What's the most common reason a 3D print fails?

For FDM, it's poor first-layer adhesion. If the first layer doesn't stick evenly to the bed, everything printed on top of it is at risk of lifting, warping or shifting later in the job, so levelling the bed, cleaning the build plate and adding a brim for small or awkward footprints solves most of it. For SLA, the equivalent risk is supports that are too sparse or badly placed, which lets the part detach mid-print.

Why do SLA resin parts come out the wrong size?

Resin shrinks slightly as it cures, both during printing and again during UV post-cure, and thin or long features shrink more than bulky ones. For parts with tight tolerances or mating features, flag the critical dimensions at quote stage so we can compensate rather than finding out after the print is done.

Can stringing, warping or support scarring be fixed after printing?

Some of it. Stringing can be trimmed or heat-cleaned off, support scarring can be sanded or filled, and light warping can sometimes be corrected with heat and clamping. Layer shifts and severe warping can't be fixed after the fact and need a reprint, which is why catching the cause early matters more than repairing the result.

3D Printing Problems: A Troubleshooting Guide

A 3D print that fails halfway through, comes out warped or stringy, or measures slightly off from the CAD file almost always traces back to one of a handful of causes. This guide works through the ones we see most often, split by process: FDM (fused deposition modelling, the layer-by-layer filament printers) and SLA (resin printers that cure a photopolymer with light). For each problem, here’s what it looks like, why it happens, and what actually fixes it.

Warping (FDM)

Symptom: corners or edges lift off the bed mid-print, or the whole base curls upward.

Cause: uneven cooling. Outer layers cool and contract faster than the still-warm layers underneath, pulling the part off the plate. It’s worse with high-temperature materials like ABS and ASA, and with large, flat parts that have more surface area to warp across.

Fix: print on a heated bed, add a brim or raft for extra edge adhesion, slow down the first few layers so they cool more evenly, and enclose the printer to cut down draughts for ABS and ASA. Parts prone to warping are also a good candidate for our FDM 3D printing service, which runs enclosed machines for exactly this reason.

Stringing (FDM)

Symptom: thin, hair-like threads of plastic strung between separate features on the same print.

Cause: the nozzle oozes a small amount of molten filament as it travels between two points, because the extruder isn’t retracting fully or is retracting too slowly.

Fix: increase retraction distance and speed in the slicer, lower the nozzle temperature slightly (too low and you risk under-extrusion instead), speed up travel moves, and dry the filament, since wet PLA strings noticeably worse than dry. Our guide to FDM print defects covers this and other FDM-specific issues in more depth.

Layer shifting (FDM)

Symptom: everything above a certain height is offset sideways from everything below it, as if the top half of the print slid across.

Cause: the print head or bed lost its position mid-print, usually because a belt is loose, a stepper motor skipped steps, or something (a stray blob, a loose cable) physically knocked the head off course.

Fix: check belt tension, make sure the X and Y axes move freely with no obstructions, and lower print speed and acceleration for models with fine, fast-moving detail. A shifted print can’t be corrected after the fact, so this is one worth catching on a quick test print before committing to a large or expensive job.

Poor first-layer adhesion (FDM)

Symptom: the print comes loose from the bed early on, or the first layer looks patchy instead of sticking down evenly.

Cause: the bed isn’t level, the nozzle is too far from the plate on the first pass, the build surface is dirty or not hot enough, or the model’s footprint is too small to hold it in place.

Fix: relevel the bed, clean the plate with isopropyl alcohol, adjust the first-layer height, and add a brim for small or oddly balanced parts. Adhesion problems show up in the first ten minutes of a print, so it’s worth ruling out before troubleshooting anything further downstream.

Scarring from support removal (FDM and SLA)

Symptom: small marks, nubs or rough patches left on the surface where support material touched the part.

Cause: supports have to bond to the model to hold overhangs up during printing, so removing them always leaves some trace, more visibly on FDM, where the support fuses to the part, than on SLA, where supports are thinner single points of contact.

Fix: orient the model so supports land on surfaces that won’t be seen, use fewer and finer support touchpoints where the slicer allows it, and sand or fill the marks afterwards. Chasing a completely scar-free print through orientation alone is rarely worth it; light finishing after printing gets the rest of the way.

Resin tolerance and dimensional accuracy (SLA)

Symptom: a resin part comes out slightly smaller, larger or warped compared to the CAD file, sometimes only in specific dimensions.

Cause: resin shrinks a small amount as it cures, both during printing and again during post-cure, and thin or long features shrink more than bulky ones. Orientation and support placement can add their own small distortions on top of that.

Fix: for parts with tight fits or mating features, flag the critical dimensions at quote stage so the file or print settings can be compensated for, rather than finding out after the print is finished. Our SLA resin printing service runs standard, tough, clear and castable resins, each with slightly different shrinkage, and we can advise which suits a tolerance-sensitive part.

Under-cured or tacky surface (SLA)

Symptom: the part feels slightly sticky or soft straight after printing, even once it’s off the build plate.

Cause: SLA parts are only partially cured when they come off the printer. Full strength comes from washing off uncured resin and then UV post-curing, and rushing or skipping either step leaves the surface soft.

Fix: wash thoroughly in isopropyl alcohol to remove uncured resin, then UV-cure for the time the resin manufacturer specifies, longer for thicker parts. Every resin part should be washed and UV-cured before it’s handled or assembled, so it reaches full strength before it’s put to use.

Cracking or layer separation (SLA)

Symptom: visible lines between layers, or the part cracking cleanly along a layer boundary under load.

Cause: usually under-curing (see above), but it can also come from printing too fast for the resin, or from a part that’s simply brittle by design in cross-section, standard resin especially.

Fix: confirm full cure first. If the part still needs to flex or take an impact, the fix isn’t a print setting, it’s a different resin, tough or durable resin instead of standard, or a different process such as FDM or SLS if the geometry allows it.

Most of these are avoidable once you know what to look for, and a quick check of a file before it’s queued catches the majority of them. Upload your STL, STEP or 3MF to our instant quote tool for a same-day quote, and we’ll flag anything likely to cause trouble at that stage. See pricing for what a reprint or a rush job typically costs if a defect makes it through anyway.