214. There is such a variety of locks for securing the doors of buildings now manufactured and on sale by hardware dealers, that it will be impossible to describe all of the different patterns, and an attempt will be made to describe only the principal features common to most locks, with the manner in which they work, and some of the special styles of locks with which the architect should be familiar.
Construction and Operation. - In regard to their construction, locks may be classified as "tumbler locks" and "cylinder locks," and as "rim locks" and "mortise locks." Rim and mortise locks, however, differ only in the shape of the case, a rim lock being made to be fastened to the face of the door, while the mortise locks are set into a mortise cut in the stile of the door, the internal construction being the same in both locks.
Tumbler Locks. - Tumbler locks are the common kind of locks operated by an ordinary key, and so called because the security of the lock depends upon tumblers or levers, which must be raised to an exact position before the bolt can be thrown. These locks also differ a great deal in some of their details, and also in the manner in which they are made. Most of the locks in common use have cast iron cases and cast bolts, with only the springs and tumblers of wrought metal, and even the tumblers are of cast iron in some of the cheaper locks. In the very latest patterns of tumbler locks, all of the parts, including the case, are made of wrought metal by means of the drop forge which cuts and stamps the parts to the desired shape, and as these locks merit a special description, they will be described in another section.
The ordinary tumbler lock consists essentially of the following parts: 1. The case, which contains the works, and to which the wards and guides are attached. 2. The bolt. 3. The levers. 4. The catch with its accompanying springs. 5. The hub, and 6 the key. The hub and catch are not a part of the locking apparatus, and many locks have no latch, but they form a very important part of the ordinary house door lock. The knobs and spindle might also be gives as a part of the ordinary lock and latch, as they are necessary to operate the latch.
To enable one to understand the general principles upon which a tumbler lock is constructed, and also the features that effect the quality of a lock, a short description of the various parts and tike-way in which they operate is given,
Fig. 367. - Sargent's. Lock.
The case is usually made of cast iron, left comparatively rough: for motised locks, and finished, usually in japan, for rim locks. A few of the old style or cast locks have cases pressed out of cold rolled steel, but perfectly plain.
The cast case is made in the form of a shallow box, as in Fig. 367, with a flat cover, fastened in place by a screw. The front of the box is usually of a separate piece of brass or bronze metal, secured to the case by lugs and rivets. In the very cheapest locks the face is of iron cast with the case.
Most cases have a post, B, cast with the box part, and also guide for the latch bolt.
Wards. - On the inside of the cover of the case near the keyhole a small projection, W, Fig. 367, is commonly cast, necessitating a corresponding cut in the sides of the key to allow it to turn. This projection is called a ward. In ancient locks the wards were made quite elaborate, and much dependence was placed upon them for the security of the lock. While it is true that wards prevent the use of any ordinary key not made to fit the lock, they do not interfere with the picking of the lock by an experienced lock picker, and in the better grades of locks they are now usually omitted.
Another device to prevent using any but the right key in the lock, often seen on cheap locks, is a projection on the side of the keyhole, as shown in Figs. 367 and 370. The projection requires a corresponding depression in the face of the key, but as ordinarily made, this is no safeguard against burglars, as a thin key can be slipped by the projection, or the projection, being of cast iron, can easily be broken off. A professional lock-picker, however, generally uses pieces of stout wire to operate the lock, and against these wards and keyhole projections are no protection.
The bolt which secures the door is generally made quite heavy where it projects beyond the face plate, but is thinned down inside the lock so as to be as light as possible and to give space for the levers. The general shape of the common cast bolt is shown in Fig. 368. The notch A is where the key catches, the post B is the part which catches in the levers, and the slots C fit over a guide post on the case. Fig. 369 shows the dead bolt of the Vulcan locks with solid bronze head and steel tail piece forged together.
Fig- 368. - Cast Deed Bolt.
Fig. 360. - Dead Bolt and Lever, of the Yale
In all the best grades of cast locks the bolt is of brass or bronze, an iron bolt being too easily broken.