How to keep a 1/4" shank 1/2" dovetail bit from climbing out of collet?

I spoke to Charlie today who warned me about the tendency of a dovetail bit to climb out of the collet. Sure as hell, as prophesized, as I was cutting the final two pieces, I noticed AFTER the cuts that the bit had come out about a 1/4"! I remember tightening that sucker up in my 7518. I wiped out the collect with a Q-tip to remove any oil residue, of which there appeared to be some. And of course I wiped the shank of the bit with a rag. Can't think of any other preventative measures.
How can I prevent this from happening in the future? The CMT bit is available only in a 1/4" shank. It's a 10 degree 1/2" for use with the Incra jig for 1/2" material and through dovetails. All my other dovetail bits are 1/2" shank.
dave
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thank you spell checker (and my inattention): "collect" should be "collet"
Bay Area Dave wrote:
I remember tightening that sucker up in my 7518.

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Hi Dave,
I use the same router (PC 7518) and have the same router lift as you (PRL), I believe. I also have used plenty of 1/4" shank router bits in my router table with this set-up, as well as dovetail bits (these were actually 8 mm shank, using a 8 mm shank collet, not the adapter thingie).
Anyway, the best and only defense for not letting the bit move, other than what you did already by cleaning the collet and bit shaft, is to really torque down on the collet when you tighten it. You may have heard the term "handshake tight". In practice, this means you tighten the collet down as much as you can without needing a lot of force, and then position the two wrenches so you can grasp them in one hand and then squeeze them together to tighten. In my opinion, this isn't always tight enough. For dovetail bits, I do this twice - handshake tight once, then set the wrenches apart and do it again. Admittedly, this get's the git VERY tight and will take effort to get the bit out. BUT, I've never had a bit slip EVER. I'm sure some will say I'm wearing my collet out prematurely, but I'd rather have to buy another $25 collet in a few years, than have a bit slip and screw up a piece, or possibly throw a 22,000 rpm piece of carbide at my face.
So, my advice - TIGHTEN THAT BIT REALLY HARD!
Mike

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Well, Mike, in preparation for tomorrow when I TRY to redo the project (essentially from scratch), I torqued the living daylights out of the collet. I couldn't get it any tighter than I did tonight. Usually, I just tighten it snugly, like I do the TS blades. If tomorrow ends up like today, want to buy a bunch of tools cheap?? ( I didn't mention yet what ELSE went wrong today in the shop... <g>)
dave
Mike in Mystic wrote:

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"Bay Area Dave" wrote in message

Generally you would expect to see this if someone had seated the bit too deeply in the collet before being tightening, It is not always the case, but is a good point to be aware of. Besides, a clean collet, it is a good practice to back the bit out of the collet an 1/8" or so before tightening.
I had this happen a couple of weeks back with a straight cut bit when dadoing drawer sides for a bottom panel. Strangely enough, I have never experienced it on any other router but my 7518, and that twice in the last year or so, both times with a 1/4" collet... once is too many, however, and I am anal about properly installing router bits so I know that was not the problem in these instances.
In any event, all the more reason to take safety precautions and use push blocks, even when doing blind cuts where the blade is not exposed.
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The weird thing was that Charlie mentioned the possibility of this happening to a dovetail bit, due to it's geometry. About an hour after discussing it, my first bit to "lose it's grip" was a dovetail! I must confess I didn't reef on it; I've been just "snugging" the collets. No more of that! I also hadn't checked for oil residue in the collet before...
At least these kinds of mishaps are the kinds you never forget.
dave
Swingman wrote:

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Ditto here. Had the same bit climb out a 7518 in my router table. Same job - dovetails using the Incra router fence. I couldn't stop it no matter how tight I clamped that sucker in there.
I switched to my Keller jig with a Keller bit in my Milwaukee Bodygrip. No problem.
Bob

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Try to wipe your collet and bit shank with some lacquer thinner then crank it down Dave. Works for me, but I don't have the same router as you do. Hope it works.

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FOW wrote:

The easiest and best way to get rid of oil residue that I know is brake cleaner spray, available from any auto parts store. It'll be absolutely bone dry after that.
--
Mortimer Schnerd, RN

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good point; I used to use that as a mechanic. fabulous degreaser.
dave
Mortimer Schnerd, RN wrote:

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Hey, how you doing?? I'll give it a try. When I woke up this morning I started thinking about that loose bit again and wondered if I should use a solvent to get ALL traces of oil off. I'll follow your suggestion this morning. Thanks!
How's everything going? I got a new email and don't think I gave it to you yet: dave1812dave1234 "at" yahoo "dot" com
unlike hotmail, this email service works! :)
remove ONLY "1234"
dave
FOW wrote:

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Bay Area Dave wrote...

Might not be entirely preventable. Make sure there are no burrs in the collet or on the tool shank. You can try removing most of the waste with a straight bit. Go slow, but keep the RPM's up. Check for climb-out between cuts.
That's about all I can think of at the moment.
Jim
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thanks Jim, I just checked the speed; it was set to 19K. I'll also feed it slower. Hadn't thought of using a straight bit first, and that sounds like good way to reduce the pressure on the wimpy 1/4" shanked bit for the final dovetail cut.
dave
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"Bay Area Dave" wrote in message

Another suggestion ... find a used PC 690 for your dovetail jigs and bits. Just the right size and power for the job. I picked up a refurbished 690 at Porter Cable's outlet store here in Houston for less than $80 a couple of years ago ... after all, one can't have too many routers. AAMOF, I keep a dovetail bit more or less permanently mounted in a 690 for my Leigh jig.
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