Coping moldings for corners is the process of cutting the end of a molding to mimic the profile milled into its face. Coped corners are used where one piece of crown molding meets another at an inside corner.

Cut crown molding at a 45-degree angle to prepare for coping moldings for corners. Outside corners are mitered, but inside corners should be coped. A coped joint is one in which one molding is cut to nest against the profile of another. This helps to disguise out-of-square corners, wall irregularities and problems caused by materials expansion.

Here you’re probably wondering why you should go through the slow, fussy process of coping when you could just miter trim at inside corners. Is it necessary? The answer is that wall corners are never quite square, and coped joints fit tight even when corners are badly out of square. Whether you’re installing crown molding, chair rails or baseboard, coping is faster than finding the right miter angle through trial and error. If you really want to avoid coping, use corner blocks (available at most home centers and lumberyards). With these decorative blocks placed at inside and outside corners, you only need to make square cuts.
With the molding in the proper position, use a 10-inch saw blade to cut a perfect 45-degree angle. It is also important here to make sure you cut the molding angle in the right direction, we have mentioned in measuring step that for an inside corner, the bottom of the molding should be longer than the top part of the molding; for an outside corner, the top of the molding will be longer than the a length of crown upside down on the miter saw so that the molding’s bottom edge—the edge that will sit on the wall—rests against the fence, and the top edge—the one that goes on the ceiling—rests against the table.
Set the saw to 45 degrees; sawing the saw left for a left-side coped corner, and vice versa for a right corner. When you make the cut, the long point of the miter should be on the back of the molding, not on the face.

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