Cutting-file accuracy states how closely a cutting file's facet angles match the 3D model of the same cut. Each cut page gives the largest angle difference and the mean.
In more detail
It compares facet directions only, not where facets meet. The page gives the girdle on its own. For the T73, every crown and pavilion facet is within 0.009° of the model, and girdle facets within 0.016°.
How we measure it
Each .asc facet becomes a normal from its angle and its index on the gear. We turn the model about its axis in quarter-index steps, in both handedness. We refine the best turn to 0.001°. We keep the alignment with the smallest area-weighted mean angle. Facets smaller than 0.02% of the largest are slivers, and we leave them out.
Related terms
- Cutting file: A cutting file is a faceting design: every facet's angle and index, in cutting order, for a faceting machine. It tells a faceter how to cut the stone.
- 3D model: A 3D model of a gemstone is a digital solid of its facets for CAD, rendering, printing or games. An exact model has flat facets, sharp edges and a closed, watertight surface at real size.
- GemCad .asc: GemCad is Robert Strickland's faceting design program for Windows, and .asc is its text design format. An .asc file gives the gear, the refractive index and every facet's angle and index.
- Index gear: An index gear is the toothed wheel on a faceting machine that sets each facet's direction around the stone. Each index is one tooth of the gear.
- Facet: A facet is one flat, polished face of a cut gemstone. Its angle and its direction around the stone decide where it sends light.