You can use the extend faces tool from the Geometry Edit toolset to create midsurface faces. The extend faces tool extends existing shell faces, so for midsurface modeling it must be used after you have created one or more shell faces. Use of the extend faces tool is discussed in detail in “Extend faces,” Section 69.7.8.
You can extend faces by selecting individual edges to extend the faces in one or more directions, or you can specify faces to extend the faces along all exterior edges. There are also several methods for determining the extension distance; the Up to reference representation option is intended specifically for midsurface modeling.
When you use the Specify edges of faces to extend option to extend faces along a set of edges, the extend faces operation may fail. If this occurs, try reducing the number of selected edges and then using a second operation to extend the faces along the remaining edges.
