3D printing troubleshooting collection: FDM and SLA problems, causes, and fixes

Almost every first-layer failure traces to the gap between nozzle and bed, not to the filament. When the extrusion looks rounded and sits on top of the surface, the nozzle is too high. When it looks translucent and squeezes out sideways, it is too low. Level the bed cold, then set the live Z offset while the skirt or brim is printing. Adjust in 0.02 mm steps.

Warping on the corners of a large flat part is a thermal problem. The top of the part cools faster than the bottom, so the lower layers stay expanded while the upper ones contract and pull the corners up. Enclose the printer or move it away from a draft. Raise the bed temperature within the filament maker's range, and keep the part on the plate until it cools to room temperature.

Adhesion additives are the last step, not the first. Clean the plate with warm water and dish soap, then IPA. Glue stick, hairspray, or a PEI sheet only helps once the surface is actually clean and the Z offset is correct. On glass, a light scuff with 800 grit restores grip after a few hundred prints.

Part removal can undo a good print. Let the plate cool below 40 °C before you flex it. Metal spatulas scratch PEI and leave marks that transfer to the next part. A flexible spring-steel sheet avoids the problem entirely.

Stringing is residual pressure in the melt zone, not a retraction setting you have not found yet. The nozzle keeps oozing while it travels because the polymer is still under pressure. Lower the print temperature in 5 °C steps and test each one. Most PLA strings disappear between 195 °C and 205 °C on a 0.4 mm nozzle.

Blobs and zits at the seam come from the pressure spike at the start of each layer. Set the slicer to wipe on retract, and if the firmware supports it, enable pressure advance or linear advance. The value is roughly 0.04–0.06 for direct drive and 0.4–0.7 for Bowden on many machines. Tune it with a test tower instead of guessing.

Under-extrusion in the middle of a long print often means heat creep, not a clogged nozzle. Filament softens above the melt zone and swells, then the extruder grinds it. Check the hotend fan is spinning at full speed and that the heatsink is not packed with dust. A cold pull with nylon clears partial carbon deposits.

Over-extrusion shows up as a rough top surface and dimensional oversize. Measure a single-wall test cube with calipers and compare to the slicer's stated wall thickness. A 0.42 mm wall against a 0.40 mm target is close enough; 0.48 mm means flow is set about 15% too high.

A layer shift is a position loss, and the cause is almost always mechanical or electrical. Check the belt tension first: pluck it and listen for a low, even note. A belt that feels springy or slaps the idler is too loose. Then check the grub screw on the pulley that drives that axis. A loose grub screw shifts layers only on fast moves, which makes it easy to miss.

Ringing or ghosting behind corners is vibration that the frame did not absorb. Reduce acceleration in 500 mm/s² steps and print a test block. Adding mass to the frame helps, but stiffening the frame is the real fix. A printer sitting on a wobbly table shows the same artifact, so rule that out before you change firmware.

Stepper drivers that overheat drop steps and cause random shifts on long prints. Feel the motor and driver heatsink after two hours. If you cannot hold a finger on the motor for five seconds, it is running hot. Lower the current slightly, or add a fan over the mainboard.

Z-axis binding produces banding rather than a full shift. Clean and lubricate the lead screws, then check that the coupler is not compressing the screw against the motor shaft. On dual-Z machines, verify both sides move freely by hand with the motors disabled.

A failed SLA print usually separates at the build plate or peels away from the supports. Both point to the same calculation: the force needed to pull the cured layer off the film is greater than the adhesion holding the part. Increase the bottom exposure time in 5 s steps, and rough the build plate with 220 grit if it is new and glossy.

Layer lines or a cloudy surface on a resin part come from over-exposure. Run an exposure test matrix and pick the time where fine features still resolve but the surface is not bloated. Resin at 20 °C behaves differently from resin at 28 °C, so keep the vat temperature stable or extend the exposure in a cold room.

Support marks are a design problem as much as a print problem. Place supports on faces that will be machined or hidden, and angle the part so the largest flat face is not parallel to the film. A face parallel to the film has a large peel area every layer, which is where delamination starts.

Resin left in the vat for days settles and the pigment separates. Stir it with a soft scraper before the next print, and filter it if you see cured flakes. Contaminated resin prints with random pits that look like a hardware fault but are not.

Printing is the right choice for fit checks, jigs, and low-stress covers. It stops being the right choice when the part carries load, seals against a mating face, or needs a tolerance tighter than about ±0.1 mm. FDM holds roughly ±0.3 mm on a well-tuned machine, and SLA improves that to about ±0.1 mm on small features but drifts on long dimensions.

Threads are a common failure point. Printed threads strip under repeated assembly, especially in PLA. Design the printed part with a pilot hole and cut the thread with a tap, or move the threaded feature to a machined insert or a CNC part.

If the printed prototype proved the geometry and you now need the production version in aluminum or stainless, send the same STEP file. We machine from the model, not from the print, so the CAD does not need rework unless the print was scaled for shrinkage.

We quote and return a free DFM analysis within 12 hours. Parts ship in 3–5 days, and 100% inspection before shipment covers the dimensions that the print could not hold.