So after the successful kerf compensation and the reminder that thickness is important, the resulting construction fixture was much better than the 3D printed version but sadly still not good enough.
The holder for each of the four sides worked well – I’m especially happy at the fact they can grip the panel with just enough force to hold it in place. This was a super encouraging result of the kerf compensation math. If I were a tiny bit off one way, the side piece would be loose. If I were a tiny bit over the other way, the side piece would be gripped too hard and cause scratches. (Or wouldn’t fit at all.) Feeling the pieces fit “just right” was very satisfying.
The problem came from the multi-piece articulated design. Even though the kerf compensation was close to exact fit between two pieces (+/- 0.1 mm) the overall dimension of the fixture depends on perfect alignment of acrylic pieces across assemblies of 5-10 pieces. I was close, but each little error adds up and the resulting box built by this fixture has errors of up to 0.5 mm. Easily detectable by the eye.
And, as should be obvious from the pictures, this fixture took a lot of work to assemble. Generally speaking, it is OK (and actually fairly typical) for mechanical design of a fixture to be more complex and time-consuming than the mechanical part itself, so the complexity itself is not a problem. The problem is that I have yet to learn all the ins and outs of designing the fixture so the desired tolerances can be maintained when my fixture starts getting complicated.
But that’s OK, learning from experiences like this is exactly why I’m doing it.