Where did I go wrong: slipped bit

[davidtu]

Was routing a 1/4" deep dado w/ 1/4" straight bit w/ 1/4" shank in hardwood. This was on a benchtop router table. Anyway, part way thru my 2nd piece, the bit poked thru my piece! That means it traveled 1/8" out of the collet (at least).

Now -- did this happen because a) shank was not far enough in collet (I think it was at least 3/4" but probably not much more); b) the collet wasn't tightened enough (thought it was, of course, but I was trying not to overdo it as would be my nature); c) I forgot to take 2 passes and was going 1/4" at once! Oops! d) something else?

Thanks!

[RodKirby]

Oh I know the feeling!

My new Triton router did this to me - with a 1/4" spiral upcut bit! RayintheUK and I are going thru a saga with Triton UK and Oz as I write. Anyway...

"Hardwood" - if it was VERY hard, I would take 2 passes for a 1/4 x 1/4 cut. But "normally" a 1/4" cut depth should be OK.

Yes, at least 3/4 of the shank length should be in the collet. A nice sharp bit I hope?

Was it a 1/4" collet, or a 1/4" reducing sleeve in a 1/2" collet? - this is the problem with mine

I now tighten my collet, with a longer wrench, almost to the point of "breaking" - not recommended, but the only way I can prevent slippage. I would add - I don't need to tighten that much using a 1/2" shank router bit (no reducing sleeve).

BTW - what brand of router are you using?

[LCHIEN]

Was routing a 1/4" deep dado w/ 1/4" straight bit w/ 1/4" shank in hardwood. This was on a benchtop router table. Anyway, part way thru my 2nd piece, the bit poked thru my piece! That means it traveled 1/8" out of the collet (at least).

Now -- did this happen because a) shank was not far enough in collet (I think it was at least 3/4" but probably not much more); b) the collet wasn't tightened enough (thought it was, of course, but I was trying not to overdo it as would be my nature); c) I forgot to take 2 passes and was going 1/4" at once! Oops! d) something else?

Thanks!

Some routers are notorious (you did not say which you have) for poor collets allowing the bit to slip and/or poor locks on the base allowing the whole motor assy to slip in the grip of the clamp and thus change depth mysteriously during the progress of a cut.

Sometimes it helps to tighten the depth lock or the collet nut and sometimes not. THis is why cheap routers can be such a pain.

This problem can be excaerbated by using a spiral upcut bit (I note you said you were using a straight router bit) which will tend to draw the bit deeper into the wood while pulling the cutting to the surface of the wood (equal and opposite reaction).

Definately you should sink as much of the shank as you can into the collet. 3/4" sounds like not enough but it would depend upon the bit, I'd say at least an inch or more or to the base of the flutes or until the bit bottoms out (if it bottoms out in the collet, pull it back out 1/16th or so and then lock it).

Using larger shanks and taking small depth cuts will both reduce the tendencey to change depth. The larger shank gives twice the circumference to grip and the shallower depth reduces the forces on the bit.

[davidtu]

Wood: Wenge
Router: Bosch 1617
Collet: 1/4" (not sleeve)

I was using 3/4" (by eye) in Collet as per Bill Hylton's book's minimum. But seems like deeper would be better. I was also trying to follow his advice on tightening the collet... he says just offset the two wrenches and bring them together w/ one hand is all the force needed... of course he doesn't say how tight to get the collet before this final measure so I'm not sure its useful advice. My tendenancy would be to overtighten, so I am being deliberate about avoiding doing that (in general).

Thanks for the info.

[LCHIEN]

Wood: Wenge
Router: Bosch 1617
Collet: 1/4" (not sleeve)

I was using 3/4" (by eye) in Collet as per Bill Hylton's book's minimum. But seems like deeper would be better. I was also trying to follow his advice on tightening the collet... he says just offset the two wrenches and bring them together w/ one hand is all the force needed... of course he doesn't say how tight to get the collet before this final measure so I'm not sure its useful advice. My tendenancy would be to overtighten, so I am being deliberate about avoiding doing that (in general).

Thanks for the info.

well. the 1617 is considered to have a good collet.
I use about the same force, i turn the collet nut by hand until I feel resistance as it begins to squeeze the shank. I use the two wrenches about an 1/8th turn apart and squeeze them together. That generally seems to do the job for 1/2" shanks. You might want to go a little tighter for 1/4" since the you have so much smaller a circumference to grab, but them the torque on a small diameter bit should be less, too.

I would def. recommend inserting the bit as deeply as possibly (w/o being totally bottomed) and keeping the working end within depth adjustment range to d o the cut.

[jwaterdawg]

The thoughts already posted are great. Only one thing I can think of to add. Have you cleaned the collet recently? It doesn't take much dirt/dust/grit etc. to reduce the holding power of even a good collet.

You might want to give it a thorough cleaning. I use rubbing alcohol, mineral spirts (one or the other, not in combination), a toothbrush and some rags. Just don't use anything too abrasive as you could damage the collet.

PS: A bottle brush for cleaning baby bottles also works well.

[JimD]

I tighten the collet of my PC 690s the way you describe. Sometimes I have to go for a second "bite", however, if it tightens too easily. That's my only additional comment.

I stopped using an old Sears Craftsman when it did what you describe. That was the router. Your router is good enough so a dirty collet or not quite tight enough plus a fairly deep cut all sound like possibilities.

Jim