I am trying to engrave a PCB on my Ox using a 0.5mm cutting bit, and consistently breaking bits. I am cutting at 200 mm/min. The reason seems to be that it judders. I have checked the pulleys, all tight. Checked the belt tension, seems OK. I have cleaned the wheels, belts, pulleys, etc. I have changed microsteps from 8 to 32, slight improvement but still a definite judder. If I increase the feed rate to around 2000 mm/min it seems better, but still judders, and that is much too fast for a 0.5 mm bit. The judder occurs on all 3 axis, worst on Y, not quite as bad on X and on Z I can tell that there is a judder but so slight that I wouldn't bother about it. I am running it from bCNC on a Raspberry Pi. Any suggestions?