Most FDM print quality problems trace back to one of four things: temperature, flow, motion, or the interface between the part and the bed. Once you can place a defect into one of those buckets, fixing it stops being guesswork.
This page is the map. It groups the common defects by what’s actually going wrong, links to a full walkthrough for each one, and gives you a quick way to narrow down where to start looking on your own printer.
Start with what you can see
Before changing any settings, look closely at the failed print (or the one in progress) and match it to one of these categories:
- The surface looks rough or has fine wispy strands between parts. That’s almost always stringing, caused by filament oozing during travel moves.
- Corners lift off the bed, or the part warps into a curved shape. That’s warping, driven by uneven cooling and shrinkage.
- You can clearly see and feel ridges running around the whole model, even where you didn’t expect them. That’s visible layer lines, a mix of mechanical and cooling causes.
- The first layer won’t stick, peels up at the edges, or the whole print detaches partway through. Start with first-layer adhesion.
- The part is missing material in some spots, or has blobs and zits in others. That’s an extrusion balance issue; see under-extrusion vs. over-extrusion.
The four root causes
Temperature. Too hot and the filament oozes, sags, and strings. Too cold and it doesn’t bond between layers or extrude consistently. Every polymer has a usable range, and it shifts a few degrees between filament brands even within the same material (see the PLA vs. PETG vs. ABS comparison for typical ranges).
Flow. This is the relationship between how much filament your firmware thinks it’s pushing and how much is actually coming out of the nozzle. A miscalibrated E-steps value or an incorrect flow percentage throws off wall thickness, layer adhesion, and dimensional accuracy at the same time, even when everything else is dialed in. Calibrating flow rate is one of the highest-leverage things you can do on a new printer.
Motion. Retraction, travel speed, acceleration, and jerk/junction settings all affect how cleanly the nozzle moves between features without dragging plastic with it. A retraction setting that works for one filament can under- or over-perform on another with different viscosity.
Bed interface. Everything from bed leveling to surface material to the first layer height affects whether a part actually stays where you put it. This is also the category most likely to produce failures that look like something else — a print that “warps” at one corner might really be a bed that’s not level there.
A troubleshooting order that saves time
When a print is coming out wrong and you’re not sure why, checking things in this order avoids fixing symptoms instead of causes:
- Confirm the bed is actually level and the first layer squish is correct. A large share of “random” print failures are bed issues in disguise.
- Check flow calibration, especially if the printer is new, the nozzle was recently changed, or you switched filament brands.
- Verify nozzle temperature against the filament you’re using, not just the printer’s default profile. Manufacturer-recommended ranges vary and your particular spool may run better a few degrees off the middle of that range.
- Look at retraction and travel behavior if the surface finish issue is stringing- or blob-specific rather than structural.
- Only then tune cooling and speed for cosmetic surface finish, once the structural fundamentals are solid.
Doing them out of order usually means re-doing an earlier step later, because a bed or flow problem can masquerade as a cooling or retraction problem.
Common mistakes
Work through the guides below in whichever order matches what you’re actually seeing, or start from calibration if you’re setting up a printer for the first time and haven’t had a failure yet.
Sources
In this section
3D Print Warping: Why Corners Lift and How to Stop It
Warping is uneven shrinkage pulling a part off the bed, usually starting at corners. Here's what actually controls it, from bed temperature to enclosures.
How to Fix First Layer Adhesion Problems
A step-by-step way to get a print to actually stick to the bed, from leveling to surface prep, without guessing at random fixes.
Stringing in 3D Prints: Causes and How to Fix It
Thin wisps of plastic between separate parts of a print almost always trace back to temperature or retraction. Here's how to tell which one, and what to change.
Under-Extrusion vs. Over-Extrusion: How to Tell Them Apart
Both show up as rough surfaces and weak parts, but the causes (and fixes) are opposite. Here's how to diagnose which one you're actually looking at.
Visible Layer Lines: What Causes Them and When to Worry
Some layer lines are unavoidable in FDM printing. Here's how to tell normal texture from a mechanical problem, and the settings that actually smooth things out.