Sunny Buxton in Derbyshire Wayne.
Art and Hood have suggested ways of measuring the backlash, which I have yet to do.
Considering, like you say, the amount of backlash, I expected to be able to feel it in the machine, but rocking the thread from the end does seem to move the zaxis instantly. this leads me to want to investigate the stepper/thread interface. I seem to remembr reading years ago that things like a short length of tubing can be used to form a crude clutch in case of a crash, and I am wondering if there is something like this that has malfunctioned. Either this or there is some direction change timing problem like you say. Also there is the problem of apparently losing steps quite badly,...I'm starting to think mechanical rathr than electronic.
thanks for your help.
Where are you Wayne?