# Simple Calculators

SFM = RPM x DIA x pi/12

RPM = SFM x pi/12 / DIA

IPR = IPM / RPM

IPM = IPM x RPM

Cubes = SFM x 12 x IPR x DOC

SFM – a combination of diameter and the velocity (RPM) of the material measured in feet-per-minute as the spindle of a milling machine or lathe. 1 SFM equals 0.00508 m/s (meter per second, the SI unit of speed). The faster the spindle turns, and/or the larger the diameter, the higher the SFM.

RPM – 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 simplification of the more complex formula: rpm = (sfm × 12) ÷ (diameter × π).

IPR – is the linear distance that the cutting edge travels during a single spindle rotation. In Milling and Drilling, it is a single rotation of the cutting tool. In Turning, Grooving, and Parting it a single rotation of the workpiece.

IPM – describes the rate at which a machine apparatus moves across a material (also known as the feed rate) and can be relevant to determining proper machine use as well as production rates for job quotes.

IN3/MIN – Similar to IPM but in 3 dimensions. Calculates how much material will be removed in cubic inches per minute.