This guide uses 45º as a default angle; although this angle is always the proper choice for scarfing, it may need to be adjusted slightly for other cuts. Since crown molding is generally made of wood, it is prudent to let it sit in the home environment for a few days before installing it. The wood will expand or contract based on the temperature and humidity in the house; it is better to let it adjust before nailing it in so that it will not crack and warp after the fact.
Place a piece of molding upside-down on the miter saw table. The side of the molding that will contact the ceiling should be against the saw table, and the side that will contact the wall should be against the saw’s vertical fence. Make sure that the decorative side is facing you, and hold the molding at the same angle at which you will install it. Secure the molding with clamps to the vertical fence. Get a piece of plywood or dimension lumber that is just as long as your saw table. Apply hot glue to the saw table on both sides, and place the plywood against the glue, pressing it snugly against the molding. When the glue is set, remove the crown molding and use the miter saw to cut away the center portion of the plywood fence at 45º angles.
Cut the first piece of crown molding square. Place it in the miter saw and cut with the blade set to 0 degrees. Cut the second piece at a 45º angle, cutting just as you would for an outside corner. Use a dark pencil to trace along the edge of the cut (of the second piece) along the molded front of the piece. Use a coping saw to cut away the bevel of the cut edge. Follow the outline that you drew closely, removing as much of the wood behind the leading edge as you want. Only the front of the molding will be seen when installed, so the cut can be made roughly as long as you follow the outline.
If a corner joint doesn’t quite fit, use a rasp to quickly and evenly grind down extra wood, testing regularly against the joint until you find a perfect fit. Boring small holes into the points of each outside corner joint allows you to secure the corners to the wall firmly with an extra finish nail in each hole.
The standard color for crown molding is white, but other colors may be appropriate depending on the effect you desire for the room you are working on. You can also paint the molding before you install it, but be aware that you’ll have to repaint anywhere that gets scuffed during installation.
