Michael but if I've read your post's right to are going to have a X-axis between 750 cm to 1500 cm on a unsupported rail

I would think you are asking for trouble??

I am no expert and have not completed a machine yet but I know how little force is required to bend ( make the ball screw arc) and your asking it to support around 25kg with out any movement

sorry but I think you will have to rethink it


James