Fixing failed prints: the usual suspects
Every 3D printer owner has a small museum of failures: the warped coaster, the stringy ghost, the sad tangle of "spaghetti." Failures aren't a sign your printer is bad — they're how you learn what the machine wants. Here are the common ones, what they look like, and what usually causes them.
Poor first-layer adhesion
Looks like: the print peels up, shifts, or drags around the bed during the first few layers. Usually caused by: the nozzle being too far from the bed, a dirty or greasy print surface (fingerprints are the classic culprit), or the bed being too cool for the filament. Fix: clean the bed (soap and water for most surfaces, then avoid touching it), re-check the nozzle distance, and make sure the bed is actually hot before the print starts. For stubborn filaments, a brim — a few extra outlines around the part's base — adds grip cheaply.
Warping: corners lifting off the bed
Looks like: the corners of a flat part curl upward, sometimes pulling the whole base off the bed. Usually caused by: uneven cooling — the lower layers contract as they cool while the upper layers are still warm, and the part pulls itself off. Fix: reduce drafts around the printer, use a brim or raft, and make sure the bed temperature suits the filament. Large, flat parts in warpy materials are the hardest case; an enclosure is the real answer there. With PLA this is usually a bed-cleanliness or cooling issue, not a crisis.
Stringing: spiderwebs between parts
Looks like: thin wisps of plastic connecting separate parts of the print, like a tiny haunted house. Usually caused by: molten plastic oozing from the nozzle while it travels between print locations. Fix: enable or tune retraction (the nozzle pulls the filament back slightly when traveling), and check that the temperature isn't higher than the filament needs — hotter plastic is runnier plastic. PETG strings more than PLA by nature; a little stringing there is normal and can be trimmed off with a heat gun or a quick pass with a blade.
Layer shifts: the print jumps sideways
Looks like: the print suddenly steps sideways partway up, so layers no longer line up. Usually caused by: something physically blocking the print head — a warped-up edge the nozzle catches on, a loose belt, or printing so fast the motors skip. Fix: slow down, check that belts are snug (they should twang slightly, like a guitar string), and make sure nothing on the bed can collide with the nozzle. One-off small shifts often trace to a single curled corner; repeatable shifts at the same height suggest a mechanical issue like a binding lead screw.
Under-extrusion: thin, gappy layers
Looks like: layers that are thin, separated, or full of tiny gaps; weak parts that crumble. Usually caused by: a partial clog in the nozzle, filament that can't feed smoothly (tangled on the spool, or wet and rough), or the print temperature being too low for the speed. Fix: check the spool feeds freely, try a slightly higher temperature, and inspect for a clog — a "cold pull" (heating the nozzle, pushing filament in, cooling, then yanking it out) clears many partial clogs without disassembly. Wet filament is a frequent hidden cause; if a spool that worked fine a month ago now prints badly, suspect moisture.
Spaghetti: total detachment
Looks like: the print came off the bed entirely and the nozzle is happily extruding plastic into thin air. Usually caused by: whatever killed adhesion — bad first layer, a knock, warping that popped the part free. Fix: it's already too late for this print; cancel it and diagnose it as an adhesion failure (see the top of this list). The real lesson of spaghetti is supervision: check the first few layers of every print before walking away. Ten minutes of watching saves hours of wasted plastic.
Elephant's foot and zits
Elephant's foot — the bottom layers bulging outward — comes from the nozzle being slightly too close to the bed or the bed being hot enough to keep the lowest layers soft. Zits and blobs (small pimples on the surface) usually mean the printer pauses at layer changes, letting plastic ooze. Both are cosmetic fixes: adjust first-layer height for the foot, and tune retraction and layer-change behavior for the zits.
The troubleshooting method
When a print fails, resist the urge to change five settings at once. Photograph the failure. Identify which symptom above it matches. Change one thing, reprint something small, and compare. Keep notes on what you changed and what happened — after a month, that notebook is a personalized repair manual no forum can match. And remember: even experienced owners get failed prints. The skill isn't avoiding failures forever; it's recognizing them quickly and knowing what to adjust.