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Prusa MK3S - ghost filament obstruction problem  

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Glebiys
(@glebiys)
Active Member
Prusa MK3S - ghost filament obstruction problem

Hello Prusa Community! 

I own my Prusa for 3 years and printer over 30 KM of PETG filament with it. And it’s first time I have the problem.

My dad accidentally ripped hotend thermistor’s wires while cleaning after print failure. So I decided to replace hotend thermistor, hotend heaterblock and the nozzle.

the problem started after that. And I replaced to the new nozzle one more time, thinking it will help.

filament is going through the nozzle normally, you start the print and 40 minutes into the print nozzle stops letting melted filament through. The extruded gear makes clicking sounds (chewing on the filament) not able to push it through the nozzle.

if I stop the print, pull out the filament, insert it back - it will start flowing no problem. And if I start the print, 30-40 mins into the print clog will happen again.

the issue consistently repeats every time I try to print.

please see the video below

 

 

Posted : 11/06/2023 10:01 pm
Tom De Winter
(@tom-de-winter)
Trusted Member
RE: Prusa MK3S - ghost filament obstruction problem

I just watched a YouTube video from Chris Riley on Heat Creep

This sounds very much like what you are experiencing. 

Posted : 12/06/2023 1:18 pm
Neophyl
(@neophyl)
Illustrious Member
RE: Prusa MK3S - ghost filament obstruction problem

The user says they replaced the nozzle, well one of the potential symptoms of not performing that procedure correctly is filament jams after awhile.  If you don't get a proper seal between the nozzle and heatbreak it forms a extra void that the filament fills up, creates a 'well' of filament, this messes the flow up and you can get all sorts of issues. When it retracts instead of pulling from a small volume of melted plastic it pulls from a much larger volume.  This can lead to the same symptoms as heat creep as it is in effect causing the same thing, just not for the same reasons.  That combined with the warmer environmental temps at the moment could be enough to tip it over. Often these things are caused by a combination of factors. 

I would expect there to also be filament leaking eventually as it works its way up and down the threads.  The little bits of filament etc on the print are an extra indicator which makes an improperly fitted nozzle a likely cause.

Other possible causes 
-a slipping extruder bondtech gear.  Check the tiny grub screw is tight.  Check the teeth are all cleaned out too while you are in there.
-foreign matter in the feedpath.  Do several cold pulls and check that nothing fell into the feedpath.  If there's a tiny bit of something in there then removing the filament will dislodge it upwards and then when you load it works its way back down to the nozzle and blocks it again.  Using the needle or reloading filament is a very temporary thing.  Cold pulls should remove anything left over in there.  If you don't know how to do one then YouTube is your friend. There's many resources on how to.

 

Posted : 12/06/2023 6:26 pm
Glebiys
(@glebiys)
Active Member
Topic starter answered:
RE: Prusa MK3S - ghost filament obstruction problem

I think you are right! Last time I’ve seen melted filament leaking from between heaterblock and hotend heatsink. 
looks like I improperly reassembled the hotend. I remember screwing heaterblock all the way up, touching heatsink, and it still felt loose.

I’ll look up a guide for Hotend reassembly. Any advice? 

Posted : 12/06/2023 8:26 pm
Glebiys
(@glebiys)
Active Member
Topic starter answered:
RE: Prusa MK3S - ghost filament obstruction problem

The problem was solved - I used incompatible nozzle, that created large gap inside heater block. Replacing with correct nozzle solved the issue.

‘thanks for help everyone!

Posted : 04/07/2023 3:16 am
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