How to Crown Mold Around a Rounded Corner

Hold two 24-inch pieces of scrap boards against the corner, one on either side. Overlap one of the boards over the top of the second board. Trace a line along the bottom board, following the top board's side edge.

Set the bottom board on a flat surface. Hold a protractor against the board's bottom edge. Use the line you traced on the board to determine the rounded corner's angle. Divide the angle by four to determine the miter angle at which you need to cut each piece of crown molding.

Set a miter saw to the angle you determined in Step 2. Measure the distance to the rounded corner and mark it onto a piece of crown molding. Place the crown molding on the miter saw, positioning it against the fence the same way it will be positioned on the wall. Line up the mark with the saw blade and make the cut.

Set a second piece of crown molding on the miter saw, positioned against the fence. Cut approximately 1 inch off the end. Measure down approximately 3/4 inches from the cut end's bottom edge and make a mark.

Flip the crown molding upside down. Place it against the miter saw's fence and line up the mark you made in Step 4 with the saw blade. Cut through the crown molding to create a small triangle.

Lift the first piece of crown molding up to the corner of the wall and ceiling. Secure the crown molding to the wall's top plate with finishing nails from a pneumatic nail gun.

Spread wood glue along one edge of the triangle piece. Set the triangle piece over the rounded corner with the glued end pressed against the first piece of crown molding. If the rounded corner is an outside corner, turn the triangle so the thin end points down. If the rounded corner is an inside corner, turn the triangle so the thin end points up. Angle a finishing nail through the triangle piece and into the first piece of crown molding.

Measure the length you need for the next piece of crown molding, which will be installed against the triangle piece's other end. Transfer this measurement to a new piece of crown molding.

Position this piece upside down on the miter saw's table, against the fence. Cut through the molding along the mark you made in Step 8. Apply wood glue to the cut end.

Lift the piece of crown molding up to the corner where the wall meets the ceiling. Butt up the mitered end against the triangle piece. Drive finishing nails through the crown molding and into the top plate. Angle a finishing nail through the triangle piece and into the crown molding.