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Crown molding is generally nailed to the wall at the studs, along the bottom edge and into the ceiling joists along the top edge. This method creates a lot of extra work with a stud finder. One way to avoid this step is to install a wood backer board to the top plate (the horizontal framing member above the wall studs). This method (see photos page for picture) allows you to nail the crown to any point along every wall. First you will need to determine the width of the backer board by holding a piece of crown molding against the inside corner of a framing square and drew a line along the crown's back. The diagonal line, minus 1/8-inch for clearance, is the width of the backer board. I used a table saw with the blade set to 45 degrees to rip the backer boards from 3/4-inch plywood, then I fastened each board to the top plate with 3-inch drywall screws spaced 16 to 24 inches apart. After doing backer board you can nail your crown at any point along a wall. This method also works well when installing crown molding in an apartment or condominium with concrete ceilings. In that case you may need to tapcon and/or use a "Ramset" type fastener to fasten backer to wall and ceiling.
Finding Crown Spring Angle:
Many people do not know that crown molding comes in three different spring angles. The spring angle is the “tilt” in which the crown molding sits against the wall. Crown molding is manufactured this way in order show off it's detail better at different wall heights. For an example... on lower ceilings you would want the crown molding to tilt up towards your eye for better viewing. In the same way, crown molding set into a high ceiling looks best when it’s tilted down. Why is finding the Crown Spring Angle Important before installation? Spring angle and the corner angle is all you need to know in order to make the perfect cut each and every time. And each piece of molding must have the exact same crown spring angle in order to work correctly. Crown molding is usually made with one of three different spring angles: 38°, 45°, or 52°. Finding your crown's spring angle is simple: start by cutting a small section of molding and hold it up the way it is to be mounted on the wall and ceiling. Next measure from the ceiling down the wall to the point where your molding touches the wall. Take this measurement and compare it with the measurement from the wall across the ceiling to the point where the molding touches the ceiling. If the wall measurement is longer, you have a spring angle of 38°. If the ceiling measurement is longer, your spring angle is 52°. If both of these measurements are the same, your spring angle is 45°. Take a look at the picture to see a visual example:
Using a Jig...
One way to make a "combination miter" is to cut the crown while it's held on an angle. When you use this technique, make sure the back surfaces of the molding are fully in contact with the fence and saw bed as it would be on the wall. Some saws have an adjustable crown molding stop accessory otherwise a jig can be made by attaching together two pieces of plywood together and making certain that they form an accurate right angle. The jig is set in place on the miter saw bed and attached with screws inserted through pre-drilled holes in the metal fence. Then place a scrap piece of crown molding onto the jig and place a wooden stop next to the edge and staple it in place.
Saw Set up:
Using a degree finder measure the degree of your wall corner, now divide that degree in half, and that’s the degree at which to set your saw. For example, say you have an inside corner you measure at 92°. Set your saw to half your corner degree, which would be 46° Remember each crown molding corner requires two angles the miter angle which is cut across the face of the molding and a bevel angle that is formed across the end or edge. When working with crown molding, both of these angles have to be cut at the same time and that's why they are called "compound angles". Accuracy is absolutely critical when making these cuts so, the proper tool to cut crown is an electric miter saw.
Upside down and Backwards (Vertically Nested): To cut crown molding using this method, position the crown upside down on your miter saw. This way, when cutting angles, you have one of the crown mold's surfaces on the saw's table, and the other up against the saw's fence. Then just make your cuts, 45° (or what ever the inside or outside corner calls for). This method often is the better way to get a accurate cut, this is because you are holding the molding firmly in place while the cut is being made. Another benefit of cutting crown molding upside-down, that you can see the mark made on the bottom side of the crown when you measure it for length. See picture below for cut examples.
Compound Method (Flat) Note: Your crown molding always lays flat on the saw using this method. Set your miter saw to bevel left at 33.9°. (some saws might say 33.8° but the .1 °is not enough to matter.) The miter will change between right and left (but at the same setting of 31.6°). Some cuts the bottom of the molding will rest against the fence. Others it will be on the top, depending again on right or left hand cuts. (Note: The bottom of the crown molding has the decorative profile.)
Installing Crown Molding Around A Bull Nose Corner:
It looks a lot more professional to cut crown molding to go around a bull nose corners opposed to strait 90° cuts. On 90° corners the miter angle is set to 22.5° for all the corners. And the transition piece should be pie shaped with the length of the base of the piece equal to 83 percent of the size of the radius of the bull nose. For a standard 3/4” bullnose the bottom of the molding should be 5/8”.
Coping Inside Corners:
The best way (and in my opinion, the only way) to cut inside corners in crown molding is to cope them with a coping saw. Mitering inside joints perfectly can be difficult and usually results in unwanted gaps between the two pieces of molding. To cope the corner joints a miter cut will expose the profile of the crown molding. Cut along the crown's profile with a coping saw. Tilting the handle of the saw higher than the other end so the cut removes the back of the molding and not the front. Next it's a good idea to test-fit the joint against a piece of scrap.
Installing On A Bull Nose Corner
Crown Molding looks more professional when you create a transition piece for going around a bull nose corner. On 90 degree corners the miter angle is set to 22.5 degrees for all the corners. The transition piece should be pie shaped with the length of the base of the piece equal to 83% of the size of the radius of the bullnose. For a standard 3/4” bullnose the bottom of the molding should be 5/8”.
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"Helpful" Crown Molding Pictures
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