i think a belt and ball screw may end up getting more complicated than r&p and i would rather try and keep it as simple as posable although i expect it would work.

Just thinking out loud...

If the z axis was mounted to one side of the y gantry and the same side as the rack and pinion and as close to the rails as posable would racking be such a issue?

At present the y rails are 360mm apart, would reducing that help and if so what sort of distance before racking would not be so much of a worry 100mm? 150mm? 200mm? im am just trying to get a good idea in my head of how much of a factor it will be.

many thanks