Bit being pulled out of collet during cut

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This topic has come up quite a few times - reference collet tightness from Nov 2022.

I’ve chewed into my spoilboard more times than I care to admit - pretty much every time when using a 3/8" endmill (usually an upcut). Never with smaller end mills. This has frustrated me to no end. I even went so far as to purchase the Amana torque wrench - which was NOT the solution. For me it was not a problem of having the collet “tight enough”.

For me the problem was the Amana bit(s) I was using have a wonderfully helpful triangle/line on them telling me how far into the collet to insert the bit. I have loved this feature - made it feel idiot proof.

However on my 3/8" endmills the “idiot line” telling me how far to insert the bit - was making the endmill stick out above the top of the collet; this was up inside the spindle so I never noticed this issue. [I usually had the collet loosely threaded onto the spindle when I jammed the bit up inside.]

So, it wasn’t until I watched this video (https://www.youtube.com/watch?v=UoHSk9dO6oM), and specifically tip #2, that I realized the Amana reference line (which I loved) was biting me in the butt on my 3/8" endmills. The suggestion is to always leave the endmill 2-3mm below the top of the collet.

Not sure if this matters for everyone, but this was definitely my issue (on my long list of issues/learning from my mistakes).

Hope this helps someone else !

-scott

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I think they key thing here is that the shank of the bit shouldn’t bottom out when tightening, as that prevents further tightening. Whether that means “don’t stick out of the collet” or just “know how deep your spindle goes” is up to you.

In my router table, I dropped an O-ring into the spindle so that when I drop a bit in and tighten it, it can compress the O-ring rather than block further tightening. I wonder if a suitable rubber stop would work for Avid spindles?

I wonder, though, if imperfect collets might benefit from having the back end “loose” so the front end can be tightened further? His collet looked really beat up, and his problem might just be uneven pressure from the collet.