Parametric CAD Modeling

CAD modeling and inspection

Provenance: maintained in earthtojake/text-to-cad. Use the installed local skill files for the current interface.

Start with the task

Read only the references needed for the request.

For 2D DXF drawings use $dxf; this skill owns any 3D part the drawing projects. Use the corresponding robot-description skill for URDF, SRDF or SDF.

Setup and paths

Run cadgen through uv, so this skill's commands share one installation, and its warm build daemon, with the CAD app's server:

• cadgen below means uvx --no-config --managed-python --python 3.13 --from cadgen==0.7.19 cadgen
• python below means uvx --no-config --managed-python --python 3.13 --from cadgen==0.7.19 python

The first run downloads that installation and the first snapshot its headless browser; later runs reuse both.

cadgen doctor <skill-dir> reports the installation in use and checks that it is the one this skill pins, and that the CAD kernel loads; use it for installation or kernel load errors. Use the relevant subcommand's --help for additional flags.

Run project commands from the CAD project root. CLI input/output paths and read_scene/read_step paths are working-directory-relative; decorator out= paths are relative to the model script. Anchor file inputs on __file__ when the model must run from any directory.

Create or edit a model

A model is a plain Python script with a parameterless decorated function returning a build123d shape. Use one model per entrypoint, with the script and its declared outputs sharing a filename stem. For example, src/bracket.py:

from cadgen import build123d as bd
from cadgen import step

WIDTH = 40.0


@step(out="../STEP/bracket.step")
def bracket():
    body = bd.Box(WIDTH, 20, 6)
    body.label = "bracket"
    return body


if __name__ == "__main__":
    bracket()

python src/bracket.py

• Edit the model source when it exists, then run it to regenerate its outputs. Document export and snapshot commands take saved files and never run source.
• Keep meaningful dimensions explicit. Use millimeters and XY/+Z unless the task or project specifies another convention; choose a useful functional datum. Prefer closed, positive-volume solids for physical parts, while honoring requests for surfaces or construction geometry.
• Put parameterized geometry in ordinary factory functions; a decorated model selects a configuration. Keep module bodies cheap: create geometry and read CAD inputs inside the model or its helpers. Use the lazy bd import above; use postponed annotations when annotations mention bd types.
• Call child models inside the assembly model. Place their results with .moved() or Location * shape to preserve shared geometry. Use meaningful occurrence labels and source-defined placements. Rerun the parent assembly to incorporate a changed child.
• Read vendor STEP inputs with cadgen.read_step. Every file a build opens is an input on its own, whatever reads it (json.load, np.load, bd.import_step, a project font): nothing is declared. Never read a model's own output as its input. Geometry must not depend on untracked time, random values, environment variables or the working directory.
• When named purchasable parts are needed, search $step-parts before making placeholders. Record an unsuccessful search and any placeholder assumptions.

For unfamiliar dimensions or interfaces, record the assumptions needed to model and verify them. Ask for missing information when it materially affects the requested result. Inspection and export requests do not need a modeling brief.

Mesh exports

Stack @stl, @threemf or @glb on the model for outputs that should be maintained on every run. A model may declare only meshes; STEP is optional. For a one-off export from an existing generated or imported STEP:

cadgen stl build STEP/bracket.step STL/bracket.stl
cadgen 3mf build STEP/bracket.step 3MF/bracket.3mf
cadgen glb build STEP/bracket.step GLB/bracket.glb

Omitting OUT writes one sibling file with the requested extension. It does not discover declared model variants. See mesh exports for decorator examples, mesh tolerances and animated GLB.