Take one of the 12” steel plates and cut out four 4” triangles to be used as a gusset at the four corners of the frame. Cutting ¼” steel plate is very difficult if you don’t have a professional machine shop. You might want to have it done by a professional. I originally thought that my 14” cut-off saw would do it, but I was wrong. I ended up using my trusty 4 ½ inch angle grinder.

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