3. The denominator of the resulting fraction

derived in step 2 is the term used to find the number of

turns and holes to index the spindle and index plate.

To index for 99 divisions, turn the spindle by an

amount equal to 60/33 or one complete turn plus 27

holes in the 33-hole circle; turn the index plate by an

amount equal to 60/27, or two complete turns plus 6

holes in the 27-hole circle. If you turn the index crank

clockwise, turn the index plate counterclockwise and

vice versa.

Differential indexing is similar to compound

indexing except that the index plate is turned during

the indexing operation by gears connected to the

dividing head spindle. Because the index plate

movement is caused by the spindle movement, only

one indexing procedure is required. The gear train

between the dividing head spindle and the index plate

provides the correct ratio of movement between the

spindle and the index plate.

4. Select two gears that have a 2 to 1 ratio (for

Figure 7-18 shows a dividing head set up for

example a 48-tooth gear and a 24-tooth gear).

differential indexing. The index crank is turned as it

5. If the selected number is greater than the

is for plain indexing, thus turning the spindle gear and

actual number of divisions required, use one or three

then the compound gear and the idler to drive the gear

idlers in the simple gear train; if the selected number

that turns the index plate. The manufacturer's

is smaller, use none or two idlers. The reverse is true

technical manuals give specific procedures to install

for compound gear trains. Since the number is greater

the gearing and arrange the index plate for differential

in this example, use one or three idlers.

indexing (and compound indexing).

6. Now turn the index crank 14 holes in the

To index 57 divisions, for example, take the

21-hole circle of the index plate. As the crank turns

following steps:

the spindle, the gear train turns the index plate slightly

faster than the index crank.

1. Select a number greater or lesser than the

required number of divisions for which an available

index plate can be used (60 for example).

2. The number of turns for plain indexing 60

In the majority of indexing operations, you can

divisions is 40/60 or 14/21, which will require 14

get the desired number of equally spaced divisions by

holes in a 21-hole circle in the index plate.

using either direct or plain indexing. By using one or

the other of these methods, you may index up to 2,640

3. To find the required gear ratio, subtract the

divisions. To increase the range of divisions, use the

required number of divisions from the selected

high-number index plates in place of the standard

number or vice versa (depending on which is larger),

index plate. These high-number plates have a greater

and multiply the result by 40/60 (formula to index 60

number of circles of holes and a greater range of holes

divisions). Thus:

in the circles than the standard plates. This increases

the range of possible divisions from 1,040 to 7,960.

In some instances, you may need to index beyond

the range of any of these methods. To further increase

the range, use a universal dividing head that has a

The numerator indicates the spindle gear; the

wide range divider. This type of indexing equipment

denominator indicates the driven gear.

7-15

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