Spent the evening trying different permutations of the ball-nut assembly and the best I can achieve on both axes is 10 microns. If this were a conventional manual machine I'd be overjoyed with 4 tenths of a thou! In fact the very expensive Swiss machines that I sell have a backlash from new of around 0.01-0.02 mm.

Anyway, the machine is running very nicely and the back-lash compensation on Mach3 is working well.

As I frequently say to my customers "it's a metal cutting machine not a grinding machine" so I don't expect nor want to machine to tolerances better than +/- 0.005. I certainly don't think it will be a problem in respect of climb milling.

More soon...