What is an Indexing Head?

Paul Scott

An indexing head is an attachment used on machine tools that allows the workpiece to be rotated around its own axis in equal steps. This facilitates the machining of exact, equal facets such as square or hex head profiles. Indexing head attachments are usually fitted to milling machines to make flat cuts and may be manually adjusted or automatically advanced. Most are capable of a 90° range of motion across their own axis, thereby allowing for a good range of cutting options. Indexing heads are typically designed to facilitate the cutting of a selection of facet numbers and are often available in sets which cover a wide range of machining requirements.

Automated indexing heads may be found on industrial CNC milling machines used in a manufacturing facility.
Automated indexing heads may be found on industrial CNC milling machines used in a manufacturing facility.

Machined parts which feature a number of equal facets or faces are typically machined on milling machines with an indexing head. This device secures the workpiece and allow it to be rotated in precise steps to allow the cutting of the individual facets. Based on a conventional chuck or clamp, the indexing head is also equipped with a indexing disc that features several concentric rows, typically 6, of equally spaced holes in its surface. Each row has a specific number of holes with each successive row having less holes towards the center of the disc. Typical hole counts range between 15 and 49 with discs generally available in sets which offer a large range of different facet pitches.

When cutting commences, the disc is locked in place with a spring loaded pin passing through a hole in the relevant row and into a locking recess. Once the cut is completed, the pin is retracted, the head advanced a set number of holes, and cutting begins on the next facet. The disc is advanced the same number of holes with each cycle allowing the cutting of precise, accurate profiles. The indexing head may present the workpiece parallel to the cutting tool or be rotated through 90° for additional flexibility in the cut geometry.

Also known as a dividing head, the indexing head is either advanced by hand or fully automated. Hand advancement is achieved with a crank or handle that turns a lead screw actuator to rotate the disc in a controlled manner. Automated advancement is typically only found on large, industrial machines and depends on a separate spindle to turn the disc. These systems are generally part of fully automated computer numerical control (CNC) milling machines which feature cutting cycles entirely controlled by computer.

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