Bed
Bed is mounted on the legs of the lathe which are bolted to the floor. It forms the base
of the machine. It is made of cast iron and its top surface is machined accurately and
precisely. Headstock of the lathe is located at the extreme left of the bed and the tailstock at
the right extreme. Carriage is positioned in between the headstock and tailstock and slides
on the bed guideways.
The top of the bed has flat or ‘V’ shaped guideways. The tailstock and the carriage
slides on these guideways. Inverted ‘V’ shaped guideways are useful in better guide and
accurate alignment of saddle and tailstock. The metal burrs resulting from turning operation
automatically fall through. Flat bed guideways can be found in older machine tools. It is
useful in heavy machines handling large workpieces. But then the accuracy is not high.
Headstock
Headstock is mounted permanently on the inner guideways at the left hand side of
the leg bed. The headstock houses a hollow spindle and the mechanism for driving the spindle
at multiple speeds. The headstock will have any of the following arrangements for driving
and altering the spindle speeds
(i) Stepped cone pulley drive
(ii) Back gear drive
(iii) All gear drive
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
leadscrew.
Tailstock
Tailstock is located on the inner guideways at the right side of the bed opposite to the
headstock. The body of the tailstock is bored and houses the tailstock spindle or ram. The
spindle moves front and back inside the hole. The spindle has a taper hole to receive the
dead centre or shanks of tools like drill or reamer. If the tailstock handwheel is rotated in
the clockwise direction, the spindle advances. The spindle will be withdrawn inside the
hole, if the handwheel is rotated in anti-clockwise direction.
To remove the dead centre or any other tool from the spindle, the handwheel is
rotated in anticlockwise direction further. The movement of the spindle inside the hole may
be locked by operating the spindle clamp located on top of the tailstock.In order to hold
workpieces of different lengths, the tailstock can be locked at any desired position on the
lathe bed. Tailstock clamping bolts and clamping pates are used for this purpose.
Tailstock is designed to function as two units-the base and the body. The base of the
tailstock is clamped to the bed. The body is placed on the base and can be made to slide
sidewards-perpendicular to the bed guideways upto a certain distance.
The uses of tailstock
1. It supports the other end of the long workpiece when it is machined between
centres.
2. It is useful in holding tools like drills, reamers and taps when performing drilling,
reaming and tapping.
3. The dead centre is off set by a small distance from the axis of the lathe to turn
tapers by set over method.
4. It is useful in setting the cutting tool at correct height aligning the cutting edge with
lathe axis.
Carriage
Carriage is located between the headstock and tailstock on the lathe bed guideways.
It can be moved along the bed either towards or away from the headstock. It has several
parts to support, move and control the cutting tool. The parts of the carriage are :
a) saddle
b) apron
c) cross-slide
d) compound rest
e) compound slide
f) tool post
Saddle:
It is an “H” shaped casting. It connects the pair of bed guideways like a bridge. It
fits over the bed and slides along the bed between headstock and tailstock. The saddle or
the entire carriage can be moved by providing hand feed or automatic feed.
Cross slide:
Cross-slide is situated on the saddle and slides on the dovetail guideways at right
angles to the bed guideways. It carries compound rest, compound slide and tool post. Cross
slide handwheel is rotated to move it at right angles to the lathe axis. It can also be power
driven. The cross slide hand wheel is graduated on its rim to enable to give known amount of
feed as accurate as 0.05mm.
Compound rest:
Compound rest is a part which connects cross slide and compound slide. It is mounted
on the cross-slide by tongue and groove joint. It has a circular base on which angular
graduations are marked. The compound rest can be swiveled to the required angle while
turning tapers. A top slide known as compound slide is attached to the compound rest by
dove tail joint. The tool post is situated on the compound slide.
Tool post:
This is located on top of the compound slide. It is used to hold the tools rigidly. Tools
are selected according to the type of operation and mounted on the tool post and adjusted
to a convenient working position. There are different types of tool posts and they are:
1. Single screw tool post
2. Four bolt tool post
3. Four way tool post
4. Open side tool post
Single screw tool post
The tool is held by a screw in this toolpost. It consists of a round bar with a slotted
hole in the centre for fixing the tool by means of a setscrew. A concave ring and a convex
rocker are used to set the height of the tool point at the right position. The tool fits on the
flat top surface of the rocker. The tool post is not rigid enough for heavy works as only one
clamping screw is used to clamp the tool
Four way tool post
This type of tool post can accommodate four tools at a time on the four open sides of
the post. The tools are held in position by separate screws and a locking bolt is located at
the centre. The required tool may be set for machining by swiveling the tool post.
Machining can be completed in a shorter time because the required tools are pre-set.
Feed mechanism
There are several mechanisms to make the carriage and crose-slide move
automatically and to change the direction of their movement. Some important mechanisms
are dealt with as follows.
Tumbler gear arrangement
Tumbler gears are located in the headstock just below the spindle gear. For the
purpose of moving the carriage towards or away from the headstock, this mechanism along
with feed rod or leadscrew is used.
Tumbler gears are two small pinions mounted on a bracket. This bracket is pivoted
about the axis of the stud gear. The position of the bracket can be arranged in three different
stages namely i) neutral ii) forward & iii) reverse. Hence, the direction of rotation of the
leadscrew and the feed rod is reversed.
Neutral position
When the bracket is held in neutral position, both the tumbler gears A and B stand
disengaged from the spindle gear and main gear train. And so carriage will not get any
movement.
Forward position
When the bracket is arranged in the forward position as shown in the diagram, only
one of the tumbler gears(B) comes between the spindle gear and the main gear train. In that
position, the leadscrew or the feed rod rotates in the direction of the headstock spindle
rotation. The carriage moves towards the headstock providing the cutting tool with
longitudinal feed.
Reverse position
When the bracket is arranged in the reverse position, both the tumbler gears come in
contact between the spindle gear and the main gear train. The carriage moves towards the
tailstock to give the tool the longitudinal feed in the opposite direction.
Apron Mechanism:
Apron is attached to the carriage and hangs over the front side of the lathe bed. It is
useful in providing power and hand feed to both carriage and cross-slide. It is also used to
provide power feed to the carriage during thread cutting through two half nuts.
Construction
Power is transmitted from the spindle to the leadscrew and feed rod through the
spindle gear and tumbler gear arrangement. A worm is mounted on the feed rod by a sliding
key. The worm meshes with a worm gear on whose axis another gear G1 is attached. Gear
G1 is attached to a small gear G2 by a bracket as shown in the diagram. Gear G4 is
positioned to be in mesh with the rack gear always. Another gear G3 is mounted on the same
axis of gear G4. The carriage handwheel meant for longitudinal feed is attached to the gear
G5 on the same axis. The gears G3 and G5 are always in mesh. The gear G6 is attached to
the cross slide screw.
The feed selection lever can be kept in neutral, up and down positions to obtain the
following movements.
1. Hand feed and power feed to the carriage
2. Hand feed and power feed to the cross slide
Hand feed to the carriage
Feed selection lever is kept in neutral position and the carriage handwheel is rotated.
The gear G4 attached to the rack gets rotation through the gears G5 and G3. The carriage
moves longitudinally.
Power feed to the carriage
When feed selection lever is kept in up position (U), the gear G2 will mesh with gear
G3. Gear G4 gets rotation through gear G3 and the carriage gets automatic (power) feed.
Hand feed to the cross slide
Feed selection lever is kept in neutral position. The cross slide will move on rotation
of the cross slide handwheel.
Power feed to the cross slide
When the feed selection lever is kept in down position (D), gear G2 will be in contact
with gear G6. The rotation of G6 will make the cross slide screw also to rotate and the
cross-slide moves automatically.
Leadscrew
The leadscrew is a long threaded shaft used as master screw. It is brought into
operation during thread cutting to move the carriage to a calculated distance. Mostly
leadscrews are Acme threaded.
The leadscrew is held by two bearings on the face of the bed. A gear is attached to
the lead screw and it is called as gear on leadscrew. A half nut lever is provided in the apron
to engage half nuts with the leadscrew.
Leadscrew is used to move the carriage towards and away from the headstock
during thread cutting. The direction of carriage movement depends upon the direction of
rotation of the leadscrew.When the leadscrew is kept stationary, the half nuts are engaged
with the leadscrew to keep the carriage locked at the required position.
Feed rod
Feed rod is placed parallel to the leadscrew on the front side of the bed. It is a long
shaft which has a keyway along its length. The power is transmitted from the spindle to the
feed rod through tumbler gears and a gear train. It is useful in providing feed movement to
the carriage except for thread cutting and to move cross-slide. A worm mounted on the feed
rod enables the power feed movements.
Spindle mechanism
The spindle is located in the headstock and it receives the driving power from the
motor. The spindle speed should be changed to suit different machining conditions like type
of material to be cut, the diameter and the length of the work, type of operation, the type of
cutting tool material used, the type of finish desired and the capacity of the machine. In
order to change the spindle speeds, any one of the following methods are employed.
1. Step cone pulley drive
2. Back geared drive
3. All geared drive
Bed is mounted on the legs of the lathe which are bolted to the floor. It forms the base
of the machine. It is made of cast iron and its top surface is machined accurately and
precisely. Headstock of the lathe is located at the extreme left of the bed and the tailstock at
the right extreme. Carriage is positioned in between the headstock and tailstock and slides
on the bed guideways.
The top of the bed has flat or ‘V’ shaped guideways. The tailstock and the carriage
slides on these guideways. Inverted ‘V’ shaped guideways are useful in better guide and
accurate alignment of saddle and tailstock. The metal burrs resulting from turning operation
automatically fall through. Flat bed guideways can be found in older machine tools. It is
useful in heavy machines handling large workpieces. But then the accuracy is not high.
Headstock
Headstock is mounted permanently on the inner guideways at the left hand side of
the leg bed. The headstock houses a hollow spindle and the mechanism for driving the spindle
at multiple speeds. The headstock will have any of the following arrangements for driving
and altering the spindle speeds
(i) Stepped cone pulley drive
(ii) Back gear drive
(iii) All gear drive
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
leadscrew.
Tailstock
Tailstock is located on the inner guideways at the right side of the bed opposite to the
headstock. The body of the tailstock is bored and houses the tailstock spindle or ram. The
spindle moves front and back inside the hole. The spindle has a taper hole to receive the
dead centre or shanks of tools like drill or reamer. If the tailstock handwheel is rotated in
the clockwise direction, the spindle advances. The spindle will be withdrawn inside the
hole, if the handwheel is rotated in anti-clockwise direction.
To remove the dead centre or any other tool from the spindle, the handwheel is
rotated in anticlockwise direction further. The movement of the spindle inside the hole may
be locked by operating the spindle clamp located on top of the tailstock.In order to hold
workpieces of different lengths, the tailstock can be locked at any desired position on the
lathe bed. Tailstock clamping bolts and clamping pates are used for this purpose.
Tailstock is designed to function as two units-the base and the body. The base of the
tailstock is clamped to the bed. The body is placed on the base and can be made to slide
sidewards-perpendicular to the bed guideways upto a certain distance.
The uses of tailstock
1. It supports the other end of the long workpiece when it is machined between
centres.
2. It is useful in holding tools like drills, reamers and taps when performing drilling,
reaming and tapping.
3. The dead centre is off set by a small distance from the axis of the lathe to turn
tapers by set over method.
4. It is useful in setting the cutting tool at correct height aligning the cutting edge with
lathe axis.
Carriage
Carriage is located between the headstock and tailstock on the lathe bed guideways.
It can be moved along the bed either towards or away from the headstock. It has several
parts to support, move and control the cutting tool. The parts of the carriage are :
a) saddle
b) apron
c) cross-slide
d) compound rest
e) compound slide
f) tool post
Saddle:
It is an “H” shaped casting. It connects the pair of bed guideways like a bridge. It
fits over the bed and slides along the bed between headstock and tailstock. The saddle or
the entire carriage can be moved by providing hand feed or automatic feed.
Cross slide:
Cross-slide is situated on the saddle and slides on the dovetail guideways at right
angles to the bed guideways. It carries compound rest, compound slide and tool post. Cross
slide handwheel is rotated to move it at right angles to the lathe axis. It can also be power
driven. The cross slide hand wheel is graduated on its rim to enable to give known amount of
feed as accurate as 0.05mm.
Compound rest:
Compound rest is a part which connects cross slide and compound slide. It is mounted
on the cross-slide by tongue and groove joint. It has a circular base on which angular
graduations are marked. The compound rest can be swiveled to the required angle while
turning tapers. A top slide known as compound slide is attached to the compound rest by
dove tail joint. The tool post is situated on the compound slide.
Tool post:
This is located on top of the compound slide. It is used to hold the tools rigidly. Tools
are selected according to the type of operation and mounted on the tool post and adjusted
to a convenient working position. There are different types of tool posts and they are:
1. Single screw tool post
2. Four bolt tool post
3. Four way tool post
4. Open side tool post
Single screw tool post
The tool is held by a screw in this toolpost. It consists of a round bar with a slotted
hole in the centre for fixing the tool by means of a setscrew. A concave ring and a convex
rocker are used to set the height of the tool point at the right position. The tool fits on the
flat top surface of the rocker. The tool post is not rigid enough for heavy works as only one
clamping screw is used to clamp the tool
Four way tool post
This type of tool post can accommodate four tools at a time on the four open sides of
the post. The tools are held in position by separate screws and a locking bolt is located at
the centre. The required tool may be set for machining by swiveling the tool post.
Machining can be completed in a shorter time because the required tools are pre-set.
Feed mechanism
There are several mechanisms to make the carriage and crose-slide move
automatically and to change the direction of their movement. Some important mechanisms
are dealt with as follows.
Tumbler gear arrangement
Tumbler gears are located in the headstock just below the spindle gear. For the
purpose of moving the carriage towards or away from the headstock, this mechanism along
with feed rod or leadscrew is used.
Tumbler gears are two small pinions mounted on a bracket. This bracket is pivoted
about the axis of the stud gear. The position of the bracket can be arranged in three different
stages namely i) neutral ii) forward & iii) reverse. Hence, the direction of rotation of the
leadscrew and the feed rod is reversed.
Neutral position
When the bracket is held in neutral position, both the tumbler gears A and B stand
disengaged from the spindle gear and main gear train. And so carriage will not get any
movement.
Forward position
When the bracket is arranged in the forward position as shown in the diagram, only
one of the tumbler gears(B) comes between the spindle gear and the main gear train. In that
position, the leadscrew or the feed rod rotates in the direction of the headstock spindle
rotation. The carriage moves towards the headstock providing the cutting tool with
longitudinal feed.
Reverse position
When the bracket is arranged in the reverse position, both the tumbler gears come in
contact between the spindle gear and the main gear train. The carriage moves towards the
tailstock to give the tool the longitudinal feed in the opposite direction.
Apron Mechanism:
Apron is attached to the carriage and hangs over the front side of the lathe bed. It is
useful in providing power and hand feed to both carriage and cross-slide. It is also used to
provide power feed to the carriage during thread cutting through two half nuts.
Construction
Power is transmitted from the spindle to the leadscrew and feed rod through the
spindle gear and tumbler gear arrangement. A worm is mounted on the feed rod by a sliding
key. The worm meshes with a worm gear on whose axis another gear G1 is attached. Gear
G1 is attached to a small gear G2 by a bracket as shown in the diagram. Gear G4 is
positioned to be in mesh with the rack gear always. Another gear G3 is mounted on the same
axis of gear G4. The carriage handwheel meant for longitudinal feed is attached to the gear
G5 on the same axis. The gears G3 and G5 are always in mesh. The gear G6 is attached to
the cross slide screw.
The feed selection lever can be kept in neutral, up and down positions to obtain the
following movements.
1. Hand feed and power feed to the carriage
2. Hand feed and power feed to the cross slide
Hand feed to the carriage
Feed selection lever is kept in neutral position and the carriage handwheel is rotated.
The gear G4 attached to the rack gets rotation through the gears G5 and G3. The carriage
moves longitudinally.
Power feed to the carriage
When feed selection lever is kept in up position (U), the gear G2 will mesh with gear
G3. Gear G4 gets rotation through gear G3 and the carriage gets automatic (power) feed.
Hand feed to the cross slide
Feed selection lever is kept in neutral position. The cross slide will move on rotation
of the cross slide handwheel.
Power feed to the cross slide
When the feed selection lever is kept in down position (D), gear G2 will be in contact
with gear G6. The rotation of G6 will make the cross slide screw also to rotate and the
cross-slide moves automatically.
Leadscrew
The leadscrew is a long threaded shaft used as master screw. It is brought into
operation during thread cutting to move the carriage to a calculated distance. Mostly
leadscrews are Acme threaded.
The leadscrew is held by two bearings on the face of the bed. A gear is attached to
the lead screw and it is called as gear on leadscrew. A half nut lever is provided in the apron
to engage half nuts with the leadscrew.
Leadscrew is used to move the carriage towards and away from the headstock
during thread cutting. The direction of carriage movement depends upon the direction of
rotation of the leadscrew.When the leadscrew is kept stationary, the half nuts are engaged
with the leadscrew to keep the carriage locked at the required position.
Feed rod
Feed rod is placed parallel to the leadscrew on the front side of the bed. It is a long
shaft which has a keyway along its length. The power is transmitted from the spindle to the
feed rod through tumbler gears and a gear train. It is useful in providing feed movement to
the carriage except for thread cutting and to move cross-slide. A worm mounted on the feed
rod enables the power feed movements.
Spindle mechanism
The spindle is located in the headstock and it receives the driving power from the
motor. The spindle speed should be changed to suit different machining conditions like type
of material to be cut, the diameter and the length of the work, type of operation, the type of
cutting tool material used, the type of finish desired and the capacity of the machine. In
order to change the spindle speeds, any one of the following methods are employed.
1. Step cone pulley drive
2. Back geared drive
3. All geared drive
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