A plate or disc cam is a 2D cam that is one of the simplest cams to design.  The cam can push the follower, pull the follower, or both.  To push the follower the surface will be an inside surface; that is, a surface that is closest to the axis of rotation.  One that pulls the follower will have what is called an outside face.  If the cam pulls and pushes the follower it will have either a groove, sometimes called a box, with both inside and outside faces.  A pull push cam can also have a rib where a two followers are riding on either side of the rib.  Examples of a translating follower shows the types cams possible. 



                              Plate Inside Face                                                                  Plate Outside Face



                              Groove (Box)                                                                                       Rib