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Surface Footage.
Calculate the speed at which the cutting edge of the tool moves relative to the workpiece.
Surface Speed
The Mathematics
SFM determines the amount of heat generated at the cutting edge. Too slow causes built-up edge; too fast causes thermal breakdown of the carbide.
Formula
SFM = (RPM × Diameter × π) / 12
This converts the rotational speed in inches per minute into feet per minute along the circumference of the tool.