Been making up a shopping list for a moving gantry I want to make.
Aim is 640x440x125 work envelope to machine wood and aluminium. Mild steel would be nice too but I'm not sure what standard of build is needed for that and I'm not about to make anything extreme in weight or budget.

My first hang up is not being sure on what size rails for the Z axis. X and Y are to use 2 HGR20 rails each with 2 blocks on each rail. For the Z axis I didn't know if I could skimp out a bit and use MGN15 or use only 1 block on each rail.

Much of the frame is 100x100x5 box section that I have hanging about. Going to have it surface ground before installing the rails