Here's why you don't put your fingers above the router bit

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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.
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J. Clarke wrote:

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?
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wrote:

I suspect that the reason it rose was that it was an upcut spiral--your analysis of the forces is correct. Still, having seen it once, I'd not want to take a chance with _any_ bit.
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"J. Clarke" wrote in message

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.
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Swingman wrote:

A funny thing about working habits - once they're there, 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 chisel point.
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.
Tanus
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On paper yes. In real life no. Craftsman routers have had a problem with ruined projects because the bit crept up with no bit in particular.
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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.
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On Sat, 20 Jan 2007 16:49:13 GMT, "Leon"

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.
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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.
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No more than the usual variation I get from one piece of wood to the other.

Me too. Thanks.
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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.
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I think the mantra "what would happen if the wood dissapeared" is a good one to have running through your head whenever pushing wood through a power tool.
J. Clarke wrote:

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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.
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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.

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SonomaProducts.com wrote:

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 in routers.
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Yes I would expect surprises from spiral cutters, more on that: At no.12 http://patwarner.com/faq.html **************************** J. Clarke wrote:

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On 20 Jan 2007 08:36:35 -0800, snipped-for-privacy@patwarner.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.

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wrote:

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.
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One of the reasons for using a box-joint jig like http://us.oak-park.com/catalogue.html?list=boxj-- see the demo. Adjusts to fit the bit in question, as does the Leigh dovetail jig.
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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 the diameter. There is a lot more to the story but that should get you thinking, PW ******************** J. Clarke wrote:

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