Overextrusion plus holes/waves in vertical walls

This… I really don’t understand what I’m seeing here.

My Mini was printing really, really well. But the print quality took a sudden nosedive, and I’ve been spending my free time the last few weekends trying to figure out the root cause. I’ve gone through every 3D-print troubleshooting guide I’ve been able to find, but nothing matches what I’m seeing.

At first I thought it was my filament. But I tried switching to a brand-new, still-sealed roll of HIPS, and still got the same exact issues. I also tried playing with temperature, and the extrusion %, but didn’t really get anywhere. My next theory was that the extruder was slipping, but the hobbed bolt is clean as a whistle (I cleaned it with the wire brush anyway, just to be safe).

Hopefully, what I’m seeing is clear in the attached photo. The 10mm “Q-bert” cubes are coming out over-size, at about 10.5mm, at 100% extrusion rate (at 110%, I still get the same issues, but the size climbs to 10.8mm). The effect is most spectacular in thin-walled objects, but thick-walled objects have it as well. I don’t see how it could be a retraction issue, since the “tower” test print and the thin-walled boxes both printed mostly in “rings,” without any jumping around. Layer adhesion seems good despite the swiss-cheese’d vertical walls. Changing layer heights doesn’t seem to have any real effect one way or the other.

The “slant” of the holes in the thin-walled objects would almost suggest some sort of resonance issue, but I’m not seeing anything else that would bear that out-- layers are not shifting in X/Y, corners are good and square. It’s just… as if my extrusion rate were randomly varying during the print.

The only other odd thing is that, when I extrude in air, the extrusion I get seems much thicker than I recall it being when the Mini was brand new. That could be an illusion, though – I don’t have measurements of extrusion from back then. But where I recall the extrusion being thin and trying to curl back up around the hot end, now it’s quite thick and drops straight away, as if it were heavier. Could my hot end tip opening have worn out to a wider diameter somehow? I’ve never put any metallic filaments through this extruder – just HIPS, PLA, and some brief tests with LayWood and LayBrick an Nylon. But even if my hot end opening were wider than it should be, I don’t see how it would produce results like this.

I wish I had a good answer for you but I don’t. My best “free” advice is if your still in warranty even if your not call Tech support or email them with pictures. Can nozzles wear out, sure. Can they wear out in 3 months with just plastic, I don’t think so unless something was wrong when they were made. Nozzles are cheap and I think the Mini came with a .5 and you can purchase from Taz but if its defective it should be free.