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Boolean Fragments

In one sentence: Split all input shapes at every mutual intersection, producing a compound of every non-overlapping fragment with no material added or removed.

Overview

Workbench: Part
Menu: Part → Split → Boolean Fragments
Shortcut: none

Takes any number of shapes, computes all pairwise intersections, and splits every shape along every intersection boundary. The result is a compound of all non-overlapping fragments. Total volume is preserved — the inputs are partitioned, not merged or subtracted.

Intuition

Standard Boolean Cut/Fuse/Common always produce one result shape, discarding the removed pieces. Boolean Fragments is different: every fragment is preserved. Nothing is thrown away.

Imagine three overlapping spheres. Boolean Fragments divides them into seven distinct regions: the three unique parts of each sphere, the three pairwise overlaps, and the triple-overlap centre. Each region becomes a separate solid in the output compound.

This makes Boolean Fragments essential for:

  • FEA/CFD meshing — adjacent parts need conforming meshes (shared nodes at boundaries). Fragmenting all parts first ensures the mesh generator sees shared boundary faces.
  • Spatial analysis — understanding exactly which regions two solids overlap.
  • Voronoi/split patterns — dividing a volume into prescribed sub-volumes.

When to use it

  • Preparing a multi-body assembly for FEA meshing (conforming mesh boundaries).
  • Analysing how multiple components overlap in an assembly.
  • Cutting a body with multiple planes simultaneously.
  • Generating all fragments of a complex overlap without discarding any piece.

When NOT to use it

  • Don't use it if you only need one result shape — use Boolean Cut, Boolean Fuse, or Boolean Common instead.
  • Don't use it on non-intersecting shapes — the result will be a compound of the original unchanged shapes, which is rarely useful.

Step-by-step

  1. Select all the shapes to fragment (any number; hold Ctrl to multi-select).
  2. Choose Part → Split → Boolean Fragments.
  3. A compound appears containing all fragments.
  4. Use Part → Explode Compound to separate them into individual objects if needed.

Parameters

Parameter Description
Objects All input shapes to fragment
Mode Standard / Split / CompSolid — controls how touching fragments are grouped in the output compound

Common mistakes and pitfalls

Non-intersecting shapes produce an unchanged compound

If none of the inputs overlap, Boolean Fragments returns a compound of the original shapes. Verify that inputs actually intersect before using this tool.

Large numbers of inputs can be slow

Each pairwise intersection is computed. With N shapes, there are N(N−1)/2 intersection checks. Keep input counts reasonable (< 20) for interactive use.

Mode affects downstream usability

In CompSolid mode, touching fragments are grouped as a compound solid — useful for FEA but may confuse tools that expect independent solids. Use Standard mode for general-purpose use.

Python API

import FreeCAD as App
import BOPTools.SplitFeatures as SF

doc = App.newDocument()

box = doc.addObject("Part::Box", "Box")
box.Length = 30; box.Width = 30; box.Height = 30

cyl = doc.addObject("Part::Cylinder", "Cyl")
cyl.Radius = 10; cyl.Height = 40
cyl.Placement = App.Placement(App.Vector(15, 15, -5), App.Rotation())
doc.recompute()

frags = SF.makeBooleanFragments(name="Fragments")
frags.Objects = [box, cyl]
frags.Proxy.execute(frags)
doc.recompute()

print(f"Number of fragments: {len(frags.Shape.Solids)}")

See also