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3D Print Troubleshooting, Calibration & Parts

Under-extrusion: thin, gappy walls

By LayerWalkerUpdated September 1, 20262 min read
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Short answer

Walls with visible gaps between lines mean less plastic is arriving than the slicer planned. Check for a partial clog and a worn nozzle before you start raising the flow rate to paper over it.

Difficulty moderate Time 30 min Parts under $15 Tools Calipers, nozzle spanner, needle

Raising flow rate is the tempting first move and the wrong one. If the cause is a partial clog, more flow just makes the extruder work harder against the same restriction.

Where to buy

Find the cause before compensating

Symptom

Gaps between adjacent lines, weak walls, visible layer voids

Most likely cause

Insufficient material reaching the plate

The fix
  1. Extrude 100 mm manually and measure what comes out. A healthy hotend delivers a steady, consistent strand.
  2. Look at the strand. Bubbling or spitting means wet filament, not a flow problem.
  3. Do a cold pull. Black or brown flecks in the plug confirm burnt residue restricting the bore.
  4. Inspect the nozzle bore with a bright light. Abrasive filament wears it oval and it never recovers.
  5. Measure filament diameter with calipers. Consistently undersized filament gives consistent under-extrusion.
  6. Only then calibrate flow rate.

Calibrating flow properly

Print a single-wall cube with the walls set to one perimeter and no top or bottom layers. Measure the wall thickness with calipers at several points and average it. Divide your intended extrusion width by the measured width and multiply the current flow rate by that ratio.

Starting settings Flow calibration test
Wall loops 1
Top layers 0
Bottom layers 0
Infill 0 percent
Extrusion width 0.42 mm
Layer height 0.2 mm

Measure at four points and average. Do not measure at a corner.

Nozzle wear is the one people miss

A brass nozzle printing carbon fibre filled filament can wear measurably within a spool or two. The bore goes oval, the extrusion width drifts, and quality declines gradually enough that nobody notices until they compare against an old print. If you run abrasives at all, treat brass nozzles as consumables and move to hardened steel.

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