All About Lathe Machine Tool
The Lathe Machine Tool blog is a comprehensive resource designed for engineering students, professionals, and anyone interested in machining and metalworking. It provides detailed answers to frequently asked questions on various aspects of lathe machines, from basic concepts to advanced techniques. Whether you're an aspiring engineer, a diploma student, or someone looking to refresh your knowledge, this blog covers all essential topics related to the lathe, its components, functions, operations, and types.
1.Write short notes on lathe
Lathe is a machine tool used for producing parts with circular sections which may be wood, plastic or metal. One of the typical parts are shown here.
• The angular feed which is at an angle to the axis of rotation of work produce tapered cylindrical surface.
2.List and explain different types of lathe
1. Speed Lathe
2. Bench Lathe
3. Toolroom Lathe
4. Capstan and Turret Lathe
5. Special Purpose Lathe
6. CNC Lathe
7. Engine Lathe or Centre Lathe
Speed Lathe
• A very high speed is available with this machine makes it suitable for wood working and polishing
• It does not have a carriage and feed mechanism. Instead the tool is supported on an adjustable slide and fed into the work by hand
Bench Lathe
• Bench Lathe is the small size lathe having all the features of a centre lathe or speed lathe
• It is usually mounted over the Bench
• Bench Lathe is suitable for small and precise work
Toolroom Lathe
• Toolroom Lathe is a precision lathe suitable for high accurate works and tool and die manufacturing
• Its bed and guide ways are made of hard steel ground with high accuracy
• Spindle and all other parts are made and assembled with high accuracy with precision bearings
• Along with all the features of a centre lathe, it will be provided with special attachments
Capstan and Turret Lathe
• These type of lathes are intended for repetitive mass production work
• A hexagonal turret head which can hold six tools at a time is the special feature of this machine.
• Each tool can be brought in to operation by rotating the turret head.
• This feature reduces considerable time for setting the tool and make it suitable for mass production work
Special Purpose Lathe
• Some of the example of special purpose lathes are : Wheel lathe, T-lathe, Missile lathe, gap bed lathe, duplicating lathe etc.
• These are specially designed for particular work
Automatic Lathe
• These are the computer controlled automatic machines called CNC Lathe
• Once the machine is programmed and the tools are being set, it will perform all the operation automatically
Centre Lathe
• Centre lathe also known as engine lathe is the most widely used general purpose machine.
• The bed is made of cast iron
• Spindle can be rotated at various speed by changing gears
• Feed mechanism enable the tool to be fed automatically
3.With a neat diagram explain the parts of a lathe
Different parts of a lathe are:
Bed
Headstock
Carriage Unit
Tailstock
Feed Mechanism
Screw cutting mechanism
Bed
It is the base of the lathe which carries all the parts over it. There is two guide ways on the top of the bed-inner ways and outer ways. The outer ways guide the carriage unit and inner ways guide tail stock Bed is made up with material of high compressive strength, wear resistance and toughness like Cast iron or cast steel.
Headstock
The headstock is the hollow casting which accommodates the spindle assembly and its variable speed driving mechanisms.
It is secured permanently on the left end of the lathe bed.
The driving mechanism may be cone pulley drive with back gear or all gear drive in modern lathes. The speed can be varied by shifting hand levers in front of the headstock.
Carriage Unit
The carriage of the lathe has several parts that serve to support, move and control the cutting tool.
This unit consist of the following parts: Saddle, Cross Slide, Compound Rest, Tool post, Apron
Tailstock
Tailstock is mounted over the bed on its right end which can be moved along the bed and locked at any position.
The two main functions of tailstock are:
1. To support the other end of the long work pieces when it is turned between centres.
2. To hold the tool for performing operation like drilling, reaming and tapping.
Feed mechanism
The feed mechanism of the lathe has different units through
which motion is transmitted from the headstock spindle to the carriage
Following are the units:
End bed gearing
Feed gear box
Feed shaft
Apron
Thread cutting mechanism
For thread cutting in lathe, the rotation of the spindle is transmitted to the carriage through end bed gearing and lead screw. The ratio of spindle rotation to the lead screw rotation can be changed by changing end bed gears either manually or by shifting levers to cut various pitches.
4.Write short notes on headstock of a lathe
The head stock is the hollow casting which accommodates the spindle assembly and its variable speed driving mechanisms.It is secured permanently on the left end of the lathe bed.The driving mechanism may be cone pulley drive with back gear or all gear drive in modern lathes. The speed can be varied by shifting hand levers in front of the headstock. The spindle of the head stock aligned accurately with the axis of the lathe and fitted with bearings. It is hollow to accommodate long work pieces. The front nose is threaded for fitting chuck flanges. The front end of the inside bore is tapered to fit lathe centre (live centre).
5.Explain about carriage of a lathe
The carriage of the lathe has several parts that serve to support, move and control the cutting tool. This unit consist of the following parts:
Saddle
It is the part of the carriage which slide over the lathe bed and provide longitudinal feed to the tool
Cross Slide
It slide on the guide ways provided on the top of the saddle and provide cross feed to the tool
Compound Rest
It is mounted over the cross slide and can be tilted at an angle and the top slide of it can be moved to provide angular feed to the tool
Tool post
Tool post is mounted over the top slide and clamp the tool rigidly by using bolts
Apron
It is the front panel of the carriage unit which accommodate the driving mechanisms to transmit the rotary movement of the feed shaft and lead screw to the longitudinal and cross feed movements.
6.Explain the tail stock of a lathe
Tailstock is mounted over the bed on its right end which can be moved along the bed guide ways and locked at any position.
The two main functions of tailstock are:
1. To support the other end of the long work pieces when it is turned between centres
2. To hold the tool for performing operation like drilling, reaming and tapping
The body is bored to act as a barrel inside which the spindle can be moved in and out by rotating the hand wheel.
The front of the spindle has a taper hole into which the dead centre or tools fit. The upper part of the body can be moved towards or away from the operator to align the spindle or for taper turning.
7.Explain different types of tool posts
Tool post is fitted over the top slide of the compound rest and holds the tool rigidly by tightening screws.
Types of tool post available are:
Single screw tool post
Four way tool post
Quick change tool post
Single screw tool post
In this tool post one single tool can be fixed by means of a set screw in the centre.The convex rocker helps to adjust the height of the tool tip.
Four way tool post
In this tool post all the four sides can be used to tight the tool by using bolts and packing strips for height adjustment.
Quick change tool post
This type of tool post is most widely used now a days. The detachable tool holder can be easily removed or locked in position. The height of the tool tip also can be adjusted by a set screw.
8.How to specify a lathe ?
1.The height of the centre measured from the lathe bed (A)
2.The swing diameter over the bed (2 x A)
3.The length between the centres (c). This is the maximum
length of the work that can be turned between centres
4.The swing diameter over the carriage (2 x K)
5.The maximum bar diameter (D). This is maximum diameter of the bar stock that will pass through the hole of the headstock spindle
6.The length of the bed (E).
9.Explain the work holding devices used in lathe
The various work holding devices used in lathe are:
Chuck
Lathe centre
Carrier and catch plate
Mandrel
Face Plate
Rest
Chuck
This is the most widely used work holding device in lathe
Work can be tight rigidly and easily by loosening or tightening the jaws of the chuck by using a chuck key.
Different types of chuck available are:
Four jaw independent chuck
Three jaw universal or self centring chuck
Combination chuck
Magnetic chuck
Collet chuck
Air or hydraulic operated chuck
Drill chuck
Four jaw independent chuck
This chuck has four jaws and each of which can be tightened independently by its screw.
It can hold work pieces other than round section also.
This type of chuck is particularly used in the setting up of heavy and irregular shaped work pieces.
Three Jaw Chuck
Three jaws and three square slots are provided on the circumference of the body. All jaws can be moved simultaneously by rotating any one of the key slot
Speedy centering of the work piece is possible
It cannot hold heavy work pieces as it is not rigid clamping as four jaw chuck. A scroll plate is used to move the jaws simultaneously.
Combination chuck
This chuck can be used both as an independent and self centering chuck.
Magnetic chuck
This chuck is used for holding very thin work pieces made of magnetic materials which cannot be held in an ordinary chuck. The holding power is obtained by an electric or permanent magnet placed within the chuck.
Collet chuck
Collet chucks are used for holding bar stock in production work where quick setting and accurate centring is needed. The body of the chuck has a taper bore into which split collets are fitted. This collet can be drawn in pus out by a lever mechanism to tight or loose the work piece.
Air or Hydraulic operated chuck
In this chuck jaws are opened or closed by hydraulic or pneumatic actuators. This fast and reliable clamping method used in mass production work.
Drill chuck
Drill chuck is used in lathe for drilling and other related operations. It has self centring jaws and is operated by chuck key or by hand. The chuck is fixed into the tapered bore of the tailstock spindle.
Lathe Centres
Long and slender work pieces are turned between centres- Live centre with headstock spindle and dead centre at the tailstock spindle.
They are made out of very hard materials to resist wear and deflection. The included angle of the centre is usually 60 degree for general work and 75 degree for heavy work. The shank of the centre is machined to morse standard taper (0-6). Different types of centres are:
Ordinary centre
Ball centre
Revolving centre
Half centre
Tipped centre
Insert type centre
Pipe centre
Ordinary centre is a general purpose centre.
Ball centre is specially used while taper turning to support the end.
Revolving centre is a frictionless centre fitted with bearing which is suited for supporting jobs running at high speed.
Half centre is used while facing operation to clear the tool.
The centres tipped with hard alloys are excellent to resist wear but expensive.
Pipe centres are used to support the hollow parts.
Carriers and Catch Plates
Carriers and catch plates are used to drive work piece when it is turned between centres.
The carrier or driving dog is attached at the end of the work piece by a set screw
The catch plate is bolted the nose of the headstock spindle
Types of carriers and catch plates are shown in figure
Single pin catch plate and straight tail carrier
Double pin catch plate and double slotted carrier
Double tail carrier
Bent tail carrier
Face Plate
Face plate is used for holding work pieces which cannot be conveniently held between centres or by chucks.
This has T-slots for clamping the work piece by nut and bolt.
Mandrel
Mandrels are used for holding and rotating a hollow work piece that has been previously drilled or bored.
The mandrel is fitted with a taper fit inside the hollow work piece and turned either between centres or by holding in a chuck.
Different types of mandrel in use are:
1. Plain mandrel
This mandrel has a plain single diameter with slight taper and is suited to hold only a particular diameter hole.
Different mandrels are used for every different size of holes
2. Step mandrel
As it has several steps different work pieces having different size of holes can be hold without replacing the mandrel each time
3. Collar mandrel
This type of mandrel is used for holding work pieces having holes of large diameter. This design not only reduces its weight but fits better than a solid mandrel also.
4.Screwed mandrel
It is threaded at its one end with a collar to hold work pieces having internal thread
5. Cone mandrel
This type of mandrel is suitable for holding work piece having hole diameters by placing the work piece on two cones and tightening the nut
6. Gang mandrel
This type mandrel is used to hold a number of hollow workpiece and tight by a nut. Considerable time is saved by using this mandrel in mass production work.
Rests
A rest is a mechanical device to support a long slender workpiece when it is turned between centres or by a chuck.
It is placed at some intermediate point to prevent the workpiece from bending due to its own weight and vibrations setup due to the cutting force.
There are two different types of rests
1. Steady rest
2. Follower rest
Steady rest
Steady rest is made of cast iron. It may be made to slide on the lathe bed ways and clamped at any desired position where the workpiece needs support. It has three jaws. These jaws can be adjusted according to the diameter of the work. One or more steady rests may be used to support the free end of a long work.
Follower rest
It consists of a ‘C’ like casting having two adjustable jaws to support the workpiece. The rest is bolted to the back end of the carriage. During machining, it supports the work and moves with the carriage. So, it follows the tool to give continuous support to the work to be able to machine along the entire length of the work.
10.Explain various operations performed in lathe
Facing
Straight turning
Step turning
Chamfering
Grooving
Undercutting
Forming
Knurling
Taper turning
11.What is knurling ?
Knurling is the process of embossing a diamond shaped pattern on the surface of the workpiece. The knurling tool holder has one or two hardened steel rollers with edges of required pattern. The tool holder is pressed against the rotating work. The rollers emboss the required pattern. The tool holder is fed automatically to the required length. Knurls are available in coarse, medium and fine pitches. The patterns may be straight, inclined or diamond shaped. The purpose of knurling is
1. To provide an effective gripping surface
2. To provide better appearance to the work
12.Explain different taper turning methods
Taper A taper may be defined as a uniform increase or decrease in diameter of a piece of work measured along its length. Taper turning methods
1. Form tool method2. Compound rest method3. Tailstock set over method4. Taper turning attachment method5. Combined feed method
(i) Form tool method
A broad nose tool is ground to the required length and angle. It is set on the work by providing feed to the cross-slide. When the tool is fed into the work at right angles to the lathe axis, a tapered surface is generated. This method is limited to turn short lengths of taper only. The length of the taper is shorter than the length of the cutting edge. Less feed is given as the entire cutting edge will be in contact with the work.
(ii) Compound rest method
The compound rest of the lathe is attached to a circular base graduated in degrees, which may be swivelled and clamped at any desired angle. The angle of taper is calculated using the formula: where D = Larger diameter d = Smaller diameter l = Length of the taper Ɵ = Half taper angle The compound rest is swivelled to the angle calculated as above and clamped. Feed is given to the compound slide to generate the required taper.
(iii) Tailstock set over method
Turning taper by the set over method is done by shifting the axis of rotation of the workpiece at an angle to the lathe axis and feeding the tool parallel to the lathe axis. The construction of tailstock is designed to have two parts namely the base and the body. The base is fitted on the bed guide ways and the body having the dead centre can be moved at cross to shift the lathe axis. The amount of set over (s) can be calculated as follows:
The dead centre is suitably shifted from its original position to the calculated distance. The work is held between centres and longitudinal feed is given by the carriage to generate the taper. The advantage of this method is that the taper can be turned to the entire length of the work. Taper threads can also be cut by this method. The amount of set over being limited, this method is suitable for turning small tapers (approx. unto 8°). Internal tapers cannot be done by this method.
(iv) Taper turning by an attachment
The taper attachment consists of a bracket which is attached to the rear end of the lathe bed. It supports a guide bar pivoted at the centre. The bar having graduation in degrees may be swivelled on either side of the zero graduation and set at the desired angle to the lathe axis. A guide block is mounted on the guide bar and slides on it. The cross slide is made free from its screw by removing the binder screw. The rear end of the cross slide is tightened with the guide block by means of a bolt. When the longitudinal feed is engaged, the tool mounted on the cross slide will follow the angular path as the guide block will slide on the guide bar set at an angle of the lathe axis. The depth of cut is provided by the compound slide which is set parallel to the cross-slide.
The advantage of this method is that long tapers can be machined. As power feed can be employed, the work is completed at a shorter time. The disadvantage of this method is that internal tapers cannot be machined.
13.Explain cutting speed, feed and depth of cut in lathe operation
Cutting Speed
The cutting speed of a cutting tool may be defined as the speed at which the cutting edge pass over the material. Cutting speed is ordinarily expressed in meter per minute.
Feed
The feed of a cutting tool is the distance the tool advances into or along the work piece each time the tool point passes a certain position in its travel over the surface. In the case of turning , the feed is the distance that the tool advances in one revolution of the work piece. On a shaper, the feed is the distance the work is moved relative to the tool for each cutting stroke. For single point tool, feed is specified in millimeter per revolution, milimeter per stroke etc. It may be expressed in millimeter per tooth for milling cutters.
Depth of cut
It is the distance the tool dig into the metal at the start of of each cutting pass.
In general cutting speed, feed and depth of cut are determined by the following factors:
1. Kind of material being cut
2. Kind of material and life of the tool
3. Geometry o the cutting tool
4. Type of finish desired
6. Type of cutting fluid used
5. Rigidity of the machine
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