1. Lathe Machines B.Tech III Year I semester R16
Subject: Metrology and Machine Tools
By Syed Zakiuddin
Assistant Professor,
Department of Mechanical Engineering
NSAKCET

2. Working Principle
A machine for shaping a piece of material, such as wood or metal, by rotating it rapidly along its horizontal axis while pressing a fixed cutting or abrading tool against it.
The working principal of lathe is to remove the excess material in the form of chips from rotating work piece held between two centers with the help of a cutting tool fed against the work piece.
The centers between which the work piece is rotating are head stock Centre (live Centre) and tail stock Centre (dead Centre). The tool can be fed parallel to the work piece (horizontal) or perpendicular to the work piece (vertical).
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3. Parts of the lathe Bed Headstock Spindle Tailstock Carriage
Feed mechanism
Legs.
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4. Parts of the lathe
Bed
This is the base of the lathe, which will support the all other parts. This is a heavy rigid structure made by casting. This is a single piece structure which is having high damping capacity for the vibration generated by machine during machining. The rigid structure will helps to avoid deflections.
Headstock
The head stock will gives the rotation motion to the job at different speeds. It is a fixed part which will present on the left side of the lathe bed. Head stock will consists of a hallow spindle and drive unit like main spindle, feed reverse level, live centre, cone pulley etc.
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5. Parts of the lathe 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.
Tailstock
The tail stock is located at the right hand side of the lathe bed, it is called loose head stock because it is a movable member for alignment of work with head stock. The moving action of tailstock can be done by hand or by a wheel depending upon the design parameters and requirements.
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6. Parts of the lathe Carriage:-
The carriage will present between headstock and tailstock which will slides on the bed ways of the lathe bed. The carriage will give feed to the tool and it holds the tool. The carriage consists of the following parts,
(a) Saddle,
(b) Cross slide,
(c) Compound rest,
(d) Tool post,
(e) Apron.
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7. Parts of the lathe
(a) Saddle:- The base of the carriage is the saddle and slides along the bed ways. It contains the cross feed mechanism for moving the cutting tool at right angles to the ways. It supports the cross slide on which compounds rest and tool post are mounted.
(b) Cross slide:-The cross slide function to provide cutting action to the tool and the action of cutting tool will be perpendicular to centre line lathe.
(c) Compound rest:-It is supported on cross slide and is equipped with hand feed only. It can be swiveled horizontally on its base to any angle through 360°. It is used for turning and boring short angles and tapers.
(d) Tool post:-The tool post holds the tool in position and it is mounted on the top of the carriage.
(e) Apron:-The apron is secured underneath the saddle of the carriage unit. The controls and mechanism for all movements of carriage are housed in the apron. Its feed mechanism converts rotary motion of the lead screw or feed rod into linear motion of the carriage on which cutting tool is clamped.
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8. Parts of the lathe Feed mechanism
Most standard engine lathes are equipped with fed rod and a lead screw. The feed rod is used to provide automatic feed for all turning operations except for thread cutting. The lead screw transmits feed motion for screw cutting. In the absence of feed rod, the lead screw may be used for carriage feeds as well as thread cutting. The feed rod and lead screw obtain motion from the lathe spindle (Via gears) and transmit it to the carriage through gears and feed clutches.
Legs
The legs are the main support for the lathe to withstand the load, generally made by casting of cast iron will be used for legs.
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9. Types of lathe Bench lathe Speed lathe Engine lathe Tool room lathe
Capstan and turret lathe
Automatic lathe
Special- purpose lathes
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10. Types of lathe Bench lathe
It is a very small lathe and is mounted on a separately prepared bench or cabinet. It is used for small and precision work since it is very accurate. It has the same features as Speed lathe or Engine lathe. It perform almost all the operations, but difference only in its size.
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11. Types of lathe Speed lathe:-
It is the simplest form of the lathe, in construction and operation. These lathes may be of bench type or they may have the supporting legs cast and fitted to the bed. It consist of bed, headstock, tailstock, and tool post. They have no gear box, carriage and the lead screw. Here the work piece held between two centres revolved at high speeds by head stock, and the tool is controlled by hand. The depth of the cut is low. The speed late is used in wood working, centering and polishing.
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12. Types of lathe Engine lathe or centre lathe:-
It is a general purpose lathe normally used all types of machine shops. The main parts of the engine lathe are the bed, headstock, tailstock, carriage, lead screw and feed change gear box. The cutting tool is mounted on tool post and can be fed in the cross and longitudinal directions with reference to lathe axis. Power from motor is transmitted to spindle by belt drive or by gear drive. The speed changes in belt drive are obtained by shifting the belt to different steps of cone pulley. It is used for producing cylindrical components. By using attachments and accessories, other operations such as taper turning, milling and grinding may also be performed.
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13. Types of lathe Tool room lathe:-
It is nothing but the same engine lathe but equipped with some extra attachments to make it suitable for a relatively more accurate and precision type of work carried out in a tool room lathe. It carries a much wider range of speeds and feeds. The usual attachments provided on a tool room lathe are taper turning attachments, follower rest, collets, chucks, etc. this lathe is made to have a comparatively smaller bed length than the usual engine lathe. The most commonly used lengths are 135 to 180 cm.
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14. Types of lathe Capstan or turret lathe:-
Capstan and turret lathes are development of the centre (engine) lathe and are used for producing large number of identical parts. The general design of these lathes is similar to engine lathe except that the tailstock is replaced by a hexagonal turret. This turret is fitted with a series of pre-set tools and can be indexed to present different tools to the work piece. With tooling these machines may be operated by semi-skilled operators.
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15. Types of lathe Automatic lathe
Automatic lathes are high speed, heavy duty lathes and are adapted in mass production. It is provided with automatic controls for movement of work and tools at the proper rates and sequences. Once the cutting tools are set up and the machine starts, it performs automatically all the operations to complete the work. The cycle is repeated automatically (i.e., without attention of operators) to complete the next job. The machine in which loading and unloading of work is done by operator, and other operations are completed automatically is called as semi-automatic machines.
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16. Types of lathe Special- purpose lathes
These lathes are designed in such a way that, it can perform certain specified operations only. These are more effective than engine lathe in some specified operations. These include the gap lathe, wheel lathe, taper lathes etc.
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17. Specifications of engine lathe
Height of the centers above the lathe bed.
The largest diameter of work that can be revolved over the ways of lathe bed i.e., swing diameter over the bed.
The largest diameter that can be accommodated over the carriage i.e., the swing diameter over the carriage.
Maximum diameter that can be turned over the gap of bed (in case of gap bed) i.e., the swing diameter over the gap of bed.
The maximum length of work that can be mounted between the centres.
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18. Taper turning on lathe Forming tool method, 2. Compound rest method,
3. Tailstock set-over method, and
4. Taper attachment methods.
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19. Taper turning on lathe Taper turning by a forming tool method
Turning of taper by form tool is shown in fig. The form tool has a straight cutting edge inclined at the desired angle with the axis of rotation of work. This angle is equal to half the taper angle. The tool is fed straight into the work to produce a taper surface. This method is limited to short tapers.
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20. Taper turning on lathe Taper turning by the compound rest method
Taper turning using compound rest is shown in fig. it is used for turning longer taper than produced by a form tool, but the length of taper is limited by linear movement of compound rest slide. The base of compound rest is graduated in degrees and can be swiveled for required angle. The taper angle must first be calculated in degrees, and the rest may be swiveled to required angle (half of the taper angle). The feeding of the tool is done with compound rest feed handle and is controlled by hand. This method is simple and easy to setup for wide range of angles. But due to hand feed, it gives low productivity and poor surface finish.
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21. Taper turning on lathe Taper turning by tailstock method
This method is used for producing small tapers on long work pieces. In this method, the tail stock is set over at a distance away from the axis of spindle and the tool is allowed to move parallel to the axis of spindle. Due to the setting of tailstock, the work piece centre line is shifted at an angle a (semi-cone angle) to the spindle axis and hence allows for taper turning by moving the tool straight (or parallel to the axis of spindle).the axis of rotation of work is inclined at an angle to the lathe axis. It is the effective method of turning small tapers on long jobs.
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22. Taper turning on lathe Taper turning by taper attachment
Taper turning attachment is shown in fig. in this method the work is aligned to lathe axis and cutting tool is fed at an angle to the axis of work by means of attachment. The taper turning attachment consists of a bracket on which a guide bar is pivoted. The guide bar is provided with graduation in degrees and can be swivelled on either side of zero graduation to set at the desired angle. It can be used for turning internal as well as external tapers, and power feed can be used to turn taper quickly and with better finish. But length of taper limited to length of slide bar.
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23. Turret lathe
It is the modification of the engine lathe. The turret lathe elements the setup time between operations, reduced production time tremendously. In turret lathe the tail stock of an engine lathe is replaced by a multiple face rotating tool holder or turret which may have 6 faces.
The 6 faces or hexagonal turret is the most common. All the 6 faces of the turret can hold 6 or more number of different tools. The turret may be indexed automatically and each tool may be brought in line with the lathe axis in a regular sequence. The longitudinal and cross fed movement of the turret saddle and cross slide are regulated by adjustable stops.
The special of the turret lathe enable it to perform a series of operations such as drilling, boring, turning, thread cutting, chambering, cutting-off and many other operations in a regular sequence
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24. Capstan lathe
The capstan lathe is a ram-type turret lathe in which hexagonal turret is mounted on a ram slide. The saddle, which supports the ram, is clamped to the bed at a desired position.
This lathe is of light construction and has a short turret stroke and an automatic index on the turret.
The turret stroke depends on the ram that varies from 100 mm to 375 mm.
capstan lathes are used for mass production of small to medium size components from bar and rod stock.
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25. Principal of Automatic and semi-automatic lathes
Automatic machine
Machine in which the handling of work-piece along with the metal cutting operations is automatically performed is known as automatic machines.
Semi-automatic machines:-
Semi-automatic lathes are production lathes in which, once the machine is setup, all the machining operations are performed automatically but loading of work pieces and unloading of finished components are accomplished by the operator.
Turret and capstan lathes are semi-automatic lathes. These lathes are used for production work where large quantities of identical work pieces are manufactured.
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26. Different types of automatic machines
Magazine loaded automatic machines
Magazine loaded automatic machines are used to machine the work- piece which are in the form of blanks. These blanks, before feeding to the automatics are appropriately machined till their accurate dimensions are obtained.
Automatic bar Machines:-
The machining of work pieces either from bar or pipe stock is accomplished by using automatic bar machines.
These are further classified as follows,
a. Single spindle machine
b. Multi spindle machine
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27. Tooling layout of automatic lathes
The tool layout for automatic turret lathe is shown in figure. The various operations performed to get
the required job is as follows,
1. Feed bar to the stop 1 and clamp,
2. Centre end of the bar and dwell to clean up index turret,
3. Turn ∅12 and drill ∅ 9.9
4. Drill ∅5 holes,
5. Cone bottom of ∅ 9.9 mm hole,
6. Ream ∅ 10 mm and cone,
7. Cut-off over cross slide.
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28. Tooling layout of automatic lathes
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