9.19 Indexing
Micky R. Jennings
Indexing, also known as dividing, is the process of manipulating a part to machine specific features at fractions of a rotation. On a milling machine, an indexing head is used for this purpose. The indexing head is capable of quickly and easily making accurate partial rotations. Before moving forward, a few terms should be explained.
Indexing Components
The worm gearis attached to the end of a shaft that is turned by the indexing crank. The worm gear works in conjunction with the worm wheel to adjust the indexing head turning ratio. The ratio between the two is generally 40: 1 for indexing heads.
The worm wheelis attached to the beginning of a shaft that turns the spindle. The worm wheel works in conjunction with the worm gear to adjust the indexing head turning ratio. The ratio between the two is generally 40: 1 for indexing heads. The worm wheel rotates one tooth for each full rotation of the worm gear.
Anindexing plateis an attachment that has predetermined hole patterns precisely placed to represent fractions of a rotation. Each manufacturer has different plates. For the examples that follow, a set of three plates will be used that have the following hole patterns.
Plate one: 15, 16, 17, 18, 19, 20.
Plate two: 21, 23, 27, 29, 31, 33.
Plate three: 37, 39, 41, 43, 47, 49.
The indexing shafthas the indexing crank attached at one end and the worm gear on the other.
The indexing crankis used to turn the shaft that has the worm gear on it. It has a slot down the middle to make it adjustable, so that during use, it can reach multiple different hole patterns on the indexing plates.
The indexing pinis attached to the indexing crank. Once the crank is turned, the pin is placed in a hole on the indexing plate to set the position.
The selector armsare loosely attached to the shaft below the indexing crank. They are held in place by gentle friction and are intended to be moved throughout the indexing process. One arm serves to indicate the position where the pin is currently in a hole, while the other arm serves as an indicator of the hole the pin should go into on the next index. The selector arms aid in the speed and accuracy of indexing.
The spindleof the indexing head has the worm wheel attached at one end and a device to locate or attach work on the other. This may be in the form of a center, a taper, or a thread. A chuck may also be attached to the working end of the spindle.
The spindle lockis used to lock the spindle in place once the indexing has been completed. Locking the spindle allows for a more rigid machining process and protects the precise components of the indexing head.
A disengagement levergives indexing heads the ability to disengage the connection between the indexing shaft and the spindle. This feature is helpful when utilizing direct indexing features.
The foot stockis set opposite to the dividing head and is used to support long parts. The footstock is similar in operation to that of the tailstock o