Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Hi all,
I already spent three nights on online support chat but still experiencing the same problem:
When I print a model with 0.2 or 0.3mm height, all goes well and I experience no issues. I decided to reprint the same model with 0.05mm height, after some 60-90 minutes underextrusion occurs. Re-tried many times with different Prusament PLA filaments and all prints ended up underextruded.
Interesting thing is, when underextrusion occurs well into the print process and I remove the filament and immediately re-insert it again, underexrtrusion is fixed and I can print for another 15-20 minutes (sometimes even longer) until the underextrusion reappears again.
I disassembled the extruder, Bondtech gears are ok, changed the PTFE tube for a brand new one but the problem persists. I also used another nozzle - no improvement. I did cold-pull, all was clean, no debris, could clearly see through the whole filament path and it seemed to be absolutely ok. The same applies to the nozzle, nice and clean, no debris or obstacles (after all, the same nozzle easily handled a 0.3mm print at 200% speed with ni issues at all).
What I haven't done yet:
1 - I can't separate the heatsink from the heatbreak - I would have to use excessive force and most likely ruin the thread on the heatbreak. But the thread seems to be very tight and I assume the old thermal paste still does it's job???
2 - I did not change the heater, nor the thermistor as I do not have spares at home at the moment but I did calibrate the temperatures but not sure if this would help in case my thermistor would give false temperatures (HERE is a thread where false temperature was the cause of underextrusion but from the very beginning of the print task)
Based on the upon written, I assume that these components are ok:
Bondtech gears
PTFE tube
Nozzle
So the problem must lay somewhere here:
1 - Extruder is heated to wrong temperature due to false reading by the thermistor, it's then too cold or too hot (tried to fix the underextrusion by rising the temperature temporarily from 215C to 240C but no change). Haven't tried to lower the temerature yet
2 - Heatbreak and PTFE tube get too hot due to bad heat transfer to the heatsink but I think this is a very unprobable case.
Anyone encountered similar issue? Any suggestions please? Would like to get rid of ruined prints asap.
Thanks in advance for your valuable input.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Try a cold pull and also try with new filament
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Hi Matteo,
I tried both, cold pull showed no particles at all, filament was absolutely clean. Also, I tried some 5-6 different filaments with the same result.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
SOLUTION to my problem:
It was underperforming thermal paste between the heatsink and the heatbreak. I got this advice on Prusa online support chat. First, I was not very convinced, I thought - what could possibly go wrong with thermal paste tightly closed and held between two threads????
But then, I gave it a try - experienced very hard times to screw these two parts apart, I was very afraid I would damage the thread, rendering the heatbreak unusable. After a few attempts I was about to give it up, ready to order brand new parts. Then I gave it one last try, this time I heated up the coupled parts and after some big effort I managed to separate them. Cleaned thoroughly the old thermal paste (it was not completely dry) and applied a new one. Slowly put the two pieces together again, tightened it by hand properly. I found a steel nut with corresponding diameter and ran it over the heatbreak thread to smooth out any damage caused by pliers during disassembly - to avoid any possible damage to the threaded hole on the heatblock made of relatively soft aluminium. Then I assembled the extruder and ran a test print. So far, so good, looks the problem is gone!!! To my astonishment, the least possible cause (at least by my opinion) was the culprit at the end.
The problem was caused by low heatflow into the heatsink which caused slow, gradual overheating of the nozzle which consequently caused partial congestion resulting in underextrusion and later led to complete stop of filament flow. As printing with 0.05mm layers means slower flow of filament material, thus carrying away very little excessive heat, heat built up over the time. This is also why underextrusion never appeared on prints with 0.2mm or 0.3mm. Flow of molten filament is much higher and the filament material managed to carry away the excessive heat. I must have printed with overheated filament for some time before noticing the problem with 0.05mm layers.
Hope this will help others experiencing underextrusion when printing very low layers e.g. 0.05mm.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
We're going to see another spike in heat-related problems as we move into the warmer months in many parts of the world. Glad you got it working. Please be sure to chime in if you see others having similar problems!
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RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Hm.... I have to apologise, my statement about solution was somewhat premature, unfortunately...
The underextrusion really went away as test prints and regular prints (totalling 24+ print hours) showed. Based on that I posted the solution. Unfortunately it occurred again on one of my new prints...
Seems like application of new heat paste solved the trouble only partly, underextrusion occurs less frequently and much later into the print process but it is still there... I will have to look into this once again...
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
If your not using an mmu, then possibly use the titanium heatbreak from E3d as this should conduct less heat from the block to the heatsink, also (unproven but I use it) maybe use thermal grizzly kryonaut heat sink paste, it is one of, if not the best thermally conducting pastes available, and every little improvement helps, and probably most important, what are your retractions set at?, you want these as small as you can get away with and definitely below 1mm.
I have mine set between 0.5 and 0.8 for PETG, PLA should be able to go lower.
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Just finished another support chat, I measuerd the thermistor resistance and seems like this might be the real cause, giving false temperature reading??? Prusa is sending me a spare one on Monday. I will run a few test prints then and surely will post the results.
@chocki: as for the retraction, I am using the preset values as set in PrusaSlicer - and I must say I never had any issues with their settings, esp. those for their Prusa and Prusament filaments. Which I am using and underextrusion occurs on them.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
OK, but it's worth trying a few test prints using lower values than the presets, if you have no issues with stringing great, the less retracting, the less heat is lifted towards the heat sink.
The PRUSA settings are like a cars tuning, it's a compromise to get decent performance in all countries, but you can eek out better performance if you tune it for your environment.
Same with the printer, the default settings should work from cold arid areas (OK, maybe not too cold), up to hot tropical-ish areas.
If you live in a slightly cooler, drier area, stringing may be less of an issue so you can get away with a lower retraction distance.
The biggest variation though is filament and how dry it is, again, if you use a dryer, you can probably print with a lower retraction value.
Ultimately reducing retraction may not make any difference in your case, but like I said, every little bit helps.
Lets hope it is just the thermistor that is at fault.
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
Thanks for your input, I will deffo mess with retraction values. At the moment, until I get the new thermistor (Tue or Wed next week), i have plenty of time to tweak the temperature and retraction as well 🙂
And yes, you are right - the Prusa settings are kind of "let's make everybody happy" and I totally understand this as their printers end up all over the world from tropical forests to places beyond (ant)arctic circles. Quite a wide range of temperatures, humidities, etc... not an easy task to make it work everywhere.
RE: Underextrusion occurs after 60-90 minutes of 0.05mm height printing
New thermistor arrived at last, replaced it and finally solved the underextrusion problem??? But very few prints made since replacement yet.
Old, supposedly faulty thermistor had resistance at room temperature about 70kOhm. Once removed, the measured values oscillated between 70-110kOhms so apparently something wrong with it. The new replacement had 120-130kOhms.
I hope it's fixed now, if you hear no more comments from me, the problem is gone!