Hi Russ, I think Stewarts suggestion is very good. I rather think the manufacturer would be reluctant to release a machine that did not
perform as advertised given that the controller is Mach3 and any problems will be aired on the forum, the very same customers the
manufacturer is trying to attract.
There are articles on the net about stepper torque and microstepping, I have lost the links tho. The upshot is that deep microstepping
causes torque to decrease even worse than running them at speed.
May I suggest that you disable microstepping, most likely switches or jumpers on your drives, and rerun your test. Given that the z axis seems to be
the problem child just the z axis will do. The articles I have read suggest that half stepping actually improves torque, 120% of full step torque. Set your
drives to half step.
It may well mean your resolution is less than you would like but probably a good experiment which may help you to home in on the fault without
having to spend anything or pull things to bits.
Craig