[Illustration: fig. 25. Action of Barron’s tumbler-lock.]
A very elaborate tumbler-lock, patented 23d February, 1790, by Mr. Rowntree, contrasts remarkably with the simplicity of Barron’s lock. Mr. Rowntree’s lock consisted of tumblers combined with revolving discs or wheels. Its mechanism may be understood from the following description and engravings. The same letters refer to the same parts in the several figures.
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.
