I finished my torsion box assembly table and hoisted it on my frame. Unfortunately, it is not flat. It is about 1/16'' off on one diagonal.
The torsion box measures 4 X 6 feet. The skins are 3/4'' MDF. The web is 2 inches deep MDF.
I'm not sure exactly where I made my error. I had to make my reference frame by shimming boards on my basement floor. Nothing was off 1/16'' then, but maybe in the process something did get that much out of alignment.
For the short term I guess I will just just live with it. As the wood whisperer points out, you don't really rely on the assembly table for squareness. You rely on your joints, so being a little off doesn't matter. Of course, 1/16'' is really not a little.
If (or probably when?) I make another, I can use my current torsion box as a starting point. It is much flatter than my basement floor, and as long as I fix the 1/16'' flaw for my new reference frame, I should have better results.
However, before I do that (actually, it won't be for a while), I wonder if I can fix the current torsion box with another piece of MDF on top? I wonder if I could stick a few shims in the low spots and just glue or screw on another piece of MDF and have a flat reference area?