Router Bit Problem

I am having trouble with one particular bit slowly pulling out of the collet when routing a dado. The bit is a Rockler 5/16" two flute straight (not spiral) bit with a 1/2" shank and the problem occurs when I have it installed in my Bosch 1617EVS router in my router table. On three separate occasions, the dado I was routing was deeper at the finish than at the start, with the change in depth being gradual. On one occasion the depth increased about 1/4" over a 10" run. On each occasion the bit was pulling out of the collet. The first time I assumed I had not tightened the bit properly, but on succeeding tries I made sure the bit was tight. I have not had this problem with other bits. Any thoughts on what is happening.
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Did you insert the bit all the way into the collet? Try inserting it so that there is 1/4" in the bottom. If it were all the way, the collet will be pushing the bit down and unable to tighten all the way. A good method is to put an o-ring in the base. Home Deport or the like seel them for faucets. OD- 1/2" get as fat a ring as you can and then place it in the collet and use pencil to bottom it. Leave it in from thispoint on. When installing bit, press to bottom. The O-ring will prevent the bit from bottoming out.
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wrote:

if you have a way to measure the shank to thousandths, try that. the shank may be a tiny bit undersized. if so return the bit.
look for damage to the shank- if there is a burr or something that would interfere with proper seating. you may be able to correct this, but if it's a manufacturing defect I'd return it.
clean it carefully with alcohol and a fine brass bristle brush. clean the collet and the collet seat as well. I have a few brass bore brushes, meant for cleaning gun barrels. I give the collets and seats a swipe from time to time.     Bridger
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If it's just that one bit, it sounds like the shank is undersize.

collet
separate
not
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At the risk of flames, checkIand verify you have your router depth adjustment locked. Not the router lift, if you have such a setup, the router depth setting itself. I say this because I have made the same error, resulting in depth change during routing. Tracked it to a loose locking lever on the router...it tends to be set and forget when using a lift, but the lock needs to be set on router itself.
If this doesn't help, then the other replies are more likely your culprit.
Drew

collet
separate
not
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I agree with JLUCAS. Back the bit out of the collet after it bottoms out.

Probably because most bits we use (or at least I use) are profile bits and are not under the same strain as a straight bit cutting a dado.

collet
separate
not
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I go along with the possible undersize shaft. In my box of bits I had one roman ogee that did that. My soloution was throw it and get a new one. Anything else isn't worth the hassatle.
bob making saedust in salem or
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I had this happen to me several times when routing dados. I found it to be what everybody else has said, the shank was a bit undersized. The odd part is that the last two times it happend it occurred with undersized plywood bits. Both bits were from the "orange" company that many people seem to be so fond of. I threw them away and got another brand.......Problem went away.
Jim

collet
separate
not
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I use an o-ring to keep the bit off the bottom. I checked the shamk diameter and found it to be right on. The only thing I could find was a dark residue in the collet when I cleaned it with laquer thinner. I did spray some TopCote on the router body a day or so ago. Perhaps I got some in the collet. Anyway, after a thorough cleaning it worked fine.

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This is very interesting - by your description, the bit is falling upwards into the work (assuming that, like most router tables, yours has the router mounted upside down).
I tend to agree with the other folk that suggest the bit's shank is undersize. However, I'd be curious to know what the mechanics are that are pulling the bit upwards, rather than letting it fall down with gravity.
If you choose to experiment with the bit, I suspose you could make a mark on the shank (perhaps with a sharpie pen) at the collet, and thus verify it is the bit moving out of the collet, and not something else.
John
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On Fri, 23 Jan 2004 20:54:59 +0000 (UTC), John McCoy

if the bit is loose at all in te collet it creeps out of the collet, irrespective of gravity. I don't have any scientific data about why it does this, but I suspect that it has to do with the cutting angles applying pulling force (albeit rotational) outside of the collet.
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