Machinery Repairman

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
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.
Figure 7-18 shows a dividing head set up for
differential indexing. The index crank is turned as it
is for plain indexing, thus turning the spindle gear and
then the compound gear and the idler to drive the gear
that turns the index plate. The manufacturer’s
technical manuals give specific procedures to install
the gearing and arrange the index plate for differential
indexing (and compound indexing).
To index 57 divisions, for example, take the
following steps:
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
divisions is 40/60 or 14/21, which will require 14
holes in a 21-hole circle in the index plate.
3. To find the required gear ratio, subtract the
required number of divisions from the selected
number or vice versa (depending on which is larger),
and multiply the result by 40/60 (formula to index 60
divisions). Thus:
The numerator indicates the spindle gear; the
denominator indicates the driven gear.
7-15
Figure 7-18.—Differential Indexing.
4. Select two gears that have a 2 to 1 ratio (for
example a 48-tooth gear and a 24-tooth gear).
5. If the selected number is greater than the
actual number of divisions required, use one or three
idlers in the simple gear train; if the selected number
is smaller, use none or two idlers. The reverse is true
for compound gear trains. Since the number is greater
in this example, use one or three idlers.
6. Now turn the index crank 14 holes in the
21-hole circle of the index plate. As the crank turns
the spindle, the gear train turns the index plate slightly
faster than the index crank.
WIDE RANGE DIVIDER
In the majority of indexing operations, you can
get the desired number of equally spaced divisions by
using either direct or plain indexing. By using one or
the other of these methods, you may index up to 2,640
divisions. To increase the range of divisions, use the
high-number index plates in place of the standard
index plate. These high-number plates have a greater
number of circles of holes and a greater range of holes
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
wide range divider. This type of indexing equipment