I have changed to a 2:1 gear ratio and made sure it is all running smooth however I still seam to be getting the problem. I am just trying the job at 50% feed rate to see if that stops it. We are wondering if it happening when there is a fast change in direction and feed rate because of the heavy z axis. We think it is sways happening during a similar movement but not at the same point in time through out the job. Wondering if possibly we need to put a gas strut on the z or go up further on the gearing at the moment I have a 20t and a 40t