Why RPM matters
The router bit's cutting edge needs to move fast enough to slice wood fibers, not rub against them. If RPM is too low, the bit rubs — generating heat, burning the wood, dulling the bit quickly. If RPM is too high, the bit can grab the wood, chipping the workpiece or causing kickback.
What matters isn't the bit's RPM — it's the surface speed, how fast the cutting edge moves through the wood. Surface speed depends on the bit diameter (larger bits = more edge contact per rotation = slower RPM needed for the same surface speed).
General RPM ranges by bit diameter
- 1/8" - 1/4" bits: 18,000 - 24,000 RPM
- 1/4" - 1/2" bits: 16,000 - 22,000 RPM
- 1/2" - 3/4" bits: 14,000 - 18,000 RPM
- 3/4" - 1-1/2" bits: 10,000 - 16,000 RPM
- 1-1/2" - 3" bits (large roundover, raised panel): 8,000 - 12,000 RPM
Feed rate matters as much as RPM
Too slow: heat builds up, wood burns, bit dulls. Too fast: tear-out, poor finish, possible kickback. The sweet spot for most operations: feed fast enough that the bit is cutting chips, not dust.
A practical test: look at the chips coming off the bit. Fine powder = too slow. Long ribbon chips = good. Chips that look burned = too slow or bit is dull.
Cutting by species
- Softwoods: Lower RPM produces cleaner cuts. The wood is easy to slice, so high speed just generates heat.
- Closed-grain hardwoods: Medium RPM. Maple can burn easily if feed is too slow.
- Open-grain hardwoods: Higher RPM works for hogging out material; lower RPM for finish passes.
- Exotic hardwoods: Sharp bits required. Silica in ipe, teak dulls carbide fast. Reduce RPM and use sharp tooling.
- Plywood / MDF: Higher RPM (24,000+) for clean cuts. MDF generates very fine dust — wear a respirator.
How to adjust your router
Most home routers have variable speed dials. Set the dial based on:
- The largest bit you're using (smaller bits can run at higher RPM safely).
- The wood species — dense woods need slower.
- The cut type — heavy cuts need slower.
- Always do a test cut on scrap — listen to the router. Smooth whir = good. Squeal or growl = something's wrong (often too slow).
When to stop and check
- The wood is smoking or browning
- The router sounds strained
- The bit is leaving burn marks
- The workpiece feels hot when you touch it
- The router is vibrating unusually
Any of these means: reduce RPM, increase feed, or both.
Frequently asked questions
Can I just run my router at full speed all the time?
For small bits (under 1/4") with light cuts, yes. For larger bits or dense wood, no — you'll burn the workpiece and risk kickback. Variable speed exists for a reason.
Why does my bit leave burn marks even at high RPM?
Almost always: bit is dull. Carbide bits dull gradually but eventually can't cut cleanly. Resharp or replace.
What's the slowest safe RPM?
Below 8,000 RPM, bits can grab aggressively. Most manufacturers warn against running below 10,000 RPM. Larger bits need even higher minimums — a 2" panel-raising bit at 8,000 RPM has very low surface speed and will burn.