If you’re asking “why is my 3D print failing?”, you’re almost certainly looking at one of a handful of repeat offenders: a first layer that didn’t stick, corners lifting off the bed, strings webbing between parts, or under-extrusion from a wet spool or a clog. The good news is that FDM failures are predictable. The bad news is that most people fix them by changing five settings at once and never learning which one actually mattered.
This guide walks through the common failure modes in the order they actually occur, gives you the concrete numbers to dial in, and — crucially — shows you how to change one variable at a time so you can trust your results. If you’d rather skip the manual triage, you can upload a photo to our AI photo diagnosis tool and get slicer-specific fixes back in seconds.
Start at the bottom: first-layer and bed adhesion
Bed adhesion failure is the single most common issue in 3D printing, and for a simple reason: everything above the first layer depends on that one foundation. If the first layer doesn’t stick, the print is already lost no matter how perfect your other settings are. So before you touch anything else, confirm these four things:
- The build plate is clean and free from oil, dust, and leftover adhesive.
- The nozzle is clean and not dragging through the first layer.
- The filament is dry, smooth, and feeding without resistance.
- The bed is levelled, or the automatic bed mesh is working correctly.
Nozzle height (Z-offset) is the big one
The nozzle’s distance from the build plate decides how well the filament grabs the surface. Too high, and the filament lands as round beads with barely any contact, then gets knocked off easily. Too low, and the nozzle scrapes the bed and blocks normal extrusion. A good first layer looks slightly flattened and smooth — not round, not overly squished.
Use the paper test: a sheet of paper should drag slightly between nozzle and bed at all four corners and the centre. If you’re running Klipper, run BED_MESH_CALIBRATE and check the variance across the plate.
Clean the plate properly
Even a small fingerprint can cause adhesion problems. Wipe the bed with IPA before each print. For stubborn residue, use 100% acetone — but only if your bed surface supports it. Never use sponges or cloths that have touched grease or oil; you’ll just spread a film of it back onto the plate.
Slow the first layer down
Drop your first-layer speed to 25–30 mm/s. This gives the extruded filament more time to bond before the nozzle moves on. Subsequent layers can run at full speed. For PrusaSlicer users, our guide to the best first layer settings lists the exact values worth copying.
Match the surface to the material
- PLA bonds well to smooth PEI.
- PETG bonds aggressively to smooth PEI — use the textured side or a glue stick as a release agent so you don’t tear chunks out of the plate. If you’re fighting this, our piece on PETG first-layer adhesion issues covers both extremes.
- ABS needs a heated, enclosed chamber more than any specific bed surface.
For most adhesion problems, add a brim — it adds material around the base without affecting the bottom surface. Save the raft as a last resort for a warped bed, a very small footprint, or difficult materials like Nylon.
Corners lifting: warping
Warping happens when the lower layers cool and contract faster than the upper layers, pulling corners and edges upward off the bed. The root cause is uneven cooling: the first layers are locked to the bed while the upper layers cool freely, and the internal stress wins. ABS shrinks the most, so warping with ABS on an open-frame printer is nearly guaranteed.
Work through the fixes in this order, changing one thing at a time:
- Clean the plate and confirm the first layer. A poor first layer masquerades as warping more often than you’d think.
- Raise the bed temperature slightly if adhesion is marginal.
- Reduce drafts. An air-conditioning vent, open window, or fan blowing across the printer cools one side faster than the other — instant warp. Move the printer or block the airflow.
- Only then reach for glue stick, an enclosure, or a new build plate.
For ABS and ASA, an enclosure isn’t optional — it maintains a stable ambient temperature that prevents the differential cooling that causes warp. PLA and PETG rarely warp enough to need one (PETG benefits only marginally, and only on very large prints in cold rooms). Be realistic about repair: for high-accuracy parts, fixing a warped print is near impossible — reprint it. We’ve broken the warping fix down further in how to fix warping in 3D prints.
Strings and webs: stringing and oozing
Stringing happens when melted filament leaks from the nozzle during travel moves — when the nozzle moves without extruding — leaving thin wisps of plastic between parts. It’s a universal FDM issue, especially with PLA and PETG. There are three main levers, plus one cause almost everyone misses.
The often-missed culprit: wet filament
Dry the filament first. Wet filament strings regardless of your retraction settings, and it’s the dominant cause of stringing far more often than people credit — yet it’s the fix most makers skip. If your spool has been sitting out for weeks, dry it before you spend an evening tuning retraction.
Retraction
When you enable retraction, the printer pulls the filament back before crossing open spaces, creating negative pressure inside the nozzle that helps prevent oozing. For most printers using 1.75 mm filament, a good starting point is 3 mm. Direct-drive extruders need far less than Bowden setups, so don’t blindly copy someone else’s number.
Temperature and travel speed
- Temperature: if prints look stringy, lower the nozzle temperature by 5°C at a time until it improves. Don’t overshoot, or you’ll trade strings for under-extrusion.
- Travel speed: slow travel gives the nozzle more time to leak; faster non-print moves usually reduce stringing. Typical values sit around 150–200 mm/s.
The golden rule: change one variable at a time
Changing too many slicer or printer settings at once makes troubleshooting harder, not easier. If you adjust speed, temperature, and nozzle height together and the print improves, you’ve learned nothing — you don’t know which change helped or hurt. Pick one variable, change it, reprint, observe. It’s slower for one print and far faster across your next hundred.
Catching problems before they waste filament is even better. Our G-code pre-flight checklist and the pre-flight check tool flag obvious failure modes before you hit print, and the defect identification tool helps you put a name to what you’re actually looking at. If you’d rather just ask, our AI print assistant can talk you through any of these fixes step by step.
Related: once you’ve got your prints dialled in, 3D printing scales well beyond hobby parts — see how it’s used as a real manufacturing method in this guide to going from prototype to production @ GMR – Graham Martin Racing.
FAQ
Why does my first layer not stick even after levelling?
Levelling sets bed flatness, but adhesion also depends on Z-offset, a clean plate, and the right surface. A single fingerprint can cause failure — wipe with IPA first. Then check your first layer looks slightly flattened, not round. Drop first-layer speed to 25–30 mm/s to give it time to bond.
How do I know if my filament is wet?
Wet filament strings persistently no matter how you tune retraction, may pop or hiss as it extrudes, and produces a rough, fuzzy surface. If retraction tuning isn’t fixing stringing, dry the spool before changing anything else — it’s the dominant cause far more often than people expect.
Do I need an enclosure to stop warping?
For ABS and ASA, yes — an enclosure is effectively mandatory to maintain stable ambient temperature. For PLA and PETG, no; they rarely warp enough to justify one. Tackle drafts, bed cleanliness and a slightly higher bed temperature first.
Why is only one corner of my print lifting?
That’s almost always a draft — a vent, open window or fan cooling one side faster than the other. Move the printer or block the airflow before you blame your slicer settings.