From FreeCAD Documentation
- Press the Additive pipe button.
- In the Select feature dialog, select a sketch to be used as first cross-section and click OK.
- Alternatively, a single sketch can be selected prior to pressing the Additive pipe button.
- In the Pipe parameters under Profile, press the Object button.
- Select the sketch to be used as path in the 3D view:
- Alternatively, edges of the body can be selected by pressing Add Edge and selecting edges in the 3D view.
- To use more than one cross-section, under Section transformation set the Transform mode to Multisection; press Add Section then select a sketch in the 3D view. Repeat for each additional cross-section.
- Set options if needed and click OK.