Molding adds visual interest to a ceiling, such as around this skylight.
A development in architecture is to create cathedral or angled ceilings. These are not flat but rather follow the slope of the roof. Traditionally, crown molding is placed on the point of intersection where the wall meets the ceiling. With a cathedral ceiling, lining up the corner angles "just right" is difficult since compound angles will have to be cut. With a special saw, called a compound miter saw, these angles can be obtained. The trick, however, is to understand the process involved with cutting .
Compound Angles Defined
A compound angle cut is difficult to visualize. Think of a picture frame. Each corner has an angle cut of 45 degrees, so the two pieces of molding line up at 90 degrees. This is a flat horizontal plane cut. Suppose the frame has to be lifted off the wall at an angle; you have to cut two angles. Cut the 45-degree angle to make the frame with 90-degree corners. Tilt the blade of the compound miter saw to cut the angle on the vertical plane, and you'll end up with two angles: one on the horizontal plane and one on the vertical plane. This is a compound angle and difficult to cut correctly.
Carpenter's Protractor Needed
A carpenter's protractor is a necessity to cut and fit compound angles. Find out the angle of the cathedral ceiling to the wall, and divide by two, which will give you the angle of the first cut. Tilt the blade of the miter saw to this angle. For the second cut, the angle is 45 degrees if the walls are perfectly square. In a home, this is never the case. Use your carpenter's protractor to find out the exact angle of one wall to the adjacent wall, and divide by two. Swing the blade of your saw over to this angle.
Altenative Method
If you do not have a carpenter's protractor or a miter saw, use an alternative method. You can always remove wood, but you can't put it back. Cut one molding flush with the walls with a small hand saw, as if you were fitting it to a flat ceiling. Using a rasp, hand fit the two moldings little by little so the angles mate up perfectly with no gaps. Use a pencil to draw lines where wood has to be removed. You will need a helper to hold up the molding pieces until the right fit is obtained, which is a slow and painstaking process since you will have to remove a little wood, refit and repeat the process until an ideal miter joint is obtained.
Practice on Scrap
Obtain some scrap molding or lumber the same dimension as the finish molding. Practice cutting the compound angles on scrap first. Chances are good you'll make mistakes on the first few attempts. The whole idea, though, is to make mistakes on cheap lumber instead of very expensive crown molding. Once you determine the right angles to cut and become proficient at it, graduate to cutting the final molding.
Tags: carpenter protractor, compound angles, , angle difficult, cathedral ceiling