This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol6", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Fig. 191, F, illustrates a simple pattern of a 4-lever mortice lock with reversible bolt for right or left-hand doors, as manufactured by Messrs. Colledge & Bridgen, with the top plate removed. At A are the wards, which fit into corresponding notches on the key. These wards are attached to the front and back plates of the lock, and when they are cast in one piece they are called solid wards; B shows the levers or tumblers, having slots in them fitting over a projection on the bolt when the levers are at rest, as in the illustration. It will be noticed that they are all level on the under side, but project to different levels in the connecting slot. These projections have all to be raised to the same level by means of corresponding notches on the key before the projection on the bolt can pass from one end of the slot to the other and so allow the bolt to be shot. The levers are assisted by springs to return to their original position and so lock the bolt. The action of the latching bolt will be readily followed from the illustration.
Weighted locks are made to do away with all springs. They are suitable for use in schools, or in other situations where they are subject to hard wear.
The details of locks vary with different makers. Messrs. James Hill & Co.'s locks are all reversible for four different hands, with the keyhole always in the right position. In the case of mortice locks this result is obtained by simply reversing the latch bolt, as can be done in many other makes; but in the case of rim locks, in addition to reversing the latch it is necessary to turn over the body of the lock in the frame, which is made separate for this purpose, and both lock and latch bolts fit holes of similar size in the face plate (see Fig. 191, G). In Messrs. Hills' mortice locks the latch bolt is reversible without opening the lock.
Messrs. J. Kaye & Sons' locks have no slots in the levers, which form a dead prop against the bolt when the door is locked, making it impossible to force the bolt. Another advantage of this arrangement is that there is a large portion of the thick part of the bolt within the case when the door is locked (see Fig. 192), which illustrates their patent Yorkshire mortice lock, in which there is no projection on the edge of the door. The latch bolt occurs in the striking plate and not in the lock, while the patent handles are securely screwed to the door and cannot work loose, as they are not supported by the spindle, but the spindle is supported by the furniture.
Messrs. Nettlefold & Sons' patent lever mortice locks have the levers and springs in one piece of metal, thereby preventing all possibility of the levers separating themselves from the springs. The same firm's patent " Guardian " locks are secured by 5 or 6 levers and also by a "Guardian," which, rising by an incline directly any pressure is applied to the bolt in the attempt to pick the lock, grasps a stud on the lock case and prevents the bolt from moving; while directly pressure is withdrawn the Guardian resumes its original position.
Messrs. Chubb & Sons' patent " Detector " locks are made in dead, spring, or two-bolt rim and mortice locks, and all other kinds. The mechanism is such that any attempt to pick or open the lock by means of false keys brings into action the " Detector." The accidental trial of a wrong key may produce the same effect; and the next time the owner tries to open the lock with the proper key he finds it fast, thereby being made aware of the fact that the lock has been tampered with. By turning the proper key sharply, as though to lock the door a second time, the " detector " is released and the door can be unlocked in the usual manner.
Night latches are made either rim or mortice, for use on street doors. They generally consist of a spring bolt actuated on the inside by a handle and on the outside by a key, and are locked on the inside by a catch or loose pin. The better kinds are made on the "Detector," "Protector," "Guardian," or some similar principle according to the manufacturer. Hills' patent cylindric lever rim night latch has the advantage over other kinds that it can be locked from the outside by a short key, the length of which is independent of the thickness of the door.
Yale locks are cylindrical locks actuated by a small flat key with an irregular edge. The keyway is in a revolving plug, and the key has to raise a set of pin tumblers working in chambers, formed partly in the plug and partly in the cylinders, before the bolt can be shot. This lock affords great security, and can be master keyed if desired.
Lt. Colonel Wethered's patent automatic and reversible locks, manufactured specially for the patentee by Messrs. Nettlefold & Sons, consist of a series of self-locking' latches. In these locks there is a pawl above the bolt and projecting through the face plate of the lock. On the door being closed this pawl engages with an incline on the striking plate, and being raised thereby releases the spring bolt. These locks are made to open by means of a key only, or can be fitted with patent locking clamp furniture, by means of which, when the clamp is pulled outwards, the lock can be used as an ordinary room door lock. When the clamp is pushed in the handles become inoperative and the door can only be opened by means of the key.
When it is desired to leave the door so that entrance can only be obtained with the key, the door must first be locked by the furniture, and then opened with the key and pulled to on going out. This operation prevents the possibility of locking oneself out without having the key in one's possession. These locks are made in various forms suitable for different purposes and positions.
Most first-class locks can be made in suites with master keys, - that is to say, that all the locks in the suite differ (i.e. no two locks can be opened by the same key), but all can be opened by a master key, which is also capable of double locking them, so that none of the other keys will open them until they have been released by the master key.