From FreeCAD Documentation
- Select the body of the movable half.
- Use the Create a clone command.
- In the new body select the Clone object in the Tree view.
- Use the Part Attachment tool to add attachment properties to the Clone object.
- The Attachment dialog opens.
- Select a vertex for the origin.
- Select an edge for the first direction.
- Select an edge for the second direction.
- Probe the attachment modes to find the best fitting one.
- Tweak rotation and coordinate values until until the geometry is in modelling position again.
- Press OK to close the dialog.
- With the hinge body still active select the PartDesign Boolean tool.
- In the dialog press the Add body button.
- select the body of the movable half .
- Press OK to finish and close the dialog.