How to unclog a Mosquito or Dragon hotend
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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.
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@luke-slaboratory, that is interesting. I did not know about that dimensional change. I would agree that my Dragon hotend would likely be based on the original version of the bimetallic heat break.
Things are back together and I will watch how things turn out.
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@luke-slaboratory You missed the chat session I had with @jen55 but essentially I was using 6 off genuine Slice Engineering Mosquito heat breaks on a 6 input mixing hot end that I was/am trying to develop. Mixing hot ends have a unique problem in that one of more filaments might be static but at print temperature for many hours. If the filament is PLA with a Tg of around 55 - 60 deg C, then the heat that creeps up through the filament itself is enough to soften it, causing it to swell and block the heat break tube. It doesn't matter how good the heat break is because the heat is conducted up through the (static) filament itself. For most "normal" hot ends, this is never an issue because fresh filament is always being fed in as the print progresses. I concluded that unfortunately, if one wants to use PLA in a mixing hot end, then all metal heat breaks are a no-no and only PTFE lined heat breaks work in this specific scenario.
I do also have a dual input hot end which uses two Genuine Mosquito heat breaks but I've butchered them but machining off the copper heat sinks such that the thin wall tubes pass through a liquid cooling block (instead of being air cooled). This has never blocked but that's more likely due to the fact that both filaments are fed concurrently at a ratio of 50:50, rather than it being anything to do with the liquid cooling.
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@mjlew I didn't had a problem with the hermera jamming until a switched to petg and forgot a set up the correct retraction profile and the hermera doesn't like a retraction of 6mm .
So I had right problems freeing the blocked petg from the heat break and finished up drilling it out and burning it out on a gas ring .
After that I forgot to heat tighten it for petg and printed a long print job overnight , and woke up to a massive petg dome which I had to replace the full hot end assembly . -
@tecno said in How to unclog a Mosquito or Dragon hotend:
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.
Were you using steel nozzle before you switched to the brass one? I did some research into the effect of deflected part cooling air on the temperature inside a nozzle. It isn't a complete picture of what happens because in order to fit the thermocouple inside the nozzle, I had to run the tests without filament loaded. You can read about it on my blog here https://somei3deas.wordpress.com/2020/05/21/the-effect-of-deflected-part-cooling-air-on-brass-and-steel-nozzle-temperatures/
But by way of summary, with the hot heated to 200 deg C with the bed to nozzle distance of 2mm or less, the deflected part cooling air would drop the temperature inside a steel nozzle to around 164 deg C, but with a brass nozzle, the temperature on;y dropped to to 189 deg C. So the temperature inside a steel nozzle (which has poor thermal conductivity), with deflected part cooling air (as opposed to the airflow being directed at the nozzle), could be as much as 25 deg C cooler than a brass nozzle (with much higher thermal conductivity). So ones needs to either not use part cooling air (or severely reduce it) or run the hot end much hotter (but that could "cook" the filament in the melt chamber. Or maybe use a copper coated steel nozzle - I haven' tested one so have no data.
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Yes, the one supplied by Phaetus.
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@deckingman, I can't help but think that 'copper coated' anything is a marketing gimmick. Yes you get higher thermal conductivity but you have such a small coating thickness that you get none of the heat conducting benefit of copper. You do get a shiny nozzle that you can marvel at though
