How to unclog a Mosquito or Dragon hotend
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@fcwilt unfortunately no. It is actually quite the puzzle to me. If I can't figure out the cause it is bound to happen again.
FWIW performance on the Dragon has been excellent up until now (other than the wrenches included for the tiny hex screws were garbage and I am still waiting for replacement wrenches which I am suspecting will never come) -
I think I have come up with a plausible explanation based on some help from another forum member.
Because the filament was broken, the extruder was unable to pull in new filament which led to the filament in the heat break tube to just sit there for the duration of the print (45 minutes). It is likely that heat traveled up the tube through the filament and melted things and somehow wedged things in there firmly.
I am declaring this mystery as 'solved' and vow to unload the filament (or somehow adjust my way of doing things) to prevent fragile filament to be fed into the extruder from now on.I currently have a long feed tube to carry the filament into the direct extruder. This made it possible to run the feed tube in the same bundle as all the other wires. It would appear that it might be easier to just run loose filament directly into the extruder rather than running it through a feed tube for easier/cleaner routing.
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@tecno I mostly withdraw the (PLA) filament at the end of printing, and always do so by first manually extruding about a centimetre and then pulling the filament out. That prevents any soft and swollen filament from being drawn back up the tube and thus reduces the possibility of clogging.
My Dragon hotend has never had a clog (yet?), which is better than my experience with the Hermera on my other printer.
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@tecno said in How to unclog a Mosquito or Dragon hotend:
What is the general perception of withdrawing filaments from hotend? Avoid this clogging issue?
I always do a cold pull to remove the filament and have never had a clog. When I want to remove the filament I heat it up to the temp when it just starts to loosen and a firm pull will remove the entire filament end in one piece. For PLA that's ~90c, and a bit hotter for other types. But when done right the tip of the filament will be a perfect moulding of the inside of the nozzle.
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Well folks I have positively identified the cause of the previous clogging.
After clearing everything up and re-assembing the hot end/extruder I run a calibration cube - came out perfect.
Today I ran another print that I decided to cancel after it was 2/3 done. All the important features I needed to verify had printed and it wasn't necessary to carry on with the print. What I failed to appreciate was that apparently cancelling a print doesn't turn off the heaters (bed and nozzle) so this thing sat again for a while cooking PLA .... and yes, the f'ing thing is totally clogged again.
So the broken filament in my earlier problem had nothing to do with the clogging and it is all about the filament sitting there and cooking ..... unbelievable!Funny thing is, this was never an issue with my clone BMG extruder and my clone Chimera printhead set up in a Bowden configuration. I am definitely NOT a happy camper !!!!!
Yes I realize that I can modify the cancel.g file to shut the hot end off, it just was never an issue before!
Actually I need to correct myself a bit here - I had asked to cancel the print forgetting that it would throw up a confirmation screen. Of course I never confirmed the cancellation so it sat there for like forever with a hot end and bed at temperature.
Point here is that maybe the fancy heat break isn't as grand a thing as people make it out to be because as I said, this was never a problem before.Boy am I
pissedannoyed! -
It gets worse than that. Imagine you get some other kind of clog in the nozzle. That prevents the filament from feeding, and you "air print" for a few hours. That entire time, the filament in your nozzle and lower part of your heat break is cooking away...
(Yes, it's happened to me.)
This makes a good argument for installing a filament sensor that not only detects if the filament is present, but also checks that it's actually moving.
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@garyd9, <shudder> .... good point !
I'd like to know why this was never an issue before though!!!!
We are talking a good hour of work unclogging this thing and then resetting Z=0.
There must be something that can be done to either prevent the blocking (first step would be avoiding PLA with it's lower glass temp) or allow unblocking that would not involve taking 3/4 of the printer apart! -
I avoid it by dropping the hot end temp to a lower standby temp in pause.g. That way if I forget to interact with it to cancel it or it takes me a while to do whatever I needed to do with it paused it will not be cooking the filament.
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@phaedrux, under what circumstances is pause.g called besides running out of filament ?
Could you post your pause.g ? -
As a side issue, I wonder how many times you can undo the bimetal heat break with the teeny weeny tiny screws it uses. They look like they would break if you looked at them funny.
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@jens55 said in How to unclog a Mosquito or Dragon hotend:
@phaedrux, under what circumstances is pause.g called besides running out of filament ?
Could you post your pause.g ?I have a G10 in start.g to set the standby temp.
Then pause.g has T-1 to deselect the tool putting it into standby.
resume.g selects it again and waits for temp before purge and returning to printing
cancel.g turns off the heaters and homes xy -
@phaedrux, thanks, will have to update those.
With practice I was able to disassemble things in a hurry, then I lost a temperature sender due to wire fatigue and then I lost my V6 adapter for the LGX extruder from too much push when the filament hung up just prior to the hotend.
I am calling it quits for today as I am breaking too much stuff ....
<sigh>
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I hate to admit it but the standard V6 clone is starting to look very attractive ....
I might have to set up a test case by feeding PLA into a 'normal' hot end (ie without the fancy bi-metallic break) loading filament and just let it sit for a while to see if it clogs up. -
@jens55 I don't think it's necessarily fair to brand all bimetallic type heat breaks as inferior, based on your experience with a clone. But as I explained in our chat session, the problem only occurs with PLA and only if it remains static but at print temperature for an extended period. This situation causes heat to creep up through the filament itself, so it could happen with any all metal heat break. Having said that, it is likely that the Mosquito style heat breaks are more susceptible to blockage because the internal bore may be a much tighter tolerance than (say) an E3D V6. If you are going to use PLA exclusively, and you are unable to mitigate having it at print temperature for an extended period of time without it moving forward, then the best option is to use a PTFE lined heat break such as the V6 "lite".
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@deckingman, good point. I should really test the Dragon hot end with PETG which is what I tend to run most of the time. I happen to be in a PLA period at the moment (well PLA on one printer an ABS on another actually)
I will do my best to avoid cooking PLA but there are some situations that can occur that I just can't foresee. If the hotend clogs up once in a blue moon that would be ok but in this case it seems to be blocking up 100% of the time when it sits at temperature.
Did you ever figure out how long on average it takes for PLA to clog up the bimetallic hot end ?
I suppose another option would be to dedicate a different printer to run all PLA prints. -
@jens55 No I don't have much of feel for how long it takes static PLA to soften inside the heat break. To some extent, I guess it might depend on how much airflow you have over the heartbreak. I do know that Slice Engineering ran a test for over 100 hours with no cooling fan and had no blockage, but that was with the filament always moving forward. So with static filament, it might help if you have high airflow over the heat sink part of the heartbreak. As I explained via chat, mixing hot ends can have one or filament static for many hours and even PET-G can be problematic under those conditions. I've had to revert to PTFE lined heat breaks but if course, that limits the type of filaments that I can use. I do have another dual input all metal hot end which uses 2 Mosquito heat breaks and both filaments are fed continuously. It doesn't block but I'm not allowed to talk about it due to intellectual copyright issues.
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Are you using the original nozzle? My first tests I got a lot of clogging, blaming partly still on BMG but tonight I changed nozzle standard brass. Running Real PETG and it looks OK just now, still 80% to go.
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@tecno, yes I am using the original nozzle but the issue is not nozzle related as the clog forms in the bimetal heat break tube.
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Well thats what I thougt too, try to change and cut 2cm of the bowden tube.
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I know that Slice made an update from gen1 bimetallic to gen2 expanding the ID of the heatbreak for jamming from PLA (as well as the new coating)
Its very likely that the clone hotends (I have a few NF-crazies clones) were based on Gen1, with a tighter ID that is more prone to PLA's tendency to expand when heated/extruded.
I haven't had issues with either gen1 or gen2 genuine breaks, but I have had one issue with a gen1 non-genuine heatbreak jamming.
