Rigid bed mounting
I followed the Micro Swiss installation instructions precisely, but found that PLA had leaked out around the threads of the nozzle and around the top of the heat chamber. I removed what I could and then reinstalled everything to finger tightness while the hotend was at printing temperature.
Since I know that my vibration issues — the left-to-right vertical lines at least — are caused by the bed bouncing around on its springs, the most straightforward way to solve this issue is to remove the springs and mount the bed directly to the carriage.
I removed the springs and spring cups and added two nuts to each screw. The first nut was the stock thumbscrew, and I put that on top of the Y carriage. The second nut was a wingnut and I put that below the carriage. I am considering changing them to M3 nylock nuts, but those are very very difficult to turn. I could at least change the wingnut to something else because it’s hard to finesse it when the wings are out of easy reach.
After some puzzling-out of the levelling process, I ended up with this:
It took longer to type than to actually do.
Changing to a rigid bed has indeed removed my vertical vibration artefacts entirely. It has even reduced the diagonal ones a little bit, although they are still visible under a bright light. It must be a bearing or extruder problem.
I checked the bore ID of the block I printed last night and found it too small, so I reprinted it after calibrating my flow rate and it came out right on 16 mm. When installed into this block, the bushing fits easily onto an 8 mm rod, slides cleanly and smoothly, and has no play on the rod.