Primo Build - unable to align after adding core

  1. Diagonals measured the same within 1mm (which is about all I can eyeball holding a tape and closing one eye, aligning sight along edge of corner).
  2. Trucks for both x and y measuring within 1 mm of each other
  3. Put on core, all bolts loosened, and made sure to back out the bolt a bit also to have gap ā€“ since the threads themselves have some holding power.
    Measurements: measurement take of the Upper Y rail (right side of core) is smaller than lower Y (right side of core). Difference ~6mm.
    Tightened core tension bolt for Y trucks - the one near the upper Y side. Difference ~4mm. tightened until there is serious resistance felt, but had to stop. Still about 4mm difference.

I am at a loss. Iā€™m thinking of just wiring up limit stops, and the steppers should take care of aligning everything so long as I re-home the machine every time the steppers are turned off and lose their position, right?

I have some experience 3D printing, and 2D laser cutting, but no CNC experience, etc.