From FreeCAD Documentation
- Switch to the Curves workbench (install from Addon Manager is necessary, if not previously installed)
- There are 2 methods to use the SketchOnSurface tool:
- You already have a sketch that you want to map on a face
- Attach the sketch to the target face:
- In the attachment dialog selet the face
- Set the mode to Deactivated while leaving the face as the first reference
- Close the Attachment dialog
- Set Placement.z=0
- Edit the sketch and add a Construction (blue) rectangle around the geometries. This rectangle will be the parametric bounds of the face.
- Exit edit mode.
- Select the sketch.
- Activate SketchOnSurface by either:
- Pressing on the button
- Using the Surfaces → Sketch on Surface entry in the Curves menu
- You have no sketch to map yet
- Select the target face in the 3D view
- Activate SketchOnSurface by either:
- Pressing on the button
- Using the Surfaces → Sketch on Surface entry in the Curves menu
- A Sketch_On_Surface object appears in the Tree view.
- Expand this object to make the Mapped_Sketch appear below.
- Edit the sketch and add geometries inside the blue construction bounds.
- A SketchOnSurface object will be created on the surface of your object based on this sketch.