Learning from Failed Prints

Use a repeatable “symptom → category → one-change test” loop: stop early when the first layer is wrong, identify the first bad layer/feature (not the aftermath), match it to a likely cause, then validate the fix with a small targeted test before you commit to another long print.

TL;DR

When a print fails, find the first bad layer/feature and classify it (first-layer/adhesion, flow, cooling/overhangs, mechanics, supports, or model). Change one major variable, then re-test on a small print (first-layer square, overhang/retraction test, or a cropped model section) before re-running the full job.

Failed print → fast diagnosis loopTopic-specific diagram for the concept, checks, and tradeoffs in this lesson.ObserveWhat changed first?LocateWhere on the part?ClassifyAdhesion, flow, cooling...Pick 1 causeMost likely + testableChange 1 thingSingle variableSmall re-testTargeted quick print
Workflow: capture evidence, locate the first symptom, classify it, run a one-change micro-test, then confirm before the next long print.

What to capture before you touch settings

Your goal is to preserve clues that disappear once you peel the part up or restart the job. Note: (1) first bad layer number or timestamp, (2) where it starts on the part (first layer, a corner, a specific overhang, a thin wall, near the seam, at a certain height), and (3) what the symptom looks like (lifting, gaps, blobs, stringing, droop, layer shift, delamination, “spaghetti”). Take a clear photo from two angles if you can, then record a quick settings snapshot: material and brand/type, dry/not dry, nozzle size, layer height, nozzle/bed temps, speed/accel (if you changed it), fan %, and any recent hardware changes (new nozzle, new bed surface, moved printer, tightened belts).

Fast triage order (don’t skip the order)

  1. If the first layer is failing, stop early and fix that first. Almost every other problem gets worse on a bad first layer.
  2. Find the first bad layer or first bad feature. Ignore the mess that happens after; it’s often just a cascade.
  3. Map the symptom to a category: adhesion/first layer, extrusion/flow, cooling/overhangs, mechanics (shifts/ringing), supports, or model/design.
  4. Pick the single most likely cause you can test quickly (one knob).
  5. Run the smallest test that reproduces the failing feature, not the whole part.
  6. Only after a fix repeats successfully should you restart a long job.

Common failure patterns and the best first fix to try

Corners lifting or part warps off the bed

Likely cause: Weak bed adhesion or uneven cooling/drafts

Fix: Clean bed; verify level/mesh; add brim; block drafts; raise bed temp slightly

First layer not sticking or looks patchy/transparent

Likely cause: Z offset too high, bed contamination, or bed too cool

Fix: Clean bed; lower Z offset slightly; slow first layer; increase first-layer temps

Elephant foot (bulged bottom edge)

Likely cause: Nozzle too close and/or bed too hot (first layer over-squished)

Fix: Increase Z offset slightly; lower bed temp; use elephant-foot compensation

Gaps/weak walls (under-extrusion)

Likely cause: Partial clog, wrong flow, or printing too cold/fast

Fix: Do a cold pull or swap/clean nozzle; verify flow/extrusion; raise nozzle temp or slow down

Blobs/zits on outer walls

Likely cause: Pressure/retraction issues, wet filament, or inconsistent extrusion

Fix: Dry filament; tune retraction; reduce temp slightly; use wipe/coast if available

Stringing between features

Likely cause: Too hot, wet filament, or insufficient retraction/travel strategy

Fix: Dry filament; lower temp; increase retraction within safe limits

Layer separation (delamination)

Likely cause: Poor interlayer bonding from low temp, too much fan, or drafts

Fix: Raise nozzle temp; reduce fan; shield from drafts/use enclosure (as appropriate)

Overhangs droop or curl upward

Likely cause: Not enough cooling for the geometry, or printing too fast/thick on that angle

Fix: Increase part cooling for PLA; slow outer walls; reduce layer height on overhangs

Top surface has holes/rough patches

Likely cause: Not enough top thickness or weak support from infill underneath

Fix: Add more top layers; increase infill density; slow top skin

Layer shift or sudden offset

Likely cause: Belt/pulley slip, collision, or accel/speed too aggressive

Fix: Check belt tension and pulley/grub screws; reduce acceleration/speed; ensure part isn’t curling into the nozzle

How to pick “one change” (and avoid chasing your tail)

During diagnosis, hold everything else steady: same filament spool, same slicer profile, same nozzle, same bed surface. Change one major variable per test: temperature, speed/acceleration, retraction, fan, or Z offset (not two at once). If you change hardware (nozzle, extruder parts, hotend), treat that as a separate experiment and revert settings to a known profile first so you can tell what actually fixed it.

Small tests that save hours

  • First-layer square: for adhesion, Z offset, bed cleanliness, and elephant foot.
  • Cropped model section: slice only the region that contains the failing feature and print it where it failed on the bed.
  • Overhang test: for droop/curl, fan effectiveness, layer height, and outer-wall speed.
  • Retraction or temperature tower: for stringing, blobs, and layer bonding tradeoffs.
  • Single-wall cube/vase mode segment: for flow/extrusion consistency and dimensional sanity checks.

Debug log template (keep it short, but consistent)

Part + requirement
What the part must do; what “good” means
Symptom
What you see; attach photos if possible
First bad layer/time
Layer number or timestamp when it starts
Location on part
Corner, seam, overhang, thin wall, top skin, etc.
Settings snapshot
Material, nozzle, layer height, temps, speed, fan
One change tested
Exactly one adjustment (include old → new)
Result
Better/worse/unchanged; what changed visually