STEP to 3MF converter
Drop your .step / .stp file — we convert it to .3mf right in your browser. Files never leave your computer.
Why convert STEP to 3MF?
3MF is the modern successor to STL — it carries units, colour, and print metadata, ending the decades-old 'is this metric or imperial?' ambiguity. Bambu Studio and PrusaSlicer both prefer 3MF now. Going STEP → 3MF skips the extra STL step and lands a metadata-rich package directly in the slicer.
Who runs this conversion
Makers on the Bambu / Prusa ecosystem that have moved to 3MF natively, engineers handing parts to a print service that wants unit metadata intact, and anyone who got bitten once by an imperial-scaled STL landing at 25.4× size.
Things that commonly go wrong
- Colour metadata does not exist in STEP — the 3MF comes out monochrome until you paint it in your slicer.
- Multi-body assemblies merge into a single mesh like STL — split in CAD first if you need separate parts.
- The 3MF "Beam Lattice" extension is not universally supported; stick to the core spec, which is what this tool emits.
Technical note for this tool
OCCT tessellates the STEP, we then write a 3MF package (zip with 3dmodel.model XML + .rels + metadata) per the 3MF Consortium core spec. Units are tagged millimetres so slicers import at real scale.
STEP vs 3MF— what's the difference?
ISO 10303 boundary-representation CAD format — the industry standard for exchanging precise, parametric solid models between engineering tools.
- Exact curved surfaces (NURBS / B-rep) — no tessellation loss
- Assembly hierarchy, part names and metadata preserved
- Supported by every major MCAD tool (SolidWorks, Inventor, Fusion, Creo, NX…)
- Open, vendor-neutral ISO standard
- Not directly consumable by 3D printers or game engines
- Files are larger and slower to open than mesh formats
- Requires a CAD kernel to read — no native browser support
Modern successor to STL for 3D printing — carries units, colours, materials, and multiple bodies in a zipped XML package.
- Real-world units baked in (no more "is this mm or inches?")
- Multi-material, multi-colour, and per-body metadata
- Compact zipped payload — smaller than equivalent STL
- Not every slicer reads 3MF yet (most do now — Bambu, Prusa, Cura)
- Less tooling for mesh editing compared to STL
Deeper context on the formats
STEP — where it came from
Standardised as ISO 10303 in 1994 to replace the aging IGES format. Application Protocols AP203 (configuration-controlled design), AP214 (automotive), and AP242 (modern merge of both) define what data travels with the geometry — AP242 is the current default for new exports and is what most fabs expect in 2026.
- Assemblies exported with external references break when the .step file is moved without its companion files — always export as a single-file package (AP242 XML or monolithic .step).
- Kernel-to-kernel round-trips (e.g., Inventor → STEP → Fusion → STEP) can introduce tiny sliver faces and edge-tolerance drift; keep the original parametric file as the source of truth.
- PMI (product manufacturing information — GD&T, annotations) only rides along in AP242 — older AP203 exports strip it silently.
Real-world use: Mechanical suppliers quote from STEP, contract manufacturers program CNC toolpaths from STEP, and electronics vendors publish component 3D models as STEP on Digi-Key and Mouser. Any time a mechanical engineer hands off a design to a machine shop or an injection-mold vendor, it ships as STEP.
3MF — where it came from
The 3MF Consortium (Microsoft, HP, Autodesk, Dassault, Shapeways, and others) published version 1.0 in 2015 specifically to replace STL's forty-year-old limitations. Bambu Studio and PrusaSlicer adopted it aggressively because it is the only portable way to ship multi-colour / multi-material print projects.
- The format is zipped XML — renaming .3mf to .zip and inspecting the contents is fair game for debugging.
- Extensions (materials, slice, production) are optional; a slicer may read the geometry but drop the colour metadata.
- Some slicers treat "print-ready 3MF" (baked supports and toolpaths) differently from "design 3MF" (just the mesh). Check the export dialog for the right flavour.
Real-world use: Multi-material Bambu X1C / A1 prints, Prusa MMU workflows, paint-by-face colour printing (PrusaSlicer, Bambu Studio), and Windows 3D Builder. Anywhere an STL would lose information, 3MF has quietly taken over.
How to convert STEP to 3MF
- 1Drop a .step or .stp file. The browser tessellates the CAD B-rep via OpenCascade (WASM) locally.
- 2Preview the generated mesh in 3D and verify the triangle count is acceptable for printing.
- 3Click Download .3MF. Load directly in Bambu Studio, PrusaSlicer, Cura, or OrcaSlicer.
FAQ
Why convert STEP to 3MF?
STEP carries exact CAD geometry but no slicer can print it directly. 3MF is the modern mesh format every current slicer prefers. This page tessellates the STEP into triangles and packages them as a units-aware 3MF — one step instead of STEP → STL → load-into-slicer.
What tessellation quality is used?
We use OpenCascade defaults (linear deflection tuned for visual fidelity). For most PCB-component and mechanical parts this gives sub-0.1 mm surface error, which is below any FDM layer height.
Are units preserved?
Yes — STEP mandates millimetres, and 3MF stores units explicitly. The output will load at the correct real-world scale in every slicer.
Do I still need a STEP viewer?
If you just need a print, no — drop STEP, get 3MF, slice. If you need to machine the part (CNC/mill), keep the STEP; mesh formats lose the B-rep a CAM tool needs.
Is anything uploaded?
No. OpenCascade runs entirely in WebAssembly inside your browser. The STEP file never leaves your device.