codecraft/server/resources/skills/cad/SKILL.md

name, description

name	description
cad	Design parametric 3D models for 3D printing with OpenSCAD – from a description, a hand-drawn sketch or a photo. Renders STL/3MF and checks previews against the sketch.

3D models with OpenSCAD (for 3D printing)

You design printable parts as parametric OpenSCAD code, render them with the openscad tool, look at the previews and refine until the part matches what the user wants.

1. Understand the part

• If the user attached a sketch or photo, describe what you see first: overall shape, features (holes, slots, ribs, chamfers, text), views shown, and every dimension written on it (with units). Hand-drawn sketches are not to scale – written numbers win over proportions.
• List what is missing for a printable part (overall size, wall thickness, hole diameters, screw sizes, fit with other parts). Ask with ask_user in one round, offering sensible defaults the user can just accept (e.g. "wall 2 mm, M3 holes 3.4 mm"). Don't ask about things you can reasonably assume.

2. Write the model

Create <name>.scad in the project (or cad/<name>.scad if the project has other content):

// <Part name> – <one-line purpose>
// All dimensions in mm.

/* [Main dimensions] */
width  = 60;   // outer width (X)
depth  = 40;   // outer depth (Y)
height = 25;   // outer height (Z)
wall   = 2;    // wall thickness

/* [Holes] */
hole_d = 3.4;  // M3 clearance

/* [Quality] */
$fn = 64;

module body() { ... }
module holes() { ... }

difference() {
  body();
  holes();
}

Rules:

• Every size is a named variable at the top with a comment; group them with /* [Section] */ (shows up in OpenSCAD's customizer). No magic numbers in the geometry.
• Small, named modules; difference() / union() / hull() / minkowski() (sparingly – slow) / linear_extrude() / rotate_extrude().
• Model sits on z = 0, centred in X/Y unless the user wants otherwise.
• Holes and cut-outs extend a little past the surface (+0.01/2*eps) to avoid coplanar faces (z-fighting, non-manifold results).

Printability (FDM defaults – adjust if the user says SLA/resin or names a printer/nozzle):

• Minimum wall 1.2 mm (3 × 0.4 mm nozzle), better 2 mm for load-bearing parts.
• Overhangs ≤ 45°; prefer chamfers over fillets on the bottom edge; bridges ≤ ~20 mm.
• Fits: +0.2 mm clearance for sliding fits, +0.3–0.4 mm for loose fits; press fits −0.05 mm. Horizontal holes come out slightly small – add 0.2 mm or use a teardrop shape.
• Print orientation: flat largest face down; mention it in the summary.
• Text: linear_extrude(0.6) text(..., size ≥ 5, font="Liberation Sans:style=Bold").
• Threads: use clearance holes plus heat-set inserts or nut traps instead of modelling threads, unless the user asks for printed threads.

3. Render and check

• Run openscad with formats: ["stl", "png"] (add "3mf" for the final version) and the views that show the important features (default iso, front, top).
• Check the bounding box against the required dimensions and the warnings (a non-manifold result must be fixed before printing).
• Compare the previews with the sketch: proportions, feature positions, counts (holes, ribs), orientation. Fix differences and render again. Two or three iterations are normal.
• For variants, use params to override variables instead of copying the file.

4. Deliver

Summarise briefly:

• Files: .scad (editable), .stl / .3mf (printable), previews.
• Final dimensions (bounding box) and the key parameters the user may want to change.
• Print hints: orientation, supports needed or not, suggested layer height/infill for the use.
• Assumptions you made. The STL/3MF can be previewed in the file manager (3D view).