filament bumps into something about 1 cm into the extruder (MK3S)
 

filament bumps into something about 1 cm into the extruder (MK3S)  

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maxim.h
(@maxim-h)
Eminent Member

In general everything is working great. Been printing a lot on this MK3. When I used to insert filament it slid in easily and the printer loaded filament automatically.

But one night when I loaded the filament it felt like it bumped into something about a centimeter in. I jiggled the filament around and it managed to get past whatever was in the way and printed. Since then I basically have to do that every time I load filament. I have tried blowing compressed air in…I don't see anything amiss through the side opening…sigh…

Any idea what is causing this and how to fix it?

This topic was modified 10 months ago by maxim.h
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Posted : 25/09/2019 6:21 am
Tim
(@tim-m30)
Illustrious Member

The filament sensor uses a ball bearing about 1 cm down the path. The filament displaces the ball and the ball pushes a lever into the path of an optical sensor.  This is one reason Prusa recommends a diagonal cut on filament ends.

It is always wise to get more than one opinion......
Posted : 25/09/2019 7:09 am
maxim.h
(@maxim-h)
Eminent Member

Thanks for the description. I have been trying all manner of angled cuts but none make it any better. I found this page explaining how to disassemble the extruder to get at the filament sensor mechanism. https://help.prusa3d.com/article/43mduc4zdn-ir-sensor-troubleshooting  

It is intended to solve a problem other than the one I have, but at least it describes how to get in to the steel ball assembly. 

I bought this printer assembled…what a blessing to get an excuse to take it apart.

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Posted : 25/09/2019 7:35 am
Tim
(@tim-m30)
Illustrious Member

Yeah, before taking it apart, try looking down the path and see if the ball is actually in the way. Or watch the LCD (select the stats I think); and see if the filament sensor is working.  Doing a disassemble to fix something that isn't broken seems severe.

It is always wise to get more than one opinion......
Posted : 25/09/2019 9:57 am
Robert-mm200
(@robert-rmm200)
Noble Member

No need to disassemble the MK3S extruder.

The filament sensor cap is attached with one screw on the top, next to the filament insertion hole.

Take that off and the filament sensor circuit board is exposed. It also has one screw.

Posted : 25/09/2019 5:05 pm
maxim.h
(@maxim-h)
Eminent Member

Thanks for the suggestion to simply remove the filament sensor cap and sensor board and examine things. I did try removing them a while back, but I will do so again.

I agree that the less I have to take apart, the better.

I have found that when the filament is unloading the glob on the end of the filament gets a bit stuck and I usually have to yank it to get past the same point (as where it tends to stop on the way in). All this makes me wonder if the recess that the ball fits in might be a bit tight. Traditionally this is where one would spray the heck of of "it" with WD40…ah, those were the days…(and no, I'm not going to do that)

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Posted : 25/09/2019 10:44 pm
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