luckily no backlash, but it's a struggle to preload the play out of the bearings.
I later told my dad about them, and he said " Oh yeah ... I remember now, that's why they were in the skip ! " LOL

Anyway, all my parts come out the correct size, and no issues cutting profiles or V carving. the play translates to 'nodding' of the Z when cutting 3D stuff though, with the short stop/start accel's. I plan to add some angle and skate bearings to the outer edges to stop this. sort of additional X rails

Like I said, I built this just to test theory and see how things work. but it worked too well to start again, so I just used it as is.

I'm more than happy with the MDF bed , Z, and gantry. No movement / flex / twist at all . which was what I wanted to test.