CNC chipload calculator
Already have a feed rate and spindle speed? Work out the chipload you are really cutting at and compare it with a starting range for your material and bit.
How to use this calculator
Chipload is the thickness of material each cutting edge removes per revolution. It decides whether a bit cuts cleanly, rubs and burns, or breaks. You can't set it directly on most machines; you set feed and RPM, and the chipload falls out of them:
Chipload = feed rate ÷ (RPM × number of flutes)
Example: 200 in/min ÷ (18,000 RPM × 2 flutes) = 0.0056 in per tooth. For a 1/4 in bit in plywood, the CNC Router Store starting chart suggests 0.009–0.011 in, so this cut is on the low side: the bit is making fine chips and will run warm. Dropping the RPM to about 11,000 at the same feed brings it close to 0.009 in.
How to read the verdict: well below the range usually means dust instead of chips, scorched edges in wood and melted, re-welded edges in acrylic. Well above the range means the bit is being pushed hard; you may see a fuzzy or wavy edge from deflection, or snap a small bit.
The chart values assume a rigid machine and solid-carbide spiral bits. Bit manufacturers publish their own charts per series, which take priority. Hobby machines often run lighter, so treat the lower end of the range as a target rather than a minimum. If you'd rather not dial it in yourself, post the job and let a maker with the right setup quote it.
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Questions about this calculator
Why is my plywood edge burnt?
Usually the chipload is too low: a fast spindle with a slow feed, or a dull bit. Lower the RPM or raise the feed so the bit makes real chips, and avoid pausing in the cut.
Does chipload change with bit diameter?
Yes. Larger bits are stiffer and can take a bigger bite, so the starting chipload rises with diameter.