OK I bit, I don't do fabricating but I saw Ernies' "Z" square and use a cast "ground inside" one (only 8x8") for machining often, So I just bit....
Went to the neighbors Wednesday and snagged 5 shorts 1 1/2"sq tube, gonna make (2) 18x24x30 squares....
Tacked the first X,Y and Z and tuned it (brought the good hardened Stanley framer from home, which is right with my 18" engineers square).
Everything good, cut the "Z" supports too quickly, (some gaps), lightly tacked supports (once), and all is still good....
Welded out!!! Too much filler needed on the "Z" supports and everything above pulled, A LOT :-(
Sawed off above the "Z" supports (looks goofy but at least it's right).
Did the 2nd the same but cut the supports longer and close enough for a hard melt bead tack (no filler).
Better, X-Y (tunes easily), X-Z (dead on), Y-Z (- 1/64" in 30") I'm very happy!!!!
Neighbor shows up today, (got his deer), sees the squares, says those are neat! I said you supplied the steel, he says "again", I said "yep".
He took the second (best) one and left saying "it's worth 15 lbs at best and no roasts".
At least I know where to get it if I need it.
I don't know how fast Ernie builds them, but it took me a good bit of the day...
Matt