As per this post 3D Print: New Reinforced Corner Mounts - Hardware - Maslow CNC Forums
I’ve printed and installed these new anchor point mounts, with a significant improvement in fitness, from 0.489 to 0.55.
I reckon that’s there’s probably another >2mm total flex (mostly across the width of the frame) for me to deal with. But for now, I’m good with just passing calibration on my modified frame.