Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

fig. 27.

fig. 29.

fig. 30.

Details of Rowntree’s tumbler-lock.

A A is the plate which encloses the whole mechanism of the lock, and fastens it to the door; B B is the bolt, guided in its motion by sliding under the bridges C D; E E are pillars which support a plate covering the works; F are the circular wards surrounding the centre or key-pin; and a shews the position of the key, which, in turning round, acts in a notch r in the bolt, and propels it; G, the tumbler, is a plate situated beneath the bolt, and moving on a centre-pin at d; it has a catch or stump e projecting upwards, which enters the notches s or g in the bolt, and thereby retains the latter for backward or forward motion, as the case may be; H is a spring which presses the tumbler forward. The key a, in turning round, acts first against the part c c of the tumbler, and raises it so as to remove the stump from the notches; it can then enter the notch r in the bolt, and move it. So far there is no particular security; but Mr. Rowntree sought to obtain it by the following means. There is a piece of metal h fixed to the lower side of the tumbler, called the pin; when the tumbler is caught in either notch of the bolt, the pin applies itself to a cluster of small wheels I, fitted on one centre-pin beneath the tumbler; the edges of these wheels stop the pin, and prevent the tumbler from being raised. But each wheel has a notch cut in its circumference I; and it is only when the wheels are so placed that all their notches lie in a right line, that the pin can enter this compound notch and allow the tumbler to rise. The wheels must therefore be all adjusted to position; and this is effected by a number of levers K centred on one pin at k; at the opposite end each lever has a tooth m entering a notch in the wheel belonging to it; so that when any lever is pressed outward, it turns its wheel round. Now this pressure of the levers is brought about by a spring n applied to each; and when so pressed, the levers rest against a pin o fixed in the plate. The key is so cut as to determine the extent to which the levers shall act upon the wheels. The key first operates from the curved part p p of the levers K, and raising them, turns all the wheels I at once into the proper positions; in turning further round, it then operates on the part c c of the tumbler, causing the latter to rise and to release the bolt; and in turning still further round, it (the key) seizes the notch r of the bolt, and shoots it. The key is cut into steps of different lengths, as shewn at V V; each step operates on its respective lever K in a different degree from the others; the notch at s acts upon the tumbler, and the plain part t moves the bolt.

We now proceed to notice the modern tumbler-lock. This was arranged by Bird, whose patent, bearing date 29th October, 1790, was for a series of four double-acting tumblers, differing in no respect from those patented by Barron, and closely resembling those in use at the present time in the best tumbler-locks. We will describe the modern tumbler-lock more particularly when we have gone through a few historical details on the subject.

Messrs. Mitchell and Lawton obtained a patent bearing date 7th March, 1815, for a lock in which were combined with the bolt and double-acting tumblers, a series of movable wards, and a revolving curtain for closing the key-hole. The action of the wards was peculiar. On introducing any key or instrument, and passing it round, a number of movable wards or pieces were thrown out so as to prevent the key from being turned back or withdrawn. It was necessary therefore to pass round the key so as to unlock the lock, and if that were not possible, as in the case of a false key being used, it was held permanently, and could only be released by destroying the lock, When the bolt was once shot, the wards were carried up so as to leave a clear passage for the key. This lock does not appear ever to have come into use, on account of the violence required in case a wrong key should be used either by accident or design.

The detention of a wrong key in this lock appears to have suggested the contrivance of a detector. This was first made by Ruxton, whose patent is dated 14th May, 1816. His detectors were of various kinds, the object of each kind being to give information to the owner in case any one of the tumblers should be overlifted in an attempt to pick the lock, which fact would be discovered on the next application of the true key. This is precisely the object of the detector in tumbler-locks at the present day, and Ruxton accomplished it by somewhat similar means. He also had a contrivance for holding a false key, as in Mitchell and Lawton’s lock; and he recommended this form of detector in the following words: “It is true that in this case the lock will have to be destroyed in order to open the door: the result is frightful; but we think the more terrible the result, the less likely would any one be to tamper with it.”