How Does a Router Collet Work?
Router collets are simply a steel sleeve that holds the router bit in your router. It sounds simple, but the design of the collet and the method of gripping the shank of the router bit is extremely important. A well designed collet must perform two important functions;
Holding the the router bit securely
It goes without saying that the router bit must be held absolutely secure in the collet. This is very important from a safety point of view as it would be disasterous if the router cutter came loose whilst in use and, secondly, to prevent vibration of the bit which will give a poor cut.
Ensuring correct alignment
The router bit must be aligned concentric to the centre axis of the router’s motor spindle. If the bit is out of alignment you will get a number of problems including poor cutting performance, vibration, premature wear of the cutter and possible failure of the router´s main bearings.
All of these problems increase in severity when you use larger cutters.
Router Collet Design
Most collets systems consist of a separate tapered collet which is inserted into a matching tapered socket in the end of the motor shaft, and a collet nut which is tightened to compress the collet and grip the cutter shank.
The demands put on the collet are pretty high. It has to be machined to extreme tolerances and be able to withstand constant and prolonged use at high speeds. To be able to do this a good collet has to have the following features;
The collet must have sufficient surface area in contact with the shank of the bit to ensure adequate grip and cutter rigidity. This will also place less stress on the cutter shank and reduce the risk of ´cutter creep´ which happens when the rotational forces allow the shank to work its way out of the collet.
For the best grip, the router bit should be fully inserted into the collet and then backed out a fraction before tightening the nut. The gap allows the collet and bit to be pulled down as the nut is tightened.
Good quality collets have a number of slits to allow even gripping around the cutter shank, so you should always look for collets with the most expansion slits.
If you don’t have enough slits the collet won’t grip the bit evenly. This means it won’t grip as tightly plus you’re more likely to get vibration.
Quality collets will have slits starting from alternate edges of the collet which provides even pressure over the full surface area of the cutter shank.
The collet must be manufactured from high quality, polished tempered steel. Collets made from poor quality steel will wear out faster and will be more likely to perform poorly as well. As with everything else, you get what you pay for.
Router Collet Maintenance
You’re asking a lot from your collet, so you have to give it some regular TLC. The collet is right at the business end of the router and so it comes into contact with a lot of dust and pitch. A build up of dust and pitch will result in the same poor performance as buying a cheap collet in the first place.
Pitch can migrate up the slits of the collet and deposit itself around the cutter shank and inside faces of the collet. This build-up will cause insufficient contact between the internal collet face and cutter shank.
Research has shown that insufficient collet maintenance is one of the most common causes of cutter damage and breakage.
Every collet will wear out eventually and need to be replaced, but you can extend its life and performance with some easy maintenance.
- Regularly clean the collet, the collet nut and the socket on the router shaft using pitch and resin remover on a rag
- Don’t forget to clean out the threads on the inside of the collet nut
- Use a wire brush to get into tight spots and pay attention to the expansion slits
- Never tighten the collet without a bit in place as this can deform the collet
- If either the collet or the collet nut are damaged you should replace them both as soon as possible.