I have started looking converting over a manual mill to cnc. In my search I did find someone that didnt change to ball screws but he did mention that he has about .004 and .006 backlash in each axis. For hobby use and if you Setup the controller to make up for this backlash I feel that it should be more than feasible to do. Something that you do have to about is that ballscrews are around 90% efficient where acme is around 40%. I just means that you might have to buy bigger motors.