Indexing is the method of dividing the periphery of a piece of work into any number of equal parts. The attachment used for performing indexing is known as indexing head.
The indexing operation can be adapted for cutting gears, ratchet wheels, keyways, fluted drills, taps and reamers. The indexing head serves as an attachment for holding and indexing the work in doing the above tasks. There are three different types of indexing heads namely
- Plain or simple dividing head
- Universal dividing head
- Optical dividing
Construction of Indexing Head
Base – The base of the indexing head is fitted in the ‘T’ – slots of the milling machine table. It supports all the other parts of dividing head.
Spindle – The spindle is situated at the centre of the dividing head. It has a taper hole to receive a live center. The spindle is supported on a swiveling block, which makes the spindle to be tilted through any angle from 5º below horizontal to 10º beyond vertical. A worm wheel is mounted on the spindle. While doing direct or rapid indexing, the index plate is directly fitted on the front end of the spindle nose.
Worm shaft – It is situated at right angles to the main spindle of the dividing head. A single threaded worm is mounted on the worm shaft, which meshes with the worm wheel. An index plate is fitted on the front end of the worm shaft and with the help of a handle the worm shaft can be rotated to a predetermined amount.
Index plate – It is mounted on the front end of the worm shaft. It is a circular disk having different numbers of equally spaced holes arranged in concentric circles. The crank is positioned in the required hole circle and rotated through a calculated amount while indexing. The sector arm is used to eliminate the necessity of counting the holes on the index plate each time the index crank is moved.
Driven shaft – It is parallel to the spindle and perpendicular to the worm shaft.
Dead center – The work is held between the center of the spindle and the dead center. It can be made to slide and positioned at the required location.
Working Principle of Dividing Head
When the crank is rotated with help of a handle through the required number of holes in the index plate, the work is rotated to required amount. This is possible because of the worm and worm wheel mechanism.
A gear train is arranged between the main spindle and the driven shaft when indexing is done by differential indexing method. The work is rotated as usual when the handle is rotated. At the same time, the index plate is also made to rotate a small amount through the gear train. When indexing is by this differential indexing method, the index plate is released from the lock pin.
There are several methods of indexing and they are
- Direct or rapid indexing
- Plain or simple indexing
- Compound indexing
- Differential indexing
- Angular indexing