M500 not saving calibrated M92 X,Y, Z values

[brent113]

I find measuring backlash easiest to do with the laser head with a bunch of circles. Between each circle I incremented the backlash compensation.

A350 - Not printing perfect circles

A better circle test would’ve been one where the laser travels in a circle, instead of what’s in the picture - an image of a circle drawn horizontal lines. The horizontal line method has the Y axis moving in the same direction, so the backlash is hidden. The X axis does appear to not have backlash, but it’s hard to see because of the adjacent partially overlapping passes. A single line would be clearer. Here’s when I did this with varying backlash compensation settings, you can see a distinct…

If nothing else, it better be the same on X and Y, since they should have the same geometry. If they don’t, maybe check the carriages for looseness internal.

Normal backlash is very small on this machine, around 0.02mm. That linked thread was after a crash, I got 0.12mm in X axis, requiring hardware fixing.

I’ve found backlash correction leads to issues for large values, there’s some bug somewhere but I can’t find it. Results in accumulated drift over long times, causing a few laser projects of mine to fail. More on that, here: Long Laser Project - Position Drift in X? - #21 by brent113, if you are interested in giving it some thought, still an open issue to me.