Fixed z axis to gantry design

[routercnc]

The design in the picture is a nice design and would work well as it uses a fixed gantry and moving bed, but if you want to have a fixed bed and moving gantry then I think you will run into problems if you make it like that.

The gantry is quite tall, which it needs to be to allow enough Z movement. When this becomes a moving axis you now have a long cantilever from the bearings at the bottom which is difficult to brace without having widely spaced X axis bearings and significant loss of travel. Getting the stiffness back could be a problem as the geometry is now against you.

Personally for a machine used mostly for aluminium then I would either go with the fixed gantry and beef up the gantry support a bit more than the one in the picture, or go with a conventional moving gantry with Y axis and then Z axis. I think it will end up stiffer and more effective than your in-between design.

Nema 23 would be fine, and 1605 ballscrew works OK (that's what I have), but many choose 1610 and then drive it with a 2:1 reduction pulley or 1:1 pulley depending on what they are cutting.