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### Differential Indexing

Differential Indexing Points : what is Differential Indexing Differential indexing has replaced the compound indexing which has become absolute because of lengthy calculations involved and chance of error in its use. Differential indexing is the automatic method of compound indexing. The differential method is used in indexing for numbers that are beyond the range of plain or simple indexing. The mechanism of universal dividing head incorporates a shaft which is parallel with the main spindle and produces from the rear of the head. This shaft is connected through equal bevels and gears, to a gear fixed on the index plate.

It is thus possible, when the index plate is unlocked, to drive it through an equal ratio from shaft “C.” When the crank plunger is registering in a hole in the plate, the crank and worm rotate as one with it. (Independent rotation of crank and plate occurs in differential indexing whilst solid movement of both takes place in spiral milling.) When the head is arranged for differential indexing the index plate is released from its locking plunger, leaving it free to turn, and at the same time it is geared back to the spindle of the head. Thus, as the spindle is rotated via the crank and worm, the gear train causes the index plate to turn backwards, or forwards, and the net result is the same as if the index plate were released and rotated by hand as in compound indexing.
Differential indexing is straighter forward, and has a wider application than compound indexing. In the differential indexing the desired division is obtained by two movements:
1. Simple indexing movement of the crank and
2. Differential movement of the index plate relative to the crank movement.
Both movements happen at a, time with the help of a train of gears arranged between the spindle and the index plate, so that the index plate will turn either in the same direction as the movement of the crank or in the opposite direction, depending upon whether the differential movement is to be added or subtracted. The movement of the index plate is made by releasing the stop pin at the back of the index plate.