Back again. After thinking I had a low power issue, I upgraded all software and settings to your recommendations, and changed the end mill I was using. All seemed to be working until yesterday when I tried to cut some 10mm hdpe. I was cutting at a feed of 15mm/s with a 3mm single flute endmill at 3mm per pass, 12k spindle.
As you can see from the pictures it seemed to be cutting perfectly with well defined chips, until the third pass of the final cut line, when suddenly it just went cutting across the whole piece.
On closer inspection of the wholes it did cut, there seemed to be a slight step to the left on the x axis.
Motors and drivers were not hot.
Any ideas what would cause this? Has I going too fast? Did I loose steps?