Rapid indexing is used when a large number of

Example 3: Index for 10 divisions

duplicate parts are to be milled.

To find the number of holes to move the index

plate, divide 24 by the number of divisions required.

When the number of divisions required does not

Number of holes to move = 24/ *N *where

divide evenly into 40, the index crank must be moved

a fractional part of a turn with index plates. A

Example: Indexing for a hexagon head bolt:

commonly used index head comes with three index

because a hexagon head has six flats,

plates. Each plate has six circles of holes, which we

will use as an example.

2 4 24

Plate 1:

15-16-17-18-19-20

Plate 2:

21-23-27-29-31-33

IN ANY INDEXING OPERATION, ALWAYS

Plate 3:

37-39-41-43-47-49

S T A R T COUNTING FROM THE HOLE

ADJACENT TO THE CRANKPIN. During heavy

The previous examples of using the indexing

cutting operations, clamp the spindle by the clamp

formula 40/*N *gave results in complete turns of the

screw to relieve strain on the index pin.

index crank. This seldom happens on the typical

indexing job. For example, indexing for 18 divisions

Plain indexing, or simple indexing, is used when a

circle must be divided into more parts than is possible

The whole number indicates the complete turns of

by rapid indexing. Simple indexing requires that the

the index crank, the denominator of the fraction

represents the index circle, and the numerator

spindle be moved by turning an index crank, which

represents the number of holes to use on that circle.

turns the worm that is meshed with the worm wheel.

Because there is an 18-hole index circle, the mixed

The ratio between worm and the worm wheel is 40 to

number 2 4/18 indicates that the index crank will be

1. One turn of the index crank turns the index head

moved 2 full turns plus 4 holes on the 18-hole circle

spindle 1/40 of a complete turn. Therefore, 40 turns

that you will find on index plate 1. The sector arms

of the index crank are required to revolve the spindle

are positioned to include 4 holes and the hole in which

chuck and the job 1 complete turn. To determine the

the index crankpin is engaged. The number of holes

number of turns or fractional parts of a turn of the

(4) represents the movement of the index crank; the

index crank necessary to cut any required number of

hole that engages the index crankpin is not included.

divisions, divide 40 by the number of divisions

When the denominator of the indexing fraction is

required.

smaller or larger than the number of holes contained

in any of the index circles, change it to a number

40

representing one of the circles of holes. Do this by

Number of turns of the index crank = *N*

multiplying or dividing the numerator and the

denominator by the same number. For example, to

where *N *= number of divisions required

index for the machining of a hexagon ( *N *= 6):

Example 1: Index for five divisions

The denominator 3 will divide equally into the

following circles of holes, so you can use any plate

There are eight turns of the crank for each

that contains one of the circles.

division.

Plate 1:

15 and 18

Example 2: Index for eight divisions

Plate 2:

21 and 33

39

Plate 3:

7-12