JOURNEYMANPROGRAMME

MECHANICAL Reference Text

ForewordMIC has produced this book for us in its Industrial Maintenance Journeyman Programme and it is specifi-cally designed to introduce the basics of maintenance.

This book is intended for use as a reference text to be supplemented by notes and explanations and does not stand alone.

Compilation of this book was completed with standard published material, Tel-A-Train and resource person-nel at MIC. No claim is made to the ownership of any material contained herein.

THIS BOOK IS NOT FOR SALE

REFERENCE TEXT USED

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TABLE OF CONTENTS

MEASUREMENT 31.0 VERNIERS 41.1 METRIC VERNIERS 41.2 ENGLISH VERNIERS 41.2.1 HOW TO READ VERNIER SCALE 51.3 THE MICROMETER 61.3.1 ENGLISH MICROMETER 7 HAND TOOLS 82.0 FILES 92.1 CLASSIFICATION OF FILES 92.1.1 FILING PRACTICE 102.1.2 CARE OF FILE 122.2 MARKING OF TOOLS 15 DRILLS AND DRILLING MACHINES 243.0 DRILLS AND DRILLING MACHINES 243.1 DRILLING 253.2 FEED RATES FOR DRILLING 253.3 SAFETY 264.0 MILLING AND MILLING MACHINES 274.1 THE MILLING MACHINE 284.1.1 INTRODUCTION 284.2 RECOMMENDED FEED PER TOOTH 294.3 FEEDS 284.4 CUTTING SPEEDS 304.5 RULES FOR DETERMING SPEED AND FEED 324.6 CUTTER TYPES 334.7 CUTTER MOUNTING METHODS 425.0 GRINDING AND GRINDING MACHINES 465.1 GRINDING SAFETY 475.2 PEDESTAL GRINDING 485.3 DRESSING TRUING, BALANCING WHEELS 505.4 SURFACE GRINDING 515.5 GRINDING WHEELS 576.0 LATHES 586.1 SAFETY 596.2 INTRODUCTION TO CENTRE LATHES 596.3 SINGLE POINT CUTTER TOOLS 606.4 SPEED OF FEEDS 626.5 LATHE OPERATIONS 63

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MEASUREMENT

1.0 VERNIERS1.1 METRIC VERNIERS1.2 ENGLISH VERNIERS1.2.1 HOW TO READ VERNIER SCALE1.3 THE MICROMETER1.3.1 ENGLISH MICROMETER

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LESSON I 1

The Vernier Caliper is one of the most versatile precision measuring instruments available to the skilled metal working craftsman. Most toolmakers and machinists prefer at least one good vernier and few micrometers for their own personal use on the job.

A Vernier Scale is the name given to any scale making use of the difference between two scales which are nearly, but not quite alike, for obtaining small differences.

The difference between the smallest division on the fixed scale and the smallest division on the vernier or sliding scale is the key basis on which the Vernier caliper works. This differ-ence is the accuracy of the Vernier.

1.1 METRIC VERNIERS:Vernier (1) On the fixed scale, real standard dimensions are accurately engraved The smallest division is 0.5mm. On the vernier scale 142mm is divided into 25equal parts. The smallest division is therefore 12/25=0.48mm. Difference in division – 0.50 – 0.48 = 0.02mm

Vernier (2) On the fixed scale the smallest division is 1mm. on the vernier scale 49mm is divided into 50 parts. The smallest division on the vernier scale is therefore 49/50 = 0.98mm Difference in division = 1.00 – 0.98 = 0.02mm

1.2 ENGLISH VERNIERS Vernier (1) On the fixed scale 1“ is divided into 10 parts, then each tenth is further sub-didvided into 4 parts 1/40 = 0.025. On the Vernier scale 6/10 is divided into 25 parts 6/10 – 25 = 6/10 x 1/25 = 0.024“ Difference – 0.025 – 0.024 = 0.001“.

ENGLISH VERNIERS (2) Fixed Scale: 1“is divided into 20 parts = 0.05“

VERNIER SCALE: 49 divisions on the fixed scale, (which is 49 x 0.05 = 2.450“) Is divided into 50 parts. The smallest division on the Vernier scale is 2.450 ÷ 50 = 0.049“ Difference – 0.050 – 0.049 = 0.001“

GENERALLY - The accuracy of metric verniers is therefore = 0.02mm.The accuracy of English verniers is therefore = 0.001“.

HOW TO READ ANY VERNIER SCALE:

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1. Note the real dimension on the fixed scale which the zero on ther vernier scale has al ready passed. i.e. The number of the whole divisions on the fixed scale to the left of the zero on the vernier scale. (These divisions maybe whole millimeters or half millimeters. 0.10“, 0.05“ , 0.025“ depending on how the fixed scale is divided).

2. Locate the line on the vernier scale which coincide exactly with the line on the fixed scale.

3. Check the number of divisions on the vernier scale between the zero and the line which coincides.

4. Multiply this number by the accuracy.

5. Add to the previous noted dimension.

This is also applicable to the height gauge.

Measuring Exercises.

Review Questions.

RANGE:

Internal measurements (error).Provision for setting dividers.Clamp nuts, fine adjustments.

1. Vernier Caliper Vernier Caliper are precision tools used to make accurate measure-ments to within 0.02mm or 0.001 ins. They consist of an L-shaped bar and movable jaws which are graduated on both sides, one side for the bar consist the main graduations and the vernier graduations are the movable jaw.Limitations arise through application of the vernier caliper due to the fact that they depend a great deal upon the skill and the capa-bilities of the user. Feel id=s essential in determining when the jaws of the instrument are truly along the line of measurement. This is especially true with inside measurements, whereby touch and ma-nipulations determine when the maximum distance on diameter id obtained. Feel is necessity in attaining precise measurements, and in addition, undue forces will cause excessive wear or damage to the instrument. Wear and manipulative factors have a direct influ-ence on reliable measurements and one must be certain to read the proper scale

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THE MICROMETERWhen parts are to be measured to the second place of decimal in the metric system, or the third place in the English system, the micrometer is commonly used.

Working Principles and Construction

A spindle with external thread for measuring and internal thread at the end for fixing the thimble to the spindle.The barrel has the internal measuring threads and is one piece unit with the frame. Over the frame is a thin walled sleeve with the graduations in inches or mm etched longitudinally. This sleeve can be turned with a special spanner for small adjustments. There is also a nut for adjusting the tightness of the external and internal measuring threads, a locking ring for locking a particular dimen-sion and an adjusting nut for adjusting the longitudinal position of the thimble.

The ratchet is mounted on the screw which holds the thimble and spindle together and held in position by a small screw. The ratchet slips when a certain fixed amount of pressure is ap-plied. This gives consistent readings.

The right end of the thimble sometimes called the rim is divided into 50 equal divisions around its periphery . The measuring threads are very accurate and are precision ground which a pitch of 0.5mm, hence for each revolution the spindle moves 0.5mm. there one divi-sion on the thimble is

=0.5 = 1 = 0.01mm this is the accuracy of the micrometer. 50 100

The barrel is graduated in mm and ½ mm.

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Reading the micrometer (0-25mm)

(1) Note the number of whole millimeters visible between 0 (zero) on the sleeve and the end of the barrel.

(2) The sleeve and the end of the barrel. Check to see if 1/2mm division is visible before the end of the Barrel on the lower half of the thimble graduations, if so add .5 to the whole mm in 1.

(3) Read off from the thimble the amount of hundreds below the Horizontal centre mark on the sleeve and add to the previous amount. Examples

English Micrometers

The measuring threads are 40 T.P.I. hence a pitch of 1-40“= 0.025 25 threads.The thimble is divided into 25 parts therefore one division on the thimble is 0.025 = 1 = 0.001 one thread 25 1000

This is the accurarcy of the inch micrometer.The barrel is divided (graduated) in 1/40 =0.025Reading the micrometer 0 – 1“.

(1) Record the tenths – the number lines before the thimble edge.

(2) Record the amount (number) of divisions between the last numbered line and the edge of the thimble and multiply them by 0.025.

(3) Record the thiousandth on the thimble below the horizontalcentre mark on the sleeve.

(4) Add 1, 2 and 3

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HAND TOOLS

2.0 FILES2.1 CLASSIFICATION OF FILES2.1.1 FILING PRACTICE2.1.1 CARE OF FILE2.2 MARKING OF TOOLS

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FILESA file is a hard cutting tool, made of high carbon tool steel, used to remove surplus metal and to produce a finished surface. Files may be produced in a variety of shapes and types, therefore the Student is required to secure the necessary knowledge, not only to distinguish one file from another, but also to determine their particular use.

Length - the distance from heel to toe Body - is that part of the file that does the cutting. It comprises the faces and the edge of the files which are made up of the large number of the cutting edges.Heel - is the uncut portion of the file.Toe - the extreme end of the file opposite the heel.Tang - pointed portion at the end of the heel used for securing handle to the file.Note: the length of the file is measured by length of body (exclusive of the tang)

2.1 CLASSIFICATION OF FILESFiles may be divided into two classes:

(1) Single cut files.These files have a series of parallel teeth run-ning diagonally across the width of the surface as shown in Fig .1. This group includes Mill Lathe and Saw files. Single cut files are used when a smooth surface is desired or where hard materials are to be finished.

2) Double cut files these files have courses of teeth crossing each other course be-

ing finer than the other. These rows produce hundreds of cutting teeth which makes for the faster removal of stock and easy clearing of chips. Both single and double cut files are manu-factured in various degrees of coarseness. This is indicated by the terms bastard, second cut and smooth. Files are manufactured in many shapes and cross sections. These are indicated by the terms , band , flat , mill , square , round , half round , triangle etc.

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Filing is highly skilled and accurate phase of the machine trade. Skill in filing can only be acquired through constant practice.

If the following rules are observed in the early stages of practice filing, the operation will require much less effort and quality of the finished work will be of a higher order.

The Filing Position 1. Hold the file in the right hand, the index finger pointing toward the toe of the file.2. Support the toe of the file with the thumb and fore finger of the left hand. Do not press heavily with the left hand as this will rock the file and produce a rounded surface.3. Assume a comfortable stance while filing, the left foot forward of the right so that the body will be well balanced.

To file a flat surface: (Note: A FILE MUST NEVER BE USED WITHOUT A HANDLE)

1. Place the work in the vise, the surface to be filled should be about 3/8“above the jaw. (Use soft jaws to protect finished work.)2. Select the file suited to your particular needs.3. Grasp the file as illustrated above.4. Apply pressure on the forward stroke, release pressure on the return. Note: the proper filing stroke is produced by the hands and the arms – do not sway the whole body backward and forward as you file.5. Strive for a straight horizontal motion to prevent rounding or the surface.6. Do not rub the surface of the work with your hands as this will leave a thin film of grease and the file cannot cut properly.7. File at about 50 to 60 strokes per minute - too fast a stroke only dulls file and tries the operator.8. Clean the face of the file frequently with a file card to prevent small chips from scratching the surface.9. Remove the work from the vise periodically to check for flatness and squares of the filed surfaces.

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Draw filing serves three purposes, it removes tool marks, gives a flat smooth surface and makes a grain line finish to the length of the work-piece. When draw filing only a single cut file is used because its cutting action will give a much smother finish then a double cut file.

To Draw File: use only as a finishing operation1) Select a single cut file, Be sure it is clean.2) Clamp work high enough in a vise so that fingers will be clear of vise jaws when filing3) Place file on work-piece and hold as shown in diagram so that index fingers are firmly pressing the file flat against the surface of the filed. This will prevent the file from rocking and giving a round surface.4) Draw file back and forth over work surface until desire finish is obtained. Check periodically for flatness using a straight edge.

Note: If the file seems to be dull use the area near the heel since this area generally does not get the wear and tear the rest of the file gets and will therefore remain somewhat sharper.

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Common shapes of files

2.1.2 CARE OF FILES

Files should be cleaned with a file card during and after use. This will help to keep the teeth clean and promote smoother cutting.

NB: Chalk is often used to prevent “pinning” during filing; ensure that file is cleaned thor-oughly immediately after to prevent corrosion occurring.

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This is a manual, high carbon, steel tool, serrated, hardened and tempered (fig .1). It is used for filing operations

CLASSIFICATIONFiles are classified by their shape, cut, and size.Figures 2 to 9 indicate the most commonly used.

TECHNICAL VOCABULARY Rounded-edged File- Mill-saw FileTriangular File – Three Square or The corner File

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Files may be of double or single cut. They are classifies as bastard, smooth and semi-smooth (figs. 10 to 15)

The most common sizes of file are 100, 150, 200, 250 and 300 mm of body length. (1)

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The following table presents the different types of files and their uses.

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This gauge consist , of an accurately machined blocked base with an adjustable pillar and attachment for holding a scriber. There is an additional fine adjustment thumb screw for the pillar. In the base may be fitted to frictionally held pins which can be pushed down to slide along the edge of the marking off table, it also has a scriber which may be adjusted to any height within the range of the pillar.

It is a manual tool consisting of a steel arch on which a saw is mounted (blades may be of high speed or carbon steels indented and tempered). The blades has perforations at its end s for fixing on to the arch by means of pins placed at the supports. The frame has a fixed support, and an adjustable one which is cylindrical and threaded, carrying a butterfly nut to tighten the blade (fig. 1).The hacksaw is used to cu materials and make or begin grooves.

Characteristics and Structure:The arch of the saw is characteristic because it can be regulated and adjusted according to the length of the blade. It has a screw with a wing nut which tightens the sawblade. For its ma-nipulation it is equipped with a handle made of wood, [lastic or fibre, or metal. The blade is characterized by: its length, which commonly measures 8”, 10” or 12” from centre to centre of the holes;by the width, which is generally of ½” ; by the number of teeth per inch, which is generally of 18, 24 or 32t/1” (fig. 2).

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The saw has set teeth, which are lateral displacements of the teeth in an alternated manner as shown in fig. 3 to 7.

Choosing of blade:

The blade is chosen according to:1- The thickness of the material which must not be less than two pitches of the teeth (fig. 8).2- The type of material, choosing those of a small pitch (p) for hard materials.

Conditions of use:The tension of the blade must be given only by hand; a wrench must not be used. When the work is finished the blade must be loosened.

SUMMARY

arch- carbon steel Saw tempered, toothed blade- high speed steel or carbon steel. handle – wood, plastic or fibre

Characteristics:length - width - number of teeth per inch

Selection: according to the thickness of the material (more than 2 pitches of the teeth); acord-ing to the type of the material (large number of teeth for hard materials).

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Blades must be strained slightly in the frame and slow firm and steady strokes (50 strokes/min) should be used , lifting the blade slightly on the return stroke.

Breakage of blades may be caused by the following:-(1) rapid and eratic strokes. (2) too much pressure .(3) blades held too loosely in the frame. (4) work not held firmly in the vice.

Solid metals should be cut with a good pressure thin sheet and tubes with light pressure.

Insufficient pressuere at the start of the cut may cause the teeth to glaze the work, and so rub away their edge.

The HAMMER is a tool of impact, consisting of carbon stell block with a wooden handle. The part with which the hammering is done is tempered. The hammer is used in a majority of industrial activities, such as: mechanics in general, civil engineering, construction and the like. The hammer is characterized by its shape and weight.

By its shape :Ball-peen hammer (fig. 1). Peen hammers (figs.2, 3 and 4)These are the most common types used in mechanic shops.

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By its weight:The weight varies between 200 to 1000 grammes.

Conditions of use:A hammer to be used must have The han-dle in good condition and well fitted at the wedge.

Care:Avoid hammering with the handle and do not use it as a lever.

The MALLET is a tool of impact, made up of a head of wood, aluminum, plastic, copper, lead or leather, and a wooden handle (figs.5, 6 and 7).It is used to strike on work or material whose surface must not be deformed by the effects of the blows. Plastics or cooper heads can be replaced when worn (fig. 6).

Conditions of use:a) the mallet head be well fitted into the handle free from burns.b) It must be used only on smooth surfaces.

TECHNICAL VOCABULARY - Mallet of rolled Leather – Hides faced Mallet; raw-hide mallet

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A cold chisel

1. The chisel is forged to shape and normalised by heating to a dull red in the smith’s hearth and then removing it and allowing free cooling in the open air. Normalising removes any internal stresses set up in the metal by the hammering.2. The chisel is filed shape, drwa field, and finished with emery cloth.3. Hardening the chisel is performed by heating 8 or 10 cm of the cutting edge half half of the chisel to a cherry red colour in the daylight and then quickly quenching it in a bath of water. The chisel may be heated in the smith’s hearth or with the blowpipe.4. Tempering the chisel is carried out by polishing one surfacewith emery cloth. It is then held in the tongs and heated at a spot about 8cm from the cutting edge with a blowpipe. Col-ours will begin to form and travel towards the cutting edge. When the light purple reaches the edge, the chisel is quickly quenched in a bath of water. Tempering removes the brittleness and sets the tools to its correct degree of hardness.5. The chisel is polished with emery clothIt is too hard to file, and would ruin the file teeth.)Another method of hardening and tempering is a combine the two processes into one. The 8 or 10 cm of the cutting edge half is heated to a cherry red then the first half only of the heated portion is quenched. The tip is quickly polished with emery clothso that the colours can be seen as they travelfrom the reservoir of heat left in the shank. When the light purple reaches the cutting edge the chisel is quenched.Small articles can be hardened and temperted by placing them on a hot red plate. ChiselsChisels are made of octagonal tool steel. They are forged to shape, then hardened and tempered. The four main types are illustrated and are known collectively as cold chisel because they are used to cut cold metal.

The flat chisel is used for general purpos-es, chipping, cutting sheet and plate metal, and removing surplus metal from surfaces.

The cross-cut chisel is used for cutting squares grooves such as slots, channels and keyways. The cutting edge is slightly wider than the supporting metal, to provide clearence.

The cutting edge of the chisel is ground half round. It is used for cutting grooves and draw-ing over the centers of holes that have run off during drilling. The chisel is drawn down to a square section.

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The flat chisel. A diagram of the chisel point in the action of cutting. As at fig. 111(a), where the angles of rake and clearance are indicated is usual, the point is ground symmetrical, the rake and clearance depend upon the angle of inclination (A) between the chisel and the A clearance of about 10° would be suitable, so that for a 60° point would be necessary to hold the chisel with angle A = 10° + 30° = 40° the rake would then be 90° -(40° + 30°) = 20°. This is shown at (b) cutting hard and brittle metals calls for less rake than soft metals, the an-gle must be less for the softer metals and the following table give able values for the angles:

Table 13. Chisel anglesMetal being cut Angle of Chisel PointCast steel . . . . . 65°Cast iron . . . . . 60°Mild steel . . . . . 55°Brass . . . . . 50°Copper . . . . . 45°Aluminium . . . . 30°

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DRILLS AND DRILLING MACHINES3.0 DRILLS AND DRILLING MACHINES3.1 DRILLING3.2 FEED RATES FOR DRILLING3.3 SAFETY

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DRILLING

Probably one of the first mechanical devices developed was a drill to bore holes in various materials. The principles of a rotating tool making a hole in various materials is the one on which all drill presses operate. The drilling machine is essential in any metal working shop. Fundamentally, a drilling machine consist of a spindle which turns the drill and which can be advanced into the work piece rigidly in position as the hole is drilled. A drilling machine is used primarily to produce holes in metal, however, operations such as tapping, ream-ing, counter boring, countersinking, boring and spot facing can also be performed. Basically a drilling ma-chine is made up of a base, column, table, and drilling head.

Base: The base, usually made of cast iron, provides stability for the machine and also rigid mounting for the col-umn.

Column:The column is an accurate cylindrical post which fits into the base, the table, which is fitted to the column, maybe adjusted to any point between the base and head. The head of the drill press is mounted near the top of the column.

Table:The table is used to support the work piece to the machined. The table, whose surface is 90° to the column maybe raised, lowered, and swiveled, around the column. On some modles it is possible to tilt the table in any way direction for drilling holes at an angle. Slots are provided in most tables to allow the clamping of jigs, fixtures or large jobs.

Drilling Head:The head, mounted close to the top of the column, contains the mechanism which is used to revolve the cut-ting tool and advance it into the work piece.The spindle which is the round shaft that holds and drives the cutting tool, is housed in the spindle sleeve or quill. The spindle sleeve does not remove but slides up and down inside the head to provide a down feed for the cutting tool.The end of the spindle may have tarpered hole to hold taper shank tools.

Feed rates for drilling The feed rate for drilling is governed primarily by the size of the drill and the material being drilled. Other factors that also affect the feed rate that can be used are the work piece configuration, the rigidity of the ma-chine tools and the work piece set up, and the length of the chisel edge.

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Cutting Speed Formulas.Most machining operations are conducted on machine tools having rotating spindles and the cutting aped in feed per meters per minute must be converted to a spindle speed or to revolutions per minute; this is accom-plished by use of the following formulas:

N= Spindle Speed : R.P.MV= Cutting Speed : f. p. n, or m/min.D=Diameter : IN or mm (for turning, D is the outside Diameter or the work piece. For milling and ream-ing, D is the Diameter of cutter.

Safety

Accidents happen every day in factories worldwide. The higher percentage of accidents are caused by the workers, the lesser by the employers. A lot of time and money is spent to increase the level of safety in indus-try in so doing the loss of lives, limbs and time is greatly reduced. Safety equipment are available in every industry and are to be at all times in the work area. There are rules that must be followed:

1. Secure loose clothing. (Ties, sleeves.) 2. Remove all jewelry. (Watches, chains, rings.) 3. Always wear eye protections. (Specified for job.) 4. Special care must be taken when handling power tools, sharp objects. 5. Report safety hazards as soon as they are noticed. 6. Report damage machinery and tools. 7. Report all accidents. 8. Do not operate machinery you know nothing off unless you are being supervised.

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4.0 MILLING AND MILLING MACHINES4.1 THE MILLING MACHINE4.1.1 INTRODUCTION4.2 RECOMMENDED FEED PER TOOTH4.3 FEEDS4.4 CUTTING SPEEDS4.5 RULES FOR DETERMING SPEED AND FEED4.6 CUTTER TYPES4.7 CUTTER MOUNTING METHODS

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THE MILLING MACHINE

1. INTRODUCTION Milling may be defined as an operation whereby material is removed by rotation of one or more multi-toothed circular cutters in contact with the work which fed into the cutter path either manually or automatically.Each individual cutter tooth successively removes an equal amount of metal, thus generating a smooth surface as the work progresses.

The more elaborate the work usually encountered is modern production workshops is just an adaptation or combination of the above fundamental principles.It is seen that the milling operation is governed by the type of cutter being used, the purpose of the machine being:

- to control the cutter rotation by giving a range speeds to suit general conditions- to provide means for holding rigidly while the operation is in process- to control the rate also at which the work is passed under the cutter.

Milling operations can also be described as horizontal milling or vertical milling.

The horizontal machine is so named because the cutter spindle is in the horizontal plate and the vertical machine has a vertical cutter spindle.

2. FEEDS The rate of the table movement past the cutter is known as the rate of feed and the move-ment can be in three directions: longitudinal, cross and vertical. It is defined as the distance in inches (or millimeter) per minute that the work moves into the cutter. The rate used on mi9lling machine depends on a variety of factors such as:

-The depth and width of cut -The design or type of cutter -Sharpness of the cutter -Work piece material -Strength and uniformity and accuracy required -Power and rigidity of the machine

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As the work advances into the cutter, each successive tooth advances into the work and equal amount, producing chips of equal thickness. It is this thickness of the chips or the “feed per tooth”, along with the number of teeth in the cutter, which form the basis for determining the rate of feed. The ideal rate of feed may be determined as follows:

Feed = number of teeth in the cutter X recommended feed per tooth X r/min of the cutter

Under average operating conditions, it is suggested that the milling machine feed be set to approximately one-third or a half the amount calculated. The feed can then be gradually in-creased to the capacity of the machine and the finished desired. Table 1 and 2 give suggested feed/tooth for various types of milling cutters for roughing cuts under average conditions. For finish cuts, the feed/tooth would be reduced to one-half or even one-third of the value shown.

3. CUTTING SPEED One of the most important factors affecting the efficiency of a milling operation is cut-ter speed. If the cutter is run too slow, valuable time will be wasted, while excessive speed results in loss of time in replacing and regrinding cutters. Somewhere between these two extremes is efficient “Cutting Speed” for the material being milled.The cutting speed of a metal may be defined as the speed, in meters/min (or in surface feet/min), at which the metal may be machined efficiently. The cutter must be revolved at a speci-fied number of revolutions per minute depending upon its diameter, to achieve the proper cutting speed. Since different metals vary in hardness, structure and machinability, different cutting speeds must be used for such type of metal. The cutting speeds for the more common metals are shown in Table 3.

Spindle Speed (rpm) = (CS×1000) (11 D)

CS in m

Speed may have to be altered because of the hardness of the metal and/ or the machine con-dition. Best results may be obtained if the following rules are observed:

-For longer cutter life, use the lower cutting speeds in the recommended range -Know the hardness of the material to be machined -When starting a job, use the lower rough of the cutting speed and gradually increase to the higher range if conditions permit -If a fine finish is required, reduce the feed rather than increase the cutter speed -The use of coolant properly applied, will generally produce a better finish and length en the life of the cutter, since it absorbs heat, acts as a lubricant and washes chip away.

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Cutting Fluids Cutting fluids serve several purposes. They carry away the heat generated during the machin-ing operation; act as lubricant and prevent the chips from sticking and fusing to the cutter teeth; and flush away chips. The lubricating qualities of the cutting fluids also influence the quality of the finish of the machined surface. It is important that the correct lubricant be used for the material being material,Fig. 12-93.

Working Holding AttachmentsOne of the more important features of the milling machine is its adaptability to a large num-ber of working-holding attachments of the machine.

VisesThe VISE is probably the most widely used method of holding work for milling. The jaws are hardened to resist wear and ground for accuracy. The milling vise, like other work-hold-ing attachments, is keyed to the table slot with LUGS, Fig. 12-94 The FLANGED VISE, Fig. 12-95 has slotted flanges for fastening the vise to the table. The slots permit the vise to be mounted parallel to or at right angles to the spindle.The body of the SWIVEL VISE, Fig. 12-96, is similar to the flanged vise but is fitted with a circular base, graduated in degrees, Fig. 12-97, permitting it to be locked at any angle to the spindle.The TOOLMARKER’S UNIVERSAL VISE, Figs 12-98 and 12-99, permits compound or double angles to be machined without complex or multiple setups.

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The size of cylindrical cutters is specified by their outside diameter, length and bore size.

Name or sketch any other ways that these cutters are used in your firm

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The size of side and face cutters is specified by their outside diameter, width, and bore size.

Name or sketch any other ways that these cutters are used in your firm

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The size of slitting saws is specified by their outside diameter, width, and bore

Name or sketch any other ways that these cutters are used in your firm:

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The size of angle cutters is specified by their out-side diameter, angle(s) and bore size.

Name or sketch any other ways that se cutters are used in your firm:

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The size of form relieved cutters are specified by their outside diameters shape and dimen-sion of the required form and bore size Gear and sprocket cutters are also grouped depend-ing on the number of teeth to be cut.

Name or sketch any other ways that these cutters are used in your firm:

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Name or sketch any other ways that these cutters are used in your firm:

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Relationship of cutter rotation and the table feed.

1. Conventional or “up cut” milling ‘Up cut”milling describes the method of milling cutter rotates against the direction of the feed of the work piece.

This is the most commonly used method of milling. When the method of milling is not specified on the plan-ning sheet set the machine for up-cut milling.

2. Climb or ‘down-cut’ milling down cut milling describes the method of milling where the milling cut-ter rotates in the same direction as the feed of the work piece.

This method of milling produces a better surface finish, but its only used when specified on the planning sheet.

For successful ‘down-cut’ milling it is essential for the milling machine to be designed for the purpose, and also to be in perfect condition.

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5.0 GRINDING AND GRINDING MACHINES5.1 GRINDING SAFETY5.2 PEDESTAL GRINDING5.3 DRESSING TRUING, BALANCING WHEELS5.4 SURFACE GRINDING5.5 GRINDING WHEELS

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Material contained in the ANSI B7.1 Safety Requirements for “Use, Care and Protection of Abrasive Wheel”. For your safety, we suggest you benefit from the experience of others and carefully follow these rules.

Post this near your grinding machine

WARNING IMPROPER USE MAY CAUSE BREAKAGE AND SERIOUS INJURY DO and DON’T

1. DO always HANDLE AND STORE wheels in a CAREFUL manner.2. DO VISUALLY INSPECT all wheels before mounting for possible damage.3. DO CHECK MACHIN SPEED against the established maximum safe oper-ating speed marked on the wheel.4. DO CHECK MOUNTING FLANG-ES for equal ad correct diameter.5. 5. DO USE MOUNTING BLOT-TERS when supplied with wheels.6. DO be sure WORK REST is properly adjusted.(Center of wheel or above; no more than 1/8” away from wheel.)7. Do always USE A SAFETY GUARD covering at least one half of the grinding wheel.8. DO allow NEWLY MOUNTED WHEELS o run at operating speed, with guard in place, for at least one minute before grinding.9. DO always WEAR SAFETY GLASS-ES or some type of eye protection when grinding.10. DO NOT TURN OFF COOLANT before stopping wheel to avoid creating an out-of balance condition.

1. DON’T use a cracked wheel or one that HAS BEEN DROPPED or has become damaged.2. DON’T FORCE a wheel onto the machine OR ALTER the size of the mount-ing hole-if wheel won’t fit the machine, get one that will.3. DON’T ever EXCEED MAXIMUM OPERATING SPEED established for wheel.4. DON’T use mounting flanges on which the bearing surfaces ARE NOT CLEAN, FLAT AND FREE OF BURNS.5. DON’T TIGHTEN the mounting nut EXCESSIVELY.6. DON’T grind on the SIDE OF THE WHEEL (see Safety Code B7.1 for excep-tion).7. DON’T start the machine until the WHEEL GUARD IS IN PLACE.8. DON’T JAM work into the wheel.9. Don’t stand directly in front of a grinding wheel whenever a grinder is start-ed.10. DON’T FORCE GRINDING so that motor slows noticeably or work gets hot.

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These are machines in which operators grinds work, principally, in the sharpening of tools.

CONSTITUTION It is composed, generally of an electric motor, on the ends of which are attached two emery stones: one, made of coarse grain, serves to trim the work and the other, of fine grain, for finishing tool edges. USUAL TYPES

Pedestal Grinders (fig.1).It is used in common rough-cutting and in the sharpen-ing of manual and machine tools in genera. The power of the standard electric motor is 1 H.P., with 1450 to1750 RPM.

OBSERVATION

There are pedestal grinders with 4 H.P. motor power. They are used principally for coarse hewing and for trimming castings.

Fig.1 Pedestal Grinder

Parts of the pedestal grinder

a) Pedestal – a grey cast iron structure which serves as a support and enables the fasten ing of the electric motor.b) Electric motor- which rotates the emery stone.c) Stone protector- it accumulates the particles loosened from the emery or, when it breaks, prevents the pieces from causing accidents.d) Work support- it may be fastened at an appropriate angle, the important thing is to maintain, as the diameter of the stone diminishes, some clearance (from 1-2 mm)so as to prevent small parts from getting in between the stone and the support.

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e) Visual protector- indicated in Fig.1. It is the most practical for work in general.f) Coolant container- used to cool the tools made of tempered steel, preventing the heat produced by the friction between the tool and the emery stone from reducing the re sistance of the cutting edge, in case they are annealed.

Bench Grinder

It is fastened to the bench and its electric motor has ¼ to ½ H.P. power with 1450 to 2800 R.P.M. It is used for finishing and resharpening the cutting edge of the tools. In fig. 3 we have a bench grinder for sharpening metallic-carbide tools.

CONDITIONS FOR USEGrinders and others related machines are the ones that cause most accidents.To avoid this, it is recommended that these points be observed:

a- When the emery stone is mounted on to the motor axle, the revolutions indicated on the stone should coincide with or be a little greater than that of the motor;b- On fastened the emery stone, the hole should be exact and be perpendicular to the flat face;c- The curved surface of the stone should remain concentric with the moto axle. If this is not the case, on turning on the motor, vibrations and undulations would be experi enced by the work.

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In order to dress the grinding wheels, various types of special dressers are used:a- Dressers with tempered steel cutters, with angular shaped grooves (start-faced, fig. 4 or undulated fig. 5); fig 6 shows the correct position for the dresser to even off the sur face of the grinding wheel.

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b- Abrasive rod dresser (fig.7.

c- Emery wheel dresser with a diamond tip (fig8). It is often used in the dressing the wheels on the grinding machine. It is also used in fine grain emery stones of the bench grinders. Figs. 9, 10, demonstrate the correct posi-tion for machining the diameter of the emery stone. The cuts should be very fine and the size of the diamond should always be greater than the grain of the crushed emery stone so as to prevent it from being rooted out from the support.

GRINDING

Grinding is one of the fastest growing areas in a machine trade. Improved grinding machine construction has permitted the construction of parts to extremely fine tolerance with im-proved surface finishes and accuracy. Grinding has also, in many cases eliminated the need for conventional machining. Often the rough part is finished in one grinding operation, thus eliminating the need for other machining processes.The role of grinding machines has changed over the years; initially they were used on hard-ened work and for truing hardened parts which had been distorted by heat treating. Today,

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grinding is applied extensively to the production of unhardened parts where high accuracy ad surface finish is required.

1. The Grinding ProcessIn the grinding process, the work piece is brought into contact with a revolving grinding wheel. Each small abrasive grain on the periphery of the wheelacts as an individual cutting tool and re-moves a chip of metal (fig.1).As the abrasive grains becomes dull, the pressure and heat created between the wheel and the work piece cause the dull face to break away, leaving new sharp cutting edges.

Figure 2. SURFACE GRINDING VERTICAL

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Regardless of the grinding method used, cylindrical, centerless or surface grinding, the grinding process is the same and certain general rules will apply in all cases.- Use a silicon carbide wheel for low tensile strength materials and aluminum oxide wheel for high tensile strength materials- Use a hard wheel on soft material and a soft wheel on hard material.- If the wheel is too hard, increase the speed of the work or decrease the speed of the wheel to make it act as a softer wheel- If the wheel appears too soft or wears rapidly, decrease the speed of the work, or in crease the speed of the wheel, but not above its recommended speed.- A glazed wheel will affect the finish, accuracy and metal removal rate. The main cause of wheel glazing:1. The wheel speed is too fast2. The work speed is too slow3. The wheel is too hard4. The wheel is too small5. The structure is too dense which causes the wheel to load

- If the wheel wears too quickly the cause may be any of the following:1. The wheel is too soft the wheel is too slow2. The wheel is too fats3. The wheel is too great4. The face of the wheel is too narrow 5. The surface of the work is interrupted by holes or grooves

FIG.3. HYDRAULIC SURFACE GRINDER

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An industrial diamond, mounted in a suitable holder on the magnetic chuck is generally used to true and dress a grinding wheel.

5. Working holding Devises

1. Magnetic Chuck In some surface grinding operations the work may be held in a vice, on V-blocks or bolted directly to the table. However, most of the ferrous work ground on a surface grinder is held on a magnetic chuck which is clamped to the table of the grinder.

2. Doubled-faced Tape Double faced tape is often used for holding thin, non-magnetic pieces on the chuck for grind-ing. The tape is often used for holding thin, non-magnetic pieces on the chuck for grinding. The tape, having two adhesive sides, is plased between the chuck and work causing the work to be held securely enough for light grinding.3. Special fixtures These are often used to hold non-magnetic materials and odd shaped work pieces, particu-larly when a large number of work pieces must be ground.

6. Surface FinishThe finish produced by a surface grinder is important, and factors affecting it should be con-sidered. Some parts that are ground do not require fine surface finish and time should not be spent producing fine finishes if not required.

It should be noted that soft materials such as brass and aluminum will not permit as high as finish as higher ferrous materials. A much finer finish can be produced on hardened steel work pieces then can be produced on soft steel or cast iron.

7. Grinding Wheels Grinding wheels are composed of abrasive materials held together with a suitable bond. The basic functions of grinding wheels are:

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- Generation of cylindrical, flat and curved surfaces - Removal of stock - Production of highly finished surfaces - Cutting off operations - Production of sharp edges and points

For grinding wheels to function properly, they must be hard and tough, and the wheel surface must be capable of gradually breaking down to expose new sharp cutting edges to the mate-rial being ground.The material components of a grinding wheel are the abrasive grain and the bond. However, there are other physical characteristics, such as grade and structure that must be considered in grinding wheel manufacture selection.

Abrasive GrainThe abrasive used in most grinding wheels is aluminum oxide or silicon carbide. The func-tion of the abrasive is to remove material from the surface of the work being ground. Each abrasive grain on the working surface of the grinding wheel acts as a separate cutting tool and removes a small chip as it passes over the surface of the work. As the grain becomes dull, it fractures and presents a new sharp cutting edge to the material.This fracturing action reduces the heat of friction which would be caused if the grain become dull, producing a relatively cool cutting action. As a result of hundreds of thousands of indi-vidual grains all working on the surface of a grinding wheel, a smooth surface can be pro-duced on the work piece.

One important factor to consider in grinding wheel manufacture and selection is the grain size. The size of the abrasive grain is important since under size grains in the wheel will fail to do their share of the work, while over size grains will scratch the surface of the work.

The factors affecting the selection of grains sizes are:- The type of finished desired: coarse grains are best suited for rapid removal of metal. Fine grains are used for producing smooth and accurate finishes- The type of material being ground: generally coarse grains are used on soft material, while fine grains are used for hard materials.- The amount of material to be removed: where a large amount of material is to be removed and surface finish is not important, a coarse grain wheel should be used. For finish grinding, a fine grain wheel is recommended.- The area of contact between the wheel and the work piece: if the area of contact is wide, a coarse-grain wheel is generally used. Fine grain wheels are used when the area of contact between the wheel and the work is small.

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Bond Types The function of the bond is to hold the abrasive grains together in the form of a wheel. They are six common bond types used in grinding wheel manufacture: verified, resinoid, rubber, shellac, silicate and metal.

Verified: Made of clay feldspan, at a high temperature and when cooled forms a glossy bond around each grain. These bonds are strong but break down readily on the wheel surface to expose new grains during the grinding operation. This bond is particularly suited to wheels used for the rapid removal of metal.

Resionoid: Synthetic resins are used as the bonding agents in resinoid wheel. They are cool cutting and remove stock rapidly. They use are used for cutting off operations, snagging and rough grinding, as well as roll grinding.

Rubber Bond: Rubber bonded wheels produce high finishes such as those required on ball bearing races. Because of the strength and flexibility of this wheel, it is used for thin cut-off wheels.

Shellac Bond: These are used for producing high finishes on parts such as cutlery, cam shafts and paper mill roll. They are not suitable for rough or heavy grinding. Silicate Bond: Rarely used in industry it is used principally for large wheels and for small wheels where it is necessary to keep heat generation to a maximum

Metal Bond: Metal bonds (generally non-ferrous) are used on diamond wheels and for electrolytic grinding operations where the current must pass through the wheel.

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8. Common grinding wheel’s shapes and applications

9. Grinding Operations - Grinding flat surfaces - Grinding shoulders - Grinding angles and slots - Form grinding

Shape Name

Straight(Type 1)

Cylindrical, centerless, internal, cutter, surface, and offhand grinding operations

Surface grinding on horizontal and vertical spindle grinders

Snagging operations. The tapered sides lessen the chance of the wheel’s breaking.

Cylindrical, centerless, internal and surface grinders. The recess providers clearance for the mounting flange.

Cutter and tool grinder and surface grinding on vertical and horizontal spindle machines

Cylindrical, centerless, and surface grinders. The recesses provide clearance for mounting flanges. Cutter and tool grinder. Used mainly for sharpening milling cutters and reamers

Cutter and tool grinder. Its thin edge permits it to be used in narrow slots

Saw gumming, gashing milling cutter teeth

Cylinder(Type 2)

Tapered(both sides)

(Type 4)Recessed

(one sides)(Type 5)

Straight Cup(Type 6)

Recessed(both sides)

(Type 7)

Dish(Type 12)

Flaring Cup(Type 11)

Saucer(Type 13)

Application

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6.0 LATHES6.1 SAFETY6.2 INTRODUCTION TO CENTRE LATHES6.3 SINGLE POINT CUTTER TOOLS6.4 SPEED OF FEEDS6.5 LATHE OPERATIONS

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SAFE PRACTICES IN LATHEWORK

Rotating chucks and work are the major dangers in lathe work.Chips and the tool bit are also potential dangers if the operator does not pay attention to what is happening.

01. Permission should be obtained to operate the machine, at the discretion of the instruc tor.02. Always roll up loose sleeves and remove ties, rings, watches, and so on before operat ing the machine.03. Always wear specified eye protection.04. Make all adjustments with the machine off.05. When installing or removing chucks, place a safety board on the ways in case the chuck falls. This will prevent damage to both the chuck and ways.06. When loosening a chuck on a threaded spindle, do not use a pry bar between the chuck jaws. It is too hard on the jaws. Use a wrench on one of the jaw, with the jaw fully supported by the chuck.07. Never leave a chuck wrench in a chuck. If the machine were turned on, the wrench could become a lethal projectile08. To check the clearance of the chuck and the work, rotate by hand before switching on the machine.09. Always keep your hands away from moving parts.10. Always keep your hands away from chips. They are hot, sharp and dangerous.11. When filing, always use a file handle. It is also best to learn to file left-handed rather than by placing your left arm over the revolving chuck. Running the lathe in reverse and filing right-handed at the back of the lathe is poor practice because the controls are at the front of the lathe, out of reach. It is also best to remove the tool post assembly.12. Do not measure work with the lathe running. It is poor practice.13. Do not adjust the cutting tool with the machine running. 14. In general, it is poor practice to change gears while the lathe is running.15. As a general rule of thumb, no more than 3 times a diameter of the work should be out of a chuck with-out being support supported by tailstock or a steady rest.16. Never walk away from a lathe when it is operating.17. When the work is complete, shut off the power and clean the machine.

THE LATHE-TURNING

INTRODUCTION

Turning is the art of producing cylinders, cones, or rather surfaces of revolution by means of rotating the work about on axis and removing the surplus material by means of a cutting tool suitable guided. The machine on which such operations are performed is termed a lathe. Essentially its con-sists of a headstock carrying a spindle to which the work is connected in order that it may be

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rotated, means for driving the spindle, a bed carrying the headstock and the tool support as well as the tailstock.

The work may be connected with the spindle in various ways. The simplest is by centres. The ends of the work are drilled by a specifically pointed drill leaving two conical depressions or “centres”. If the work is short as compared with its diameter it may be “chucked”. The chuck consist of a cylindrical body fixed to the spindle and carrying two, three or four radically ad-justable members which may be arranged to grip the work and drive it against the resistance of the cutting tool.

In many lathes the spindle is hollow so that long bars may pass through it for operating on one end. In this case the chuck is used.

2. Cutting Tools

Various materials are used for making cutting tools:1. Carbon Steel - Light finishing cuts - Machining soft material - Fairly slow cutting speed - Cutting edge softens during cutting 2. High Speed Steel (HSS)- Tough enough to withstand most cutting shocks - Retains its hardness at high speed- Cut most material satisfactory

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- Useful for general purpose work 3. Stellite - Withstands heat very well - Hard chilled castings and similar material 4. Tungsten Carbide (tip)- Hardest cutting material normally used - Higher speeds can be used.

The two most common type of cutting tools are the high speed steel and tungsten carbide tipped tools.

High Speed Steel (HSS)- Work to great accuracy on small diameters - Turning small diameters, if the machine is not capable of a high RPM - Screw cutting - Intermittent turning

Tungsten Carbide Tool- Fast metal removal rate is required- Cutting hard and non-ferrous materials such as cast iron and brass - General machining - Screw cutting pipe

3. Work holding and Setting 1. Three jack saw 2. Between centres 3. Four jack saw 4. Fixed and travelling speed

1. Three jack sawThe advantage of a three jack saw is that the jaws are self- centering, enabling the work to be easily set central.

2. Between Centres The work is mounted between the live centre and the dead centre.Normally used for large length to diameter ratio work piece.

3. Four Jack Chuck The four jack chuck has jaws which are reversible and are adjusted independently. The ad-vantages are: 1. Both symmetrical and irregular shaped work can be held. 2. Work pieces may be set either concentrically or eccentrically 3. Greater holding potential than the three jaw chuck.

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4. Fixed and Travelling Steady Steadies are used for supporting long, slender work against the pressure of the work piece. There are two types of steadies used on a lathe:- Fixed steady- Travelling steady

Fixed Steady

The fixed steady is clamped to the body of the lathe an supports the work piece being ma-chined by means of three jaws at 120 to each other. As the steady is clamped to the machined bed the saddle cannot pass it. Thus a bar being turned must be machined at one end, reversed in the chuck, and then, machined at the other end. The most common applications of the fixed steady are for:- Facing the end of long bars too large in diameters to pass through the machine spindle - Drilling, boring or tapping of long bars.

Travelling Steady

The travelling steady is fixed to the carriage of the lathe and travels along with the tool. The two steady points should be set to travel just behind the tool, so that the steady pads bear on the portion of work which the tool has just machined. The most common application is for turning long shafts where it is inconvenient for the bar to be reversed in the chuck.

5. Cutting Speeds

Lathe work cutting speed may be defined as the rate at which a point on the work circumfer-ence travels past the work cutting tool. It is always expressed in meters/mm (m/mm) or feet/min (ft/min). If a cutting speed is too high, the cutting tool edge breaks down rapidly, result-ing in time loss in recondition the tool. With too slow cutting speed, time will be lost for the machining operation, resulting in low production rates. Recommended cutting speeds for various materials using a High Speed Tool bit is showed in Table 1. These speeds may be varied slightly to suit factors such as condition of the machine, the type of work material and sand or hard spots in the metal.

The revolutions/min at which the lathe should be set for cutting metals is as follows:

rev/min= -cutting speed in (meters) π ×diameter of work piece (metres)

= Cutting Speed ×12 (inches) π ×diameter of work piece (inches)

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5. Lathe Feed

The feed of a lathe is defined as the distance of the cutting tool advances along the length of the work for every revolution of the spindle. Table 2 list recommended feeds for cutting vari-ous materials using high speed tool bit.

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6. Turing Operations 1. Parallel 2. Drilling holes and boring 3. Partying off 4. Knurling 5. Screw cutting Vee-form threads: - external -internal 6. Taper turning

When selecting cutting speed, feeds and depth of the cut following factors should be taken into consideration:

1. Type and hardness of the work material2. The grade and shape of the cutting tool3. The rigidity of the cutting tool 4. The rigidity of the work and the machine 5. The power rating of the machine

Table 3 gives the recommended cutting speeds and feed for single point carbide tools.

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Turning Operations

Screw-cutting Vee Form Threads

1. Prepare work piece (a) Turn diameter to be screw-cut.(b) Undercut to provide a run-out recess of thread depth and of approximately two pitches width.

2. Set machine to cut required pitch of thread(a) Set levers in position as indicated on machine (b) Determine at which positions of the screw-cutting lever can be engaged

3. Set screw-cutting tool (a) Check tool shape with the aid of a screw-cutting gauge, e.g., 60° for unified threads, 55° for B.S.F and B.S.W threads.(b) Set top slide parallel to machine bed and clamp.(c) Set tool on correct centre height and clamp lightly(d) Set tool point square to work centre line.(e) Position the tool into an appropriate cut-out of the screw-cutting gauge whilst holding the gauge in contact with the work diameter or face. Gently tap the tool to align tool form with setting gauge. Clamp securely and re-check.

4. Position tool for first cut (a) Take up any backlash in the topside by turning the hand wheel clockwise.(b) Set topslide index to zero (c) Set machine to run at a slow r.p.m.(d) Feed the tool slowly in until contact is made with the diameter to be screwcut. Contact will be indicated by a fine ring being cut around the diameter.(e) Set cross-slide index to zero and clamp.(f) Retract tool from work surface

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5. Make a trial cut (a) Position on saddle to bring the tool approximately ¼ clear of the end of work piece(b) Re-index the cross-slide to zero. Apply cut of .003” memorize setting. (c) Apply coolant.(d) Apply a light engaging pressure to the screw cutting lever just before an engagement position is indicated on the screw-cutting dialNote:Ensure the lever engages fully or a false start will be made. Obtain the feel of the lever movement before commencing the work.(e) Disengage the screw cutting lever with a sharp single movement as the tool is seen to enter the run-out re cess.(f) Retract tool from work.

6. Check pitch of thread (a) Select correct pitch gauge and offer it to the lightly screwed work surface. Pitch to thread must correspond to that of the gauge. (If incorrect check gear lever setting and/or the change gears of machine.)

Safety Isolate the machine before opening guard to inspect gearing

7. Cut Thread (a) Re-position tool beyond the end of the work piece.(b) Re-index cross-slides to apply a .003” cut.(c) Index top slide forward .001”

Note:This movement relieves the pressure on the trailing edge of the tool. A thin thread will result if top slide is moved much above a third of the cross-slide movement.(d) Engage screw-cutting lever at appropriate screw cutting dial indication.(e) Disengage as tool enters run-out recess.(f) Retract tool from work.(g) Re-position for next cut.(h) Repeat these operations until within.005” of full cutting depth.

8. Check Thread(a) Check for fit using a screw ring gauge of mating component.

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9. Check thread Check for fit using screw plug or mating component.

SAFETYWork to be stationary whilst checking

10. Finish threads to size (a) Take fine cuts. Check for fit after each pass until full depth is reached. (b) At depth setting index top slide back, and with tool running along the thread take a very light cut off opposite side of thread.(c) Run cut over length of thread(d) Check thread(e) Continue to take fine cuts until correct fit gauge is obtained.Note:For left hands thread the lead-screw rotation is reversed causing the saddle to travel from left to right. The tool is set in the recess for the commencement of each cut.

Screw-cutting Square and Acme Threads

General note

When producing a one off thread and nut it is best to aim to make one of the three fitting elements of the threads a close fit, whilst the other two are varied within limits, to give a required condition.

Three elements 1. Outside diameter of male thread: Make this the close fitting element, i.e., turn diameter to basic size.2. Root diameter of male thread: Make this slightly smaller than basic size.3. Width of thread form both threads Make tool widths lightly wider than the basic half pitch.

For the female thread 1. Bore to basic size. 2. Cut thread to depth to give required fit.

The screw-cutting tool

To avoid interference between tool flanks and the side walls of the threadform, the tool side clearance angles must be designed so that the tool can fit into form it is cutting. The side clearance angle must be ground a few degrees larger than the helix angle of the thread being cut, and trailing edge ground sufficiently to clear the thread while maintaining maximum tool strength.

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Turning Operations (g) Position tool with point adjacent to the run-out recess. Pencil mark the bed to indicate the position of the saddleNote:Do not scribe the bed.

(h) Slowly feed the tool into the recess to full cutting depth. Listen and look for any contact between shank and work.

6. Make a trial cut (a) Re-position saddle to set tool ¼ clear of work face.(b) Index cross slide outwards and apply a .003” cut. Memorize this setting.(c) Apply coolant.(d) Engage lever at appropriate dial reading.(e) As the saddle come up to the pencil mark disengage the lever with a sharp single movement.

7.Check pitch of thread(a) Select correct pitch gauge and offer to screwed surface.(b) Check gear lever settings and/or the change gears if pitch is incorrect.

8.Cut thread(a) Re-position saddle to set tool ¼ clear of work.(b) Index cross-slide outwards to apply a .003” to.005” cut.(c) Index top slide forward ½ the amount of cut applied on cross-slide.(d) Engage screw-cutting lever at an appro priate dial reading.(e) As saddle reaches pencil mark disengage lever.(f) Retract tool from bore.(g) Repeat operation until within .005” of depth

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Internal Screw-cutting1. Prepare work (a) Machine bore to required depth and diameter(b) Cut run-out recess at inner end of bore

2. Set machine to cut required pitch of thread

3. Select internal screw cutting tool(a) Ensure shank will pass freely down bore (b) Ensure tip is small enough to allow point to enter recess before fouling back face of work.(c) Check using screw cutting gauge that point angle is correct, e.g., 60° Unified threads 55° B.S.F. and B.S.W.

4. Set screw cutting tool(a) Set top slide parallel to machine and clamp.(b) Clamp tool lightly in tool post slight ly above true centre height. (This al lows for downward spring when cut ting).(c) Set tool point square to work centre line.(d) Position the tool in to an appropriate cut-out of the screw cutting gauge whilst the gauge is held in contact with work diameter, or face.(e) Gently tap the tool align tool form with setting gauge.(f) Clamp securely and re-check set tings. 5. Position tool to take first cut (a) Take up backlash in topslide.(b) Set topslide index to zero and clamp.(c) Set machine to run at slow r.p.m.(d) Enter tool point about ¼ into bore. Touch too lightly on to bore wall, indicated by a fine ring being cut.(e) Set cross-slide index to zero and clamp.

Note:When cutting internal threads it is more convenient to set the depth of thread on cross-slide index so that on reaching full

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depth the index reading is at zero.

(f) Retract tool from work surface.

Note:When working with little clearance between tool shank and bore wall, note the index reading as the tool moves clear of the work surface, i.e., after backlash has been taken up.Retract to this reading after each cut.

9. Finish Thread to Size a) Take fine cuts. Check for fit after each pass until depth is reached.b) At depth setting, index top slide back with tool running along thread until a very light cut is taken off opposite side of thread.c) Run cut over length of thread.d) Check thread e) Continue to take very fine cuts until correct fit gauge is obtained.

Note: For a left hand thread the leads screw rotation is reversed causing the saddle to travel from left to right. Hence the tool is set in the run-out recess to commence each cut.

An alternative method of cutting vee-threads 1. Set tool (a) Set top-slide at ½ tread angle and clamp for B.S.F.., 30° for Unified (b) Set the tool square to work.(c) Set top-slide dial at zero(d) Touch tool on to work diameter.(e) Set cross-slide index to zero.2. Cut thread(a) apply a cut of .004” using top slide.(b) Retract tool from run-out recess using cross slide.(c) Re-position the tool for the next cut.

Apply a cut of .004” with top slide, set across-slide to zero. Repeat to required depth of thread.Screw-cutting up to a shoulderWhere no recess is permissible, as the tool ap-proaches the shoulder it is necessary to disengaged the screw cutting lever, and at the same moment to retract the tool from the work with a quick move-ment of the cross slide.

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Taper Turning Using a Form Tool

A method for producing short tapers of any angle either external or internal.External 1. Prepare work piece(a) Mount work piece in machine, keeping section to be tapered as close to support as possible(b) Finish turn to length and diameter2. Select form tool(a) For 30°, 45° and 60° angles standard tool may be available. For other angles select tool approximating to required angle.(b) Check tool face is long enough to produce complete taper in one cut.

3. Set tool(a) Set tool slide square and clamp.(b) Set tool on true centre height keeping tool over hang to a minimum.(c) Release toolpost. Set cutting edge to required angle using an angle gauge or protractor, register-ing from chuck or other suitable surface.Note:The tool will not cut the angle required unless it is set accurately on centre height.(d) Lock tool post and re-checking setting.Note:Where a self-indexing toolpost is to be used for more than one of the following procedure s more suitable: (a) Set tool slide square on lock (b) Lock tool post (c) Set tool to approximate angle on true cen tre height and clamp lightly. Keep tool overhang to a minimum. (d) Set tool accurately to required angle us ing an angle gauge or protractor, registering from chuck or other suitable surface.

Note:The tool will not cut the angle required unless it is positioned on the true centre height.(e) Clamp tool securely.3. Turn taper (a) Rotate work at cutting speed.(b) To produce a taper to a given diameter (i) Touch outer end of tool cutting face lightly to work corner. (ii) Lock saddle

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(iii) Set cross slide index to zero (iv) Apply coolant(c)To produce a taper to a given length. (i) Touch leading end of tool cutting face lightly to work corner using tool slide. (ii)Lock saddle (iii)Set tool slide (iv)Apply coolant (v) Feed along required length

Note: Chatter marks tend to developed as the width of cut increases. These may be eliminated by a reduction in work speed.

Taper Turning Using the Compound Slide

A method of both external or internal tapers of any angle to produced. Taper lengths is limited to the travel of the hand operated top slide.External taper 1. Ensuring top slide movement will enable full length of taper to be turned.Note:As the angle of taper is increased the maximum axial length becomes progressively less. 2. Prepare work pieceTurn parallel diameters to maximum diameter of tape.

3. Set top slide angle (a) Release top slide clamping screws.(b) Set top slide to half included angle of work taper.(c) Re- clamp top slide and re-check setting

4. Set tool(a) Set tool on true center height, normal to the surface to be turned.Note: a true taper will not result if the tool is set above, or below, centre height.(b) Bring the tool to working position and by using the top slide ensure the full taper length can be turn without obstruction.

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Note:When working with the tails stock it may be found necessary to position the hand wheel for-ward the head stock.

SAFETY When set in this position ensure there is freedom to rotate before switching on. Keep hands

clear of chuck or catch plate, when operating the tool slide control.

5. Turn taper(a.) Set top slide to rearmost position.(b.) Position saddle to clear tool of length to be tapered(c.) Lock saddle in position(d.) Rotate work at normal cutting speed(e.) Position tool to take a light cut(f.) Apply coolant(g.) Using top slide take the cut until tool runs outNote: For fine angles, small changes in work diameters result in big changes in the taper length. On such work care must be taken to avoid the first cut being too large(h.) Return top slide to rear position, apply further cuts until taper reaches about 2/5 full length 6. Check angle of taper (a.) Make a chalk line along the work taper(b.) Holding a taper gauge firmly in contact with the work piece rotate it about ¼ turn(c.) Observe where chalk line has been removed. Where com-plete line removed –paper is correct. Where part line removed-taper incorrect(d.) Where necessary reset topslide to correct error. Take light cuts. Recheck.

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7. Position tool for final cut to length(a.) Position tool point required length from front face of work piece(b.) Lock saddle(c.) Adjust cross slide to allow tool lightly trap a feeler gauge against work piece(d.) Remove feeler gauge(e.) Index tool in thickness of feeler gauge(f.) Set cross slide to zero(g.) Retract tool clear of work using cross slide(h.) Return top slide to rearmost posi-tion(i.) Re index cross slide to zero posi-tion(j.) Proceed with final cutInternal taperFor an internal taper a similar procedure is followed using a suitable sized standard boring tool, setting the top slide parallel to the taper being cut.

Taper Turning Using the Offset TailstockA method limited to the production of slow tapers on work turned between centres.1. Prepare work for turning between centres2. Mount work between centres3. Turn all parallel diameters and faces4. Calculate tailstock set over. Slow tapers are usually dimensioned as a given amount of taper on diameter per foot of length.Note:This set over allows an approximate first setting to be made. Final adjustment is made by checking work to a taper gauge.5. Set over tailstock (a.) Remove work piece from centres(b.) Release tailstock clamp and lightly tighten(c.) Release locking screw on rear face of tailstock(d.) Position a dial gauge to indicate amount of set over(e.) Adjust the two opposing setting screws in the side faces of the tailstock base, to offset the tailstock the calculated amount as registered on the dial indicatorNote: Adjust tailstock towards tool to turn taper smaller at tailstock end.(f.) Tighten the free setting screw(g.) Tighten rear lock screw(h.) Fully tighten tailstock clamp

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6. Remount work between centres

7. Turn taperNote:Proceed as for normal parallel turning. Cuts taken must be light otherwise offset tailstock centre will damage work centre(a.) Take roughing cuts to produce a taper long enough to check to gauge(b.) Adjust tailstock as necessary. Take light cut and recheck(c.)Finish turn tapered diameterNote:The taper as set will only be reproduced on successive work pieces if the length between work centres remains constant

8. Reset tail stock in true plane