Q: We have a lathe machine with GSK 928TF CNC control, sometimes there is error of the Z axis, but the X axis is fine and stable, and we have checked he coupling, bearing, ball screw nuts and carriage, all is in good condition, even there is problem the error should not be exceed few mm? Why?

A: Are you using stepper motors, it could be step lose problem, try lower the speed.

GSK928TF Specification:

http://www.cncmakers.com/cnc/controllers/CNC_Controllers_for_Lathes/GSK928TF_CNC_Control.html