I’m puzzled by the unload procedure (I have an X1C). Looking from bottom and up, we have the nozzle with the hot zone, then the cold zone, then the cutter, then extruder gears and above that it’s just the tubing to the hub, buffer or external spool.
When you hit “unload”, first the nozzle is heated (and we’re waiting for it), then filament is cut, then filament is retracted back to the AMS.
So here is the $10,000 question… just why did we heat the nozzle?
I tried manual unloading with a stone cold printer, by engaging the cutter lever with my hand, then pushing the retract button with my right hand while pulling back the filament to the external spool with my left hand. No problem (obviously).
The only reason for heating I can think of (apart from a brain fart) is that the firmware retracts 10-20 mm just before cutting (kinda like A very simple way to reduce (50% to 75%) poop losses), which indeed makes sense but I doubt that is what they are doing as they are so reluctant to adopt the suggestions in that thread (I will check this next time my printer is idle though). And anyway if that is the reason, it could be enhanced to only do so if the nozzle was already heated at all. This not only saves time, it also lets an unseasoned user unload the filament even though there is some hardware problem with heater/thermistor (which might be why the user wants to unload in the first place, for fixing the problem).
It needs to heat the nozzle both to make it easier to push the filament towards the nozzle when cutting (it is not a saw :)), and also because when it retracts, it actually extrudes a bit to make it easier to load a new filament afterwards. I believe this is the place Bambu could improve it (push more, then quickly retract more).
It might apparently work for you when cold but it will not be as reliable when you need to repeatedly do it hundreds of times when multicolor printing…
This makes sense, although it would be easily fixed by using a flush cutter, sending all of the movement upwards. Like the one you’d use in the old days for cutting the legs of a glass diode without breaking it.
Maybe, maybe not. If you look at the nozzle and what it looks like when it is clogged and you have to heat it ouside of the printer, you will notice that the filament sits flush with the top, making it impossible to push efficiiently inside by another filament. If you look at the nozzle when a normal unload cycle completes, this filament is pushed inward, so a new filament can push it in.
I don’t think this is important at all, I’m pretty sure BL tested those modifications community has developed and deemed them insufficiently reliable for general audience. You and I might be fine with occasional failure, heat creep or extruder tangle due to this modification, if it made the waste lower, but an “ordinary” user of the printer sometimes has no idea how it all works and wants to just print. Just look around about the questions people still have about “what those seams-looking-things are on their prints”
Just cut it manually when it’s cold and see, I’ve tried it and the cutter gets slightly jammed and doesn’t pop out. Probably because the filament is getting forced to one side and bent over slightly, which then pushes up on the blade and jams it. If it were hot it would just extrude a bit to make space for the blade. Well my theory anyway.
Like I said, I did try it and it didn’t jam for me. I’ll try it again just for kicks but you’ve guys have pointed out some valid reasons for the behavior so I’m fine now, thank you all!
