I disagree with Torston. Your design does in fact work to eliminate backlash. I firmly believe that a spring need to be in the design when using non-precision screws, or any screw in an environment that a speck of dust can find its way to the screw. I use a similar setup, with an aluminum block tapped to 15/16-16, and a bronze block tapped the same. My ballnuts thread into them. There are SS guide pins that run through the bronze block for alignment. I set the "preload" (to me, that is the tension/compression between the nuts) to about 50 lbs. As long as my machining load is less that 50 lbs, I effectively have no backlash. Without the springs, an imperfection in the ball screw, or dirt in the ball screw could cause binding, or require a lot of torque to rotate the screw.
It truly does not matter wither you compress the nuts together, or push them apart. Hell, when the nuts start to wear, then use a mechanism to push them apart. Just like new!
Rob |