Looking good! I might have to give this one a go.

 

Im new to the forums and I am just in the planning stage of building my first machine, but I like the idea of the quad X axis rails. If you have the room on either side of the acme screw you could build a truss between the upper and lower rails, cross bracing like the lacing on an offroad buggy frame. That would add a ton of rigidity.

 

can you share plates Drawings