3D Print Troubleshooting: Fix Stringing, Warping & Under-Extrusion by Material
Most 3D print troubleshooting starts with the slicer, and most of the time that's the wrong place. Usually it's the material, the moisture in the spool, or a 10-degree miss on the hotend. We've printed a lot of PLA, PETG, ABS, and TPU across the bench, and the same symptom means different things depending on what's loaded. A stringy PLA print is a retraction problem. A stringy PETG print is almost always a wet-filament problem. Same whiskers, different fix.
This guide is organized by what you see on the part, not by setting. Find the symptom, then jump to the material notes under it.
How to use this 3D print troubleshooting guide
Start with the defect in front of you. Each section below walks a single symptom — stringing, under-extrusion, warping, layer shifts, bed adhesion — and gives you the fix broken out by material. Scroll to the symptom, then read the paragraph for the filament in your printer. Skip the rest.
The reason we do it this way: the same visible defect has different root causes across materials. Under-extrusion on PLA at 215C is usually a partial clog or heat creep. Under-extrusion on PETG at 215C is a temperature problem: the slicer default was too low from the start. Treating PETG like PLA is the single most common mistake we see in support tickets, and it costs people a weekend before they figure it out.
Keep a notebook or a text file. Change one thing at a time, log the result, and keep the failed prints until you know what fixed it. If you prefer a general reference instead of this symptom-first format, our 3D printer repair guide: 15 common problems & fixes covers hardware fault isolation in more depth.
Stringing and oozing: dial in retraction by material
Stringing is molten plastic leaking from the nozzle during non-print travel moves. You see it as fine whiskers between parts, hair across the top of a Benchy, or little snot-trails on the sides of towers. The physics are simple: pressure in the melt zone has to be released before the nozzle moves, or it drools.
PLA. The easiest material. Start with 5mm retraction at 45mm/s on a Bowden setup, 0.8-1.5mm at 35mm/s on direct drive. Nozzle temperature between 200-210C. If you still see strings, drop the hotend 5C and increase travel speed to 150-200mm/s. PLA cools fast, and the faster the nozzle gets away, the less time it has to ooze.
PETG. The hard case. PETG is naturally stringier than PLA because it stays molten longer and the melt is tackier. The usual culprit is moisture. PETG pulls water out of the air aggressively, and a wet spool will string no matter how clean your retraction is. Dry it first (a filament dryer at 55C for 4-6 hours), then tune. Expect to run retraction lower than PLA with PETG, not higher: 3-4mm Bowden, 0.6-1mm direct drive, because long retracts pull filament back into the heat break and cause clogs. Z-hop of 0.2mm helps. Travel speed 200mm/s if the printer can hit it. The Prusa printing troubleshooting handbook has good reference values if you need a starting point for a specific brand.
ABS. Moderate. Retraction behavior sits between PLA and PETG: 4-5mm Bowden, 1-2mm direct drive, 230-245C. ABS strings less than PETG but will blob at corners if your acceleration is high and part cooling is on (which it shouldn't be, more on that in the warping section).
TPU. A different problem entirely. Flexible filament behaves like a wet noodle in a Bowden tube because the retraction force compresses the filament instead of pulling it back cleanly. Direct drive is effectively mandatory. Retraction 0.5-1mm, max. Print speed 20-30mm/s. If you're trying to run TPU on a Bowden setup, strings are the least of your problems; you'll fight blobs, under-extrusion, and jams the whole way.
Under-extrusion: gaps, thin walls, and missing layers
Under-extrusion shows up as gaps between perimeters, missing top-layer coverage, pinholes, or walls that look thinner than the model. The extruder may click rhythmically. That's the motor skipping steps because something downstream is blocked.
Work the diagnostic in order. First, is the hotend temperature right for the material and the speed? Second, is the filament dry? Third, is there a partial clog? Fourth, is the extruder gear worn or loose?
PLA. Most slicer defaults get PLA right. If you're seeing under-extrusion, suspect heat creep first. The heat break is getting warm enough above the melt zone that filament softens before it reaches the nozzle and jams the throat. Common on long prints at high speed. Check your hotend fan is actually spinning and the heatsink is clean. Nozzle temperature 200-215C is normal; above that on PLA and you're asking for cooked filament and partial clogs.
PETG. The slicer default of 230C is often too low. We run PETG at 240-250C for anything above 50mm/s print speed, and 245-255C for 0.6mm nozzles. If the extruder is clicking on PETG, raise the hotend 5C and try again before you tear anything apart. PETG also wants slightly more flow — around 102-105% — because it shrinks less than PLA and underfills gaps more visibly.
ABS. 240-250C for most brands. ABS under-extrusion usually points to a cooked hotend. Residue from previous prints has carbonized in the melt zone and is restricting flow. A cold pull with cleaning filament clears it. If cold pulls don't help, pull the nozzle and inspect; sometimes the internal taper has carbon buildup that no pull will shift.
TPU. TPU under-extrudes when you print too fast. The extruder gear slips on the soft filament, and the harder you push, the worse it gets. 20-30mm/s is the ceiling for most TPU. Check extruder tension: too tight deforms the filament into an hourglass shape and makes slipping worse, too loose and the gear can't grip. The sweet spot is firm but not biting.
Wet filament is the invisible under-extrusion cause. PETG, TPU, and nylon pull moisture out of the air within hours of being opened. If a spool has been sitting on a shelf for a month, dry it before you change any settings.
Warping and cracking: temperature control for ABS, PETG, and large PLA
Warping is thermal contraction. Plastic cools unevenly across a large part, the edges pull up before the center, and the corners lift off the bed. It scales with print size and with the material's shrinkage rate: ABS shrinks around 1.5% as it cools, PETG about 0.6%, PLA about 0.3%.
ABS. You will not print ABS reliably on an open-frame printer above a few centimeters in any dimension. The fix is an enclosure holding 40-50C ambient so the whole part cools together. Also: bed at 100-110C, brim of 8-10mm, part cooling fan OFF entirely, and block drafts even inside the enclosure. ABS cracking between layers (delamination) is the same problem as warping, because one layer cools before the next bonds to it. See the Prusa printing troubleshooting handbook for enclosure build notes if you're putting one together.
PETG. PETG rarely warps the way ABS does, but it surprises people by delaminating instead. The part looks fine, then splits along a layer line under load. The cause is part cooling that's too aggressive. PETG wants only 30-50% fan, not 100%, and the first 2-3 layers should run with the fan off. Bed at 75-85C. If you're seeing cracks on tall PETG prints, drop fan speed before you touch anything else.
Large PLA. PLA warps too, just less. On parts over 150mm, we run a brim, raise the bed to 65C from the usual 60C, and add mouse ears (small discs printed at corners) on anything with sharp 90-degree angles. The All3DP common 3D print problems rundown has pictures of what each warping pattern looks like, which helps when you're not sure which contraction mode you're seeing.
TPU. Doesn't warp. If a TPU part is lifting, your bed adhesion is wrong, not your temperature.
Layer shifts and ringing: belts, motors, and acceleration
These are two different problems that both come from the motion system, so people conflate them.
A layer shift is a sudden horizontal offset. The top half of the print is translated 2-5mm from the bottom half, with a clean seam between them. That's a stepper losing position. Causes, in order of frequency: belt is loose or stretched, a pulley grub screw has backed off the motor shaft, stepper driver current is set too low for the acceleration, or the print head is physically hitting something (a clip, a cable chain, a warped corner it should've traveled over). Check the pulley first. A grub screw loose on a flat-ground shaft is a 30-second fix that solves a surprising number of these.
Ringing (also called ghosting) is a repeating echo of a corner or feature across the surface after the print head changes direction. That's vibration from the frame or gantry resonating after an abrupt acceleration. Fixes: lower acceleration (start at 1000-1500 mm/s² if you're above that), lower jerk, tighten frame screws, make sure the printer is on a solid surface. Input shaping on Klipper or similar modern firmware largely solves ringing if you can run it.
A loose eccentric nut on a V-slot wheel will show up as both — intermittent shifts and visible ringing — and will have you blaming the slicer for a week. If the gantry has play when you push it by hand, that's your problem.
Bed adhesion failures: first-layer fixes by surface and material
The first layer sets the whole print. Get it right and most other problems get easier; get it wrong and nothing downstream saves you.
Start with Z-offset. A properly dialed first layer squishes the extruded line slightly flat. You can see a continuous bead with no gaps between passes, and the top surface should look faintly textured, not round like fresh pasta. If you can see the shape of each extruded line clearly, you're too high. If the nozzle is dragging and leaving thin, translucent patches, you're too low.
Bed level (tramming) matters next. Mesh bed leveling helps compensate, but it can't fix a bed that's tilted 1mm corner-to-corner because the first layer will squish differently in each quadrant.
PEI (smooth or textured). Clean with 90%+ isopropyl alcohol every few prints and dish soap and water weekly. Skin oils are the enemy. PLA sticks aggressively to clean PEI; let the bed cool fully before trying to remove parts or you'll chip the sheet. PETG sticks too well to bare PEI and will tear chunks out of it. Use a glue stick as a release agent (see our notes on the best glue for PETG for options that work).
Glass. Needs an adhesion aid for most materials. Hairspray or an ABS slurry (ABS scraps dissolved in acetone) for ABS. Glue stick for PLA and PETG. Clean with IPA between prints.
Textured sheets. Great for PLA and PETG, mediocre for ABS. The texture gives mechanical bite that chemistry alone doesn't.
TPU. Sticks to almost anything, and often too well. Blue painter's tape over the build surface is the classic release trick if you can't get parts off.
A regular 3D printer maintenance schedule keeps the bed, nozzle, and belts in the state where this troubleshooting even applies. A dirty bed and a worn nozzle will defeat any amount of setting tuning.
Material cheat sheet: typical settings and failure modes
| PLA | PETG | ABS | TPU | |
|---|---|---|---|---|
| Nozzle temp | 200-215C | 240-250C | 240-250C | 220-235C |
| Bed temp | 55-65C | 75-85C | 100-110C | 40-50C |
| Part cooling | 100% | 30-50% | OFF | 30-60% |
| Enclosure | Not needed | Not needed | Required for parts >50mm | Not needed |
| Retraction (DD) | 0.8-1.5mm | 0.6-1mm | 1-2mm | 0.5-1mm |
| Retraction (Bowden) | 5mm | 3-4mm | 4-5mm | Not recommended |
| Print speed | 50-150mm/s | 40-80mm/s | 40-60mm/s | 20-30mm/s |
| Signature failure | Heat creep clogs on long prints | Stringing from wet filament | Warping/delamination without enclosure | Under-extrusion when printed too fast |
Treat these as starting points. Every printer and every brand of filament has its own quirks; the cheat sheet gets you to 80%, and you tune from there.
FAQ
Why is my 3D printer stringing even after retraction tuning? Wet filament is the usual culprit once retraction is dialed in. PETG and TPU absorb moisture fast and will string regardless of retraction distance. Dry the spool at 55-65C for 4-6 hours and retest.
What causes under-extrusion halfway through a print? A partial nozzle clog or heat creep from inadequate hotend cooling. The extruder keeps clicking as the melt zone backs up. Drop print speed, raise temperature 5-10C, and clean the nozzle with a cold pull.
How do I stop ABS from warping without an enclosure? You usually can't on parts larger than a few centimeters. Use a brim, raise the bed to 100-110C, kill all part cooling, and block drafts. But an enclosure holding 40-50C ambient is the real fix, and nothing else matches it.
Why do my first layers stick in some spots and not others? The bed is not level or the Z-offset is wrong. Run a first-layer calibration print and watch for a consistent squish across all four corners; a tramming issue shows up as one corner too high.
Can I use the same troubleshooting steps for TPU as for PLA? No. TPU needs direct drive, minimal retraction (0.5-1mm), and slow print speeds (20-30mm/s). Bowden setups and PLA-style retraction will cause under-extrusion and jams on flexible filament.