Principle of lathe:
The most originate and basic function of lathe is to remove excess metal material from work piece to give it the required shape and size to make it final product.
Basically it is defined as m/c too that holds the work piece between two rigid and strong supports, called CENTERS. Or in a Chuck or faceplate while the latter revolves, the chuck or the faceplate is mounted on the projected end of m/c spindle.
Cutting tool is rigidly held and supported in a tool post and is fed against the revolving work piece; while work piece revolves about its axis the tool is made to move either parallel to or at an inclination with this axis to cut the desired material. In doing so it produces a cylindrical surface, if it is fed parallel to the axis, or will produce a tapered axis, if it is fed at an inclination. The metal removed by tool from work piece is in the form of chips.
To cut the material properly the tool used should be harder than the material of the work piece, and should be rigidly held on the m/c and should be fed or progressed in a definite way relative to the work; as we learned previously.
Types of lathe:
Basic usage of a lathe is for metal machining; but there are different lathes of different designs, different construction to suit the various conditions of usage. But all of them employ the same fundamental of operation with same function.
The types generally used are:
1. Speed lathe
(a). Wood working
2. Engine lathe
(a). Belt drive
(b). Individual motor drive
(c). Gear head lathe
3. Bench lathe
4. Tool room lathe
5. Capstan and Turret lathe
6. Special purpose:
(a) Wheel lathe
(b) Gap bed lathe
(d) Duplicating lathe
7. Automatic lathe
(1) The Speed Lathe:
It is the simplest of all types of lathe because of its simple construction and way of operation. The “SPEED LATHE” has been so named b’coz of the very high speed of the headstock spindle.
It consists of a bed, a head stock and a tailstock and a tool post mounted on an adjustable slide. There is no feed box, lead screw or conventional type of carriage.
Here the tool is mounted on the adjustable slide and is fed in to work purely by hand control. This such characteristic of the lathe enables the designer to give high spindle speeds which usually range from 1200 to 3600 r.p.m. As the tool is controlled by hand, the depth of cut and the thickness of chip are very small.
There are two to three spindle speeds are available. Light cuts and high speeds necessitate the use of this type of machine where cutting force is minimum such as in WOOD WORKING, SPINNING, CENTERING, POLISHING, etc.
(2) The Engine Lathe or Centre Lathe:
One of the most important and widely used lathes to deal with .The term “engine” is associated with the lathe owing fact that in its early days it was fed by steam engines.
The basic components of this lathe are bed, headstock and tailstock but in practice we can see that the construction of its headstock is much complicating and contains additional mechanism for driving the lathe spindle at multiple speeds.
Unlike the speed lathe, this type of lathe can feed the cutting tool longitudinal as well as cross direction with reference to the lathe axis with help of a carriage, feed rod and lead screw. So, this lathe can be used for any type of lathe work.
They are classified on the basis of the design of the headstock and the methods of power transmitting to the machine used.
A lathe that receives power from an over-head line shaft is a belt-driven lathe and is equipped with a speed –cone and or more back gears to get a wide range of spindle speeds.
A lathe that receives its power from an individual motor integral with the machine is called a motor driven lathe.
A geared head lathe gets its power from a constant speed motor, and all speed changes are obtained by shifting various gears located in the headstock. It has no cone pulley.
(3) The Bench Lathe:
A small lathe usually plotted on a bench and has all parts as in speed or engine lathe. Although it is small in size it performs all operations and does small precision work.
(4) The Tool Room Lathe:
It has its features similar to the engine lathe. It is built with more accuracy and has a wide range of spindle ranging from a very low to a quite high speed up to 2500 r.p.m. This is equipped, besides other things, with a chuck, taper turning attachment, draw in collet attachment, thread chasing dial, relieving attachments, steady and follower rest, pump for coolant, etc. This lathe is mainly used for precision work on tools, dies, and gauges and in machining work where accuracy is needed. The machine is costlier than an engine lathe of the same size.
(5) Capstan And Turret Lathe:
They are the results of further development of the engine lathe and are used for the production purpose.
The main and distinguished feature of this lathe is that the tailstock of an engine lathe is replaced by a hexagonal (some times octagonal) turret, on the face of which multiple tools may be fitted and fed in to the work in proper sequence.
The basic most advantage is that number of different types of operations can be done on a work piece without re-setting of work piece or tools, and a number of identical parts can be produced in the minimum time.
(6) Special Purpose Lathe:
As we can get some over viewed idea by its name that this types of lathes are used for special purposes and for jobs which can’t be accommodated or conveniently machined on a standard lathe.
As in the case of ‘THE WHEEL LATHE’ is made for finishing the journals and turning the thread on railroad car and locomotive wheels.
The ‘GAP BED LATHE’, in which a section of bed adjacent to the headstock is recoverable, is used to swing extra-large diameter pieces.
The ‘T-LATHE’ is intended for machining of rotors for jet engines.The axis of lathe bed is at right angles to the axis of the head stock spindle is the form of a T.
The ‘MISSILE LATHE’ , which has a very large swing for accommodating long missile components of very large diameter , is the most modern and latest in lathe design.
(7) Automatic Lathe:
Under this banner a high speed, heavy duty, mass production lathes with complete automatic control are working.
Once the tool is set and the m/c is started all the operations are performed in pre-settled manner until the work piece takes an end as a final product.
Even after completion of job the m/c will continue to repeat manner of operation until its auto feeder fees more work. It is like a formation of production cycle; with which we can produce identical parts even without attention of operator.
A operator who has to look at five to six auto lathes at a time can simply do his job, after the general maintains of the machine and cutting tools, load up a bar stock and remove finished products from time to time.
As a general view auto lathes are demand of fast and furious present as well as future in for cases of Mass Production.
Different parts of engine lathe :
There are six parts of Lathe Machine. They are given below.
The Bed :
It is a part of lathe machine which is the base of the machine. The all other parts are located on it. It carries all the weight of the machine.
The lathe bed being the main guiding member of the tool for accurate machining work must satisfy the following conditions:
- It should be sufficiently rigid to prevent deflection under tremendous cutting pressure transmitted through the tool-post and carriage to the lathe bed.
- It must be massive with sufficient depth and width to absorb vibration.
- It must resist the twisting stress.
- The bed should be seasoned naturally to avoid distortion or warp.
There are two sets of slides or guide ways
- Outer ways.
- Inner ways.
Types of bed ways:-
- Inverted V-bed way
- Flat bed way
- Box section
- Flat bed way for saddle
Generally, the material use in bed of lathe machine should have high compressive strength, should be wear resistant and absorb vibration. Cast iron alloyed with nickel and chromium forms a good material suitable for lathe bed.
- It resists all the weight of machine’s parts.
- It can resist the vibration of working machine.
The Headstock :
The head stock is secured permanently on the inner way at the left hand end of the lathe bed. It provides mechanical means of rotating the work at multiple speeds. It comprises essentially a hollow spindle and mechanism for driving and altering the spindle speed. All the parts are housed within the headstock casting.
The headstock is made of carbon or nickel-chrome steel. This is usually of a large diameter to resist bending and it should be perfectly aligned with the lathe axis and accurately machined for producing true work surface. In this way the working job is perfectly made in shape.
The parts of headstock:-
- Threaded end
- Taper sleeve
- Live center
- Treaded nose
- Spindle hole
- Gear box
The gear box is generally used for a speed changing. The speed changing is necessary to vary the speed of the work to suit the different machining conditions.
Speed changing is depends on following conditions:-
- The type of materials to be cut.
- The types of cutting tool material used.
- The types of finishing.
- The types of cutting fluid used.
- The diameter of work piece.
- The types of operations.
Tail Stock :
It is also known as loose head stock. It is located on the inner ways at right hand end of the bed. To accommodate different lengths of work, the body of the tail stock can be adjusted along the ways chiefly by sliding it to the desired position where it can be clamped by bolts and plates.
The main uses:-
- It supports the other end of the work piece when it is being machined between centers.
- It holds a tool for performing operations such as drilling, reaming, tapping etc.
The different parts of tail stock:-
- Dead center
- Spindle clamp
- Square threaded screw
- Hand wheel
- Split lug
- Tail stock clamping blot
- Lathe bed ways
- Clamping plate
- Set over screw
- Key way
Other features some times incorporated on tail stocks are graduated spindle and micro meter dials on the hand wheels for accurate length setting, and felt wiper pads on the base and spindle.
The carriage of a lathe has several parts that serve to support, move and control the cutting tool.
Parts of carriage:-
- The cross-slide
- Compound slide or compound rest
- Tool post
The saddle is an H-shaped casting that fits over the bed and slides along the ways. It carries the cross slide and tool post. With use of saddle to prevent any movement when surfacing operations are carried out.
The cross slide comprises a casting, machined on the underside for attachment to the saddle and carries location on the upper face for the tool post or compound rest. The cross piece of the saddle is made at right angles to the centre axis of the lathe.
The compound slide or compound rest:-
The compound rest is mounted on the top of the cross-slide and has a circular base graduated in degrees. It is used for obtaining angular cuts and short tapers as well as convenient positioning of the tool to the work. By loosening the two set screws and after then setting the angle, we obtaining the taper cutting.
The tool post:-
This is located on the top of the compound rest to hold the tool and to enable it to be adjusted to a convening working position.
The types of tool post are given below.
- Single screw tool post
- Four bolt tool post
- Open side tool post
- Four way tool post
The apron is fasted to the saddle and hangs over the front of the bed, so the working of machine is vary fast. It contains gears, clutches and levers. It carriage by hand and power feeds.