Intermittent under-extrusion, strange cold-pull shape
I'm experiencing intermittent under-extrusion on my MINI+. I'd get (very roughly) around 8 seconds of normal extrusion and then 2 seconds of severe .
I've had this issue in the past, back then I've just changed the nozzle which fixed it. Since then, I had no issues, until a few days back.
Fillament type is PETG (I only print PETG) and nozzle is 4mm.
What I've tried:
Changing the nozzle
- I've made sure it is tight and that there is still gap between the heater block
Cleaning the extruder teeth + making sure it doesn't skip
Cold pull
- I did it with PETG, as it is my only fillament
- It has fairly strange shape (the photo of white filament in attachments)
Changing the PTFE tube (link) that goes through the cooling block
- previous PTFE tubes had heat damage and slightly deformed bottoms (photo in attachments)
- last one even had a bit of filament stuck in its bottom part
The first time this issue manifested, it was after I lost power, so the fan cooling the metal cooling block above the heat brake and heated block stopped and the whole cooling block got fairly hot. Still, I print at 225 - 230˚C, so PTFE should be able to handle that, but somehow the tubes end-up damaged.
I've thought that maybe the cooling block fan is not blowing at full power, but if that was the case, the PTFE tube in the cooling block would work for at least a bit, but the very first layer test after change already had under-extrusion issue (photo in attachments).
Still it seems that perhaps the heat brake isn't fully working. I'm thinking of maybe replacing the fan (link) (is it a standard 40x40x10 non-RPM controlled fan, found in PC part stores?), as that is quite simple. Beyond that, I have no idea. I was very surprised how suddenly the issue appeared. The PTFE tube is sticking out the right amount there should not be a gap anywhere, I'm a bit baffled by this.
