Jazz, now you're taking the proverbial! The frame doesn't swell at all with heat or moisture. The bed goes up and down in the middle instead!

I'll try chasing backlash and leadscrew float. However, the leadscrew is something like 1.25mm pitch so I'm seeing more than a half-thread backlash if so. I have anti-backlash pairs of delrin nuts on each axis so I'd be surprised if backlash were that bad but I shall check. The nuts are running on commercial stainless studding so while it's a bit smoother than BZP studding, I know that the nuts are going to wear.

Steps per - I did check a while back with a dial gauge (ever tried getting a magnetic base to stick to MDF?) and it was pretty much spot on. Those parameters should be locked in to the software and hardware so I hope they don't drift!

I'll also try a different cutter or two cutting a standard size piece and see what happens.