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SFM Support

Surface Feet per Minute Formula Guide

Start with the SFM range for your material and tool, then convert it into machine RPM by cutter or workpiece diameter. This support page chooses the cutting-speed assumption; the RPM calculator handles the conversion.

Direct answer: SFM is cutting-edge surface speed; RPM = (SFM x 3.82) / diameter.

Guide focus: choose the SFM assumption, then hand conversion to the RPM calculator.

How to Use SFM

  1. Pick a conservative SFM from material and toolmaker guidance.
  2. Enter cutter diameter or workpiece diameter.
  3. Convert SFM to RPM, then feed that RPM into chip-load and feed-rate planning.

RPM = (SFM x 3.82) / Diameter

Use diameter in inches. For metric, use RPM = (Vc x 318.3) / diameter in mm.

Calculator Handoff

Use the SFM to RPM calculator to convert SFM into spindle speed and check the reverse calculation from RPM back to SFM.

SFM to RPM Guide
Read the full conversion method with examples.
CNC Feeds & Speeds Guide
Move from RPM into feed rate, chip load, and MRR.