I tried running a 3/8" 45° lead 3 flute end mill yesterday and kept having it suck the holder out of the R8. I was cutting 6061 .125dp, full width @ 20ipm. I can run the same end mill with a 30° lead no problem.
Is this a bad R8? I have had this happen a couple other times when I try to get aggressive with my cut speed.

R. -

Degrease the collet and the tool holder, and then torque the drawbar to around 20 Ft-Lbs (which should be good-n-tite with the supplied wrench).

The degreasing will work wonders.

Good Luck!

- Just Gary

I did the degrease twice, had read about that before.

I had similar problems with R8 holders and if you get too carried away tightening the draw bolt you have difficulty knocking them out.

Make sure the bore of the holder and the tool is free of grease but smear a thin film on the taper; you do want this to slide as easily as possible.

Snug the tool as far as possible up in the holder without gripping the flutes, this gives the end less leverage. I think the cutter doesn't exactly pull straight out it walks its way out as it wobbles a teeny bit under the cutting load. You have to remember the R8 is a single taper so the hole closes more at the outer end than at the inner end and does not grip the tool evenly along its full length.

Have you thought about acquiring a 3/8 weldon holder with an R8 shank? That eliminates the one link in the chain that relies strictly on friction rather than positive retention, and the holders are not expensive.

The holder is coming out of the R8 collet not out of the er20 holder. I am just of the opinion the those high helix cutters will do that. Like I said the 30deg. doesn't have those issues. I was think of getting a different R8 collet, I did notice that the threads in mine don't seem to be centered.

The holder is coming out of the R8 collet not out of the er20 holder.

If you'd rather use er20 than weldon you can get those with R8 shanks too. Should do the trick if replacing your R8/TTS collet doesn't work.

I have only used 30 degree as the steepest. I did notice some similar issues with it before I bought some Tormach tool holders. Since then, no more issues. You need to keep collet and spindle socket clean and lightly oiled as mentioned. My mill is likely between a Tormach and X3. Therefore I don't take huge DOC's. About .05" is the most on alumunim. 6600 RPM spindle. .025" on steel. The only high helix is used on aluminum from time to time. I have used it in my trim router too with better results than through the spindle. The higher spindle speed likely had something to say about it's preformance.
I sure hope you get it fixed up. Tool slippage is is an unhappy situation made even worse under cnc control.