Chapter (8)

INDEXING JIGS AND FIXTURES8.1. Introduction

Indexing is a process of quick, accurate location of w.p. or fixture in a number of specific positions. Indexing involves periodic linear or rotary movement of the indexed part to the next position.

Three drill bushes are required.

One drill bush is required.

Used when holes have to be drilled on a large pitch circle. One drilling station is used, and the component is rotated about the axis of the pitch circle to position it for drilling each hole in turn.

Four slots are to be milled in the periphery of a circular w.p.

8.2. The Basic Features of an Indexing Jig or Fixture

The jig or fixture must include:

1- Component location and clamps mounted on the movable member.

2- A slide or a bearing system to control the movement of the movable member.

3- An indexing device to position the member and a locking device to secure it in position during the machining.

* It must be emphasized that the locking device for the movable member must be separate from the w.p. clamp; it must be convenient to operate because it must be operated each time the w.p. is indexed.

For example, in the example shown in Fig. 8.6 the w.p. is clamped once during the milling operation, but the movable member must be clamped four times during the operation.

8.3. Indexing Devices

The indexing device is usually mounted in the fixed part of the jig or fixture, and it engages in slots or holes that are suitably spaced in the moving member.

Useful for light work

As a refinement

The end of the plunger can be coned and the locating holes in the movable member can be coned or vee shaped, so that wear can be compensated for.

When the plunger is in an awkward position it may be operated by a rack and pinion system.

Plunger gives positive location (used for heavy work)

BURR GROOVE

8.4. Typical Indexing Jigs and Fixtures

workpiece

(Isometric view)