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Every printer has bad prints

Failed prints are part of 3D printing - even for experts. The skill is not avoiding every failure; it is diagnosing what went wrong and fixing it. Because you understand the full print journey, you can trace almost any problem back to one of a few causes: adhesion, temperature, calibration, filament, or mechanics.
Remember the “fail forward” mindset from the contest. A failed print you understand is worth more than a lucky success you cannot explain.
Visual guide to common 3D print defects: warping, stringing, under-extrusion, layer shifting, poor overhangs, and spaghetti

The most common print defects and what they look like

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First-layer and adhesion problems

The first layer causes the most failures. Fix these first.
Causes: the print cools unevenly and contracts, pulling corners off the bed. Worst with ABS, better with PLA.Fixes:
  • Increase bed temperature and use glue
  • Add a brim or raft
  • Keep the printer away from cold drafts and open windows
  • For warp-prone materials, use an enclosure
Causes: first layers squished too much by heat and weight.Fixes:
  • Lower the bed temperature slightly
  • Reduce first-layer squish (raise the nozzle a hair via Z-offset)

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Extrusion problems

Thin wisps of plastic strung between parts of the print.Fixes:
  • Dry your filament - moisture is the top cause
  • Increase retraction in the slicer
  • Lower the nozzle temperature slightly
Not enough plastic coming out - weak, gappy prints.Fixes:
  • Check for a partial clog and clean the nozzle
  • Raise the nozzle temperature a little
  • Make sure filament feeds freely and the spool is not tangled
Too much plastic, leaving blobs and messy surfaces.Fixes:
  • Lower the extrusion multiplier / flow rate in the slicer
  • Lower the nozzle temperature slightly
Nothing (or very little) extrudes, sometimes with clicking from the extruder.Fixes:
  • Heat the nozzle and gently push filament through by hand
  • Use the unclogging pin from your kit to clear the tip
  • Try a “cold pull” to remove debris
  • Replace the nozzle if it stays blocked

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Layer and quality problems

Layers suddenly offset sideways, ruining alignment.Fixes:
  • Slow the print speed down
  • Make sure nothing is obstructing the print head or bed
  • Check that belts are tensioned and pulleys are tight
The print pops loose and the printer keeps extruding into the air.Fixes:
  • Fix first-layer adhesion (see above)
  • Add supports for tall or top-heavy models
  • Use the app or camera to catch failures early and stop the print
Steep overhangs sag or curl.Fixes:
  • Enable and increase part cooling fan speed
  • Add supports in the slicer for overhangs beyond ~45 degrees
  • Slow down on overhang layers
The top surface has holes or looks incomplete.Fixes:
  • Increase top layer count in the slicer
  • Increase infill density so top layers have more to rest on

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A simple troubleshooting method

1

Observe

Look closely. When did it fail - first layer, mid-print, or overhang? What does the defect look like?
2

Isolate the stage

Match the symptom to a stage of the print journey: adhesion, temperature, extrusion, or mechanics.
3

Change one thing

Adjust a single setting at a time so you know what actually fixed it.
4

Test and record

Re-print and note the result. Keep a short log of what worked - future you will thank you.

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Quick reference

If you are stuck on your contest print, do not just retry the same thing. Use the method above to change one variable, and remember - the problem-solving is worth 15 points in judging.
You can trace a failed print to its cause and apply a targeted fix. You know where the unclogging pin, glue stick, and slicer settings come in.