Why is my 3D print failing? Fixing adhesion, stringing, warping and layer splits

TUREFF• •0

Every 3D printer fails sometimes, and most failures have a short list of causes. The trick is to change one thing at a time and to print small test pieces rather than repeating a ten-hour job. Here are the four problems beginners meet most often on FDM printers, and what usually fixes them.

Before anything else

Is the filament dry? Damp filament causes rough surfaces, stringing and weak layers all at once.
Are you using the filament maker's recommended temperatures?
Is the build plate clean? Wash it as its maker recommends; skin oil is enough to stop a print sticking.
Is anything loose? Check that belts are snug and the nozzle is not partly blocked.

Problem 1: the print will not stick to the bed

Symptoms: the first lines drag around, the part comes loose mid-print, or you return to a nest of spaghetti. Fixes, roughly in order:

Adjust the Z offset. The most common cause is a nozzle slightly too high. The first layer should be gently squashed, with lines merging into each other.
Re-level the bed while it is at printing temperature.
Clean the surface thoroughly.
Slow the first layer and check the bed temperature against the filament's recommendation.
Add a brim for small footprints or sharp corners.
Turn off the part-cooling fan for the first layer or two.

Problem 2: stringing

Symptoms: thin hairs or cobwebs between separate parts of the print. Fixes:

Dry the filament. Moisture is a frequent and overlooked cause, especially with PETG.
Lower the nozzle temperature a little, within the maker's range. A temperature tower shows you where stringing starts.
Tune retraction, the small pull-back of filament when the nozzle moves without printing. Too little gives strings; too much can cause jams. Change it in small steps and use a retraction test model.
Increase travel speed so the nozzle spends less time oozing over gaps.
Enable any option that keeps travel moves inside the part, so strings end up hidden.

A few fine hairs can be removed afterwards with a quick pass of a heat gun, held at a distance and with care.

Problem 3: warping

Symptoms: corners lift off the bed and curl upwards, or a long flat part rocks when you set it down. Plastic shrinks as it cools. If the top cools faster than the bottom, it pulls the corners up.

Improve adhesion using everything from Problem 1, and add a wide brim.
Keep the air warm and still. Draughts from windows, fans and air conditioning cause a surprising amount of warping. An enclosure is close to essential for ABS and ASA.
Check the bed temperature is right for the material.
Reduce cooling for materials that warp easily.
Redesign the part: rounded corners and slightly chamfered bottom edges warp less than sharp square ones.

Problem 4: layer separation and cracks

Symptoms: layers split apart, often near the top of tall prints, or a part snaps cleanly along a layer line. Layers need to fuse while hot.

Raise the nozzle temperature a little, within the maker's range.
Reduce part cooling, especially with PETG and ABS.
Stop draughts and use an enclosure for warping-prone materials.
Check for under-extrusion: thin, gappy walls suggest a partial clog, a slipping extruder or a speed too high for the hot end to keep up.
Orient the part so the forces it will meet run along the layers, not across them. A hook printed lying down is much stronger than the same hook printed standing up.

When nothing works

Go back to the printer's default profile and a fresh, dry spool of PLA, and print a small calibration cube. If that prints well, the problem is in your settings or material. If it does not, the problem is mechanical, and the community for your printer model will have seen it before. Post a description or a photo of your failed print and what you have tried, and others can help diagnose it in the comments.