What under-extrusion looks like
- Gaps between adjacent wall lines, or walls that feel papery
- Infill that looks sparse and wispy next to solid walls
- Top surfaces with visible pinholes between lines
- Extruder clicking or grinding while printing
Rule out a clog first
A partial blockage mimics every calibration problem, so cold-pull first and confirm the hotend is clear, then calibrate. If the extruder grinds, check the feed path too — tuning numbers around a clog just means redoing everything later.
Calibrate E-steps
E-steps tell the extruder how many motor steps push one millimetre of filament. Mark 100mm on the filament above the extruder, command 100mm through the printer menu, and measure what actually went in. New E-steps = old E-steps × 100 ÷ actually extruded. Repeat until 100mm in means 100mm gone.
Dial in flow (extrusion multiplier)
E-steps fix the hardware; flow trims the last few percent per material. Print a single-wall hollow cube with 0.4mm line width, then measure the wall with calipers — it should read close to 0.42–0.45mm. If it reads 0.38mm, raise flow by roughly the same ratio (about 110%); if it reads fat, lower it. Save the value per material, not globally: PLA+, PETG and TPU all land in different places.
Check the filament itself
- Measure the diameter in several spots with calipers — 1.75 mm filament reading 1.68 mm under-extrudes by about 8% no matter the settings
- Wet filament bubbles and sputters, which reads as under-extrusion — dry it first
- A tangled or cross-wound spool adds drag the extruder cannot overcome — rewind it cleanly
- Slicer set to the wrong diameter (2.85mm vs 1.75mm, see filament sizes) starves every print