How to Fill Holes in Meshes in FreeCAD

Filling holes in a polygon mesh is a crucial step for repairing damaged 3D scans, fixing non-manifold geometry, and preparing models for 3D printing or CAD solid conversion. This guide explains how to quickly identify open boundaries and patch holes in a 3D mesh model using the native tools provided in the FreeCAD Mesh Workbench.

Step 1: Switch to the Mesh Workbench

  1. Open your project in FreeCAD.
  2. In the workbench dropdown menu at the top of the interface, select Mesh.
  3. In the tree view on the left, click on the mesh object you wish to edit to ensure it is selected.

Step 2: Use the Interactive "Fill Hole" Tool

FreeCAD provides a direct tool for manually patching specific openings on a mesh surface:

  1. Go to the top menu and click Meshes > Fill hole (or click the Fill hole icon in the Mesh toolbar).
  2. Move your cursor over the 3D model. The edges along open boundaries will highlight when hovered over.
  3. Click an edge belonging to the hole you want to close. FreeCAD will generate new triangular faces spanning the boundary, closing the hole.
  4. Continue clicking additional open hole boundaries if necessary.
  5. Right-click anywhere in the 3D view or press Esc to exit the tool.

Step 3: Automatically Detect and Fill All Holes

If your mesh contains numerous or microscopic holes that are difficult to select manually, use the automated repair dialog:

  1. Select your mesh object in the tree view.
  2. Go to Meshes > Analyze > Evaluate & Repair mesh....
  3. In the dialog box that appears, locate the Find holes test.
  4. Click the Analyze button next to it. FreeCAD will scan the geometry and report the total number of detected holes.
  5. Click Repair to automatically generate faces across all detected boundaries.
  6. Click Close to exit the dialog.

Step 4: Validate and Clean Up the Mesh

After closing the openings, ensure the new faces share proper orientation with the rest of the model:

  1. Select the repaired mesh object in the tree view.
  2. Go to Meshes > Harmonize normals to ensure all face directions are consistent.
  3. Re-open Meshes > Analyze > Evaluate & Repair mesh... and run a full analysis to confirm the mesh is completely closed and manifold.