This problem is going to drive me to drink.. Mmmmm Beer!!!

While doing complex engraving/relief cuts the Z axis will slowly cut deeper and deeper. I checked the ball screw and there is minimal backlash. Checked the velocity settings and thats all fine, checked all the bearings and they seem to be as tight as they were when i first preloaded them. Checked everything with a dial gauge and and all looks good.

As far as I can tell there seem to be no missing steps and there is little to no load on the machine when its engraving due to the fact im using a 0.01mm V bit.

The collet is tight and there is no slippage at all in the tool.

I am kind of at my whits end trying to work out where the problem may be and coming up with things to check so if anyone has any ideas I would love to hear them.

Regards
B