How to Mirror a Feature Across a Plane in FreeCAD

Mirroring a solid feature across a plane in FreeCAD allows you to duplicate symmetrical elements efficiently without redesigning them from scratch. This article provides a direct, step-by-step guide to using the Part Design Workbench to select a feature, apply the Mirrored transformation tool, and define the correct mirror plane to ensure a clean, parametric result.

Step 1: Switch to the Part Design Workbench

  1. Ensure your model is active within the Part Design Workbench.
  2. Confirm that the feature you want to mirror (such as a Pad, Pocket, or Hole) belongs to an active Body.

Step 2: Select the Feature

  1. In the Model tree view on the left, click on the specific feature you wish to duplicate.
  2. Alternatively, you can select the feature directly in the 3D viewport.

Step 3: Apply the Mirrored Tool

  1. In the top toolbar, click on the Mirrored icon (a shape reflected across a dashed line).
  2. Alternatively, go to the top menu and select Part Design > Apply a pattern > Mirrored.
  3. The Tasks panel will appear on the left, displaying the mirror parameters.

Step 4: Choose the Mirror Plane

In the Tasks panel under Plane, define the reference plane to mirror across:

  • Standard Planes: Select Vertical sketch axis, Horizontal sketch axis, Base XY plane, Base XZ plane, or Base YZ plane from the dropdown menu.
  • Custom Face: Choose Select reference..., then click any flat face on your solid model in the 3D view to use it as the reflection boundary.
  • Datum Plane: If you have created a custom Datum Plane, you can select it from the tree or viewport.

Step 5: Finalize and Confirm

  1. Review the preview in the 3D viewport.
  2. Click OK in the Tasks panel to apply the transformation.

Troubleshooting Common Issues

  • Resulting shape does not intersect the Body: In the Part Design Workbench, features must typically touch or fuse with the existing solid body. If the mirrored feature floats in empty space, the operation will fail. If you need separated solids, consider using a separate Body or the Mirror tool located in the Part Workbench instead.
  • Multiple Features: To mirror more than one feature at a time, use the MultiTransform tool found in the same Part Design pattern menu.