MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
You can determine the number of minutes represented by one turn of the index
crank by multiplying the number of degrees covered in one turn of the index
crank by 60:
9 x 60 = 540'
Therefore, one turn of the index crank will rotate the index head spindle
The number of minutes (540) divided by the number of minutes in the
division desired, indicates the total number of holes required in the index
plate used. (Moving the index crank one hole will rotate the index spindle
through the desired number of minutes of the angle.)
This method of
indexing can be used only for approximate angles since ordinarily the
quotient will come out in mixed numbers, or in numbers for which no index
plate is available.
However, when the quotient is nearly equal to the
number of holes in an available index plate, the nearest number of holes can
be used and the error will be very small. For example, the calculation for
24 minutes would be:
or one hole on the 22.5-hole circle. Since there is no 22.5-hole circle on
the index plate, a 23-hole circle plate would be used.
If a quotient is not approximately equal to an available circle of
holes, multiply by any trial number which will give a product equal to the
number of holes in one of the available index circles. You can then move
the crank the required number of holes to give the desired division. For
example, the calculation for determining 54 minutes when an index plate that
has a 20-hole circle is available, is as follows:
or 2 holes on the 20-hole circle.