CONTROLLING YOUR ROUTER’S SPEED AND FEED RATE
Router speed isn’t just a convenience—it’s critical for safety, cut quality, and keeping large bits from moving at blistering speeds. Match your router’s RPM to bit size and adjust your feed rate to get cleaner cuts, less burning, and a much safer shop experience.
Most new routers these days have a variable-speed option, and many folks who own older single-speed routers equip them with aftermarket variable-speed controllers. Why? Why do you need to control the speed of a router’s motor?
The answer is a little more complex than you might think. It involves safety and cut quality, but you also have to consider other variables, such as feed rate. Let’s cover these briefly.
Why Router Speed Matters
The biggest reason to have a variable-speed adjustment on your router is to slow down the rotation of large router bits.
At 24,000 RPM, the cutters on the outer perimeter of a 1-inch-wide profile bit are moving at a respectable 71 mph. But on a larger bit spinning at the same 24,000 RPM—such as a 3-inch panel raiser—the cutters move at a blistering 213 mph. Router bits are not designed to endure the centrifugal forces generated at those speeds. You must slow down your router to use large bits safely.
Source: WOOD Magazine
Here’s a simple chart illustrating the safe speeds for various sizes of router bits, based on manufacturers’ recommendations. I suggest copying it onto a piece of paper and keeping it with your router bit collection.
Cut Quality and Heat
Safety isn’t the only reason to slow down a router’s speed. Cut quality can also be affected.
A bit that’s spinning too quickly will generate more friction and heat, potentially scorching the wood and damaging the bit.
A bit that’s spinning too slowly can leave a fuzzy or rippled surface behind.
Some of these issues can be remedied by adjusting the feed rate—the speed at which you pass stock over a router table or move a handheld router across the workpiece. If a bit is spinning too quickly and taking too many cuts per second, increasing the feed rate can reduce the number of cuts per second.
But feed rate alone won’t solve every problem. As the bit gets larger, it cuts faster, and if you can’t slow it down at the motor, you’ll reach a point where you simply can’t safely feed the stock quickly enough to compensate.
A bit that’s spinning too quickly may also vibrate and leave chatter marks on the workpiece no matter how you adjust the feed rate. Even small vibrations can cause the collet to loosen—and you can imagine how that might end.
Finding the Right Speed
Experience will help you develop a feel for the optimal feed rate, but you should still adjust your router’s speed at the motor to match the bit you’re using.
If your router’s speed dial uses numbers instead of actual RPM settings, you’ll need to do a little testing.
Securely install a bit and slowly increase the speed until it begins to vibrate. You may feel the vibration, or you may even see it. Back the speed off until the vibration stops. Try this with bits of different sizes—the profile doesn’t matter, only the diameter.
If the bit isn’t vibrating, chances are you’re within the safe speed range for that bit and others of similar size. Note that dial setting on your chart for future reference.
Fine-Tuning for Best Results
These speeds are only a guide. They’ll keep you safe, but they may not produce the best cut for the material you’re using or the rate at which you’re feeding the stock.
It never hurts to make a practice cut on scrap before running your good workpieces.
If you see scorching, or the bit is chattering or skipping along the edge, slow the speed or increase your feed rate.
If the edge is fuzzy, shows fine ripples, or you’re getting tear-out in figured wood, increase the speed (while staying within the safe range) or slow the feed rate.
If you’re routing a dado, groove, or mortise and the dust is hot when you’re finished, decrease the speed to reduce heat buildup and extend the life of the bit.
And don’t forget to control the depth of cut. Removing too much material in a single pass can ruin a cut regardless of speed—but that’s a topic for another day.
If you’re shopping for a new router, here are some options:
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