How do cold pulls work? The articles on the wiki and academy don’t really make sense, so I’m wondering how to actually do a cold pull.
A cold pull is needed when the nozzle is contaminated. Some burnt plastic, dust accumulating, having residue of a high melting temp filament remaining in the nozzle for a colder print… There are plenty of possible causes. A recent post featured a literal bug in the PTFE which would have led to a nozzle clog…
If the clog is so severe that it can not be resolved by pushing it out in normal extrusion, we need to pull it back out the other end.
For this purpose, we insert filament and melt it in the nozzle in the hope that it gets a good hold on the clog. Once cooled to somewhere between 100 and 140°C, we pull it out. There are a number of means for this. With the auto-cold pull, you need to be careful not to put it back in, i.e. best to cut of the tip of the filament afterwards.
I myself always go straight for the hot hex wrench cold pull (Nozzle/Hotend Unclogging Procedure for X1/P1 | Bambu Lab Wiki) and do it a number of times in a row. It is quite effective also when recovering from a bad heat creep.
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I typed “give me a video showing how to do a cold pull (3D printing)” into Google and got some links to Youtube videos. You can Google the same and click at the links to watch the videos.
Remove the nozzle. Never do this on the printer. Forces required can damage mechanics.
Take the 1.5mm Allen Key that came with the printer, heat it up with a Lighter, and jam it in to the filament that’ll be visible in the top of the hot end you already removed from the printer. Wait 60 seconds for it to cool down, then pull. It should yank the filament that’s in the nozzle out of the nozzle, along with any debris that were plugging things up.