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.

Optional — pick your machine once and results here will flag anything that exceeds its rated RPM or horsepower.

Surface feet per minute — how fast the cutting edge should move through the material. Look this up on the Cutting Speed Chart or your tool's data sheet.
The largest diameter the facing pass starts at, at the outer edge of the part.
The smallest diameter the pass reaches — use a small nonzero value since the RPM needed at true center is undefined.

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.

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