Surface Speed is the speed difference (relative velocity) between thecutting tooland the surface of the workpiece it is operating on. It is expressed in units of distance along the workpiece surface per unit of time, typicallysurface feet per minute(sfm) ormetersperminute(m/min).
Formula:
SFM = RPM x D x π/12
where,D - Cutter diameter
RPM - Revolutions per minute
SFM - Surface Feet per Minute