Design of Fixtures Introduction Fixture is a work

Design of Fixtures

Introduction Fixture is a work holding device that holds, supports and locates the work piece for a specific operation but does not guide the cutting tool.

Types of Fixtures • • • Boring Fixtures Turning Fixtures Milling Fixtures Broaching Fixtures Grinding Fixtures Planning Fixtures Shaping Fixtures Assembly Fixtures Inspection Fixtures Welding Fixtures Modular Fixtures

Boring Fixtures • According to the type of boring operation, boring fixture are used. • Boring Fixture may have characteristics of a drill jig or a mill fixture. • The work piece always has an existing hole which is enlarged by the boring operation. • It may be final or may be preliminary to grinding and other sizing operation.

Types of Boring Fixtures i. Fixtures for work piece mounted in reciprocating table with fixed rotating bar. ii. Fixtures for work piece mounted in fixed table with reciprocating and rotating bar. iii. Fixtures for rotating work piece with stationary bar on reciprocating table.

Lathe or Turning Fixture The standard work holding devices or fixtures for lathe are: • Three and four jaw chucks • Collets • Face plate • Mandrels • Milling vice

• If the job can be held easily and quickly in the above mentioned standard devices, then there is no need for special work holding devices. • However many jobs particularly casting and forging, because of their shapes, cannot be conveniently held by any of the standard devices. • It then becomes necessary to build a special work holding device for the job. Such a device is called lathe fixture.

Basic Design Principles for Turning or Lathe Fixtures: 1. To avoid vibration while revolving , the fixture should be accurately balanced. 2. There should be no projections of the fixture which may causes injury to the operator. 3. The fixture should be rigid and overhang should be kept minimum possible so that there is no bending action. 4. Clamps used to fix the fixture to the lathe should be designed properly so that they don’t get loosed by centrifugal force. 5. The fixture should be as light weight as possible since it is rotating. 6. The fixture must be small enough so that it can be mounted and revolved without hitting the bed of the lathe.

Milling Fixtures • A milling fixture is usually located on the machine table and bolted in position • The work piece in turn is located and clamped in the fixture. • Unlike a drill jigs, a milling fixture should be strong and rigid.

Elements of Milling Fixtures • Base • Tenon Strip • Setting block • T- bolts • Clamping device • Locating and positioning element