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What is a Dividing Head?

By Paul Scott
Updated May 17, 2024
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A dividing head, or indexing head, is a machine tool attachment that allows a work piece to be rotated in precise, pre-determined increments for machining of repeated profiles. For instance, if a section of round steel bar needs a hexagonal profile machined into one end, a dividing head could be used to rotate the bar in precise increments to machine each flat section of the profile. Typically the rotation or advancement of the dividing head is achieved manually using a crank handle equipped with a locking pin which locks the head into position for each machining cycle. Dividing heads may also be tilted through 90 degrees along their own axis to provide flexibility of adjustment. A dividing head is generally used as an accessory on milling machines to machine any product consisting of several equal radial facets.

The use of milling machinery to cut geometrically accurate, multi-faceted profiles requires that the work piece be advanced or rotated in very precise increments for each cut. The dividing head achieves this exact rotation by making use of a disc mounted to the spindle with concentric rows of equidistant holes drilled through it. A crank handle equipped with a spring loaded locking pin then turns the spindle the required distance whereupon the locking pin is inserted through one of the holes to lock the spindle in position. The pin is pulled out once the cut is completed, and the spindle is rotated the same number of holes and locked again with the pin. This allows for the work piece to be rotated exactly the same distance each time.

Since the disc or index plate has several rows of holes, a great range of different rotational distances can be achieved. Each concentric ring or row will have less holes placed at differing pitches as the rows get closer to the center of the disc. An indexing plate will generally be equipped with six rows of holes and are often purchased in sets of three plates each having different hole pitch settings. A typical set of indexing plates will feature hole numbers ranging from 15 to 49 holes per row giving a wide range of incremental flexibility.

The dividing head accessory is used on milling machines to produce most equally faceted items such as reamers, gears, machine tool bits, and geometric shoulders used to accept faucet handles and power bars. The dividing head assembly may be used in a straight axis orientation or tilted through 90 degrees for additional machining flexibility. Most dividing heads are manually indexed although larger units may be fully automated.

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