How to Decimate a Mesh in FreeCAD

This guide explains how to reduce the polygon count of a 3D model in FreeCAD using the built-in Mesh Design workbench. Whether you are preparing a heavy STL file for 3D printing, improving viewport performance, or optimizing assets for rendering, decimating a mesh simplifies its geometry while preserving its overall shape. The following steps outline the exact process for importing, reducing, and exporting your optimized mesh.

Step 1: Switch to the Mesh Design Workbench

  1. Launch FreeCAD and open your project, or import your mesh file (File > Import) such as an STL, OBJ, or PLY format.
  2. In the workbench dropdown menu located in the top toolbar, select Mesh Design.

Step 2: Select the Mesh Object

  1. Look at the Tree view panel on the left side of the screen.
  2. Click on the mesh object you wish to simplify to highlight it.

Step 3: Open the Decimation Tool

  1. With the mesh selected, navigate to the top menu bar.
  2. Click on Meshes and select Decimation... from the dropdown list.

Step 4: Adjust the Decimation Settings

A dialog box will appear with parameters to control how aggressively FreeCAD simplifies the mesh geometry:

  • Tolerance (Maximum Deviation): This value defines the maximum allowed geometric error (distance) between the original surface and the simplified surface. A higher value reduces more polygons but softens sharp edges and fine details. A lower value preserves original geometry at the cost of keeping more triangles.
  • Target Polygon Count / Reduction Percentage: Depending on your FreeCAD version, you may specify a target percentage of reduction or an absolute maximum number of faces.

Set the tolerance value according to your needs. For standard 3D printing applications, a tolerance between 0.05 mm and 0.2 mm typically yields significant polygon reduction without noticeable loss of detail.

Step 5: Apply and Verify the Result

  1. Click OK to execute the decimation process. FreeCAD will recalculate the surface geometry.
  2. Inspect the resulting mesh in the 3D view.
  3. You can toggle the display mode by pressing V then F (or setting the display to Wireframe) to inspect the new triangle density.
  4. If the result is too coarse or still too dense, press Ctrl + Z to undo the operation and repeat the process with an adjusted tolerance value.

Step 6: Export the Simplified Mesh

  1. Highlight the simplified mesh in the Tree view.
  2. Go to File > Export.
  3. Choose your preferred file format (such as **STL Mesh (*.stl)**) and save your optimized model.