Less material comes out than expected (under-extrusion)
Under-extrusion means less plastic is fed than the slicer calculated. It can stem from the extruder, the hotend, the filament or the settings; troubleshoot them in order so you don't change five things at once.
What the failure looks like
Lines do not touch each other, walls remain translucent and fragile, and the infill looks like a mesh full of holes. The part breaks by hand.
Causes, most likely first
- 01
Temperature too low
The plastic doesn't flow enough for the requested speed.
- 02
Excessive speed
The hotend has a maximum volumetric flow rate (mm³/s). Exceeding it causes under-extrusion even if everything else is fine.
- 03
Extruder steps poorly calibrated
The motor thinks it is pushing 100 mm when it is pushing 92.
- 04
Partial clog
See the clogged nozzle guide.
- 05
Irregular filament diameter
Cheap filament that fluctuates between 1.65 and 1.80 mm.
- 06
Loose extruder tension
The gear slips on the filament.
Step-by-step fix
1. Calibrate the e-steps
Mark 120 mm of filament, extrude 100 mm and measure what remains. If you extruded 92, correct: new e-steps = current x 100 / 92.
2. Increase by 5-10 °C
The flow rate increases significantly with temperature. If the problem disappears, that was it.
3. Lower the speed by 20%
Especially on large parts with long walls.
4. Measure the filament
Using callipers, measure at three separate points. Enter the actual diameter into the slicer.
5. Calibrate the flow
Print a single-walled hollow cube, measure the wall thickness and adjust the flow to match the configured line width.
6. Check extruder tension
It should grip without crushing. If you see filament dust, it's slipping.
So it doesn't happen again
- Recalibrate e-steps and flow when changing filament brands.
- Keep the volumetric flow rate below 80% of the hotend's actual maximum.
Related questions
How much flow rate can a standard hotend handle?
A V6-style hotend with a 0.4 mm nozzle and PLA operates comfortably at 10-12 mm³/s. High-flow hotends can reach 25-30 mm³/s.
Is increasing flow to 110% a solution?
It is a quick fix. It masks the symptom and ruins the part's tolerances. Calibrate e-steps first.
Keep reading
What if it isn't worth your time?
Sometimes the part is more urgent than the learning curve. We're a workshop in Viladecavalls: send us the file and we'll print it with the right material and settings.
Still not working?
Tell Marco which printer and material you use and he'll tell you what to change.
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