4' x 4' x 8" Router Build

[routercnc]

There is probably a theoretical small gain with the rails set such that the line between them is somewhere around the centre of the overall L shape, and they are furthest apart. But I can’t help thinking you would loose more in the box plates around the outside with vibration and flex. Personally I would put the lower rail directly below the upper so they are close to the front where the Z axis is.

Also the top and bottom plates look a bit thin. 20mm is ideal then the closer plate on the back is less critical. You can delete it, or if you still want it then 6mm would be fine.