Ch23 Machining Processes Turning and Hole Making2

7/23/2019 Ch23 Machining Processes Turning and Hole Making2

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Chapter 23Machining Processes Used to Produce Round

Shapes: Turning and Hole Making


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Lathe CuttingLathe Cutting

OperationsOperations

Figure 23.1 Miscellaneous cuttingoperations that can e per!or"ed

on a lathe. #ote that all parts are

circular $ a propert% kno&n as

a'is%""etr%. The tools used( their

shape( and the processing

para"eters are descried

throughout this chapter.


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Lathe Cutting OperationsLathe Cutting Operations

Turning:to produce straight, conical, curved, or groovedworkpieces (Figs. 23.la through d), such as shafts, spindles, and

pins.

Facing: to produce a flat surface at the end of the part and

perpendicular to its axis (Fig. 23.1e), useful for parts that are

assemled with other components. Face grooving produces

grooves for applications such as !"ring seats (Fig. 23.1f).

Cutting with form tools# (Fig. 23.1g) to produce various

axis$mmetric shapes for functional or aesthetic purposes.

Boring:to enlarge a hole or c$lindrical cavit$ made $ aprevious process or to produce circular internal grooves (Fig.

23.1h).


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Drilling:to produce a hole (Fig. 23.1i), which ma$ e

followed $ oring to improve its dimensional accurac$ and

surface finish.

Parting: also called cutting off, to cut a piece from the end of

a part, as is done in the production of slugs or lanks for

additional processing into discrete products (Fig. 23.1%).

Threading:to produce external or internal threads (Fig.

23.1k).

Knurling:to produce a regularl$ shaped roughness on

c$lindrical surfaces, as in making knos and handles (Fig.

23.1l).

Lathe Cutting OperationsLathe Cutting Operations


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Lathe Cutting Operations and Lathe ToolsLathe Cutting Operations and Lathe Tools


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Characteristics of Machining Processes and TypicalCharacteristics of Machining Processes and Typical

Dimensional TolerancesDimensional Tolerances


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Turning OperationTurning Operation

Figure 23.3 Sche"atic illustration o! the asic turning

operation( sho&ing depth)o!)cut( d* !eed( f* and spindle

rotational speed( Nin re+,"in. Cutting speed is the

sur!ace speed o! the &orkpiece at the tool tip.

&urning ma$ e performedat various speeds, dep and

feeds ' (Fig. 22.3),

depending on#

-workpiece and tool

materials

-surface finish and

dimensional accurac$

reuired

-characteristics of themachine tool.


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Designations for a ight!"and Cutting ToolDesignations for a ight!"and Cutting Tool

Figure 23. /esignations !or a right)hand cutting tool. Right)hand "eans the tool

tra+els !or" right to le!t( as sho&n in Fig. 23.3.


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T"# T$%&%' POC#((T"# T$%&%' POC#((

Tool 'eometryTool 'eometry


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'eneral ecommendations for Tool )ngles in'eneral ecommendations for Tool )ngles in

TurningTurning


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&ale 23.2# eneral *ecommendations for &urning &ool +ngles

*ake angles are important in controlling oth direction of chip flow andstrength of tool tip

ositive rake angles improve cutting operation $ reducing forces andtemperatures. -owever, positive angles result in a small included angle oftool tip

*elief angles control interference and ruing at tool workpiece interface f relief angle is too large, tool tip ma$ chip off. f it is too small, flank

wear ma$ e excessive

/utting"edge angle affect chip formation, tool strength, and cutting forcesto various degrees

&he nose radius affects surface finish and tool"tip strength

&he smaller the nose radius, the rougher the surface finish of theworkpiece and the lower the strength of the tool. 0arge nose radii can leadto tool chatter.

T"# T$%&%' POC#((T"# T$%&%' POC#((

Tool 'eometryTool 'eometry


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T"# T$%&%' POC#((T"# T$%&%' POC#((

Material emo*al ate +M,Material emo*al ate +M,


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T"# T$%&%' POC#((T"# T$%&%' POC#((

Material emo*al ate +M,Material emo*al ate +M,


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T"# T$%&%' POC#((T"# T$%&%' POC#((

Forces in TurningForces in Turning

&hree forces acting on a cutting tool are shown in Fig. 22.3

Cutting force- Fc# acts downward on the tool tip. &his is the

force that supplies energ$ reuired for cutting operation. t

can e calculated, using &ale 21.2.

Thrust force- Ft: acts in longitudinal direction. &his force is

also called the feed force ecause it is in the feed direction.

adial force- Fr: acts in radial direction and tends to push the

tool awa$ from the workpiece


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Forces )cting on a Cutting Tool in TurningForces )cting on a Cutting Tool in Turning

Figure 23.0 Forces acting on a cuttin tool in turning( Fcis the cutting !orce( Ftis the thrust o!

!eed !orce in the direction o! !eed( and Fris the radial !orce that tends to push the tool a&a%

!ro" the &orkpiece eing "achined.

T"# T$%&%' POC#((


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T"# T$%&%' POC#((T"# T$%&%' POC#((

(ummary of Turning Parameters and Formulas(ummary of Turning Parameters and Formulas *otational speed of workpiece, rpm

' Feed, mmrev or inrev

4 Feed rate, or linear speed of tool along workpiece length, mmmin or

inmin '

5 6urface speed of workpiece, mmin or ftmin 7 8o (for max

speed) 7 8avg (for average speed)

l 0ength of cut, mm or in

8o !riginal diameter of workpiece, mm or in

8' Final diameter of workpiece, mm or in

8avg +verage diameter of workpiece, mm or in (8o9 8')2

d 8epth of cut, mm or in (8o" 8')2

t /utting time, s or min 0'

:** mm3min or in.3min 7 8avgd '

&orue . m or l.ft (Fc) (8avg2) ower k ; or h &or ue < where < 2 7 radiansmin


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(ummary of(ummary of

TurningTurning

ParametersParameters

and Formulasand Formulas


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oughing and Finishing Cuts.

n machining, the usual procedure is to first perform one ormore roughing cuts at high feed rates and large depths of cut(and thereforehigh material=removal rates), ut with little

consideration for dimensional tolerance and surface roughness. &hese cuts are then followed $ a finishing cut, at a lower feed

and depth of cut in order to produce a good surface finish.

T"# T$%&%' POC#((T"# T$%&%' POC#((

(ummary of Turning Parameters and Formulas(ummary of Turning Parameters and Formulas


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ange of )pplica/le Cutting (peeds and Feeds forange of )pplica/le Cutting (peeds and Feeds for

Tool MaterialsTool Materials

Figure 23. The range o!

applicale cutting speeds and

!eeds !or a +ariet% o! tool

"aterials.

4 l R d ti ! T i 5 ti


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4eneral Reco""endations !or Turning 5perations


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4eneral Reco""endations !or Turning 5perations( con6t.


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4eneral Reco""endations !or Turning 5perations( con6t


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(pecific energy for cutting(pecific energy for cutting


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4eneral Reco""endations !or Cutting Fluids !or Machining


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T"# T$%&%' POC#((T"# T$%&%' POC#((

>?+:0> 23.l :aterial"removal *ate and /utting Force in &urning

+ 1@Amm long, 12.@mm"diameter 3AB stainless steel rod is eing reduced in

diameter to 12.A mm $ turning on a lathe. &he spindle rotates at BAA rpm,and the tool is traveling at an axial speed of 2AA mmmin. /alculate the cutting

speed, material"removal

rate, cutting time, power dissipated, and cutting force.

6olution#

5 78!

(3.1BC12.@CBAA)1AAA [email protected] mmin

&he cutting speed at the machined diameter is

5 78!

(3.1BC12.ACBAA)1AAA [email protected] mmin

the depth of cut is d (12.@"12) 2 A.2@mm

the feed is f 2AABAA A.@ mmrev.

:** 7 8avgd' [email protected]@CA.@CBAA 1E2B mm3min 2C1A" m3min

:** df5 A.2@ C A.@ C [email protected] 2C1A"

m3min


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&he actual time to cut is t 0 f 1@A A.@CBAA A.D@ min &he specific energ$ for stainless steel from tale 21.3 is B

;.6mm3

&he power needed is G C :**

(B C 1E2B) A 12H watt

one watt 1 .msec A .mmin

6o the power p 12HCA DHA .mmin

ower (&orue) (


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Lathe ComponentsLathe Components

Figure 23.2 4eneral +ie& o! a t%pical lathe( sho&ing +arious co"ponents.

Source: Courtes% o! Heidenreich 7 Hareck.


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L)T"#( )%D L)T"# OP#)T&O%(L)T"#( )%D L)T"# OP#)T&O%(


0. Bed# &he ed supports all ma%or components of the lathe. Ieds

have a large mass and are uilt rigidl$, usuall$ from gra$ or

nodular cast iron. &he top portion of the ed has two wa$s

1. Carriage: /onsists of an asseml$ of cross"slide, tool post,

and apron

&he tool post, usuall$ with a compound rest that swivels for tool

positioning and ad%ustment.

&he cross"slide moves radiall$ in and out

&he apron is euipped with mechanisms for oth manual andmechaniJed movement of carriage and cross"slide $ means of

the lead screw


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2. "eadstoc3:have a hollow spindle to which ;orkholding

devices, such as chucks and collets, are attached, and long ars

or tuing can e fed through for various turning operations.

4. Tailstoc3:t is euipped with a center that ma$ e fixed (dead

center) or ma$ e free to rotate with the workpiece (live center).

8rills and reamers can e mounted on tailstock uill to drill axial

holes in the workpiece

+ uill is a hollow c$lindrical part with a tapered hole

5. The feed rod and Lead (crew.: is powered $ a set of gears

from the headstock. t rotates during the operation of the lathe

and provides movement to the carriage and the cross"slide $

means of gears




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Lathe (pecificationsLathe (pecifications

) lathe generally is specified /y the following parameters:

6wing# the max diameter of the workpiece that can e machined

&he max distance etween the headstock and tailstock centers

(distance etween centers)&he length of the ed

&ale 23.# &$pical /apacities and :aximum ;orkpiece

8imensions for :achine &ools

For example, a lathe ma$ have the following siJe# 3A"mmswing $ DA mm etween centers $ 1H3A"mm length of ed.

:aximum workpiece diameters ma$ e as much as 2 m.


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Typical Capacities and Ma6imum 7or3pieceTypical Capacities and Ma6imum 7or3piece

Dimensions for Machine ToolsDimensions for Machine Tools


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7or3holding De*ices and accessories ! ) chuc37or3holding De*ices and accessories ! ) chuc3

3 or B %aws 3 %aws generall$ have a geared"scroll design that makes the %aws

self"centering. Gsed for round workpieces Kar stock, pipes tuingL

B %aw independent chucks. Gsed for suare, rectangular, or odd

shaped more ruggedl$ than three %aw chucks, four"%aw chucks areused for heav$ workpieces

%aws can e reversed

chucks# power actuated Kpneumaticall$ or h$draulicall$L or manual

chuc3s a*aila/le in *arious designs 8 si9es: selection depends on:1. t$pe M speed of operation

2. workpiece siJe

3. production M accurac$ reuirements.

B. %aw forces reuirements


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) collet is asicall$ a longitudinall$"split, tapered ushing.

&he workpiece (generall$ with a maximum diameter of 2@mm) is placed inside the collet.

&he tapered surfaces shrink the segments of the collet radiall$,

tightening onto the workpiece.

!ne advantage to using a collet (rather than a three" or four"%aw chuck) is that the collet grips nearl$ the entirecircumference of the part, making the device well suited

particularl$ for parts with small cross sections.


7or3holding De*ices and accessories ! ) Collet7or3holding De*ices and accessories ! ) Collet


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Face plates are used for clamping irregularl$ shaped

workpieces. &he plates are round and have several slots and

holes through which the workpiece is olted or clamped (Fig.

23.Dd).

Mandrels (Fig. 23.H) are placed inside hollow or tuular

workpieces and are used to hold workpieces that reuire

machining on oth ends or on their c$lindrical surfaces.

6ome mandrels are mounted etween centers on the lathe.

a. oth the c$lindrical and the end faces of the workpiece can e

machined

. onl$ the c$lindrical surfaces can e machined


7or3holding De*ices and accessories Face Plates7or3holding De*ices and accessories Face Plates

and Mandrelsand Mandrels


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Collets

Figure 23.8 a and Sche"atic illustrations o! a dra&)in t%pe collet. The

&orkpiece is placed in the collet hole( and the conical sur!aces o! the collet are !orced

in&ards % pulling it &ith a dra& ar into the slee+e. c 9 push)out t%pe collet. d

orkholding o! a &orkpiece on a !ace plate.


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Mandrels to Hold orkpieces !or Turning

Figure 23.;


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Lathe OperationsLathe Operations

0ong and slender parts must e supported $ a steady rest and

follow restplaced on the ed otherwise the part will deflect under thecutting forces.

&hese rests usuall$ are euipped with three ad%ustale fingers or

rollers that support the workpiece while allowing it to rotate freel$

(teady rests are clamped directl$ on the wa$s of the lathe, whereasfollow rests are clamped on the carriage and travel with it.

+ right"hand tool travels toward the headstock, and a left"hand tool

travels toward the tailstock.

Form tools are used to produce various shapes on solid, roundworkpieces $ moving the tool radiall$ inward while the part is

rotating.

Form cutting is not suitale for deep and narrow grooves or sharp

corners, ecause viration and chatter ma$ result and cause poor

surface finish.


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(teady rests and Follow rests(teady rests and Follow rests



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Boringon a lathe is similar to turning. t is performed inside hollowworkpieces or in a hole made previousl$ $ drilling or other means.

!ut"of"shape holes can e straightened $ oring.

Drilling&he workpiece is clamped in a work holder on the headstock,and the drill it is advanced $ rotating the handwheel of the tailstock.

-oles drilled in this manner ma$ not e sufficientl$ concentricecause of the tendenc$ for the drill to drift radiall$. &he concentricit$

of the hole can e improved $ suseuentl$ oring the drilled hole.8rilled holes ma$ e reamed (6ection 23.) on lathes in a manner

similar to drilling, thus improving hole dimensional tolerances and

surface finish. &he tools for parting- groo*ing- threading, and various otheroperations are speciall$ shaped for their particular purpose or are

availale as inserts. Knurlingis performed on a lathe with hardenedrolls


Lathe OperationsLathe Operations



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Types of LathesTypes of LathesBench Lathes.

(pecial!purpose Lathes.

6pecial applications (such as railroad wheels, gun arrels, and rolling"mill

rolls) with workpiece siJes as large as 1.D m in diameter $ H m in length and

capacities of B@A k;

Tracer Lathes

;ith attachments capale of turning parts with various contours

have een replaced largel$ $ numerical"control lathes.

)utomatic Lathes

medium to high volume production, parts are fed and removed

automaticall$, 0athes that do not have tailstocks are called chucking machinesor chuckers. &he$ are either single" or multiple"spindle t$pes.

)utomatic Bar Machines +(crew Machines,: high production rate of screws



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Turret Lathes

multiple cutting operations Kturning, oring, drilling, thread cutting,

and facingL

several cutting tools are mounted on the hexagonal main turret which

is rotated for each specific operation

5ertical turret lathes also are availaleN the$ are more suitale for

short, heav$ workpieces with diameters as large as 1.2 m.

ram!typeturret lathe"one in which the ram slides in a separate ase

on the saddle.

&he short stroke of the turret slide limits this machine to relativel$

short workpieces and light cuts in oth small" and medium"uantit$

production.

n the saddle type, the main turret is installed directl$ on the saddle,

which slides along the ed.


Types of LathesTypes of Lathes


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Turret LatheTurret Lathe

Figure 23.= Sche"atic illustration o! the co"ponents o! a turret lathe. #ote the t&o

turrets: s>uare and he'agonal "ain.



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Figure 23.1? a 9 co"puter nu"erical)control lathe.

#ote the t&o turrets on this "achine. These "achines

ha+e higher po&er and spindle speed than other lathes in

order to take ad+antage o! ne& cutting tools &ith

enhanced properties. 9 t%pical turret e>uipped &ith

ten tools( so"e o! &hich are po&ered.

&he$ are euipped with automatic

tool changers (+&/s)

&heir operations are relial$

repetitive, maintain the desired

dimensional accurac$, and

reuire less skilled laor.


Types of LathesTypes of Lathes

C%C Lathe


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#6amples of Turrets#6amples of Turrets


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Parts Made on C%C LathesParts Made on C%C Lathes

Figure 23.11 T%pical parts "ade on C#C lathes.


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#6ample 12.2: Machining of Comple6 (hapes#6ample 12.2: Machining of Comple6 (hapes

Pu"p sha!t

Cranksha!t

Tuular part &ith internal

threads


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#6ample 12.2: Machining of Comple6 (hapes#6ample 12.2: Machining of Comple6 (hapes

Figure 23.12 @'a"ples o! "ore co"ple' shapes that can e produced on a C#C lathe.


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Turning Process Capa/ilitiesTurning Process Capa/ilities

&ale 23.H shows t$pical prod rates for various cutting operations.

6urface finish and dimensional accurac$ in various operations

depend on (see figs 22.1B M 22.1@)#

1. characteristics and condition of the machine tool

2. stiffness

3. viration and chatter

B. process parameters

@. tool geometr$ and wear. cutting fluids

D. machinailit$ of workpiece material

H. operator skill


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TypicalTypical

ProductionProduction

ates forates for

;arious;arious

MachiningMachining

OperationsOperations


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ange ofange of

(urface(urface

oughnesses inoughnesses inMachiningMachining

ProcessesProcessesFigure 23.13 The range o!

sur!ace roughnesses

otained in +arious "achiningprocesses. #ote the &ide

range &ithin each group(

especiall% in turning and

oring.


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ange ofange of

DimensionalDimensional

Tolerances inTolerances in

Machining as aMachining as a

Function ofFunction of

7or3piece (i9e7or3piece (i9e

Figure 23.1 Range o!

di"ensional tolerances otained

in +arious "achining processes

as a !unction o! &orkpiece siAe.

#ote that there is an order os

"agnitude di!!erence et&eens"all and large &orkpieces.


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Design Considerations for Turning OperationsDesign Considerations for Turning Operations

arts should e designed so that the$ can e fixtured and

clamped in workholding devices with relative ease

8imensional accurac$ and 6F# as wide as permissile

+void 6harp corners, tapers, and ma%or dimensional variations

Ilanks# e as close to final dimension as possile

arts should e designed so that cutting tools can travel across

the workpeice without ostruction

8esigns# use availale standard cutting tools :aterials chosen according to machinailit$ as possile


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'uidelines for turning operations'uidelines for turning operations

&ale 23.E# general trouleshooting guide

for turning operations

general guidelines#

1. :inimiJe tool overhang (length to

diameter ratio) to minimiJe viration

2. 6upport workpiece rigidl$

3. Gse machine tools with high stiffness and

high damping capacit$

B. ;hen tools egin to virate and chatter,

modif$ one of the process parameters


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Trou/leshooting 'uide for TurningTrou/leshooting 'uide for Turning



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(crew!thread Cutting on a Lathe(crew!thread Cutting on a Lathe

0- counterclockwiselocking or *-

clockwise locking

a. 6tandard nomenclature

for screw &hreads

. Gnified ational

thread and d of

threads

c. 6! metric thread andd of threads

d. Iritish 6tandard

;hitworth

(I6;) d of threads

a

cd


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CuttingCutting(crew(crew

ThreadsThreads

Figure 23.10 a Cutting scre& threads on a lathe &ith a single)point cutting tool. Cutting scre& threads &ith a single)

point tool in se+eral passes( nor"all% utiliAed !or large threads. The s"all arro&s in the !igures sho& the direction o! the!eed( and the roken lines sho& the position o! the cutting tool as ti"e progresses. #ote that in radial cutting( the tool is !ed

directl% into the &orkpiece. Bn flank cutting( the tool is !ed inot the piece along the right !ace o! the thread. Bn incremental

cutting( the tool is !irst !ed directl% into the piece at the center o! the thread( then at its sides( and !inall% into the root. c 9

t%pical coated)caride insert in the process o! cutting scre& threads on a round sha!t. d Cutting internal scre& threads

&ith a caride insert. Source: c: Courtes% o! Bscar Metals Bnc.


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Chasers and Die for Thread CuttingChasers and Die for Thread Cutting

Figure 23.1 a Straight chasers !or cutting threads on a

lathe. Circular chasers. c 9 solid threading die.


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Design Considerations for (crew Thread CuttingDesign Considerations for (crew Thread Cutting

Gndercut termination efore shoulders

nternal threads in lind hole# unthreaded length at ottom

+void shallow lind tapped holes

/hamfers at the ends

&hread sections should not e interrupted with slots, holes

Gse standard thread inserts

:in engage length of a fastener should e 1.@ times its diam

+ll cutting operations in one setup


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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Boring and Boring MillBoring and Boring Mill

Figure 23.18 a Sche"atic

illustration o! a steel oring ar&ith a caride insert. #ote the

passage&a% in the ar !or cutting

!luid application. Sche"atic

illustration o! a oring ar &ith

tungsten)allo% inertia disksD

sealed in the ar to counteract

+iration and chatter during

oring. This s%ste" is e!!ecti+e

!or oring ar length)to)dia"eter

ratios o! up to .

Figure 23.1; Sche"atic illustration o! a +ertical

oring "ill. Such a "achine can acco""odate

&orkpiece siAes as large as 2.0" =; in. in

dia"eter.


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Chisel)Point

/rill and

Cranksha!t

/rill

Figure 23.1= T&o co""on t%pes o! drills: a Chisel)point drill. The !unction o! the pair o! "argins is to pro+ide a

earing sur!ace !or the drill against &alls o! the hole as it penetrates into the &orkpiece. /rills &ith !our "argins double-

margin are a+ailale !or i"pro+ed drill guidance and accurac%. /rills &ith chip)reaker !eatures also are a+ailale.

Cranksha!t drills. These drills ha+e good centering ailit%( and ecause chips tend to reak up easil%( these drills are

suitale !or producing deep holes.


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4eneral Capailities o! /rilling

Figure 23.2?


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T%pes o! /rills

Figure 23.21


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4un /rill

Figure 23.22 a 9 gun drill sho&ing +arious !eatures.

Sche"atic illustration o! the gun)drilling operation.


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Trepanning

Figure 23.23 a Trepanning tool. Trepanning &ith a drill)"ounted single cutter.

4 l R d ti ! S d d F d


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4eneral Reco""endations !or Speeds and Feeds

in /rilling


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Trouleshooting 4uide !or /rilling


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Three)9'is Co"puter #u"erical)Control /rilling

Machine

Figure 23.20 9 three)a'is co"puternu"erical)control drilling "achine. The

turret holds as "an% as eight di!!erent

tools( such as drills( taps( and rea"ers.


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Helical Rea"er and Bnserted)Elade 9dustale Rea"er

Figure 23.2 a Ter"inolog% !or a helical rea"er.

Bnserted)lade adustale rea"er.


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Tapping

Figure 23.28 a Ter"inolog% !or a tap. Tapping o! steel nuts in production.

Cer+ical Spine B"plant


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Cer+ical Spine B"plant

Figure 23 2; 9 cer+ical spine i"plant

Documents

Ch23 Machining Processes Turning and Hole Making2