Type 31H · Calculator and shop maths
Surface speed
What this does. converts RPM and cutter diameter to surface feet per minute, or back to the RPM you should run.
Use it when. the book says 200 SFM for the material and you need a spindle speed for that cutter.
SFM = 0.262 × RPM × diameter. RPM = SFM / (0.262 × diameter)