CADSkill

---
name: cad
description: Create, modify, inspect, and validate STEP-first parametric CAD parts and assemblies. Use for natural-language CAD specs, reference images, 2D technical drawings, STEP/STP generation or direct inspection, Python CAD source, source-level joints, selector references, geometry facts, measurements, mating deltas, snapshots, and secondary STL/3MF/native GLB outputs from CAD geometry.
---

# CAD generation, inspection, and validation

Provenance: maintained in 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.

## Use this skill when

Use this skill when the user asks for CAD files, STEP/STP files, build123d source, 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.

## Default assumptions

- Units: millimeters.
- Base plane: XY; up/extrusion axis positive Z.
- Output geometry: closed, positive-volume solids unless surfaces or construction geometry are requested.
- Small plastic enclosure wall: 2.0-3.0 mm when unspecified.
- Cosmetic fillet: 1.0-3.0 mm when safe for local geometry.
- M3/M4/M5 normal clearance holes: 3.4/4.5/5.5 mm unless another standard is requested.

## Required workflow

1. Classify the task (new part, new assembly, source modification, direct inspection, measurement/alignment check, snapshot review, secondary output).
2. Write a natural-language CAD brief capturing dimensions, units, feature intent, and validation targets.
3. Check named purchasable components against a parts library before creating placeholder geometry.
4. Plan parameters, intent labels, and datums before editing.
5. Edit source (build123d Python), not generated artifacts; generate STEP via `scripts/step`.
6. Validate geometrically with `scripts/inspect refs --facts --planes --positioning`, then targeted measure/align/frame/diff checks.
7. Snapshot the primary STEP output with `scripts/snapshot` and review it — this step is mandatory, not optional.
8. Repair and rerun the smallest responsible section if a check fails.

## Non-negotiables

- STEP is the primary validated artifact; STL/3MF/GLB are secondary derived exports.
- Use named parameters, closed solids, and source-controlled geometry intent.
- Do not use file-size or git diff churn to compare large CAD artifacts — compare source and inspection output instead.
- Report only checks that actually ran.