fusion-agent-kit

name	fusion-agent-kit
description	Use when building, modeling, editing, or 3D-printing a part in Autodesk Fusion 360 from an AI agent (Claude Code, Codex, etc.) via the Fusion MCP bridge - any "design/model/CAD this part", parametric modeling, screw threads, enclosures, brackets, or STL export task.

fusion-agent-kit

Overview

Drive Fusion 360 from an AI agent by writing a re-runnable Python build script that calls fusion_helpers.py. The model is defined by code, not clicks: every dimension is a named parameter, every feature is rebuilt by a build_*() function, and set_param(...); build_all() regenerates the whole part. This makes design iteration cheap and the result fully reproducible (you can kill Fusion and rebuild in one call).

Core loop: brainstorm the part -> write build_<part>.py -> run it -> screenshot -> adjust params -> export. You see what you build at every step.

Prerequisites

• The Fusion 360 MCP bridge tool mcp__fusion360__fusion_execute (runs Python with full adsk.* API inside Fusion). fusion_screenshot exists but its inline base64 usually exceeds the token limit -- use the helper's screenshot() (saves a PNG you then Read).
• fusion_helpers.py from this repo (load it with exec(open(path).read())).

Workflow

1. Brainstorm first. Don't model immediately. Clarify the object, its real measurements, how it mounts/assembles, and the retention/joining mechanism. Confirm with the user (sketches/ASCII help). Wrong assumptions here waste the most work. Write a short spec.
2. Load helpers + a fresh doc. In one fusion_execute call: exec(open('/abs/fusion_helpers.py').read()) -> set_output_dir('/abs/project/output') -> new_design_doc(). Always build into a fresh doc; re-running into a stale one leaves dead features.
3. Write build_<part>.py following the structure below. Load it the same way and call add_*_params(); build_all().
4. Verify visually every step. screenshot('iso.png', 'iso-br') then Read the PNG. For internal features, render a cross-section (cut a copy with a big box, screenshot, undo).
5. Iterate by parameter. set_param('wall','4 mm'); build_all(). Never hand-edit geometry you can re-derive.
6. Export. export_stl('Body','part.stl') for printing; export_f3d('/abs/Part.f3d') to hand the user an openable file (the API saveAs is blocked in MCP/headless contexts, so .f3d export is how you deliver a file).

Build-script structure

Mirror examples/puck-cradle/build_puck_cradle.py:

MM = 0.1  # mm -> cm (Fusion internal units)

def add_part_params(silent=False):
    return add_params({ "wall": ("3 mm","mm","wall thickness"), ... })

def _dims():                 # derive everything from params (returns mm)
    ...

def build_body():            # re-runnable: delete old body + its features first,
    ...                      # then sketch/extrude/cut. Bake sketch points from
    return body              # get_param_mm(); bind extrude DISTANCES to param exprs.

def build_demo():            # screenshots: assembled / exploded / cross-section
def build_export():          # export_stl + export_f3d

def build_all(shoot=True, demo=True, export=False):
    add_part_params(silent=True); build_body(); ...; state_compact()

Each builder must clean its own features (delete_matching('Prefix') + delete its body) so build_all() is idempotent.

Quick reference (helpers)

Need	Helper
Fresh parametric doc	new_design_doc()
Params	add_params(spec), get_param_mm(n), set_param(n, expr)
Find	find_body, find_sketch, find_feature, find_component
Sketch (cm coords)	sketch_rect_by_corners, sketch_rect_centered, sketch_rounded_rect
Solids	extrude_new_body, extrude_cut_from_profile, combine_cut, combine_join
Patterns/edges	pattern_rect, fillet_all_edges, cp_offset
Timeline	delete_matching, suppress_matching, group_timeline
Inspect	state_dump(), state_compact(), count_circular_faces
Output	set_output_dir, screenshot, export_stl, export_f3d

Threads: use ThreadFeatures with isModeled=True and a standard designation from threadDataQuery (e.g. M62x3, TR60x3). See gotchas.

Read this before you build

REQUIRED: references/gotchas.md - hard-won Fusion API traps (units, ASCII encoding, sketch-axis flips, mesh-boolean timeouts, modeled threads, the save block). Skipping it will cost you a rebuild.

Common mistakes

• Modeling before brainstorming -> wrong mechanism, repeated rework.
• Stale doc -> dead features error out. Use new_design_doc().
• Unit mix-ups -> sketch coords are cm (*MM); extrude distance strings are mm ("12 mm") or param expressions. Never *10 an already-mm value.
• Trusting it built -> always screenshot/section and check lumps==1.
• Mesh booleans -> converting an STL mesh to BRep then joining is slow and can exceed the tool timeout (Fusion keeps working -- wait and re-query, don't kill).