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CNC Feeds & Speeds Calculator illustration

CNC Feeds & Speeds Calculator

Computes spindle RPM and feed rate from the surface speed and chipload of the chosen material and tool: RPM = 1000·Vc / (π·D), feed = RPM × flutes × chipload. Chiploads are interpolated between 3, 6 and 12 mm tool diameters, slotting reduces the chipload, and RPM is capped at your machine maximum with the feed recomputed to match.

Read the full guide to this tool

Carbide runs 2–4× the surface speed of HSS.
1–2 flutes for aluminium and plastics (chip clearance), 2–4 for wood and steel.
Slotting engages the full diameter, so the chipload is reduced to 70%.
Blank uses the 0.5 × diameter rule of thumb.

Notes

  • Surface speeds and chiploads are mid-range starting values from common tooling catalogs (machining handbooks and carbide makers for metals, router-bit makers such as Onsrud for wood and plastics) — start there and adjust by chip color, sound and finish.
  • If the machine cannot reach the target RPM, keep the chipload by slowing the feed proportionally — that is what the cap does automatically.
  • Too low a feed rubs instead of cutting and overheats the tool (especially in plastics and aluminium); when in doubt, feed harder rather than slower.

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