Ugly Prints, Sorted by Symptom: A Visual Diagnosis Index

Diagnose by Symptom, Not by Slider

When a print comes out ugly, the instinct is to open the slicer and start moving sliders. That works about as well as taking random medicines until you feel better. The faster route is the one every good repair process uses: observe the symptom precisely, map it to its most likely cause, and apply the fixes for that cause in order of probability.

This page is the map. Find what you are actually seeing in the table below — the physical evidence on the failed print, plus anything you heard while it printed — and follow the link to the full guide. Each linked guide is ordered the same way: most likely cause first, so you can work down and stop when the problem stops.

One habit before the table: change one thing at a time. A fix applied alongside three other changes teaches you nothing, and slicer profiles accumulate scar tissue that way.

The Master Symptom Table

What you see (or hear)	Most likely cause	Where to go
Fine hairs and cobwebs between towers or islands	Moisture, then retraction tuning	Stringing: The Complete Fix List
Popping, crackling, or hissing sounds while printing	Wet filament	Is Your Filament Wet?
Rough, pitted, bubbly surface texture	Wet filament	Is Your Filament Wet?
Corners lifting off the bed mid-print	Cooling shrinkage (warping)	Warping and Corner Lift
Cracks or splits between layers on tall parts	Part cooling too fast (delamination)	Warping and Corner Lift
First layer will not stick anywhere	Greasy plate or wrong bed temperature	First-Layer Problems
First-layer lines separated, not joined	Nozzle too high (z-offset)	First-Layer Problems
First layer translucent, ridged, dragged	Nozzle too low	First-Layer Problems
Extruder clicking; filament ground to dust	Blockage or heat creep downstream	Nozzle Clogs
Extrusion stops partway through long prints	Heat creep	Nozzle Clogs
Gradual under-extrusion with carbon-fiber or glow filament	Nozzle abrasion	Nozzle Clogs
Sudden stringing on a profile that used to print clean	Moisture	Is Your Filament Wet?
Parts snap easily along layer lines	Moisture, or printing too cold	Wet filament guide first, then temperature
Blobs and zits on outer walls	Pressure and seam behavior	Stringing guide, travel section
Thin, inconsistent, wavering extrusion lines	Partial clog or wet filament	Clog guide — it covers telling them apart
Whole print shifted sideways partway up	Mechanical: belts, collisions	Check belts and pulleys; not covered above

Reading the Evidence

A few notes on using the table well, because some symptoms overlap.

Sound is data

Two of the most diagnostic signals are audible, not visible. Popping and crackling during extrusion is wet filament, full stop — it is steam escaping, and it makes a mess of surfaces, strings, and layer strength all at once. Rhythmic clicking from the extruder is the motor losing its fight against resistance: usually a clog forming, occasionally over-tension or a too-cold nozzle. If you hear either, you can skip a lot of guessing.

Moisture imitates everything

Notice how often the wet-filament guide appears in the table. Moisture produces stringing, rough surfaces, weak layers, poor adhesion, and clog-like extrusion problems — five symptoms, one cause, one cheap fix. That is why our standing advice is to rule out moisture before tuning anything: it is the most common root cause and the easiest to test. The two-minute listen test in the wet filament guide settles it.

Location matters

Where the defect lives tells you which system failed. Problems confined to the first layer are bed problems — cleanliness, z-offset, bed temperature. Problems that begin partway up a tall part are thermal-environment problems — drafts, part cooling, chamber temperature. Problems spread uniformly over the whole print are filament or extrusion-system problems. A defect that appears at the same height on every print is usually mechanical: a damaged belt tooth, a bent rod, a binding lead screw at that position.

When it is the pairing, not the printer

Some failures are neither machine fault nor settings fault — they are a mismatch between what a filament demands and what a printer provides. Big ABS parts on an open-frame printer will warp no matter how carefully you tune, because the fix is an enclosure. Carbon-fiber filament through a stock brass nozzle will degrade no matter how clean your settings are, because the fix is hardened steel. TPU through a long bowden tube fights you on every retraction. Before tuning a stubborn combination, check the filament compatibility matrix — it exists precisely to flag pairings that need hardware, not patience. If the matrix says your machine is the limiting factor, the printer guide covers which features (enclosure, direct drive, hardened nozzle, high-temperature hotend) actually unlock which materials.

Two Cheap Tools That End Most Guessing

Two pieces of hardware come up across nearly every guide above, because they remove whole categories of failure rather than single symptoms.

A filament dryer like the SUNLU S2 turns "is it moisture?" from a recurring suspicion into a solved problem — dry the suspect spool overnight and either the symptoms vanish or you have eliminated the most common cause and can tune with confidence.

A hardened nozzle, such as a hardened steel nozzle kit, does the same for anyone printing filled filaments: it converts the slow, confusing decay of an abrading brass nozzle into a non-event.

Neither tool fixes a greasy bed or a bad z-offset. But between them they cover the two failure modes that most often masquerade as something else.

A Suggested Order for Multi-Symptom Disasters

Some prints fail in three ways at once. When everything is wrong, this order untangles fastest:

1. Dry the filament. Cheapest test, most symptoms explained, zero risk.
2. Fix the first layer. Clean plate, correct bed temperature, dial the squish. Nothing built on a bad foundation can be evaluated.
3. Resolve extrusion. Clear clogs, confirm the extruder pushes smoothly and consistently.
4. Then tune. Temperature, retraction, cooling, speeds — in that order, one change at a time.

Tuning last is the point. Slicer settings are precision adjustments, and precision adjustments on top of wet filament or a half-clogged nozzle just encode the malfunction into your profile.

FAQ

I have several symptoms at once. Where do I start?

Follow the order above: dry the filament, fix the first layer, clear the extrusion path, then tune settings. Moisture and first-layer problems sit upstream of everything else — many "multiple problems" collapse into one after a night in the dryer and a soap-washed plate.

How do I know whether it is the printer or the filament?

Swap one variable. Print the same model with a fresh, known-dry spool: if the problem vanishes, it was the filament. Or print a previously successful model with the suspect settings: if an old reliable file fails too, look at hardware and filament rather than the new model's slicing. One controlled swap beats an evening of forum threads.

After fixing a problem, do I need to re-tune everything?

Often the opposite — remove the compensations. If you raised retraction to fight wet-filament stringing or cranked first-layer flow to fight a greasy bed, those settings are now wrong for a healthy machine. After a root-cause fix, walk the related settings back toward profile defaults and confirm with a test print.

Why does the table not include every defect, like ghosting or layer shifts?

This index covers the failure families our diagnostic guides walk in depth — moisture, adhesion, warping, stringing, and clogs, which between them account for most ugly prints. Ringing, layer shifts, and resonance artifacts are mechanical tuning topics with different tooling. The blog is where those guides will land as the series grows.