Re: Bolt Together CNC Router - Newbie looking for design critique
Aluminium extrusion is not that flat either, but is probably a bit better than raw RHS.
You should plan on doing self leveling epoxy to make the rail mounting surface.
I'm not sure of the benefit of the angle pieces. A wider tube would be much much stiffer, and you can mount the the bottom of the tube in to the top of the cross tubes. You just tap holes in the long tube and bolt from below.
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)