Electric Comet wrote in news:mc22gu$k7o$2 @dont-email.me:
After reading Bodger's comment, I realized what the problem is here: you don't know what the word "deflection" means.
from thefreedictionary.com: "deflection - the movement of a structure or structural member when subjected to a load"
(the "structural element" in this case being the router bit).
What you are talking about is (as Bodger said) runout. He explained the causes of runout. If it changes with the speed of the router, it could be an unbalanced bit, or it could be bad bearings - more likely the latter. If it doesn't change with speed, it's most likely a bent bit.
I've stayed on the sidelines but this thread has gone on so long I finally thought I'd see what was going on... :)
...
You're reading it wrong, yes methinks... :)
He's saying the shaft isn't stiff enough but what the mass on the end causes flexure when at high speed. The case where he goes on to later to mention the 6" long shaft is clearly what he's speaking of. Now whether that's the actual mechanism can't tell w/o actually seeing it or measurements, but seems clear what he thinks is happening.
Iff'en as he says it occurs in two separate routers I'd judge not the collet/router runout but associated with the bit. It could be there's sufficient imbalance to cause the problem if it were an inexpensive bit that didn't muster quality control checks that a more expensive would have failed at the manufacturer. Or, given the fact it has double bearings it may just be that indeed the mass is too much for a 1/4" shank and with _any_ imbalance is an issue. If this is an issue, I'd put it back in the toolbox and never get it out again in anger--a flying router bit head from a fractured shaft is too spooky to venture a chance...
I'd venture the solution would be to set the bit deeper into the collet if have that much exposed shank that flexure is an issue and use the router depth adjustment to control the depth. If the shank is so long that even set a full depth it causes this, see above.
If it were a decent manufacturer and the bit is fully inserted in a collet, I'd contact them with the symptoms; some Chinese import thru eBay or whatever source, "not so much"...
ADDENDUM: Perhaps it's hitting a critical axial moment--at that point bending resistance magically becomes much less and all kinds of bad things can happen. Once't upon a time in a former life with centrifuges for a casing of approx. tractor-trailer length and feet in diameter, operating speed was at roughly router rpm's. To get up and down from rest required passing through 5(yes, five, count 'em!!!) criticals; early on the failure rates were quite the issue...
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