Converts STL, 3MF, OBJ, AMF, and IGES files to clean STEP solids using OpenCASCADE - the same engine that powers FreeCAD, CATIA, and other professional CAD tools.

If this project helps you, you can support development on Ko-fi:

The name has a deliberate double meaning: "to STEP" - whatever format you throw at it, the output is always a clean STEP file - and "two steps" - drop your files into models/, run the launcher. Unlike online converters that wrap the mesh as-is in a STEP container (leaving thousands of flat triangular faces), 2STEP-Converter sews the mesh into a proper solid, repairs it, and merges co-planar faces - the same pipeline FreeCAD uses internally.

Left: typical online converter. Right: 2STEP-Converter. Same source file.

Auto-generated .png previews showing the same model at 20%, 40%, 60%, and 80% reduction.

• Installation
• Usage
• First Run
• How It Works
• Configuration
• Troubleshooting
• Limitations
• Requirements
• Project Structure
• Credits
• Disclaimer
• License

No system Python required - the launcher creates a self-contained portable environment on first run.

1. Download the project:

   • Click the green Code button on the repository page and choose Download ZIP
   • Or grab the latest tagged release from Releases
   • Or clone with git: git clone https://github.com/yaneony/2STEP-Converter.git

2. Extract the archive to a folder of your choice. Keep the path short on Windows (e.g. C:\Tools\2STEP-Converter) to avoid the 260-character path limit - see Windows 260-character path limit.

3. Run the launcher. First launch auto-installs micromamba and all dependencies (~7.5 GB on disk, 5-15 min depending on connection speed):

   • Windows - double-click 2STEP-Converter.bat
   • macOS / Linux - make executable once with chmod +x 2STEP-Converter.sh, then ./2STEP-Converter.sh

4. The launcher will ask once where to install the Python environment: portable (next to the script in lib/) or platform default (under your user profile). See Install location for the exact paths and trade-offs.

5. Once the environment is built, drop input files into models/ and run the launcher again - or pass files on the command line. See Usage.

1. Drop files into the models/ folder
2. Run the launcher:
   • Windows - double-click 2STEP-Converter.bat
   • macOS / Linux - ./2STEP-Converter.sh (one-time chmod +x 2STEP-Converter.sh)
3. Output .stp files appear in the same folder

Supported formats: .stl .3mf .obj .amf .igs .iges

Windows

2STEP-Converter.bat model.stl
2STEP-Converter.bat model.stl -o out.stp

macOS / Linux

./2STEP-Converter.sh model.stl
./2STEP-Converter.sh model.stl -o out.stp

Pass any number of files directly - no need to use the models/ folder:

Windows

2STEP-Converter.bat a.stl b.obj c.3mf

macOS / Linux

./2STEP-Converter.sh a.stl b.obj c.3mf

Windows

2STEP-Converter.bat --reduce 25 model.stl
2STEP-Converter.bat --reduce 25,50,75 model.stl
2STEP-Converter.bat --format ap214 -d C:\out model.stl
2STEP-Converter.bat --no-preview --dry-run
2STEP-Converter.bat --watch

macOS / Linux

./2STEP-Converter.sh --reduce 25 model.stl
./2STEP-Converter.sh --reduce 25,50,75 model.stl
./2STEP-Converter.sh --format ap214 -d ~/out model.stl
./2STEP-Converter.sh --no-preview --dry-run
./2STEP-Converter.sh --watch

When REDUCE_INTERACTIVE is enabled (default), each batch file pauses on a reduction prompt:

On first launch the launcher downloads everything automatically:

Total fresh install: ~7.6 GB on disk, split roughly in half between the live env and an extracted-package mirror:

Inside lib\env\ (~3.5 GB):

• ~1.6 GB in Library\bin\ - native DLLs. Biggest: MKL (~280 MB across multiple kernels), Qt6 (~70 MB), libclang (~125 MB), VTK (~150 MB), Mesa/Vulkan software renderers (~110 MB), Open3D (~34 MB).
• ~700 MB in Lib\site-packages\ - Python packages. Biggest: OCC (308 MB), open3d (79 MB), plotly (57 MB), vtkmodules (43 MB), PySide6 (38 MB), numpy (30 MB), dash (29 MB), matplotlib (26 MB).
• Roughly ~170 MB of that site-packages total is indirect visualization dependencies (plotly, dash, PySide6, vtkmodules) pulled in by Open3D's optional renderer code but not used by the converter.
• ~1.2 GB in Library\lib\, Library\share\, and other support folders.
• Open3D and Qt6 also bundle their own copies of native DLLs inside site-packages (e.g., Open3D.dll exists once in Library\bin\ and once in site-packages\open3d\cpu\), so some content is duplicated within the env itself.

lib\https\ (~4.1 GB):

This is not a compressed cache - it's micromamba's package directory. Every conda package is extracted in full here (e.g., mkl 425 MB, qt6-main 372 MB, vtk-base 346 MB, pythonocc-core 314 MB, open3d 210 MB) so that envs can be (re)built quickly by linking files out of this mirror. On filesystems where hardlinks across the directories aren't available - which is the common case on Windows - the contents end up as full copies, effectively doubling the disk usage.

The launcher checks for an existing environment in this order:

1. lib/ next to the script - used if present (portable mode)
2. Platform default - used if present
3. Neither found - you are asked where to install

To enable long paths manually in an elevated PowerShell:

Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem" -Name LongPathsEnabled -Value 1

Then reboot. This does not apply to macOS or Linux.

Replicates the FreeCAD Part workbench conversion pipeline. Mesh inputs (STL/3MF/OBJ/AMF) go through a mesh-cleanup stage first, then a CAD-kernel stage. IGES inputs skip straight to the CAD stage since they already contain B-Rep geometry.

Steps 5-7 run in isolated subprocesses so a crash inside the CAD kernel doesn't take down the converter.

All settings live in data/config.json, created automatically on first run. Edit it with any text editor.

{
    "DEFAULT_TOLERANCE": 0.01,
    "DEFAULT_REDUCE": 0,
    "REDUCE_INTERACTIVE": true,
    "SKIP_EXISTING": true,
    "ANGULAR_TOLERANCE": 0.01,
    "SEW_TIMEOUT": 1800,
    "DEFAULT_FORMAT": "ap203",
    "GENERATE_PREVIEW": true,
    "MODELS_DIR_NAME": "models",
    "STL_EXT": ".stl",
    "TMF_EXT": ".3mf",
    "OBJ_EXT": ".obj",
    "IGS_EXT": ".igs",
    "AMF_EXT": ".amf",
    "STP_EXT": ".stp"
}

Invalid values are reported as warnings at startup and fall back to their defaults.

When a file fails, the red error line at the bottom of its box tells you what happened. Common messages and what to try:

This is a mesh-to-STEP converter; it intentionally doesn't try to be everything.

• Holes are not filled. Source mesh must be watertight or near-watertight. The converter preserves geometry as-is - if there are tiny gaps, sewing will produce an open shell instead of a solid. Fix holes in Blender/MeshLab/etc. before converting.
• No color, materials, or textures. STEP output is geometry only. Surface colors, vertex colors, and UV-mapped textures from the source mesh are discarded.
• No assembly hierarchy. All resulting solids end up at the root of the STEP file. Sub-assemblies and named parts in 3MF / OBJ sources are flattened.
• No automatic self-intersection repair. If two parts of the mesh pass through each other, the sewer may crash or produce invalid geometry. Run a repair pass in a mesh tool first if you suspect this.
• IGES inputs are not reducible. .igs / .iges files already contain B-Rep geometry, not a triangle mesh - --reduce is silently ignored for them.
• STL color extensions are ignored. The non-standard color attributes some slicers embed in binary STL aren't read.
• Animations and time-varying data are not supported. Only static geometry is converted.

• Windows 10/11, macOS (Intel & Apple Silicon), or Linux (x86_64 & ARM64)
• Internet connection on first run only
• ~8 GB free disk space for the Python environment (~7.6 GB used)

Converted STEP files have been tested in Plasticity and import correctly.

2STEP-Converter.bat      - launcher for Windows: auto-setup + run
2STEP-Converter.sh       - launcher for macOS / Linux: auto-setup + run
converter.py             - the converter itself
README.md                - this file
LICENSE.md               - MIT license
models/                  - drop input files here (.stl .3mf .obj .amf .igs .iges)
data/                    - persistent state (auto-created on first run)
  config.json            - tunable constants
  estimator.json         - conversion time history for ETA estimates
docs/                    - screenshots and comparison images used in the README
lib/                     - portable Python environment (auto-created, ~7.5 GB)

Built on these open-source projects:

• OpenCASCADE via pythonocc-core - the CAD kernel that does the actual sewing, fixing, and STEP export.
• FreeCAD - the inspiration for the Part workbench pipeline replicated here.
• Open3D - mesh cleanup (dedup, degenerate-triangle removal) and the primary quadric-decimation reducer.
• trimesh and fast-simplification - mesh reduction fallbacks when Open3D doesn't cope.
• matplotlib + Pillow - the wireframe .png preview renderer.
• micromamba - portable conda-compatible environment manager that bootstraps the whole stack.

Contributions are welcome. Open a pull request, report issues, or fork and adapt the project to your own needs.

This software is provided "as is", without warranty of any kind. The converter itself has been written and tested in good faith, but it relies on a large set of third-party packages (OpenCASCADE, Open3D, Qt6, VTK, MKL, trimesh, fast-simplification, and others) that the launcher downloads automatically from the public conda-forge channel on first run. I have no control over those packages and cannot guarantee their correctness, stability, or that they will never ship a bug or harmful change in a future version.

By running the launcher you accept that:

• Output STEP files may contain errors, invalid topology, or geometry that differs from the source. Always inspect critical results in your CAD tool before relying on them.
• Third-party dependencies may change at any time. The launcher installs whatever conda-forge serves on the day you run it.
• I am not responsible for any data loss, incorrect output, system instability, or other damages resulting from use of this software or its dependencies.

The full legal text is in LICENSE.md.

MIT © 2026 YaneonY