Types of Lathe Machine

Types of Lathe Machine

Various designs and constructions of lathe have been developed to suit different
machining conditions and usage. The following are the different types of lathe
 1. Speed lathe
        a. Woodworking lathe
        b. Centering lathe
        c. Polishing lathe
        d. Metal spinning lathe
2. Engine lathe
        a. Belt driven lathe
        b. Individual motor driven lathe
        c. Gear head lathe
3. Bench lathe
4. Tool room lathe
5. Semi automatic lathe
        a. Capstan lathe
        b. Turret lathe
6. Automatic lathe
7. Special purpose lathe
         a. Wheel lathe
         b. Gap bed lathe
         c. ‘T’ lathe
         d. Duplicating lathe

1.Speed lathe

Spindle of a speed lathe operates at very high speeds (approximately at a range of
1200 to 3600 rpm) and so it is named so. It consists of a headstock, a tailstock, a bed and
a toolslide only. Parts like leadscrew, feed rod and apron are not found in this type of lathe.

1. Centering lathes are used for drilling center holes.
2. The woodworking lathes are meant for working on wooden planks.
3. Metal spinning lathes are useful in making tumblers and vessels from sheet metal.
4. Polishing of vessels is carried out in polishing lathe


2.Engine lathe or centre lathe

Engine lathes are named so because the early lathes were driven by steam engines.
As the turning operations are performed by holding the workpiece between two centers, it is
also known as centre lathe. Engine lathes are widely used in industries. It consists of parts
like headstock, tailstock and carriage. Parts like leadscrew and feed rod which are useful in
providing automatic feed are also found in this type of lathe.


3.Bench lathe

Bench lathe is a small lathe generally mounted on a bench. It consists of all the parts
of a engine lathe. It is used for small works like machining tiny and precise parts and parts of
measuring instruments

4.Tool room lathe

A tool room lathe has similar features of an engine lathe but is accurately built and
has wide range of spindle speeds to perform precise operations and different feeds. It is
costlier than a centre lathe. This is mainly used for precision works like manufacturing tools,
dies, jigs, fixtures and gauges.


5.Semi automatic lathe

Turret and Capstan lathes are known as semi-automatic lathes. These lathes are used
for production work where large quantities of identical workpieces are manufactured. They
are called semi-automatic lathes as some of the tasks are performed by the operators and
the rest by the machines themselves.
A semi skilled operator can do this at low cost and at shorter time. So, the cost of
production is reduced. There are two tool posts in the machine namely four way tool post
and rear tool post. Four tools can be mounted on the four way tool post and parting tool is
mounted on the rear tool post. The tailstock of an engine lathe is replaced by a hexagonal
turret. As many tools may be fitted on the six sides of the turret, different types of
operations can be performed on a workpiece without resetting of tools.

6.Automatic lathe

Automatic lathes are operated with complete automatic control. They are high speed,
mass production lathes. An operator can look after more than one automatic lathe at a time.

7.Special purpose lathe

Special purpose lathes are used for special purposes and for jobs, which cannot be
accommodated and conveniently machined on a standard lathe. Wheel lathe, ‘T’ lathe,
duplicating lathe are some examples of special purpose lathe.

Lathe Machine

Lathe machine

 

Introduction

 Lathe is considered as one of the oldest machine tools and is widely used in industries. It is called as mother of machine tools. It is said that the first screw cutting lathe was developed by an Englishman named Henry Maud slay in the year 1797. Modern high speed, heavy duty lathes are developed based on this machine.

The primary task of a lathe is to generate cylindrical workpieces. The process of machining a workpiece to the required shape and size by moving the cutting tool either parallel or perpendicular to the axis of rotation of the workpiece is known as turning. In this process, excess unwanted metal is removed. The machine tool useful in performing plain turning, taper turning, thread cutting, chamfering and knurling by adopting the above method is known as lathe

                                             

                                                                   or

 
Lathe is a machine which use for working on a piece of metal or wood about a horizontal axis 
and rotating it against a static tool. 


Parts of lathe machine

1. Bed 
2. Headstock 
3. Spindle 
4. Tailstock 
5. Carriage 
     a. Saddle 
     b. Apron 
     c. Cross-slide 
     d. Compound rest 
     e. Compound slide 
     f. Tool post 
6. Feed mechanism 
7. Leadscrew 
8. Feed rod 
9. Thread cutting mechanism

1. 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

 

2. 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

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 leadscrew

4. 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

 

5. 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. A single screw toolpost is illustrated in Fig 1.6
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.

 

6. 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.

                                 Forward position                    Reverse position

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.
 

Power feed to the carriage for thread cutting
When the two half nuts in the apron are made as one unit, leadscrew makes the
carriage to move automatically and cut threads of required pitch value

 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.