A well-prepared STL file produces a clean print with dimensions close to what you designed. A poorly prepared file can result in missing geometry, incorrect scale, walls too thin to print, or a model that simply can't be sliced correctly. This guide covers what to check before submitting your file.
1. Export at the right resolution
STL files represent curved surfaces using flat triangles. If you export at too low a resolution, curves will appear faceted and flat spots will be visible. If you export at too high a resolution, the file becomes unnecessarily large without any improvement in print quality (since the printer's layer height is the limiting factor anyway).
Most CAD tools have a "deviation" or "tolerance" setting for STL export — a value of 0.01–0.05 mm is usually appropriate for functional parts. In Fusion 360, use the "Refinement" setting: "Medium" or "High" is usually right. In FreeCAD, keep the "Surface deviation" setting around 0.02 mm.
2. Check wall thickness
FDM printers extrude plastic through a nozzle — typically 0.4 mm diameter. Features thinner than approximately 0.8 mm (two nozzle widths) may not print reliably, and features below 0.4 mm will be ignored entirely. If your design has thin walls, gaps or fine detail, check them before submitting.
A quick way to check: open your STL in a free slicer like Bambu Studio or Cura and review the layer preview. Any sections where the preview shows nothing being printed indicate features too thin to reproduce.
3. Check the model is manifold (watertight)
A manifold mesh is one with no holes, no reversed faces and no internal geometry — effectively, a solid object that could hold water. Non-manifold geometry causes slicing errors and print failures. Most CAD tools produce clean geometry, but if you've been editing meshes in Blender or similar, errors can creep in.
Free tools for checking and repairing meshes:
- Meshmixer (free, Autodesk) — Analysis → Inspector to find and repair holes
- Microsoft 3D Builder — automatically repairs most mesh errors on import
- Netfabb Basic (free version) — mesh analysis and repair
4. Check scale and units
STL files contain no unit information — just coordinates. If you designed in millimetres and your software exports the STL assuming inches, your part will arrive at 25.4× the intended size (or vice versa). Always verify the printed dimensions match design intent before submitting.
Our quote tool displays the calculated volume — you can cross-check this against your expected part volume as a quick sanity check. If something looks drastically off, the scale is likely wrong.
5. Orient for strength, not just aesthetics
FDM parts are stronger parallel to the build plate than they are perpendicular (in the Z direction). When designing or orienting your part, consider where the loads will be:
- Tension loads should act parallel to the layer lines where possible
- Features that will be drilled or tapped are best if the drill axis is perpendicular to the layers
- Long flat parts tend to warp — add a brim or design a slight chamfer on the bottom edge
We orientate parts for optimal printability, but if your design has specific requirements, let us know in your order notes.
6. Think about support material
Overhangs greater than about 45° from vertical typically need support structures. Our quote tool calculates volume-based pricing and doesn't explicitly account for heavy support requirements — for parts with extreme overhangs (large horizontal spans, fully unsupported bridges), the actual material and time cost may be slightly higher than quoted. We'll confirm before starting if this applies.
If you can redesign the part to reduce overhangs — chamfers instead of sharp horizontal transitions, splitting into two parts that are glued or fastened together — it will typically give a better result.
7. Quick checklist before submitting
- ✓ STL exported at appropriate resolution (0.01–0.05 mm deviation)
- ✓ All walls at least 0.8 mm thick
- ✓ No non-manifold geometry or internal faces
- ✓ Correct scale (millimetres, dimensions as intended)
- ✓ Reviewed in a slicer preview if in doubt
Common questions
Why does my STL import at the wrong size?
STL files carry numbers but no units. If your part arrives ten or twenty-five times too small, the exporter wrote inches or centimetres where the slicer expected millimetres.
What does non-manifold mean?
It means the mesh is not a sealed solid: there are holes, duplicate faces or edges shared by the wrong number of surfaces, so the slicer cannot tell inside from outside.
Do I need to repair my STL before sending it?
No. Send what you have and we check it. We repair ordinary mesh faults at no charge and tell you before doing anything that would change how the part looks.
What resolution should I export at?
Fine enough that curves look smooth at full size, not finer. A chord tolerance around 0.01 mm is plenty. Beyond that the file grows for no visible benefit.
Should I send an STL or a STEP file?
Send STEP if you have it. STEP keeps true curves and real units, so we can adjust a hole or a clearance properly instead of editing a triangle mesh.
Why are my thin walls disappearing?
A wall thinner than the nozzle width has nowhere for a bead of plastic to go, so the slicer drops it. Below about 0.8 mm, expect features to vanish.
Published 9 September 2026 · last reviewed 5 October 2026.
Ready to print?
Upload your STL and get an instant quote based on your file's actual geometry. No account needed.