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CAD (Computer-Aided Design) is how you describe a 3D shape to a computer with enough precision that a machine can build it. The differences between CAD tools come down to one thing: how the shape is represented internally. Once you understand that, picking the right tool for any job becomes obvious.
Three ways CAD represents a 3D shape.
difference() and cube() primitives. The 'code-first' approach is striking.1. MESH (Polygon) — Tinkercad, Blender, Meshmixer
The shape is a collection of triangles (or quads).
Pro: easy to manipulate organically (sculpting)
Con: a 'cube' has just 12 triangles; a 'sphere' has thousands.
Resizing distorts the mesh; precision is approximate.
Used for: organic shapes (figurines, sculptures), quick prototypes.
2. B-REP (Boundary Representation) — Fusion 360, OnShape, FreeCAD, SolidWorks
The shape is a mathematical surface (a 'NURBS' patch) plus rules.
A cube is literally six planes meeting at edges.
Pro: precise. A 10mm cube is EXACTLY 10mm.
Con: organic shapes are harder; you must define them via curves + lofts.
Used for: engineering, mechanical parts, anything dimensional.
3. CSG (Constructive Solid Geometry) — OpenSCAD
The shape is a tree of boolean operations on primitives.
"Cube minus cylinder" = a cube with a hole through it.
Pro: code-based; reproducible; parametric by default.
Con: no GUI for shape design; everything is typing.
Used for: parametric mechanical parts, batch-generated designs.
HYBRID TOOLS:
Fusion 360: B-rep primary; can import mesh; mesh workspace converts.
OnShape: B-rep primary; cloud-only.
Blender: mesh primary; supports both for different workflows.
KEY INSIGHT:
For 3D printing, B-rep is usually right.
A 3D-printed mechanical part needs dimensions; meshes blur them.
Use mesh tools (Tinkercad, Blender) for sculpting; B-rep for fitment.
PARAMETRIC vs DIRECT:
Parametric CAD: every feature has parameters. Change one number, the whole
model regenerates. Recommended for engineering work.
Direct CAD: you push/pull geometry directly. Faster for art; harder to maintain
relationships between parts.
Tinkercad: not parametric (purely direct).
Fusion / OnShape / SolidWorks: parametric by default.
Blender: direct (mostly); some addons add parametric features.