TaskJunction

Lathe RPM and Cutting Speed Calculator

Spindle RPM and achieved peripheral speed from work diameter and cutting speed.

Inputs

Results

Spindle Speed
—
Peripheral Speed
—

Formula

  • n = (Vc × 1000) / (π × D)
  • Vc_actual = (π × D × n) / 1000

About this calculator

Part of our Machining & CNC Calculators collection. Cutting speed, feeds, RPM, cycle time, and tap drill charts.

How it works

Spindle RPM equals cutting speed times 1000 divided by pi times diameter. Peripheral speed is recalculated from the rounded RPM to match lathe readouts. Use your material and insert supplier chart for the starting Vc value.

Enter your values in the inputs above and click CALCULATE. Results appear on the right without a page reload. No login and no server upload.

Worked example

Turning 60 mm diameter at 120 m/min cutting speed.

  1. n = 120 × 1000 / (π × 60) = 637 RPM (rounded)
  2. Vc_actual = π × 60 × 637 / 1000 = 120.0 m/min

Result: 637 RPM achieves 120 m/min on a 60 mm diameter.

When to use

  • Setting lathe spindle speed for a given work diameter
  • Checking actual surface speed after rounding RPM
  • Switching between jobs with different diameters

Limitations

  • Assumes constant surface speed; no tailstock or part-off exceptions
  • Does not compute feed rate or depth of cut
  • Large diameters may exceed machine RPM before Vc limit

FAQ

Do I use work diameter or insert size?
Use the workpiece diameter at the cutting point. For facing from centre, RPM is limited by max spindle speed as diameter increases.
Why recalculate Vc after rounding?
Integer RPM rarely hits the target Vc exactly. Recalculated Vc shows what you actually get on the machine.
Is this the same formula as milling?
Yes. Vc-to-RPM uses tool or work diameter. Milling adds feed per tooth for table feed.

Privacy and accuracy

Every calculation runs locally in your browser. Your design data never leaves your device. Results are intended for preliminary engineering work. Always verify critical designs with qualified review and applicable standards before production use.

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