fusion-reconstruct-mcp

An MCP server that lets an LLM turn an STL/3MF mesh (or a reference photo) into a parametric Fusion 360 model - rebuilt feature by feature (sketches, extrudes, fillets, patterns...), not imported as a dumb mesh body.

Why

Slicers (Bambu Studio, PrusaSlicer, ...) only understand STL/3MF: baked triangle meshes. Fusion 360 only understands parametric feature trees. Importing an STL into Fusion gives you a solid you can look at but can't meaningfully edit - no parametric dimensions, no editable sketches, nothing you can push a slider on. This project bridges that gap by letting an LLM look at the mesh, figure out what it's made of (plates, holes, bosses, ribs...), and rebuild it as real Fusion features - so you get a model you can actually resize, add holes to, or otherwise modify the way you would something you built by hand.

Scope (read this first)

This targets mechanical/functional parts - brackets, enclosures, mounts, plates with bolt holes, bosses - reconstructed from primitives (extrude, revolve, fillet, chamfer, pattern, mirror, boolean ops). It does not attempt free-form/organic surface reconstruction; that's a much harder, less reliable problem this project doesn't try to solve. See docs/RECONSTRUCTION_STRATEGY.md for the intended workflow.

How it works

flowchart LR
    LLM["LLM client"] -- MCP --> Server["MCP server<br/>(mesh analysis + Fusion bridge client)"]
    Server -- HTTP, localhost --> Addin["Fusion 360 add-in<br/>(runs inside Fusion)"]
    Addin --> Fusion[("Your live Fusion design")]

The MCP server exposes two families of tools:

• mesh_summary, find_circular_holes, find_circular_faces, list_planar_facets, get_cross_section, render_orthographic_views, compare_meshes - pure mesh analysis (trimesh), no Fusion required. Used to understand the input file and to check the reconstruction's accuracy against it afterwards.
• fusion_* (create sketch, add line/circle/rectangle/arc, extrude, revolve, fillet, chamfer, pattern, mirror, combine, set/list parameters, export, screenshot, ...) - talk to a companion Fusion 360 add-in over http://127.0.0.1:6172, which executes them against the real adsk.fusion API inside a running Fusion session.

See docs/ARCHITECTURE.md for why it's split this way (short version: Fusion's API only runs inside Fusion's own process, on its main thread, with no pip access - so the add-in has to be a small stdlib-only HTTP bridge).

Setup

See docs/SETUP.md for full instructions. Short version:

git clone https://github.com/<your-username>/fusion-reconstruct-mcp.git
cd fusion-reconstruct-mcp
python -m venv .venv && source .venv/bin/activate  # .venv\Scripts\activate on Windows
pip install -r requirements.txt

Then copy fusion_addin/FusionReconstructBridge/ into Fusion's AddIns folder and start it from Utilities > Add-Ins > Scripts and Add-Ins, and point your MCP client (claude mcp add ... or your mcp.json) at python -m server.mcp_server in this repo.

Usage

With Fusion running and the add-in started, ask your LLM client something like:

Reconstruct ~/Downloads/bracket.stl as a parametric Fusion 360 model, then export it and check how close it is to the original.

It will inspect the mesh, look at rendered views, locate holes/bosses, rebuild the part feature by feature in Fusion, and validate the result by exporting and diffing against the source mesh. For a photo instead of a mesh, it builds a first pass from your description/the image and refines it interactively with you - there's no ground-truth dimension data in a single photo, so treat that path as "assisted modeling," not "scan-to-CAD."

Status / limitations

• Circle/hole detection is a mesh-tessellation heuristic (facet outline circle-fitting)
  • it works well on typical printable parts but isn't a general feature-recognition engine.
  • Photo-based reconstruction estimates proportions; it does not measure real-world dimensions from a single image.
• render_orthographic_views uses a plain matplotlib wireframe/solid renderer (no GPU dependency) - good enough to see overall shape, not photorealistic, and can show minor z-ordering artifacts on complex parts.
• One Fusion document/bridge connection at a time.
• fusion_create_sketch's named-base-plane path (plane="XY"/"XZ"/"YZ", optionally offset_mm) is thoroughly live-verified. Its arbitrary-plane path (origin+normal) had a real bug fixed (setByThreePoints needs point entities, not raw Point3D - see git history) but was never confirmed working afterward: a second, different error ("Environment is not supported" from ConstructionPoints.add) appeared on the next attempt and went away after restarting the add-in, which looks like transient Fusion state rather than a code bug, but that path was worked around rather than re-tested. Treat it as unverified until someone confirms it live.
• Built and smoke-tested against mcp>=2.0.0's MCPServer API. The Fusion-side actions have all been exercised against a real, running Fusion 360 session (not just written against the docs) - see tests/smoke_test_fusion_live.py (sketch → extrude → cut/join → export, verified against the original mesh to within 0.01mm) and tests/smoke_test_fusion_live_features.py (fillet, chamfer, mirror, circular pattern, revolve, explicit combine). sketch_add_line, sketch_add_arc_three_point and pattern_rectangular share code paths with tested siblings but don't have their own dedicated live test yet. None of this runs in CI (there's no headless Fusion) - issues/PRs against fusion_addin/ very welcome regardless.

License

MIT - see LICENSE.