FreeCAD: Parametric 3D Modeling
First session with FreeCAD — learning the Part Design workflow, constraints, and how parametric modeling thinks.
What FreeCAD Is
FreeCAD is a free, open-source parametric 3D CAD modeler — the same category as SolidWorks or Fusion 360, but without the subscription. “Parametric” means dimensions are variables: change a number and the model updates everywhere that number was used.
It’s aimed at mechanical engineering and product design. The workflow is fundamentally different from mesh-based tools like Blender — you’re defining geometry by constraints and dimensions, not pushing vertices around.
The Core Workflow: Part Design
FreeCAD is organized into Workbenches — context-specific toolsets. For solid modeling, the one to start with is Part Design.
The basic loop:
1. Create a Body
2. Start a Sketch (on a plane or face)
3. Draw 2D geometry and apply constraints
4. Close the sketch
5. Apply a feature: Pad (extrude), Pocket (cut), Revolution, etc.
6. Repeat — each feature builds on the last
The result is a feature tree: a history of every operation, in order. You can go back and edit any step and the entire model regenerates.
Sketcher and Constraints
The Sketcher is where most of the real work happens. You draw lines, arcs, and circles — but raw geometry has no meaning until it’s constrained.
Constraints come in two types:
Geometric constraints — relationships between elements:
- Coincident (two points share a location)
- Horizontal / Vertical
- Parallel, Perpendicular, Tangent
- Symmetric, Equal
Dimensional constraints — actual numbers:
- Fixed length, radius, angle
- Distance between two points or lines
The goal is a fully constrained sketch — every element locked in place, nothing free to float. FreeCAD shows under-constrained geometry in white and fully constrained geometry in green. Chasing green is the whole game.
Pad and Pocket
Once the sketch is constrained and closed:
- Pad — extrudes the 2D profile into a 3D solid. Specify a depth.
- Pocket — cuts the profile into an existing solid. Same idea, subtractive.
Most physical parts are just a series of pads and pockets. A bracket is a padded rectangle with pocketed holes. A housing is a padded outer shell with a pocketed cavity.
What Makes It Click
The parametric model behaves like a spreadsheet — cells reference each other. If the hole diameter is defined as mounting_hole_d = 4mm and you use that variable in three sketches, changing it once updates all three. This is the actual value of CAD over just drawing shapes.
The other thing that clicks: the feature tree is an undo history that you can edit in the middle. Add a fillet to step 3, and everything built on top of it rerenders. Blender has nothing like this.