Batch STL Export

A Fusion 360 add-in that exports many bodies or components to STL in one pass, with refinement settings that are remembered between runs.

Fusion's own 3D Print dialog does neither. It exports one object per invocation and forgets every setting the moment it closes, so producing a tray of parts at a fixed tolerance means opening it once per body and retyping the same four numbers each time.

This reports the triangle count and file size read back out of the files it wrote, not predicted — and writes an optional manifest next to them recording exactly what was used.

Install

1. Clone or copy this folder anywhere.
2. Run powershell -File install.ps1. It copies the add-in into %APPDATA%\Autodesk\Autodesk Fusion 360\API\AddIns\BatchSTLExport.
3. In Fusion: Utilities → ADD-INS → Scripts and Add-Ins → Add-Ins → Batch STL Export → tick Run on Startup → Run.
4. The button appears in Utilities → Make, next to 3D Print, and in Mesh → Export.

No dependencies. It runs entirely inside Fusion's bundled Python, stdlib only.

What it exports

Export	Meaning
Selected bodies and components	one file per selected solid body, mesh body or component
All visible bodies	one file per visible body anywhere in the design
All bodies	the same, hidden ones included
Top-level components	one file per component directly under the root, each holding everything inside it, plus any body sitting loose in the root

Bodies inside components are taken as proxies, so each file is written in assembly coordinates and the parts still fit together when reopened.

File names

The File name field is a template:

token	is
{body}	body name, or the component name for a component
{comp}	the component the body belongs to
{occ}	the occurrence, instance number included (Guide:2)
{doc}	the document name
{n} {nn} {nnn}	position in the run, zero padded to 1/2/3 digits
{date} {time}	when the run started, 20260903 and 162233
{kind}	solid, mesh or component

<>:"/\|?* and control characters become _, a trailing dot is dropped, and .stl is appended unless the template already ends in it.

If a file exists chooses between numbering the new one, overwriting and skipping. Whatever that is set to, two objects that resolve to the same name inside one run are always numbered apart — silently collapsing them into one file would lose a part without saying so.

Refinement

The four numbers are always visible. Hiding the surface deviation behind a preset is the thing that makes the 3D Print dialog awkward to tune, and the deviation is the number worth tuning.

Picking High, Medium or Low fills them in with what that preset resolves to for the first object, so you can see what it means. Typing over any of them flips the dropdown to Custom, exactly as Fusion's own dialog does. What the panel shows is always what gets applied.

The two modes differ in a way that matters for a batch:

• a preset is applied as a preset, so Fusion scales the deviation to each body's own size — every file gets a different absolute tolerance;
• Custom applies the numbers verbatim, so every file gets the same absolute tolerance. For a print tray that is usually what you want.

Measured: Custom 0.003 mm gave a 30 mm ball 24 648 triangles and an 80 mm cylinder 2 566; High gave the same ball 28 560 and the same cylinder 1 348 — finer on the small part, coarser on the large one.

Maximum edge length and Aspect ratio take 0 for no limit, which is the default. That loses nothing: the presets set maximum edge length to the body's own bounding-box diagonal, and no triangle can be longer than that, so a preset does not limit it either.

Reset all settings puts the panel back to its defaults. The output folder is kept, because re-picking that is the one thing a reset should not cost you.

Everything, the folder included, is written to last_export.json beside the add-in and comes back next time.

What gets written

A report, and — unless you turn it off — a stl_export_<timestamp>.txt manifest in the output folder holding the same text: every setting used, and for each file its name, triangle count, size and source object. The counts are parsed out of the written files (the binary header, or a scan for facet normal), so the manifest records what actually happened rather than what was intended. That matters when the export is part of a controlled record.

Things Fusion does quietly

Two behaviours worth knowing about, both handled here and both documented with the measurements in docs/FUSION-STL-API.md:

• The API reference gives the wrong unit for half the refinement properties. surfaceDeviation and maximumEdgeLength are millimetres, not centimetres, and normalDeviation is degrees, not radians. They carry the same numbers the 3D Print dialog shows.
• A hidden body exports nothing. exportManager.execute() returns true and no file appears. This add-in switches the light bulb on for the duration and puts it back, and marks those rows was hidden in the report.

Repository layout

BatchSTLExport.py        add-in shell: lifecycle and the dev bridge, nothing else
bse_core.py              all the working code, plus the command, its handlers
                         and its button; re-imported on every event
install.ps1              push into Fusion's AddIns folder
resources/               toolbar icons
docs/                    FUSION-STL-API.md, index.html
tools/                   dev-bridge client, icon generator
tests/                   offline tests, no Fusion required

bse_core.py hot-reloads — it is re-imported on every command event, so pushing it takes effect on the next click; only BatchSTLExport.py needs a Stop/Run. Because of that reload, nothing may keep state in a module global between events: dropdown choices are resolved from the item label, never a remembered index.

Tests

py -3.10 tests/test_export.py

45 checks covering names, collision policy, reading triangle counts back out of both STL flavours, settings persistence and migration, and the report. tests/stub fakes adsk, so it runs without Fusion.

The dev bridge

Fusion has no headless mode and no CLI, so the only way to test an add-in automatically is from inside a running Fusion. Creating a devbridge.on file next to the add-in starts a folder watcher that runs jobs on Fusion's main thread:

py -3.10 tools/bse.py export_make_test      # scratch doc with the awkward cases
py -3.10 tools/bse.py export_probe          # enums and per-body defaults
py -3.10 tools/bse.py preset_values         # what High/Medium/Low resolve to
py -3.10 tools/bse.py export_run '{"source": "All bodies", "folder": "C:/out"}'
py -3.10 tools/bse.py export_dialog         # then export_set_inputs, export_press_ok

Off by default. Nothing in normal operation depends on it.

Licence

MIT — see LICENSE.