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Mesh Difference

In one sentence: Subtract one solid mesh from another, removing the volume of the second mesh from the first.

Overview

Workbench: Mesh
Menu: Mesh → Meshes → Boolean → Difference
Command: Mesh_Difference
Shortcut: none

Computes the Boolean difference — removes the volume of the second mesh from the first. Selection order matters: the first selected mesh is the base; the second is the cutter.

Intuition

Mesh Difference is the mesh equivalent of Part Boolean Cut. It is useful for cutting holes or slots through a solid mesh shape using another mesh as the cutter. Unlike the Part operation, it works directly on triangle meshes without converting to B-rep.

When to use it

  • Cutting a slot or hole through a solid mesh.
  • Subtracting a tool shape from a workpiece mesh.
  • Creating negative-space features in an STL for printing.

When NOT to use it

  • Don't use it when exact geometry matters — use Part workbench Boolean Cut for engineering-accurate results.
  • Both meshes must be solid — open meshes produce corrupt results.

Step-by-step

  1. Select the base mesh (the mesh to cut from).
  2. Ctrl+click the tool mesh (the cutter).
  3. Choose Mesh → Meshes → Boolean → Difference.
  4. A new mesh appears with the tool volume removed.

Selection order matters

First selected = base (what gets cut from). Second selected = tool (what is subtracted). Reversing the order cuts from the wrong mesh.

Common mistakes and pitfalls

Both meshes must be solid

Run Evaluate Solid on both meshes first. Open meshes produce silent failures or corrupt results.

The tool mesh must intersect the base

If the tool mesh is entirely outside the base, the result is identical to the base (no material is removed).

Python API

import Mesh
import FreeCAD as App

base = App.ActiveDocument.getObject("Mesh")
tool = App.ActiveDocument.getObject("Mesh001")

result = base.Mesh.copy()
result.subtract(tool.Mesh)

feature = App.ActiveDocument.addObject("Mesh::Feature", "Difference")
feature.Mesh = result
App.ActiveDocument.recompute()

See also