Vintage Mortise Lock Service: step by step

Servicing the original lock is usually the better choice for an older home, for practical reasons as much as sentimental ones. Cutting a period door for a modern cylindrical lockset means boring a large hole through the stile and leaves the old mortise to be filled; a repaired mortise case avoids all of that. Where the home is a designated heritage property, keeping the hardware may also be what the municipality expects. The service treats the door as something to preserve: minimal disturbance, parts matched to the original, a strike adjusted rather than replaced, and the old lock left running smoothly for decades to come.

Bit key or cylinder

Older mortise locks come in two families, and the check sorts out which one is on the door. A keyhole shaped like a small keyhole silhouette takes a bit key, the skeleton key style, and the case works on wards and levers that the key's bit must match. A round face on the door with a slot for a flat key is a pin-tumbler cylinder threaded into the case. The distinction matters for everything that follows: how a lost key is replaced, whether the lock can be rekeyed, and what to do if the mechanism is worn out. It also settles whether a spare can be filed on the bench or cut on a key machine.

Cutting a bit key to the lock

For a bit-key lock, keys are made to the case rather than copied from a pattern. A blank with the right bow, shank and bit size is chosen, then the bit is filed by hand to clear the wards inside the case and to lift each lever to the correct height. The key is tried, marked, filed again and tried again until it turns the bolt cleanly from both sides. A second key is made to match while the first is fresh. Where a working original exists, it is used as a guide and the new key is cut to it, and a worn original can itself be gently restored if the customer wants to keep using it.

Looking after the finish

The brass or bronze knobs and escutcheons on an old door have earned their patina, left alone unless you ask otherwise. Paint cleaned from a faceplate or strike leaves the bare metal as found, not polished bright. If you would rather see them shine, check the finish first: unlacquered brass takes a gentle polish well, kept off the keyhole and spindle; polishing a lacquered piece can scratch through it and start tarnish underneath. Lacquered reproduction parts resist tarnishing rather than darken to match; an unlacquered reproduction is built to age and blend in over a season or two. A light wipe when dusting is all the upkeep the trim needs; wet cleaners find their way into the case.