--- name: gen-part description: Generate a PartCAD part from a natural-language description (and optional reference images/requirements) by authoring a CAD script and validating it with the PartCAD CLI. Use for /pc:gen-part or when the user asks to generate, create, or model a single mechanical 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: | Kind | Good for | | --- | --- | | `build123d` | general parametric solids (recommended default) | | `cadquery` | fluent / CSG-style modeling | | `scad` (OpenSCAD) | simple constructive geometry, no Python | | `sdf` | organic / implicit shapes | ## 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 `$ARGUMENTS` (plain type — never `ai-*`), then register it — `pc add part` requires the file to already exist: ```sh pc --no-ansi add part --desc "" . # e.g. build123d bracket.py ``` Language conventions for the script: - **build123d / cadquery / sdf (Python):** import everything you use (including `math` and the library itself); call `show_object()` to expose the part; do not export anything. For cadquery, avoid `tetrahedron` / `hexahedron`. - **OpenSCAD:** a complete script defining all functions and constants; no external modules; no export. Then mark the part **not manufacturable** in `partcad.yaml` — a generated part is not a catalog/supplier item, and this is what lets `pc test` pass: ```yaml parts: : type: path: . desc: manufacturable: false ``` If you started the project with `pc init`, also delete the empty `sketches:` and `assemblies:` sections it leaves — a null section crashes `pc render` on older PartCAD (fixed in partcad/partcad#470). ## 6. Validate `pc test` is the build gate: with `manufacturable: false`, its CAD check passes only if the geometry instantiates cleanly, and the manufacturability checks are skipped. ```sh pc --no-ansi test ``` ## 7. Render it from several angles, compare, and iterate `pc test` proves the geometry instantiates. It says nothing about whether the geometry is the part that was asked for — that is decided by looking at it. One picture is not enough to decide it. A projection hides everything behind it, so a hole in the wrong face, a feature on the wrong side, a chamfer that never got cut, or a shape that is right in outline and wrong in depth all survive the one view that happens to conceal them. Render **four**: `front`, `top` and `right` to read proportions and dimensions off, and `iso` to see how the features go together. A rendered file is named after the object, so give each view a directory of its own or they overwrite each other: ```sh for view in front top right iso; do mkdir -p /tmp/pc-render/$view # -O expects it to exist pc --no-ansi render -t png --view $view -O /tmp/pc-render/$view done ``` Then view all four — `/tmp/pc-render//.png` — and compare them against the description and any reference images: - the overall form and the bounding size, in all three axes; - every dimension the description states — each is measurable in one of the orthographic views, and a dimension no view confirms is one still assumed; - every feature that was asked for, on the face it was asked for, and nothing present that was not. Add `back`, `left` or `bottom` whenever the part is not symmetric about the axis in question: an asymmetric part has a face you have not seen, and a face you have not seen is a face you are guessing about. When no named view shows the feature you need to check, `--viewport-origin X,Y,Z` and `--viewport-up X,Y,Z` look from an arbitrary direction. `/pc:render` covers these options in full. Fix any error or mismatch, then re-test and re-render. Iterate until every view matches — no fixed retry count. If the part is right and the numbers are what need checking, `/pc:describe` renders a dimensioned drawing of it. ## 8. Finalize Summarize what you built — key dimensions and assumptions — and how to view it: `pc inspect `. If the part is meant to connect to something — a bolt pattern, a plug, a rail — say so and offer `/pc:add-interfaces`, which adds the ports and interfaces that let PartCAD mate it automatically. Once it has them, `--with-all` draws them on the very views you have been comparing against, so a port that is in the wrong place or facing the wrong way is visible rather than inferred: ```sh for view in front top right iso; do mkdir -p /tmp/pc-render/ports/$view pc --no-ansi render -t png --view $view -O /tmp/pc-render/ports/$view --with-all done ``` Four views again, and for the same reason: a port is a coordinate frame, and one projection collapses the axis it is offset along just as it does for geometry. `--no-ansi` because every port drawn is also named on stderr, which is where the exact string to write in an ASSY file comes from. `/pc:add-interfaces` covers reading these drawings in full.