Cutter Diameter for a Spindle RPM

The cutter or work diameter that runs at a target (or the machine's maximum) spindle RPM for a given surface speed.

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Example

You enter

You get

Details, formula, and sources

diameter = 12 x SFM / (pi x RPM). 100 SFM at 1,000 RPM is a 0.382 in diameter. Because a larger diameter turns slower, a machine RPM ceiling sets the SMALLEST cutter that still reaches the full SFM - a smaller one tops out the spindle first. Surface speed from the tool / material chart; the machine and rigidity govern.

diameter(in) = 12 * SFM / (pi * RPM); the inverse of RPM = 12 * SFM / (pi * dia); 12/pi = 3.8197.

First-principles cutting geometry; the speeds-and-feeds method as in Machinery's Handbook (Industrial Press), by name, solved for the diameter.

Pure geometry, public; the surface speed (SFM) is user-supplied from the tool / material chart.

Estimate. AHJ and licensed professional govern.

Field names used by the API: surface_speed_sfm, target_rpm, diameter_in

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