The need to secure precious objects is so innate to humans and many other animals that it is not surprising the earliest locks appear as long ago as 4000 years. The oldest known locks employed a pin tumbler mechanism much like that of our modern "Yale" lock but on a far larger scale. They have been found in cultures as diverse as those of Egypt, Japan and Norway. The Romans can be credited with the invention of the metal lock and in fact developed the "warded lock" which uses the familiar skeleton key still common enough today. Warded locks rely on sections of concentric ridges around which the key must fit in order for it to act on the locks sliding bolt (see diagram below). Time passed and the increasing complexity of these locks became a source of much pride to the locksmithing profession and some misplaced assurance to the person with much to protect. Of course the lock picker was never far behind these advances and being engaged in a prideful profession demanded job satisfaction only more advanced locks could provide. The late 18th century gave him a more challenging device, the double action lever lock (see diagram below). This mechanism is found in most furniture grade cabinet locks today. As the key slides the bolt into or out of the lock it also moves one or more spring loaded levers away from the bolt's path. The more levers, the harder the lock is to pick.
Today the use of locks on furniture has become somewhat redundant. In earlier times locks in the domestic realm were intended to frustrate not outsiders but children or those in the employ of the household. These days a locked drawer might deter a passing child but the real predators are more likely to come from outside and rarely have the time or interest to develop skill in the craft of lock-picking. Their modus operandi more likely involves the use of wrecking bars etc and in any case they might realize the contents of a nice piece of furniture is in all likelihood of less value than the furniture itself and simply abscond with the whole thing, locks and all. Whether they serve any practical function or not, we have become so used to seeing locks on fine antiques that a drawer without one seems as blank as a face without a nose.
In many situations the key of a lock served as the handle for a door or drawer while the lock itself took the place of the catches we are so familiar with today. Aside from the finger turn type of catch the 18th century was remarkably short on door catch technology so the lock would find application wherever a door needed positive closure. Today we like the convenience of our magnetic and ball type catches and often wish to use then on reproduction style cabinetry. Attempting to find an appropriate knob or handle to take the place of an escutcheon and key is no easy matter and leads many otherwise respectable cabinetmaking efforts to fail needlessly. It will always be worth the extra effort to do the job right and fit a lock.
Traditional cabinet locks are available in an array of mounting, material and size choices to suit most preferences. Three alternative mounting configurations are the "Half Mortise", "Full Mortise" and "Surface Mount" style lock cases. The "Half Mortise" lock is the one found on almost all fine English and American antiques prior to the middle of the 19th century. This type of lock is mortised into the back side and edge of the work and lays flush. The "Full Mortise" lock is mortised into the edge of the work. The "Surface Mount" lock is simply screwed to the inside face of the work. Each of these types has its advantages.
Our English cabinet locks are supplied with keys but no keyhole escutcheon or strike plate. Escutcheons are available in many shapes and sizes. See Escutcheons.
The various names for the parts of a lock and the definition of a left or right hand lock are a source of endless confusion!. Here is our glossary. (Beware: our definition of left and right hand are the opposite of some others, including even our own lock manufacturers!)
Bolt - When you turn the key the bolt is the part that projects out of the lock.
Selvedge - The face of the lock through which the bolt projects.
Plate - The face of the lock onto which the mechanism is attached.
Distance to pin - The measurement from the selvedge to the center of the keyhole.
Backset - The same as distance to pin.
Full Mortise - A lock whose body is entirely mortised into the wood.
Half Mortise - A lock mounted into a shallow mortise in the back of the work.
Surface mounted - A lock that is screwed to the back of the work with no mortising required.
Left Hand - A lock mounted to a door hinged on its left hand edge (or the reverse, depending on where you get the lock).
Right Hand - A lock mounted to a door hinged on its right hand edge (or the reverse, etc as above).
Levers - Spring loaded obstructions that the key moves out of the path of the bolt. The more levers the more difficult it will be to pick the lock.
Half Mortise Locks
The half mortise lock strikes a good balance between ease of installation and unobtrusive utility. The work necessary to fit these locks makes greater demand on finesse than muscle, all the cuts are of the wide, shallow nature rather than the more problematic narrow, deep variety demanded by the full mortise lock. This attribute suited the pre-power tool cabinetmaker. Because the half mortise lock is always registered against the inside surface of the work the bolt is biased to the rear. Traditional cabinetmaking accommodated this rearward bias with casework drawer dividers constructed of sufficient width material. In modern face frame construction this characteristic can lead to problems and either the full mortise or surface mounted lock could be a better choice.
Half mortise locks were rarely paired with a strike plate. The bolt of the lock would engage into a simple mortise cut directly in the adjacent woodwork. Aside from the remote possibility of catastrophic wear taking place there is no downside to this method. Strike plates serve no useful purpose and cost the cabinetmaker time and money.
Due to the internal mechanical layout of the half mortise lock the key is invariably off center in relation to the lock body. Before laying out the cuts for these locks take note of this fact!
Full Mortise Locks
These locks were virtually unknown before the days of mechanized woodworking. Because a full mortise lock is fitted into a deep mortise cut into the edge of the work it is troublesome to install without a mortising machine, with one it could hardly be easier. The reverse is true of the half mortise lock.
Though conceived with rapid and mechanized installation in mind they are not without some drawbacks. The bolt will generally be centered in the work rather then biased to the rear as in the case of the half mortise lock. This may result in certain benefits related to constructional simplicity but also brings the bolt nearer the front of the casework making it more likely for that area to break out under force (a strike plate can compensate by reinforcing this area).
A full mortise lock can also be a problem installed in thinner material. For any given lock thickness a full mortise lock will leave two walls half the thickness of the one wall left by a half mortise lock. An additional minor consequence of this forward positioning is the attachment of the keyhole escutcheon. Keyhole escutcheons are normally attached with brass escutcheon pins. If the wall thickness left after the lock mortise is cut is limited then these pins will have little to secure themselves to.
As with a half mortise lock, the keyhole is off center in the lock.
Surface Mount Locks
Surface mount locks are simply screwed to the back of the door or drawer front, no cutting required. Most surface mounted locks have a dual keyhole allowing them to function as both hands of door lock as well as a drawer lock. The keyhole is usually centered in the upright width of the lock and the bolt can exit from either side depending on which way the key is turned.
The bolt of a surface mount lock will engage behind the adjacent face frame or door to prevent opening.
These attributes make surface mounted locks versatile and popular, but like many things easy and convenient they are not going to impress anyone with their refinement. Surface mount lock appears to have historical credibility on country styles of furniture particularly as door locks but should probably be avoided on more formal work.