global-skills/skills/cad-3d-print/SKILL.md

name, description, scope

name	description	scope
cad-3d-print	Design, generate, and verify parametric 3D models for 3D printing using code-first CAD (OpenSCAD, build123d).	global

CAD 3D Print

Design, generate, and empirically verify 3D-printable parts using programmatic CAD. Follow the shared workflow.

Workflow

1. Dimensional Budgeting & Tolerances

   • Establish bounding box, mounting points, and mating interfaces from user specifications.
   • Apply standard FDM 3D printing tolerances:
     • Horizontal hole clearance: Add +0.2 mm to +0.3 mm for screw pass-through (e.g. M3 hole diameter = 3.2 mm; tap hole = 2.9 mm).
     • Fit clearances: Snug/snap fit 0.15 mm; sliding fit 0.3 mm; loose/hinged fit 0.4–0.5 mm.
     • Wall thickness: Multiples of nozzle width (minimum 1.2 mm for 0.4 mm nozzles).
     • Bed contact: Add 45° chamfers to bottom edges touching the build plate to prevent "elephant's foot" binding.
     • Overhangs: Keep unassisted overhangs \le 45^\circ to minimize support material.

2. Parametric Script Generation

   • Author a standalone, self-documenting OpenSCAD (.scad) script:
     • Place all customizable dimensions at the top as labeled parametric variables.
     • Set curvature resolution: $fn = 60; or $fs = 0.5; $fa = 5; for smooth circular features.
     • Use Constructive Solid Geometry (CSG): union(), difference(), intersection(), hull().
     • Prevent non-manifold coincident faces (Z-fighting): always extend cutting bodies slightly beyond the target surface (e.g., translate([0, 0, -0.1]) cylinder(h = height + 0.2, ...)).

3. Empirical Verification

   • Compile STL mesh:

     openscad -o model.stl model.scad
     

     Inspect compiler output to ensure Simple: yes (a manifold, watertight solid).
   • Render visual preview:

     openscad --render --imgsize=800,600 -o preview.png model.scad
     

   • Verify the rendered image to check geometry, clearances, and aesthetic proportions.

4. Handoff Artifacts

   • Keep the editable .scad source in the workspace.
   • Provide the compiled .stl or .3mf for slicing (PrusaSlicer, Bambu Studio, OrcaSlicer).
   • Embed or link the rendered .png preview.