Router problem with MDF

[Seth Clayton]

Hi y'all!

First post here...beginner woodworker hoping to be able to call myself intermediate soon!!

I VERY carefully setup my router table to cut rabbets in some MDF panels. While making a pass, the collet on my router came loose and the bit jumped up for about 2" of the cut and then dropped down. Any suggestions as to how I should go about fixing this? I'd prefer to try to salvage the piece, because I don't have any leftover MDF and buying an entire sheet just to remake that panel isn't really what I'd like to do...I'm very short on space, and I'd have to move the leftover panel often to work until I found a use for the remainder. The options I've come up with are:


Don't worry, glue the piece up and carry on with life.
Fill the affected area of the rabbet with wood filler or other material and recut.
Glue the piece up and fill the gap with wood filler at that time.


This panel is either the top or bottom of my new router table cabinet. There could be some lack of structural integrity if I leave a gap. Any suggestions would be great. Also would like to make sure it doesn't happen again...I've read that a lot of people overtighten their router collets, which probably lead me to under-tighten mine this time. I'll just go a little snugger from now on!

[Myk Rian]

When you tighten the collet, make sure the bit isn't bottomed out. Leave up to 1/4".
Make it the bottom, and start anew.

[Jim Becker]

The very first thing you need to do is make sure that your collet isn't damaged or aged unless you truly know it was "operator error" where you failed to tighten the collet properly and fully. You indicate that but be sure...this is a very dangerous thing to happen as a bit spinning at high speed that comes out could shoot around the room and even hit you. Collets are designed to be tightened pretty darn far...some machines even provide expected torque settings.

You can conceivably repair the existing material by removing a "pocket" that you can fill with a piece of scrap MDF that you form into the same size shape and then recut the problem area.

[Seth Clayton]

Thanks guys!! I think I can flip it over and turn it 180° as the base. That will leave a gap at the front of the panel, but it carries no weight there and I can fill most of it with a strip that matches the rabbet and then fill the small gap with filler if the gap is even noticeable.

How can I test my collet? I’d like to be sure before I use the “see if it happens again eventually” method.

[Richard Coers]

Collets wear out. Buy a new one. What kind of bit? Spiral? They come loose more easily.

[Curt Harms]

Thanks guys!! I think I can flip it over and turn it 180° as the base. That will leave a gap at the front of the panel, but it carries no weight there and I can fill most of it with a strip that matches the rabbet and then fill the small gap with filler if the gap is even noticeable.

How can I test my collet? I’d like to be sure before I use the “see if it happens again eventually” method.

If you're able to get a good clean rabbet you may not even notice any gap. Well, YOU will because you know it's there but others likely won't.

[Robert Engel]

I've never heard of collects wearing out or why a spiral bit would come loose more easily.

Review your technique for tightening: bit not bottomed out, adequate torque.

Beyond that, check both the bit and the bore of the collect for corrosion. Even if you don't see any, a quick clean up with 400 grit sandpaper on a piece of dowel is a good thing to do.