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.
Your pictures are not quite sharp enough to be certain but it looks like you could use a fraction more 'squish' - perhaps your nozzle has worn faster recently.
If your fan is temperamental first of all clean the blades and make sure there is no fine stringing clogging the hub then dismount it and carefully peel back the sticker on the back - drop just one drop of light machine oil into the back of the bearing and replace the sticker.
... and the short PTFE tubes do wear out every couple of years.
Cheerio,
RE: Intermittent under-extrusion, strange cold-pull shape
Your pictures are not quite sharp enough to be certain but it looks like you could use a fraction more 'squish' - perhaps your nozzle has worn faster recently.
If your fan is temperamental first of all clean the blades and make sure there is no fine stringing clogging the hub then dismount it and carefully peel back the sticker on the back - drop just one drop of light machine oil into the back of the bearing and replace the sticker.
... and the short PTFE tubes do wear out every couple of years.
Cheerio,
Hello, I'm sorry for the late reply.
I've done multiple 1st layer tests and I think the squish is set well enough. 80% of what is laid down is fine, it's just when there is the short "underextrusion phase", when issue manifests.
Nozzle being worn was my firs guess, that's why I've changed it.
On the PTFE tube, maybe the wear on it was normal. Glad I've changed it and thanks for assurance 🙂 .
On the fan maintenance, that is good advice, not just for this fan. I'll order replacement in case it won't survive the treatment, but I'll apply this bot to this and my other PC fans.
As for the issue iteslf, I've had 2 longer prints, where intermittent under-extrusion wouldn't be such a problem. On the second print, mid-way through, the issue stopped and hasn't re-occured since (though I've only done 2 or 3 prints since).
I don't know if some of the fixes above just took a while to take effect or if the issues is still there and will re-appear.
RE: Intermittent under-extrusion, strange cold-pull shape
I had once or twice that issue, the reason was some interference or loose cables, resulting in increased temperature reading from the thermistor - thus the software started to cool down the nozzle. Yet there were also temperature spikes that were triggering alarms and stopping prints.
Since I repositioned the cables next to the fan area the issue never happened again. So make sure that the cables are properly twisted on the whole length to minimize interference and separate them from each other by few milimeters.
See my GitHub and printables.com for some 3d stuff that you may like.