Thanks for your reply

Yes I thought that the y axis plate may flex to much, I could make a structure from 20mm box section steel which would be say 70mm thick in total and then fly cut the surfaces flat for accuracy but this would obviously be heavier, or just put a few box sections bolted to the back of that plate. As for the Z axis I thought about doing it the way you mentioned but does that then make the whole thing to heavy for the z axis motor to move as it has the weight of the rails + plate + motor + spindle or is it fine as the pitch of the screws if quite fine so it does not load the motor to much.

can I ask what sort of feed rates you can get with those drivers?