CNC Machining worked example

Surface Speed with spindle speed of 20,000 RPM: a worked example

Push spindle speed up to 20,000 RPM and the picture changes. This example computes every intermediate figure at that operating point. checking actual SFM on a toolpath, turning pass, bore, drill, or setup sheet before increasing RPM or changing tooling

The inputs for this scenario

  • Spindle speed: 20,000 RPM (raised for this scenario; the documented default is 8,000)
  • Tool diameter: 0.5 in (unchanged)
  • Conversion factor: 0.26 x (unchanged)
  • Override: 1 x (unchanged)

Working through the calculation

  • Applying the documented formula (Surface speed = spindle speed × tool or work diameter × inch-to-feet SFM factor × speed override) to the inputs above produces each figure below.
  • At this operating point the engine returns 2,620 SFM for cutting surface speed, the number this scenario is built around.
  • At this operating point the engine returns 2,620 value for base product.
  • At this operating point the engine returns 1 x for multiplier.
  • At this operating point the engine returns 10,000 value for factor a x b.

How this compares with the baseline

  • Against the tool's baseline example, where spindle speed sits at 8,000 RPM and the headline result is 1,048 SFM, this scenario comes in 150% above the baseline at 2,620 SFM.
  • Computes cutting surface speed in SFM by multiplying spindle RPM, tool diameter, the inch-to-feet conversion factor, and an optional speed override. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • cutting surface speed: 2,620 SFM (headline result)
  • Base product: 2,620 value
  • Multiplier: 1 x
  • Factor A x B: 10,000 value

Run it with your numbers

  • Every input above is editable in the live Surface Speed calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.