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Last updated 19 days ago
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CSPLESDEITFRJA

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.

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. 
  1. 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.
  1. 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.
  2. 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.
  3. 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.
  4. 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).
  5. 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, MK3.9, and XL. Although the component does not prevent extruder blobs, in case this occurs, it makes it easier to remove it. 

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