Cadalyst columnist Bill Fane shares a few tips on extruding faces of 3D objects.
"Instant 3D! Contrary to popular opinion, it is not necessary to create a single, contiguous object such as a pline or spline to serve as the boundary for an extrusion. The PressPull command simply asks you to pick a point within the area to be extruded. The area can be defined by overlapping line segments, arcs, circles, or whatever. It then searches outward from that point and defines its own boundary, just like the Hatch or Boundary commands. Now you can drag the profile to the desired height, or you can input a specific value.
"But wait — there's more! You don't even need to start the PressPull command. At the Command prompt in AutoCAD 2009 and later, simply click inside the desired area as you press and hold the Ctrl+Shift+E key combination to start PressPull. In AutoCAD 2008 and earlier, the key combination is Ctrl+Alt. This works with new profiles or with existing faces on an existing solid."
Notes from Cadalyst Tip Patrol: The Extrude and PressPull commands are similar, but not identical. The Extrude command can create a surface from an unclosed object; PressPull can't. Extrude requires you to select an object; PressPull needs a point inside an object. If an object is irregular, one command could work when the other might not. When using the Extrude command on a 3D object's face, you may need to press the Ctrl key to select the face. In AutoCAD 2010, when working with mesh objects, you can stretch a face by pressing the Ctrl key and selecting a face. It won't extrude the face, but it will move it away from your object, stretching the faces adjacent to it. This only works on mesh objects, not regular 3D objects.