Tom, as usual, very helpful and enlightening.
It's not entirely clear what you are doing or expecting. Did you apply any smoothing? Do you think the high frequency stuff is real?
My goal is to improve positional accuracy. I would say it is within +/-0.001" now, if I sort of ignore the backlash. Overall, I am happy with it.
Regarding the "high frequency" stuff, yes, I think it is real. The data is the actual physical measurements from a 1 micron scale while stopped at various points. The noise is a cumulation of the rolled, not ground, ballscrew that has some warbles in it, the mechanical stiction and slop, and the scale reader head a bit farther from the ball nut than desirable. It is interesting to see, but not entirely surprising considering all that.
Smoothing? I don't know how I would smooth physical measurements without a grinder
My increments of my correction table could be larger than the 0.1" I have been playing with, but would that have a smoothing affect? Not really sure.
With the seemingly linear growth in error I saw when measuring to see if the mapping worked, I had a thought (mostly pay attention to the green line). It is so linear, at least to my eye, I was wondering if it could be thermal. We are in winter here in Missouri. I let the machine run the axis back a fourth a couple dozen times and re-ran the check pattern. From my thermal camera, I think the screw warmed up about 2deg C. And shazam, the error was positive instead of negative. Exactly what I would expect if the screw was warmer when I had taken the measurements that are in the screw map correction table vs. the cooler temperature the screw was when I did the mapping check earlier today. The error amount and the variability of it is more similar to the path of the mapping as well. Sorry, I realize I may be poorly describing all of this.
I have been wondering about temperature and when would be best to take the mapping measurements. My shop is climate controlled, but really cold or hot days keep my HVAC struggling to keep up. Summer is worse than winter. Realistic that I could operate as low as 55F in the winter down low near the floor and pushing 90F in the summer on the over 100F days outside.