compound indenxing

 

compound indenxing 

Compound indexing is a combination of two plain

or one complete turn plus 9 holes on the 18-hole

indexing procedures. You will index one number of

circle.

divisions by using the standard plain indexing

method, and another by turning the index plate

When indexing angles are given in minutes, and

(leaving the crankpin engaged in the hole as set in the

approximate divisions are acceptable, you can

determine the movement of the index crank and the

first indexing operation) by a required amount. The

difference between the amount indexed in the first

proper index plate by the following calculations. To

and second operations results in the spindle turning

determine the number of minutes represented by one

the required amount for the number of divisions.

turn of the index crank, multiply the number of

Compound indexing is seldom used because (1)

degrees covered in one turn of the index crank by 60:

differential indexing is easier, (2) high-number index

9° × 60´ = 540

plates are usually available to provide any range of

divisions normally required, and (3) the computation

and actual operation are quite complicated, making it

Therefore, one turn of the index crank will rotate the

easy for errors to be introduced.

index head spindle 540 minutes.

We will briefly describe compound indexing in

The number of minutes (540) divided by the

the following example. To index 99 divisions proceed

number of minutes in the division desired gives you

as follows:

the total number of holes there should be in the index

plate used. (Moving the index crank one hole will

1. Multiply the required number of divisions by

rotate the index head spindle through the desired

the difference between the number of holes in two

number of minutes of angle.) This method of

circles selected at random. Divide this product by 40

indexing can be used only for approximate angles

(ratio of spindle to crank) times the product of the two

since ordinarily the quotient will come out in mixed

index hole circles. Assume you have selected the 27-

numbers or in numbers for which there are no index

and 33-hole circles.