Snapped filament, help please!  

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alasdair
(@alasdair)
Eminent Member

Hi all,

Had my Mk3S for a week or so. Enjoying it. I've done a handful of prints successfully. I'm enjoying the Prusa experience.

Last night it was running a 13 hours print. This morning when I went to look, the machine had finished the print (or so it thought), but the printed part was only half complete (i.e. half height). Everything that had been laid down looked good. No error messages.

Upon inspection it turned out that the PETG filament had snapped at the extruder drive gears, so the printer had spent approx 7 hours printing nothing as there was no filament to push to the print head. The reel of Prusa PETG was still engaged into the feed hole at the print head top cover, so initially it didn't look like there was a problem, and of course, the filament sensor detected filament, so the G code kept running.

Questions:

Is having the filament snap like this 'a thing'? Or is it suggestive of an issue with the printer?

How do I get rid of the short piece stuck in the print head? There's barely enough sticking up to grab with pliers.

Anything I can do to stop this recurring?

I'd be very grateful for your input.

Cheers.

Posted : 03/05/2020 11:25 pm
Ondrowicz
(@ondrowicz)
Eminent Member

Hi, I would try to heat up the hotend to the PETG temperature, open the extruder idler and either try to remove the filament using pliers (probably will not work if there is not sufficient space to hold it) or press the stuck filament piece down by a piece of fresh filament or hex key with a suitable diameter. If both operations fail, you will probably have to remove and disassemble the hotend.

Posted : 04/05/2020 6:34 pm
alasdair
(@alasdair)
Eminent Member

Thank you. I will try this.

I wonder what caused it to fail??..

Posted : 05/05/2020 9:26 am
With_maltodextrin
(@with_maltodextrin)
Trusted Member

Main reasons for filament snapping I've experienced are moisture in the filament, or the inner diameter of the filament spool is a bit too small, so the filament 'remembers' the curve of the spool and snaps when it's forced to straighten out to go into the extruder.

This is primarily a problem with PLA since it tends to break instead of bending, compared to say, PETG.

Also it could be several issues at once - for example, if pulling the filament off spool is more difficult due to its mounting, it makes the filament more likely to snap because more force is causing the filament to straighten back out from the curve it's slightly shaped as.

This post was modified 7 months ago by With_maltodextrin
Posted : 05/05/2020 5:30 pm
alasdair
(@alasdair)
Eminent Member

UPDATE

It proved impossible to extract the broken filament from the top using pliers. I followed the Knowledge Base article for replacing the PTFE tube as my suspicions were the filament was clogged within, and indeed this proved to be the case.

Article here:

https://help.prusa3d.com/en/guide/how-to-replace-ptfe-tube-on-the-mk3s-mk2-5s-mmu2s_21664

I don't know why it got snagged up, but the filament was well and truly stuck within the PTFE tube. I wonder if too much pressure exerted from the Bondtech feed pulleys can distort/mark the filament such that it is then prone to jamming in the PTFE tube.. I dunno.

The fact that Prusa very kindly provided a couple of spare PTFE tubes within the kit makes me realise that this situation happens periodically.

Thanks all.

Posted : 05/05/2020 11:32 pm
JoanTabb
(@joantabb)
Moderator

the PTFE tube is an expendable item. 
with standard PLA they usually last a good while,  abrasive filaments wear them out faster, 
on the Mini and Mk1, they are subject to higher temperatures because they go down into the heatblock,
In the  mk2, mk2s, Mk2.5,  Mk2.5s Mk3 and Mk3S do not go into the heatblock, but they must be installed firmly against the recess in the heat beak to pevent a gap between the heatbreak and the PTFE tube end
there are jigs to help cut the PTFE, on Thingiverse, and there is a Knowledgebase article on cutting PTFE Tube to size and shape!

https://help.prusa3d.com/en/guide/how-to-trim-ptfe-tube-original-prusa-i3-printers_22424
regards Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 05/05/2020 11:43 pm
alasdair
(@alasdair)
Eminent Member

Thanks Joan.

As i write this the printer is happily doing its thing again, so hopefully all ok. Long may this continue!

Regards,

Alasdair.

Posted : 05/05/2020 11:49 pm
JoanTabb
(@joantabb)
Moderator

Excellent news, Alasdair, 
I have just had two Maxtemp errors, I was tempted to check the wiring for the thermistor, looking for intermittent short circuits... 
but I remembered I had bumped the temperature for the nozzle. 
so I resliced the file with basic settings and it's printing fine at the moment, there is a possibility that I cocked the temperatures up... the error was on the switch from layer one to layer two, when the temperatures change... 

I could have looked at the g code to see what temperatures I had set, but I was a bit lazy.  🙂 

60% c0mplete  so far

Regards Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 06/05/2020 12:25 am
alasdair
(@alasdair)
Eminent Member

I am learning there is more to this business than meets the eye (of course) !

I just noticed the print fan was not working. I worried that I might have damaged the wiring during the PTFE replacement. I paused the print and faffed around with the menu, played around with the fan override speed but no good.. Stating thinking that I better cancel the print and take it all apart again..

Then realised the print fan doesn't kick in for the first 3 layers.. duh! 😊 

Posted : 06/05/2020 12:37 am
JoanTabb
(@joantabb)
Moderator

🙂 ...   Good catch

If I get a jam, I bump the extruder up to 280c and try manually pushing the filament through into mid air. if the filament breaks I open the bondtech door and then use a 1.5mm allen wrench to push the filament through!...   
usually works.

Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 06/05/2020 1:41 am
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