【Mechanical Design】🛠️ 06. Zero GUI Operations in FreeCAD — Generating Geometric Solids Using Only Function Definitions

topics: [“mechanical design”, “cad”, “freecad”, “python”, “mathematics”]

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🧭 Introduction

FreeCAD is widely known as a parametric CAD system.
However, what is far less known is that:

Using only Python code,
FreeCAD can generate surprisingly rich geometric shapes

—without using:

• Sketches
• Constraints
• Part Design
• Or almost any GUI operation

In this article, we introduce pure code-driven solid geometry created with:

• No sketches
• No Part Design
• Nearly zero GUI interaction

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👀 First, Look at the Final Results

Function-defined Loft + Twisted Solid

This solid is generated by:

• Defining the radius as a function r(z)
• Modulating the cross-section using periodic functions
• Stacking profiles along the z-axis via Loft
• Applying an additional Twist transformation

All of this is done entirely in Python code.

No sketches. No constraints.

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🌀 Another Example: A Branched Spiral Solid

Next is a shape that is even more hostile to GUI-based modeling.

This model is constructed by:

• Generating spatial curves (spirals) in code
• Defining cross-sections via functions
• Introducing phase jumps to create branches
• Converting the result into a solid using Sweep / Loft-like logic

Because the geometric properties change mid-way,
this type of model is notoriously fragile in history-based GUI CAD.

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🔍 What Is the Key Point?

The important point is not that the shapes look exotic.

Geometry as the Result of Rules

In these examples:

• Dimensions
• Wave amplitude
• Twist magnitude
• Branch locations

are all defined as variables and functions in Python.

In other words:

Geometry is not the result of manual operations
but the result of executing rules

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⚔️ The Fundamental Difference from GUI CAD

Trying to create the same shapes in GUI CAD typically results in:

• Too many sketches
• Constraint breakage
• Loss of understanding of why the shape exists

In contrast, with code-based design:

def r(z):
    return base + amp * math.sin(freq * z)

The design intent itself is preserved as code.

Change a parameter → re-run → new geometry.

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🧰 Practical Benefits in Real Work

This approach is not just for artistic modeling.

It is highly effective for:

• Special-purpose shafts
• Mixing or agitation geometries
• Cooling fins
• Experimental fixtures
• Parametric shape exploration

Because everything is code-based:

• Git diff tracking works naturally
• Reasons for design changes remain visible
• Derivative designs are easy to generate

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🧾 Summary

FreeCAD can be used not only as:

• A tool for drawing sketches

but also as:

• A geometric engine that executes rules

There is no need to reject GUI workflows.
However, simply adding the option to:

Describe shape-generation rules in code

dramatically expands how CAD can be used.

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💻 Source Code Used

The code used to generate the shapes in this article is available here:

• Function-defined Loft + Twisted Solid
  loft_twist_solid.py

• Branched Spiral Solid
  branched_spiral_sweep.py

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📜 License

The code used in this article is released under the MIT License.

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