Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

The lock-manufacture in America has undergone some such changes as in England. The insufficiency of wards to the attainment of security has been for many years known; and the unfitness of even tumblers to attain this end, without auxiliary contrivances, has been fully recognised for a dozen years back. In this, and in other mechanical arts, the American machinists depended primarily on the invention of the artisans in the mother country, rather than on those of any continental European state. But the development of the art in the United States has not been wanting in originality; the varieties of locks have been very numerous, and many of them exceedingly ingenious. It is not necessary, however, to describe or depict any of those of simple form. The warded locks of different countries very much resemble each other; the intricate warded locks made in France in the last century have long fallen into disuse, in consequence of the general conviction that no arrangement of wards, however intricate, can afford the degree of security required in a good lock. It will be more to the purpose, therefore, to proceed at once to a notice of those American locks which, during the last few years, have acquired some celebrity; first, however, noticing one of older date.

Stansbury’s lock, invented in the United States about forty years ago, may be regarded as a modification of the Egyptian lock. It had a bolt, case, and key-hole somewhat similar to those of modern locks; but there were peculiarities of construction in other respects. There was a revolving plate, pierced with a series of holes, and having a bit or pin which moved the bolt. On the lock-case were a series of springs, each having a pin at one end; and the arrangement was such that, when the bolt was locked or unlocked, each pin would be pressed into some one of the holes. Like as in the Egyptian lock ([figs. 1] to [4]), each pin had to be pushed out, and all of them simultaneously, to allow the plate to turn and move the bolt. The key was made with a barrel and bit; and on the front end of the bit was a series of pins corresponding in position with the holes in the plate. The mode of locking or unlocking was as follows: the key was inserted in the key-hole, and turned to a certain position; it was then pressed in with some force, until the pins on the key met those in the plate; when the latter, yielding to the pressure, left the plate free to turn and move the bolt. Modifications of the Egyptian lock, more or less resembling this, have been brought out in some variety on both sides of the Atlantic; but scarcely any have equalled in simplicity the curious wooden relic of by-gone ingenuity in the art of lock-making.

A lock made a few years ago by Mr. Yale, in the United States, somewhat resembles the Bramah lock in having a cylinder or barrel, or rather two concentric cylinders, one working within the other. These cylinders are held together by pins which pass through them both into the key-hole. On the back of the inner cylinder is a pin that fits into a slot in the bolt, and moves it whenever the cylinder is turned. The pins that hold the cylinders together are each cut in two; the pieces of the various pins differing in lengths as irregularly as possible. The key is so peculiarly formed, that, on inserting it in the key-hole, it thrusts the pins radially outwards; each pin being pushed just so far that the joint of the pin shall coincide with the joint between the two cylinders. The inner cylinder can then be turned, by which the bolt is locked or unlocked. If, by the use of a false key, any pin be pushed in too far, it will be as ineffectual in opening the lock as if it were not thrust in far enough; and some of these locks having been made with as many as forty pins, the chances are very numerous against the right combination being hit upon. There is a combination of something like the Egyptian with something like the Bramah lock, here attempted.

One of the principal constructions adopted in America a few years back for bank-locks is that of Dr. Andrews of Perth Amboy, in New Jersey. It was up to that time (1841) believed that the best locks, both of England and America, were proof against any attempts at picking derived from knowledge obtained by inspection through the key-hole; but there still remained the danger that the sight of the true key, or the possession thereof, for only a few minutes, would enable a dishonest person to produce a duplicate. It was to contend against this difficulty that Dr. Andrews directed his attention; and he sought to obtain the desired object by constructing a lock, the interior mechanism of which could be changed at pleasure. The lock of his invention is furnished with a series of tumblers and a detector. The tumblers are susceptible of being arranged in any desired order; and the key has movable bits which can be arranged so as to correspond with the tumblers. When the lock is fixed in its place, no change can be made in the tumblers, and consequently only one arrangement of the bits of the key will suit for the shooting and withdrawing of the bolt. The owner can, however, before the fixing of the bolt, adopt any arrangement of tumblers and bits which he may choose. But though the tumblers cannot be actually re-arranged in any new order within the lock while the latter is fixed, yet by an ingenious contrivance the tumblers can be so acted upon as to render the lock practically different from its former self. The purchaser receives with his lock a series of small steel rings, each ring corresponds in thickness with the thickness of some one of the bits of the key; so that, by suitable adjustment, any one of the bits may be removed from the key, and a ring be substituted in its place. The effect of this substitution is, that the particular tumbler which corresponds with the ring is not raised by it; it is drawn out with the bolt, as if it were part of the bolt itself. Supposing the lock to be locked by this means, the original key would not now unlock it; for one of the tumblers has now been displaced, and can only be re-adjusted by the same ring which displaced it. If an attempt be made to open the lock by the original key, or by the key in its original adjustment, a detector is set in action, which indicates that a false key or other instrument has been put into the lock. One, or more than one, of the bits may be removed from the key, and rings be substituted, and consequently one or more of the tumblers may be disturbed in this peculiar way; so that the lock may change its character in all those permutating varieties which are so observable in most “safety-locks.” The shape of the tumblers is, of course, such as to facilitate this action; they have each an elongated slot, and also two notches; when a tumbler is raised by one of the bits of the key, one of the notches closes around a stump fitted into the case of the lock, and prevents the tumbler from being moved onward with the bolt; but when a ring has been substituted for a bit on the key, the tumbler cannot be raised at all; it is carried onward by a stump on the bolt.

Dr. Andrews is also the inventor of a lock which he terms the snail-wheel lock. In this lock a series of revolving discs, or wheels, taking the place of the tumblers, are mounted on a central pin, on which the pipe of the key is inserted. Each disc has a piece cut out of it, into which the bit of the key enters, and in turning round moves the discs according to the various lengths of the steps on the key. On the outer edge of each disc is a notch, and by the turning of the key all these notches are brought into a line, so that a moveable tongue, or toggle, attached to the bolt, falls into the notches; the key is then turned the reverse way, by which means the bolt is projected.

About the time when Dr. Andrews invented his first lock, Mr. Newell, of the firm of Day and Newell of New York, constructed a lock which possessed the same distinctive peculiarity as that of Andrews, viz. that the key might be altered any number of times without rendering it necessary to remove the lock or change its internal mechanism. This was brought about, however, in a different manner. Instead of having, as in the Andrews lock, a two-fold movement to every tumbler, Mr. Newell employed two sets of tumblers, the one set to receive motion from the other, and having different offices to fill, to be acted upon by the key in respect to the first series, and to act upon the bolt in respect to the second. Calling these two sets primary and secondary, the action of the lock may be briefly described as follows. A primary tumbler being raised to the proper height by the proper bit in the key, raises the corresponding secondary tumbler; the secondary tumbler is held up in a given position during the locking, while the primary becomes pressed by a spring into its original position. It results from this arrangement that the bolt cannot be unlocked until the primary tumbler has been raised to the same height as before, so as to receive the tongue of the secondary tumbler. And as this is the case in respect to any one primary and its accompanying secondary tumblers, so is it the case whether each set comprises four, five, or any other number. The key may be altered at pleasure, and will in any form equally well shoot the bolt; but the lock can only be unfastened by that arrangement of key which fastened it.

It is, however, desirable to trace the course of improvements more in detail, because every successive change illustrates one or other of the several properties required in a good lock. Messrs. Day and Newell’s lock was not finally brought to an efficient form without many attempts more or less abortive. Mr. Newell conceived the idea of applying a second series of tumblers, so placed as to be acted on by the first series. Each of these secondary tumblers had an elongated slot, such that a screw could pass through all of them; the screw having a clamp to overlap the tumblers on the inside of the lock. The head of the screw rested in a small round hole on the back of the lock, so placed as to form a secondary key-hole, to which a small key was fitted. There was thus a double system of locking, effected in the following way: when the large key had been applied, and had begun to act on the primary tumblers, the small key was used to operate on the clamp-screw, and thus bind all of the secondary tumblers together, ensuring their position at the exact heights or distances to which the primary key had caused them to be lifted. The bolt was then free to be shot, and the first series of tumblers reverted to their original position.

But such an arrangement has obvious inconveniences. Few persons would incur the trouble of using two keys; and besides this, there were not wanting certain defects in the action and reaction of the several parts; for if the clamp-screw were to be left unreleased, the first series of tumblers would be upheld by the second series in such a way that the exact impression of the lengths of the several bits of the key could be obtained through the key-hole while the lock was unlocked or the bolt unshot. To remedy one or both of these evils was the next object of Mr. Newell’s attention. He made a series of notches or teeth in each of the secondary tumblers, corresponding in mutual distance with the steps or bits of the key; and opposite these notched edges he placed a dog or lever, with a projecting tooth suitable to fall into the notches when adjusted properly in relation to each other. When the key was used, the primary tumblers were raised in the usual way, and acted on the secondary tumblers; these latter were so thrown that the dog-tooth caught in the notches and held them fast, thereby rendering the same service as the clamp-screw and the small key in the former arrangement. No other relative position of the bits of the key could now unlock the lock.

Still, improvement as it was, this change was not enough; Mr. Newell found that his lock, like all the locks that had preceded it, was capable of being picked by a clever practitioner; and candidly admitting the fact, he sought to obtain some new means of security. He tried what a series of complicated wards would do, in aid of the former mechanism; but the result proved unsatisfactory. His next principle was to provide a number of false notches on the abutting parts of the primary and secondary tumblers, with alterations in other parts of the apparatus. The theory now depended upon was this, that if the bolt were subjected to pressure, the tumblers would be held fast by false notches, and could not be raised by any lock-picking instrument. To increase the security, a steel-curtain was so adjusted as to cover, or at least protect, the key-hole. Great anticipations were entertained of this lock, but they were destined to be negatived. A clever American machinist, Mr. Pettit, accepted Messrs. Day and Newell’s challenge (500 dollars to any one who could pick this lock); he succeeded in picking the lock, and thus won the prize.

Once again disappointed, Mr. Newell re-examined the whole affair, and sought for some new principle of security that had not before occurred to him. He had found that, modify his lock how he might, the sharp-eyed and neat-fingered mechanician could still explore the interior of the lock in such a way as to find out the relative positions of the tumblers, and thus adapt their means to the desired end. How, therefore, to shut out this exploration altogether became the problem; how to make a lock, the works of which should be parautoptic—to coin a word from the Greek, which should signify concealed from view. The result of his labours was the production of the American bank-lock now known by that name. The details of this lock may now conveniently be given.