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Shape from Mesh

In one sentence: Wrap a Mesh object as a Part shell shape so it can participate in Boolean operations and other Part workbench tools.

Overview

Workbench: Part
Menu: Part → Shape from Mesh…
Shortcut: none

Takes a Mesh object (from the Mesh workbench or an imported STL/OBJ) and creates a Part::Feature containing a shell of triangular faces. The result is not a clean B-rep solid — it is a Part shape whose faces are the original mesh triangles.

Intuition

FreeCAD has two fundamentally different geometric representations:

  • Meshes — a cloud of triangles, used by STL files and the Mesh workbench
  • B-rep shapes — precise boundary-representation geometry used by Part, Part Design, and OCCT

These two worlds don't mix directly: you cannot Boolean-cut a mesh with a Part sphere. Shape from Mesh builds the bridge by wrapping the mesh triangles in a Part shell, making the mesh accessible to Part tools.

This is typically the first step in the STL → solid repair pipeline:

STL file → Shape from Mesh → Convert to Solid → Refine Shape → usable solid

When to use it

  • You imported an STL and need to Boolean-cut it or measure it with Part tools.
  • You have a Mesh workbench object and need to convert it to Part geometry.
  • You are following the standard mesh-to-solid repair workflow.

When NOT to use it

  • Don't use it as a final step — the result is a shell of triangles, not a clean solid. Follow up with Convert to Solid and optionally Refine Shape.
  • Don't use it if the mesh has gaps — the sewing tolerance helps bridge small gaps, but large holes must be repaired in the Mesh workbench first.

Step-by-step

  1. Import the STL/OBJ (File → Import) — it arrives as a Mesh::Feature.
  2. Select the Mesh object in the tree.
  3. Choose Part → Shape from Mesh….
  4. A dialog appears asking for the sewing tolerance (default 0.1 mm).
  5. Click OK. A Part::Feature shell appears.
  6. Proceed to Convert to Solid to close the shell.

Parameters

Parameter Default Description
Sewing tolerance 0.1 mm Maximum gap between mesh triangle edges to be considered connected. Increase this value if the mesh has small gaps.

Common mistakes and pitfalls

Result is a shell, not a solid

Shape from Mesh creates a shell (open or closed surface), not a solid volume. You cannot use it directly in PartDesign or for Boolean operations that require a solid. Use Convert to Solid next.

Large sewing tolerance may bridge holes unintentionally

If the sewing tolerance is too large, gaps that should remain open will be bridged, creating incorrect topology. Start with the default 0.1 mm and increase only if necessary.

Non-watertight meshes cannot become solids

If the original mesh has holes (boundary edges), Convert to Solid will fail after Shape from Mesh. Repair the mesh in the Mesh workbench first using Mesh → Fill Holes and Mesh → Close Holes.

Python API

import FreeCAD as App
import Mesh, MeshPart

doc = App.newDocument()

# Load a mesh from a file
mesh_obj = doc.addObject("Mesh::Feature", "ImportedMesh")
mesh_obj.Mesh = Mesh.Mesh("/path/to/file.stl")
doc.recompute()

# Convert mesh to Part shape with 0.1 mm sewing tolerance
shape = MeshPart.meshToShape(mesh_obj.Mesh, 0.1)
feat = doc.addObject("Part::Feature", "ShapeFromMesh")
feat.Shape = shape
doc.recompute()

print(f"Shell faces: {len(feat.Shape.Faces)}")

See also