Hi Jonathan,

I had it pretty well clamped I think. Please remember the roughness doesn't seems recessed from the rest of the cut, so possibly not just re-cut chips embedded in it?

I was using:

700mm/min
11,000RPM
2 flute 3.17mm cutter
1mm multiple passes
0.3mm finishing pass

I'm not sure how it would have lost position at such a low feedrate. I guess I might need to check the rotating ballnuts to make sure the cogs aren't working loose.

By the way I got my vacuum extraction working just the other day.