Dividing Head Settings

There are four methods of indexing;
(a) Rapid indexing;
(b) Plain indexing;
(c) Compound indexing, and
(d) Differential indexing.

Rapid Indexing –
This is the simplest method and is suitable for dividing into 2,3,4,6,8,12 and 24 divisions.. For this rapid indexing, the worm is first dropped from engagement with the worm wheel by means of a knob by the side of the index head. Then the pin P in the hole of the index plate I1 is disengaged by the lever L. The job is then rotated through the number of holes required to get the necessary division. Then the pin P is reengaged. Due to dropping of the worm out of engagement, it is easy to rotate the job from the front.

Plain indexing –
This will be explained with the help of an example. Suppose we want to cut a gear with 23 teeth, i.e., we need to index the job through 1/23 of a revolution. For this the index plate handle J will have to be rotated through 40/23=117/23 revolution. To get 17/23 of a revolution, we will use the circle with 23 equi-spaced holes on the index plate I2. To aid this counting of 17 holes, the sector on the index plate is used. With the nut N loosened, the arm carrying the crank-lkever handle is moved to position the pin in one of the holes of the circle with 23 holes. Then one arm is positioned to touch one side of the latch pin of the handle. Then the other arm of the sector is positioned 18 holes away., on the further side of the hole. With the sector thus positioned, the nut N is locked. Then the pin P is withdrawn and one revolution is carried out and the hand is further rotated so that the pin will rest in the hole touching the second arm of the sector. The sector is then loosened and rotated for the other arm to touch the latch-pin in new position for the next indexing.

Compound indexing –
Many a time the number of divisions required cannot be obtained by plain indexing. Then compound indexing is used in which in one motion the crank handle is rotated through a certain rotation and its latch pin engaged. Afterwards the index plate itself is rotated through a certain rotation either in the same direction or in the opposite direction depending on the requirement. Normally index plate is prevented from rotating by a stationary pin at the rear which engages one of the holes of the same index plate I2. After this stop pin is removed, the index plate can be rotated. Let us consider milling a 93- teeth gear. The job will have to be rotated through 1/93 revolution or the crank lever through 40/93 revolutions, which will not be possible with the standard index plate. For this purpose, then the crank lever will be rotated through 11/33 revolution and the index plate through 3/31 revolution in the same direction.


Differential indexing –
This case is similar to the compound indexing. Only difference is that in this case the index plate is rotated through gearing connected to the dividing head spindle.