AI CAD agent guide: text to CAD for 3D printable parts

The PrintPal CAD Agent is a text-to-CAD tool. You describe a part in plain words, it writes OpenSCAD code, and your browser renders the model in 3D. Then you adjust it with sliders or more chat, and export an STL or 3MF for your slicer.

What the AI CAD agent does

The agent writes a complete OpenSCAD program for each design. OpenSCAD is a code-based CAD language, so every size is a named number you can change later. The program compiles in your browser with OpenSCAD WebAssembly, and the BOSL2 and MCAD libraries load the first time the code uses them.

You never have to read the code. In the default Simple mode it stays hidden, and the numbers at the top of the program show up as sliders.

Simple mode vs Advanced mode

The agent opens in Simple mode, a chat-first layout for people who have never used CAD. The Advanced switch in the top bar turns on the full editor. Your choice is remembered in this browser.

The Open in editor button on code blocks in these docs opens the agent in Advanced mode with that code loaded.

Your first text-to-CAD prompt

Say what the part is, how big it is and what it attaches to. Concrete numbers get you a finished part in one turn.

"I need a bracket" also works, but the agent will ask about size and mounting before it builds.

The agent sorts every request into one of three cases:

• Specific. You gave the key sizes, so it builds straight away.
• Missing details with sensible defaults. It picks the defaults, lists them in its brief and builds.
• Ambiguous. It asks 2–5 short questions with clickable answers, then builds.

Prompts can be up to 4,000 characters. For structure and templates, see how to prompt AI for CAD.

The design brief and checklist

Before it writes geometry, the agent posts a brief: units, where the origin is, the overall size (the envelope), the feature plan and any defaults it assumed. It follows with a checklist of 3–8 build steps and ticks them off in its reply.

Read the brief first. If the envelope is wrong, say so before you look at anything else. On later turns, a short update list shows what changed.

After each render, the app compares the model's real size with the envelope in the brief and shows a warning if they differ by more than 1 mm.

When you don't say, the agent assumes millimetres, a part centred on X and Y with its bottom at Z = 0, and a 220 × 220 × 250 mm bed. The design guide lists more of its printing defaults.

Adjust sizes with sliders

Each number at the top of the program, with a comment above it, becomes a labelled slider. In Simple mode they're in the Adjust tab. In Advanced mode they're in the Params tab while you're in Code mode.

• Sliders don't call the AI. The model re-renders in your browser and no credits are used.
• Direct parameter edits skip the AI too. If your whole message just sets existing parameters by name, such as set wall_thickness to 3, the change is applied directly.
• Anything else goes to the agent. New features, new shapes and "make it look sturdier" need an AI turn.

Point at parts with @feature references

The agent tags each part of the model with a comment like // @feature: mounting_holes. These names stay the same when the code is rewritten, so you can aim an edit at one part.

// @feature: mounting_holes
module mounting_holes() {
  for (p = [[5, 5], [35, 5], [5, 25], [35, 25]])
    translate([p[0], p[1], -1])
      cylinder(h = 10, d = 3.4, $fn = 32);
}

In Advanced mode, the feature names appear as chips above the chat box. Clicking a chip highlights that part in the 3D view and adds @feature[mounting_holes] to your message. Typing @ opens a picker with four kinds of reference:

The hardware list covers M2 to M5 socket-head screws, M3 and M4 hex nuts, an M3 captive-nut pocket, an M3 heat-set insert, an M3 washer, M3 brass standoffs, and 608ZZ and 625ZZ bearings.

Iterate in small steps

One change per message is easier to check and cheaper to fix. A typical run:

1. Base part. "Wall bracket for a 25 mm rod, 60 mm arm…"
2. Strength. "Add a 5 mm gusset under the arm."
3. Hardware. "Make the holes countersunk for 4 mm wood screws."
4. Printability. "Add a 0.5 mm chamfer to all bottom edges."
5. Fit. "Make the cradle 0.4 mm wider, my rod is 25.3 mm."

When there's already a model, each message also sends the agent your current code, its measured size and a labelled four-view picture of the render. So it sees your hand edits and slider changes.

Auto-fix and auto-iterate

• Auto-fix. If code the agent wrote fails to compile, the app sends the error back and asks for a corrected program. It tries up to 2 times, then asks you to adjust the prompt. It never fires on code you typed yourself.
• Auto-iterate. After a successful render, the agent can check its own work against a picture of the model. It runs when you attached a reference image, when the design has mating parts like threads, gears or snap fits, or when the size is more than 2 mm off the brief. It stops early once the model matches. Turn it off with the Auto-iterate button under the chat box.

Reference images

Attach sketches, photos or screenshots with the image button under the chat box, or paste them straight into it. You can send PNG, JPEG, GIF or WebP, up to 4 per message. Each image is scaled so its longest side is 1024 px before sending.

On follow-up turns, the picture of your current render takes one of those four places, so attach up to three new images then. For the full workflow, see image to CAD.

Save, share and publish

• History. Sessions autosave to your account once you start working. The History button reopens any past session with its chat and code.
• Share. Creates a public link. People who open it can remix their own private copy.
• Publish. Lists the design in the PrintPal gallery as a customizable model, with your sliders on its page.
• Order Print. Where available, sends the model to a print service for a quote.
• Project files. The File menu also saves and opens projects as .json and opens .scad files.

Export formats

Exports come from the File menu and run in your browser.

What uses credits

Using the agent requires a signed-in PrintPal account. Each AI turn uses credits based on its actual usage, and you need a small minimum balance to start one.

Keyboard shortcuts

Check yourself

Frequently asked questions

Tools for thisAll tools

CAD AgentDescribe a part in plain English and get editable OpenSCAD with a live 3D preview and STL or 3MF export.

Watch it doneVideo library

0:28 OrcaSlicer plugins you should knowTools 0:19 Win a Bambu Lab A1 Mini in PrintPal's free 3D design competitionsIdeas 16:36 9 FREE 3D Printing Tools You'll Wish You Found SoonerTools

Was this article helpful?

Yes Not really

Send

Thanks! We read every note and use them to decide what to update next.