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Filament Jam on Runout Eject  

Eminent Member
Filament Jam on Runout Eject

Hi all,


I have a MK3s (not +). I have only tried to use the filament runout function 3 times to use up the end of a roll, and every time it's caused a jam. I think what's happening is that the printer sucks in the last bit of filament past the sensor, realizes it's out and tries to eject. But then the end doesn't quite match the hole and it gets stuck.


I'm wondering if there's anything I can do to make this better. I suppose I could pause the print early and swap filament. Seems like I should be able to rely on the runout not to jam the machine though.


Thank you!


Posted : 03/04/2021 10:22 pm
Noble Member
RE: Filament Jam on Runout Eject

I have the filament run out sensor turned off, and knowing that I'm going to be using the end of a spool, I keep an eye on the print and simply start feeding the new filament in as the last spool runs out, this has worked great for me since the filament sensor has more problems then Carter's got little liver pills. 

The Filament Whisperer

Posted : 04/04/2021 7:03 am
New Member
RE: Filament Jam on Runout Eject

Following this post.

I have the same problem.

I wonder if upgrading extruder to mk3s+ will fix this? 

Posted : 04/04/2021 8:39 am
Noble Member
RE: Filament Jam on Runout Eject

I have seen the function work and not work. Seems to depend on the ends of the filament. In my case it seems to work in general but for some Sunlu spools I have had jams every time. When I look at the filament in those spools (more than 15), the very end of each and every one has quite a bend (I guess to keep it on the spool), which leads to the filament being misaligned with the ejection hole when the sensor triggers.

As to the question of the Mk3S+ being better or not, I don't know because I haven't upgraded — my printers are humming nicely without the + sign — but I believe they made changes to the filament path, which may lead to improvements. Having said that, the way the Sunlu filament was bent, I highly doubt that anything could handle this unless the sensor were placed in a different location.

Posted : 04/04/2021 11:04 am
Eminent Member
Topic starter answered:
RE: Filament Jam on Runout Eject

Interesting. It's good to know I'm not the only one with this issue.


I'm not surprised if it depends on the filament. I should try taking a cutting of filament from the outside of the roll where the curve radius isn't as severe and see if that works. For my prints I've always snipped off the little hook used to anchor the filament on the reel, I figure a 90 degree bend isn't going to work well going through the extruder. On this last attempt I even waited until there was less than a cm poking out and tried to cut an angle into the filament to help it get through the hole easier. Didn't work.


I don't often use this feature, but I wonder if adding a small piece of PTFE tube to help guide it back through the hole would work. I have no idea if that would fit, I haven't done any actual measurements or testing.

Posted : 04/04/2021 12:24 pm
Reputable Member
RE: Filament Jam on Runout Eject

I have seen this on my MK3s and also after the + upgrade.


The problem is like fuchsr said. The end of the filament often has a hook or sharp bent. Or isn't cut neatly. This the part that gets stuck.

When I know I will use the last of the filament I cut of the end just like you should cut the start of the filament when loading it. Cut it at an angle.


I have a made a small taper at the underside of the hole for the filament in the filament sensor cover. This have made it much better and only filament with a very crooked get stuck if I forget to cut the end.

Posted : 04/04/2021 5:45 pm
New Member
RE: Filament Jam on Runout Eject

Hi Baklin, can you share you modified part.


Posted : 12/02/2022 6:40 pm