Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

The key is represented in [fig. 32]. It has six steps, besides a terminal step to act upon the bolt. The height of each step, or the distance to which it extends from the pipe of the key, depends of course on the height to which its corresponding tumbler is to be lifted; and it matters not whether the steps of the key are adjusted to the slots of the tumblers, or the slots to the steps, provided the agreement be brought about. It is simply a matter of manufacturing convenience that the key-steps are cut first and the tumbler-slots afterwards. We may here remark that bit, or bitt, is the name given, somewhat indefinitely, either to the whole flat part of a key, or to the small stepped portions of it. The flat part was formerly termed the web of the key, probably from the webbed appearance of the keys to complex warded locks.

After the reading of Mr. Chubb’s paper before the Institution of Civil Engineers, Mr. Owen narrated one or two circumstances connected with the early history of Chubb’s lock. A convict on board one of the prison-ships at Portsmouth dockyard, who was by profession a lock-maker, and who had been employed in London in making and repairing locks for several years, and subsequently had been notorious for picking locks, asserted that he had picked with ease one of the best of Bramah’s locks, and that he could pick Chubb’s locks with equal facility. One of the latter was secured by the seals of the late Sir George Grey, the Commissioner, and some of the principal officers of the dockyard, and given to the convict, together with files and all the tools which he stated were necessary for preparing false instruments for the purpose, as also blank keys to fit the pin of the lock. A lock exactly the same in principle was placed in his hands, that he might examine it and make himself master of its construction. If he succeeded in opening the lock, he was to receive a free pardon from the Government, and a reward of 100l. from Messrs. Chubb. After trying for two or three months to pick the sealed lock—during which time, by his repeated efforts, he frequently over-lifted the detector, which was as often re-adjusted for his subsequent trials—he gave up the attempt. He stated that Chubb’s were the most secure locks he had ever met with, and that it was impossible for any man to pick or to open them with false instruments.

Mr. Owen further stated, that in order to compare the merits of Bramah’s and Chubb’s locks, he had suggested a mechanical contrivance, which was applied to one of Bramah’s six-spring padlocks belonging to the Excise. It was hung upon a nail, in a vertical position, secure from lateral oscillation. A self-acting apparatus was then applied, consisting of a pipe with hexagonal grooves, and a stud or bit corresponding with the division of the lock, and secured to it by a spring. In the grooves of this pipe small slides were inserted, which pressed against the spring keys of the lock; to these slides were attached levers, acted upon by eccentrics, moved by a combination of wheels, whose teeth differed in number so as to perform the permutation required for the different depths of the spring keys, corresponding with those of the proper key to the lock. The automaton machine was set in motion by a line working over a barrel, and acted upon by a weight; and was thus left acting upon the mechanism for a considerable time. At right angles to the pipe or false key was attached a rod and weight; and when the notches in the spring keys were brought in a line with the plane of the plate or diaphragm of the lock, the rod and weight turned the false key, opened the lock, and stopped the further motion of the automaton. In that state the slides indicated the exact depth of the grooves in the proper key, and gave the form of a matrix by which to make a key similar to the original one. The automaton worked during a period varying from half an hour to three hours, according to the state of permutation of the apparatus at the moment of being applied, compared with that of the slides in the lock. We confess that it is difficult to understand the action of this automaton from Mr. Owen’s description. We imagine that the false notches would effectually prevent the operation of the instrument, and openings would be required on each slide to bring it back, so as to meet the motions of the machine.

Mr. Owen did not state whether his apparatus had been successful with one only of Bramah’s locks or with several; nor did he describe any apparatus invented with the view to the picking of Chubb’s locks. He stated, however, that in order to ascertain the effect of friction on one of these last-named locks, it was subjected to the alternate rectilinear motion of a steam-engine in Portsmouth dockyard, and was locked and unlocked upwards of 460,000 times consecutively, without any appreciable wear being indicated by a gauge applied to the levers and the key, both before and after this alternate action. Mr. Owen concluded by expressing his individual opinion that Chubb’s lock had never been picked. “The detector was the main feature of its excellence; and additional precaution, therefore, was only departing from its simplicity, and adding to the expense, without any commensurate advantage.”

In a subsequent chapter the degree of security afforded by various descriptions of locks, and the obstacles which they present of being picked, will come under notice; we therefore now proceed to describe briefly a few other tumbler-locks, or application of the tumbler-principle.

In Mr. Somerford’s lock, for which the Society of Arts gave a premium in 1818, an attempt was made to improve upon the ordinary action of tumblers. In most such locks, all the tumblers must ascend, although to different heights, before the stud of the bolt can pass through the slots; “which arrangement,” says Mr. Somerford, “gives an opportunity of introducing a nail, or a piece of stout wire, into the lock, and thus raising the tumblers without the necessity of using the key.” In his new lock, however, he made one lever to ascend while the other descended, by a somewhat complicated arrangement of slotted plates above and below the bolt. The key was so perforated as to be much endangered in respect to strength.

In Davis’s lock there is a double chamber with wards on the side of the key-hole. The key is inserted into the first chamber and turned a quarter round; it is then pushed forward into the inner chamber, where there is a rotating plate containing a series of small pins or studs, which are laid hold of by the key. By turning the key, the plate is moved round, the tumbler is raised, and the bolt is shot backwards and forwards. This lock, which is somewhat expensive, is used to some extent on Cabinet despatch-boxes.

The lock invented by Mr. Nettlefold is so constructed, that when the bolt is shot out by the key, two teeth or quadrants are projected from the sides of the bolt, which take a firm hold of the plate fixed on the door-post or edge. This construction is said to answer well for sliding-doors.

Mr. Alfred Ainger, in 1820, received a silver medal from the Society of Arts for a draw-back spring latch, in which the objects proposed were the two following—to render the lock more difficult of violation by a pick than those ordinarily in use; and to apply to it a key of which no ordinary person could take an impress, and which would be difficult of access even in a workman’s hand. The key is very peculiar; its pipe consists of three divisions, the section of the upper and lower divisions being circular, and that of the middle division triangular; the triangular portion is intended to give motion to some part of the interior of the lock during the rotation of the key. There are collars fixed on the extremity of the key, to act each on one tumbler; and there are modes, by varying the arrangement of these collars on an octagonal stem, to give something like a permutation to the number of variations to which the action of the key may be subject. The notches or slots are rather in the bolt than in the tumblers; and there are many peculiarities in the general arrangement.

In a lock invented and patented by Mr. Parsons, the tumblers are of a particular form, being hinged on a pivot at their centres, and working into and out of two notches cut in the under side of the bolt. It must be obvious that many variations in the adjustment of the tumblers of locks might be made, without vitiating the principle on which the action depends.