Material removal rate
Material removal rate is feed rate times depth of cut times width of cut, in cubic units per minute. It is how you compare two settings that look nothing alike, and how you know whether a change actually made the job faster or just louder.
The formula
In consistent units. Inches per minute times inches times inches gives cubic inches per minute.
Why it is worth knowing
Two setups can look completely different and remove material at the same rate:
| Setup A | Setup B | |
|---|---|---|
| Feed | 60 in/min | 300 in/min |
| Depth | 0.5 in | 0.1 in |
| Width | 0.25 in | 0.25 in |
| Removal rate | 7.5 cubic in/min | 7.5 cubic in/min |
Setup A looks slow and is doing exactly the same work per minute as B. It is loading the tool much harder to do it, in a single deep engagement, where B spreads the same work over a shallower, faster cut. Knowing the removal rate lets you have that conversation with yourself honestly.
What it is good for
- Comparing before and after a change. Did doubling the feed and halving the depth actually help, or did you just move the load around?
- Finding your machine's ceiling. Creep the removal rate up on scrap until the machine complains, and note the number. That is your practical limit, and it applies across bits and materials far better than a single feed rate does.
- Estimating whether a job is realistic. A pocket with a known volume divided by your removal rate is a floor on cutting time.
What it is not good for
Removal rate says nothing about whether the settings are sane. You can achieve a high removal rate with a chipload of 0.001 by running an absurd depth of cut, and burn the bit to a stub doing it. Use it alongside chipload, never instead of it.
Finding your machine's limit safely
- Pick one bit and one material you use often. Clamp a piece of scrap properly.
- Start well below what you think the machine can do.
- Increase depth of cut in steps of about 25 percent, cutting a short slot each time.
- Stop at the first sign of real trouble: chatter, visible flex, a change in tone, steps lost, a wall that is no longer square.
- Back off one step. That is your working limit for that combination.
Write it down. That single number, honestly measured on your own machine, is worth more than any chart you will find online, because it includes your frame, your router, your workholding and your habits.