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LATHE MACHINES

Lathe:-

A machine for shaping a piece of material, such as wood or metal, by rotating it rapidly along its

horizontal axis while pressing a fixed cutting or abrading tool against it.

Working principal of lathe:-

The working principal of lathe is to remove the excess material in the form of chips from rotating work

piece held between two centers with the help of a cutting tool fed against the work piece.

The centers between which the work piece is rotating are head stock Centre (live Centre) and tail

stock Centre (dead Centre). The tool can be fed parallel to the work piece (horizontal) or perpendicular

to the work piece (vertical).

To cut material properly,

1. The tool should be harder than the work piece.

2. Work piece should be rigidly held on the machine.

3. The cutting tool should be fed in different way relative to the work.

Specifications of engine lathe:-

The size of lathe is specified or designated by the following items.

1. Height of the centers above the lathe bed.

2. The largest diameter of work that can be revolved over the ways of lathe bed i.e., swing

diameter over the bed.

3. The largest diameter that can be accommodated over the carriage i.e., the swing diameter over

the carriage.

4. Maximum diameter that can be turned over the gap of bed (in case of gap bed) i.e., the swing

diameter over the gap of bed.

5. The maximum length of work that can be mounted between the centres.

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Parts of the lathe :-

The lathe carries the following main parts,

1. Bed 2.Headstock 3. Spindle 4. Tailstock 5. Carriage 6.Feed mechanism 7. Legs.

1. Bed:-

This is the base of the lathe, which will supports the all other parts. This is a heavy rigid structure made

by casting. This is a single piece structure which is having high damping capacity for the vibration

generated by machine during machining. The rigid structure will helps to avoid deflections.

2. Headstock -

The head stock will gives the rotation motion to the job at different speeds. It is a fixed part which will

present on the left side of the lathe bed. Head stock will consists of a hallow spindle and drive unit like

main spindle, feed reverse level, live centre, cone pulley etc.

3. Spindle:-

The spindle rotates on two large bearings housed on the headstock casting. A hole extends through the

spindle so that a long bar stock may be passed through the hole. The front end of the spindle is threaded

on which chucks, faceplate, driving plate and catch plate are screwed. The front end of the hole is

tapered to receive live center which supports the work.



On the other side of the spindle, a gear known as a spindle gear is fitted. Through this

gear, tumbler gears and a main gear train, the power is transmitted to the gear on the lead screw. The

construction of a lathe spindle is shown in Fig.

4. Tailstock:-

The tail stock is located at the right hand side of the lathe bed, it is called loose head stock because it is a

movable member for alignment of work with head stock. The moving action of tailstock can be done by

hand or by a wheel depending upon the design parameters and requirements.

The use of the tailstock,

i. It supports the other end of the long workpiece when it is machined between centres.

ii. It is useful in holding tools like drills, reamers and taps when performing drilling, reaming and tapping.

iii. The dead centre is off-set by a small distance from the axis of the lathe to turn tapers by set over

method.

iv. It is useful in setting the cutting tool at correct height aligning the cutting edge with lathe axis.

5. Carriage:-

The carriage will present between headstock and tailstock which will slides on the bed ways of the lathe

bed. The carriage will give feed to the tool and it holds the tool. The carriage consists of the following

parts,

(a) Saddle,

(b) Cross slide,

(c) Compound rest,

(d) Tool post,

(e) Apron.



(a) Saddle:-

The base of the carriage is the saddle and slides along the bed ways. It contains the cross feed

mechanism for moving the cutting tool at right angles to the ways. It supports the cross slide on which

compounds rest and tool post are mounted.

(b) Cross slide:-

The cross slide function to provide cutting action to the tool and the action of cutting tool will be

perpendicular to centre line lathe.

(c) Compound rest:-

It is supported on cross slide and is equipped with hand feed only. It can be swiveled horizontally on its

base to any angle through 360°. It is used for turning and boring short angles and tapers.

(d) Tool post:-

The tool post holds the tool in position and it is mounted on the top of the carriage.

(e) Apron:-

The apron is secured underneath the saddle of the carriage unit. The controls and mechanism for all

movements of carriage are housed in the apron. Its feed mechanism converts rotary motion of the lead

screw or feed rod into linear motion of the carriage on which cutting tool is clamped.

6. Feed mechanism:-

Most standard engine lathes are equipped with fed rod and a lead screw. The feed rod is used to

provide automatic feed for all turning operations except for thread cutting. The lead screw transmits

feed motion for screw cutting. In the absence of feed rod, the lead screw may be used for carriage feeds

as well as thread cutting. The feed rod and lead screw obtain motion from the lathe spindle (Via gears)

and transmit it to the carriage through gears and feed clutches.



7. Legs:-

The legs are the main support for the lathe to withstand the load, generally materials made by casting

method will be used for legs.

Types of lathe:-

The following types are,

1. Bench lathe 2. Speed lathe 3. Engine lathe 4.Tool room lathe 5. Capstan and turret lathe

6. Automatic lathe 7. Special- purpose lathes.

1. Bench lathe:-

It is a very small lathe and is mounted on a separately prepared bench or cabinet. It is used for

small and precision work since it is very accurate. It has the same features as Speed lathe or Engine

lathe. It perform almost all the operations, but difference only in its size.

2. Speed lathe:-

It is the simplest form of the lathe, in construction and operation. These lathes may be of

bench type or they may have the supporting legs cast and fitted to the bed. It consist of bed, headstock,

tailstock, and tool post. They have no gear box, carriage and the lead screw.

Here the work piece held between two centres revolved at high speeds by head stock,

and the tool is controlled by hand. The depth of the cut is low. The speed late is used in wood working,

centering and polishing.

3. Engine lathe or centre lathe:-

It is a general purpose lathe normally used all types of machine shops. The main parts of the engine

lathe are the bed, headstock, tailstock, carriage, lead screw and feed change gear box. The cutting tool

is mounted on tool post and can be fed in the cross and longitudinal directions with reference to lathe

axis. Power from motor is transmitted to spindle by belt drive or by gear drive. The speed changes in

belt drive are obtained by shifting the belt to a different steps of cone pulley.

It is used for producing cylindrical components. By using attachments and accessories,

other operations such as taper turning, milling and grinding may also be performed.

4. Tool room lathe:-

It is nothing but the same engine lathe but equipped with some extra attachments to

make it suitable for a relatively more accurate and precision type of work carried out in a tool room

lathe. It carries a much wider range of speeds and feeds. The usual attachments provided on a tool room

lathe are taper turning attachments, follower rest, collets, chucks, etc. this lathe is made to have a

comparatively smaller bed length than the usual engine lathe. The most commonly used lengths are 135

to 180 cm.



5. Capstan or turret lathe:-

Capstan and turret lathes are development of the centre (engine) lathe and are used for producing large

number of identical parts. The general design of these lathes is similar to engine lathe except that the

tailstock is replaced by a hexagonal turret. This turret is fitted with a series of pre-set tools and can be

indexed to present different tools to the work piece. With tooling these machines may be operated by

semi-skilled operators.

6. Automatic lathe:-

Automatic lathes are high speed, heavy duty lathes and are adapted in mass production. It is provided

with automatic controls for movement of work and tools at the proper rates and sequences. Once the

cutting tools are set up and the machine starts, it performs automatically all the operations to complete

the work. The cycle is repeated automatically (i.e., without attention of operators) to complete the next

job. The machine in which loading and unloading of work is done by operator, and other operations are

completed automatically is called as semi-automatic machines.

7. Special- purpose lathes:-

These lathes are designed in such a way that, it can perform certain specified operations only. These are

more effective than engine lathe in some specified operations. These include the gap lathe, wheel lathe,

taper lathes etc.

Work holding devices:-

A device used to hold a workpiece. Work holding devices used on lathe are

1. Centres 2.Catch plates and carries 3.Chucks 4. Face plates 5. Angle plates 6. Mandrels 7.rests.

1. centres:-

The most common method of holding the work in a lathe is between the two centres that is live centre

and dead centre. The live centre is fitted in the spindle nose of a head stock and the dead centre is

placed in the tail stock spindle. The line centre always rotates with the work (so named live), whereas

the dead centre remains stationary (so named dead). The dead centre is subjected to more wear

because it does not rotate and must withstand the friction of the work piece against it.

Oil, graphite may be used at the dead centre point to reduce friction. They include angle of the dead

centre usually 60 for general purpose work and 75 for heavy work.

The different types of lathe centres commonly used, along with their applications are shown in below.

(a) Ordinary centre

- Used for general work

(b) Half centre

- Used for facing the end of a bar without removing the centre.



(c) Ball centre

- Used to support the work during taper turning by set over method.

(d) Antifriction ball bearing centre

- It eliminates the friction and permits work to turned at high speed.

2. Catch plates (drive plates) or carries:-

Drive plate is a slotted circular plate attached to lathe spindle. The drive-plate is used to drive a work

piece with the help of carriers (dogs). A lathe dog or carrier is securely clamped to the work piece and its

bent tail fits into one of the slots in the face of the plate. Thus the rotation of drive plate (catch plate or

dog plate) is transferred to workpiece through dog.

3. Chucks:-

It is the most important device used for holding and rotating the work piece in a lathe. Work pieces of

short length, irregular shape or large diameter which cannot be conveniently mounted between centres

are held quickly and rigidly in a chucks.



Different types of chucks are follows:

(a) 3- jaw or universal chuck,

(b) 4-jaw or independent chuck,

(c) Combination chuck,

(d) Magnetic chuck,

(e) Air or hydraulic chuck,

(f) Drill chuck,

(g) Collet chucks.

(a) 3-jaw chuck :-

It consists of a cylindrical body having 3-jaws fixed radially as its front. In three jaw universal chuck or

self-centering chuck all the jaws move together in equal amounts to clamp the work. Therefore the job

is automatically centered and reduce the time of set-up. The jaws are not reversible, and separate

internal and external jaws have to be used. Also it has less gripping capacity and centering accuracy is

soon lost due to wear. The chuck is used for holding cylindrical or hexagonal work.

This chuck is unsuitable for irregular shaped work pieces which demands the use of 4-jaws chuck.

(b) 4- jaw chuck:-

In these chucks each jaw moves independently of the others so that work piece may be trued to run

accurately. It has superior gripping power than self-centering chuck, and used for holding square,

octagonal or large irregular components. Jaws of four jaw chuck can be reversed for holding externally

on the workpiece and, therefore, separate internal and external jaws are not required. The other

advantage of four jaw chuck is that work can be set to run concentrically or eccentrically, and there is no

loss of accuracy due to wear. However, the chuck is bulky and setting time is more.



(c) Combination chuck:-

It is a very useful development which carries the combination of both the above principals. Normally it is

provided with four-jaws which can be operated either by the scroll disk or individually separate screws.

(d) Magnetic chuck:-

Magnetic chucks are used to hold the steel work pieces (or work piece made by magnetic material) that

are too thin to be held in an ordinary chuck. The face of the chuck is magnetized by permanent magnets

contained within the chuck. Due to magnetic effect, the work piece are held on face of the chuck. This

type of chuck is suitable for the work that required only light cuts.

(e) Air or hydraulic chuck:-

In these chucks, air or hydraulic pressure is used for pressing the jaw against the job. The pressure is

provided by a cylinder and piston mechanism, fitted at the rear of the head stock, and is controlled by a

valve by the operator. These chucks are very quick acting and provided a very firm grip.

(f) Drill chuck:-

Drill chuck is used for holding straight shank reamers or drills for reaming or drilling. It has

self –centering jaws and is operated by key. The chuck is held in lathe tail stock.



(g) Collet chucks:-

Collect chuck provides a quick means of holding the bar stock. It is in the form of thin cylindrical bushing

with a slot cut length wise on its periphery. The inside bore of the collet depends on the shape of the

workpiece that will pass through it. Precision expanding collets are used for chucking on internal

surfaces. The collect assembly holds the workpiece in a previously machined bore.

4. Face plate:-

A face plate is similar to drive plate but larger in diameter, and contains more open slots or T-slots. Work

piece is clamped to the face plate by using bolts or T-bolts. It is used for holding cup’s …etc. That cannot

be conveniently held between chucks or centres.

5. Angle plate:-

This is a cast iron plate having two faces machined. To make them absolutely at right tangles to each

other. Angle plate in conjunction with a face plate provides an efficient means of holding work of

complex and irregular shape which is inconvenient or even impossible to clamp in jaw- type chuck. The

angle plate is attached to face plate and work is clamped to the angle plate as in fig shows. The counter

weights are attached to opposite side of face plate to counter balance the work and angle plate.



6. Mandrels:-

A mandrel is a device mounted between two centres. Mandrels are used to hold and rotate hollow

works between centres. It is a hardened and tapered steel bar with centres on its flat ends. The work is

forced to fit on the mandrel. The mandrel is rotated by the lathe dog and catch plate, and the work is

driven by friction.

The following mandrels are

a. Plain mandrel,

b. Step mandrel,

c. Cone mandrel,

d. Gang mandrel,

e. Expansion mandrel,

f. Collar mandrel,

g. Screw mandrel.

a. Plain mandrel:-

This type of mandrel is most commonly used in shops and finds wide applications in mass production.

The body of the mandrel is slightly tapered, 1 to 2 mm for meter length, for providing proper gripping of

the work. This type of mandrel is suitable for only one size of boor. For different size of boors different

types of mandrels are used.



b. Step mandrel:-

A step mandrel have steps of different diameters, used to drive different work pieces having different

size of holes, without replacing the mandrel each type. This type of mandrel is used for turning of

washers and odd size of jobs.

c. Cone mandrel:-

A cone mandrel consists of a fixed cone attached to one end of the body and a sliding cone which can be

adjusted by turning a nut at the threaded end. It is suitable for holding work pieces of different hole

diameters. By placing the work piece on two cones and tighten the nut.

d. Gang mandrel:-

This type of mandrels is used to hold a set of identical hollow work pieces between fixed collars and

washers by tighten the nut. The friction between the sides of the work and by the collar is sufficient to

drive the work without slipping in the mandrel. Gang mandrel will reduce setting and machining time.



e. Expansion mandrel:-

It consist of a tapered pin which is driven into a sleeve that is parallel outside and tapered inside. This

construction makes an expansion to grip varies work piece with different diameters that cannot be held

in an ordinary mandrel.

f. Collar mandrel:-

a collar mandrel have solid collars, used for turning work pieces of larger diameter holes more than

100mm. this construction reduces weight and fits better than a plain mandrel.

g. Screw mandrel:-

This type of mandrel is threaded at one end with a collar work piece having internal threaded are

screwed on to it, against the collar for machining. External surfaces of screw flanks, nuts back plates of

chucks…etc. These are matched on lathe by holding them on screwed mandrel.

7. Rests:-

It is a mechanical device. A long work piece must be provided additional support while a cut being taken.

A device, called rest perform this function. It helps to prevent the deflection of workpiece under the

action of cutting tool.

The following rets are commonly used on engine lathe.



(a) Steady rest, and

(b) Follower rest.

(a) Steady rest:-

Study rest consists of a cast iron base that may be made to slide on the lathe bed. It is clamped on the

bed ways in the required position between headstock and tailstock. It has three adjustable jaws. The

work piece is supported between these three jaws and two on the lower base and one on the upper

flame. The jaws may be adjusted radially by rotating individual screws to accommodate work pieces of

different diameters. The upper portion of the rest is hinged at the one end. One or more rests may be

used at a time depending on the job length.

It is also used to support the free end of a long work piece for drilling, boring, taping…etc.

(b) Follower rest:-



The follower rest have two adjustable jaws to support the work piece. It perform the same function as

the steady rest but it has two jaws which support the work opposite the tool. The tool is set slightly in

advanced position than the jaws, and as the tool is feed longitudinally by the carriage. The jaws always

flow the tool giving continuous support to the work piece and prevent any deflection of the work. The

entire work piece will be turned without disturbing the setting.

Tool holders:-

The device used to rigidly hold a carbide insert in place. Tool holders are available in standardized sizes.

There are there three tool holders are used on lathe that is

1. Single tool post.

2. American type tool post.

3. Four way tool post.

1. Single tool post:-

The single tool post can take only one tool. It can be rotated and clamped at any desired position. It

generally used when small champers are to be cut.

2. American type tool post:-

It consist of a pillar with a slotted hole in the center for fixing the toll by means of a set screw. The tool

post with a seating and boat piece, slides in a T-slot on the top of the compound rest. The highest of the

tool point can be adjusted by tightening the boat piece and clamping it in position by the set screw. The

tool post can be moved its vertical axis. The disadvantages with this type of tool is that adjustment to

highest by tightening. The tool post is not so rigid enough for hive works as only one clamping screw is

used to clamp the tool.

3. four way tool post:-

The 4-way tool post consist of a 4 slides to accommodate four tools at a time. The tool is held in position

by separate screws and a locking bolt is located at the center. The tools are fix in proper sequence of

operations and by indentions the tool post through 90°, any one of the tools may be fit into the work.

This type of tool post can be used for hive lathes or engine lathes.

Different methods of taper turning on lathe:-

A job said to be tapered, if the diameter changes uniformly along its length. Taper turning is a process of

producing taper on a workpiece. The taper may be external or internal according to the requirement.

The various methods used for taper turning operations are,

1. Forming tool method,

2. Compound rest method,

3. Tailstock set-over method, and

4. Taper attachment methods.



1. Taper turning by a forming tool method:-

Turning of taper by form tool is shown in fig. The form tool has a straight cutting edge inclined at the

desired angle with the axis of rotation of work. This angle is equal to half the taper angle. The tool is fed

straight into the work to produce a taper surface.

This method is limited to short tapers.

2. Taper turning by the compound rest method:-

Taper turning using compound rest is shown in fig. it is used for turning longer taper than produced by a

form tool, but the length of taper is limited by linear movement of compound rest slide. The base of

compound rest is graduated in degrees and can be swiveled for required angle. The taper angle must

first be calculated in degrees, and the rest may be swiveled to required angle (half of the taper angle).

The feeding of the tool is done with compound rest feed handle and is controlled by hand. This method

is simple and easy to setup for wide range of angles. But due to hand feed, it gives low productivity and

poor surface finish.

3. Taper turning by tailstock method:-

This method is used for producing small tapers on long work pieces. In this method, the tail stock is set

over at a distance away from the axis of spindle and the tool is allowed to move parallel to the axis of

spindle. Due to the setting of tailstock, the work piece centre line is shifted at an angle a (semi-cone

angle) to the spindle axis and hence allows for taper turning by moving the tool straight (or parallel to



the axis of spindle).the axis of rotation of work is inclined at an angle to the lathe axis. It is the effective

method of turning small tapers on long jobs.

4. Taper turning by taper attachment:-

Taper turning attachment is shown in fig. in this method the work is aligned to lathe axis and cutting tool

is fed at an angle to the axis of work by means of attachment. The taper turning attachment consists of a

bracket on which a guide bar is pivoted. The guide bar is provided with graduation in degrees and can be

swiveled on either side of zero graduation to set at the desired angle. It can be used for turning internal

as well as external tapers, and power feed can be used to turn taper quickly and with better finish. But

length of taper limited to length of slide bar.



Thread cutting on lathe:-

Thread cutting is a operation of a produce helical grooves on a cylindrical surface by feeding the tool

longitudinally, when the job is revolved between centres. The longitudinal field should be equal to the

pitch of the thread to be cut per revolution of the workpiece.

APRON Mechanism:-

A lever, hand wheel, pinion, automatic feed clutch, half-nut and lead screw are the major parts of apron

mechanism, which are used for saddle movement and also for operating carriage manually or

automatically.

A half-nut is fixed at the inside position of apron and it connects the lead screw to the carriage, which is

driven by the worm gears, provided on the feed shaft.

APRON is mounted over the front face of the bed and it is fastened to the saddle. The function of apron

is to transmit motion from the feed shaft to the carriage and half-nut, which engages with lead screw

during tapping operation by means of gears and clutch.



The rotary motion of lead screw is transformed into translator motion of the cross slide transversely on

the carriage or of the carriage longitudinally on the bed through the apron mechanism.

The longitudinal and transverse motions of carriage and cross-slide can be controlled by the apron

mechanism. Generally, a lever is used to enlarge the half nut for tapping operation.

Back gear mechanism:-

Back gear mechanism is housed within the headstock of the lathe. A step cone pulley having steps ABCD

and a small pinion ‘P’ are mounted on the spindle and rotates freely on it. The gear ‘S’ is keyed to the

headstock spindle. So, the spindle will rotate only when the gear ‘S’ rotates.

The step cone pulley ABCD and the gear ‘S’ can be kept separately or made as one unit with the help of

a pin ‘T’. When the pin is disengaged, the cone pulley along with the gear P will rotate freely on the

spindle and the spindle will not rotate. There is another shaft parallel to the spindle axis having back

gears Q and R mounted on it. These back gears can be made to mesh with gears P and S or kept

disengaged from them. The spindle can get drive either from the cone pulley or through back gears.



Turret lathe:-

It is the modification of the engine lathe. The turret lathe elements the setup time between operations,

reduced production time tremendously. In turret lathe the tail stock of an engine lathe is replaced by a

multiple face rotating tool holder or turret. Which may have 6 faces. The 6 face or hexagonal turret is

the most common. All the 6 faces of the turret can hold 6 or more number of different tools. The turret

may be indexed automatically and each tool may be brought in line with the lathe axis in a regular

sequence. The longitudinal and cross fed movement of the turret saddle and cross slide are regulated by

adjustable stops.

The special of the turret lathe enable it to perform a series of operations such as drilling, boring, turning,

thread cutting, chambering, cutting-off and many other operations in a regular sequences.

Capstan lathe:-

The capstan lathe is a ram-type turret lathe in which hexagonal turret is mounted on a ram slide. The

saddle, which supports the ram, is clamped to the bed at a desired position. This lathe is of light

construction and has a short turret stroke and an automatic index on the turret. The turret stroke

depends on the ram that varies from 100 mm to 375 mm. capstan lathes are used for mass production

of small to medium size components from bar and rod stock.



Difference between turret and capstan lathes:-



Principal of Automatic and semi-automatic lathes:-

Automatic machine:-

Machine in which the handling of workpiece along with the metal cutting operations are automatically

performed is known as automatic machines.

Semi-automatic machines:-

Semi-automatic lathes are production lathes in which, once the machine is setup, all the machining

operations are performed automatically but loading of work pieces and unloading of finished

components are accomplished by the operator.

Turret and capstan lathes are semi-automatic lathes. These lathes are used for production work

where large quantities of identical work pieces are manufactured.

Different types of automatic machines:-

The automatic machines are classified into two categories. They are,

1. Magazine loaded automatic machines,

2. Automatic bar machines.

1. Magazine loaded automatic machines:-

Magazine loaded automatic machines are used to machine the work piece which are in the form of

blanks. These blanks, before feeding to the automatics are appropriately machined till their accurate

dimensions are obtained.

2. Automatic bar Machines:-

The machining of work pieces either from bar or pipe stock is accomplished by using automatic bar

machines.

These are further classified as follows,

a. Single spindle machine

b. Multi spindle machine

Difference between single spindle and multi spindle automatic lathes:-

Single spindle automatic lathe Multi spindle automatic lathe

1. The single spindle machines operate on a single components at a time. 2. These lathes produces short components, and perform operations like drilling, threading, turning, forming etc.

1. The multi spindle machines usually operate on 2 to 8 spindle one at a time. 2. These machines have capacity to machine different diameter components effectively.



3. The example of single spindle automatic lathes are Swiss type automatic screw machine and automatic cutting off machines. 4. The rate of production is low. 5. The machining accuracy of single spindle automatic lathe is high. 6. There is no chance to index the spindle, as it has only one spindle.

3. The examples of multi spindle automatic lathes is automatic bar machine. 4. The rate of production is high. 5. The machining accuracy of multi spindle automatic lathe is low. 6. The indexing of spindles taken place through 90° to 60°. Which depends on whether there are 4 or 6 spindles.

Tooling layout of automatic lathes:-

The tool layout for automatic turret lathe is shown in figure. The various operations performed to get

the required job is as follows,

1. Feed bar to the stop 1 and clamp,

2. Centre end of the bar and dwell to clean up index turret,

3. Turn ∅12 and drill ∅ 9.9

4. Drill ∅5 holes,

5. Cone bottom of ∅ 9.9 mm hole,

6. Ream ∅ 10 mm and cone,

7. Cutoff over cross slide.



Operations performed in a lathe:-

Various operations are performed in a lathe other than plain turning. They are

1. Facing:-

Facing is the operation of machining the ends of a piece of work to produce flat surface square with the

axis. The operation involves feeding the tool perpendicular to the axis of rotation of the work. Facing

operation is shown in Fig.

2. Turning:-

Turning in a lathe is to remove excess material from the workpiece to produce a cylindrical surface of

required shape and size. Straight turning operation is illustrated in Fig.

a. Straight turning:-

The work is turned straight when it is made to rotate about the lathe axis and the tool is fed parallel to

the lathe axis. The straight turning produces a cylindrical surface by removing excess metal from the

work pieces.



b. Stepped turning:-

Step turning is the process of turning different surfaces having different diameters. The work is held

between centres and the tool is moved parallel to the axis of the lathe. It is also called shoulder turning.

3. Chamfering:-

Chamfering is the operation of beveling the extreme end of the workpiece. The form tool used for taper

turning may be used for this purpose. Chamfering is an essential operation after thread cutting so that

the nut may pass freely on the threaded workpiece. Chamfering is shown in Fig.

4. Grooving:-

Grooving is the process of cutting a narrow groove on the cylindrical surface of the workpiece. It is

often done at end of a thread or adjacent to a shoulder to leave a small margin. The groove may be

square, radial or beveled in shape. Different types of grooves are shown in Fig.

5. Forming:-

Forming is a process of turning a convex, concave or any irregular shape. For turning a small length

formed surface, a forming tool having cutting edges conforming to the shape required is fed straight

into the work.

6. Knurling:-

Knurling is the process of embossing a diamond shaped pattern on the surface of the workpiece. The

knurling tool holder has one or two hardened steel rollers with edges of required pattern.



The tool holder is pressed against the rotating work. The rollers emboss the required pattern. The tool

holder is fed automatically to the required length.

7. Undercutting:-

It is a process of enlarging the diameter if done internally and reducing the diameter if done externally

over a short length. It is useful mainly to make fits perfect. Boring tools and parting tools are used for

this operation.

---------------------------------------------------All the best----------------------------------------------------------------------



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