Quick, easy, cheap DIY corner clamp (jig) for wood or metal work. I'm too cheap to buy ready made ones. This is made from a couple of dollars of 6mm plate steel purchased at a hardware store. I found a trick to keep it really square, 90 degree angles so work pieces sit solidly in place. I did not use angle iron for the edges (they have rounded "corners").
Tip: Before using the corner clamp, rub an old cutting or grinding wheel over the surfaces to knock off anything from prior jobs that will keep the work pieces from laying flat (like BBs).
Welded at about 62 amps with Kobe 6013 2.6 mm rod. DC welder with electrode positive. No, I'm not a pro welder, just a weekend welding warrior, home DIY fixit guy. Comments on improvements are welcome.