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.
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!
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>)
Mike in Mystic wrote:
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.
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.
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
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"
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
That's about all I can think of at the moment.
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.
Jim Wilson wrote:
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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