Set builders are the magicians in charge of conjuring the theater magic that transports an audience from an auditorium to the world of the play. One of the most basic tools of their craft is the flat, a standing frame of wood covered with muslin onto which any background can be painted or built. They also must make sure that the flats will not fall and can hold up to the abuse of stumbling actors or heavy set dressing pieces. The most common way of bracing a flat is to build two jacks and attach them to both sides of the back of the flat.
Cut three pieces of wood to create a jack to brace the set. Cut the first piece, which is called the stile, so that it is 2/3 the height of the flat. Cut the second piece, which is called the diagonal brace, so that it is about 5/8 of the height of the flat. Cut the third piece, which is called the rail, so that it is 1/4 the height of the flat. Use a miter saw to cut the ends of the diagonal brace to create a 45 degree angle.
Screw the bottom rail and the stile together to form a right angle with drywall screws. Hammer the bottom of the diagonal brace into the end of the bottom rail using scaffolding nails. Lean the brace onto the stile and hammer the top of it onto the stile. Allow the top corner to overlap slightly if it will be bracing a stand-alone flat that is not flush with another flat.
Stand the flat up against the stile of the jack with the bottom rail on the stage. Screw the stile onto one side of the flat in at least three places along the height of the stile.
Repeat steps 1 to 3 to create a second brace for the other side of the flat.
Secure the flat and the jacks to the floor if the set piece will be stationary throughout the production and there is a floor built onto the stage. Do not screw the flat to the actual stage floor. Secure the flat to any mobile piece set on casters that will be moved during the show. Hinge the jack to the floor with an L bracket.
Depending on the height of your flat, you may want to have a cross-hatch piece on the center of your jack for additional stability.
Drape a sandbag over the bottom rail for additional stability.
Use personal protective devices such as eye goggles when using power tools.