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Troubleshooting

Common FDM print defects, what causes them, and how to fix them. Symptoms often overlap — work top-down (adhesion first) and change one setting at a time.

Quick diagnosis

Symptom Most likely cause First thing to try
Print won't stick Bed too far / dirty / cold Re-level, clean with IPA, raise bed temp
Corners lifting Warping (shrinkage + draughts) Enclosure, brim, hotter bed, no fan (ABS)
Wispy hairs Stringing (ooze) Dry filament, tune retraction, lower temp
Gaps / thin walls Under-extrusion Check for clog, raise temp, calibrate flow
Blobs / rough surface Over-extrusion Lower flow, dry filament, tune temp
Layers split apart Delamination Hotter nozzle, less cooling, enclosure
Print knocked loose Adhesion / collision Brim, clean bed, check for warping
Ripples near edges Ringing / ghosting Slow down, tighten belts, input shaping
Bulge at the base Elephant's foot Lower bed temp, tune Z-offset, chamfer base

First layer won't stick

The most common failure. Almost always bed prep or Z height.

  • Re-level / set Z-offset. Nozzle too high = lines don't adhere; too low = no plastic comes out. Use auto-level/mesh if available.
  • Clean the plate with isopropyl alcohol — fingerprint grease is the #1 killer. Wash textured/PEI sheets with dish soap periodically.
  • Raise bed temperature to the top of the material's range for the first layers.
  • Slow the first layer (20–30 mm/s) and add a brim.
  • Use the right surface (glue stick on glass/PEI for ABS/PC/nylon; glue as a release for PETG so it doesn't tear the sheet).

Warping (corners curl up)

Plastic shrinks as it cools; uneven cooling pulls corners off the bed. Worst on ABS/ASA/PC/nylon, occasional on big PETG/PLA parts.

  • Enclosure to keep ambient temperature high and even (essential for ABS/ASA).
  • Hotter bed, and turn the part-cooling fan down/off for ABS/ASA/nylon.
  • Brim or raft for more grip; add mouse-ears to sharp corners.
  • Eliminate draughts — no open windows or AC blowing across the printer.
  • Clean bed + adhesive. Consider rounding/chamfering large flat corners in CAD.

Stringing & oozing

Fine hairs strung between features as the nozzle travels.

  • Dry the filament — moisture is the top cause, especially for PETG, nylon, TPU, PVA.
  • Tune retraction (distance and speed) with a stringing test.
  • Lower the nozzle temperature 5–10 °C.
  • Enable "combing"/avoid-crossing-perimeters and reasonable travel speed.

Under-extrusion

Too little plastic: gaps in walls, thin/weak layers, missing sections.

  • Clog or partial jam — do a cold pull, check the nozzle, replace if worn.
  • Raise nozzle temp so the plastic flows; slow the print if it can't keep up.
  • Calibrate flow / e-steps; check the extruder isn't slipping or the spring tension is wrong.
  • Check for a worn or wrong-size nozzle, or abrasive filament that oval-ed a brass nozzle (switch to hardened).
  • Make sure the filament path is clear and the spool turns freely.

Over-extrusion

Too much plastic: blobs, rough/bulging top surfaces, dimensional bloat.

  • Lower flow rate / extrusion multiplier.
  • Lower nozzle temperature slightly.
  • Dry the filament (wet filament over-extrudes and foams).
  • Verify the correct filament diameter (1.75 mm) is set in the slicer.

Layer separation / delamination

Layers visibly split or peel apart; part is weak along layer lines.

  • Raise nozzle temperature for better layer bonding.
  • Reduce part cooling, especially for ABS/ASA/PC/nylon — use an enclosure.
  • Dry the filament.
  • Lower layer height slightly, or reduce print speed so layers bond.

Elephant's foot

The bottom few layers bulge outward wider than the model.

  • Lower the bed temperature a few degrees.
  • Raise the Z-offset very slightly (nozzle a hair higher on layer one).
  • Enable "elephant's-foot compensation" in the slicer, or chamfer the bottom edge ~0.4 mm in CAD.

Ringing / ghosting (echoes)

Repeating ripples/echoes on the surface after sharp features — vibration.

  • Slow down print/travel speed and acceleration.
  • Tighten belts; make sure the frame is rigid and on a stable surface.
  • Enable input shaping (Klipper) or linear/pressure advance.

Clogs & heat creep

Nozzle stops extruding mid-print or grinds.

  • Cold pull / atomic pull to clear debris; poke with a cleaning needle.
  • Heat creep — heat travelling too far up the heat break softens filament early. Check the heatsink fan is running; don't idle at temp for long; avoid enclosures for PLA.
  • Dust/grit on the filament, or an all-metal hotend running too cool for the material, both cause jams.

Pillowing / gaps in top surface

Holes or fuzzy, incomplete top layers.

  • Add top layers (aim for ≈ 1 mm of solid, e.g. 5× 0.2 mm).
  • Increase infill density so top layers have more to bridge onto.
  • Increase part cooling so top bridges solidify.

Spaghetti / print detached mid-way

A tangle of stringy plastic where the part came loose or a layer failed.

  • Usually a first-layer/adhesion or warping failure that let the part pop off — fix adhesion (above).
  • Tall thin models can topple: add a brim, supports, or print flat/orient better.
  • Filament runout or tangle on the spool. Enable runout detection if available.

When in doubt

  1. Is the filament dry? Rule this out first — it mimics half the defects above.
  2. Is the first layer clean and well-adhered?
  3. Are the temperatures right for this spool (temp tower)?
  4. Change one setting, reprint a small test, compare.

Sources & further reading