Was cutting a 3/16" wide dado in a piece of Lyptus using an Amana
upcut spiral bit. Was cutting 3/16 deep in half inch stock. Router
is a Porter-Cable 7518 in a lift.
All was going well, when, after cutting four pieces, on the fifth one
I'm about three inches along and all of a sudden the bit comes right
through the top--it's still cutting just decided to pull out of the
end of the collet. So I put it back, socked it down hard, and
continued the cut and three inches along it did it _again_.
This time I pulled the bit and the collet and cleaned both with
lacquer thinner and got a lot of black crud off both, but I'm pretty
sure I didn't get it all out of the collet. Whether the problem is
fixed I don't know--I only had two short cuts after that.
If I had been holding the piece above the bit then it would have gone
right through my fingers. The notion that there's wood between you
and the bit is false security.
Okay, that was something I'm glad you shared.
Am I correct to calculate that the upcut spiral creates a force that is
trying to pull the bit out, and a non-spiral or a downcut would lessen
the chances of that happening but not remove it completely?
Not necessarily the upcut spiral.
I had the same thing happen to me with my table mounted 7518 a few years
back using a straight dado bit. I've always used pads when table routing,
but I now also make damn sure that I crank down _hard_ on the collets of the
7518, no matter the bit, and keep them very clean.
IIRC, there was a similar thread here about that same time (03) of this
happening to others with the 7518, so while not common, it does happen.
A funny thing about working habits - once they're there,
I injured myself on the table saw last year, and ever since I've been a
lot more careful around all my tools, powered and otherwise. I'd read a
lot on this forum about asking "What can go wrong here?" and had never
really ingrained it into my work habits until the accident. Now it's
unconscious and I'm not always aware of it. In reading this thread and
others about near hits, I've thought about my habits in the shop and I'm
a lot happier knowing that something in the back of my head is doing
just a bit of analysis before each cut, each rout, and each time I aim a
Some guys get that immediately as soon as they start working in a
hazardous environment. Others, like me, have to get graphic
illustrations of how bad it can be. In my case, since the injury was
minor, I'm glad it worked out that way and grateful it wasn't losing a
limb or worse before those habits became part of me. I hope that
unconscious analysis never leaves me.
Quite true. A study of the forces acting on a router bit would show that any
bit would tend to come out of the collet. A spiral would have a bit more
chance of doing so though. Despite a certain router guys advice, I use
spiral bits whenever possible. I have never had one come loose. I only use
end mills though, not what is sold for routers. Their tighter tolerances on
shank diameter mite have something to do with it.
While cleaning the collets today (of course the .50 cal jag doesn't
fit my cleaning rod, but the bore brush from the same company does,
while the .25 cal jag has a nice point on the end that fits exactly
into a new hole in the palm of my hand) I think I discovered a
contributing factor--the Porter-Cable collets seem to be machined so
that the service that gets wedged into the shaft bore is at the bottom
(the end farthest from the tip of the bit) and the bits I was using,
when the flute is fully exposed, don't quite seat that far, so
possibly the collet was applying a little bit of wedging force of its
own trying to push the bit out. In the future I'm going to have to
make it a point to check this.
Incidentally there was quite a lot of crud in both collets--took
several patches before they were coming out clean.
The bit came through 1/2" stock during the a 3/16" dado and you never felt
or heard a difference as the bit was rising ??
This has happened to me before, but I can usually feel/hear the difference
as the router starts working harder.
Glad you are ok.
I wouldn't have believed that could happen! I had a collet on a Sears
router (which I promptly ebayed) ruin a piece by creeping up a eight inch,
but I thought PC was better than that.
But, since putting my finger into a bandsaw blade a couple months ago
(nearly healed, optimistic it will be 100% in a month or two) I make sure I
DO NOT run my finger over the router bit, the jointer knives, etc.
I got away with it once; twice is too much to ask for. So did you.
Good thing it wasn't from Sears, or all the "Crapsman" phrases would crop up
about spontaneous depth adjustment.
Betting that a little bit of computation - almost said slide rule work -
would show that unless you're grossly overfeeding, the climb force of the
spiral would be insufficient to overcome the clutch of the collet. Fault
lies not with the bit, but elsewhere. Just a couple chips in the would do
it, or bottoming the bit with that bash. Never want to bottom a bit.
Just 'cause you don't want to hear it doesn't mean it's not true.
BTW, it happens that the *last* handheld Craftsman tool I own is the
infamous self adjusting router. I've got a 1/2 dovetail bit in it
setup for 1/2 blind dovetails in drawers.
In my mind, jointers and shapers are the scariest of the bunch.
When the wood disapperas in a jointing operation, you'd be in the thing
up to your elbow.
A gruesome tool, that.
I would never use a shaper without a power-feeder.
For some (false) reason, I don't seem to be too intimidated by 3" bits
On 20 Jan 2007 08:36:35 -0800, email@example.com wrote:
Reading your faq leads me to a question. First thing I cut using my
Incra jig many years ago was a box joint. Used a Freud straight bit
and the joint ended up not just loose but sloppy loose. I diddled
everything I could think of to get it tight and finally decided that
the bit was oversized. Went down to Coastal and they were out of
straight bits that size but had an Amana spiral. Tried that and the
cut was dead on. I've been using them for box joints ever since (and
since they're paid for quite a lot else).
Now, my question--all the straight bits I have seem to cut oversize,
the spirals don't. Is this an artifact of the different cutter
geometry or does Freud just make their bits oversized and Amana
maintain tighter tolerances?
I suppose I could just get some Amana straight bits to compare with
the spirals but the original Freuds are still in good shape.
I have a MCLS spiral I bought for box corners that is undersized; when I
complained they said they were all unsized, but within spec. I have never
measured it, but I think my Freud straight is correct. My craftsman
straight IS correct; I have measured it.
Indeed diameter specs are all over the map; independent of supplier. I
would mike all diameter dependent cutters before use.
And solid carbide is a hell of a lot stiffer than steel. Given the
correct measured diameter, with a slot width greater than the tool,
Blame: Fixturing, technique and cutter deflection for the wide cut.
Solid carbide deflects too , especially when the flute length is > 3 x
There is a lot more to the story but that should get you thinking, PW
J. Clarke wrote:
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