Technology

Many different sort of indexing can be done with a dividing head. Hear we shall deal with division of a revolution into 2, 3, 4,5,6,6 parts etc. and angular divisions of 10, 15, 20⁰ etc. the dividing head permits direct, simple and differential indexing.

Direct indexing

Direct indexing can be produced with the aid of the plate for direct division (1) mounted on the dividing head spindle. The plate usually has 24 positions for the locking plunger (2). All divisions that are exactly divisible by 24 or 360⁰ can be obtained - 2, 3, 4, 6, 8, 12 and 24 and corresponding angles 180⁰ , 120⁰ , 90⁰ , 60⁰ , 45⁰ , 30⁰ and 15⁰ .

For direct indexing the dividing head spindle must be disengaged. This is usually done with screws on the front of the dividing head. The spindle can then be turned into the desired position and locked with the plunger (2).

If other divisions are required, simple indexing is used.

Indirect indexing

Indirect indexing is done with the aid of the index crank connected to the dividing head spindle through a worm gear.

The gear ratio is 40:1. The worm- wheel is mounted on the spindle, whilst the worm is on the crank shaft, if the crank is turned 40 revolutions, the spindle will make 1 revolution.

The dividing head usually has three index plates. These have a number of circles of holes, each circle having a different number of holes.

The plunger of the crank can be set to suit a particular circle of holes. The number of complete revolutions or parts of a revolution that the crank must be turned to obtain the required division is determined by calculation or reference to a table. See calculations, tables.

The adjustable sector arms are set for the number of holes that the crank must be turned in addition to complete revolutions or, certain cases, for the number of holes only. The crank must not be rotated beyond the correct hole and turn back again, as there could be backlash in the worm gear. If this does happen, the crank must be turned back again and setting stated again.

The sector arms are turned until stopped by the plunger- new starting position. The procedure is then repeated.

When a particular number of divisions cannot be obtain by indirect indexing, differential indexing must be used.

Differential indexing

Differential indexing is done with the index crank and the worm gear engaged. The index plate is released and can rotate on the crank shaft. It is connected to the dividing head spindle through a gear train.

The index plate obtains its rotary motion from the dividing head spindle through change wheels. The spindle obtains its motion from the crank through the worm gear.

The change wheels are selected with the aid of table or by calculation.