stepper motor stall?

[Doddy]

from your description I don't see any thing wrong

I quite agree. Thanks, Richard, for the reply. It does sound as though the steppers are underdriven... but I can't see any cause.Not sure about sw4 - you do say it stalls when operating so half-current setting shouldn't come into play. How warm are the steppers after a protracted period energised?, if not hand-hot then try upping the current setting on the drivers. After that I'm out of ideas.

You've not got any silly-long lengths of cable in the system?, no dodgy fine gauge cables to drop the supply voltage at the stepper driver?

Ah, one point - you still have the trapezoidal lead screws... ah - they will put a larger load on the steppers than a ballscrew... but you do use powerful steppers. Nope, I'm out of ideas.