SFM to RPM [Easy Guide to Surface Speed/SFM in Machining]
The simple machining formula you'll use is the following equation: Spindle RPM = SFM / Circumference. Where the circumference is that of the workpiece on a lathe or the cutter on a mill. In other words, you want the circumference of whatever is spinning. And circumference is diameter times pi. So for a mill, it's tool diameter times pi.
