Questions about milling machines with linear scales

Slop and play in a mechanical system can never truly be eliminated. Here is where the law of diminishing returns starts to rear its ugly head. Pick all of the low hanging fruit, and hopefully the results will be good enough. From there it gets harder/more expensive to improve, and you will pay more for smaller and smaller increments of improvements. You may need to resort to scraping ways, improving ball screw mounts (the mounting bearings for screws are notorious sources of slop), higher precision ball screws (less worn).

(At some point you might be better off cutting your losses and getting a better condition machine, or just decide to live with what you've got.)

I had a badly worn (1938) manual Bridgeport that I converted to CNC by adding a ballscrew assembly. Everything had some amount of spring to it, but there was a lot of wear in the ways that made it possible for the table to rock in several different ways. I finally found a much newer R2E3 Bridgeport (BOSS8) machine that was built for CNC from the ground up. Also, the ways are in vastly better condition. Well, there is SURE a difference in accuracy of machining! The old machine was tolerable, the new one is excellent! I also made a MUCH more compact CNC retrofit in the existing servo cabinet on the right side, and completely removed the electrical cabinet on the back of the base.
Jon