Well, since I originally posted, I've been learning a bit about my mill and no more endmills have been broken.

I now use the Alu-power carbide 2 flute and 3 flutes from Cutwel. They are a little more expensive but they work well. I know it's overkill but I like good quality sharp and shiny tools :)

My mill can only do 2000revs. which I always use.

Using Fusion360 with Adaptive to cut a pocket or remove material I use an 8mm 3 flute cutter, Helix plunge down fairly slowly (20degree angle) to about 6mm depth with a plunge feed of 300 and WOC of 0.5mm. Once it reaches the 6mm depth, I go faster at 350 feed and 0.5mm to enlarge the pocket. Then repeat the same with the next 6mm depth and so on.

I use no coolant or air, just a vacuum to suck the swarf. No problems at all at these settings.

It's fairly conservative, I am sure I could go deeper at these settings.

I have tried more WOC, up to 1mm, but that's when the problems start. The TTS type tools can start pulling out of the collet with the consequent accident to follow.

I am sure that if I just used a normal R8 collet only, I would be fine with 1mm width cuts, but with an 8mm cutter it seems to be too much force for the collet to grip the TTS tooling properly. It's fine with smaller diameter endmills though.

Edward