Plywood Miter Box

CUT inside and outside corners in a miter box made from 3/4-in. plywood. Clamp the piece of cornice into the miter box upside down and cut it with a 12-in. metal-cutting blade in a reciprocating saw. Be sure to position the cornice so that the pattern on it will correspond with the other side of the corner. For a clean cut, run the saw at full speed and ease the blade slowly through the cornice.

BEGIN inside corners with an uncut end of cornice. Then hold a cut piece against it to check the fit. Chances are you'll have to do a little trimming with aviation snips to get a tight fit.

FIT outside corners by tacking one cut side in place. Leave the nails sticking out so you can adjust the position of the cornice if need be. Then hold the other cut side in place to check the fit before nailing it. When the corner is done, smooth the sharp edges by filing them lightly with a fine “rattail” (round) file.