Luke11CNC Build Log ,I'm so naïve

[Jonathan]

Yes the Gantry will more than likely twist at the point where the sides meet cross brace at one side but the Ballnut is attched to the side so will twist against the screw unless the screw roates the same amount as the gantry twists.

No, as the gantry sides will not twist at the point where the ballnut is mounted. Looking at the machine facing the Y/Z plane from the top it's cross brace, gantry side, X bearings, X ballnut. The gantry sides will twist between cross brace and X-bearings, but not much at all if any between the X bearings and ballnut as the bearings fix it. The twist will be tiny as the sides are very thick/strong aluminium plate. The same is true for machines configured like ours - the gantry 'ends' have the ballnuts mounted roughly at the same level as the gantry, and the X bearings provide support between so there's nothing to twist the screw. If the X-axis linear rails were not there then yes the screw will definitely be twisted, but that's just silly anyway. Imagine resolving each of the forces, any force not parallel to X that could cause twisting must appear as a contact force on the X-bearings and thus prevent twisting as there should be no clearance in the bearings.
In either case if there is any twist on the screw it's going to be a tiny negligible amount and the extra force that would apply is surely small compared to say the force from screw whipping.