Set the miter saw to a left-hand, 45-degree angle. Place the molding upside down on the saw so the top touches the saw table and the bottom touches the saw fence. Cut the molding to size.
Set the miter saw to a right-hand, 45-degree angle. Place a scrap piece of crown molding upside down on the saw so the top touches the table and the bottom touches the fence. Cut the piece.
Set the miter saw to zero degrees. Place the piece of scrap face down on the saw. Cut the crown at the bottom point of the mitered edge.
Fit the cut V-shaped molding butt into the end of the crown molding.
Glue the molding butt into place. Do not nail the molding return, or you may crack it.