To use a piano hinge, you don't need to own a piano. This type of hinge may have been invented for, and appears most frequently as, the hardware attaching the piano's lid to its body. But, the long solid brackets, close-spaced fasteners and sturdy construction make it ideal as a secure hinge for all kinds of projects where the weight of wood or reliable repeated use are considerations. Piano hinges work well for bifold doors and hinged tables or counters. Follow the steps below to install a piano hinge, whether as part of restoring a piano or building another project.
Measure piano lid for hinge. Open hinge and lay it flat on cabinet edge, with rounded hinge section just over the edge. Mark screw holes with pencil. Double-check alignment by closing hinge and placing lid on top--rounded hinge should show evenly between cabinet and lid (like a sandwich).
Lay lid flat (inner side up) and place hinge on lid. Mark holes to be drilled with pencil. Drill holes and attach hinge with screws to lid. Make screws fast but save final turn until you have attached the lid to the cabinet.
Drill holes in cabinet edge. Summon your other set(s) of hands--this is not a one-person job. You have very little tolerance for unexpected movement at this point because your screw-holes are drilled into narrow pieces of wood. Have helper(s) hold lid/hinge assembly still while you insert screws. Insert first screws at each end of hinge, then work toward the middle.
Check lid/cabinet alignment, then do final tightening on all screws. You're done!
Lay door panels flat. Remember any outside/inside issues you may have when laying out panels. For example, your door is blue on the side facing the living room and white on the side facing the den. When you open the door from the living room, you want it to fold inward into the bedroom. You will therefore be attaching the hinge with screws to the white side of the door. The blue sides will fold in toward each other and the door itself will fold in toward the bedroom.
Line up panels, leaving just enough room between them to insert the rounded part of the hinge. Mark holes on both panels, drill and attach screws. Your door is now ready to be mounted with conventional door hinges.
Use the piano-lid method for mounting a folding shelf, desk or counter (that is, attach the hinge strip to the item first, then to the wall--round up your second set of hands, if needed, to hold things still while you attach). Remember, when installing your hinge, which way you want your shelf to fold--it's easy to get mixed up. In general, when the shelf is closed/folded up, all you should see is the hinge-ridge; when it's open/down, you should see the whole strip. Others disagree. The important point is to attach the hinge so that your shelf opens and closes the way you want. Test before setting screws.
In general, piano hinges should be 1 inch total shorter than the wood they are attached to, but you can run it flush to the edges if you like the look. Get help with all hanging/hinging projects if possible. It's better to have more help than you need rather than risking a tear in your wood.