Quote Originally Posted by John S View Post
Check the Z axis for freedom and binding and also reduce the acceleration and velocity in motor tuning.
I think it's been working ok on same piece of code then just happens John so I kind of ruled missed step out has it would happen pritty much all the time if overtuned.? Or at least move some random amount.?

The little 3020 chinese bag of shit that I have here had a similiar issue in that it would change direction on its own and other crazy stuff like move down too far or not stop moving when expected. Turned out to be cheap nasty wire to Z axis motor changed it and it's sorted.

Seen has this is a chinese machine and possibly made in same place then it wouldn't surprise me if it hisn't a similiar issue.? Certainly worth a look or changing the wire for sake of £10-20.?