Pardon if this question has been asked before.
I have watched a bunch of videos on YouTube recently about building a torsion box workbench top. Various kinds of tops, various materials. It seems like most of them are more-or-less slapped together with little consideration for the concept that a torsion box is meant to be FLAT. Dead-flat without sag, bow, warp or any other malaise which would throw off subsequent construction. It should be a reference surface. The concept is there, the capability to produce such an end product is available, but the method leaves me shaking my head and wondering how it's possible. I never see any straightedges, winding sticks, or even a good sightline.
So the question - what does one do to make a torsion box flat? It seems to be an offshoot of the adage that you need a workbench to build a workbench; similarly you should have to use a flat reference surface to build a flat reference surface, no? I can't trust a concrete floor to be flat; I know for certain it isn't. I can't trust a 27" x 40" tablesaw top when my torsion box is four times that size and will sag just from it's own weight.
Or, is it just not worth agonizing over and I should just hope for "flat enough" and be done with it?