Thanks for your welcome guys, been working a little bit in the dark until now I suppose.

Add at least two more vertical pieces on either side of the frame to better support the rails - it will make a huge difference.
I have a bit of a problem doing that because my ballscrews are under the machine, therefore the gantry is driven from under the rails.

Is that a 12Nm motor on Y?!
Yep, I did have a 4nm nema 23 but I thought it would be way underpowered for the 2510 ballscrew...

Your rotating ballnut designs are impressive, but I'm slowly realising that this might be more complicated than I first thought... I don't really want to go to rack and pinion now I have the ballscrews and nuts... however its driving me nuts!!

The design I first attached was found by just searching for "rotating ballnut" in google. I first liked it because its very compact and maximises the travel of the ballscrew, which is important if I want to be able to to cut 8' x 4'

I have 2 x 12Nm nema 34's for the X (1 for each ballscrew), do you think I would get away with the rotating ballnut I found with my motors?. I know with them being bigger motors that the moment of inertia is greater than say a 4Nm, but I plan to drive them with 68V 8A drives.