CHAPTER XIV.
FENBY’S PATENT STOP-LOCK.
This lock has been designed with a view to doing away with several weak points in the construction of lever locks.
The introduction of the movable stump by Mr. Hobbs, in order to defeat picking by the tentative method of applying pressure to the bolt, so as to cause binding between the stump and the levers, was a great advance in the art of lock-making.
The movable stump, as so constructed, was, however, open to this objection, that while sufficiently delicate and certain in its action to render picking very difficult, it was at the same time, through the smallness of its parts—resulting from the confined space available for its action—unsuited to withstand any amount of force applied to push back the bolt.
fig. 65.
In the lock under notice the stump s is formed in the solid on the shorter arm a1 of a cranked lever or oscillating stop a. This stop a works on the steel pin or centre b, which latter has a bearing in both plates of the lock. At the end a of the stop a is a recess formed to fit the corner d of the bolt-head. c is a stud limiting the range of a in an upward direction, so that when in its normal position the stop a may just clear the bolt-head, as shown in [figs. 65], [66], and [67]. The tail of the bolt, instead of being in the form usually adopted, is formed of the bar e set on edge so as to reach from the back to the front plate of the lock, completely dividing the lower part, in which the keyhole lies, from the upper, in which the main parts of the works are placed.
This bar e works between the guide pieces g g, so that in whatever position the bolt may be, the division of the lock into two chambers is complete. At f is the recess in which the key acts to move the bolt. The levers l turn upon the pin i formed in the solid of the bolt-head. The part of each lever on which the key is to act passes through a slot or recess in e, the parts h and h1 of the levers being struck to the arcs of circles, having their centres coincident with that upon which the levers turn at i.
As it is not possible to lift the levers out of this slot in the bar e, and further, as the levers and bolt move together in a longitudinal direction, the movements necessary to locking and unlocking open no communication between the upper and lower chambers of the lock.