Suggestions to remedy hot end jam?



  • Apologies for not relying on Google searches of "nozzle jam" and so forth, the results weren't found to be helpful for the situation and as blockages are always frustrating I thought that I may be able to get up and running again with some personal attention from the group.

    Click click click goes the extruder now near the starts of my print files. Thousands of hours already on the printer and this is a first for me. Printing PLA at 210/60, 0.3mm nozzle, 0.15mm layer height and 30mm/s it began, with hot filament creeping up and ruining the heat break before I'd noticed what was going on.

    I replaced the heat break and nozzle, problem returned ~ten minutes into the print. Switched to a 0.4mm nozzle and tried a short (2hr) print, things appeared to be better. I then switched to Proto Pasta CF PLA to print a new component and once again returned the starved extrusion.

    When persistent problems such as this appear from nowhere I'm inclined to suspect a hardware issue. I'm wondering whether perhaps the thermistor (E3D) is going bad again, though last time it was resulting in a higher than reported nozzle temp and this time it would perhaps be running cool.



  • I found a spare thermistor and installed it. Turning the Bondtech gear by hand the CF PLA still exhibits far higher than usual resistance, but when feeding eSun cleaner filament through the system it flows easily. Hmm – getting wierder.



  • Bingo, thermistor it was. I guess it's important to have spares of these on hand at all times!



  • Arrrgh! No, that wasn't it after all. Other ideas please?



  • Heater Cartridge?



  • I don't think so, and it does seem much better now – it's printing now but the problem isn't totally gone. With a new thermistor, were it a heater cartridge issue would the thermistor not report failure to hold temp?



  • My experience with this has been to measure temp at the nozzle with an accurate device like a K type thermocouple. If it's correct then it's a mechanical problem. Check extruder gear isn't clogged.

    If it's tough to push filament through by hand the nozzle may be partially blocked. Cleaning with microdrills, burning it out with a blowtorch for a good long while these work. But nozzles are often cheap swap it out. Make sure when you tighten the new nozzle to the heatbreak you do it as hot as your setup allows 270 degC or so any loose fit between nozzle and heatbreak will cause problems.

    Make sure the heatbreak is clean and be careful not to scratch the inside surface with any tools. Quality all metal heat breaks only work if highly polished or coated in some way. Ptfe lined ones are more tolerant, but make sure the ptfe isn't old and degraded which it does become even at 250 deg C max over long periods.

    Also I'd recommend using heatsink compound between heatbreak and heatsink, nothing between heatbreak and heater block and copper grease between the nozzle and heater block.



  • Have you tried lowering your print speed to allow the filament more time to melt completely? also you could try and increase your temperature in stages until the problem goes away.
    Do you use different settings as regard to speed and temperature for each type/manufacturer filament?



  • Random thoughts….........

    Lower the retraction - it could be that molten filament is being drawn up into or above the heat break then solidifying.

    Fan not working efficiently so heat the heat sink isn't doing it's job and you have a long transition between hot end and cold end. Try a bigger fan if you can.

    Use Lite Heat sinks. I've seen posts from a few people who have cured this issue by switching to the Lite version which had PTFE all the way though the heat break. It restricts the maximum temperature you can print at though.

    Use a 0.5mm nozzle - area is about 50% greater than a 0.4 so less back pressure.



  • @DjDemonD:

    My experience with this has been to measure temp at the nozzle with an accurate device like a K type thermocouple. If it's correct then it's a mechanical problem. Check extruder gear isn't clogged.

    If it's tough to push filament through by hand the nozzle may be partially blocked. Cleaning with microdrills, burning it out with a blowtorch for a good long while these work. But nozzles are often cheap swap it out. Make sure when you tighten the new nozzle to the heatbreak you do it as hot as your setup allows 270 degC or so any loose fit between nozzle and heatbreak will cause problems.

    Make sure the heatbreak is clean and be careful not to scratch the inside surface with any tools. Quality all metal heat breaks only work if highly polished or coated in some way. Ptfe lined ones are more tolerant, but make sure the ptfe isn't old and degraded which it does become even at 250 deg C max over long periods.

    Also I'd recommend using heatsink compound between heatbreak and heatsink, nothing between heatbreak and heater block and copper grease between the nozzle and heater block.

    Thank you Simon! As this is the second thermistor failure in a couple of months I'll certainly be picking up a thermocouple to help diagnostics when it happens again. Are (decent) thermistors normally this prone to failure? Surprising that I've not seen more discussions of the issue online. That extrusion problem the first time was rather a trick to pin down on my own. Also appreciated are your tips regarding the use of the thermal paste, etc.

    @appjaws:

    Have you tried lowering your print speed to allow the filament more time to melt completely? also you could try and increase your temperature in stages until the problem goes away.
    Do you use different settings as regard to speed and temperature for each type/manufacturer filament?

    Thanks appjaws! I hadn't thought to try the test you mention as I already had that spare thermistor on hand, but had I not then your suggestion would certainly have been my next step.
    And yes, certainly – settings always require tuning (sometimes even for identical spools from the same manufacturer IME. Typically followed by tweaking on-the-fly in reponse to peculiarities of the model being printed.

    @deckingman:

    Random thoughts….........

    Lower the retraction - it could be that molten filament is being drawn up into or above the heat break then solidifying.

    Fan not working efficiently so heat the heat sink isn't doing it's job and you have a long transition between hot end and cold end. Try a bigger fan if you can.

    Use Lite Heat sinks. I've seen posts from a few people who have cured this issue by switching to the Lite version which had PTFE all the way though the heat break. It restricts the maximum temperature you can print at though.

    Use a 0.5mm nozzle - area is about 50% greater than a 0.4 so less back pressure.

    Thank you deckingman!

    Good advice, surely actions which I would have followed had the trouble continued. I like the point you make about the minor switch to 0.5mm easing the back pressure, and I'll be sure to remember that in the future.


    [Edit] Sorry deckingman, first thing I need to learn to do is read!
    I guess I was still feeling a bit frazzled first time I ran through this, so I failed to realize that you were outlining possible causes. Addressed in order …

    • Retraction – I did make that mistake early on in my 3DP education, my retractions are now typically 3mm or less.

    • Fan – I've never felt that the teeeeny breeze coming off of the stock fans was any more than, at the very most, adequate. I now have a really cool little 30mm Yokomo RP-033 Racing Performer Hyper Cooling Fan on the heat sink. These things sound like tornados full-blast! I use PWM to bring the noise to a comfortable level (barely audible) and it's still a much stronger airflow than any of the usual 4010 units.

    • Lite Heat Sink – interesting, is it to do with the architecture of the sink?


    So …

    After a day of frustration, I awoke yesterday morning to a completed and fairly nice print. I decided to wait until today to proclaim the problem solved, just in case. So it was indeed a thermistor issue even though there were, following its replacement, a few scattered instances of filament starving from what I can only attribute to an unrelated issue but which has since sorted itself.

    Having a laid-up printer is no fun, so thanks again to all for the replies!

    • Michael






  • Looks great is it expensive? I bought a chinese multimeter which is actually great quality and value a UNIT UT210E for about £30. It has a clamp ammeter, autoranging, and comes with a thermocouple. So great for this type of work.


  • administrators

    @papilio:

    Lite Heat Sink – interesting, is it to do with the architecture of the sink?

    Nope its due to the fact its PTFE lined and thus more tolerant to insufficient heatsink cooling.



  • @DjDemonD:

    Looks great is it expensive? I bought a chinese multimeter which is actually great quality and value a UNIT UT210E for about £30. It has a clamp ammeter, autoranging, and comes with a thermocouple. So great for this type of work.

    Simon, I put the Amazon link above the photo, it's $30 US. Either way, sounds like a must have!

    @T3P3Tony:

    Nope its due to the fact its PTFE lined and thus more tolerant to insufficient heatsink cooling.

    Ah, okay. Thanks Tony. Well now a day later I think that I can categorically say that it was a bad thermistor … smooth sailing (for now)!


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