Your Prompt Is the Blueprint
When you use text-to-CAD, your description is the only thing the AI has to work with. There's no drawing to reference, no existing part to modify, no dimension you can point to on a screen. Every detail that matters needs to be in your words.
The good news is that you don't need to write a novel. You need to write a clear, specific description with the right kinds of information. Here's what actually makes a difference.
The Basics: What to Include
Dimensions First
This is the single biggest factor in getting useful output. Compare these two prompts:
Vague: "A small bracket for mounting a sensor"
Specific: "An L-bracket, 40x30mm base, 40x25mm vertical wall, 3mm thick, with two M4 clearance holes on the base spaced 25mm apart and one M3 hole centered on the vertical wall"
The first prompt will produce something. The second prompt will produce something you can actually use. Dimensions remove guesswork and give the AI concrete targets to hit.
Feature Names
Engineering vocabulary matters. The AI knows what these terms mean and translates them directly into CAD operations:
- Fillet and chamfer with specific radii/sizes
- Counterbore and countersink with standard sizes
- Through-hole, blind hole, tapped hole with thread specs
- Pocket, slot, groove with dimensions
- Boss, rib, gusset for structural features
- Draft angle for molded parts
Using "countersunk M5 hole" tells the AI far more than "a hole where a screw goes flush."
Functional Context
Describing what the part does helps the AI make reasonable decisions about things you didn't explicitly specify:
- "A wall-mount bracket for a security camera" implies weather resistance, cable routing, and specific mounting hole patterns
- "A test fixture for holding PCBs during soldering" implies heat resistance, proper clamping features, and access to the board surface
- "A desktop phone stand with cable pass-through" implies viewing angle, stability, and a channel for a charging cable
You don't need to specify every detail. Just give enough context that the AI can fill in reasonable defaults.
Common Mistakes
Being Too Vague
"Make me a bracket" gives the AI almost nothing to work with. What kind of bracket? How big? What's it holding? Where does it mount? A bracket for a shelf is completely different from a bracket for a servo motor.
Being Too Wordy Without Being Specific
"I need a really nice looking, well-designed, professional quality bracket that would work great for mounting things on a wall and would look good in an office environment" has a lot of words but very little useful information. No dimensions, no materials, no features, no mounting specifications. Cut the adjectives and add numbers.
Specifying Everything at Once
If you describe a complex part in one massive paragraph, you're more likely to get something where the AI nailed some features and missed others. For complex parts, start with the basic shape and dimensions, review it, then add features incrementally:
- "An enclosure box, 120x80x50mm, 2mm wall thickness, open top"
- "Add four M3 mounting bosses in the corners, 6mm tall"
- "Add a 25x10mm rectangular cutout on the left wall for a USB connector"
- "Add ventilation slots on the right wall, five slots, 30mm long, 2mm wide, 4mm spacing"
Each step builds on the last. This produces better results than trying to specify all of it in one go.
Contradictory Descriptions
"A thin but sturdy bracket" doesn't help. "A 3mm thick steel bracket with a support rib" does. Watch for descriptions where features conflict with each other or where the dimensions don't add up physically. If your 10mm hole is supposed to go in a 8mm wall, the AI will struggle with that.
Iteration: The Secret Weapon
The best text-to-CAD workflow isn't "write the perfect prompt and get the perfect model." It's "write a good enough prompt, review, and refine."
After the first generation, check:
- Are the overall proportions right?
- Are the critical dimensions correct?
- Is anything obviously wrong or missing?
Then iterate:
- "Make the base 10mm wider"
- "The holes are too close to the edge, move them 5mm inward"
- "Add 1mm fillets on all external edges"
- "The wall is too thin, make it 4mm"
Each iteration preserves the existing geometry and applies your change. Three or four rounds of refinement usually gets you to a model that's ready for export.
Real Examples
Here are some prompts that consistently produce good results:
Mechanical: "A motor mount plate, 80x60x4mm aluminum, with four M4 holes on 60x40mm spacing, a central 25mm bore, and 2mm fillets on all corners"
Enclosure: "A rectangular electronics enclosure, 100x60x30mm, 2mm wall thickness, with a snap-fit lid, two M3 mounting bosses inside, and a 15x8mm slot on one end for cable exit"
Structural: "A 90-degree gusset bracket, 50mm on each side, 3mm thick, with a triangular support web, and three 5mm mounting holes along each face"
Consumer: "A minimalist phone stand with a 70-degree viewing angle, space for a charging cable at the bottom, and a non-slip ridge along the front edge"
Start Experimenting
The best way to learn what works is to try it. Head to app.ragnar.build and generate a few models. Start simple, pay attention to what the AI gets right and wrong, and adjust your descriptions accordingly. You'll develop a feel for it quickly.