OpenSCAD 3D Modeling

Overview

OpenSCAD is a programmer's solid 3D CAD modeller that uses scripts to generate 3D models. Unlike interactive 3D tools, OpenSCAD models are described declaratively in code, making them ideal for AI-driven generation. Models are built from primitives (cube, sphere, cylinder) combined with boolean operations (union, difference, intersection) and transformed (translate, rotate, scale).

Key Concepts

Constructive Solid Geometry (CSG): Combine simple shapes into complex models using boolean operations

• union() - Combine multiple shapes into one
• difference() - Subtract shapes from each other
• intersection() - Keep only overlapping regions

Primitives: Basic building blocks

• cube(size=[x,y,z]) - Rectangular box
• sphere(r=radius) - Sphere
• cylinder(h=height, r=radius) - Cylinder
• polyhedron(points, faces) - Arbitrary shape

Transformations: Position and orient shapes

• translate([x,y,z]) - Move shape
• rotate([x,y,z]) - Rotate around axes
• scale([x,y,z]) - Resize shape
• resize([x,y,z]) - Resize to specific dimensions

Render Pipeline

OpenSCAD Script (.scad)
         ↓
    Preview (Fast, GPU, approximate)
         ↓
    Full Render (Slow, CPU, exact)
         ↓
    Export (STL, 3MF, OFF, DXF)

Workflow Decision Tree

User Request
    ↓
    Is this for 3D printing?
    ├── YES → Generate OpenSCAD script
    │         ↓
    │     Validate script syntax
    │         ↓
    │     Render preview (openscad -o preview.png input.scad)
    │         ↓
    │     Full render for export (openscad -o output.stl input.scad)
    │         ↓
    │     Return .stl + .scad + preview image
    │
    └── NO → May need Three.js (different skill)
             or clarify user intent

Step 1: Generate OpenSCAD Script

Syntax Basics

// Resolution control for 3D printing quality
$fa = 1;  // Minimum angle (degrees)
$fs = 0.4;  // Minimum size (mm)

// Simple box
cube([20, 20, 10]);

// Sphere
sphere(r=10);

// Cylinder
cylinder(h=20, r=5);

Combine Shapes with CSG

// Union - combine shapes
union() {
    cube([20, 10, 10]);
    translate([20, 0, 0])
        cube([10, 10, 10]);
}

// Difference - subtract shapes
difference() {
    cube([20, 20, 10]);
    translate([5, 5, -1])
        cylinder(h=12, r=3);
}

// Intersection - keep overlap
intersection() {
    cube([20, 20, 20]);
    sphere(r=15);
}

Transformations

// Translate
translate([10, 10, 0])
    cube([10, 10, 10]);

// Rotate
rotate([90, 0, 0])
    cylinder(h=20, r=5);

// Scale
scale([2, 1, 1])
    sphere(r=10);

// Chain transformations
translate([10, 0, 0])
    rotate([0, 90, 0])
        cylinder(h=10, r=5);

Modules for Reusability

module gear(teeth=8, radius=20, thickness=5) {
    union() {
        cylinder(h=thickness, r=radius);
        for (i = [0:teeth-1]) {
            rotate([0, 0, i * 360/teeth])
                translate([radius, 0, 0])
                    cube([5, 3, thickness], center=true);
        }
    }
}

// Use module
gear(teeth=12, radius=15, thickness=3);

Step 2: Validate Script

Common Validation Checks

1. Syntax errors: Missing semicolons, unmatched brackets
2. Valid geometry: Manifold edges, no self-intersections
3. Overlap tolerance: Use 0.001mm overlap between touching surfaces

Validation Script

Use scripts/validate_openscad.py to check:

python3 scripts/validate_openscad.py model.scad

Returns:

• ✅ Valid: Script compiles successfully
• ❌ Error: Syntax error message

Step 3: Render Model

Quick Preview (for iteration)

openscad -o preview.png input.scad

• Fast GPU rendering
• Good for checking geometry
• Not export-quality

Full Render (for export)

openscad -o output.stl input.scad

• Slow CPU rendering with CGAL
• Produces exact geometry
• Ready for 3D printing

Export Formats

Best Practices

1. Resolution Control

Always set resolution variables at the top:

$fa = 1;   // Minimum angle: 1 degree
$fs = 0.4; // Minimum size: 0.4mm

• $fa: Minimum angle for circle segments (lower = smoother)
• $fs: Minimum segment size (lower = finer detail)
• Default values may create faceted curves

2. Overlap Tolerance

When shapes touch, ensure small overlap (0.001mm):

difference() {
    cube([20, 20, 10]);
    translate([5, 5, -0.001])  // Small overlap
        cylinder(h=10.002, r=3);
}

3. Use Modules

Encapsulate complex geometry in modules:

module bolt_hole(length, diameter) {
    cylinder(h=length, r=diameter/2);
}

// Use multiple times
difference() {
    plate();
    translate([10, 10, 0]) bolt_hole(10, 5);
    translate([20, 10, 0]) bolt_hole(10, 5);
}

4. Parameterize Design

Make designs configurable:

module box(width=50, depth=50, height=20, wall_thick=2) {
    difference() {
        cube([width, depth, height]);
        translate([wall_thick, wall_thick, wall_thick])
            cube([width-2*wall_thick,
                  depth-2*wall_thick,
                  height]);
    }
}

// Use with parameters
box(width=60, depth=40, height=15, wall_thick=3);

Common Patterns

Hollow Box

module hollow_box(width, depth, height, wall_thick) {
    difference() {
        cube([width, depth, height]);
        translate([wall_thick, wall_thick, wall_thick])
            cube([width-2*wall_thick,
                  depth-2*wall_thick,
                  height-wall_thick]);
    }
}

Fillet (Rounded Edge)

module fillet(radius, length) {
    difference() {
        cube([radius, radius, length]);
        translate([radius, radius, -1])
            cylinder(h=length+2, r=radius);
    }
}

Bracket

module bracket(width=40, height=30, thickness=5, hole_diameter=8) {
    difference() {
        // L-shape
        union() {
            cube([width, thickness, thickness]);
            cube([thickness, height, thickness]);
        }
        // Holes
        translate([width/2, -1, thickness/2])
            rotate([-90, 0, 0])
                cylinder(h=thickness+2, r=hole_diameter/2);
        translate([-1, height/2, thickness/2])
            rotate([0, 90, 0])
                cylinder(h=thickness+2, r=hole_diameter/2);
    }
}

Gear

module gear(teeth=8, radius=20, thickness=5, hole_diameter=5) {
    difference() {
        union() {
            // Main body
            cylinder(h=thickness, r=radius);
            // Teeth
            for (i = [0:teeth-1]) {
                rotate([0, 0, i * 360/teeth])
                    translate([radius, 0, 0])
                        cube([radius/2, radius/teeth*2, thickness], center=true);
            }
        }
        // Center hole
        cylinder(h=thickness+1, r=hole_diameter/2, center=true);
    }
}

Resources

scripts/

• validate_openscad.py: Validate OpenSCAD scripts for syntax errors
• Use when checking generated scripts before rendering

references/

• primitives.md: Complete list of OpenSCAD primitives with examples
• transformations.md: Transformation operations and patterns
• modules.md: Common reusable modules and patterns
• export_formats.md: Export format specifications and use cases

assets/

• templates/simple_box.scad: Basic box template
• templates/mechanical_part.scad: Mechanical part template
• templates/parametric_design.scad: Parametric design template
• templates/assembly.scad: Assembly template

Resources

See references/primitives.md for complete primitive reference. See references/modules.md for reusable module patterns. See assets/templates/ for starting templates.

Use scripts/validate_openscad.py to validate scripts before rendering.