D.KRISHNAIAH

ASSOC.PROF

LATHE

• Lathe is machine, which removes metal from a piece of work to the required shape and size.

• Lathe is one of the most important machine tool in the metal working industry.

• A lathe operate on the principle of a rotating work piece and a fixed cutting tool.

• The cutting tool is feed into the workpiece, which rotates about its own axis, causing the workpiece to be formed to the desired shape.

Treadle Wheel Lathe

• Computer controlled lathe:

Modern Engine Lathe

• Electric Motor

• Tolerances of 0.001 inch

• Multiple Screws

• Geared Head– Variable Spindle Speeds (Rotation)

– Variable & Accurate Feeds (Tool Movement)

• Lathe is the oldest machine tool invented, starting with the Egyptian tree lathes.

• It is the father of all machine tools

• Its main function is to remove material from a work piece to produce the required shape and size

• This is accomplished by holding the work piece securely and rigidly on the machine and then turning it against the cutting tool

• Cutting tool will remove material from the work piece in the form of chips.

• Working Principle: The lathe is a machine tool which holds the workpiece between two rigid and strong supports called centers or in a chuck or face plate which revolves. The cutting tool is rigidly held and supported in a tool post which is fed against the revolving work. The normal cutting operations are performed with the cutting tool fed either parallel or at right angles to the axis of the work.

Parts of the Lathe

LATHE PARTS

Lathe Accessories

• Divided into two categories

– Work-holding, -supporting, and –driving devices

• Lathe centers, chucks, faceplates

• Mandrels, steady and follower rests

• Lathe dogs, is a device that clamps around the work piece and allows the rotary rotation

– Cutting-tool-holding devices

• Straight and offset tool holders

• Threading tool holders, boring bars

• Turret-type tool posts

Lathe Bed

• Heavy, rugged casting

• Made to support working parts of lathe

• On top section are machined ways

– Guide and align major parts of lathe

Setting Speeds on a Lathe

• Speeds measured in revolutions per minute– Changed by stepped pulleys or gear levers

• Belt-driven lathe– Various speeds obtained by changing flat belt and

back gear drive

• Geared-head lathe– Speeds changed by moving speed levers into proper

positions according to r/min chart fastened to headstock

Safety Note!! NEVER change speeds

when lathe is running.

Lathe Centers

• Work to be turned between centers must have center hole drilled in each end

– Provides bearing surface

• Support during cutting

• Most common have solid Morse taper shank60º centers, steel with carbide tips

• Care to adjust and lubricate occasionally

Chucks

• Used extensively for holding work for machining operations

– Work large or unusual shape

• Most commonly used lathe chucks

– Three-jaw universal

– Four-jaw independent

– Collet chuck

Types of Lathe Dogs

• Standard bent-tail lathe dog– Most commonly used for round

workpieces

– Available with square-head setscrews of headless setscrews

• Straight-tail lathe dog– Driven by stud in driveplate

– Used in precision turning

Types of Lathe Dogs

• Safety clamp lathe dog

– Used to hold variety of work

– Wide range of adjustment

• Clamp lathe dog

– Wider range than others

– Used on all shapes

Left-Hand Offset Toolholder

• Offset to the right

• Designed for machining work close to chuck or faceplate and cutting right to left

• Designated by letter L

Right-Hand Offset Toolholder

• Offset to the left

• Designed for machining work close to the tailstock and cutting left to right– Also for facing operations

• Designated by letter R

Straight Toolholder

• General-purpose type

• Used for taking cuts in either direction and for general machining operations

• Designated by letter S

Lathe parts

• 1.Bed: The bed is a heavy, rugged casting in which are mounted the working parts of the lathe.

• 2. Legs: The legs carry the entire load of machine and are firmly secured to floor by foundation bolts.

• 3. Headstock: It serves as housing for the drivingpulleys, back gears, headstock spindle, live centreand the feed reverse gear.

• 4. Gear Box: The quick-change gear-box is placed below the headstock and contains a number of different sized gears.

Lathe Parts• 5. Carriage: The carriage is located between the headstock and

tailstock and serves the purpose of supporting, guiding and feeding the tool against the job during operation. The main parts of carriage are:

• a). The apron is fastened to the saddle and it houses the gears, clutches and levers required to move the carriage or cross slide. The engagement of split nut lever and the automatic feed lever at the same time is prevented she carriage along the lathe bed.

• b). The saddle is an H-shaped casting mounted on the top of lathe ways. It provides support to cross-slide, compound rest and tool post.

• c). The cross slide is mounted on the top of saddle, and it provides a mounted or automatic cross movement for the cutting tool.

• d). The compound rest is fitted on the top of cross slide and is used to support the tool post and the cutting tool.

• e). The tool post :tool holder at the proper height relative to the work centre line.

Lathe parts

• Tailstock: The tailstock can slide along the bed to accommodate different lengths of workpiece between the centers.

• A tailstock clamp is provided to lock the tailstock at any desired position.

• The tailstock spindle has an internal taper to hold the dead Centre

• And the tapered shank tools such as reamers and drills.

LATHE OPERATIONS

• 1 Plain Turning: Plain turning is the operation of removing excess amount of material from the surface of a cylindrical job.

• 2. Step Turning: Step turning produces various steps of different diameters.

• 3. Facing:by which the end surface of the work piece is made flat by removing metal from it.

• 4. Parting: dividing the workpiece in two or more parts

• 5. Drilling: producing a cylindrical hole in the workpiece

• 6. Reaming:It finishes and sizes the hole already drilled into the workpiece.

• 7. Boring:The boring operation is the process of enlarging a hole already produced by drilling.

• 8. Knurling:The knurling is a process of embossing (impressing) a diamond-shaped or straight-line pattern into the surface of workpiece.

• 9. Grooving:the act of making grooves of reduced diameter in the workpiece.

• 10. Threading: the act of cutting of the required form of threads on the internal or external cylindrical surfaces.

• 11. Forming:is an operation that produces a convex, concave or any irregular profile on the workpiece.

• 12. Chamfering:removes the burrs and sharp edges, and thus makes the handling safe.

• 13. Filing and Polishing:That removes burrs, sharp corners and feed marks from the workpiece. with the help of emery cloth of fine grades

• 14. Taper Turning: Producing a conical surface by gradual reduction in the diameter of a cylindrical workpiece.

LATHE OPERATIONS

TYPES OF LATHE

• 1. Bench Lathe:

• 2. Speed Lathes:

• 3. Engine Lathe:

• 4. Tool Room Lathe:

• 5. Capstan and Turret Lathe:

• 6. Automatic Lathe:

• 7. Special Purpose Lathes:

• 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.

• Speed Lathes: they may have the supporting legs cast and fitted to the bed.

• They have no gear box, carriage and the lead screw. With the result, the tool is fed and actuated by hand.

• Such lathes are usually employed for wood turning, polishing, centring and metal spinning, etc

• Engine Lathe: It is probably the most widely used type of lathe.

• . Its headstock is bigger in size, headstock spindle may receive power, provide different speeds to the spindle.

• The lathe is known as geared head lathe.

• Tool Room Lathe: same engine lathe but equipped with some extra attachments to make it suitable for a relatively more accurate angle of speeds and feeds.

• It is made to have a comparatively smaller bed length than the usual engine lathe.

• Capstan and Turret Lathe: vastly used in mass production.

• a very wide range of operations can be performed on them.

• These machines are actually of semi-automatictype

• In operating these machines, a very little skill is required of the operator.

• Setting of tools has been successfully accomplished further operation of these machines is more or less automatic.

Difference between TL and CL

TURRET LATHE CAPSTAN LATHE

Tool head is directly fitted on saddle.Saddle is moved to provide feed to the tool

Tool head is mounted on a slide called ram.To provide feed to the tool, saddle is locked at a particular point and the ram is moved

It is difficult to move the saddle for feed It is easy to move the ram for feed

As the saddle can be moved along the entire length of the bed, it is suitable for longer workpices

As the movement of the ram is limited, it is suitable for machining shorter workpicesonly.

Limit dogs are used to control the distance of tool movement.

To control the distance of tool movement, feed stop screws are provided at the rear side of the turret.

Some turret lathes have the facility of moving the turret at right angles to the lathe axis

No such facility

Heavy Lighter in construction

Suitable for machining heavy and large workpices

Only small and light workpices are machined

Machining can be done by providing more depth of cut and feed

Only limited amount of feed and depth of cut are provided for machining.

• Automatic Lathe: Enhancing the quality as well as the quantity of production.

• all the working and job handling movements of the complete manufacturing process for a job are done automatically.

• No participation of the operator is required during the operation.

• Automatic lathes are available having single or multi spindles.

• They fall in the category of heavy duty, high speed lathes mainly employed in mass production.

• Special Purpose Lathes: Lathes are designed to suit a definite class of work and to perform certain specified operations only.

Name of Machine Special Description Application

Precision Lathe Capable of giving a dimensional accuracy of 0.002 mm

Precision turning of previously rough-turned workpiece

Facing Lathe the carriage is driven by a separate motor, independent of the main spindle. It carries no tailstock

Used to machine the end faces of bulky cylindrical jobs.

Vertical Lathe It carries a vertical column, on which are fitted the cross slide and vertical slide.

These machines are specifically employed for jobs like heavy flywheels and large gear blanks etc.

• Frontal Lathe: machining short jobs

• Crankshaft Lathe: turning very long parts such as turbine and engine shafts and crankshafts.

• Production Lathe: suitable for mass production of cylindrical parts.

• Duplicating Lathe: It is used for mass production of identical parts where either a previously machined part works as a template

• Screw Cutting Lathe :for mass production of screwed parts

TAPER TURNING• When the diameter of a piece changes uniformly

from one end to the other, the piece is said to be tapered.

• It is gradual reduction in diameter from one part of a cylindrical workpiece to another part

• Tapers can be either external or internal.• There are three basic methods of turning tapers with

a lathe.• the operator will either use• the compound rest, offset the tailstock, or use the

taper• attachment

Compound Rests

• The compound rest is favorable for turning or boring short, steep tapers,

• it can also be used for longer, gradual tapers providing the length of taper does not exceed the distance the compound rest will move upon its slide.

• This method can be used with a high degree of accuracy, but is somewhat limited due to lack of automatic feed and the length of taper being restricted to the movement of the slide.

taper

• The compound rest base is graduated in degrees and can be set at the required angle for taper turning or boring.

• The angle of the taper with the centerline is

• one-half the included angle and will be the angle the compound rest is set for.

• For example, to true up a lathe center which has an included angle of 60°, the compound rest would be set at 30° from parallel to the ways

• For example, the compound rest setting for the workpiece shown in Figure would be calculated in the following manner

• TPI = D - d / L

• angle = TAN (TPI)/2

• Where TPI = taper per inch

• D = large diameter,

• d = small diameter,

• L = length of taper

• angle = compound rest setting

• The problem is actually worked out by substituting

• numerical values for the letter variables:

• TPI = 1.000 - 0.375/0.750

• TPI = 0.625/0.750

• TPI= 0.833

• Apply the formula to find the angle by substituting the

• numerical values for the letter variables:

• angle = TAN (0.833)/2

• angle = TAN 0.41650

CARE AND MAINTENANCE OF LATHES

• Lathes are highly accurate machine tools designed to operate around the clock if properly operated and maintained.

• Lathes must be lubricated and checked for adjustment before operation.

• Improper lubrication or loose nuts and bolts can cause excessive wear and dangerous operating conditions.

• The lathe ways are precision ground surfaces and must not be used as tables for other tools and should be kept clean of grit and dirt.

• The lead screw and gears should be checked frequently for any metal chips that could be lodged in the gearing mechanisms.

• Check each lathe prior to operation for any missing parts or broken shear pins.

• Change the lubricant frequently if working in dusty conditions.

SAFETY

• Must know all safety precautions to avoid accidents and injuries.

• Carelessness and ignorance are two great menaces to personal safety.

• Correct dress is important, remove rings and watches, roll sleeves above elbows.

• Always stop the lathe before making adjustments.

• Do not change spindle speeds until the lathe comes to a complete stop.

• Handle sharp cutters, centers, and drills with care.

• Remove chuck keys and wrenches before operating

• Know where the emergency stop is before operating the lathe.

• Never attempt to measure work while it is turning

TOOLS AND EQUIPMENT• GENERAL PURPOSE CUTTING TOOLS: The lathe

cutting tool or tool bit must be made of the correct materialand ground to the correct angles to machine a workpieceefficiently.

• The most common tool bit is the general all-purpose bitmade of high-speed steel.

• HSS generally inexpensive, can handle the high heat that isgenerated during cutting and are not changed after cooling.

• Tool bits made from special materials such as carbides,ceramics, diamonds, cast alloys are able to machineworkplaces at very high speeds but are brittle andexpensive.

• Shapes of Tool Bits: The overall shape of thelathe tool bits can be rounded, squared, oranother shape as long as the proper anglesare included.

• A right-hand turning tool bit is shaped to be fed from right to left.

• A left-hand turning tool bit is the opposite of the right-hand turning tool bit, designed to cut when fed from left to right.

• This tool bit is used mainly for machining close in to a right shoulder.

• The parting tool bit, is also

known as the cutoff tool bit.

• This tool bit has the principal

cutting edge at the squared end

of the bit that is advanced at a

right angle into the workpiece.

• Besides being used for parting operations, this tool bit can be used to machine square corners

• . Thread-cutting tool bits, are ground to cut the type and style of threads desired.

• Thread-cutting tool bits can be ground for standard 60° thread forms or for square, Acme, or special threads.

SPECIAL TYPES OF LATHE CUTTINGTOOLS

• Besides the common shaped tool bits, special lathe operations and heavy production work require special types of cutting tools.

• Tungsten carbide, tantalum carbide, titanium carbide, ceramic, oxide, and diamond-tipped tool bits and cutting tool inserts are commonly used in high-speed production work .

• when heavy cuts are necessary and where exceptionally hard and tough materials are encountered

• Specially formed thread cutter mounted in a thread “cutter holder

• This tool is designed for production high speed thread cutting operations

• The special design of the cutter allows for sharp and strong cutting edges

• The cutter mounts into a special tool holder that mounts to the lathe tool post

• The common knurling tool: consists of two cylindrical cutters, called knurls, which rotate in a specially designed tool holder. The knurls contain teeth which are rolled against the surface of the workpiece to form depressed patterns on the workpiece.

Classification of automatic lathes

Manufactured by CNC M/C

Constructional Features And Uses Of General Purpose Semiautomatic And Automatic Lathes.

• Automation is incorporated in a machine tool or machining system as a whole for higher productivity with consistent quality aiming meeting the large requirements and overall economy.

• automation enables quick and accurate auxiliary motions, i.e., handling operations like tool – work mounting, bar feeding, tool indexing etc.

• These systems may be of mechanical, electro-mechanical, hydraulic or electronic type or their combination .

• according to degree of automation machine tools are classified as,

• Non automatic where most of the handling operations irrespective of processing operations, are done manually, like centre lathes etc.

• Semiautomatic

• Automatic where all the handling or auxilliaryoperations as well as the processing operations are carried out automatically.

• The conventional general purpose automated lathes can be classified as,

• (a) Semiautomatic : – 1. capstan lathe (ram type turret lathe) – 2. turret lathe – 3. multiple spindle turret lathe – 4. copying (hydraulic) lathe

• (b) Automatic : – • Automatic cutting off lathe – • Single spindle automatic lathe – • Swiss type automatic lathe – • multiple spindle automatic lathes

Semiautomatic lathes

• The characteristic features of such lathes are ;

• some major auxiliary motions and handling operations like bar feeding, speed change, tool change etc. are done quickly and consistently with lesser human involvement

• the operators need lesser skill and putting lesser effort and attention

• suitable for batch or small lot production

• costlier than centre lathes of same capacity

Capstan and Turret lathes

• The semi-automatic lathes, capstan lathe and turret lathe are very similar in construction, operation and application. Fig. schematically shows the basic configuration of capstan lathe

Schematic configuration of CAPSTAN LATHE fig.1

Schematic configuration of Turret lathe Fig.2

In contrast to centre lathes, capstan and turret lathes • are semiautomatic • It possess an axially movable indexable turret (mostly hexagonal)

in place of tailstock • holds large number of cutting tools; upto four in indexable tool

post on the front slide• one in the rear slide and upto six in the turret (if hexagonal) as

indicated in the schematic diagrams. • are more productive for quick engagement and overlapped

functioning of the tools in addition to faster mounting and feeding of the job and rapid speed change.

• enable repetitive production of same job requiring less involvement, effort and attention of the operator for pre-setting of work–speed and feed rate and length of travel of the cutting tools

• are relatively costlier • are suitable and economically viable for batch production or

small lot production.

There are some differences in between capstan and turret lathes such as,

• Turret lathes are relatively more robust and heavy duty machines

• Capstan lathes generally deal with short or long rod type blanks held in collet, whereas turret lathes mostly work on chucking type jobs held in the quick acting chucks

• In capstan lathe, the turret travels with limited stroke length within a saddle type guide block, called auxiliary bed, which is clamped on the main bed as indicated in Fig

• whereas in turret lathe, the heavy turret being mounted on the saddle which directly slides with larger stroke length on the main bed as indicated in Fig.2

• One additional guide rod or pilot bar is provided on the headstock of the turret lathes as shown in Fig.2, to ensure rigid axial travel of the turret head

• External screw threads are cut in capstan lathe, if required, using a self opening die being mounted in one face of the turret,

• whereas in turret lathes external threads are generally cut, if required, by a single point or multipoint chasing tool being mounted on the front slide and moved by a short leadscrew and a swing type half nut.

• Multiple spindle Vertical Turret lathe • Turret lathes are mostly horizontal axis single spindle

type. • The multiple spindle vertical turret lathes are

characterised by : • Suitably used for large lot or mass production of jobs of

generally ; – chucking type – relatively large size – requiring limited number of machining operations

• Machine axis – vertical for – lesser floor space occupied – easy loading and unloading of blanks and finished jobs – relieving the spindles of bending loads due to job weight.

• Number of spindle – four to eight.

• vertical turret lathes are of three categories

• 1.Parallel processing type :

• The spindle carrier remains stationary.

• Only the tool slides move with cutting tools radially and axially.

• Identical jobs (say six) are simultaneously mounted and machined in the chucks parallely at all stations each one having same set of axially and / or radially moving cutting tools.

Basic configuration of multispindle automatic vertical lathe

2.Progressively processing type : • The spindle carrier with the blanks fitted in the chucks

on the rotating spindle is indexed at regular interval by a mechanism.

• At each station the job undergoes a few preset machining work by the axially and / or radially fed cutting tools.

• The blank getting all the different machining operations progressively at the different work stations is unloaded at a particular station where the finished job is replaced by another fresh blank.

• This type of lathes are suitable for jobs requiring large number of operations.

3.Continuously working type

• Like in parallel processing type, here also each job is finished in the respective station where it was loaded.

• The set of cutting tools, mostly fed only axially along a face of the ram continuously work on the same blank throughout its one cycle of rotation along with the spindle carrier.

• The tool ram having same tool sets on its faces also rotate simultaneously along with the spindle carrier

• which after each rotation halts for a while for unloading the finished job and loading a fresh blank at a particular location.

• Such system is also suitable for jobs requiring very fewand simple machining operations.

Single spindle automatic lathe

• The general purpose single spindle automatic lathes are widely used for quantity or mass production (by machining) of high quality fasteners

• Like bolts, screws, studs etc., bushings, pins, shafts, rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks.

• single spindle automats are : • Preferably and essentially used for larger volume

of production i.e., large lot production and mass production

• Used always for producing jobs of rod, tubular or ring type and of relatively smaller size.

• Run fully automatically, including bar feeding and tool indexing, and continuously over a long duration repeating the same machining cycle for each product

• Provided with upto five radial tool slides which are moved by cams mounted on a cam shaft of relatively smaller size and power but have higher spindle speeds

Hydraulic copying (tracer controlled) lathes

• The machine employs a dust proof electrical system.

• The hopper feeder is hydraulic operated, while the tailstock center is hydraulically operated to clamp the workpiece.

• Hydraulic copying attachment were widely used until the 1970’s as a cheap and efficient way of mass producing.

• This is for used in different printing and textile industries

• Jobs having steps, tapers and / or curvedprofiles, as typically shown in Fig. areconveniently and economically produced inbatch or lot in semiautomatically operatedtracer controlled hydraulic copying lathe.

• The movement of the stylus along thetemplate provided with the same desired job-profile) is hydraulically transmitted to thecutting tool tip which replicates the templateprofile.

• FIG: A typical job suitable for copy turning

Turning attachment for lathe

• Machine tools in which components are machined automatically.

• The working cycle is fully automatic that is repeated to produce duplicate parts with out participation of operator

• All movements of cutting tools, their sequence ofoperation applications, feeding of raw material, partingoff, unloading of finished parts all are done on machine.

• All working & idle operations are performed in definitesequence by control system adopted in automatic which isset up to suit a given work.

• Only operation required to be performed manually isloading of bar stock/ individual casting/forged blanks

• These machines are used when production requirementsare too high for turret lathes to produce economically

AUTOMATIC LATHES

General Purpose Automatic lathes

• Automatic lathes are essentially used for large lot or mass production of small rod type of jobs.

• Automatic lathes are also classified into some distinguished categories based on constructional features, operational characteristics, number of spindles and applications as follows

• • Single spindle – Δ Automatic cutting off lathes – Δ Automatic (screw cutting) lathe – Δ Swiss type automatic lathe

• • Multispindle automatic lathe

• Automatic cutting off lathe

• These simple but automatic lathes are used for producing short work pieces of simple form by using few cross feeding tools.

• In addition to parting some simple operations like short turning, facing, chamfering etc. are also done.

Single spindle automatic lathe

• The general purpose single spindle automatic lathes are widely used for quantity or mass production (by machining) of high quality fasteners; bolts, screws, studs etc., bushings, pins, shafts, rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks

• Unlike the semiautomatic lathes, single spindle automats are :

• Preferably and essentially used for larger volume of production i.e., large lot production and mass production

• Used always for producing jobs of rod, tubular or ring type and of relatively smaller size.

• Run fully automatically, including bar feeding and tool indexing, and continuously over a long duration repeating the same machining cycle for each product

• Provided with upto five radial tool slides which are moved by cams mounted on a cam shaft of relatively smaller size and power but have higher spindle speeds

Swiss type automatic lathe

• The characteristics and applications of these single spindle automatic lathes are :

• • In respect of application :

• Used for lot or mass production of thin slender rod or tubular jobs, like components of small clocks and wrist watches, by precision machining;

• o Job size (approximately)

– ⎯ Diameter range – 2 to 12 mm

– ⎯ Length range – 3 to 30 mm

• Dimensional accuracy and surface finish – almost as good as provided by grinding

• • In respect of configuration and operation – The headstock travels enabling axial feed of the bar

stock against the cutting – There is no tailstock or turret – High spindle speed (2000 – 10,000 rpm) for small job

diameter – The cutting tools (upto five in number including two

on the rocker arm) are fed radially – Drilling and threading tools, if required, are moved

axially using swivelling device(s) – The cylindrical blanks are prefinished by grinding and

are moved through a carbide guide bush as shown.

Multispindle automatic lathes

• Multispindle automatic lathes having four to eight parallel spindles are preferably used. Unlike multispindle turret lathes, multispindle automatic lathes are;

• Horizontal (for working on long bar stocks) • work mostly on long bar type or tubular blanks

Multiple spindle automats also may be parallel action or progressively working type.

• Machining of the inner and outer races in mass production of ball bearings are, for instance, machined in multispindle automatic lathes.