I had some spare C-Beam aluminum frames that I wanted to use to make a mini 3d printer. I designed a 3d file to figure out how to lay out the XYZ axes and how to connect them together.

 This structure requires the use of aluminum angle brackets and hex flat head bolts:

 However, when tightening, the bolt head was worn out, after trying again many times and still had the same problem with the connection not being secure, with slight play. I redesigned another right angle bracket by removing the protruding edge.

 I proceeded to put them together.