: I've put up another video. This one shows setting up forms on in
: internal strongback using pre-cut spacers. This is a quick and
: accurate method for setting up the forms.

By essentially placing a jack on only one side of the strongback going from one end to the other, I'm surprised you don't get lateral bending the more you jam the single side wedge - same for downward bending of the single top wedge( but to a lesser degree because of the much greater depth). Possibly the effect would be more noticable with a more flexible (say plywood) strongback.
Individual form adjustment would also be very touchy.

Anyway, take the hammer out and hit that sidewedge one more time and tell us if the cornering gets any better, heh heh.

**
Although I use a related process, possibly a simple modification to what you are doing would be to use saddle spacers and place the wedges on each side only. That way the stress is symmetrical, just as effective (as 2 spacer pieces still are used), and needs a much simpler single central spacer(the wedge will slip against the form - the form won't move doing this). The saddle spacers would be quite easy with wood, rope, webbing or 2" wide stapled fabric for the part over the top - ie two 11 1/2" (or whatever for ply thickness) x 4" pieces of plywood on each side with the scrap stapled along the top edge so it straddles the strongback. Then drive the wedges with approx the same number of taps. Symmetrical strongback expansion /spacer compression.
anyway, an alternative.

-mick