Lathe machine

Lathe machine

Lathe:- 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. 

Working principal of lathe:- 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). To cut material properly, 

1. The tool should be harder than the work piece. 

2. Work piece should be rigidly held on the machine. 

3. The cutting tool should be fed in different way relative to the work. 

Specifications of engine lathe:- The size of lathe is specified or designated by the following items. 

1. Height of the centers above the lathe bed. 

2. The largest diameter of work that can be revolved over the ways of lathe bed i.e., swing diameter over the bed. 

3. The largest diameter that can be accommodated over the carriage i.e., the swing diameter over the carriage. 

4. 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. 

5. The maximum length of work that can be mounted between the centres.

The lathe carries the following main parts, 

                                    

1. Bed 

2.Headstock 

3. Spindle 

4. Tailstock 

5. Carriage 

6.Feed mechanism 

7. Legs. 

1.Bed:- This is the base of the lathe, which will supports 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. 

2. 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. 

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.

4. 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. 

The use of the tailstock,

 i. It supports the other end of the long workpiece when it is machined between centres.

 ii. It is useful in holding tools like drills, reamers and taps when performing drilling, reaming and tapping.

 iii. The dead centre is off-set by a small distance from the axis of the lathe to turn tapers by set over method. iv. It is useful in setting the cutting tool at correct height aligning the cutting edge with lathe axis.

5. 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.

6. 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.

Types of lathe:- The following types are, 

1. Bench lathe 

2. Speed lathe 

3. Engine lathe 

4.Tool room lathe 

5. Capstan and turret lathe 

6. Automatic lathe 

7. Special- purpose lathes. 

1. 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. 

2. 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. 

3. 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 a 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. 

4. 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.

5. 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. 

6. 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. 

7. 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.