Use the Surfaces: Extend
tool to create tangent or normal extension surfaces.
New surfaces are organized in the same component as the surface being extended.
From the Geometry ribbon, click the Surfaces > Extend tool.
Select edge(s).
Click an arrow to switch between creating a tangent or normal extension
surface.
If an edge has multiple adjacent surfaces, use Tab to
cycle between them.
Optional: Select one or both of the extend options in the microdialog.
Click to
maintain edge angles.
Click to
auto-trim intersecting surfaces.
Extend surfaces in the following ways:
Enter a length in the microdialog and press
Enter.
Drag the arrow in the modeling window.
Tip: Constrain line drag to one direction, then use snap points to extend
surfaces by distances relative to existing geometry, even if the reference points
are not on the same plane as the surface being extended.