[QUOTE=handlewanker;1630692]Hi no matter what the cost of a hobby machine, if it has backlash due to cheap single ball nut screws from day one it will only get worse, and as backlash is not tolerable in any form whatsoever.......who ever heard of programming out .005" of backlash due to a worn screw.
Having a "bit of backlash" is like saying "I'm a bit terminally sick, and that cannot be tolerated in any form ever..
I congratulate you on your dedication to zero lash, but if we all insisted on that kind of accuracy, there would simply be no such thing as a hobby machine and companies like NOOK and THOMSON would be out of business. Sort of like saying " Anyone who cannot afford a Rolls Royce should just walk to work" As far programming out backlash, for straight linear moves it works fine. For circular interpolation it's trickier at the quadrants, but I have been able to keep my circles round and to within 0.001". If you want to get to 0.0001", then you will have to buy that Rolls Royce machine.
Getting back to the original poster's question, I think most of these companies producing low cost rolled screws probably use undersized balls to be sure that they will fit within the manufacturing tolerances of the screws and nuts. For an owner with a little time to spare, trying larger balls may solve the problem, but if you feel any tightness or binding you will need to try a smaller ball until you find the proper size. It's the kind of fiddling that an owner can afford to do, but would be prohibitive for a manufacturer. The double nut modification can solve the problem as well, but there are usually issues of space, mounting and loss of travel to contend with.