CNC router feeds and speeds calculator
The feed rate for a solid carbide up-cut or down-cut spiral bit in softwood, hardwood, MDF or plywood. It starts from the chip load the bit makers publish for that size and material, adjusts for a deep pass, and shows every maker's figure behind the answer.
Fractions like 1/4 are fine.
The makers’ charts are written for 18,000 RPM.
Feed rate
216 in/min
- Chip load per tooth
- 0.006 in
- Makers’ range
- 180 in/min – 396 in/min
Median of 3 sources
A starting point for test cuts in scrap, at the low end first.
Why: Three makers’ chip loads for a 0.25 in bit in hardwood have a median of 0.006 in per tooth; at 18,000 RPM with 2 flutes that is 216 in/min.
Why these numbers?
The situation
A 0.25 in, 2-flute bit in hardwood, 18,000 RPM, 0.25 in deep.
From your input: material, bit, spindle speed and depth
What that means
Freud / Diablo 0.008–0.011, Amana Tool 0.005–0.007, Onsrud 0.005–0.007 in per tooth: median 0.006.
The number
18,000 RPM × 2 flutes × 0.006 in = 216 in/min.
Arithmetic: exact by definition
Sources
- Freud / Diablo, Get the most out of your Freud bits by routing at ideal feed rates and speeds: chip loads for Freud solid carbide router bits (2017), read 2026-11-07
- Amana Tool, 2 Flute Solid Carbide Spiral Plunge for Solid Wood: CNC speed chart (18,000 RPM, depth 1 × D), read 2026-11-07
- Onsrud, Cutting data sheets: softwood, hardwood, MDF, soft and hard plywood, chip load per tooth by series (series 56-200 row; hosted by WOODWEB), read 2026-11-07
How the feed is worked out
Chip load is how thick a chip each cutting edge takes. Bit makers publish it by material and bit diameter. Multiply it by the spindle speed and the number of flutes and you have the feed: feed = RPM × flutes × chip load. A 1/4 in two-flute bit in hardwood at 18,000 RPM takes about 0.006 in a tooth, so 18,000 × 2 × 0.006 = 216 in/min. If your machine can't feed that fast, lower the spindle speed instead of the chip; the calculator works out how far when you enter the machine's top feed.
The makers' charts don't agree closely, and for MDF they differ by more than two times, so the result shows each one, the range they cover, and the tier of the answer. Every maker's figure, size by size, is in the CNC chip load chart.
What the bit makers say
Chip loads are for a cut as deep as the bit is wide. At 2 × the diameter take at least 25% off; at 3 × the diameter at least 50%.
Chip load = feed rate ÷ (RPM × number of flutes); feed rate = RPM × flutes × chip load.
Too small a chip, little more than dust, carries too little heat away from the edge and dulls the bit early; too big a chip leaves a rough cut.
One source: Freud / Diablo, the maker of those bits , sources [1]
These are starting points: make test cuts in scrap with shallow passes, starting at the low end, and check your machine’s manual for its limits.
One source: Freud / Diablo, the maker of those bits , sources [1]
Make sure the bit’s rated speed is at least the spindle’s top speed; a bit run over its rated speed can break and fly apart.
One source: Freud / Diablo, the maker of those bits , sources [1]
Sources
- Freud / Diablo, Get the most out of your Freud bits by routing at ideal feed rates and speeds: chip loads for Freud solid carbide router bits (2017), read 2026-11-07
- Amana Tool, 2 Flute Solid Carbide Spiral Plunge for Solid Wood: CNC speed chart (18,000 RPM, depth 1 × D), read 2026-11-07
- Onsrud, Cutting data sheets: softwood, hardwood, MDF, soft and hard plywood, chip load per tooth by series (series 56-200 row; hosted by WOODWEB), read 2026-11-07
What this calculator doesn't cover
Compression bits and single O-flute plastic bits have their own charts, and the makers print different figures for them, so they are not mixed in here. Plastics, aluminum, bits under 1/8 in and over 1/2 in, and passes deeper than three times the bit's diameter have no answer yet: fewer than two makers publish a chip load that fits. Use the chart for your bit from its maker.