The stiffening is a lot worse than other axis though and I can see the leadscrew is bent so I think I'm satisfied with that as the fault diagnosis. The gantry runs nice and free up and down the rails with the leadnut disconnected, so I'm happy that things are square. I can't feel any play.

I don't think I can do these other tests being mentioned because the leadscrew is bent, therefore it's going to make the leadnut not align with the bearing hole when looking through, etc. If it was the leadnut alignment that bent it, well I'm ditching that anyhow.

So what I need now is to spec and purchase a suitable replacement ballscrew system. Then once I have that I can do these trueness checks. I'm going to have to do them anyway to work out the mounting for the ballnut aren't I?

I'll start a new thread for the ballscrew.