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Print defect
Under-extrusion and gaps
Walls have gaps, top surfaces show grooves, and the extruder may skip or grind the filament.
How to use this page
- Step one
- Confirm the symptom matches the print in front of you, not a photograph of a different defect.
- Step two
- Run the discriminating check before changing any setting.
- Step three
- Apply one change, reprint the same part and record the result.
No setting on this page is a validated profile. Direction words describe which way to move, not how far.
What you see
If none of these describe the print, the defect is probably a different one in the index.
- Thin or missing walls on a part that should be solid.
- Grooves or pinholes on top surfaces.
- A clicking or skipping extruder motor.
- Prints that start well and thin out later in the job.
Likely causes
These causes commonly produce this symptom. Several can be present at the same time, which is why the next section starts with a check rather than an adjustment.
- Partially clogged nozzle or a worn nozzle
Flow is restricted, so the slicer's demand cannot be met.
First check: Extrude into open air and watch whether the strand curls or pulses. - Feeder tension or a chewed filament section
The drive cannot push the requested volume.
First check: Inspect the filament where it left the feeder for flats or dust. - Flow demand above the hot end's melt capacity
The extruder skips because the melt zone cannot keep up.
First check: Reduce speed only and see whether the clicking stops. - Incorrect filament diameter or a worn feed path
The slicer assumes a diameter the spool does not have.
First check: Measure the filament in several places along the spool. - Spool binding or a tangled wind
Feed resistance pulls back against the extruder.
First check: Pull filament by hand from the spool with the feeder disengaged and feel for resistance.
The check that separates them
Is the restriction at the nozzle, the feeder or the spool?
Heat the nozzle and extrude by hand with the feeder disengaged, then repeat with the feeder driving. Finally, pull filament from the spool with the feeder open.
How to read the result
If it indicates: Resistance when extruding by hand points to the nozzle or melt zone; resistance only with the feeder points to feeder tension; resistance at the spool points to winding.
If it rules out: Free movement at all three points means the demand is simply higher than the profile can sustain and speed or flow is the variable.
Change one variable at a time
Work down the sequence only as far as you need to. After each change, reprint the same part with the same profile and keep the failed print for comparison.
Feed path resistance
Release and re-route the spool so the filament unwinds freely.
Observe: Confirm the clicking stops before changing slicer settings.
Nozzle condition
Clean or replace the nozzle with the same size.
Observe: Check the open-air extrusion strand for a steady, straight flow.
Speed
Reduce print speed only.
Observe: Watch for the return of consistent wall thickness without changing flow calibration.
Flow calibration
Adjust flow in a small step after the mechanical checks pass.
Observe: Measure a single wall and compare it with the intended thickness.
Material-specific notes
Family context changes which cause to check first. These notes do not replace the grade guidance or a document request.
| Family | Note |
|---|---|
| PLA | Heat creep is a common cause on long prints at high temperature; the failure appears late rather than at the start. |
| TPU | A long or constrained feed path causes under-extrusion that looks like a clog; confirm the path before the nozzle. |
| ABS / ASA | An enclosure that is too warm can soften filament before the feeder and cause a partial stall. |
When to ask us
- A new nozzle and a free feed path still under-extrude on the published grade guidance.
- The strand diameter varies noticeably along one spool.
- The problem appears on every spool of a grade but not on another grade.
What to include
- Grade identifier and spool or lot reference.
- Printer, nozzle size and material of the nozzle.
- Slicer profile name and the values you changed.
- A photograph of the defect and the failed part next to the model.
- What you already ruled out, with the prints that show it.
Boundary of this page
- These pages describe a diagnosis order, not a guaranteed fix. A defect can have more than one cause at the same time.
- No numeric setting is published here. A validated profile depends on the printer, nozzle, part geometry and grade, and a number copied from a page would not be a validated profile.
- Guidance values elsewhere on the site are starting points, not recommended profiles for your machine.