Underextrusion Troubleshooting



What is Underextrusion?

Underextrusion occurs when resistance in the plastic material feeding system limits the rate at which the nozzle can dispense plastic, leading to visible gaps or stringing on roofs of printed parts. You can also identify underextrusion by listening for a clicking noise coming from the left side of your printer, which would indicate that the plastic extruder does not have the strength to overcome the level of resistance in the feeding system. 


Typically, defects on vertical walls are not the result of underextrusion. If your printed parts have defects and you are unsure as to why, please contact Markforged Support.

Causes of Underextrusion

  • Loosely wound plastic material protruding past the walls of the spool and tangling around the spindle
  • Material exiting off the bottom of the plastic spool and causing friction at the drybox adapter
  • Desiccant packs rubbing against the plastic spool
  • Twists or bends in the plastic load tube, creating friction with the plastic material
  • Worn-out plastic feed tubes
  • Worn-out drybox adapter

Note: If your drybox has a brass adapter and you are experiencing underextrusion problems while printing with Onyx, you will need to replace your drybox adapter with the recently developed A2 tool steel adapter, which is more resistant to wear. If you have an active Markforged Success Plan, a replacement A2 steel drybox adapter is covered under wear and tear. Please contact Markforged Support for this replacement item. You may also purchase an A2 steel drybox adapter at markforged.com/shop.

Running the Underextrusion Troubleshooting Utility

This utility will prompt you to examine or change components in four areas of the plastic material feeding system. In between each prompt, the printer will run an extrusion check to evaluate whether  your troubleshooting actions have improved the printer's extrusion. Each check will heat up the plastic material nozzle, home the print head to the back right corner of the print chamber, and extrude approximately 0.25cc of plastic material.

Starting the Utility 

  1. Clear your print bed of prints and debris. 
  2. Wash your print bed and apply an inch-wide layer of glue to the rearmost edge of the print bed to ensure that the purge line adheres to the print bed. 
  3. Start the utility by navigating to Menu > Utilities > Maintenance > Underextrusion Troubleshooting.
  4. Confirm that the part shows signs of underextrusion (see above).
  5. Wet Plastic Purge Line:
    1. Print a purge line to ensure that there is no wet plastic to affect the results of the underextrusion test. You may skip this step if the utility allows. 
      • When the Skip button is not available, you must run the purge line since your printer has been idle for long enough to have potential wet material around the plastic extruder. 
    2. Clear the purge line from the print bed when it completes and push the print bed down to the bottom of the stage. 
  6. Skip Ahead:
    1. Only use the Skip Ahead selection if you have been told by later instructions to do so. This function allows you to exit the utility if consumables aren't on hand and resume at the point the utility was closed. 
    2. If using the Skip Ahead function, replace any necessary components before resuming the utility. For example, if you exit the utility while waiting for a replacement drybox adapter, replace the drybox adapter when you receive it, restart the utility, and then select Drybox Adapter from the Skip Ahead screen.

Extrusion Checks

The utility begins with an initial extrusion check, which evaluates whether the printer shows the symptoms of underextrusion that this utility can address.

Each subsequent extrusion check will run through the same steps as the initial extrusion check to evaluate whether the printer's extrusion has improved. An improvement will present as a reduction or elimination of clicking from the extruder.

Every time the utility runs an extrusion check, you will be asked whether you hear clicking coming from the plastic extruder. Selecting Yes will let you continue troubleshooting; selecting No will exit the utility; selecting Retry will extrude additional plastic material. If you select No but your printed parts still show signs of underextrusion, you should contact Markforged Support with a picture of your part and the printer logs. 

 If the clicking noise goes away after changing a component, it usually means that the source of resistance has been eliminated. If the clicking decreases but does not completely disappear, you will need to continue the troubleshooting workflow to locate and fix any other causes of underextrusion.

Checking for Basic Setup Errors

Complete these basic setup checks every time that you suspect there may be underextrusion in the system, as the way that the material feeds from the drybox to the plastic extruder can change while printing and unspooling material, and new errors may occur without user intervention.

  1. Open the drybox to check for tangled or unspooling plastic material. Re-spool any material that has become tangled in the drybox.

  2. Ensure that the plastic material feeds over the top of the material spool. If the spool is feeding upside-down, with material coming up to the adapter from the bottom of the drybox, simply remove the material and spindle and flip it over in the drybox.

  3. Check that there are only two desiccant packs, and that both packs lay flat against the bottom of the drybox.

  4. Ensure that the drybox location allows for an easy path between the drybox and the printer that does not force the plastic load tube to twist or bend. 

Once you have finished checking for basic setup errors, ensure that the drybox is closed and fully latched. Leaving the drybox open for too long will allow the plastic material to absorb moisture and negatively impact print quality.

Replacing Plastic Material

This utility will follow the same steps as the Unload Plastic and Load Plastic utilities but will only allow you to reload the same type of material as was previously loaded.

Before discarding the unloaded material, record the spool ID located on a barcode sticker on the material spool (starting with EX0 or X0). If this utility does not improve the quality of underextrusion, please provide the spool ID of the discarded material to Markforged Support.

Replacing Worn Plastic Tubes

Note: The plastic Bowden tube, which runs between the plastic extruder and print head, should be replaced every 3-6 months, or around 1000 print hours. However, some printing conditions can accelerate this wear. The plastic load tube, which runs between the drybox and plastic extruder, should be changed around this time as well. 

If you have an active Markforged Success Plan, replacement plastic Bowden tubes are covered under wear and tear. Please contact Markforged Support for this replacement item. You may also purchase plastic Bowden tubes at markforged.com/shop. Ensure that you purchase the correct plastic Bowden tube for the printer - either for the Desktop or Industrial series.

If you have a plastic Bowden tube on hand, select Retract to pull the plastic material out of the print head and Bowden tube. Follow the steps here to replace the plastic Bowden tube.


At this time, also replace the plastic load tube. When you have finished, select Reload to load material back into the print head and continue the utility.



If you do not have a plastic Bowden tube on hand, or cannot perform the replacement at this time, you may exit the utility here.


When you are ready to replace the plastic feed tubes, follow the instructions here and then restart the utility. After printing a purge line, select Skip Ahead and then Plastic Tubes. This will bring you back into the utility, where you can test whether replacing the plastic feed tubes improved the printer’s extrusion.

Replacing the Brass Drybox Adapter


If you have an A2 steel drybox adapter on hand, select Retract to unload the plastic material from the print head and Bowden tube. Pull the material back into the drybox, then follow the steps here to replace the drybox adapter.


When you have finished, select Reload to load material back into the print head and continue the utility.


If you do not have an A2 steel drybox adapter on hand, or cannot perform the replacement at this time, you may exit the utility here.


When you are ready to replace the drybox adapter, follow the instructions here and then restart the utility. After printing a purge line, select Skip Ahead and then Drybox Adapter. This will bring you back into the utility, where you can test whether replacing the drybox adapter improved the printer’s extrusion.

Contacting Markforged Support 

If you have completed the underextrusion utility and still see signs of underextrusion, or if you have been instructed to contact Markforged Support at any time during the utility, please follow these guidelines to resolve your issue as quickly as possible.


  • Submit a ticket through support.markforged.com and input all device information.

  • Attach an image of the part(s) where you are seeing underextrusion. Include pictures of the part from multiple angles if possible.

  • Supply the current material spool ID of the plastic material loaded into the printer and any spool IDs you have recorded while replacing material.

  • Attach the printer logs. You may save the printer logs to your computer from the device screen on Eiger or to USB from your printer.