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· 4 min read
How to Diagnose a Failed 3D Print
Manesh Jayawardhana
CIO & Co-founder
A print fails at 60% after nine hours. You change the temperature, the retraction distance and the print speed, run it again, and it works.
You now have a working print and no idea which change fixed it — so the next time it fails, you are starting from nothing.
Diagnose by symptom, in cost order
Each defect has a small set of causes, and they differ enormously in how expensive they are to check.
Take layer shifting partway up a print. The causes, cheapest first:
A loose belt. Free to check, thirty seconds, and the most common cause.
The nozzle catching on a warped or curled section. Free to observe on the next attempt.
Acceleration or jerk set too high. A settings change, free.
A binding axis or a failing stepper driver. Requires disassembly or replacement.
Checking in that order finds most failures in under a minute. Checking in the order that occurs to you means sometimes replacing a stepper driver on a machine with a loose belt.
| Symptom | Check first | Then |
|---|---|---|
| Layer shifting | Belt tension | Nozzle catching, acceleration |
| Warping | Bed adhesion, draughts | Bed temperature, enclosure |
| Stringing | Filament dryness | Temperature, retraction |
| Poor first layer | Bed levelling, Z offset | Bed temperature, surface |
| Under-extrusion | Partial clog | Temperature, extruder tension |
Change one thing at a time
The rule everyone knows and nobody follows, because prints take hours and testing one variable at a time feels slow.
It is slower per test and faster overall. Three changes and a successful print teaches you nothing; one change and a successful print teaches you the cause, which you then know permanently.
Where a print takes many hours, test on a small representative model rather than the real part. A calibration cube or a short section of the actual geometry tests the same variable in twenty minutes.
Filament moisture explains a surprising share
Worth separating out because it presents as several unrelated symptoms at once.
Wet filament produces stringing, popping or hissing sounds during printing, rough surfaces, poor layer adhesion, and inconsistent extrusion. Chasing those individually leads in contradictory directions — stringing suggests lowering the temperature, poor adhesion suggests raising it.
PETG, nylon and TPU absorb moisture quickly, within days in a humid environment. PLA is slower but not immune.
A filament that printed well a month ago and prints badly now, with no settings changed, has almost certainly absorbed water. Drying it is the first thing to try, not the last.
Keep a log of what changed
The habit that converts troubleshooting from repeated guesswork into accumulated knowledge.
A printer’s settings drift over months — a nozzle change, a firmware update, a new spool, a belt tensioned. When a print fails, the useful question is what has changed since the last one that worked, and nobody remembers.
A short log of changes with dates answers it in seconds. Filament brand and colour, nozzle changes, firmware versions, and any settings altered outside the slicer profile.
The same log makes a working configuration reproducible. A printer that has been quietly tuned over a year is difficult to restore after a firmware reset unless somebody wrote down what was tuned.
Common mistakes to avoid
- Changing several settings between test prints.
- Testing on the full model rather than a small representative print.
- Chasing symptoms individually when wet filament is causing several at once.
- Replacing hardware before checking the free mechanical causes.
- Not writing down what was changed, so the next occurrence starts from scratch.
How to do it with 3D Print Failure Diagnosis
The 3D Print Failure Diagnosis orders the causes by likelihood and cost.
- Choose the symptom and when in the print it appeared.
- Work through the causes in the order given — cheapest and most likely first.
- Change one thing, and test on a small model rather than the full part.
- Write down what you changed and what happened.
Other reference guides are in the tools directory.
Frequently asked questions
Why does warping happen?
Uneven cooling. Material contracts as it cools and pulls the corners up, which is why ABS warps far more than PLA. A heated bed, reduced part cooling on early layers and an enclosure all address it.
What causes stringing?
Molten filament oozing during travel moves — from too high a temperature, insufficient retraction, or wet filament boiling in the nozzle. Drying the spool fixes more stringing than people expect.
Why change one setting at a time?
Because changing three and getting a good print tells you nothing about which one worked. Printing is slow enough that a systematic approach is faster than a scattergun one.
Final thought
Check the belt before you buy anything. The cheapest cause is the most common one, and diagnosing in cost order finds most failures in under a minute.