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Odd behavior when spool is empty  

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mire3212
(@mire3212)
Member
Odd behavior when spool is empty

I’m using an MK4 with MMU3 and everything works great except if my spool runs out mid print. 

It leaves a section of filament in the PTFE tube between the MMU and the Nextruder, requiring me to remove the tube and pull the filament out.
From what I understand, what it’s suppose to do is retract the filament towards the buffer, move the MMU selector head and then bring the filament out maybe 1-2 inches (2-4cm) to remove what’s left. 

I’m not sure why it does this or what parts may be necessary to inspect, but I’m hoping someone here can help out. 

I did make sure to configure the SuperFINDA, and that seems to be working just fine (since it knows the filament ran out), so I’m wondering if there’s something wrong with the filament sensor on the Nextruder?

This topic was modified 3 weeks ago 2 times by mire3212
Posted : 25/05/2024 10:07 pm
mire3212
(@mire3212)
Member
Topic starter answered:
RE: Odd behavior when spool is empty

Update: I tested the calibration of the Filament Sensor (the one in the Nextruder) and it’s fine. It was already working (otherwise the printer doesn’t work at all) so I doubt this is the issue. I did re-calibrate it anyway, so I’m still trying to understand why filament gets left in the PTFE tube. 

Posted : 26/05/2024 4:29 am
Zwirbel
(@zwirbel)
Member
RE: Odd behavior when spool is empty

I also don't understand how this is supposed to work. It happened to me only once, and the only option I saw was to cancel the print and start will a fresh roll of filament. However, I haven't had time to test this properly and figure out, how it is supposed to work.

Posted : 27/05/2024 8:05 am
hkruse
(@hkruse)
Active Member
RE: Odd behavior when spool is empty

I have had an end-of-filament situation once, and it worked fine. Once the end of the filament had moved past the FINDA sensor, the sensor detected that condition. The print paused, the filament was pulled back until it had cleared the selector. The selector then moved out of the way, and the filament was ejected to the front. The printer then waited for me to remove that filament and load new filament into the same slot. After that the usual "purge more?" dialog that also happens without the MMU, and the print continued.

If for you the filament got stuck in the tube between the MMU and the extruder then this is probably because the end of the filament was bent too sharply. Keep in mind that by the time the MMU detects the end of filament, the filament has already completely cleared the tube leading into the MMU, the pulley gears and the little tube leading to the selector. The extruder gears then need to push the end of the filament back through that path so the pulley gears can grab it, which won't work if the end is bent too sharply.

Posted : 27/05/2024 2:07 pm
mire3212
(@mire3212)
Member
Topic starter answered:
RE: Odd behavior when spool is empty

I don’t see any oddities on the extracted filament that might lead me to think this is the cause.

There is some sign of the extruder gear “rubbing away” part of the filament, implying that the extruder was slipping and unable to move the filament. This is also consistent with my experience in having to remove the filament; it feels stuck in the extruder and takes a bit of force to remove (not lots, but enough to be noticeable). 

Posted : 28/05/2024 1:50 pm
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