Lathe
Industrial revolution demanded
• More production
• More Precision
• Changes in Manufacturing process
• Lead to the Development of High speed and
• Special purpose lathes
Inventor
Engine lathes were invented by Henry maudsley
Function of lathe
Lathe is to remove excess material in the form of chips by rotating the work piece against a stationary cutting tool
Working principle of lathe• It holds the work between two supports called centers.
• Chuck or Face plate is also used for holding the work.
• Chuck or face plate is mounted on machine spindle
• Cutting tool is held and supported on a tool post.
• If the tool moves parallel to work piece cylindrical surface is formed
• If the tool moves inclined to the axis it produces a taper surface and is called taper turning.
• If the tool moves inclined to the axis it produces a taper surface and is called taper turning
What type of operations are performed on lathe?• Turning
• Facing
• Boring
• Drilling
• Reaming
• Threading
• Knurling etc
Other operations with special attachment are:
• Key way cutting
• Milling
• Grinding etc
Classification• Speed lathe
• Engine lathe
• Bench lathe
• Tool room lathe
• Turret lathe
• Capstan lathe
• Special purpose lathe
• Automatic lathe
Speed lathe• So named because of high speed of head stock spindle
• Consists of a simple head stock, tail stock and tool post
• No gearbox, lead screw and carriage
• Tools are hand operated
• Adjustable slide is provided to support the cutting tool & carriage
• Different speeds are obtained by cone pulley
• Used for light machining operations
Engine lathe• Also known as geared head lathe
• Main parts are bed, head stock, tail stock,
carriage, lead screw, feed change gear box
• Stepped cone pulley or geared head is used for varying the speed
• Tail stock is provided to facilitate the work between centers
• Tail stock also permits the use of drills, taps etc
• Cutting tools are controlled either by hand or power
• Tools can be fed both in cross and longitudinal directions with respect to lathe axis
• Carriage feed rod and lead screw are used to perform these operations
Bench lathe• It is a small engine lathe mounted on work bench
• For doing small precision and light work
Tool room lathe• It is modern engine lathe equipped with necessary accessories for accurate and precision work.
• Best suited for dies, gauges and small tools.
Capstan and Turret lathe• Production lathes
• Used to perform large number of operations simultaneously
• Used for mass production
Turret lathe• Several tools are pre set on revolving turret
• Facilitate for doing large number of operations on the job
• Usually accommodated with six tools for different operations
• Also available with special tool holders to perform simultaneous multi tool operations
• Used for repetitive batch production
Capstan lathe• Similar to turret lathe
• Capstan head moves on an auxiliary slide and can be clamped at any position
• Used for fast production of small parts
Special purpose lathes• Some lathes have characteristics that enable them to do certain work well
• These lathes are meant for specific work which cannot be done on ordinary lathes
Examples
• Facing lathe: For end facing of bulky cylindrical jobs
• Duplicate lathe: Mass production of identical parts
• Gap lathe : To accommodate Large diameter works
• Screw cutting lathe: Mass production of threaded parts
Automatic lathe• Intended for quality as well as quantity
• Movement of work and tool are done automatically
• No participation of operator is required (cycle repeated automatically)
Semi - Automatic lathe• In semi automatic lathe loading and removal of work is done by operator
• Other operations are performed automatically
we have learnt to specify• Hand saw :by its length and pitch
• Hammer : by its weight
• File : by its length, teeth pattern and grade
• Chisel : by its length ,type and cross section
How a lathe can be specified• The size of lathe is specified or designated in many
ways.
• Practice usually differs with different countries
Lathe is generally specified by
• Swing
• Distance between head stock and tail stock centre
Swing denotes the maximum diameter of the work
Which can be accommodated on the lathe.
• Height of the centers above the lathe bed
• Swing over bed :
• Largest diameter of work that can be revolved over the ways of lathe bed
• Swing over carriage:
• Largest diameter of work that can be accommodated over the carriage
• Swing over the gap of bed :
maximum diameter that can be turned over the gap of bed
• Maximum job length that may be held between centers (Head stock and tail stock)
• Diameter of hole through lathe spindle for turning bar work
Other factors to be considered• Size of bed
• Range of spindle speeds
• Lead screw diameter and threads
• Motor specifications
Engine lathe
Bed
• Acts as the base of machine
• Tail stock and carriage slides on the ways in alignment with the head stock
• Upper surface is ground to give true alignment
• Ways are accurately machined parallel to axis of spindle
• Ways takes most of the down word thrust
• Made of cast iron (high compressive strength
wear resistance)
• Inverted V -ways are preferred to disallow the entry of chips
• Provided with gap bed to facilitate turning of larger diameters.
Head stock• Location – left side of the bed
• Head stock houses the
main spindle
speed change mechanism and
change gears
Driving mechanism:
Belt driven type:
• head stock consists of cone pulley which drives the
spindle directly or through back gears
• Spindle speeds are changed by shifting the belt
Driving mechanism:
Geared head stock :
• used for modern lathes.
• Speed is changed by shifting gears.
• Driven either by direct line or from an independent
motor.
• Sliding gears is generally used for speed changes.
• Main spindle is hollow to allow long bars to extend through the work
• Spindle runs in precision bearings
• Fitted with work holding devices like
chucks
face plates
• End of the spindle have included taper (Morse) to accommodate live centre
• Accessories mounted on head stock are
three jaw chuck
four jaw chuck
lathe centre or lathe dog
collet chuck
face plate and magnetic chuck
Back gear mechanism:
use : for reducing the spindle speeds
application: turning hard materials,
operations like threading,
rough machining,
turning of large diameters.
Back gear Mechanism• Gear G1 is firmly keyed to the shaft
• Pinion P1 is firmly keyed to the sleeve
• Cone pulley is firmly secured to sleeve
• Spring knob engages with gear G1
• Cone pulley is driven by belt
• G2 and P2 are compound back gears mounted on eccentric shaft.
Back gear mechanism
• When back gears are disengaged and gear G1 is keyed with stepped cone pulley
• Smaller step :fast speed
• Medium step : medium speed
• Higher step :low speed
Back gear mechanism• For further reduction of speed:
• Back gear is engaged and lock pin is disengaged from the gearG1.
• Speeds of cone pulley are transferred to spindle through pinion P1, back gears( G2 and P2) and gearG1
Tail stock• Also called loose head stock or puppet head
• Located on left side of bed
• Support the other end of work
• Hold tools like drill, reamer and taps etc
• Moved along the length of the bed to accommodate different lengths
• Provided the screw for adjusting the tail stock set over for taper turning
• Can be fixed at any position by clamping the bolt
• Upper part of body is made hollow to accommodate spindle, feed screw, hand wheel and spindle clamp
• Hand wheel is provided for longitudinal movement
• Front end is fitted with dead centre
Carriage
• Supporting, guiding, and feeding the tool against job
• It provides three movements to the tool
longitudinal feed
cross feed
angular feed
Main parts are
Cross slide
Saddle
Compound rest
Tool post
Apron
Saddle• slides along the bed ways and support the cross slide, compound rest and tool post.
• has V guide ways and flat guide ways on one side for mounting on lathe bed.
• Other side is provided with dovetail to accommodate the cross slide
Cross slide
• Mounted on top of the saddle
• Moves always in a direction normal to the axis of main spindle
• Operated by hand or
cross feed screw or
power feed
• Front side is graduated in degrees
• Facilitate swivelling of the compound rest to desired angle
Compound rest• Also known as tool rest
• Mounted on the cross slide
• Provided with swivel plate
• May be swiveled on the cross slide to any angle in the horizontal plane
• Necessary in turning angles
Tool post
• Top most part of the carriage
• Used for holding the tool or tool holder
• Gets movement by the movement of the saddle and cross slide
Commonly used types:
standard tool post
4- Way tool post
• Standard tool post:
Height of the tool can be adjusted with help of ring and rocker
• 4-Way tool post:
Provision for holding four separate tool holders.
Swiveled to required positions
Apron• Hanging part in front part of the carriage.
• Serves as a housing for number of gear trains.
• Equipped with power feed mechanism for carriage and cross slide.
• Carries clutch mechanism and half nut (Split nut) mechanism.
• Clutch mechanism:
Used to transmit motion from the feed rod.
• Half nut mechanism:
Moves the carriage in thread cutting operation with the help of lead screw.
Engaged only for thread cutting operation
Feed and lead screw• Feed screw is along drive shaft
• Allows a series of gears to drive the carriage mechanism.
• Feed and lead screws are driven either the change gears and or an intermediate gear box.
• Intermediate gear box is known as quick change gear box.
• Intermediate gears allows the correct ratio and direction to be set for thread cutting.
• Tumbler gears are provided between the spindle and gear train along with quadrant plate.
• Tumbler gears enables a gear train of the correct ratio and direction to be introduced
• Tumbler gears provide constant relationship between the number of turns the spindle makes, to the number of turns the lead screw makes.
• This ratio allows the screw threads to be cut on the work piece with out the aid of die.
Lathe Operations
• Standard / common operations
• Special / rare operations
Standard / Common Operations• Facing
• Turning
• Eccentric turning
• Knurling
• Taper turning
• Drilling
• Reaming
• Boring
• Threading
• Parting off
• Key way cutting
Special or Rare operations:
• Grinding
• Milling
• Copying or duplicating
• Spherical and Elliptical turning
• Tapping
• Dieing etc.,
Facing:• Facing is an operation which produces flat surfaces.
• In this operation the tool is fed at right angle to
the axis of the work piece.
Turning• Turning is the machining operation in which excess material is
removed by rotating the work piece against a cutting tool.
The common methods for holding work piece
for turning work:
1. Between centers
2. On a face Plate
3. In a chuck
1. Between centers (L/D > 4):• When the work is held between centers for any
sort of turning operation one end is firmly gripped in
a lathe dog and then the same end is supported on
the tip of the lathe center.
• It is mainly used for long work pieces.
2. On a face plate• eccentric jobs are supported.
• Jobs which cannot be conveniently held in chucks
are supported on a face plate.
3. In a chuck• Regular shaped , particularly cylindrical , jobs are very
readily and conveniently held in chucks
Eccentric Turning:• Machining of two or more cylindrical surfaces to
be turned which are eccentric to each other is
known as eccentric turning.
Step Turning:
• The shoulder is the section where the size changes form
one diameter to another
Taper Turning
• A conical surface produced on a lathe is called taper
turning.
The tool moves at an angle to the axis of rotation
Knurling:• It is the process of indentation of various forms
on cylindrical look surface
• A knurl tool tool is held in tool post and preened
against .the rotating work.
• It is done to provide grip on holders, screw
heads.
Drilling:
It is the process of making holes on work piece
• The drill is fed slowly into the work piece which is
revolving in a chuck.
The drill is held stationary in the tail stock spindle
Reaming:• Reaming is the process of making hole smoothly
and accurately to size.
• The work with drilled hole is held in a chuck and
reamers are inserted in tailstock spindle and rotated.
Boring:• Boring is the operation of enlarging the previously
drilled hole with the aid of single point cutting tool
called boring tool.
• If the hole is enlarged only through a certain length
then it is referred as counter boring
• If the tool is fed at an angle to the axis of rotation ,
it is called internal taper turning.
Parting – Off:• Parting–off is the operation of separating the
finished work piece from a bar stock.
• The operation involves feeding the cutting tool
into the rotating work piece.
Key Way Cutting• For cutting key ways (grooves) on the lathe work is held
in special attachment on cross slide.
• The cutter is held in a chuck and made to rotate.
• The work is fed against rotating cutter to from a key
way/groove.
Threading:
Cutting helical groove over a cylindrical/conical work piece is called thread cutting
Taper Turning:• A conical surface produced on a lathe is called taper
turning
The tool moves at an angle to the axis of rotation.
Methods of Taper Turning
1. Forming tool method
2.Compound rest method
3.Taper attachment method
4.Tailstock set over method
Taper turning by forming tool method:
• The tool has a cutting edge inclined
at the desired angle with the axis of rotation.
• The angle is equal to half the taper angle.
• The angle is equal to half the taper angle.
The tool is fed straight into the work.
Only short tapers can easily be turned
Taper turning by compound rest method:
• Used for turning longer tapers than produced by a
form tool.
• The length of taper is limited to compound rest slide
movement.
• Compound rest graduated with degrees can be
swiveled to desired angle.
• The taper angle calculated first, and then compound rest is
swiveled to half the calculated taper angle.
• Due to hand feed, productivity is low and poor surface finish
Taper turning by taper attachment• For using taper turning attachment, the cross slide is disconnected with cross feed screw and rear end of cross slide is attached to guide bar.
• It can be used for turning external tapers
• Length of taper is limited to length of slide bar
Taper turning by tail stock set-over method• This method is used for small tapers on long jobs.
• The tail stock centre is moved to an offset.
• Amount of offset depends upon length of work and
taper dimensions.
• Tool is fed parallel to the lathe axis.
Thread cutting :
• Thread cutting is the process of producing a helical
groove on a cylindrical component.
• The saddle receives motion from lead screw.
• In one revolution of the spindle, the tool traverse a
distance equal to the pitch of the thread to be cut.
• This is achieved by a gear train
Gear train for cutting metric threads on a lathe
with English lead screw:
• Pitch of lead screw is given in inches.
• An additional gear with 127 teeth is incorporated in gear
train.
Gear ratio = pitch to be cut
pitch of lead screw
Work holding devices used on lathe
1. Chucks
2. Collets
3. Driving plates
4. Carriers
5. Rests
6. Mandrels
7. Face plates
Chucks• Lathe chucks posses gripping jaws.
• They are capable of holding and rotating the work piece on lathe.
• The jaws are adjusted in and out by turning a screw with chuck key.
• Chuck is attached to lathe spindle with the help of back plate.
Commonly used chucks are:
1. Three jaw universal chuck
2. Four-jaw independent chuck
3. Magnetic chuck
4. Collet chuck, and
5. Drill chuck
Three jaw universal chuck• All the three jaws move simultaneously to clamp the work
• The job is automatically centered.
• This chuck is used for holding cylinder or hexagonal work.
• This chuck is not suitable for irregular shaped work pieces.
Four-jaw independent chuck
• All four jaws are moved independently
• It has superior gripping power than self centering chuck.
• Used for holding square, octagonal and irregular components
• The setting time is more.
• Also known as Independent chuck
Magnetic chuck• These chucks are used to hold the steel work piece (or work pieces made of magnetic material) that are too thin to be held in an ordinary chuck.
• The face of the chuck is magnetized by permanent magnets.
• Suitable for work that requires only light cuts.
Collet chucks:
• It is mostly used for holding bars of small size (below 63 mm) and used for production work.
• 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 work piece
• Used for chucking internal surfaces.
Drill chuck
• Used for holding straight shank reamer or drills for reaming or drilling.
• It has self centering jaws and is operated by key.
• The chuck is held in lathe tail stock.
Lathe centers• Lathe centers are hardened devices used for holding and locating the work to be turned between centers.
• They are provided with a standard taper on one end and a 600 point at the other end.
• The center that is fitted in the headstock spindle is called live center.
• The center that is used in tailstock spindle is called dead center
The various forms of lathe center are
1. Ordinary center
2. Half center
3. Ball center
4. Antifriction ball bearing center
Ordinary center: used for general work
Half center :
used for taper Turning and offers minimum wear and strain. Half of the center is ground away
Ball center:
Used while facing the job without disturbing the setting.
Antifriction ball bearing center:
It eliminates the friction and permits work to be turned at
high speed. It revolves with the work.
Carriers
A lathe dog or carrier is securely clamped to the face of the Plate.
The rotation of the drive plate is transferred to work piece through dog.
Used to drive the work piece when it is held between two
centers.
Face plate
It is open slotted circular plate with large diameter.
Work piece is clamped using T- bolts.
Mounting work on face plate provides an ideal way of
supporting works which cannot conveniently held by
chucks
Drive Plate
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 (dog).
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.
Rotation of drive plate is transferred to work piece through dog.
Angle Plate
Angle plate provides an efficient means of holding work of complex and irregular shape which is inconvenient or even impossible to clamp in jaw chuck.
The angle plate is attached to face plate and work is
clamped to angle plate.
The counter weights are attached to opposite of face plate to counter balance the work and angle plate.
Mandrels Mandrels are used to hold and rotate hollow works
between centers.
It is a hardened and tapered steel bar with centers on its
flat ends.
The mandrel is rotated by the lathe dog and catch plate,
and the work is driven by friction.
Types of Mandrels
1. Solid Mandrel
2. Gang Mandrel
3. Expanding Mandrel
4. Cone Mandrel
Rests Provide additional support for long work pieces.
It helps to prevent deflection of work piece under the action of cutting force of tool.
The use of rest is recommended where the length of work piece is 10 to 12 times the diameter.
Types of Rests
1.Steady Rest
2.Follower Rest
Steady Rest
Steady rest is clamped on the bed ways in the required
position between head stock and tail stock.
Used when a long piece is machined or drilled at its end by holding the job in a chuck.
It avoids the chances of deflection of job at the other end.
Follower Rest
It is mounted on lathe saddle and move together with the
carriage.
It performs the same function as the steady rest but it has two jaws which support the work opposite to the tool.
Tool Holding Devices• The cutting tools used in the hexagonal turret requires special holding devices.
• Tool fitted in a holder is designated according to the type of holder.
Types of tool holders used on capstan / turret lathe:
1. Straight cutter holder
2. Multiple cutter holder
3. Knee tool holder
4. Flange tool holder
5. Knurling tool holder
6. Form tool holder
7. Roller study tool holder
8. Die holder
Straight cutter holder
• Tool is held perpendicular to the holder shank axis by three set screws.
• The shank can be mounted directly into the hole of the turret face.
• It is used for turning, facing, chamfering
Multiple cutter holder:
• It can accommodate double tool in its body.
• It facilitates the cut simultaneously with more than one tool from the same tool station.
• Its shank is mounted directly in a hole of turret face.
Knee tool holder
• It is directly bolted to the turret face.
• Additional support is given by the overhead pilot which is located in the bush.
• It is useful for simultaneous turning and boring or drilling.
Flange tool holder:
• Tool holder is bolted to the hexagonal turret.
• It is widely used for holding boring bars, centers and shank type tools
Knurling tool holder:
• It is fitted to the turret face.
• The knurls can be adjusted to knurl on different diameter work.
Form tool:
• Tool holder is mounted on a dovetail slide and its height is adjusted by moving within the slide.
• Circular form tool is held in similar way and its height is adjusted by rotation.
• Form tool holder is usually held on cross-slide.
Roller study tool holder:
• Rollers and tool are contained within a box-like structure.
• Both rollers independently mounted on slides, can be adjusted for wide range of diameters.
• Improved surface finish.
• No deflection of the work piece leading to inaccurate work.
Die holder:
• Self opening die head used for cutting an external threads by using a capstan lathe.
• By this tool holder accurate threads produced by adjusting of the cutting dies.
• The machining time is reduced
Lathe tool geometry• Cutting tool used in lathe operations is single point cutting tool.
• Means having only one cutting edge at end
Classification of Single point cutting tool :
According to the direction of feed:
• Right hand tools
• Left hand tools
Right hand tool:
• Fed in cutting the metal from right to left.
• Cutting edge on left side.
Left hand tool:
• Fed in cutting the metal from left to right.
• Cutting edge on right side
Classification according to purpose:
• based on operations like facing ,parting etc
Classification according to the method of manufacturing:
• Forged or solid tool
• Tipped tool
Terms used in lathe tool geometry:• Shank :
Body of the tool or part on one end of which the cutting edge is formed.
Face:
• Top surface of the tool
between the shank and the
point of the tool.
• Chips will flow along this
surface
Point:
• Wedged shaped portion where the face and flank of the tool meet.
• Cutting part of the tool.
• Also called nose ( for
round nose tools)
Flank:
• Portion of the tool Which faces the work.
• Surface adjacent to and below the cutting edge
Base:
• Surface of the tool shank which bears against the supporting tool holder.
Heel:
• Portion at the bottom of the tool where the base and flank of the tool meet
Nose radius:
• Curve formed by joining the side cutting edge and end cutting edge.
• Nose provided with a radius called nose radius
Lathe tool geometry
• Sharp cutting nose weakens the cutting tip.
• Nose radius provides greater strength, prolonged tool life.
• Tool with too large nose radius leads to chatter.
Cutting edge:
• Portion of the face edge along which the chip separated from the work.
Side cutting edge:• Edge formed by the intersection of face and side flank.
• Is the actual cutting edge.
End cutting edge:
• Edge formed by inter section of face and end flank.
Principal tool angles
Rake angle:
• Angle between the tool face and a plane parallel to the base of the tool.
Back rake angle:• The angle between the face of the tool and base of the shank measured in a plane through the side cutting edge and at right angles to the base
Positive rake:• Tool faces downwards from the point towards the shank.
Negative rake:• Cutting edge faces upwards towards the shank
Side rake angle:
• Angle between the base of the tool shank and face of the tool .
• measured in a plane perpendicular to the plane through the side cutting edge and right angles to the
Positive side rake:• Tool face is sloping upwards towards the side cutting edge
Negative rake:• Tool face is sloping downwards towards the side cutting edge
Relief angle:• Angle between a plane perpendicular to the base of a tool and ground flank immediately adjacent to the cutting edge
Side relief angle:
• Angle between the portion of the flank immediately below the cutting edge and a line drawn through the cutting edge perpendicular to base
End relief angle:
• angle between the portion of the end flank immediately below the cutting edge and a line drawn through the cutting edge perpendicular to the base
Clearance angle:
• Angle between a plane perpendicular to the base of the tool and portion of flank immediately adjacent to the base
Side clearance angle:• Clearance on the side cutting edge.
• Angle between the portion of the side flank immediately below the cutting edge and a plane drawn from the cutting edge perpendicular to base
End clearance angle:• clearance provided on end cutting edge.
• Angle between the plane perpendicular to the base and end flank adjacent to the base.
Functions and influence of tool angles:
Rake angles:
• Controls the direction of chip flow
• Reduces friction
• Keenness to the tool
• Prolonged tool life
Positive rake angles:
• General machining work.
• Small rake angles: hard metals
• Larger rake angles: softer metals
Zero rake angles:
• Relatively softer materials like brass
• Decreases the power consumption
• Increases the surface finish
Negative rake angles:
• Provided on carbide tipped tools.
• Increases the strength of cutting tool
• Application of higher cutting speeds
Clearance angles:
• Keeps the tool flanks clear of the work surface
• Prevents the rubbing between work and flank
Higher clearance:
• Reduces the wear
• Result in a clean cut
• For low strength metals
Lower clearance:
• Better support to cutting edge
• For cutting tougher materials.
Tool signature :• Known as tool designation
• Represents the various angles( rake, relief, cutting
edge) and nose radius in sequence.
• Comprises seven elements
• Ex: designation of single point cutting tool is
• 8 14 6 6 20 15 0.75
What is a Production Lathe
• Modification of engine lathe
• To meet production demands
• Suitable for mass / batch production
• To hold / machine complicated jobs
• To keep them in continuous production lines
How they differ from conventional engine lathes• Can hold complicated jobs
• Setting times reduced
• Minimized production time
• Component accuracy is more
• One worker can look after more than one machine at
a time
• High production rates
Types of Production Lathes
Special purpose lathes:
• Crankshaft turning lathes
• Wheel turning lathes
• Cam shaft turning lathes
• Automatic Lathes
• Semi-automatic Lathes
• Turret lathes
• Capstan lathes
• Numerically controlled lathes (NC)
• Computer controlled lathes (CNC)
Turret Lathes
• Designed for short continuous runs
• Turret is mounted in place of tailstock
• Indexable square tool post on cross slide
• Suitable for Drilling, countersinking, reaming, tapping like operations
Vertical Turret lathes
• Suitable for turning large components like motor bodies
• Turret head is capable of moving in 2 axis
• If table size is more than 900mm they are known as vertical boring mills
DRUM Turret lathes
• Similar to turret lathe
• Tool turret in the form of drum
• No cross slide
Capstan Lathes
• Ideal for fast production of small parts
• Capstan slide (instead of Turret slide)
• Slide moves on an auxiliary slide
• Auxiliary slide can be clamped conveniently on the machine bed
Automatic Lathes• Available with single or multi spindles
• Operating sequences are carried out by cam or actuator
• Simultaneous multi feature operation is its common feature
• Manual controls are replaced by mechanism
Number of attachments available
• Work loading magazines
• Cross drilling attachment
• Polygon tuning attachment
• Slot milling attachment
Copying Lathes• Used for profile turning
• Profile duplication on work
• Duplication carried out by hydraulic or electrical copying device
• Copying by means of a sensitive device called stylus
• The master piece is called template
• Used for shafts, axles, piston rods in batch production
Slant bed copying lathe
• Latest versions have a slant bed
• Slant bed facilitates heavy duty copy turning
Chucking lathes
• Short work piece machines
• Mono block type bed
• Suitable for mass production
• Cannot accommodate if L /d ratio > 1
NC Lathes• Numerically controlled lathes
• All the operations are controlled by pre-programmed numerical data
• The data input in the form of punched tapes
CNC LATHES• Controlling the NC machines using Computers
• Radical changes in industries due to these machinery
• Features
• Variable speed headstock
• Automatic tool changers
• Antifriction lead screws
Turret lathe• To eliminate the amount of skilled labour
• Adopted to quantity production work
• It can hold number of cutting tools at a time
• Tools may be set up in the turret head in sequence they need to be used
• Feed movement of each tool is regulated by stops and feed trips
• Saddle bolted to the bed of the lathe
• Also called saddle type lathe
• It is heavier in construction
• Initial cost is considerably higher
Features of Turret lathe
• Hexagonal turret replaces the tailstock
The turret is a tool holder
• On which six tools can be mounted
• Can be rotated about a vertical axis
• Entire unit can be moved longitudinally
• It is mounted on the saddle or carriage on bed ways
• It is provided with indexing mechanism
• Indexing mechanism will rotate the present tool away and bring another tool in position for next operation
Main advantage• Different machining operations
• Drilling,
• Reaming,
• Boring can be performed in a single setting by a hexagonal turret.
• considerably reduces tool setting time.
• Minimized production time
• Skilled operator not essential
• Large scale production of identical parts
Capstan lathe
The capstan lathe
• It is small or medium size machine
• Carries a hexagonal turret on a ram
• Lighter in construction
• Ram slides longitudinally on saddle
• relatively short stroke of the tool head
• automatic indexing
• Usually carries six cutting tools
• rapid presentation of the tools
Differences between turret & capstan lathes
The main question asked by people looking at Capstan and Turret lathes, is
"What is the difference?".
• Picture shows turret of a
Turret lathe;
• The turret itself moves
with the saddle at all
times.
Capstan lathe turret
• The turret is the tool
holding and rotating part
which is carried on a
movable saddle.
• The turret itself moves
on the saddle.
• Turret of turret lathe is rigid
• Capstan lathe ram
• Non rigid construction
• Bending
• Deflection
• Vibration
Turret lathe suitable for
• larger
• heavier chucking works
Capstan lathe suitable for
• bar work
Turret lathe
• Hand feeding is laborious
• Generally equipped with power feeding
• The turret and dead stops on turret lathes have to be indexed into position by hand.
Capstan lathe
• Ram can be moved rapidly
• Handy for small ariticles
• Light and fast cuts
Automatic Lathe Features• Minimum man power utilized
• Meant for mass production
• Manual machine controls replaced by various mechanisms
• To eliminate the amount of skilled labour
• Mechanisms enable to follow certain prescribed frequency
• Parts are fed and removed automatically
• Minimizing the loading and unloading time
• May have single or multiple spindles
• Tool set up may be permanent
• May have horizontal or vertical spindles
• More accuracy can be obtained
• Operating sequences will be carried out by cam or actuator
• Simultaneous multi feature operation is common feature
• Automatic lathes can machine irregular jobs also
• These are suitable for medium to high volume production
Number of attachments available
• Work loading magazines
• Cross drilling attachment
• Polygon turning attachment
• Slot milling attachment
Types of Automatic lathes
• Chucking Lathes
• Screw (Automatic Bar) Machine
Chucking Lathes
• Automatic lathes without tailstock are called Chucking machines (Chuckers)
• Short work piece machines
• Mono block type bed
• Suitable for mass production
• Cannot accommodate if l/d ratio > 1
Automatic Bar Machines
• Also called automatic screw machines
• Essentially a screw machine is an automated turret lathe
• screw machine sits at the top when large volume of product is needed
Semi automatic lathe
Limitations with automatic lathes
• Costlier
• Complicated mechanism
• Job size limitations
• Maintenance problems
How to overcome these?
• Eliminating or decreasing level of automation
• By allowing human intervention
Where to eliminate automation?
• Loading of work pieces
• Unloading of finished jobs
Semi automatic lathes
• Semi automatic lathes are production lathes with human involvement for certain operations
• Capstan and turret lathes with additional attachments become semi automatic lathes
• Also called retrofitting
• Vide range of jobs can be accommodated
• Higher production rates
Additional attachments?
• Bar stock feeding mechanism
• By providing stops for saddles at appropriate places
• Automatic indexing of saddles
• By providing collet chucks and pneumatic chucks
Other types of Semi Automatic Lathes• Single spindle
• Multi spindle
• Chucking type
• Bar type
• Horizontal spindle
• Vertical spindle
Features
• Special/automatic tool changer
• Automatic work feeding into chuck
• Special operations can be performed
• Vide ranges of jobs
Advantages of SA lathes
• Higher production rates than ordinary lathes
• Cheaper than automatic lathes
• Easy loading and unloading of jobs
• Easy repair and maintenance
• Handle wide range of jobs
• Batch production targets can be achieved easily
Limitations
• Indexing of tools require special skill
• Intermittent inspection is difficult
• Special attachments to the cutting tools required
• Costlier compared to ordinary lathes
Copying Lathe• The copying technique was introduced in 1923 in the USA.
• For quite some time the copying lathe was important
• To reproduce accurately the shape of the template.
production of intricately shaped parts such
• Pistons
• Worms
• Shafts
However, now, largely been replaced by electronically controlled machines
Working Principle of Copying Lathes
• Copying lathes reproduce or duplicate any desired number of pieces
• A profile tracer follows the outline of a sample workpiece (Master /Template).
By means of
hydraulic controls,
• turning tool moves synchronously
• with the profile tracer
• transfers the contours of the model to the workpiece.
• The longitudinal feed and crossfeed of the machine are regulated electrohydraulically.
• The spindle speed is the only function which is still set
mechanically.
The major limitations
• Master piece is to be produced first by other means.
• Master piece surface properties dictate entire batch of production
Production Rate Rankings
1. Automatic lathes (Highest)
2. Semi-automatic lathes (Higher)
3. Engine lathe (Lowest)
Tool holding capacity
Automatic Lathes
• Can hold large no. of tools at a time (30)
• More No. of tools in machining action simultaneously(3-5)
• More no. of tool posts
Semi-automatic Lathes
• Can hold 10-15 tools at a time
• One to three tools in machining action simultaneously
• Two to Three tool posts
Engine Lathe
• Can hold maximum 4 tools at a time
• Hardly two tools in machining action simultaneously
• Only one tool post, but sometimes tailstock holds one tool
Power Requirements
For the same size of the machine
Engine lathes :
• require less power motor
• Spindle rotates at moderate speeds (900 rpm)
• Operate with only one motor
Product variety
Engine lathes
• Large ranges of variety and sizes
Semi automatic lathes
• medium ranges of variety and sizes
Automatic lathes
• Limited ranges of variety and sizes
Translatory motion
Automatic lathes
• Servo motors
Semi automatic lathes
• Chasing screw
Engine lathes
• Lead screw
Finished job
Automatic lathes
• High precision
• Complicated shapes
• Large accuracy
• Uniform jobs through out
• Requires random inspection only
Semi automatic lathes
• Precision is good
• Moderate shapes
• Medium accuracy
• Uniform jobs through out the batch
• Requires batch inspection
Engine lathes
• Precision requires skill
• General shapes
• low accuracy
• Uniformity of the jobs not assured
• Requires 100% inspection
Suitability
Engine lathe
• Job production
Semi automatic lathes
• Batch production
Automatic lathes
• Mass production
Labour
Engine lathe
• Requires skilled for tool setting, job setting and machining
Automatic & Semi automatic lathe
• Requires skilled for tool setting only
Importance of Production Lathes
• Improve production rate
• Improve productivity
• High quality
• Reduce human involvement
• Machine complicated jobs
Types of Production Lathes
Semi-automatic Lathes
• Turret lathes
• Capstan lathes
Automatic Lathes
Tool room Lathes
Special purpose lathes
• Machining specific types of jobs also called
special purpose lathes
Copying lathes
Chucking lathes
• Numerically controlled lathes (NC)
• Computer controlled lathes (CNC)
Semi automatic lathes
• Semi automatic lathes are production lathes with human involvement for certain operations
• Designed for short continuous runs
• Turret or ram in place of tailstock
• Indexable square toolpost on cross slide
• Suitable for Drilling, countersinking, reaming, tapping like operations
• Turret and Capstan lathes are examples
• In Turret lathe Turret moves along with saddle
• In Capstan lathe turret slides over the ram
Automatic Lathes
• Manual machine controls replaced by various mechanisms
• Parts are fed and removed automatically
• May have single or multiple spindles
• Operating sequences will be carried out by cam or actuator
• Simultaneous multi feature operation is common feature
• Automatic lathes without tailstock are called Chucking machines (Chuckers)
Suitable for mass/batch production
Number of attachments available
• Work loading magazines
• Cross drilling attachment
• Polygon turning attachment
• Slot milling attachment
Copying Lathes
Production of intricately shaped parts such
• Pistons
• Worms
• Shafts
• Master piece surface properties dictate entire batch of production
• Copying lathes duplicate any desired number of pieces
• A profile tracer follows the outline of a sample workpiece (Master).
Advantages of Production Lathes
• High production rates
• Machining in more than 2 axes possible
• Inspection some times not necessary
• No. of operations can be performed simultaneously
• No. of tools can be mounted at a time
• No. of jobs can be machined simultaneously
• Increase in productivity
• Decrease in unit cost
• Improved accuracy
• Less wastage through automatic controls
• More resources utilization with better safety
• Reduction of human involvement
• Job setting time is minimum or negligible
• Complex contours like spirals may be prepared easily
• Mass/batch production targets may be easily achieved
Applications of Production Lathes
• For performing operations on special jobs
• Crank shaft turning
• Wheel turning
• Cam shaft turning
Applications of Turret Lathes
• Generally used in batch production
• Suitable for performing sequential operations like drilling, boring, tapping etc.
• Machine medium size to large size jobs
Applications of Capstan Lathes
• Ideal for fast production of small parts
• Suitable for batch production
• Suitable for bar work also
Applications of Automatic Lathes
• Mass production of medium to large size jobs
• Some times can be used in transfer lines
• Machining irregular shaped jobs
Applications of Copying Lathes
• Generates/Copies profile on the work pieces
• Batch production
• Generally used for turning of parts such as
• Shafts
• Axles
• Piston rods
