From FreeCAD Documentation
Automatic testing and repairing
- Open FreeCAD and the sample FreeCAD file containing the mesh object
- Switch to mesh workbench
- Make sure that your mesh object is selected in the tree view
- Choose Meshes → Analyze → Evaluate & Repair mesh... from the top menu
- Make sure the pull down menu on the top right corner displays the name of your mesh object
- With the last point in the list reading "All above tests together" click on Analyze
- The texts beside the tick boxes will change to reflect results of the different tests
- If errors had been detected the corresponding check-boxes will be ticked and you will be able to select Repair
- Choose Close to close the menu