Troubleshooting Failed Prints#
Overview#
When a print fails, the cause lives in one of four places: the model (your Fusion design), the export (mesh quality and units), the slicing (orientation, supports, settings), or the machine and material (calibration, hardware, filament or resin condition). Beginners tend to blame the printer first; experienced users go in reverse order of effort and start with what is cheapest to check.
This page is organized by symptom. For each, it lists likely causes ordered roughly by probability, and the fix, with attention to what you can change in Fusion. Most details are for FDM, since it is the most common; resin and powder-bed notes are included where they differ.
Where to find it#
There is no single Fusion command for troubleshooting, but these tools help you diagnose design-side causes:
| Check | Tool (verify in your version) |
|---|---|
| Wall thickness | Inspect > Section Analysis; Inspect > Measure |
| Overhang angles | Slicer overhang preview; Inspect > Draft Analysis as a proxy |
| Unit or size mismatch | Inspect > Measure vs. slicer dimensions |
| Mesh errors | Slicer's error report; Mesh workspace repair |
| Interference between bodies | Inspect > Interference |
| Component timeline issues | Timeline, Browser |
| Printer configuration | Machine Library (if using a Fusion additive setup) |
Step by step#
A general diagnostic routine#
- Describe the failure precisely. Take a photo. Note at which layer or height it started, whether it is on one side or everywhere, and whether it appears on every print or only this one.
- Check if it is repeatable. Print a known-good test (a calibration cube or the benchy-style boat) with the same settings. If the test also fails, the problem is machine or material; if not, it is model or slicing.
- Check the model. Open the Fusion design: units, wall thickness, overhangs, thin features, tolerances.
- Check the export. Open the file in the slicer and look for errors, the correct dimensions and smoothness.
- Check the slicer preview. Scrub through the layers near the failure height.
- Change one thing at a time. Changing three settings at once removes the ability to learn.
- Record the result so the next failure is shorter.
Symptom table (FDM)#
| Symptom | Likely causes | Fixes |
|---|---|---|
| First layer does not stick | Bed not level, nozzle too high, dirty bed, bed temperature too low | Re-level, lower Z offset, clean with soap or IPA, raise bed temperature; in Fusion add a chamfer-free flat base with larger footprint |
| Corners lift (warping) | Cooling shrinkage, drafts, large flat footprint, ABS or nylon | Brim, enclosure, glue, fillet the footprint corners in Fusion, reduce thick bottom areas |
| Elephant foot (flared bottom) | First layer too squished, bed too hot | Raise Z offset, lower bed temperature; add a 0.4-0.6 mm chamfer at the bottom edge in Fusion |
| Stringing | Moisture in filament, high temperature, poor retraction | Dry filament, lower nozzle temperature, tune retraction; increase spacing between parts |
| Under-extrusion (gaps, thin walls) | Clog, wrong filament diameter, low temperature, flow too low | Clean nozzle, check extruder gear, raise temperature, calibrate flow |
| Over-extrusion (blobs, rough) | Flow too high, wrong filament diameter | Calibrate flow and extrusion multiplier |
| Layer shifting | Loose belt, stepper skip, too fast, collision | Tighten belts, reduce speed and acceleration, check for obstructions |
| Layer separation / delamination | Low temperature, drafts, too much cooling, thick layers | Raise temperature, reduce fan, thin layers; in Fusion orient so loads align with layers |
| Sagging overhangs | Overhang too steep, insufficient cooling | Add chamfers in Fusion, add supports, increase cooling |
| Bridges droop | Span too long, hot extrusion | Shorten span, add rib, increase fan |
| Holes too small | Plastic expansion, path compensation | Model holes with clearance parameters, drill |
| Dimensions off | Shrinkage, flow, scale | Calibrate, adjust parameter-driven clearances |
| Part wrong size by 25.4 | Unit mismatch | Export 3MF, check document units |
| Thin walls missing | Wall thinner than nozzle can print | Thicken in Fusion to a multiple of line width |
| Small features missing | Below resolution | Enlarge features |
| Spaghetti (print detached) | Poor adhesion, support collapse, tall wobble | Better adhesion, brim, redesign base, check supports |
| Supports fused to part | Z gap too small | Increase Z gap, use interface layers |
| Supports will not stay | Too sparse, tree wobble | Increase density, use grid |
| Visible seam | Seam position | Move seam to concave corner; adjust design |
| Rough top surface | Too few top layers, low infill | Increase top layers, use ironing |
| Gaps between infill and walls | Overlap too low | Increase infill overlap |
| Z wobble (ripple pattern) | Lead screw issues | Check mechanical alignment |
| Ghosting / ringing | Vibration at corners | Lower acceleration, input shaping (firmware) |
| Nozzle clog | Dirty filament, low temp, heat creep | Cold pull, clean, check cooling |
| Print stops mid-job | Runout, power, thermal protection, file | Check sensors, supply, SD card |
| Broken at layer line when loaded | Orientation | Reorient in Fusion/slicer, add fillets, more perimeters |
| Snap-fit snaps | Brittle material, sharp root | Fillet, longer arm, tougher material |
Symptom notes for resin#
| Symptom | Likely causes | Fixes |
|---|---|---|
| Print does not stick to plate | Plate not leveled, low bottom exposure, cold resin | Re-level, raise bottom exposure, warm the resin |
| Part falls off supports mid-print | Weak supports, big peel force, wrong orientation | More and thicker supports, tilt, hollow, add drain holes |
| Missing layers or holes | Suction cups or air bubbles, vat film worn | Add vents, replace film |
| Soft, tacky surface | Under-cure, wash residue | Longer cure, clean in fresh IPA |
| Cracking after cure | Trapped liquid, over-cure, brittle resin, thick solid | Hollow with at least two drain holes, shorter cure, tougher resin |
| Warped part | Unsupported long span, shrinkage | Add ribs, reorient, support evenly |
| Dimensional error | Exposure calibration | Calibrate, adjust parameters in Fusion |
| Layer lines too visible | Layer height, tilt | Use thinner layers, orient so layers hide on cosmetic face |
Symptom notes for powder-bed (SLS, MJF, metal)#
| Symptom | Likely causes | Fixes |
|---|---|---|
| Powder trapped inside | No escape holes | Add two or more 4-5 mm holes in Fusion |
| Small holes closed | Powder growth | Enlarge holes, drill after print |
| Parts fused together | Gaps too small | Increase gaps to vendor minimum |
| Warping | Large flat areas, thermal gradients | Add ribs, thicken edges, reorient |
| Metal build crash | Curled overhang hit the recoater | Add supports, reorient, simulate |
| Support removal difficult | Access limited | Redesign for access, use machining |
| Surface rough | Process nature | Add stock and finish |
| Dimensional drift | Shrinkage compensation | Apply vendor compensation |
Options reference#
The following table maps common slicer or design levers to the problems they influence.
| Lever | Where | Affects |
|---|---|---|
| Nozzle temperature | Slicer/printer | Adhesion, stringing, strength |
| Bed temperature | Slicer/printer | First layer, warp |
| Print speed | Slicer | Quality, layer adhesion |
| Cooling fan | Slicer | Overhang, bridge, adhesion |
| Retraction | Slicer | Stringing |
| Flow rate | Slicer | Over/under-extrusion |
| Z offset | Printer | First layer |
| Layer height | Slicer | Resolution, strength |
| Wall count | Slicer | Strength |
| Orientation | Slicer or Fusion | Strength, supports |
| Supports | Slicer or Fusion | Overhangs |
| Clearance parameters | Fusion | Fits |
| Wall thickness | Fusion | Printability |
| Chamfers/fillets | Fusion | Overhangs, strength, elephant foot |
| Export refinement | Fusion | Smoothness, hole size |
| Units | Fusion/export | Scale |
Tips and pitfalls#
Tip: Keep a failure log. A simple table of date, part, material, settings, symptom and fix pays off after a few months.
Tip: Print a standard calibration set (cube, bridging test, overhang test, temperature tower) when you change filament brand or after maintenance. It is a faster path than debugging a large part.
Warning: Do not "fix" a design-side problem with slicer hacks when the geometry is the issue. A 0.3 mm wall that you coax into printing is a liability; thicken it in Fusion.
Warning: Moisture is a hidden culprit. Nylon, PETG, TPU and even PLA absorb water, which causes stringing, bubbles and weak parts. Dry filament before printing.
Tip: If the same failure occurs at the same height every time, look at the model at that height in the slicer preview: a transition from one geometry to another (a thin neck, a small island, an overhang start) is a common culprit.
Warning: Never leave a failing print unattended with a heated nozzle. Thermal and fire safety matter; use a printer with thermal runaway protection and, ideally, a smoke detector nearby.
Tip: When a part breaks in use, examine the break: a clean line along a layer shows orientation failure; a break at a sharp corner shows stress concentration. Use both to modify the Fusion model (add fillets, reorient, thicken).
Warning: For resin, wear gloves and eye protection when clearing failures; failed prints leave uncured liquid in the vat and on the plate.
Practice exercise#
Take a part that failed or print one deliberately designed with problems: a 0.3 mm wall, a 90-degree overhang, a 2 mm round horizontal hole, and sharp internal corners. Print it. Photograph the failures. For each failure, state the cause and then fix the Fusion model: thicken the wall to 1.2 mm, add a 45-degree chamfer under the overhang, replace the hole with a teardrop, and add 1 mm fillets. Reprint. Expected result: the second version prints cleanly, and you have a pair of before-and-after photos plus a short list of design rules you proved on your own machine.
Related#
- 3D Print Workflow Overview
- FDM Design Guidelines
- Orientation and Support Generation
- Exporting STL and 3MF