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How To Cut And Install Crown Molding And Trim

Construction How-To, Finish Carpentry, Molding, Trim Carpentry April 18, 2006 Sonia


 To cut your crown molding to fit the corner, you must know the angle formed by the two walls. The easiest way to do this is by using a 360-degree adjustable protractor such as the Original True Angle tool manufactured by Quint Measuring Systems, Inc. (Fig 3 & 4). The True Angle tools have the angle dial printed on the tools for direct reading and are available for purchase at www.compoundmiter.com .

 

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Once you have the angle of the corner, you are ready to place your crown on your saw and cut the crown for the type of corner you need; outside corner, LH (left-hand) or RH (right-hand) or an inside corner, LH or RH (Fig 5 & 6).

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The ends of your crown should look typically like these photos and, if cut using the miter setting from Table 1, will fit your corner perfectly.

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Crown Molding on Cathedral/Sloped Ceilings using a Miter Saw

When installing crown on a cathedral/sloped ceiling, you must know the slope of the ceiling. To obtain the ceiling slope, measure the angle between the wall and ceiling at a location where the top of the wall is horizontal. Place your angle measuring tool perpendicular to the wall (Fig. 9).

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In this example, the ceiling slopes 20 degrees (110-90 = 20). You will now use the ceiling slope to determine the corner angles for turns of the crown molding made in a vertical plane (i.e. upward/downward turns) when installing crown molding on a sloped ceiling.

Figure 10 is a typical installation of crown molding on a cathedral ceiling. The crown is installed with a combination of horizontal and vertical turns. Joints A & E are turns made in a horizontal plane (just like the turns made while installing crown on a horizontal ceiling). Joints B, C & D are turns made in a vertical plane (the wall). Joints B & C are outside corner turns in the vertical plane (upward turn), and joint C is an inside corner turn in the vertical plane (downward turn).

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The combination turns (horizontal and vertical) will look like Fig. 11 before they are installed. Notice that crown molding piece No. 2 is cut so that the top of the crown has no length and it forms a point. This is how you will always cut this transition piece when making a horizontal to vertical turn.

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When cutting vertical plane turns with a miter saw, you will position the bottom of the crown molding held firmly on the saw table (Fig. 12). The angle of the crown bottom of your crown determines the crown spring angle. That is why it is so important to hold the bottom firmly against the fence for horizontal turns or firmly against the saw table for vertical turns.

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There are four cuts that you can make in the vertical plane just like there are four cuts that you can make in a horizontal plane (i.e., inside and outside corners with each having a LH and RH cut, see Fig. 13 & 14).

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To obtain the corner angle for joints B and D (Fig. 10), you will use your ceiling slope (in this example, the ceiling slope = 20 degrees). Joints B and D have a corner angle of 200 degrees (180 + ceiling slope = 200). Joint C has a corner angle of 140 degrees (180 – twice the ceiling slope = 180 – 40 = 140). You can also measure thecorner angle for joint C directly with your 360-degree protractor (Fig. 15).

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When you have a sloped ceiling where crown piece No. 3 runs into a vertical wall (Fig. 16), joint C would then be an inside corner (160 degrees) turn in the vertical plane and joint D would be and inside corner (90 degrees) turn in the horizontal plane. You would get your miter saw setting from Table 1.

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The crown molding cuts for vertical turns (plane of the wall) will look like these templates (Fig. 17 & 18). I highly recommend that you make yourself a full set of eight crown molding templates, label them and use them as a guide to prevent cutting your crown molding backwards. Make the longest edge about 3 inches long. Drill a 3/8-inch hole in each and place them on a string and keep with your saw for quick reference (Fig. 19).

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Crown Molding on Horizontal Ceilings using a Compound Miter Saw

The difference between using a compound miter saw (has blade tilt adjustment) versus a miter saw is that you can lay your crown molding flat on its back, face up and set a miter and blade tilt angle. Table 1, of course, will not work because there is no blade tilt angle in Table 1 and the crown molding is not propped up.

When cutting your crown molding laying flat, you will need to know the crown spring angle. The crown spring angle is the angle between the back of the crown and the wall when the bottom of your crown molding is held firmly on the wall.

To obtain your crown spring angle, measure the bottom of your crown as shown in Fig. 20. This crown molding has a spring angle of 38 degrees (52/38 crown). The other most common crown molding is 45/45 degrees. However, there are many others. Also, quite often the crown molding will be undercut at the mill as much as 2 to 3 degrees. You should measure your crown spring angle accurately to avoid any gaps in your joints. It is much easier to hold your crown molding flat while making your cut, especially for the small pieces of crown molding that are frequently needed.

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To determine how to position your crown molding flat (face up) on your compound miter saw and which direction to adjust your miter and blade tilt for the cut you want to make, use your crown molding templates that you made in the previous section. You should have eight templates in all (four for horizontal turns and four for vertical turns). Let’s cut a horizontal turn, inside corner, left-hand (LH) piece to show you how to use your crown molding templates. Find the template for the cut you want and place it flat, face up, with either the top or the bottom of the crown molding template next to the fence. (You should label all eight of your templates for the corner each represents as shown in Fig. 21.)

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Now move your miter and blade tilt so that your saw blade will match the bevel cut on the crown molding template. If necessary, you may need to switch your template to the other side of the blade and/or place the opposite edge of the template next to the fence.

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