Some machining operation are so simple’ which are done quite easily, such as turning, the job is held in position in the chuck and turning operation is done easily. No other device is required to hold the job or to guide the tool on the machine in such an operation. But some operations are such type in which the tool is required to be guided by means of another device and also some jobs are of such forms which are required to be held in position on the machine by means of another device. The device which guides the tool is called jig and the device which holds the job in position is called fixture. Jigs and fixtures are special purpose tool which are used to facilitate production (machining, asslembling and inspection operations), when work piece is based on the concept of interchangeability according to which every part will be produced within an established tolerance. Jigs and fixtures provide on means of manufacturing interchangeable parts since they establish a relation with predetermined to tolerance between the work and cutting tool. They eliminate the necessity of a special set up for each individual park. So’ A jig can be defined as a device which hold and position the work; locate or guides the cutting tool relative to the work piece and usually not fixed to the m/c table. It is usually light in construction.
