Gen Part

pc:gen-part

Generate one PartCAD part. The text after the command ($ARGUMENTS) is the part description — what to build. You author the CAD script yourself and prove it works with the PartCAD CLI; do not use any built-in ai-* part type or generation pipeline. Hard requirement: the finished part passes pc test (its geometry instantiates cleanly).

Steps 4–7 are the reference flow — the same shape the legacy pc add part --ai pipeline used (plan geometry → write script → validate → compare → refine). Treat it as a strong default, not a script: skip, reorder, or replace steps as the part warrants, but always finish by validating.

1. Understand the request

• $ARGUMENTS is the description. Read it and any requirements, and view reference images directly. Ask the user to clarify only genuinely load-bearing ambiguities; otherwise proceed and state your assumptions.
• Work in millimeters and degrees unless told otherwise.

2. Make sure PartCAD is available

Resolve a command as /pc:init does (pc, then partcad, then python -m partcad_cli.click.command). If none is found, stop and run /pc:setup executable first.

3. Choose a representation

Pick the script kind that best fits the part — you decide:

4. (Optional) Plan the geometry

For anything non-trivial, sketch the constructive-solid-geometry plan first — coordinate system, primitives with dimensions/positions/orientations, then unions/differences/intersections and fillets/chamfers. This mirrors the legacy "CSG" step and usually cuts iterations. Skip it for simple parts.

5. Author, register, and mark it

Write the script file first from $ARGUMENTS (plain type — never ai-*), then register it — pc add part requires the file to already exist:

pc --no-ansi add part --desc "<the description>" <kind> <name>.<ext>   # e.g. build123d bracket.py

Language conventions for the script:

• build123d / cadquery / sdf (Python): import everything you use (including math and the library itself); call show_object(<result>) to expose the part; do not export anything. For cadquery, avoid tetrahedron / hexahedron.
• OpenSCAD: a complete script defining all functions and constants; no external modules; no export.

Then mark the part not manufacturable in partcad.yaml — a generated part is not a catalog/supplier item, and this is what lets pc test pass:

parts:
  <name>:
    type: <kind>
    path: <name>.<ext>
    desc: <the description>
    manufacturable: false

If the part was modelled from reference images — a drawing, a photo, a sketch — name them under images: as well, as paths relative to the package. That is what puts them beside the part in the README pc render writes, so a reader sees what the model was made to match; nothing else reads them.

    images:
      - drawing.png
      - photo.jpg

If you started the project with pc init, also delete the empty sketches: and assemblies: sections it leaves — a null section crashes pc render on older PartCAD (fixed in partcad/partcad#470).

6. Validate

pc test is the build gate: with manufacturable: false, its CAD check passes only if the geometry instantiates cleanly, and the manufacturability checks are skipped.

pc --no-ansi test <name>

Three of its checks fail geometry that instantiates perfectly, and all three are about a part that would look right in the pictures rendered below: shell (the part is a surface rather than a body — the faces do not close, so it has no inside and every boolean against it is meaningless), degenerate (it has no size left in some direction) and solidity (its faces are oriented inward, so its volume is negative). None of them can be turned off on the part — there is no such setting, and inventing one is rejected by pc lint. Fix the geometry: close the shape, keep the feature that collapsed, orient the faces outward. A part that fails one of these is a part nothing downstream can compute with, however good the picture of it looks.