3d Cad Skill

1. Capture The Design Brief

Before modeling, extract:

• Target output: stl, step, 3mf, source code only, or all of them
• Modeling stack: prefer the user's requested tool; otherwise default to the simplest proven option
• Critical dimensions and units
• Mating parts, clearances, print orientation, and strength constraints
• Whether the goal is appearance, fit, mechanism, or manufacturability

If requirements are incomplete, make explicit assumptions and keep the first version simple.

2. Choose The Modeling Representation

• Use OpenSCAD for straightforward constructive solid geometry, parameterized print parts, jigs, spacers, brackets, trays, and enclosures.
• Use build123d when the part benefits from sketch-extrude workflows, fillet/chamfer-heavy operations, or more structured Python logic.
• Prefer simple primitives and boolean composition before introducing advanced operations.

3. Build The Smallest Correct Parametric Skeleton

Start with a coarse model that proves overall proportions and alignment:

• Define top-level parameters first.
• Separate base body, cutouts, mounts, and cosmetic details.
• Keep transforms and coordinate frames obvious.
• Delay fillets, chamfers, text embossing, and decorative features until the base geometry is correct.

Structure code so a later pass can adjust one concern without rewriting the whole model.

4. Render And Inspect

After each meaningful change, inspect the result deliberately:

• Check silhouette and proportions from multiple angles.
• Check critical dimensions numerically.
• Check whether holes, cutouts, and mating faces are centered and aligned.
• Check printability: unsupported spans, wall thickness, trapped voids, and impossible overhangs.
• Check whether the model matches the user's stated intent, not just whether the code runs.

Read references/geometry-iteration.md when the task needs a stricter inspection loop or when you are debugging repeated geometry mistakes.

5. Fix One Geometric Issue At A Time

When something looks wrong:

• Name the defect precisely.
• Identify the smallest parameter or operation likely causing it.
• Change one thing.
• Re-render and compare against the previous result.

Avoid broad rewrites unless the part architecture is clearly wrong.

6. Deliverables

Default deliverables:

• The source model
• A short list of exposed parameters
• Assumptions and unresolved risks
• Export instructions if the environment cannot generate meshes directly

When useful, also provide:

• Recommended print orientation
• Suggested tolerance ranges
• Notes on likely failure points or reinforcement options

Quality Bar

The final result should be:

• Parametric rather than hard-coded
• Easy to inspect and revise
• Dimensionally explicit
• Realistic for the intended fabrication method
• Honest about assumptions and unverified fit