[trurle]

Not sure about the underperforming stepper idea. Usually, when a stepper starts to lose steps or get pushed around, the whole axis stutters to a stop.

You can test this. Halve the axis speed and acceleration and see if the problem persists. Then up them by (say) 50% and test again.

Cheers
Roger

Tested. Problem is speed-related. To be exact, in last batch i have tried to cut a round corner 60 mm radius at 2mm deep and 3000 mm/min. After making about 60 degrees curve into X axis (of required 90), end mill repeatedly cut the jagged diagonal instead of remaining part of curve, with severe vibrations (at which point i press abort button).