After I tightened the X-axis belts by three teeth, most of the ringing went away. Not all, but enough for me to look elsewhere for the next improvement. The obvious thing to do is to try the same thing with the Y-axis. It was also pretty easy to do but since the improvement was not as dramatic. I still have ringing on both X and Y axis but at least the worst of it went away.

While working with the Y-axis belt, something felt a little bit off. A few minor details didn't line up the way I would have expected. Pulling out the caliper confirmed the eyeball diagnosis: the Y-axis components do not line up.

I measured the distance between edge of chassis and edge of belt at the idler pulley sitting in front of the printer.

YPulleyWithout moving the caliper, I compared that distance with the equivalent in the back, between the chassis and the drive pulley mounted on the Y-axis motor shaft. We're off by more than the width of the belt.

YMotor

The first question: Is there an adjustment I should use to fix this? The idler pulley in front is pretty fixed in its place with no room for adjustment. This is also true of the motor bracket in the back. So the answer seems to be: No, there is no adjustment.

The next question: Is there a quick modification I can make to address this misalignment? There's no good candidate in the front - swapping positions of the idler pulley and the holding nut would just make things worse. In the back, we could try to flip the pulley around on the motor shaft, but the set screws were installed tight.

While I was debating how much force I should use before I risk ruining the set screw... I realized I forgot to ask an important question. This should have been the zeroth question, so to speak: Is this misalignment causing a problem?

Um... well, I guess it isn't the biggest problem at the moment.

So we'll leave this on the to-do list for now and revisit later.