SketchUp Step Importer

A SketchUp extension that imports STEP assemblies and keeps their structure: parts become groups, repeated parts (screws, nuts…) become components, and heavy sub-assemblies such as a populated PCB can be merged into a single mesh. The result is saved next to the STEP file as a .skp.

SketchUp's Ruby API cannot read STEP (a B-Rep / NURBS format), so the extension delegates the geometry to FreeCAD running headless, then rebuilds the model in SketchUp.

Assembly hierarchy preserved as nested groups

Identical parts detected automatically → one component definition, many instances

Big containers (default: 50+ parts) merged into one mesh, so a PCB with ~1200 components imports in seconds instead of creating 1200 groups

Native progress window: stage, current part, log, elapsed time, Cancel

FreeCAD console window is hidden

Result saved as <name>.skp next to the STEP file

Progress log in %TEMP%\step_import.log

How it works

STEP ──► FreeCADCmd + step2stl_fc.py ──► def_XXXX.stl + manifest.json │ SketchUp (Ruby) ◄───────────────┘ groups / components with placement matrices ──► .skp

FreeCAD opens the STEP, walks the assembly tree and tessellates each unique shape once.

Parts are compared by a position-independent fingerprint (solids, faces, edges, volume, area, bounding box of the local shape). Matches share one STL.

manifest.json records the hierarchy, the definitions and a 4×4 placement matrix for every instance.

The extension reads the STL files, creates groups / component definitions and places the instances with the matrices.

Requirements

Windows (the launcher and FreeCAD discovery are Windows-specific)

SketchUp 2021 or newer (Ruby 2.7+). Developed and tested on SketchUp 2024.

FreeCAD installed (FreeCADCmd.exe). Tested with: FreeCAD version — fill in. No separate Python is needed; the script runs inside FreeCAD's own interpreter.

Installation

Download eugenyh_step_import-<version>.rbz from the Releases page (or build it yourself, see below).

SketchUp: Window → Extension Manager → Install Extension and pick the .rbz.

Restart SketchUp.

On first run the extension looks for C:\Program Files\FreeCAD*\bin\FreeCADCmd.exe; if it is not found you are asked to point to it, and the path is remembered.

Extensions → Import STEP assembly (FreeCAD), choose a .step / .stp file and watch the progress window. When it finishes, the model is in SketchUp and a .skp is saved next to the STEP file.

Don't edit the model while the import is running: the model is built inside a single undoable operation, which is rolled back on cancel or error.

Constants at the top of eugenyh_step_import/main.rb (inside the installed extension folder under Plugins):

Colors and materials are not imported. FreeCADCmd has no GUI and does not read STEP colors; STL carries none.

Units are assumed to be millimetres (FreeCAD's native unit).

Assemblies built from App::Link objects may come out incomplete (links are skipped).

If a part's geometry is baked into global coordinates instead of a placement, repeated copies are not recognised and come out as separate groups.

SketchUp cannot represent edges shorter than 0.001″ (≈ 0.025 mm): the tiniest sliver triangles of dense meshes disappear (≈ 0.16 % of the area on a test PCB).

Parts whose shapes differ by less than 0.01 mm may be treated as identical.

The user interface is currently in Russian only.

Windows only; not tested on other platforms.

Troubleshooting

Progress and errors are written to %TEMP%\step_import.log (readable while the import runs).

On errors the temporary folder %TEMP%\step2stl… is kept: it contains the STL files, manifest.json, freecad.log and error.txt.

If the FreeCAD window is visible, Windows Script Host is probably disabled; the extension then falls back to a normal launch.

Performance notes for SketchUp extension developers

Findings from building this, measured on a ~160k-triangle PCB mesh:

tools/step_bench.rb and tools/step_check.rb are the small scripts used for these measurements (run them from the Ruby Console).

python build_rbz.py

produces dist/eugenyh_step_import-<version>.rbz. The .rbz is a ZIP archive with the loader in the root; the script makes sure paths use forward slashes.

This project is not affiliated with or endorsed by Trimble / SketchUp or the FreeCAD project. FreeCAD is started as a separate process and is not bundled.