A condition where the extruder delivers less filament than required, resulting in gaps, weak layers, and incomplete infill.
Under-extrusion occurs when the volumetric flow demand exceeds the actual delivered flow. Root causes include: partial clog reducing nozzle bore; print speed too high for hotend melt capacity; retraction causing filament grinding (skipping/clicking extruder); wet filament creating steam bubbles; incorrect flow rate calibration; or worn extruder gears that cannot grip filament reliably. The symptom is incomplete layers with visible gaps between perimeters or infill lines.
Diagnose by printing a single-wall cube and measuring wall thickness against target. If measured < target: check for partial clog (cold pull), verify flow rate calibration, check extruder gear tension, and inspect filament for grinding marks. Reduce print speed as a temporary fix. Check hotend temperature with a PID autotune. Replace extruder gears if worn. Dry filament if crackling is heard.
Increasing flow rate to compensate for under-extrusion caused by a partial clog only makes the clog worse. Under-extrusion on a transparent filament appears as visible air voids (delamination layers) rather than surface gaps: do not mistake for layer adhesion issues. Extruder clicking without grinding marks usually indicates a hotend temperature issue, not a mechanical extruder problem.
Related terms: Flow Rate, Retraction, Filament Drying, Nozzle
| Field | 3D printing |
|---|---|
| Also called | underextrusion, skipping extruder, grinding filament |
| Source | EDi Brain: tech/fdm |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert