Thanks for diagnosing this.

Thats not belt tension, it looks purely like an extrusion issue.  So look at partial clog, feed gears- tension, ptfe tubes, confirm the extruder thermistor is reading accurately etc.  Basically anything that can cause problems with extrusion.

Thanks. Especially the feed gears tension I'll have a look into. I had to clean the filament sensor on the printer (mk4s) and needed to remove the gear cover for that lately. I'll let you know.

I recently got some issues with an error pattern, that I am unable to match to a cause (yet). Maybe somebody else has seen this?

The pictures below show two different models with two different types of PETG filament from different vendors.

Here is what I see:

• The surface on outer walls gets uneven, develops occasional spots and cracks easily.
• The first couple of layers of a print usually are acceptable, but with increasing height, the problem appears, but doesn't seem to get worse as higher it gets.
• There are occasional breaks in the pattern on bigger prints which then return to the normal quality, before decaying again.
• Especially the model 02.07 has been printed with the same print settings before without problems.
• Other models seem to print fine (with different filaments), but these do not include straight walls or are of significant height.
• I was guessing the belt tension might have caused this, but the problem is persisting after re-tensioning.

I take suggestions of what to look into.

thx, d.