cad

# CAD generation, inspection, and validation Provenance: maintained in [earthtojake/text-to-cad](https://github.com/earthtojake/text-to-cad). Use the installed local skill files as the runtime source of truth; the repository link is only for provenance and release review. ## Purpose Create or modify parametric CAD models from natural-language requirements, generate validated STEP/STP artifacts, inspect geometry references, and return checked outputs. Treat STEP as the primary CAD artifact. Treat STL, 3MF, and native GLB as secondary export workflows that branch from a STEP-first process. For assemblies, prefer `cadpy.assembly.AssemblyHelper` with source-level build123d joints, named mating datums, and native labels when the parts have functional assembly relationships. There are two ways into the STEP workflow: generate from build123d Python source (the default when designing from scratch or modifying a generated model), or import an existing STEP/STP file directly (when no generator exists or the user explicitly targets the STEP file). Both produce the same inspectable artifacts. ## Use this skill when Use this skill when the user asks for CAD files, STEP/STP files, build123d source, selector refs such as `#o1.2.f1`, mechanical parts, assemblies, enclosures, brackets, fixtures, holes, counterbores, countersinks, slots, pockets, bosses, standoffs, ribs, fillets, chamfers, shells, source-level joints, mating, or measurements. Also use it when the user supplies reference images or 2D technical drawings of a part to reproduce or take design intent from. Also use it when the user asks for STL, 3MF, or native GLB output from CAD geometry. Keep those workflows secondary and load `supported-exports.md` for details. For 2D DXF drawings, use the `$dxf` skill; when a DXF projects from a 3D part, this skill owns the STEP geometry and `$dxf` owns the drawing. Do not use this skill for render-only concept art, CAM toolpaths, engineering certification, FEA conclusions, architectural BIM, or freehand illustration unless the user also needs CAD geometry. ## Default assumptions Use these defaults unless the user specifies otherwise. These are first-pass modeling defaults, not manufacturability, tolerance, or certification claims: - Units: millimeters. - Origin: per the part-type defaults in `references/positioning.md`; center of the main part or assembly when nothing better applies. - Base plane: XY. - Up/extrusion axis: positive Z. - Output geometry: closed, positive-volume solids unless the user requests surfaces or construction geometry. - STEP structure: one valid solid, a compound of solids, or a labeled assembly compound. - Assembly structure: fixed root part, part-local frames, named mating datums, `AssemblyHelper` relationships backed by build123d joints where applicable, explicit generated placements, and verbose native labels. - Small plastic enclosure wall: 2.0-3.0 mm when unspecified. - Cosmetic fillet: 1.0-3.0 mm when safe for local geomet