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On the Construction of Locks and Keys by John Chubb
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CONSTRUCTION OF LOCKS AND KEYS. 25
in a slot, but the key itself had no communication with the bolt, as in all other locks.
The steel sliders, which should be at least six in number, were lodged in as many detached grooves, cut out lengthways in the metal of the barrel, so as to allow each slider to have an independent endway motion in its own groove. The barrel was held in its place in the lock sideways and endways, by being truly fitted into a circular hole in a fixed steel plate, in which hole the barrel could be turned round by the key, after it had been inserted, and had moved all the sliders, to their unlocking positions. On removing the key from the lock, all the sliders were pushed endway forwards, by their spring, interlocking into corresponding radial notches in the steel plate, so as to fasten the barrel and prevent it from turning round.
The unlocking position of each slider was, when that slider was move'd so far in its groove, that an unlocking notch in the outer edge of the slider, came precisely opposite to the edge of the fixed steel plate, which would then allow the barrel to turn round, provided that every one of the sliders was so moved to its unlocking position at the same time; but any slider which was not moved far enough in its groove, would not arrive at its unlocking position ; or any slider, being moved in its groove beyond its unlocking position, would interlock anew with the steel plate, and hold the barrel fast.
The machines, before mentioned, were adapted for cutting the grooves in the barrels, and the notches in the steel plates, with the utmost precision. The notches in the keys, and in the steel sliders, were cut by other machines, which had micrometer screws, so as to ensure that the notches in each key should tally with the unlocking notches of the sliders in the same lock. The setting of these micrometer screws was regulated by a system, which ensured a constant permutation in the notches of succeeding keys, in order that no two should be made'alike. Mr. Bramah attributed the success of his locks to the use of those machines, the invention of which had cost him more study than that of the locks; without the machines, the locks could not have been made in any great number, with the requisite precision, as an article of trade. There was great originality in those machines, which were constructed before analogous cases (beyond the clock-maker's wheel-cutting machines) were in existence.
The security of Bramah's lock against being picked, depended upon the circumstance that its several sliders must, each one for itself, be pushed in so far and no farther; but how far, the lock afforded no indication. It was nevertheless very objectionable, that the sliders should be so completely exposed to view. It had been suggested, that an universal false key for Bramah's locks might be
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On the Construction of Locks and Keys by John Chubb