Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

Several of these names are well and publicly known in England and the United States.

This event gave rise to much newspaper controversy; and attempts were made to shew that, as this was not a test lock, prepared expressly for challenge, the picking proved nothing as regards the finest of the manufacturers’ locks. Two circumstances, however, have to be noticed—that the lock was of sufficient commercial importance to be placed on a door enclosing valuable papers, and that the makers had an opportunity to attend and witness, and comment on the trial, if they so chose. We may here remark, that one of the ingenious contrivances of the Chubb lock, the detector, excited some doubt no less than fifteen years ago, as will be seen from the following. The writer of the article “Lock” in Hebert’s Engineers’ and Mechanics’ Encyclopædia, while speaking with much commendation of Chubb’s locks, points out a curious feature, which seems to him to render somewhat doubtful the surety of the detector apparatus. “In Barron’s and Bramah’s locks,” he observes, “the picker has no means of knowing whether the tumblers are lifted too high or not; but in Chubb’s he has only to put the detector hors de combat in the first instance, by a correct thrust from the outside of the door (which might be accurately measured), so as to fix it fast in its place; the detector then becomes a stopper to the undue ascent of the tumblers, and the extent of their range is thereby correctly ascertained. Thus, it appears to us, the detector might be converted into a director of the means for opening the lock.”

Much will depend on the view which is taken of the circumstance just noted. The object of the detector is, not to prevent the lock from being picked, but to shew that an attempt has been made to pick it; or, at least, to attain a given purpose by an indirect instead of a direct method. But if there be really any truth in the surmise, that the detector actually guides a skilful hand in determining how high the tumblers should be raised, the supposed advantage will be purchased at rather a dear rate. As we are here, however, speaking of facts and not of mere opinions, it is proper to say, that the lock opened by Mr. Hobbs had the detector apparatus, but that it was not disturbed by him in picking the lock.

But instead of reiterating opinions, we will state the method by which most of the tumbler-locks made in England, up to the date of the Great Exhibition, can be opened or picked.

Bearing in mind the principle on which the picking of locks is said to depend, namely, that “whenever the parts of a lock which come in contact with the key are affected by any pressure applied to the bolt, or to that portion of the lock by which the bolt is withdrawn, in such a manner as to indicate the points of resistance to the withdrawal of the bolt, such a lock can be picked,” the first step is to produce the requisite pressure.

fig. 49.

If the end of the bolt were exposed, this pressure might be applied by some force tending to shoot back the bolt; but as the bolt, whenever it is shot, is buried in the jamb of the door, or otherwise concealed from view, the pressure can in general only be applied through the key-hole. In order, therefore, to apply this pressure, the operator provides himself with an instrument capable of reaching the talon of the bolt, which in the case of the Chubb lock was a pipe-key of the form shewn at a b, [fig. 49], furnished at the pipe-end with that portion of the bit of the key b c which moves the bolt (see [fig. 32], page 57, where the step which acts on the bolt is called the terminal step). The other end of the pipe-key is made square, as at a, for the purpose of receiving the square eye e of the lever e f, [fig. 50], to the further end of which f a weight w is attached by means of a string s. Now it is evident that if this pipe be introduced into the lock as far as it will go, and be turned round as in the act of unlocking, and the lever and weight be attached to the end a, the bit b c of the pipe-key will maintain a permanent pressure on the bolt, which, if the weight be sufficient, will throw back the bolt as soon as the tumblers are raised to the proper height to allow the stump to pass.

fig. 50.