Router Bit coming loose when attached to router table

[Kevin Jenness]

Collets are an overlooked wear item that should be cleaned frequently and replaced when worn.

Bits can be out of tolerance too. I once had an Amana bit show up so bad that I could see something was off right out of the package. The shank measured something like .025" under 1/2". The collet would never have held it securely.

If you really have to reef on your collet take a close look at it. Manufacturers usually provide wenches long enough to tighten their collets properly with normal torque.

[Thomas Wilson]

Bits that have an up cut angle put some pressure on the bit pulling it out of the collet. Real bummer when a dovetail bit walks down 1/8” while making a pass in the dovetail jig. Light passes reduce the pulling load. In the case of the dovetail jig, plowing out the bulk of the waste with a 1/4” straight bit helps a great deal.

[Frank Pratt]

I guess I'll be buying more 1/2 in shanks as those have worked well and I really like them so far.

That's a good plan. Never use a 1/4" shank where you could use a 1/2". They're just so much more stout.

[Grant Wilkinson]

All of the above, plus, be sure to measure the real shaft size of those cheap bits from amazon. We are finding that many of the "1/4" bits are really 6mm bits, especially the ones from China. Those bits have a shank size of .236" and will be loose in the collet, no matter how tight you make it.

[Roger Feeley]

Don't drop the bit shank all the way into the collet. Lift it off the bottom.
Tightening a collet will push the bit into it, preventing the collet from tightening.

+1 on not bottoming the bit. I make it a habit to lift the bit just a little before tightening.

I’ve read that an easy way to prevent bottoming is to find a nice thick but squishy o-ring and just leave in there.

[Curt Harms]

Definitely change the collet. They wear a bit like an hour glass on the inside bore. Replacements are not expensive.

There is another thread active here about router collets. I haven't needed a replacement yet but when I do I'll probably get one from Elaire Corp. I have 2 Porter Cable routers, one Freud FT2000E and one Grizzly trim router that is 1/4" only. None of them have an issue with the bit coming loose and I don't use much force to tighten them. All but the Freud use two wrenches and it's pretty easy to get a fair bit of torque using two wrenches. Interesting comment about 6 mm vs. 1/4" upthread, that would certainly be something to check.

[Mel Fulks]

Leaving a space between bit and collet doesn’t get much press. I worked with a guy who did mostly laminate work , one time he had a
problem with a bit moving . I told him to leave about a slight 1/8th . He replied “I ain’t never heard that before”. He tried it and it worked.
More would know about it if there were more slipping bits , then the fix would get ‘famous’. He had worked for many years and never had
a slip until that day.

[Mark W Pugh]

Or, if you have a Space Ball from building cabinet doors, drop one down the collet before putting bit in. Cut in half if you're worried about it being too thick.

[Lee Schierer]

+1 on not bottoming the bit. I make it a habit to lift the bit just a little before tightening.

I’ve read that an easy way to prevent bottoming is to find a nice thick but squishy o-ring and just leave in there.

A 1/4" space ball dropped into the collet will prevent the bits from bottoming out.

[johnny means]

Your problem is the 1/4" collet. Nothing bigger than an 1/4" round over should even be made with a 1/4" shank. They just don't have enough of a mechanical advantage or gripping surface to resist slippage.