The Patrick Yerby machine is a custom-built precision faceting machine produced in small numbers by American lapidary Patrick Yerby and used by competition-level and custom faceters who require repeatable indexing and fine angle adjustment beyond what most production machines deliver. Yerby's machines are not production-line products; they are made-to-order workshop pieces, each assembled by Yerby himself and adjusted to the individual cutter's specifications. The total number produced is small — well under a few hundred — and the machines are sought after on the secondary market within the custom-faceting community, where they trade at premiums and rarely appear for resale.

Construction and tolerances

Yerby machines are built around a rigid mast and platen architecture, with the mast carrying the precision angle adjustment and indexing head, and the platen carrying the lap. Construction emphasises low play in the mast bearings, fine adjustment of the cheater (the small angular displacement used to compensate for index or angle errors), and indexing gears with high tooth count for fine cylindrical-symmetry control. Angle settings are typically resolvable to better than 0.05 degrees, and the index is repeatable across the full circle without measurable drift. The machines accept standard dop transfer fixtures and a range of lap diameters.

Use in the trade

Yerby machines are most often found in the workshops of competition cutters — those who enter the United States Faceters Guild's Single Stone Competition or comparable international events — and in custom-cutter studios producing one-off designs that demand high meet-point precision. Common large-volume production machines, including those from Facetron, Ultra Tec, and others, are entirely capable of producing high-quality work; the Yerby's appeal to its users is the marginal improvement in repeatability and the ergonomic refinements that come from a machine assembled by a single working faceter for working faceters. The machine is overkill for routine commercial cutting and is not intended for that market.

In the trade

For practical purposes, the Yerby machine is a community-circulated tool: cutters know who has one, when one becomes available it sells privately within the community, and the machines accumulate provenance through their successive owners. New machines are no longer in regular production. For the gem trade as a whole, the Yerby is a footnote — a maker's-machine in a market dominated by a handful of production manufacturers — but for the custom-faceting community it is one of the small set of machines that defines the high end of the practitioner's toolkit.

Further reading

• United States Faceters Guild — competition standards and custom faceting reference
• International Gem Society — faceting machine and lapidary reference
• GIA Gems & Gemology — gem cutting articles