Feet per minute

Surface feet per minute (SFPM or SFM) is the combination of a physical quantity (surface speed) and an imperial and American customary unit (feet per minute or FPM). It is defined as the number of linear feet that a location on a rotating component travels in one minute. Its most common use is in the measurement of cutting speed (surface speed) in machining. It is a unit of velocity that describes how fast the cutting edge of the cutting tool travels. It correlates directly to the machinability of the workpiece material and the hardness of the cutting tool material. It relates to spindle speed via variables such as cutter diameter (for rotating cutters) or workpiece diameter (for lathe work).