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How To Build A Crown Moulding Miter Box

Installing crown moulding, like playing the piano,
takes practice. Unlike playing the piano, however, most people can get the hang of it with only a little practice. Before you take the time to become a master, however, you may want more information on preassembled corner pieces that simplify the project tremendously.

Many large molding profiles cannot be mitered using a power miter saw or radial arm saw. For some profiles it may be necessary to cut miters using a miter box and a hand saw.

How to build a miter box?

1. Measure the height and projection of your molding. If you are using several large pieces of moldings, build the miter box to accommodate the largest profile.

2. Using 3/4″ plywood approximately 6 feet long, cut the width of the bottom piece exactly to the projection of the molding you are using.

3. Cut the sides of the miter box a minimum of 1 3/4″ wider than the height of the largest profile.

4. Screw the side pieces to the side of your bottom piece.

5. Cut four 2″ strips of plywood and cut them to a length that is the same width as the bottom of the miter box. Secure them to the top of the miter box making sure the sides are square to the bottom.

Note: Keep a 2 1/2 foot opening at the center of the miter box to allow the angles to be cut in.

6. Using a framing square, mark out the 45 degree angles. Square the marks down the side walls. With a handsaw, cut your angles, making sure to follow your lines down the side wall.

7. For the smaller molding profiles, measure the projection and mark that distance from one wall of the miter box. Cut a piece of blocking to fill the space left over. This will act as a wall to rest against the edge of your molding.

Blocking is an important part of a good installation.

Proper blocking should be installed to secure moldings in place. This is especially important with larger molding profiles to limit expansion and contraction.


We recommend using a quality urethane adhesive as part of the installation process when installing moldings. We have found that urethane adhesive is superior to other adhesives that we have tried. We recommend its use with all of our products. Ask one of our representatives if you need to order a quantity of our urethane adhesive. See the installation instructions for further information.

Worthington molding installation instructions are included with every molding order. Look for the box with the red stamp. If for some reason the instructions did not come with your order, please call us and we will fax or e-mail them to you.


Moldings should not be installed until the Installation Instructions have been read.

1. Install moldings on a solid backing with studs or joists 16 on center or less. Note: Large profiles require additional blocking.

2. Mark the distance on the wall to be covered by the first piece of molding. Oversize and cut the molding, adding 1/8 for every 5 feet of molding required. Example: If the distance to be covered is 15 cut your molding at 15 3/8.

3. Run a bead of urethane adhesive along the top and bottom edge of the molding where it will meet the backing.

4. Using galvanized screws, fasten one end of the molding at your starting point. Pull the center of the molding away from the wall, which will draw the free end of the molding back to the 15 mark. Secure the free end of the molding the mark.

5. Push the center of the molding flat into the surface. The molding should snap into place. Secure with galvanized screws, 16 on center or less. If the molding does not push flat, you need to unfasten one end and resecure the molding approximately 1/8 past your 15 mark.

6. For continuous long runs for molding.

A. Install the first piece using the procedure above.
B. For the second piece, follow steps 1 through 3.
C. Step 4 (above) anchors the end of the molding on your mark. Then apply urethane  adhesive to the end of the first piece, this will adjoin the nest piece of molding
D. Butt the free end of the molding to your first piece and follow step 5 to secure in place.