build123d

rawwerks's avatarfrom rawwerks

CAD modeling with build123d Python library. Use when creating 3D models, exporting to GLB/STEP/STL, or doing boolean operations (union, difference, intersection). Triggers on: CAD, 3D modeling, sphere, box, cylinder, mesh export, GLB, STEP, STL, solid modeling, parametric design, threads, fasteners, bolts, nuts, screws, gears, pipes, flanges, bearings, bd_warehouse, spur gear, helical gear, bevel gear, planetary gear, ring gear, cycloid gear, rack and pinion, gggears, herringbone, gear mesh, gear train.

⭐1stars🔀0forks📁View on GitHub🕐Updated Dec 18, 2025
[Code Generation]

When & Why to Use This Skill

This Claude skill provides a comprehensive environment for programmatic 3D CAD modeling using the build123d Python library. It enables users to generate complex 3D geometries through code, perform advanced boolean operations, and export models to industry-standard formats like STEP, STL, and GLB. By leveraging parametric design and specialized libraries for gears and fasteners, it streamlines the transition from conceptual engineering to manufacturable assets.

Use Cases

  • Mechanical Engineering: Designing precise parametric components such as spur gears, planetary gear systems, and custom fasteners using integrated libraries like gggears and bd_warehouse.
  • Rapid Prototyping: Generating 3D-printable STL files for functional parts, allowing for quick iterations of mechanical designs through Python scripting.
  • Web-Based 3D Visualization: Creating and optimizing GLB models for integration into web applications, AR/VR environments, or interactive 3D product showcases.
  • Automated Hardware Design: Using algorithmic logic to create complex assemblies, hole patterns, and structural frames that require high precision and repeatability.
namebuild123d
descriptionCAD modeling with build123d Python library. Use when creating 3D models, exporting to GLB/STEP/STL, or doing boolean operations (union, difference, intersection). Triggers on: CAD, 3D modeling, sphere, box, cylinder, mesh export, GLB, STEP, STL, solid modeling, parametric design, threads, fasteners, bolts, nuts, screws, gears, pipes, flanges, bearings, bd_warehouse, spur gear, helical gear, bevel gear, planetary gear, ring gear, cycloid gear, rack and pinion, gggears, herringbone, gear mesh, gear train.

build123d CAD Modeling

Zero-Setup with uv

No installation required. Run any build123d script with:

uvx --from build123d python script.py

This automatically downloads build123d and runs your script. First run takes ~30s, subsequent runs are instant.

Install uv (if not already installed):

curl -LsSf https://astral.sh/uv/install.sh | sh

Critical: Imports

All exports are in the main module:

from build123d import Sphere, Box, Cylinder, export_gltf, export_step, export_stl

NEVER use from build123d.exporters import ... - this module does not exist.

Quick Start Example

#!/usr/bin/env python3
from build123d import Sphere, Box, export_gltf, Pos

# Create shapes
sphere = Sphere(radius=20)
box = Pos(15, 0, 0) * Box(10, 10, 10)

# Boolean union
result = sphere + box

# Export to GLB (for web viewers, Three.js)
export_gltf(result, "./model.glb", binary=True)
print("Exported model.glb")

Run it:

uvx --from build123d python my_model.py

Geometry Inspection (Optional)

To inspect geometry properties, add this to your script:

def inspect(shape):
    bbox = shape.bounding_box()
    print(f"Size: {bbox.max.X - bbox.min.X:.1f} x {bbox.max.Y - bbox.min.Y:.1f} x {bbox.max.Z - bbox.min.Z:.1f}")
    print(f"Volume: {shape.volume:.1f}")
    print(f"Faces: {len(shape.faces())}, Edges: {len(shape.edges())}")

inspect(result)

A full inspection harness is available in scripts/harness.py for advanced use.

Quick Reference

Shapes

Box(length, width, height)
Sphere(radius=20)
Cylinder(radius=10, height=25)
Cone(bottom_radius=15, top_radius=5, height=20)
Torus(major_radius=20, minor_radius=5)

Boolean Operations

union = shape1 + shape2           # Fuse
difference = shape1 - shape2      # Cut
intersection = shape1 & shape2    # Common volume

Positioning

from build123d import Pos, Rot
moved = Pos(x, y, z) * shape      # Translate
rotated = Rot(rx, ry, rz) * shape # Rotate (degrees)

Export

export_gltf(shape, "./out.glb", binary=True)  # GLB for web
export_step(shape, "./out.step")              # CAD interchange
export_stl(shape, "./out.stl")                # 3D printing

Examples by Capability

21 runnable examples in references/examples/:

Basics (01-08)

  • 01_simple_shapes.py - Box, Sphere, Cylinder, Cone, Torus
  • 02_boolean_operations.py - Union (+), difference (-), intersection (&)
  • 03_export_formats.py - GLB, STEP, STL, BREP export
  • 04_positioning.py - Pos(), Rot() transforms
  • 05_sketch_extrude.py - 2D sketch to 3D solid
  • 06_fillet_chamfer.py - Edge rounding and beveling
  • 07_csg_classic.py - Classic CSG operations
  • 08_hole_pattern.py - GridLocations for hole patterns

3D Operations

  • loft.py - Connect multiple profiles
  • vase.py - Revolve + edge filtering + shelling
  • tea_cup.py - Revolve + sweep for handle

Advanced Techniques

  • roller_coaster.py - Helix + Spline curves
  • packed_boxes.py - pack() algorithm
  • toy_truck.py - Joints for assembly
  • dual_color_3mf.py - Multi-color 3MF export

Run any example:

uvx --from build123d python references/examples/01_simple_shapes.py

Advanced Patterns

For builder mode, edge filtering, loft, sweep, revolve: See references/advanced-patterns.md

bd_warehouse - Parametric Parts Library

For threads, fasteners, simple gears, pipes, flanges, and bearings: See references/bd-warehouse-reference.md

uvx --from build123d --with bd_warehouse python script.py

Examples: 09_bd_warehouse_threads.py through 14_bd_warehouse_bearings.py

gggears - Advanced Gear Generation

For advanced parametric gears (spur, helical, bevel, planetary, cycloid, racks): See references/gggears-reference.md

uvx --from build123d --with "gggears @ git+https://github.com/GarryBGoode/gggears" python script.py

Examples: 15_gggears_spur.py through 20_gggears_rack.py

Quick example:

from gggears import SpurGear, UP
from build123d import export_gltf

gear1 = SpurGear(number_of_teeth=12, module=2.0, height=10.0)
gear2 = SpurGear(number_of_teeth=24, module=2.0, height=10.0)
gear1.mesh_to(gear2, target_dir=UP)

assembly = gear1.build_part() + gear2.build_part()
export_gltf(assembly, "./gears.glb", binary=True)

Post-Processing Pipeline

After exporting GLB, you can optimize and verify:

# 1. Optimize for web delivery (optional)
bunx @gltf-transform/cli optimize model.glb optimized.glb --compress draco

# 2. Render to image for visual verification
bunx render-glb model.glb preview.png

See the gltf-transform and render-glb plugins for full documentation.

Source Repositories