The following equation is used to calculate spindle speed: rpm = sfm ÷ diameter × 3.82, where diameter is the cutting tool diameter or the part diameter on a lathe in inches, and 3.82 is a constant that comes from an algebraic simplifica-tion of the more complex formula: rpm = (sfm × 12) ÷ (diameter × π).

Generally speaking, when machining stainless steels a SFM of between 100-350 is recommended, with a chip load ranging between . 0005” for a 1/8” end mill up to . 006” for a 1” end mill.

Acetal, PEEK and PVC plastic materials have superior machining characteristics, plus they resist melting and chipping while offering good dimensional stability.