From FreeCAD Documentation
- Press the
Extend edge button.
- Select a line or an arc.
- In the 3D view, move the mouse pointer toward the direction to extend.
- Click on an arbitrary location in space, or
- To extend to another edge, place the mouse pointer over the target edge; when it is highlighted and the
Point on object constraint icon appears besides the mouse pointer, click to confirm. A point on object constraint will be added.
- To extend to a point in the sketch, place the mouse pointer over the target point; when it is highlighted and the
Coincident constraint icon appears besides the mouse pointer, click to confirm. A coincident constraint will be added.