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.

That a single ball screw will wear is the same as using a radial ball race and subjecting it to axial loads instead of using angular contact bearings designed specifically for axial loading.

I assume that the tracks of a high precision ground ball screw are super hard and so can better resist the end loads generated when the screw is driving against a load, so as the difference is then only the hardness of the track ways, making a cheap rolled ball screw and having the ball track ways super hard too without grinding them should prolong the life.....theoretically......the difference in quality is the rolling process that injects a tolerance factor for pitch accuracy over a distance.

A single nut ball screw will eventually have backlash no matter how expensive it started out at.......we are really using the same principle of the deep groove radial ball race to resist axial loading and as soon as a smidgeon of wear occurs, as Thomas showed in his drawing on post # 58, you get backlash.

Having a "bit of backlash" is like saying "I'm a bit terminally sick, and that cannot be tolerated in any form ever..

Applying the same design as a deep groove ball race, you can to some degree use them as replacements for angular contact bearings provided you have two that have some means to press them apart to simulate angular contact bearing characteristics........they won't be good for radial forces after that, but for a while they will track accurately and act as radial/angular contact bearings lightly loaded.

That being said, the same applies to the ball screw........have two ball nuts with a means to press them against one another and you have a means to eliminate backlash........it just depends on the hardness of the tracks during manufacture for longevity of duty cycle.

If the tracks of both rolled and ground screws are of equal hardness then you will have equal wear rates and so can use double ball nuts to eliminate backlash.

When wear occurs it's not for the full length of the screw, but probably more in the centre or wherever the most work is done, so you have a screw, rolled or ground that will have backlash in the middle and none at the ends etc.

Having two ball nuts with a resilient coupling will take care of the tight and loose spots without jamming dead tight if they were merely backed against one another with hard screw pressure.

For hobby use, ground screws are like "Gilding the Lilly" without realising the full potential of the grinding process, but rolled screws with simple resilient anti backlash measures applied can make a mongrel into a thoroughbred without breaking the bank or spending the kid's inheritance.

BTW, if undersized balls were fitted to the rolled nuts in the beginning you would have a ball screw with undue backlash from the beginning, but progressively occurring backlash over time is an indication of either wear in the trackways (most probable) both for the screw and the nut or the balls.
Ian.