Cornice moulding creates a decorative transition between the wall and the ceiling. Wood cornice moulding can be made from dimensional lumber and routed on a router table. There are many cornice moulding router bits on the market to suite any room's design aesthetic, from simple to ornate. The mitred edges that allow the moulding to sit at an angle between the wall and the ceiling also can be cut on a router table, using a moulding edge cutter. With a little work, you can make a completely custom moulding treatment for your room.
Calculate the dimensions of the room to determine the number of boards you will need. Plan to make extra moulding in case you make a mistake or need a replacement piece later on.
Set up the router table with the cornice moulding bit. Adjust the depth of the bit so it will rout the complete profile of the bit onto the 3-inch-wide side of the boards. Adjust the router table's fence so that it will rout the complete profile into the 3-inch-wide side of the boards. The distance from the fence to the bearing on the bit should equal the 1-inch thickness of the board.
Turn on the router. Run the boards through the router with one 3-by-96-inch side flat against the fence and one 1-by-96-inch side flat against the router table. This will rout the decorative profile onto the 3-by-96-inch side of the board. Turn off the router.
Remove the cornice moulding bit. Insert the moulding angle bit. Adjust the height so it will cut off an angle on the edge of the 1-inch thickness of the boards. Position the board so the router will cut the angle on the back side of the decorative cornice moulding profile. Adjust the fence so the 3-inch-wide side can be run flat against the surface of the router table. The bearing on the bit should ride on the 1-inch-thick side.
Run the boards through the router table with the decorative cornice moulding profile facing up. Rout each 1-inch side of the boards so there is an angle on both edges of the 3-inch-wide side that is opposite the side with the moulding profile.
Sand the cornice moulding boards, using a progression of medium and fine-grit sandpaper until the moulding is smooth.
Apply a finish to the moulding before you install it.
Wear eye protection when working with wood.