Facing Speed Calculator
A facing pass crosses every diameter from the outside to the center — see the full RPM range that takes to hold constant cutting speed.
Why facing needs a range, not a single RPM
Every other diameter on a facing pass is different from the last, and RPM = (SFM × 12) ÷ (π × diameter) means smaller diameters need higher RPM to hold the same surface speed — run a fixed RPM sized for the outer diameter, and cutting speed at the center is far lower than it should be, leaving a visibly rougher finish right where the tool ends its pass.
The center is mathematically undefined
As diameter approaches zero at the exact centerline, the RPM needed approaches infinity — that's why this calculator asks for a small but nonzero ending diameter rather than 0. In practice, use CSS mode (see the Constant Surface Speed Calculator) with a sensible max RPM cap, and accept that the very last sliver near dead center runs at whatever speed the cap allows.
What to do with a wide RPM range
If the calculated range is very wide, check the ending RPM against your machine's actual max spindle speed before committing to CSS mode for the pass — and if it's a workholding concern (loose stock, an unbalanced chuck jaw setup, thin material), a very high RPM near center may be a bigger practical risk than the finish quality it buys you.