Using a Compound Miter Saw

Intro

In recent years, two woodworking trends have helped fuel each other -- the popularity of crown molding installations and the proliferation of compound miter saws.

One of the major challenges in using a compound miter saw is visualizing how to position the crown molding on the saw before you make the cut. To overcome this, you'll make four templates -- one for each of the basic saw positions used for running crown around a flat ceiling.

You'll need an accurate protractor -- preferably with legs at least 18 inches long -- for each outside corner in the room and for inside corners that are not exactly 90 degrees. Because you'll cope an inside corner against a square-cut piece that butts into a corner, you don't have to be so finicky about the inside angles. Back-cut the cope and you'll easily fit corners.

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Step 1

Cut two lengths of crown molding about 24 inches long. Lay them on your workbench so their bottom edges are near each other, then duplicate the writing shown in the photo.

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Step 2

If you have 52/38 crown molding (see Understanding the Spring Angle), set the miter at 31.6 degrees left and bevel the blade 33.9 degrees left. Some compound miter saws have a miter stop at this setting. If you're working with 45/45 molding, the miter angle is 35.3 and the bevel is 30 degrees. Slice apart the LH cope/RH miter templates.

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Understanding the Spring Angle

The spring angle of crown molding refers to the angles that the flat back of the molding makes with the ceiling and the wall. There are two common types: 52/38 and 45/45. As you'll notice in the drawings, the first angle also describes a complementary angle, the slope of the installed molding relative to the floor. When buying molding, make sure all the pieces have identical spring angles.

Step 3

Without changing the bevel setting, swing the miter angle to the right side of the zero mark and all the way to the opposite setting you made in the first cut. In this case, that is 31.6 degrees right. Cut apart the LH cope/RH miter templates.

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Step 4

Because the completed templates will last a long time, paint part of the wood a bright color to make them easy to find -- even if one gets accidentally mixed in with some molding scraps.

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Choosing the Correct Template

The left- and right-hands you marked on the template do not refer to directions on the stick of molding. Instead, they refer to the corner of the wall where the molding is installed. The drawings identify right and left as judged when you're facing the corner -- whether it's an inside or outside corner. After you make the templates, hold them up to walls to understand how the directions relate to each other.

Step 5

Measure an outside corner with your protractor, holding it where the bottom of the molding will hit the wall. A protractor with long legs will give you a more accurate reading because it will measure well beyond the corner. Because that area was formed by the drywall finisher who applied the compound at the corner, its surface may not truly represent the angle between the walls.

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Step 6

Lock the protractor's angle (in this case, by turning a small brass knob). Check that the setting didn't change when you turned the knob, then read the angle on the protractor. Refer to the Crown Molding Cutting Angles chart for the spring angle of the molding you have -- either 52/38 or 45/45. Set your bevel setting to the angle listed in this chart or the chart that came with your compound miter saw.

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Step 7

Place the appropriate template sample for the right- or left-hand miter onto your saw table, then set the miter to match the direction of the cut on the template. The exact miter angle you set will be the one you found on the chart in the last step. Observing how the molding is oriented on the table (bottom or top toward the fence), slide the template away from the fence and place your molding in the same relative position. Move the template out of the cutting path, then make the cut.

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Step 8

Swing the miter setting to the same number but on the other side of zero to make the matching miter cut. You can now install the two pieces of crown molding with a crisp outside miter.

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