The Keys to Antique Furniture Locks

Most of us who are interested in antique furniture have, at one time or another, run across what seemed liked an intractable problem at the time: the locks on an antique chest or desk. The usual approach is to either ignore the locks or take the attitude that if the key is around, great, if not, no big deal. But locks don’t have to be such an enigma. In fact, most 18th-, 19th- and early 20th-century American and some European locks are quite simple and easy to repair and key.

Cabinet and chest locks come in three major designs: full mortise, half mortise and surface mount. Mortise refers to the cut out portion of wood in which the lock is mounted. A full mortise lock is fully enclosed by the drawer front or door in which it is mounted. Only the selvage—or top edge—of the lock is visible on the lip of the drawer or door, and nothing shows on either side. Full mortise locks are usually found on higher-quality 20th-century pieces, although they are used in rare cases in 19th-century goods.

A full mortise lock is completely enclosed in the wood with only the selvage visible.

A full mortise lock is completely enclosed in the wood with only the selvage visible.

A half mortise lock is exactly as it sounds—half exposed. The top selvage is visible, but so is the back or lock plate of the lock on the inside of the drawer front. Also, usually visible on a half mortise lock are the screws or nails that hold the lock in place. The half mortise lock is almost universal on 19th-century American and English case goods.

A half mortise lock is implanted part way in the wood but leaves the back plate visible form the inside.

A half mortise lock is implanted part way in the wood but leaves the back plate visible form the inside.

The simplest design is the surface-mounted lock that is not inset in the wood at all, but is mounted with screws or nails flush to the inside surface of the drawer or door. These locks are most common on early 20th-century pieces and on inexpensive reproductions, and are commonly used as replacement locks by inexperienced restoration “experts.”

A surface mount lock is simply nailed or screwed to the interior surface.

A surface mount lock is simply nailed or screwed to the interior surface.

The purpose of a lock, of course, is to keep someone out of a private place. But since most locks are designed only to keep honest people honest, a determined trespasser can almost always find a way in. Most older and antique furniture locks work on the simple idea of a key moving a bolt through the lock and into the adjoining frame member. The key usually fits over a center pin of a given size and rotates around it. The blade of the key engages a semi-circular cavity in the bolt and moves it forward or back as the case may be. The bolt, however, may have a built-in resistance to impede the use of an unauthorized key. The resistance is a notch in the bolt that engages a surface of the lock housing and prohibits the bolt from moving. A spring holds the bolt notch fast to the face of the lock housing. The key must not only be the right size to move the bolt forward and back, it must be the right size to compress the spring and release the bolt so it can move. Most bolts have two notches, one in the locked position and one in the unlocked position.

This diagram show the parts of a half mortise lock.

This diagram show the parts of a half mortise lock.

In addition to correct barrel size and blade size, a lock may employ other features to prevent the entry or use of a bogus key. The most common is an inside ring of raised metal, concentric to the pin that requires a notch in the key.

These keys are all “notch” keys with cuts in the face of the blade.

These keys are all “notch” keys with cuts in the face of the blade.

This illustration shows how a notch key works over the internal security ring of a lock plate.

This illustration shows how a notch key works over the internal security ring of a lock plate.

This feature is easy to overcome by inserting a new blank key in the lock and working it back and forth. This will put a mark on the blank where the notch should be and it can be cut out with a hack saw. A little practice makes nice notches. A variation is two inside rings of different heights that require two notches of different depths but that’s a detail. A more serious impediment to the interloper is the accursed English “lever” lock. This lock relies on a series of spring loaded levers, each of different thickness to deny entry. The levers must be aligned in a perfect line to allow the bolt to pass but since their thickness is random and hidden, figuring out a cut pattern is very difficult. This lock requires notches to be made on the bottom of the key blade rather than on the face of the blade and is much more difficult to fabricate. Most lever locks are labeled as such. Apparently, the 19th-century English had more of a need for security than we did. This is one case where if you don’t have the key, don’t worry about it.

The key to a lever lock requires notches to be made on the bottom of the key blade rather than on the face of the blade and is much more difficult to fabricate.

The key to a lever lock requires notches to be made on the bottom of the key blade rather than on the face of the blade and is much more difficult to fabricate.

The second most-common problem in the old locks, besides no key, is a broken spring. Symptoms of broken springs include bolts that can be moved without keys, bolts that don’t lock into position or bolts that do not line up with the holes in the selvage. Removing the housing around the pin and bolt will reveal the condition of the spring. Most springs are merely flat pieces of tension steel inserted in a slot in the bolt and wedged against the housing. If the spring is broken, remove it from the slot by punching it out with a small screw driver. Then replace it with the spring from a salvaged lock, or better yet, with a piece of a modern bobby pin. It works very well.

The most common problem with old locks is neglect, especially if the piece has been worked on before and the locks were not removed before stripping and finishing. In this case the locks should be removed, cleaned thoroughly and submitted to liberal applications of WD-40 before any key is tried at all.

Blank keys are available from lots of places including, Van Dyke Restorers in Woonsocket, SD., or your local locksmith and flea markets. Collect as many steel keys as you can to try stubborn locks with before you cut soft brass ones. Brass keys may break in a reluctant bolt. Good luck.

Fred Taylor is a Worthologist who specializes in American furniture from the Late Classicism period (1830-1850).

WorthPoint—Discover Your Hidden Wealth

Ready to invest in WorthPoint? →

Securities offered through North Capital Private Securities, Member FINRA/SIPC