Thanks! Hmmm…. I might try putting it all back together and cutting some more tests. The 20cm square I cut above is about 1-1.5mm off in the diagonals, so it’s fairly close. Maybe it will hold square better now with the new PLA parts I’ve printed. If that doesn’t work, I’ll try printing the new center design.
I actually did the extruder step calibration you describe, and it was pretty spot on (slightly under-extruding if anything). I’ve also dialed down the extrusion % until I could visibly see it under-extruding, and the parts were still a little over-sized; so I’m not sure what’s going on there.