I can't recall where I saw it, but it probably was a CNC machine, not too far off from a 3D printer, especially the coreXY design. My Emblaser I laser engraver is coreXY and works well as a general design.

The CNC machine I saw used square tubing but turned the x/y tubes 45? to place them in a diamond shape. This provided a stiffer frame in the vertical and horizontal as well as allowed for wheels to engage the edges of the tubing rather than the faces. Allowing for the lower forces involved in 3D printing, you would not need the two inch square tubing I recall from the CNC design, but larger is better. Thin wall is fine, saving weight without sacrificing rigidity.