LATHE

INTRODUCTION

The lathe is father of all machine tools; in early days it was equipped with a fixed tool rest and was used for woodworking. In operation, the lathe holds the job between two rigid supports called centres or by some chuck or face plate screwed to the nose or and of the spindle.

Function of lathe

The main function of lathe is to remove metal from a piece of work to give it the required shape and size. This is accomplished by holding the work securely and rigidly on the machine and then turning it against cutting tool, which will remove, metal from the work in the form of chips.

Types of lathes

Lathes of various designs and constructions have been developed to suit the various conditions of metal machining. But all of them employ the same fundamental principle of operation and perform the same function. The lathes are classified as follow.

1. Speed lathe

 Wood working

 Centering

 Polishing

 Spinning

2.Engin lathe

 Belt drive

 Individual motor drive

 Gear head lathe

3.Bench lathe

4.Tool room lathe

5.Capstan and turret lathe

6.Special purpose

Wheel lathe

 Gap bed lathe

 T-lathe

 Duplicating lathe

7.Automatic lathe

The speed lathe

 The speed lathe, in construction and operation, is the simplest of all types of lathes. It consists of a bed, a headstock, and a tailstock and tool post mounted on an adjustable slide. There is no feed box, lead screw or conventional type carriage. The tool is mounted on the adjustable slide and is fed into work purely by hand control. This characteristic of the lathe enables the designer to give high spindle speeds, which is usually, range from 1200 to 3600 r.p.m. As the tool is controlled by hand, the depth of cut and thickness of chip is very small.

 Light cut and high speed necessitate the use of this type of machine where cutting force is minimum such as in wood working, spinning, centering, polishing, etc.

The engine lathe or center lathe

This lathe is most important member of lathe family and is most widely used. Similar to the speed lathe, the engine lathe has got all the basic parts, e.g. bed, headstock, and tailstock. But the headstock of an engine

lathe is much more robust in construction

and it contains additional mechanism of driving the lathe spindle at multiple speeds.

The engine lathe that can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with help of a carriage feed rod and lead screw.

The bench lathe

This is a small lathe usually mounted on bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations, its only difference being in size this is used for small and precision work.

The tool room lathe

A tool room lathe having features similar to an engine lathe is much more accurately built and has a wider range of spindle speeds ranging from a very low to a quite high speed up to 2500 r.p.m.This lathe is mainly used for precision work on tools, dies, and gauges and in machining work where accuracy is needed

Numerically Controlled Lathes

In these lathes the path of the tools to produce the desired shape, along with other auxiliary functions like speed/feed changes, turret indexing, tail stock positioning, coolant supply, etc., are controlled by pre-programmed numerical data input in the form of punched tape to an electronic control system. One of the latest developments is the computer control of NC machines which is popularly called the computer numerical control (CNC). With the concept of numerical control, the configuration of lathes has undergone radical changes with features like slant bed design infinitely variable seed headstock, antifriction lead screws, auto-tool changing, etc. Numerically controlled lathes are available in various versions. The control system employed on NC lathes enable straight cut and continuous path control.

The cutting tools on a CN C turning center are usually mounted in a device called a turret. The turret is then mounted on a heavy cross slide and carriage similar to that of a conventional lathe. The turret can be indexed very rapidly to automatically change to the next tool.

A number of smaller CNC lathes have also come to market in recent years to compete with the turret lathes and automatic screw machines.

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