In Bramah's combination lock (fig. 45), which has frequently been used on money safes, the tumblers take the form of straight movable lamelloe, which do not directly prevent the movement of the bolt, but effect the revolution of a cylinder which acts upon the bolt throug-li an eccentric pin. Therefore the key has no wards, properly speaking, but only a num ber of slots of different depths, in its tube-shaped extremity. All these and other combination locks have acquired practical value by extensive use in securing fire-, burglar-proof, and other safes (fig-. 47).
Time Locks, now in general use on burglar-proof safes, are so con structed that the lock mechanism is controlled by a train of clock-work in such a manner that the bolts of the lock can be moved only at a given pre determined time. The controlling mechanism consists of a supplementary bolt, whose purpose is to prevent the throwing back of the locking bolts until the prearranged time, when the gearing throws out the supplement ary bolt, leaving the locking bolts free to be thrown back by turning the knob. Locks on this principle are now considered the most efficient as safeguards against picking, and they are generally adopted for the protec tion of bank vaults, etc.
the simple forms of locks used on the doors of dwelling-houses, a dormant bolt with single or double knob is combined for Ilse in connection with a night-latch, as shown in Figure 36 Go/. 7).
Kik Locks.—ln the United States, a number of inventions pertaining to locks nsed on doors have been extensively introduced. One of the most ingenious is represented by a lock invented by the late Linus Yale, Jr.; it was first introduced about 1861, and was subsequently improved by a com pany engaged in its manufacture. Prior to this invention, the keys of all door locks were of a form or shape similar to that of the keys shown in connection with the illustrations of door locks described above. Leading features of his improvements in key locks consisted, first, in separating the key mechanism of a door lock from the case of the lock (which contains the bolt) and in enclosing it in a separate shell, or escutcheon, inserted from the front of the door and connected permanently throne:1i the door with the lock case behind. This made it possible to adopt a uniform size of keys for doors of all thicknesses.
The original Yale key is illustrated in Figure (16/. 8), and the man ner in which it aided to accomplish the results attained is shown in Fig ures 2 and 3. Figure 3 shows a longitudinal section of the escutcheon of a Yale lock. The key is shown iu the lock raising the pins, or tum blers, to such heights that the joints between the two pins contained in each hole coincide exactly with the joint between the plug and its hole, leaving the plug free to revolve, and thus to actuate the lock. Figure 2 is a trans verse section of the escutcheon taken through one of the pin-holes on the line c a' of Figure 3. Figure 5 is a front view of the escutcheon, showing the keyhole and plug. When the key is withdrawn, the small brass springs press the pins to the bottom of their respective holes; so that the upper pin in each hole crosses the joint of the plug and effectually bars its mo tion. As the variation of one-fiftieth of an inch in the depth of any one
notch of a key will so alter it that it will not open the lock to which it belongs, it is evident that an immense variety of keys can be made with out duplication. This construction enabled a flat key to be used, and led ultimately to the adoption of the small and convenient form embodied in the Yale-lock key.
At a later stage of development and at a comparatively recent period the new Yale corrugated key was devised. This new key consists of the original plate key altered only by having its blade, or portion which enters the lock, corrugated in longitudinal lines. By these apparently simple means and a corresponding change in the form of the keyhole, it is claimed that notable additions have been made to the advantages possessed by the original Yale lock. They include, among other things, these qualities— namely, the lock cannot be operated by any key but its own; it cannot be picked except by some tool which will raise the tumblers, and it is alleged that the shape of the keyhole renders it impossible for any tool to raise the tumblers; should an unauthorized person temporarily get possession of the kev, he would be unable to have a duplicate made, because the corrugated key, shown in Figure 4 Go/. 8), must conform to the exact contour of its keyhole, shown in Figure 5, with an accuracy attainable only by the use of special and expensive machinery.
Figure 12 exhibits the Vale standard front-door lock, with sectiou removed to show the operating mechanism. The ordinary street-door lock, combining- bolt and night-latch, requires two keys, but in this improved form of lock only one key is necessary, both bolts of the lock being con trolled by a single key; so that its possessor can never be locked out. An other key is furnished with the lock intended for the inside locking of th.e main bolt only, but this key will not operate either bolt from the outside.
Figure 16 illustrates a form of concealed bolt which is mortised into the edge of the door-leaf, and is operated by a metal thumb-piece.
The Door Check and Sioring (fig. 6) is a simple and effective device for automatically closing the doors of apartments and for preventing the annoy ance caused by their slamming. It consists principally of a spring the strength of which is gauged according to the resistance presented by the door to which it is attached, and a cylinder furnished with a piston, the latter being set in motion by the movement of the door in opening and clos ing, and provided with a valve which permits the air to enter the cylinder freely when the door is being opened, but which closing exhausts the air more or less according to the force exerted in the operation, and thus acts as an air-cushion, bringing the door to a stop for an instant just before the point of closing„ when, as the air pressure is equalized, the tension of the spring quietly closes and laiches it. The device is provided with suitable brackets, adapting it to be attached by one to the frame over the door and by the other to the top of the door itself.