When prints go wrong: troubleshooting

Here is the first thing to know, and the most important: a failed print is normal. Not "normal for beginners," normal for everyone. People who have run printers for years still peel ugly blobs off the bed, still come back to a tangle of plastic spaghetti, still mutter at a part that warped overnight. The difference between them and a first-week beginner is not that they fail less. It is that they can read the failure.

That is the whole goal of this chapter. A bad print is not a verdict on you. It is information, like an x-ray. The shape of the mess tells you what went wrong, and once you can name the symptom you are usually one small change away from a fix. So when something fails, do not feel bad and do not throw the part across the room. Look at it. Ask what it is telling you.

By the end of this chapter you will have a mental table: I see this, so the cause is probably that, so I try this fix first. You used some of these ideas already in Chapter 4 and Chapter 5. Here we put them in one place you can come back to.

The beginner debugging mindset

Before any specific fix, three habits will save you more grief than any single setting. Read these first. They are the part most people skip, and the part that actually matters.

Change one thing at a time. When a print fails it is tempting to raise the temperature, drop the speed, re-level the bed, and add a brim all at once. Then the next print works and you have no idea why, so you cannot repeat it. Change one variable, print again, see what moved. Slower, yes. But you are learning the machine instead of guessing.

The first layer is king. A large majority of failures either start in the first layer or trace back to it. If that first layer goes down clean, flat, and stuck, you have already dodged most of the classic disasters. So when in doubt, watch the first layer go down. Do not walk away during it. We will come back to this idea constantly.

Keep brief notes. A scrap of paper or a notes app is enough. Write the date, the filament, the nozzle temperature, and what you changed. "PETG, 235C, raised bed temp to 80, stringing better" is a full lab notebook in one line. Future you, three weeks from now, staring at the same problem, will be grateful.

Don't be confused. Warping and poor bed adhesion look similar but are not the same. With poor adhesion, the part never really sticks: the whole thing comes loose, slides, or pops off early, often within the first few layers. With warping, the print sticks fine at first, then the corners slowly curl and lift up off the bed as the plastic cools and shrinks while the rest keeps printing. Adhesion is "it would not hold on." Warping is "it held on, then peeled itself back up." The fixes overlap (clean bed, brim, less cooling) but the cause is different: adhesion is about the bed surface and leveling, warping is about cooling and shrinkage.

The centerpiece: symptom, cause, fix

Here is the table to come back to. Read across: what it looks like, why it happens, and the one or two fixes that move the needle first. After the table, a few of the trickier ones get their own short section.

A few of these deserve more than a table row.

First layer will not stick

This is the big one, so we start here. The print either never grabs the bed, or it sticks for a layer or two and then a corner lets go and drags. Picture it:

   nozzle too HIGH            nozzle about RIGHT
   ~~~~~ (gap) ~~~~~          _________________
   o o o  loose beads         ===============  flat, joined line
   ----------------- bed      ----------------- bed

When the nozzle sits too high, the plastic comes out as a loose round bead that does not press into the bed, so it will not stick. When it is about right, that first line gets gently squished into a flat ribbon with no gaps. The fixes, in order: re-level the bed (or lower the nozzle a hair using your printer's Z offset, which is the setting that controls how close the nozzle starts to the bed); make sure the bed is genuinely clean, because skin oils from your fingers are enough to stop adhesion (a wipe with isopropyl alcohol works); and if it still resists, add a brim, the flat skirt of extra plastic around the base that you met in Chapter 5. A brim gives the part more grip and is the single most reliable rescue for a stubborn first layer.

Warping

Warping shows up most on bigger flat parts and on materials that shrink more as they cool, especially PETG and ABS. The corners lift because the outer edges cool and contract first while the center is still warm, and the contracting plastic pulls the corners up like a sandwich curling at the edges.

   side view of a warped part:

     \_______________/   <- corners pulled UP
       (still stuck in the middle)
   ------------------------- bed

Heat is your friend here. Keep the bed warm so the bottom of the part stays relaxed. Cut or reduce the part cooling fan for the first several layers so nothing chills too fast. Use a brim for extra grip at the corners that want to lift. And keep the printer out of cold drafts: an open window or an air-conditioning vent blowing across an open-frame printer is a classic warping cause. An enclosure (even a cardboard box over the printer, carefully, away from anything that gets hot) helps a lot with ABS.

Nothing or too little plastic

If the nozzle is moving correctly but the part is thin, full of gaps, or simply absent, you have under-extrusion (not enough plastic) or a clog (the path is blocked). First, watch the filament: is it actually being pulled in, or is the drive gear slipping and grinding a flat spot into the strand? If it is slipping, the filament may be too cold to flow, so raise the nozzle temperature 5 to 10 degrees and try again. If nothing comes out at all even at temperature, you likely have a clog, a bit of burnt or hardened plastic stuck in the nozzle. The gentle first move is to heat the nozzle and try pushing fresh filament through by hand; many printers also support a "cold pull," and your printer's manual or community (Chapter references) will show the exact steps for your model.

Note the difference, because the fix differs: under-extrusion still puts some plastic down, just not enough, giving thin walls and small gaps. A clog usually gives you nothing, a printhead miming the motions over an empty bed. Thin and patchy points to extrusion settings; completely empty points to a blockage.

Stringing and wisps

Stringing is the fine cobweb of hairs strung between separate parts of a print, like spun sugar. It is extremely common with PETG. It happens because when the nozzle lifts and travels to a new spot, molten plastic keeps oozing out and leaves a trail. Two settings fix almost all of it. Retraction tells the printer to pull the filament back slightly before a travel move, relieving the pressure so it stops oozing; turn it on or increase it modestly. And temperature: a nozzle running hotter than it needs to keeps the plastic runnier and stringier, so try dropping it 5 degrees at a time. One more cause people forget: wet filament. Plastic absorbs moisture from the air, and damp filament hisses, pops, and strings no matter how good your settings are. Drying the spool can transform a "broken" roll.

Layer shift

A layer shift is a clean, sudden sideways jump in the print, as if someone slid the top half over. Everything below is fine, everything above is offset by the same amount.

        ____________
       |            |   <- top half shifted right
    ___|            |
   |                |
   |________________|   <- bottom half lined up

This is mechanical, not a slicing problem. Either a belt slipped a tooth, or the printhead bumped something (a blob it could not climb over, a clip, a stray tool) and lost its place because most hobby printers cannot tell they were knocked off course. Slow the print down and lower acceleration so moves are less violent, check that the belts feel firm rather than loose, and make sure nothing is in the printhead's path.

Spaghetti

Spaghetti is the dreaded one: you come back and the bed is buried in a wild nest of loose plastic strands, with no recognizable part. It looks catastrophic but the cause is almost always simple. The print detached from the bed (or a tall thin part snapped off), and the printer, unaware, kept dutifully extruding into thin air where the part used to be. So spaghetti is not really its own problem. It is the aftermath of an adhesion failure or a knocked-loose part. Fix the first layer and the part's grip on the bed, and spaghetti disappears with it. Many newer printers have a camera that can detect this and stop; if yours does not, the lesson is to check on tall or finicky prints now and then.

Elephant's foot

Elephant's foot is a bottom layer that bulges out wider than the rest of the part, as if the print is standing in slightly melted shoes. The weight of the part above, plus a nozzle that is a touch too close or a bed that is a touch too hot, squashes that first layer outward. Raise the nozzle very slightly (a small Z-offset change), drop the bed temperature a few degrees, and if your slicer has an "elephant's foot compensation" or chamfer option, a small value cleans it up. This one matters for the squeezer in Chapter 15, because a bulged base can stop two parts from fitting together cleanly.

Gaps in the top, weak infill

If the top surface of a part has small holes or looks like rough netting, the top layers are bridging over the infill (the partially hollow honeycomb inside the part) and not quite closing up. Add a couple more top layers so there is more material to span the gaps, and bump the infill density a little so the top layers have more to rest on. If the infill itself looks sparse, weak, or visibly stringy through the walls, that is usually under-extrusion or wet filament again, so check those too.

Drooping overhangs and bridges

An overhang is part of the model that sticks out over empty space, and a bridge is a flat span between two raised points (think the top of a doorway). Steep overhangs and long bridges droop because the plastic has nothing under it and sags before it cools. Three levers: turn up the part cooling fan so each strand freezes faster; add supports, the temporary scaffolding the slicer builds under overhangs that you then snap off; or simply reorient the model so the tricky face points up or sits flat, avoiding the overhang entirely. Reorienting is free and often the best answer.

Layers cracking or splitting

If a finished part cracks along the layer lines or peels apart under light stress, the layers did not bond well to each other. This is common in PETG and ABS. The bond depends on each new layer arriving hot enough to fuse to the one below, so raise the nozzle temperature a little, reduce the cooling fan (which can chill layers before they weld), and once again dry the filament, because moisture sabotages layer adhesion as much as it does stringing.

First aid: my print failed, what do I check first

When a print fails and you do not yet know why, run down this quick list before changing any setting. Most failures are caught in the first three.

1. Is the bed clean and level? Oils, dust, and an uneven gap cause more failures than anything else. Wipe it, re-check the level.
2. Is the filament dry and feeding? Look for slipping at the drive gear and for the popping or hissing of damp filament.
3. Is the temperature right for this material? Check the value on the spool against what the slicer is sending.
4. Is the nozzle clear? No plastic at all usually means a clog.
5. Is the model oriented sensibly, with supports where needed? A tall, top-heavy, or steeply overhanging part may just need turning or supporting.

Takeaways

• Failed prints are normal for everyone, including experts. A failure is readable information, not a personal verdict.
• Change one thing at a time, watch the first layer (where most failures begin), and keep one-line notes of what you changed.
• Learn the symptoms by sight: warping curls corners up, layer shift jumps sideways, spaghetti means the part came loose, stringing leaves hairs, elephant's foot bulges the base.
• Warping is not the same as poor adhesion: one held on then peeled, the other never held.
• Under-extrusion still lays down some plastic; a clog lays down none. The fixes differ.
• Dry filament, a clean level bed, and the right temperature solve a surprising share of problems before you touch anything fancy.
• When stuck, run the first-aid checklist top to bottom, and remember the community is there to help (Chapter references).

You now have a diagnostic eye, which is genuinely the hard part. You will put it to work on a real object in Chapter 15, when the squeezer comes off the bed and may need a tweak or two. But first, it is time to stop printing other people's designs and make your own.

👉 Next up: CAD basics with Tinkercad, where you design a part from a blank screen.