Five Parts, One AI, and the Same Lesson Every Time

A week of letting an AI agent run Fusion 360 — and the one habit that decided how fast each part went.

Thanks for the inspiration, Matthew! 🙏

For a week I let an AI agent drive Fusion 360. I handed it photos, a hand drawing, an STL, and a lot of corrections; it ran the model. Each part below is the same story — a reference on the left, what the AI built on the right — and the gap between them came down to one thing.

TL;DR

The AI did the CAD. I supplied the eyes, the references, and the fixes.
The lesson, every time: the reference is ground truth — a clear photo or drawing beats any amount of clever guessing.
A ski clip took 28 tries from photos; a steel part took one pass from a dimensioned drawing.
Parametric models made corrections free — a wrong size was one number, not a rebuild.
And the one that quietly democratized a five-figure workflow: a downloaded 3-D-print mesh, turned back into an editable parametric model.

Where it started: a van

The first build wasn't a tutorial cube — it was the deck for my Toyota Sienna camper, from Matt's layout rather than a photo. Twenty-five parts, all parametric. The point was to see if an AI could hold a model that size together without it falling apart. It could. That's what made the rest worth doing.

SIENNA LE CAMPER PLATFORM

2007 Toyota Sienna · removable 3-section deck

48"W × 80"L · floor 83" · ceiling 45" · well 12"

A · 26"B · 30"C · 24"

Matt’s layout

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Fusion model of the Sienna camper deck with wood textures

28 tries on one ski clip

Then something tiny: the plastic connector that clips a climbing skin to a ski tip. The white insert came together fast. The black receiver took 28 versions — not because the CAD was hard, but because we kept mis-reading how it locks. The fix wasn't a better tool. It was a photo of the part by itself, which had existed the whole time.

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Full story: Reading a Ski-Skin Connector.

Wrong from photos, right from the file

A drysuit gasket tool, copied from a 3-D print online. We sized it from pictures and got it wrong — built it 10.5″ when the real one is 9.5″. The maker emailed the actual file, and the fix was a single number, because the model was parametric.

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Reverse-Engineering a Drysuit Repair Tool.

A drawing beats a hundred photos

Then a steel jack adapter for a Pilatus PC-12, from a hand shop drawing with four numbers on it. One pass. No revisions. Same AI, same me — the only difference from the ski clip was that this time the reference was exact.

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From a Shop Drawing to CAD.

What it actually taught me

The reference is ground truth; my reasoning about a part I can't see is not. Every wasted version came from modeling on a guess when a photo or a file was a search — or an email — away.

And one of these used to take a five-figure tool and an expert. The fifth part started as a downloaded 3-D print — a frozen mesh, the kind of file you normally can't edit at all — and came back as a real, editable parametric model. That wasn't impossible before: it meant specialist software that runs into five figures and a trained operator, or an hour of careful hand-remodeling. What's new is that an AI agent now does it conversationally in a free Fusion install — and the specific trick of letting it slice the mesh to measure itself, then rebuild from those measurements, is something I haven't found anyone else doing. That's the quiet headline of the week.

Three smaller lessons, none about CAD software:

Parametric makes corrections free. Get a dimension wrong, change the number, done — no rebuild.
The save that matters is the file on your disk. Fusion's cloud save turned out flaky; the model that's actually safe is the one exported to a folder I control.
One Fusion, many helpers, needs a traffic light. Running several AI threads into a single Fusion, they trampled each other — until a tiny shared lock made them take turns.

The fast builds and the slow ones used the same tools and the same agent. The only variable was the quality of what I handed it. Feed a fast builder a good reference and get out of the way.