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Mesh Boolean

In one sentence: Perform a union, intersection, or difference on meshes using OpenSCAD's CGAL boolean engine as an alternative to OCCT's B-rep booleans.

Overview

Workbench: OpenSCAD
Menu: OpenSCAD → Mesh Boolean
Requires: OpenSCAD binary installed
Shortcut: none

Converts selected objects to STL meshes, passes them to OpenSCAD's CGAL engine for the boolean operation, and imports the result back as a Mesh::Feature. Used as a fallback when Part workbench boolean operations fail due to near-degenerate or self-intersecting geometry.

Intuition

FreeCAD's native boolean operations use OCCT (OpenCASCADE) which is excellent at exact B-rep booleans but can fail on "difficult" geometry (very thin walls, near-zero-thickness features, self-intersections). CGAL (the geometry kernel OpenSCAD uses) approaches booleans differently and can often succeed where OCCT fails — but it outputs a triangle mesh, not a parametric B-rep.

When to use it

  • A Part Boolean fails with "bad result" and you've tried geometry repair.
  • You are working primarily with mesh geometry and don't need B-rep output.
  • You need any of: Union, Intersection, Difference, Hull, or Minkowski sum on mesh input.

When NOT to use it

  • When you need B-rep output — the result is a mesh, not a solid. It cannot be used in Part Design without converting via Part → Shape from Mesh.
  • Without OpenSCAD installed — this tool requires the OpenSCAD binary.

Step-by-step

  1. Select the input objects (meshes or Part solids — solids are converted to meshes automatically).
  2. Choose OpenSCAD → Mesh Boolean.
  3. A dialog appears. Select the operation (Union, Intersection, Difference, Hull, Minkowski).
  4. Click OK. The result is imported as a Mesh::Feature.

Parameters

Operation Description
Union Combined volume of all inputs
Intersection Volume common to all inputs
Difference First object minus all subsequent objects
Hull Convex hull of all inputs
Minkowski Minkowski sum of all inputs

Common mistakes and pitfalls

OpenSCAD executable not found

Cause: Path not configured.
Fix: Edit → Preferences → OpenSCAD → set the OpenSCAD executable path.

Result is a mesh, not a solid — can't use in Part Design

Cause: CGAL outputs triangle meshes; the result is a Mesh::Feature.
Fix: Use Part → Shape from Mesh to convert back to a B-rep solid before using it in Part Design.

Python API

import FreeCADGui as Gui
Gui.doCommand("Gui.runCommand('OpenSCAD_MeshBoolean', 0)")

See also