Cold Pull
Hi everybody,
I’ve been experiencing frequent false positives with stuck filament detection (this happens on all five print heads — could this be a common issue?).
I suspect the nozzles may have minor partial clogs, so I attempted an automatic cold pull (which is a great feature, by the way). However, as soon as the cooldown begins, the display shows: “Takes too long, will skip soon.” After around 1 minute and 45 seconds, the nozzle temperature drops to around 36°C then heating to 90°C (I’m not 100% sure if it was 90°C), and then the filament is retracted.
This behavior occurs identically on all five heads. I’m confused:
Is this message a warning that the cold pull is failing? Or is it just an overly sensitive timer, and the cold pull actually completed successfully?
Could someone confirm whether this is expected behavior? Also, I’ve attached an image of the pulled filament — does this look like a typical/ideal cold pull result, or does it suggest a more serious clog? (The image is cropped, so you have to click on it to get full image)
Thanks in advance for your help and insights!
Best regards,
Floh
RE: Cold Pull
That picture looks like normal cold pull results to me. When I've had partial clogs when printing PETG-CF, you could barely see a spec of black at the very tip after the cold pull. Like a hair sized something. That was enough to cause all my problems & fix things after it got removed with the cold pull.
I really haven't paid attention to any messages on the printer while doing a cold pull in a good while. Just start it & walk away to do something else for a few minutes.
RE: Cold Pull
Hi Fallon,
thanks for your reply! I’m a bit unsure about the result of my Cold Pull – the tip looks more like a narrow, arrow-shaped point without a preceding cylindrical section. In most reference images I’ve seen, the ideal Cold Pull tip has a distinct cylindrical shaft (roughly the same diameter as the nozzle bore) that tapers smoothly into a sharp point.
In my case, there’s almost just a thin “string” leading to the arrowhead, with no visible cylinder above it. This makes me wonder if the pull wasn’t good enough. Do you have image of your result of automated cold pull?
Thanks again for your help!
Floh
RE: Cold Pull
No pictures offhand, but the tip on mine swells a bit, even on normal filament changes. The nozzle is slightly larger than the diameter of the filament. So if you heat it up & squish it in, it's going to expand to fill the whole nozzle, however much wider than the 1.75mm filament it is.
Really the tip is the important part. There is a little melting that happens upstream from the very tip, but obstructions there are much less common as it's wider. The area where it necks down from 1.75mm (plus whatever the clearance tolerances are) down to .4mm (or whatever size nozzle you are running) & the length of that small hole in the nozzle are where obstructions are going to catch & be a problem. High flow nozzles actually put metal bits through that wider part of the nozzle to get better heat transfer.
Take a look at some of the CnC Kitchen videos on CHT nozzles. Pretty sure you can't cold pull them.
RE: Cold Pull
Thanks so much for the help! 😊
After some printing, I think the nozzles are actually fine — the real issue was the temperature inside of the enclosure. I’d been running at 38°C ambient inside my enclosure, and I think that was causing the PLA filament being stuck.
Now printing with opened enclosure-door and finger crossed that the issue is gone now — lesson learned!
Thanks again, everyone!
Floh