It seems unlikely to be the problem, but I would check that the ballnut is concentric to the screw. When the ballnut rotates does the ballscrew move up and down a bit? If so you should tweak it until it doesn't.
Good to hear the X-axis is working well, you've got 10m/min on a RM1610 ballscrew - can you remind me what length the screw is please, 1.5m?

Quote Originally Posted by Tenson View Post
I do wish I didn't bother with a rotating ballnut on the X axis and just had them on the main gantry.
So do I...