@Greg Holloway ,I am still trying to see if the set square I have isn't square, so I have a new one on order, but I can't move the bottom of the z-axis extrusion far enough forward for my square to say that it was square with the bottom plate. Does this mean that the corner extrusions aren't properly aligned? The table I am building it on is probably not perfectly flat. Any construction hints would be greatly appreciated. Thank you. update: My set square came in. After loosening all of the extrusion bolts again, flipping one extrusion around and using the weight of the frame to align extrusions, I think I got it!