Looks like Z axis ball screw has issues too. Noticed while driving it up and down, with the front plate off, the ball nut and bracket were fine at the bottom but the more they reached the top the more they oscillated side to side. I took it all to bits and found two things, the turned down section at the driving end was slightly off centre and the the whole turned down section was bend to one side. With the ball screw resting in two V blocks it was rotated and a DTI measured a deviation of 0.8 mm at the end where the pulley sits, this reduced to 0.35 where the BK12 bearing sits. So I did what any self respecting person would do, put it in the vice and knocked seven bells of shite out of it ! to say I was upset would be an understatement. Actually I put it in my mini lathe chuck with a DTL fitted and 'coaxed' it back straight. It's a lot better but not perfect due to the off centre turned down section. Next I'll have to see what can be done with the Y ball screw. Who's idea was it to get stuff from China ?