obtain surfaces that aretruly flat and smooth. Lapping is alsoused to finish round work, such asprecision plug gages, to tolerances of0.0005 to 0.00002 inches.

Work that is to be lapped should bepreviously finished close to the finalsize. While rough lapping can removeconsiderable metal, it is customary toleave only 0.0005 to 0.005 inches ofstock to be removed.

Lapping, though it is an abrasiveprocess, differs from grinding or hon-ing because it uses a ‘loose’ abrasiveinstead of bonded abrasives like grind-ing wheels (Fig. 18.2).

These abrasives are often purchased‘ready mixed’ in a ‘vehicle’ often madewith an oil-soap or grease base. Thesevehicles hold the abrasive in suspen-sion before and during use. The pasteabrasives are generally used in hand-lapping operations. For machine lap-ping, light oil is mixed with dry abra-sive so that it can be pumped onto thelapping surface during the lapping op-eration.

18.2.1 Lapping MachinesThese machines are fairly simple

pieces of equipment consisting of arotating table, called a lapping plate,and three or four conditioning rings.Standard machines have lapping plates


Chap. 18: Lapping and Honing

from 12 to 48 inches in diameter. Largemachines up to 144 inches are made. 1to 20 HP motors run these tables. Atypical lapping machine is shown inFigure 18.3.

The lapping plate is most frequentlymade of high-quality soft cast iron,though some are made of copper orother soft metals. This plate must bekept perfectly flat. The work is held inthe conditioning rings. These rings ro-tate as shown in Fig. 18.4. This rotationperforms two jobs. First it ‘conditions’the plate, that is, it distributes the wearso that the lapping plate stays flat for alonger time. Secondly, it holds theworkpiece in place. The speed at whichthe plate turns is determined by the jobbeing done. In doing very criticalparts, 10 to 15 RPM is used, and whenpolishing, up to 150 RPM is used.

one step. Also, less time is required forcleaning parts and processing waste;throughput, along with overall produc-tivity, is increased.

Lapping plates are manufacturedfrom various materials as describedbelow, and are available in standardsizes from 6 to 48 inches in diameter.Plates are supplied with square, spiral,and concentric and radial grooves asshown in Figure 18.5.

Iron - Aggressive Stock Removal:• Excellent primary/roughing lap

plate, with long service life• Often used as an alternative to

cast iron plates• Produces a good surface finish on

most materials, especially metals andceramics.

Copper - Moderate to AggressiveStock Removal:

• Most widely used, universal com-posite lap plate

• Excellent when primary and fin-ishing lap are combined in a one stepoperation

• Suitable for virtually any solidmaterial: metal, ceramic, glass, car-bon, plastic, etc.

Ceramic - Moderate Stock Removal:• Generally used to lap/polish ce-

ramic parts and other stain- sensitivematerials.

• Used in applications where metal-lic-type contamination cannot be tol-erated

• Affordable, more machinable al-ternative to ‘natural’ ceramic plates.

Figure 18.3. Typical dual plate lapping ma-chine. (Courtesy Engis Corporation)

Figure 18.2. Abrasive grit must be uniformly graded to be effectivein lapping.

Workpiece

LapA pressure of

about 3 poundsper square inch(PSI) must be ap-plied to thew o r k p i e c e s .Sometimes theirown weight is suf-ficient. If not, around, heavy pres-sure plate isplaced in the con-

ditioning ring. The larger machines usepneumatic or hydraulic lifts to placeand remove the pressure plates. Figure18.5 shows various lapping plates.

The workpiece must be at least ashard as the lapping plate, or the abra-sive will be charged into the work. Itwill take from 1 to 20 minutes tocomplete the machining cycle. Timedepends on the amount of stock re-moved, the abrasive used, and the qual-ity required. Figure 18.6 shows a pro-duction-lapping machine.

18.2.2 Grit and Plate SelectionFlatness, surface finish, and a pol-

ished surface are not necessarilyachieved at the same time or in equalquality. For example, silicon carbidecompound will cut fast and give goodsurface finish, but will always leave a‘frosty’ or matte surface.

The grits used for lapping may occa-sionally be as coarse as 100 to 280mesh. More often the ‘flour’ sizes of320 to 800 mesh are used. The grits,mixed in slurry, are flowed onto theplate to replace worn-out grits as themachining process continues.

The case for using diamond superabrasives ratherthan conventionalabrasives such asaluminum oxideor silicon carbidecan be summedup in three words.Diamonds arefaster, cleaner,and more cost-ef-fective.

With diamondslurries, the lap-ping and polish-ing phases of afinishing opera-tion can often becombined into Figure 18.4. Conditioning rings used in lapping operations.



Tin/Lead - Fine Stock Removal:• Most widely used finishing lap/

polishing plate• Often used in place of polishing

pads• Suitable for metal, ceramic and

other materials.

Tin - Fine Stock Removal• Often used where lead-type con-

tamination cannot be tolerated• Suitable for charging of extra-fine

particulates.

18.3 Advantages and LimitationsAny material, hard or soft, can be

lapped, as well as any shape, as long asthe surface is flat.

Advantages: There is no warping,since the parts are not clamped andvery little heat is generated. No burrsare created. In fact, the process re-moves light burrs. Any size, diameter,and thickness from a few thousandthsthick up to any height the machine willhandle can be lapped. Various sizesand shapes of lapped parts are shownin Figure 18.7.

Limitations: Lapping is still some-what of an art. There are so manyvariables that starting a new job re-quires experience and skill. Eventhough there are general recommenda-tions and assistance from the manufac-turers, and past experience is useful,trial and error may still be needed toget the optimum results.

18.4 Honing ProcessesAs stated earlier, honing is a low

velocity abrading process. Material re-moval is accomplished at lower cuttingspeeds than in grinding. Therefore,heat and pressures are minimized, re-sulting in excellent size and geometrycontrol. The most common applicationof honing is on internal cylindricalsurfaces. A typical honing operation isshown in Figure 18.8.

Machining a hole to within less than0.001 inch in diameter and maintain-ing true roundness and straightnesswith finishes less than 20 u inches isone of the more difficult jobs in manu-facturing.

Finish boring or internal grindingmay do the job, but spindle deflection,variation in hardness of the material,and difficulties in precise work hold-ing, make the work slow and the re-sults uncertain. Honing, because ituses rectangular grinding stones in-stead of circular grinding wheels, asshown in Figures 18.9a and 18.9b, cancorrect these irregularities.

Honing can consistently producefinishes as fine as 4 u inches and evenfiner finishes are possible. It can re-move as little as 0.0001 inch of stockor as much as 0.125 inch of stock.However, usually only 0.002 to 0.020inch stock is left on the diameter forhoning. As shown in Figure 18.10,honing can correct a number of condi-

tions or irregularities, left by previousoperations.

18.5 Honing MachinesFor most work, honing machines are

quite simple. The most used honingmachines are made for machining in-ternal diameters from 0.060 to 6inches. However, large honing ma-

chines are made for diameters up to 48inches. Larger machines are some-times made for special jobs.

The length of the hole that can behoned may be anything from 1/2 inchto 6 or 8 inches on smaller machines,and up to 24 inches on larger ma-chines. Special honing machines aremade which will handle hole lengthsup to 144

18.5.1 Horizontal Spindle MachinesHorizontal-spindle honing ma-

chines, for hand-held work with boresup to 6 inches, are among the mostwidely used. The machine rotates thehone at from 100 to 250 FPM.

Figure 18.5. Typical lapping plates. (Cour-tesy Engis Corporation)

Figure 18.7. Various sizes and shapes of lappedparts. (Courtesy Engis Corporation)

Figure 18.8. Typical vertical honing operation.(Courtesy Sunnen Products Co.)

Figure 18.6. Single plate lapping produc-tion machine equipped for diamond abrasiveslurry use. (Courtesy Engis Corporation)



The machine operator moves thework back and forth (strokes it) overthe rotating hone. The operator must‘float’ the work, that is, not press itagainst the hone or the hole will beslightly oval. Sometimes the work-piece must be rotated.

Horizontal-spindle honing machines

are also made with ‘power stroking’. Inthese, the work is held in a self-align-ing fixture and the speed and length ofthe stroke are regulated by controls onthe machine.

As a hone is being used, it is ex-panded by hydraulic or mechanicalmeans until the desired hole diameteris achieved. Various mechanical andelectrical devices can be attached tothe honing machine to control the rateof expansion, and stop it when finalsize is reached.

On the simplest hand-held ma-chines, the operator may check thebore size with an air gage, continuehoning, recheck, etc. until the size iscorrect. A horizontal-spindle honingmachine is shown in Figure 18.11.

18.5.2 Vertical Spindle MachinesVertical-spindle honing machines

are used especially for larger, heavierwork. These all have power stroking atspeeds from 20 to 120 FPM. Thelength of the stroke is also machinecontrolled by stops set up by theoperator.

Vertical honing machines are alsomade with multiple spindles so that sev-eral holes may be machined at once, asin automobile cylinders (Figure 18.8).

Hone Body: The hone body is madein several styles using a single stonefor small holes, and two to eight stonesas sizes get larger (Fig. 18.9b). Thestones come in a wide variety of sizesand shapes. Frequently there are hard-ened metal guides between the stonesto help start the hone cutting in astraight line.

Cutting Fluid: A fluid must be usedwith honing. This has several pur-poses: to clean the small chips fromthe stones and the workpiece, to coolthe work and the hone, and to lubricatethe cutting action.

A fine mesh filtering system mustbe used, since recirculated metal canspoil the finish.

A vertical honing operation wasshown in Figure 18.8. A few of theparts honed on such a machine areshown in Figure 18.12.

18.6 Abrasive Tool SelectionThe abrasive honing stone must be

selected for the proper abrasive type,bond hardness and grit size to deliverthe fastest stock removal and desired

surface finish. This selection is simpleif done in the following three steps:

Step One: Select the abrasive typewith respect to the material composi-tion of the bore. There are four differ-ent types of abrasives: aluminum ox-ide, silicon carbide, diamond, andCBN. All four of these were discussedin the previous chapter. Each type hasits own individual characteristics thatmake it best for honing certain materi-als. Some simplified guidelines fortheir use are:

• Mild steel hones best with alumi-num oxide.

• Cast iron, brass, and aluminumhone best with silicon carbide.

• Glass, ceramic, and carbide honebest with diamond

• High speed tool steels, and superalloys hone best with CBN.

Mandrel

Honing shoe

Honing stone

Workpiece

(a)

Figure 18.9a. Schematic illustration of the com-ponents of an internal hone.

Figure 18.9b. Typical honing tool is shown be-ing Checked (Courtesy: Gehring L.P.)

Alignment of tandem holes

Correcting bellmouth

Correcting taper

Correcting rainbow-shaped holes

Figure 18.10. Undesirable conditions that canbe corrected by honing.



Diamond and CBN are consideredsuper abrasives because they are muchharder than conventional abrasives.They cut easily and dull slowly, there-fore allowing them to hone certainmaterials much faster and more effi-ciently than conventional abrasives.

However, as shown above, super abra-sives are not suited to honing all mate-rials. For instance, diamond does nothone steel very well, and CBN may notbe as economical as using aluminumoxide to hone soft steel.

Step Two: Use the stone hardnesssuggested in the manufacturer’s cata-log. If the stone does not cut, select thenext softer stone; if the stone wears toofast, select the next harder stone. Stonehardness does not refer to the hardnessof the abrasive grain, but to thestrength of the bonding material hold-ing the abrasive grains together, asdiscussed in the previous chapter. Abond must be strong enough to holdsharp abrasive grains in position to cut,but weak enough to allow dulled grainsto be sloughed off to expose underly-

Figure 18.13. Plateau honed finish surface at 100x (Cour-tesy: Gehring L.P.)

Figure 18.12. Parts honed on a vertical honing ma-chine. (Courtesy Sunnen Products Co.)

Figure 18.11. Horizontal-spindle honingmachine (Courtesy Sunnen Products Co.)

ing sharp grains. If the bond is toohard, the dulled abrasive grains willnot be allowed to fall off, and the stockremoval rate will be reduced. If thebond is too soft, the stone will wearexcessively because sharp abrasivegrains fall off before they are fullyused.

Diamond and CBN abrasive grainsdull so slowly that standard ceramic orresin bonds may not be strong enoughwhen honing rough out-of-round boresin hard materials, or when CBN is usedto hone soft steel. Metal bonds are bestsuited for these applications becausethe grains are held in a sintered metalmatrix that is much stronger than stan-dard bonds. As with choosing abrasivetype, stone bond hardness must bematched to the application to maxi-mize life and stock removal rates.

Step Three: Select the largest abra-sive grit size that will still produce thedesired surface finish. Surface finish isa function of the height of microscopicpeaks and valleys on the bore surface

and honing can produce al-most any degree of rough-ness or smoothness throughthe use of different abrasivegrit sizes.

Honing oil can improvestock removal rates by help-ing the cutting action of theabrasive grains. It preventspickup (spot welding of toolto bore) and loading (chipscoating the stone). Honingoil does this, not by acting asa coolant, but through

chemical activity. The ingredients inthe oil produce this chemical activity.Whenever the temperature rises at oneof the microscopic cutting points, thesulfur in the oil combines with the ironin the steel to form ironsulfide, an unweldablecompound, and weld-ing is prevented. Theantiwelding property ofhoning oil also pre-vents chips from stick-ing together and coat-ing the stone. Waterbased coolants cannotproduce this type ofchemical activity. Useof water-based coolantswill result in weldingof metallic guide shoes

to the part and loading of vitrifiedabrasive honing stones.

18.7 Cylinder Block HoningBores sometime require a prelimi-

nary rough honing operation to removestock, followed by finish honing to getthe desired surface finish. A character-istic feature of a honed surface finishis crosshatch, which makes an excel-lent oil retention and bearing surface.The crosshatch pattern is generated inthe bore surface as the workpiece isstroked back and forth over the rotat-ing honing tool.

Plateau Honing: A few years ago aspecial surface finish generated inter-est in the engine rebuilding market.With this finish, the valleys are deepand the peaks have been removed toform plateaus, giving the name plateauhoning or plateau finish as shown inFigure 18.13. A recent test by a ringmanufacturer has shown that an enginewith a true plateau finish consumedone-tenth the oil and had 80 percentless cylinder bore wear than the en-gines with conventional finishes.

Laser-Honing: With this process,considerably better results areachieved compared to traditional hon-ing. Precisely defined surface struc-tures can be obtained with Laser tech-nology. Laser-honing is a combinationof honing and Laser processing. Thisprocess generates Laser-produced lu-bricant reservoirs into a specificallydefined area in order to achieve anideal plateau surface finish. Such ahydrodynamic system can be producedexactly where it is required as shown inFigure 18.14.

Application of the Laser-honingprocess requires three steps. In the firststep – rough honing – the macro-form



Figure 18.15. Single-stroke honing tools useexpandable diamond-plated sleeves on a ta-pered arbor. (Courtesy Sunnen Products Co.)

Figure 18.14. Laser generated honed finished surface (Cour-tesy: Gehring L.P.)

of the bore is produced. In the secondstep, precisely defined lubricant reser-voirs are produced with the Laser. Instep three –finish honing – an ex-tremely fine surface finish is obtained,resulting in increased engine life byreduction of wear in the cylinder sur-face and on the piston rings.

18.8 Production HoningHoning will not only remove stock

rapidly, but it can also bring the bore tofinish diameter within tight tolerances.This is especially true if the honingmachine is equipped with automaticsize control. With every stroke, theworkpiece is pushed against a sensingtip that has been adjusted to the finishdiameter of the bore. When the bore isto size, the sensing tip enters the boreand the machine stops honing. Sizerepetition from bore to bore is .0001inch to .0002 inch. The operator sim-ply loads and unloads the fixture andpresses a button; everything else isautomatic.

Single-Stroke Honing: A still fasterand more accurate method of honing abore to final size is Single-Stroke hon-ing. The Single-Stroke tool (Fig.18.15) is an expandable diamondplated sleeve on a tapered arbor. Thesleeve is expanded only during set up,and no adjustments are necessary dur-ing honing. Unlike conventional hon-

ing, where the work-piece is stroked backand forth over the tool,in Single-Stroke hon-ing the rotating tool ispushed through thebore one time, bring-ing the bore to size.The return stroke doesnothing to the bore ex-cept get the workpieceoff the tool. Single-Stroke honing is so ac-curate and consistent,that honed bores donot require gaging.

Although Single-Stroke honing hasmany advantages, it islimited in the types

and volumes of material that can beremoved. The size and overall volumeof chip produced in one pass must beno more than the space between thediamond grits, or the tool will seize inthe bore.

Workpieces are best suited forSingle-Stroke honing when they aremade of materials that produce smallchips, such as cast iron, and that haveinterruptions that allow chips to bewashed from the tool as the bore isbeing honed. Conventional honingshould be used whenever the materialto be honed produces long stringychips, or the amount of stock to beremoved is large.

18.9 Advantages and LimitationsHoning has developed into a produc-

tive manufacturingProcess, some advantages and limi-

tations will be discussed below:Advantages: The workpiece need

not be rotated by power, there are nochucks, faceplates, or rotating tablesneeded, so there are no chucking orlocating errors. The hone is drivenfrom a central shaft, so bending of theshaft cannot cause tapered holes as itdoes when boring. The result is a trulyround hole, with no taper or high orlow spots, provided that the previousoperations left enough stock so that the

hone can clean up all the irregularities.Honing uses a large contact area at

slow speed compared with grinding orfine boring, which use a small contactarea at high speed. Because of thecombined rotating and reciprocatingmotion used, a cross hatched pattern iscreated which is excellent for holdinglubrication. Diameters with 0.001 to0.0001 inch and closer accuracies canbe repeatedly obtained in productionwork.

Honing can be done on most materi-als from aluminum or brass to hard-ened steel. Carbides, ceramics andglass can be honed by using diamondstones similar to diamond wheels.

Limitations: Honing is thought ofas a slow process. However, new ma-chines and stones have shortened hon-ing times considerably. Horizontalhoning may create oval holes unlessthe work is rotated or supported. If theworkpiece is thin, even hand pressuremay cause a slightly oval hole.

Documents

Cutting Tool Applications