ExtrudoWhy is my 3D print under-extrusion?
Under-extrusion is usually caused by a partial clog, worn extruder gear, or incorrect flow settings mean less plastic comes out than the slicer expects. The printer is putting out less plastic than it should, leaving gaps, weak walls, or thin, patchy layers
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Quick reference
| Defect | Most likely cause | First thing to try |
|---|---|---|
| Under-extrusion | A partial clog, worn extruder gear, or incorrect flow settings mean less plastic comes out than the slicer expects | Do a cold pull |
What it looks like
The printer is putting out less plastic than it should, leaving gaps, weak walls, or thin, patchy layers
Most likely cause
A partial clog, worn extruder gear, or incorrect flow settings mean less plastic comes out than the slicer expects
How do I fix under-extrusion? Step-by-step
- 1
Do a cold pull
Heat the nozzle to printing temperature, then let it cool to about 90°C and firmly pull the filament out. This often removes debris causing a partial clog.
Done when: The pulled-out filament tip shows a clean cone shape, not burnt or ragged plastic
- 2
Check your flow rate
Print a simple calibration cube and measure the wall thickness with calipers. Adjust your slicer's flow percentage up or down to match the target thickness.
Done when: Measured wall thickness matches the slicer's target within 0.05mm
- 3
Inspect extruder gear tension
Open the extruder and check that the drive gear is biting into the filament firmly, leaving light tooth marks, not grinding a groove.
Done when: Filament shows even, light tooth marks with no shavings
- 4
Replace a worn nozzle
If the nozzle opening looks worn or oval instead of round under a magnifier, replace it — a worn nozzle can't extrude consistently.
Done when: New nozzle installed and first layer looks even
Frequently asked
What causes under-extrusion in 3D prints?
A partial clog, worn extruder gear, or incorrect flow settings mean less plastic comes out than the slicer expects
How do I fix under-extrusion on my printer?
Follow the step-by-step fix above, starting with "Do a cold pull". Each step includes a "done when" check so you know whether it worked before moving on.
Is this fix confirmed by other makers?
This entry is part of Extrudo's seeded defect library. Confirmation counts appear once real users report the fix worked.
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