Building My First CNC Router, Looking for Advice & Other Info

[Neale]

If you look at the geometry of the Z plates and imagine both ways of positioning rails and bearings, you will see that you get better support of the moving plate through its full travel if you put the bearing carriages on the fixed plate. It feels wrong at first, but it's the right thing to do! The rails also provide a slight stiffening effect on the moving plate as well, although if you use the usual 20mm plate, that's not going to matter much.