The illustration above is an example of what a machinist would call a grinder or lap, but a dental lab or jewelry maker would call a lathe.

It has little in common with the lathe used for turning round shapes in wood or metal.

An optical instrument maker would have used both kinds of machines.

Diamond work uses circular saws with thin copper blades to divide a rough stone in two. The flat facets are created using laps with tin or copper disks rotating in a horizontal plane. The girdle is the only part of a faceted diamond that has a cylindrical shape and the girdle is not highly polished. Diamonds are not normally finished with spherical or cabochon surfaces.

Larry