Why Run a Router Bit at High Speed

Why Run a Router Bit at High Speed?

In the story of Goldilocks, we know the three bears each had their own mattress sleep numbers.  One was too hard, one was too soft, and the third was just right.

So it is with router bit speeds: 

  • Too Fast.  If the router speed is too high, you run the risk of burn marks on the wood or tear-outs.  The wood piece becomes unusable, and you have to start all over again.  You’ll find, too, that the router bit will dull faster.
  • Too Slow.  If the router speed is too low, the cuts will not be clean.  Instead, they’ll be choppy, ragged and rough, or even rippled.  Again the wood piece becomes unusable, and you will have to begin again.
  • Just Right.  If the router speed is just right, you’ll find no burn marks or tear-outs, and the cuts will be clean and smooth.

To put a fine point on this, too, be aware and knowledgeable about the material.  Some are more burn prone than others, for instance.  Woods also have their own densities, with hard materials on one end of the scale and soft materials on the other.  Each will have its own “just right” router speed setting for optimum results.  So, know your wood.

Testing a route on a piece of scrap wood can help you make any necessary adjustment in router bit speed before you begin work on the intended project.

What Speed Should I run My Router?

As a general rule, router speeds should be set ever slower as the bit size increases.  The larger the bit size, the slower the rate should be.

You should be “just right” if you follow these speed ranges based upon bit size:

Bit SizeMaximum Speed
Up to 1”24,000 rpm
1” to 2”18,000 rpm
2” to 2 ½ “16,000 rpm to 14,000 rpm
2 ½ “ to 3 ½ “12,000 rpm to 10,000 rpm

Again, know your wood, and, make a test pass on a piece of scrap to make sure you’ve chosen the right speed.  In router-speak, this is the equivalent of measuring twice, cutting once.

Is Router Bit RPM The Same as Rim Speed?

This can be a tricky and complicated question.  RPM stands for revolutions per minute, as we know.  But, what is router bit rim speed?

The outer edge of a router bit is referred to as the rim.  Geometry and physics tell us that the wider the router bit, the greater the rim speed will be based upon the rpm.  This is so because the rim of the bit will be moving much faster than the bit’s inner part as the bit spins at the rpm you have selected for it.

This high speed can contribute to a burn or tear out when the router makes a pass on your wood.  If you can bear just a few minutes of geometry and physics, here’s an excellent video that explains this.

How Can I Reduce The Speed of My Router?

Many new manufacturers models of routers have speed dials that allow you to adjust bit speed easily.  With the router off and to be safe unplugged, turn the dial to the desired speed. 

It’s no more difficult than setting the speed on a blender or mixer in the kitchen.  Turn the dial, make sure it’s in the notch of the chosen speed, and you’re good to go.

Follow the speed guidelines in the chart, and make that test pass on a piece of scrap wood to make sure it’s the right speed for the right wood. 

How Deep Should The Router Bit Be?

To make that smooth and clean cut, the router bit must be stable and secure.  The bit shank is inserted into the router collet – a type of chuck that forms a collar around the shank and provides a strong clamping force around it – and the collet is tightened.

This will hold the bit in place securely.  It is essential for a clean and smart cut and for the safety of the bit.  Here’s a good video that shows you how this works:

The depth of the shank in the collet will usually be ¾”, which will give you a very positive control.  If it is less than this depth, you run the risk of a creeping bit, one that wobbles and ruins the cut.  Worse still, it might bend or break the shank, and you’ll need a new bit.

The “Three Bears” of Router Speed

Too fast, too slow, just right.  Know the wood; use quality router bits; set the right router bit speed; make that test run on a scrap piece of wood; make any adjustment indicated, and then make the cut.

It only takes a few moments to set the job up correctly, and the result is a clean and smart cut.