Agentic CAD Run 2: Injection molding brief, full documentation

AI CAD demos are full of it. Harsh criticism, but there is a point to it: creating a nice 3D model is a small part of the equation. Drawings, BOM, assembly order, moldability: that is where most demos stop. This time I did not stop at the part. I named the process and expected the full package. Every file from the run is downloadable below, unedited.

The setup: one brief, process included

Claude Opus 5.5 sat in my live CAD session via MCP. One brief, with the decisive difference to my first Pi 4 test: this time I named the process.

A pole-mounted room booking sign. Raspberry Pi 4, 7-inch touch display, two-part ABS housing. Manufacturing process: injection molding.

Last time I complained about missing draft angles. This time I told it the process, and it designed for the process. Mostly.

What came back besides the CAD

• Five sheets of manufacturing drawings for parts and assembly.
• A BOM with supplier part numbers and buy links, down to the heat-set inserts.
• An assembly guide with torques, adhesive dwell times and a service procedure.
• A DFM checkagainst the molder's design rules: draft, wall thickness, ribs, bosses, three side actions.
• Snap-fits with a strain calculation instead of a guess.

Did it remove work, or just move it?

Both: it removed the creating and moved me to checking. What the checking found:

• Every document said seven snap hooks. The model has eight. The documentation had not followed the revision.
• The top part had no draft angles on the outer surfaces. As a molded part, it would not have ejected cleanly.
• Too much material in some corners, a likely source of sink marks.

I sent these back as revisions: draft angles on both housing parts and the corrected hook count. Fixed, and nothing else moved. That tightness of change may be the most underrated part of the run.

What stayed on my desk: the prices. Some supplier sites blocked the lookup, so quoting was still my job. In total I spent 1 houron revising, checking, getting quotes and the manufacturer's DFM feedback.

Time and cost, honestly broken down

222 million tokens sounds insane, but it is the most honest description of how an agent works: it re-reads almost everything, all the time. It only wrote about 730,000 new ones. Opus 5.5 removed roughly 99 percent of the modeling time, and it did the revisions clean. I had to step in on the geometry zero times.

What is still open

Can it be molded, inspected, and assembled? The test print is running, and the manufacturer's feedback looks promising so far. The next question for future runs: can the same model be used for design for cost, not just design for manufacturing?

The takeaway

The difference between a demo and a tool is the brief: name the process and you get geometry for the process. Ask for just a part and you get a picture of a part. The work shifted away from creating, toward reviewing and judging. And that judging is what I bring: seven hooks in the documents and eight in the model is something the agent will not flag on its own. I design housings that work as prototypes and survive series production. Whether with agentic support or classically is a per-project decision.

Anton Steenken

B.Eng. · Hardware R&D Engineer · Founder of engineer your idea