Diagnosing Under Extrusion

Logan F.

Not Enough Plastic

Under extrusion occurs when the printer is not pushing enough filament through the nozzle to match the amount requested by the slicer. The slicer calculates a specific volume of material for every movement path, but less plastic actually reaches the nozzle tip during printing.

This creates a range of common print defects, including gaps in top surfaces, weak layer adhesion, inconsistent extrusion lines, rough surface texture, and in more severe cases, missing sections in walls or layers entirely. Because under extrusion can be caused by several different issues, diagnosing it properly requires a systematic approach rather than guessing.

One of the most frustrating parts of under extrusion is that many different causes can produce very similar looking symptoms. A partial nozzle clog, wet filament, incorrect flow rate calibration, or extruder tension problems can all create nearly identical print failures, even though the solution for each issue is completely different.

Trying to fix the wrong problem often wastes time and can sometimes make the issue worse. The best approach is to work through the possible causes methodically, starting with the most common and easiest things to test first.

Systematic Diagnosis: Start Here

Step 1 — Check for a partial clog: 

• Extrude 100mm of filament manually through the terminal at a slow speed (10mm/s).
• Watch the nozzle, does the plastic come out as a smooth, consistent strand, or does it come out unevenly, squirting sideways or with irregular thickness? Any irregularity suggests a partial clog. 
• Perform a cold pull (see our nozzle cleaning guide) and retest. This resolves partial clogs in most cases. 

Step 2 — Check for wet filament: 

• Listen for popping, hissing, or crackling sounds from the hotend.
• Look for bubbles or roughness on extruded material.
• Wet filament creates steam bubbles that interrupt flow; ensure that you dry the filament at an appropriate temperature (see storage guide) and retest.

Step 3 — Check for extruder slipping: 

• Watch the extruder gear during a print. On direct drive printers, you can often see the gear directly. It should rotate smoothly and consistently.
• Slipping (the gear rotating without moving the filament) appears as an intermittent skip or click.
• Causes include worn or dirty gear teeth, filament that is too slippery (such as some speciality filaments), and arm tension that is too loose.
• Clean the gear teeth with a small brush, adjust tension, and retest. 

Step 4 — Flow rate calibration: 

• If all of the above check out, the issue is systematic under calibration.
• Follow our flow rate calibration guide to correct it.

Speed Related Under Extrusion