How do I fit a piano hinge?

A piano hinge — properly a continuous hinge — is the right answer wherever the load has to be spread rather than concentrated: a long lid, a thin plywood door, a fold-down desk, a toolbox top, a bench seat. The difficulty is not the hinge, it is that a long straight line of small screws shows up every millimetre of error.

What you'll need

• A continuous hinge, longer than you need
• A hacksaw and a fine file
• A bradawl or a self-centring hinge bit
• A square and a marking gauge
• Clamps or double-sided tape

Step by step

1. Decide whether it is surface mounted or recessed.Most piano hinges are surface mounted on the inside face, which is by far the easier job. A recessed one needs a shallow rebate cut in both parts to the leaf thickness, and both rebates have to match exactly.
2. Cut it to length.Cut with a hacksaw through the leaves and the pin. Aim to finish just inside a knuckle rather than through the middle of one, and file the cut end smooth and square — a rough end is sharp and catches.
3. Set out the knuckle position.The centre of the knuckle sits on the joint line between the two parts. Mark that line on both pieces with a marking gauge so the hinge cannot wander.
4. Clamp or tape the hinge in position and check it end to end.Double-sided tape holds a long hinge exactly while you drill. Sight along it and check both ends are on the line before making a single hole.
5. Drill every pilot hole through the hinge.A self-centring hinge bit is the tool for this — it centres in the countersink so the screw pulls the hinge to where you marked rather than dragging it sideways. A bradawl through each hole is the manual equivalent.
6. Fix the middle and the two ends first.Three screws, then open and close it and check the action before committing to the rest. Correcting three screws is easy; correcting forty is not.
7. Drive the remaining screws working outwards from the centre.This keeps any accumulated error symmetrical rather than pushing it all to one end.
8. Use screws that sit fully in the countersink.A head standing even slightly proud stops the leaf closing flat and the lid will not shut. Countersunk heads of the gauge the hinge was made for, no larger.
9. Check for binding and adjust.If the lid is tight, the hinge is likely too far onto one side of the joint line, or a screw is proud. Slacken, check, and re-fix rather than forcing it.

Tips

• Buy the hinge longer than you need and cut it. Standard lengths rarely match a real project and the cut is straightforward.
• On plywood and MDF, pilot every hole. The tiny screws a piano hinge uses will snap or strip in board without one.
• For a heavy lid, a continuous hinge plus a lid stay is the correct pair — the hinge takes the weight along the edge and the stay stops the lid falling.

Common mistakes

• Driving screws without pilot holes — Each screw pulls the hinge slightly towards its own hole. Over a long hinge those small movements accumulate into a visibly curved line and a lid that will not close.
• Cutting the hinge through the middle of a knuckle — It leaves a half knuckle that can let the pin migrate out, and a sharp edge. Cut so you finish with a complete knuckle at each end.