Struggling to align your 3D printer  20X20 Aluminium profile frame, keep it in square, and in the same time not have the frame corners clogged by connectors that limit your gantry travel by 25mm at each end reducing your printing area wiht 50mm is hard.
But it does not have to be hard, so I decided to design connectors to make that easy.

Connectors that you 3D print yourself, solid, perfectly aligned, keeping them 90 degrees corners sharp, and one of them is not protruding at all in the path of your gantry travel.  So using them wiselly increases your printing surface by 50mm (that is bloody 2 more inches) while keeping your profiles perfectly aligned and stiff.