mechanical-cad

name

mechanical-cad

description

Create, revise, execute, and validate parametric mechanical designs in build123d, including parts, enclosures, brackets, shafts, fixtures, assemblies, and PCB-housing geometry. Use when the requested deliverable includes CAD Python, STEP/STL exports, dimensional checks, or rendered geometry. Do not use for requirements-only work or for certifying manufacturability without process-specific evidence.

Mechanical CAD with build123d

Workflow

1. Inspect the specification, prose, reference images, technical drawings/models, existing code, and requested outputs. Classify the task as a new part, assembly, modification, inspection, or export.
2. Write a compact internal CAD brief using references/cad-brief.md. Record inputs/revisions, units, coordinate convention, manufacturing intent, controlling dimensions, features, datums, paths, validation targets, assumptions, and conflicts before modeling.
3. Prefer dimensioned evidence over image proportions. If two dimensioned sources conflict, report the conflict instead of silently choosing. Ask one focused question only when the conflict affects feasibility, fit, safety, interfaces, or compliance.
4. Establish the coordinate convention before modeling. Default only when unspecified: millimetres, XY base plane, +Z up, and a documented origin.
5. Separate controlling parameters from derived dimensions. Name datums, mating planes, hole patterns, keep-out envelopes, and clearances. Do not scatter magic numbers through geometry operations.
6. Select dimensions from the controlling source in this order: approved specification, manufacturer drawing/model, applicable standard, dimensioned task drawing, measured value, then explicitly labeled estimate. Never treat a generic clearance, wall, fillet, or fastener table as universally valid.
7. Choose the build123d API style:
   • Prefer Algebra mode for explicit solids, Boolean expressions, transforms, and compact parametric parts.
   • Use Builder mode when sketch/workplane context, repeated placement, or last-operation selection makes construction clearer.