The blob (mass of plastic accumulated around the hotend) is one of the most scary-looking printing problems you might face with your 3D printer. Removing it after it happens is quite tricky, though not impossible.
Please note that damage caused by the blob is not covered by the warranty as it is neither hardware nor software related. It can be prevented by properly calibrating the printer as well as by stopping the print as soon as the filament starts to stick to the nozzle.
See the Safety Instructions on the 3D Printing Handbook bundled with each of our printers. Do not leave the printer unattended while it's switched on.
See the Safety Instructions on the 3D Printing Handbook bundled with each of our printers. Do not leave the printer unattended while it's switched on.
We prepared a short video on how to remove an extruder blob. The video features our Original Prusa MK3, but the same principles of heating the filament blob in order to soften it and carefully removing it with pliers apply to all our FDM printer models.
How to clear the extruder blob
Before doing anything, please note that the cables of the hotend thermistor and the heater cartridge are most likely entangled in the blob. The heater cartridge cable in particular is very vulnerable as its insulation ends before the wire enters the cartridge body.
- Preheat the nozzle in the LCD Menu -> Settings/Control -> Temperature -> Nozzle. The temperature needs to be approximately 30°C higher than the temperature at which the blob has formed. For example, if the blob is made of:
- PLA: preheat to 250°C
- ABS/PETG: preheat to 280°C
On MK3/S/+, it is also possible to preheat the printer through the Preheat menu, but note that a Thermal anomaly error might happen.
- If MINTEMP or Preheat error message appears on the LCD, it means the thermistor or the heater cable (respectively) is already broken. In this case, your only option is to use a heat gun to heat the plastic. Work very carefully, you don't want to melt the printed parts surrounding the hotend. Clear the blob little by little.
- After the hotend reaches the right temperature, leave it this way for at least 5 minutes. Turn the printer off before the next step, or you might cause an electrical short.
- Smaller blobs will start to fall off by themselves. As for the bigger ones, use a pair of pliers to remove the now soft plastic mass from the hotend carefully. Again, be very cautious around the leads coming from the hot end, in particular, the thermistor leads.
- Once the big chunks of the amassed plastic are removed, use a small brass brush to get rid of what's left (as shown in the video above).
- In case you do not succeed, as well as in case the blob has damaged some of the extruder parts, you can find your spare parts here. To see the spare parts section, you have to be logged into the account you used to purchase the printer.
How to prevent this problem from happening
Unlike the Spaghetti monster issue, the blob issue often occurs early during the print. In general, the blob forms if the first layer detaches from the print surface and sticks to the moving hot nozzle while it keeps extruding, causing the blob to grow.
In order to prevent this situation from happening, bear in mind these simple rules:
- Always make sure to clean the print surface before starting the print. See this guide for more details.
- Take the time to adjust the first layer height at the beginning of the print. Make sure that the first layer is sticking properly to the entire print surface.
This step does not apply to Original Prusa MK4, MK3.9, XL, as they are equipped with loadcell, although minor first layer adjustment is still possible on these printers.
- Check the print every now and then. If you observe any potential problem, pause the print and give yourself the time to solve it. As a last resort, you can always stop the print, adjust the settings, and start again.
Silicone sock
Consider installing a silicone sock. This is available in our shop for MK4/S, MK3.9/S, and XL. Although the component does not prevent extruder blobs, in case this occurs, it makes it easier to remove it.
6 comments
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mad4stroke
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In my case the first layer came out just fine, and blobs would only build up and drop later in longer running prints.
The reason was that the nozzle was a tiny bit loose, and plastic would slowly ooze out through the threads.
Took me a couple of days to figure out, so thought this might save someone a little time :)
The reason was that the nozzle was a tiny bit loose, and plastic would slowly ooze out through the threads.
Took me a couple of days to figure out, so thought this might save someone a little time :)
Dyktafon
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I know i am digging up an old thread, but what did you do to fix it? In my case there is pla 'extruding' from upper part of heating block, from heatbreaker's thread, and then causing a blob that moves heat bed.
MWF
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I have (inherited from my son) an i3 MK3 with what I believe is "blob". When trying to heat the nozzle it appears that I get a mintemp error. The instructions say that this means the system is broken and use a heat gun. Is the system permanently broken or just not functioning? If I clear the blob will the mintemp error likely go away. (I do not have a heat gun so am using a solder iron in a very slow and tedious way. Is this likely to work or should I buy some TBD new parts?)
Giuliano - Official Prusa CS
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Hello. If the blob caused the MINTEMP error, it means that the hotend thermistor is damaged. After cleaning the blob, the thermistor should be replaced.
TimmayCrackn
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Ugh. This happened to me last night. This was my third print on my printer, and the filament is EVERYWHERE. I'm pretty frustrated. I can't get prints to stick to the bed, have read and followed all the instructions, and now this. This looks like it is going to take hours to fix, if it can be fixed at all. My bed has been immaculate each print, I've adjusted the first layer height per the instructions, and now this. Massively frustrating. Hoping my extruder isn't completely ruined after three prints.
jed
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In case this helps someone else ... I built the printer, printed that boat thing, everything was perfect so my son and I quickly drew something up in Fusion 360 and left it printing overnight. What could go wrong? Well turns out an entire nights worth of blob that fully encased all of the cables and bent them significantly but somehow didn't snap any of the wires. I tried a number of things including turning the nozzle up to PLA melt temperature ... nothing worked - the wires were fully entombed a good 15mm away from the nozzle. What did work: soldering iron - I have one which you can set the temperature so I set it around 250 deg and just carefully worked at removing the plastic and exposing the wires like surgery. If you saw the mess it was to start with you would think just throw the whole thing in the bin. NOTE: I had to partially remove the extruder - undid it so it could be freed from the guide rails and cut the cable ties holding it to the bearings etc and removed the fans to get better access, but after cleaning it up, putting it back together, and re-running that calibration wizard its back printing again. The problem with my print was I don't think I properly calibrated the z axis ... this time I moved it closer to the surface and it seems to have produced a better base layer. Anyhow if your blob is way larger and impossible looking to fix try the soldering iron and some patience first. Hope that helps someone.