【Mechanical Design】🧩 11. Defining Assemblies by Code — Using FreeCAD as a Placement Engine

topics: [“Mechanical Design”, “CAD”, “FreeCAD”, “Python”, “Assembly”, “Git”]

🏁 Introduction

In the previous articles, we covered:

• Generating part geometry by code
• Treating geometry as functions
• Managing design changes using Git diffs

This article focuses on a single fact:

Multiple parts can be assembled using Python code only, without any GUI-based operations in FreeCAD.

The scope is intentionally limited to a minimal, reproducible assembly example.

📦 Target Repository

• Repository
  https://github.com/Samizo-AITL/full-code-mechanical-design

• Assembly definition code
  src/assembly/demo_assembly.py

🧱 Assumptions

• Each part can be generated independently under parts/
• Each part has a clearly defined origin and orientation
• No constraint solvers or Assembly Workbenches are used

Only explicit numerical placement is applied.

📐 Placement Is Defined Numerically

import FreeCAD as App

placement = App.Placement(
    App.Vector(x, y, z),
    App.Rotation(App.Vector(ax, ay, az), angle)
)

🧪 How to Execute

Windows

cd src
"C:\Program Files\FreeCAD 0.21\bin\FreeCADCmd.exe" build.py

Linux

cd src
freecadcmd build.py

🖥 Generated Result

🎯 Summary

• Part generation lives in parts/
• Assembly placement lives in assembly/
• Execution is handled by build.py