[CAMmando]

Speed is usually Feet Per Minute. For milling (routing) RPM would be calculated based on tool diameter. For turning RPM is calculated based on work diameter (or constant surface speed is commanded).

I use a simple formula (with no Pi) for easy calculation on the fly.

RPM = 4 X SFM / DIA (cutter)

This formula is simple because you figure for a 4 in cutter RPM = SFM.

For a 2 in. Cutter RPM = 2XSFM

For a 1 in cutter RPM = SFM X 4 etc.

I suspect the value given in the tech data cited is 12 times the SFM which would give IPM so divide by 12

So RPM = Surface Speed (ipm) / (Cutter Dia x Pi)