Design
Exporting STEP files for manufacture: a checklist
Send STEP when the part has precise holes or mating faces. STL is a mesh and loses true geometry.
HenleyPrint3D engineering2 min readUpdated Published
Key takeaways
- Send STEP (.step or .stp) with the STL.
- Export solid bodies, in millimetres, in build position.
- Re-open the export and compare volume and bounding box.
- Put critical tolerances on a drawing.
Suits
Designers sending a first file for quote, or a repeat file to a new supplier.
Worth knowing
A STEP file carries geometry but not tolerances, so send a drawing for critical features.
Which format to send
| Format | Holds | Use for |
|---|---|---|
| STEP (.step, .stp) | Exact surfaces and solids | Quoting, review, any part with precise features |
| STL | Triangle mesh; units and colour in the file header only | Simple geometry; fallback if STEP fails |
| 3MF | Mesh with units, colour, materials | Multi-colour or multi-material builds |
| Native CAD | Full history | Collaboration and design history |
Checklist
- Export solid bodies only, in millimetres.
- Orient the part in the position you want it built.
- Remove hidden construction bodies and unused parts.
- Note the volume and bounding box in CAD.
- Re-open the exported file and compare both numbers.
- Send a drawing for critical tolerances and threads.
We accept STL, STEP and STP up to 100 MB each. For tolerance guidance see 3D printing tolerances.
To send a model, upload it for a quote, and use the 3D printing quote comparison checklist to compare what comes back.
Frequently asked questions
Is STEP better than STL for 3D printing?
Usually yes. STEP keeps exact geometry, so the manufacturer chooses the mesh resolution, and holes and curved surfaces print more accurately than from a coarse STL.
Which STEP schema should I use?
AP214 or AP242 where offered. AP203 is older and can lose colour and some assembly data.
Why is my exported part the wrong size?
Usually units. Check that the export is in millimetres and measure a known dimension after reopening the file.
Do STEP files include tolerances?
No. A STEP file carries geometry only, so send a drawing or a note for critical tolerances, datums and fits.
What is a good STL export tolerance?
A chord deviation of about 0.01 to 0.02 mm is a common starting point. Check the mesh is watertight before sending.
Get started
Talk to an engineer about your part.
Send us your CAD or describe the problem. We recommend the process, material and finish, and quote with the lead time up front.
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