Imagine having two pinions riding on two side by side racks. You tighten down the inside rack and leave the outside rack slightly loose. Push the gantry on one side (with the power to the motor on so they are locked) tight against the tightened rack. Now with a bolt mounted to push on the end of the loose rack you tighten the bolt to push the entire rack to pinch so to speak the tooth on the pinion. Sort of like having a double pinion that the two pinions are counter rotated to do the same. Bear with me I have a reason for this! The reason being to use helical rack and have a herring bone rack to alleviate sideways thrust. Or would it be better to just fix the inside pinion and rotate the outside pinion to pinch the teeth?

Or is the whole idea useless?