Extruder blob

Updated 4 days ago ​by Martin Lexa

The blob (mass of plastic accumulated around the hotend) is one of the most scary-looking printing problems you might face together with your 3D printer. It is quite tricky, though not impossible, to remove it after it happens. To better explain the process, we have prepared a short video for you:

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. Especially the heater cartridge cable is very vulnerable as its insulation ends before the wire enters the cartridge body. 
  1. Preheat the nozzle in the LCD Menu ->  Settings ->  Temperature -> Nozzle (or just preheat the printer as you do before you load a filament). 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:
    1. PLA: preheat to 250°C
    2. ABS/PETG: preheat to 280°C
      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. 
  3. Smaller blobs will start to fall off by themselves. As for the bigger ones, use a pair of pliers to carefully remove the now soft plastic mass from the hotend. 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 on the video above).
  5. In case you would 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 in the account you have used to purchase the printer.
Please note that damage caused by the blob is not covered by the warranty as it is neither hardware nor software related and 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 bundled 3D Printing Handbook, chapter 3.3 Safety instructions, point 10. : Do not leave the printer unattended while it's still on!

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 still 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. 
  • 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.

Find out more troubleshooting tips here: community forums | assembly manuals | youtube channel | info@prusa3d.com

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