2. lathe operation

8/12/2019 2. Lathe Operation

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Manufacturing Technology

8

DEPARTMENT OF MECHATRONICS & MECHANICAL ENGINEERING

U. V. PATEL COLLEGE OF ENGINEERING,

GANPAT UNIVERSITY

CLASS: - SEM.

IV

th

ME SUBJECT:-MANUFACTURINGTECHNOLOGYEXPT NO.: - DATE: -

AIM: To t!"# "$%%'(t O)'*t$o( )'%o'+" o( L*th +*h$(.

INTRODUCTION:

In order to perform different machining operation in a lathe, the work piece may be

supported and driven by any one of the following methods:

1. Held between centers and driven by carries and catch plates.

2. Held on mandrel, which is supported between centers and driven by, carries catchplates.

. Held and driven by chuck with the other end supported on the tailstock centers.

!. Held and driven by a chuck or a faceplate or an angle plate.

"he above methods of holding the work may be broadly classified under two headings:

1. #orkpiece held between centres.

2. #orkpiece held by a chuck or any other fi$ture.

O)'*t$o(, h$h *' )'%o'+" $( * *th $th' /# ho"$(0 th o'1 )$

/t( (t' o' /# * h!1, *':

1% &traight turning 8% "aper turning

2% &houlder turning '% (ccentric turning

% )hamfering 1*% +olishing

!% "hread *cutting 11% rooving-% acing 12% &pinning

/% 0nurling 1% &pring winding

% iling 1!% orming

O)'*t$o(, h$h *' )'%o'+" /# ho"$(0 th o'1 /# h!1 o' * %*)*t o' *(

*(0 )*t, *':

1% rilling /% Internal thread cutting

2% 3eaming % "apping

% 4oring 8% 5ndercutting!% )ounter boring '% +arting6off

U. V. Patel College of Engineering, GanpatVidyanagar


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'-% "aper boring

O)'*t$o(, h$h *' )'%o'+" /# !$(0 )$* *tt*h+(t, *':

1% rinding 2% 7illing

CENTERING:

#here the work is reuired to be turned between centers or a chuck and a centre, conical

shape holes must be provided at the ends of the workpiece to provide bearings surface forlathe centers. )entering is the operation of producing conical holes in workpiece. "o

prepare a cylindrical workpiece for centering, it is first necessary to locate the centre hole

by making off. 3ubbing the end with chuck does this and the centre may be located byany one of the following instruments:

1% 5sing a centre head and steel rule obey combination set,

2% 5sing a hermaphrodite caliper,% 5sing a divider and surface plate,

!% 5sing a surface gauge, and

-% 5sing a bell centre punch.

TURNING:

"urning in lathe is to remove e$cess material from the workpiece to produce a cone6

shaped or a cylindrical surface. "he various types of turning for various purposes, which

are described under:

STRAIGHT TURNING:

"he work is turned straight when it is made to rotate about the lathe a$is, and the tool isfed parallel to the lathe a$is the straight turning produces a cylindrical surface by

removing e$cess metal from the workpiece.

"here are two kinds of cuts in a machine shop work:

1. 3oughing cut orrough turning.

2. inishing cut orfinish turning.

ROUGH TURNING:

"he rough turning is the process of removal of e$cess material from the workpiece ina minimum time by applying high rate of feed and heavy depth of cut. "he roughing cutshould be so made that the machine, the tool, and workpiece can bear the load and it does

not make too rough a surface and spoil the center. "he depth of cut for roughing operation

in average machine shop work is from 2 to - mm and the rate of feed is from *. to 1.-mm per revolution of the work. In fig. 3ough turning operation is shown.



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FINISH TURNING:

"he finish turning operation reuires high cutting speed, small feed, and a very smalldepth of cut to generate a smooth surface. 9 finish turning tool having sharp cutting edge

is held securely on the tool post for this purpose. In finish turning operation shown in fig.

"he depth of cut ranges from *.- to 1 mm and feed from *.1 to *. mm per revolution of

the workpiece. nce the correct setting is made, the rest is finished by the automatic feed.)opious supply of coolant and lubricant should be used to produces smooth surface.

SHOULDER TURNING:

#hen a work piece having different diameters is turned, the surface forming the step

from one diameter to other is called the shoulder, and machining this part of theworkpiece is called shoulder turning.

"here are four kinds of shoulder:

1. &uare shoulder2. 9ngular orbeveled shoulder

. 3adius shoulder

!. 5nder cut shoulder

"he location of the shoulder is first marked on the workpiece by a hermaphrodite caliper,

measuring from one end by a steel rule. "he first diameter is then turned to the finished

si;e within *.- to 1 mm of the shoulder mark. or suare or beveled shoulder a right cutfacing tool is used to finish up to the shoulder mark. 9 round nose tool will produce a



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11radius shoulder. 9n undercut shoulder may be machined by using a parting tool, being fed

into the work below the first diameter surface to the desired depth.

TAPER ELEMENTS:

9 tapered piece shown in fig. may be designated by the following symbols:

"he amount of taper in a work piece is usually specified by the ratio of difference indiameters of the taper to its length. "his is termed as the conicity and its designated bythe letter 0.

0 < 6 d

=

TAPER TURNING METHODS:

9 taper may be turned in a lathe by feeding the tool at an angle to the a$is of rotation of

the workpiece. "he angle formed by the path of the tool with the a$is of the workpiece

should correspond to the taper angle.#hile the workpiece is correctly in centers then we get the correct taper shape. 9 taper

may be turned by any one of the methods:

1. 4y a broads nose from tool.

2. 4y setting over the tailstock centre.

. 4y swiveling the compound rest.!. 4y a taper turning attachment.

-. 4y combining longitudinal and cross feed in a special lathe.



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TAPER TURNING BY A FORM TOOL:

9 broad nose tool having straight cutting edge is set on to the work at half taper angle andis fed straight into the work to generate a taper surface. In this method the tool angleshould be properly checked before use. "his method is limited to turn short length of

taper only. "his is due to the reason that the metal is removing by the entire cutting edge,

and any increase in the length of the taper will necessitate the use of a wider cutting edge.In fig. "here are shown as method of turning taper by a form tool.

TAPER TURNING BY SETING OVER THE TAIL STOC2:

"he principle of turning taper by thismethod is to shift the a$is of rotation of the

workpiece and feeding the tool parallel tothe lathe a$is. "he angle at which the a$is ofrotation of workpiece is shifted is eual to

half angle of taper. "his is done when the

boly of the tailstock is made to slide on its

base towards or away from the operator by aset over screw as illustrated in fig. "he

amount of set over being limited, this

method is suitable small taper on long >obs.7oreover the lathe carrier being set an

angle, the angular velocity of the work is not

constant.

TAPER TURNING BY S3IVELLING THE COMPOUND REST:

"his method employs the principle of turning taper by rotating the workpiece on the lathe

a$is and feeding the tool at an angle to the a$is of rotation of the workpiece. "he tool



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1mounted on the compound rest is attached to a circular base, graduated in degree, which

may be swiveling and clamped at any desired angle. "his is shown in fig. "his method is

limited to turn a short taper owing to the limited movement of the compound rest. "he

compound rest may be swiveled at !-? on either side of the lathe a$is enabling it to turn asteep taper. "he movement of the tool in this method being purely controlled by hand,

this gives a low production capacity and poorer surface finish.

TAPER TURNING BY A TAPER ATTACHMENT:

"he principle of taper turning taper by a taper attachment is to guide the tool in a straight

path set at an angle to the a$is of rotation of the workpiece, while the work is being

revolved between centres or by a chuck aligned to the lathe a$is. 9 taper turning

attachment is shown in fig.

#hen the taper turning attachment is used, the crosslide is first made free from the lead

screw by removing the binder screw. "he rear end of the crosslide is then tightened which

the guide block by means of a bolt. "he reuired depth of cut is given by the compoundslide, which is placed at right angle to the lathe a$is. "he guide bar must be set at half

taper angle and the taper on the must be converted in degrees. "he ma$imum anglethrough which the guide bar may be swivelled is 1*? to 12? on either side of the centre

line.

tan < 6 d

2l



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TAPER TURNING BY COMBINING FEEDS:

"his is a more speciali;ed method in which certain lathes both longitudinal and crossfeeds may be simultaneously causing the tool to follow a diagonal path which is theresultant of the magnitude of the two feeds. @arying the rate of feeds by change gears

provided inside the apron may change the direction of the resultant. "aper turning by

combining feeds is shown in fig.

ECCENTRIC TURNING:

If a cylindrical workpiece has two separate a$is of rotation one being out of center to theother the workpiece is termed eccentric and turning of different surfaces of the workpiece

is known as eccentric turning which is shown in fig.

"he shaft is first mounted on its true center and the part forming the >ournal is turned. "he>ob is then remounted on the offset center and the eccentric surfaces are machined. In

eccentric turning, counterbalance weights are mounted on the face plate to get uniform

turning movement.



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CHAMFERING:

)hamfering, is shown in fig., is the operation on beveling the e$treme end of a

workpiece. "his is done to remove the burrs, the protect the end of the workpiece frombeing damaged and to have a better look. "he operation may be performed after knurling,

rough turning, boring, drilling or thread cutting. )hamfering is an essential operation

after threads cutting so that the nut may be pass freely on the threaded workpiece.

THREAD CUTTING:

"hread cutting is one of the most important operations performed in a lathe. "he principle

of thread cutting is to produce a helical groove on a cylindrical or conical surface byfeeding the tool longitudinally when the >ob is revolved between the centers or by a

chuck. "he longitudinally feed should be eual to the pitch of thread to be cut perrevolution of the workpiece. "he leadscrew of the lathe, through which the saddle

receives its traversing motion, has a definite pitch. 9 definite ratio between the

longitudinal feed and rotation of the headstock spindle should therefore be found out sothat the relative speed of rotation of the work and the leadscrew will result in the cutting

of a screw of the desired pitch. )hange gears arranged between the spindle and the

leadscrew or by the change gear mechanism or feed bo$ used in a modern lathe where it

provides a wider range of feed and the speed ratio can be easily and uickly changedaffect this. ig illustrates the principle of thread cutting.



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FACING:

acing is the operation of machining the ends of a piece of work to produce a flate

surface suare with the a$is. "he operation involves feeding the tool perpendicular thea$is of rotation of the workpiece. 9 properly ground facing tool is mounted in a toolholder in a tool post. "he cutting edge should be set at the same height as the center of the

workpiece.

2NURLING:

0nurling is the process of embossing a diamond shaped pattern on the surface of a

workpiece. "he purpose of knurling is to provide an effective gripping surface on a

workpiece to prevent it from slipping when operated by hand. In some press fit work

knurling is done to increase the diameter of a shaft. "he operation is performed by aspecial knurling tool which consists of 1 set of hardened steel rollers in a holder with the

teeth cut on their surface in a definite pattern. ig., illustrates a revolving holder with

three sets of knurls. 9ny one set or pair may be brought into operation by revolving theunit.



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FILING:

iling is the finishing operation performed after turning. "his is done in a lathe to remove

burrs, sharp corners and feed marks on a workpiece and also to bring its si;e by removingvery small metal. "he operations consist of passing a flate single cut file over the

workpiece at high speed.

POLISHING:

+olishing is performed after filling to improve the surface uality of the workpiece.

+olishing with successively finer grades of emery clothe after filing result in verysmooth, bright surface. "he lathe is run at high speed from 1-** to 18** m per min, and

oil is used on the emery cloth.

GROOVING:

rooving is the process of reducing the diameter of a workpiece over a very narrowsurface. It is done at end of the thread to a shoulder to leave a small margin. "he work is

revolved at half the speed of turning and a grooving tool of reuired shape into the work

by rotating the cross6slide screw. 9 grooving tool is similar to a parting of tool. "his is

shown in fig.

SPINNING:

&pinning is the process of forming a thin

sheet by revolving the >ob at high speed

and pressing it attach to the headstockspindle. 9 support is also given from the

tailstock end. "he pressure applied to the

revolving sheet metal by a long ground

on the special too, when the piece is

slowly acuires the shape of the formershown in fig.



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FORMING:

orming is the process of turning a conve$, concave or of any irregular shape. romturning may be accomplished by the following method:

1. 5sing a forming tool.2. )ombining cross6land longitudinal feed.

. "racing or coping a template.

or turning a small surface, forming tool having cutting edge conforming to the shapereuired is fed straight into the work. orming tools are used mainly for finishing formed

surfaces. 5sually two types of forming tools are used A &traight and )ircular. &traight

type is used for wider surface and the circular type for narrower surfaces fig. shownforming operation performed by straight or )ircular tools. "he cross feed ranges from

*.*1 to *.*8 mm per rev. #hen the length of the formed surface is sufficiently grate, the

reuired shape may be obtain by using straight turning tool. "he process is tedious andreuires much skill.



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DRILLING:

rilling is the operation of producing a cylindrical hole by the rotating cutting a edge of a

cutter known as the drill. "here are two methods to drilling in a lathe.

1. "he workpiece is revolved in a chuck and the drill is held in the drill holder. "he

movement of the tailstock spindle effects feeding.

2. "he drill is held and driven by a drill chuck attached to the headstock spindle. "hemovement of the tailstock spindle effects feeding. #hen workpiece is in irregular

shape, which cannot be accommodated on a chuck.

&peeds and feeds for drilling in a lathe are 2-B lower than the corresponding figures for

drilling in a drilling machine.

REAMING:

3eaming is the operation of finishing and si;ing a hole, which has been previously drilled

or bored. "he tool used is called the reamer, which has multiple cutting edges. "hereamer is held on the tailstock spindle, either direct or through a drill chucks and is held

stationary while the work is revolved at a very slow speed. "he feed varies from *.- to 2

mm per revolution.

BORING:

4oring is the operation of enlarging and truing a hole producing by drilling, punching,

casting or forging. 4oring cannot originate a hole. 4oring is similar to the e$ternal

turning operation and can be performed in a lathe by the following two methods:



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1. "he work is revolved in a chuck or a faceplate and the tool, which is fitted to the

tool post, is fed into the work. ne piece6forged tool is used for boring small hole,

whereas a boring bar with a tool bit attached to it is suitable for machining a largehole. "he depth of cut is given by the )rosslide screw and the feed is effected by

the longitudinal travel of the carriage.

2. "he work is clamped on the carriage and a boring bar holding the tool is supported

between the centers and made to revolve. In fig. &hown a operation of boring bar.

INTRNAL THREAD CUTTING:

"he principle of cutting internal thread shown in fig. &imilar to an e$ternal thread,

difference being in the tool used. "he tool is similar to boring tool with cutting edgesground to the shape conforming to the thread to be cut. or cutting metric thread, the

compound slide is swiveled *? towards the headstock. "he tool is fi$ed on the tool post

after setting it at right angle, using a thread gauge. "he depth of cut is given by thecompound slide and the thread is finished in the usual manner.

UNDERCUTTING:



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215ndercutting is shown in fig., similar to grooving operation. It is the process of boring a

groove or a large hole at fi$ed distance from the end of a hole, e$cept that a suare nose6

parting tool is used. 5ndercutting is done at the end of an internal thread or a counterbore

to provide )learance for the tool or any mating parts.

PARTING-OFF:

In fig parting6off, the operation of cutting workpiece after it has been machined to the

desired si;e and shape. "he process involves rotating the workpiece on a chuck at half thespeed by narrow parting of tool perpendicular to the lathe a$is. 4efore the operation is

started, the carriage is locked in a position on the lathe bed and the cutting tool is held

rigidly on the tool post with the compound slide set parallel to the lathe a$is. "he feed

varies from *.* to *.1- mm per rev. and the depth of cut tool ranges from 6to1* mm. Instages the parting tool is first fed through a certain depth, two more cuts are made at the

two slides of the central groove.


2. lathe operation

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