An essential component of any router, the collet is what holds the router bit in place as it rotates at over 20,000 RPM.
The collet is a piece of precisely machined steel bored to match the shank of a router bit and tapered on the outside to slide into the hollow spindle of the router motor. The collet nut fits over the collet and as it is threaded onto the spindle it forces the collet into the spindle, causing the collet to compress and squeeze the router bit.
Although router collets have slits to allow them to expand and contract to enable them to clamp and release bits, the range of clamping is very limited. Only use a collet to clamp a round object of the specified diameter — doing otherwise can damage the collet. For example, router bits and collets in Europe are commonly 12 mm, which converts to 0.47″. This is very close to 1/2″, but not close enough to be compatible.
To secure a router bit in a router motor, first insert the collet into the spindle and thread on the collet nut by hand until you feel resistance. Then slide in the bit. As a rule of thumb, a router bit shank should be inserted a distance of at least double the diameter of the shank. For example, a 1/4″ shank bit should be inserted at least 1/2″. Having said that, inserting the bit further is usually good practice. Finally, tighten the collet nut using the correct size wrench, immobilizing the spindle with either a second wrench or spindle lock.
Removing a router bit can be a little trickier. In theory, you would simply reverse the procedure — immobilize the spindle and use a wrench to loosen the collet nut. The collet then opens up, releasing the bit and you remove it.
However, that doesn’t always happen. Sometimes the router collet remains stuck in the spindle and doesn’t open up and the bit is “frozen”. Unfortunately, there is no sure-fire way to release the router bit. I have always been able to remove a frozen router bit by tapping it out with a small hammer and a block of wood to soften the hammer blow. I have heard recommendations of using hot or cold to release the bit. This situation doesn’t happen with all collets and routers.
Fortunately, most collets made nowadays can be described as self-releasing. This means that the collet is connected to the collet nut so the collet nut can be used to pull the collet out of the spindle. When removing a bit from a self-releasing collet, first immobilize the spindle and use the wrench to loosen the collet nut. Once loosened, the collet nut can be turned several times further by hand before it gets tight again. The wrench is required at this point to further loosen the collet nut and pull the collet out of the spindle. The bit should now slide out of the collet without difficulty.
Collets are fairly easy to maintain. Ensure they are kept clean and smooth, and free of rust or grease. Keeping collets in good working order is fundamental to safe and accurate machining.