Horrible Nozzle Clog  

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Jonathon
(@jonathon)
Active Member

Hey There

I'm very new to 3D printing. I just got my Prusa Mini last week. The initial prints using the included Prusament roll all went off with no problems. Then I started using some, shall we say "inexpensive" filament (This here). Within the first ~40 minutes of using it, I had a fail print, and a choked up extruder gear (I've taken it apart and cleaned the gear. Several times). I won't go all into all the things I did, but I've been fighting with my printer now as a result of this filament for a couple days.

I've given up on this filament for the time being, I'm now just trying to get the printer to print again reliably with the Prusament that came with it. Now, when I try any print, the first layer goes fine (when it's slower and at 215c), but the second layer (faster and 210c) instantly starts causing the extruder to click and skip. I can see notches in the filament where the extruder has ground at it, trying to make it move. If I boost the temperature to about 220c, it will start printing ok again (but also not perfectly).

I've narrowed down the problem to a clog either in the nozzle or right above it. I've tried almost everything I have read about. I've lost count of the number of cold-pulls I've done (Though most of them break, rather than pull things out). I've used the little cleaning needle, I've gently used a thin metal rod to push down from the top, I've used high temperatures to help melt things about, and even removed the nozzle (although, admittedly, I wasn't really able to do anything with it once I got it off) and still it has trouble with the second layer, needing a higher temperature.

Have I totally messed up my nozzle or something else? Is there some other trick I can try? Do I need to replace the nozzle?

(A note on cold pulls: I have no idea if I'm doing this right. I've found several different methods for doing this, but the filament usually snaps rather than pulls things out, or I'm pulling so hard I'm worried I'll break something. If I make it hot enough that it comes out easily, it's just melted.)

Thanks

Posted : 04/06/2020 12:55 pm
joan.t
(@joantabb)
Veteran Member Moderator

Hi Jonathon, 

Have you tried raising the nozzle until there is a reasonable space below the nozzle, then  heating the nozzle up to PETG or ASA temperatures, and after the temperature settles,  try pushing the filament firmly into the  the extruder, rather than trying to pull it out? 

I find that I get more clogs with the default .8mm retraction distance than I do with Shorter retractions of 0.4mm on my Mk3S

On My Mk2 MMUv1 I use 2mm retraction instead of the 4mm default for the bowden feed nozzle, for the same reason

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 : 04/06/2020 1:42 pm
Jonathon
(@jonathon)
Active Member

@joantabb

Yeah, I've tried making the nozzle quite hot (260c), raising the Z axis, and pushing filament in from the top (after unscrewing the feed bowden tube, of course). This is in fact what has let the printer print again at all (originally it was totally plugged). I have also used a ~1.5mm metal rod to gently push the filament out without adding more.

Filament does come out, just well enough for the second layer and up.

Thank you for the suggestion.

Posted : 04/06/2020 5:36 pm
steve.e3
(@steve-e3)
Trusted Member

There is a specific technique to cold pulls...it should not be done cold but warm! But that aside, the extruder grinding away at the filament is a very clear and bad sign. I would suspect that after all your activity the nozzle might be an issue. Nozzles are dirt cheap - change it. Note nozzles need to be changed at printing temperature, not cold. Google it (use the Prusa guidance) or come back for directions.

After all this, when you get it working again, don't buy crap filament - stick with the name brands or better yet, Prusament.

...
Posted : 05/06/2020 1:25 am
Jonathon
(@jonathon)
Active Member

@steve-e3

Alright, took a look at the instructions. Looks simple enough to change the nozzle. Do you have any suggestions where I source them from? (I don't want to make the same mistake as the filament). Is there any benefit to getting a premium nozzle like this (Apparently they don't clog very easily)?

Also, do you have any suggestions for "name brands"? Since I'm new to this, there are no brands I recognize, so they're all sort of 'no name' to me (Except Prusament, of course 😀 ).

Thank you

Posted : 05/06/2020 12:55 pm
steve.e3
(@steve-e3)
Trusted Member

@jonathon

My personal advice - just order from PRUSA ( LINK ). Admittedly there are plenty on Amazon and many of them are fine (there's not a lot to these as long as they're not bad quality) but if you order from Prusa 1) you know it's a real PRUSA replacement, and 2) might as well support Prusa, Bezos is almost a trillionaire.

Nozzles need to be removed when heated to temperature, so get a socket and handle, make sure they fit, heat the nozzle and quickly remove it and drop it in a heat resistant container. Careful not to burn yourself.

Also while you're doing all this take a close look at the Bondtech gears - looks for filament shavings, that the gears are properly aligned with the filament, etc.

Let us know how you make out.

...
Posted : 06/06/2020 1:19 am
Jonathon
(@jonathon)
Active Member

Hey all

So, an update:

I've completely taken apart the hot end, working with the theory that there may be an issue in either the plastic tube or the heat-break tube. I have discovered a small ring of white plastic (same colour as the PTFE tube above the heat-break) inside at the base of the heat-break tube (that the PTFE tube presses against).

According to step 20 in this article, I should see bare metal, not a plastic ring. Can anyone verify? It doesn't look like filament residue.

Also, if it's not supposed to be there, any idea how to get it out?

Thanks again!

Posted : 07/06/2020 6:19 pm
joan.t
(@joantabb)
Veteran Member Moderator

Could it be Residual Heatsink Paste? 
Does it come out?

If you remove the nozzle can you still see the white? 

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 : 07/06/2020 6:23 pm
Jonathon
(@jonathon)
Active Member

@joantabb

No ... I don't think it's thermal paste. It's on the inside of the heat-break tube, so I doubt it should be there. It's only visible from the top of the tube, not from the bottom/nozzle end. It kinda makes me think it might be like a seat or seal for the PTFE tub, if it is supposed to be there at all.

I also haven't been able to remove it. It's stuck tight to the inside of the heat-break tube, and the tube is so small as to prevent most tools from getting at it, much less gripping it.

Also, I've only used the smallest amount of white filament in the printer, which casts some doubt on the idea that it's filament residue. There's some black reside, and it's obvious that it's not supposed to be there.

Thanks

Posted : 07/06/2020 6:33 pm
Jonathon
(@jonathon)
Active Member

So, it turns out it was all just filament residue. It was a trick of the lighting to make me think it was a white plastic ring. (It's really hard to get light inside a small tube)

The PTFE tube is supposed to be under pressure, so the ends seal. But there was quite a bit there/ I'm wondering if things we're tight enough, or got loose as the printer "broke in".

Posted : 07/06/2020 7:25 pm
Jonathon
(@jonathon)
Active Member

Update:

I had cleaned the heat-break, and changed the PTFE tube. The original was about 1mm short. I then successfully printed four more things. Then this morning, it clogged up again.

I immediately checked the (replacement) PTFE tube again - it is now about 1mm shorter than it should be - it was fine when it went in.

I have discovered that this seems to be a known issue on the forums: https://forum.prusaprinters.org/forum/general-discussion-announcements-and-releases/psa-check-your-ptfe-tube-length/

The short version is a number of people have had the same issue: The heat and pressure on the PTFE tube causes it to shrink slightly. I am glad to know I'm not the only person, but a little disappointed that this flaw exists. Hopefully future revisions of the printer will take this into account in the design and material selection.

Posted : 08/06/2020 5:46 pm
steve.e3
(@steve-e3)
Trusted Member

@jonathon

Hey thanks for all the updates along the way, great info. I have not experienced this yet with my Mini but it's very good to know. I wonder if this is a design issue or related to assembly techniques and only affects a certain percentage of machines. I have a lot of hours on my Mini and have yet to experience any problems.

That said, I'd be very interested in peoples' experience with the Bondtech Mini heatbreak product...i.e. does it solve the issue, does installing it break anything else, etc. If I do experience this PTFE tube issue in the future I don't mind investing a few bucks to solve it permanently.

...
Posted : 09/06/2020 1:19 pm
Jonathon
(@jonathon)
Active Member

@steve-e3

You're very welcome. It's rare that the Google doesn't instantly have all the answers, so I don't mind contributing.

I also had a look at the Bondtech heatbreak, (originally linked from the other thread I referenced above) and certainly looks like it addresses the issue to a certain extent. The PTFE tube is about 1cm shorter, so it's farther from the heat, and there is a narrow part of the metal tube (I guess so less heat is transferred).

----------

I posted this in the other thread, but I'll post it here too:

I have a theory (completely untested at this point), but I'm wondering if this may be caused by insufficient (or poorly distributed) thermal paste between the heat-break tube and the heat sink.

My reason for thinking this: As I posted earlier, I swapped my PTFE tube for the spare, and it lasted less then a day (~4 prints). When I swapped it, I had the heat-break tube completely removed to clean out plastic from the inside of it. Through doing this, even though I was being as careful as I could, some paste was lost to my hands and tools. Since I don't have any more (I've ordered some now), I hoped what was left would be enough. And then it clogged again only a few prints later.

I suspect that if the heat-break is not cooling to heat sink correctly, the PTFE tube gets too hot, and shrinks more or faster than intended.

Like I said, just a theory. I'm cleaning it all again, and then will have to wait for my thermal paste before I can put it back together and try it out.

Posted : 09/06/2020 11:33 pm
steve.e3
(@steve-e3)
Trusted Member

@jonathon

Sounds reasonable.....please keep us posted after you get your thermal paste. Thanks!

...
Posted : 10/06/2020 4:24 am
Jonathon
(@jonathon)
Active Member

So, at risk of jinxing it, I think I have it fixed.

I have printed for a couple days straight on my fix, and it seems to be holding.

Fix was a combination of:

  • Cleaning the heat-break tube
  • Re-tapping the threads in the heater block (they got messed up some how. I may have over tightened the nozzle in previous attempts to fix)
  • New thermal paste (Corsair TM30) between heat-break tube and heatsink
  • Re-install heat-break and heater block into heat sink, putting PTFE tube under pressure as indicated in the Prusa instructions
  • Adjust the bed level sensor, since the nozzle is a little less than 1mm higher now (because the PTFE tube is shorter)
  • Re-calibrate initial Z level

Lets hope it keeps going 😀 

Posted : 19/06/2020 9:30 pm
steve.e3
(@steve-e3)
Trusted Member

Interesting the heater block threads were stripped...I don't think you had mentioned that before.  The nozzle not attached to the heater block is very suspect and may have some or all of the issue all along. Everything else would have been a consequence of that.

 

Fingers crossed keep exercising it and see if its fixed.

...
Posted : 20/06/2020 1:45 am
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