Function

The index pin is the small spring-loaded pin on a faceting machine that engages the teeth of the index gear, locking the rotational position of the stone relative to the cutting lap. Together with the index gear, it allows the cutter to rotate the stone through known angular increments between facets, producing the symmetric facet pattern characteristic of standard cuts.

Construction

The pin is typically a hardened steel rod with a tapered tip that fits between the teeth of the index gear. It is mounted in a spring-loaded housing on the faceting machine head, with a release lever that allows the cutter to disengage the pin briefly while rotating the gear to the next position. The pin reengages automatically when the lever is released.

The fit between the pin tip and the gear teeth is critical to cutting precision. Wear on either the pin or the gear teeth introduces angular error, which manifests as misaligned facets in the finished stone. Faceting machines are designed for the pin and gear to be replaceable as wear components.

Use in cutting

The cutter operates the index pin via a release lever, momentarily lifting the pin to allow the gear to rotate to the next position, then releasing the lever to lock the pin into the new tooth gap. The action is performed many times during the cutting of a single stone, and faceting machines are designed for smooth, repeatable operation under continuous use.

The pin's reliability and wear characteristics are among the principal factors distinguishing professional-grade faceting machines from amateur or beginner equipment. High-end machines use precision-ground pins and gears with minimal lateral play, allowing facet meet-points within fractions of a degree of geometric ideal.