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Fusion - the Fusion 360 Bridge

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Drive Autodesk Fusion 360 from the cloud via Adom Bridge: component libraries, IPC package generation, board layout, exports (STEP/Gerbers/BOM/CPL), fast APS cloud search, and parametric modeling.

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fusion-bridge / docs / mechanical-bom.md
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Mechanical BOM and physical properties

Two verbs that turn a Fusion mechanical assembly into a purchasing bill of materials, and read per-part volume and mass for costing.

These exist because fusion_export_bom is electronics-only. Point it at a Design-workspace assembly and it tells you No board open (current workspace: Design). There was no mechanical equivalent, so anyone who wanted a parts list had to hand-write an occurrence walk inside fusion_run_modeling_script.

Contributed by Oliver, who built BOM Forge on this bridge, hit both gaps, and sent a PR with the fix.

The counting problem these solve

Walk allOccurrences naively and you count every screw in the model. But when you buy a "bracket with fasteners" kit, the screws arrive in that box. Counting them separately means ordering hardware you already have.

Measured on a real assembly:

part flat walk kit-aware error
T Nut Drop In 2020 M5 28 14 2.0x over
T Nut Eco 4040 M8 44 18 2.4x over
BHCS M8x16 46 20 2.3x over
BHCS M5x8 (fully bundled) counted 0 should not be ordered at all

The kit-aware counts match Fusion's own Manage -> BOM.

Below is a real Adom mechanical assembly, the 4040 T Plate, open in the Design workspace (captured with Fusion in the background). It is an aluminum T-plate with 5 BHCS M8x16 on top and 5 T Nut Eco 4040 M8 underneath. Running fusion_assembly_bom on it returns exactly that kit-aware list, 3 parts across 11 instances (plate x1, BHCS_M8x16 x5, T Nut Eco 4040 M8 x5), which is what a flat occurrence walk would over-count.

The 4040 T Plate mechanical assembly open in Fusion's Design workspace

fusion_assembly_bom

Structured, kit-aware BOM for the active assembly. Recurses organizational subassemblies, but stops at a physical part or a purchased kit.

adom-desktop fusion_assembly_bom '{}'
adom-desktop fusion_assembly_bom '{"treatAsUnit":["with fasteners","bearing unit"],
                                   "outputPath":"C:/tmp/bom.csv"}'
arg meaning
treatAsUnit name substrings counted as ONE unit and not exploded. Default ["with fasteners"], case-insensitive substring match
exclude top-level component-name prefixes to skip entirely
includePhysicalProperties adds volume_cm3 / mass_kg per line (slow, see below)
outputPath also write a CSV to this Windows path

Returns parts[] of {componentName, partNumber, description, material, quantity, bodies}, plus partCount and totalInstances.

The leaf rule, which is the whole trick: a component is a leaf when its name matches treatAsUnit or it has bRepBodies.count > 0. Anything else is organizational and gets recursed through.

fusion_physical_properties

Per-component volume, mass, density, area and center of mass, read directly rather than through a modeling script.

adom-desktop fusion_physical_properties '{}'
adom-desktop fusion_physical_properties '{"names":["Bracket A","Idler"],"accuracy":"high"}'
arg meaning
names component names to measure. Default: all
accuracy low | medium | high | veryhigh. Default low

Returns properties keyed by component name, each {volume_cm3, mass_kg, density, area_cm2, center_of_mass}.

Performance, and why the timeout is 300s

getPhysicalProperties runs per component on Fusion's main thread. On a large assembly this is the slow part, not the walk. Two consequences:

  • includePhysicalProperties defaults to false on the BOM. Leave it off unless you need it.
  • When you only need a few parts, call fusion_physical_properties with an explicit names list instead of pulling properties through the whole BOM.

Both verbs carry a 300s add-in timeout for this reason. If a call returns a relay timeout at ~60s, the work is still running on the bridge; poll rather than treating it as failure.

Worked example: a costed BOM

# 1. structured parts list, CSV for purchasing
adom-desktop fusion_assembly_bom '{"outputPath":"C:/tmp/bom.csv"}'

# 2. volumes only for the printed parts, to price filament
adom-desktop fusion_physical_properties '{"names":["Spool Holder","Guide Block"]}'

That is the shape BOM Forge uses: the BOM for quantities, targeted physical properties for the printed parts, then pricing applied downstream.

Limits worth knowing

  • The BOM aggregates to a flat parts list with quantities, not a hierarchy with a Level column. That matches Manage -> BOM, which is what purchasing needs. If you want the hierarchy, open an issue and it can be added without breaking the response shape.
  • treatAsUnit is a case-insensitive substring match on the component name. Kit naming conventions beyond "with fasteners" must be passed explicitly.
  • A component with bodies and children is treated as a leaf, so its children are not counted. That is intentional: a physical part is a leaf.