AIPRINTGEN WIKI · №06
How to write a technical prompt for a CAD model
Published: Updated:
Short answer. A technical CAD prompt should describe the construction rather than its visual impression: units, base shape, dimensions, feature positions, thicknesses, radii, symmetry, tolerances and purpose. The fewer ambiguous words it contains, the easier the result is to verify.
An artistic prompt allows variation. A CAD prompt should resemble a compact technical brief. It must give the system enough information to build the part while leaving a clear list of testable criteria for the person reviewing it.
Prompt structure
Use seven blocks:
- Purpose: what the part does and what it connects to.
- Units: millimetres or inches.
- Overall dimensions: X, Y, Z and the basic shape.
- Features: holes, cut-outs, posts, channels and slots.
- Position: distances from faces, axes and centres.
- Assumptions: what may be chosen automatically and what must not change.
- Acceptance criteria: which dimensions, solid closure and fit must be confirmed after generation.
Open the AIPRINTGEN CAD generator
Describe relationships, not just numbers
The phrase ‘two holes near the ends’ is ambiguous. Prefer: ‘two Ø5 mm through holes; centres lie on the longitudinal centreline, 10 mm from each end’. State the symmetry plane for a symmetric part. For a pattern, specify the number of features, spacing and direction.
When one dimension depends on another, define the relationship: ‘inside width = object width + 0.6 mm’. That parameter is easier to adjust after a fit test.
Example of a good prompt
Create a U-shaped holder for a 32 mm-wide enclosure. Units: mm. Inside width 32.6 mm, inside height 18 mm, length 45 mm, wall and base thickness 3 mm. Add two Ø4.2 mm through holes on the base centreline, 28 mm between centres. Fillet the outside vertical edges to a 2 mm radius.
Every requirement in this description can be checked separately.
How to use an image
A sketch is useful for showing the relationship between features, but provide exact dimensions in text or fields. Label important sides and make dimension arrows readable. Do not attach a perspective render when an orthographic view is available.
With a PDF, first determine whether it is a vector drawing or a scan. Vector lines can be imported and cleaned; a scan must be calibrated against a known dimension.
Check the prompt before generation
Read the description as if you were a contractor who had never seen the task. Could top and bottom be confused? Are the units stated? Is at least one known dimension provided? Is it clear which holes are through holes? Is the coordinate origin unambiguous? If not, add the missing data before generation.
Mistakes and limitations
Do not overload the first request with several pages of manufacturing documentation. Establish the correct base form first, then refine local features. Do not ask for a model to ‘be strong’ without stating the load, material and force direction; that is not a testable requirement.
Frequently asked questions
How should chamfers and fillets be specified?
What if the system invents dimensions?
Should I write the prompt in English?
Conclusion
A good CAD prompt is a measurable technical brief. Save a successful template and change only its parameters; generation then becomes a repeatable production tool rather than a one-off attempt.
Related guides
Which CAD parts can AI generate without manual modeling?
Simple parametric plates, brackets, bushings, spacers, lids, enclosures, templates and organisers are the best candidates for AI CAD generation.
Check and repair an STL before 3D printing
Inspect watertight geometry, normals, intersections, shells, wall thickness, scale and bed contact, then review every sliced layer after repair.
Our community
