How to Build a Wood Frame to Support a Heavy Mirror

Cut both ends of four 1/2-by-3-by-39-inch boards at a 45-degree angle, so that they slope toward each other making one side of the board 39 inches and the other side 33 inches. Cut each board by placing it in the miter box and lining up a 45-degree cut from the corner on one side to a point 3 inches from the end on the other side. Cut the wood using a saw with even back and forth motions.

Drill a hole into the center of each cut face of the four boards perpendicular to the 45-degree cutting angle and about ½-inch deep. Use a drill bit the same diameter as the pegs. Insert pegs in four of the holes and press the boards together making a 39-inch square frame. Make any adjustments with cutting necessary allowing the four boards to evenly press together. Remove the boards, apply wood glue to both sides of each peg and along the cut faces. Press the surfaces back together and let them dry for six hours.

Follow the same procedure and cut four 1/4-by-1 1/2-by-39-inch boards. Lay the boards over the frame and arrange them so that their outside edges are even with the original boards. Position a 1/4-by-36-by-36-inch mirror in the frame, so that the smaller boards snugly wrap around it. Adjust the smaller board arrangements slightly if necessary. Predrill four evenly spaced holes through the center of each small board and into the larger boards. Attach boards together using 1/2-inch wood screws.

Arrange four 1/2-by-3-by-36 inch boards around the frame without cutting them so that they form an evenly square frame with one end of each board butting up the side of another. Predrill four evenly spaced holes through the boards’ edges into the other two layers of boards. Do not accidentally hit the mirror with the drill bit. Attach the boards to the frame with 1-inch wood screws.