Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

In the position of the lock shown in [fig. 53], the bit N has been inserted into the vacant space of the radial slot in the cylinder C, in front of the slide block R. The size of this vacant space is ³⁄₈ths inch long by ¹⁄₈th inch wide and ³⁄₈ths inch deep; and in the two front cover plates of the lock, and also in the door to which the lock is attached, a hole is made of the same shape. In the door there is no bearing for the centre boss F, but only a small keyhole corresponding in size with that in the boss F for inserting the stem of the key.

fig. 56.

In the position of the parts shown in [fig. 53], it will be seen that the levers L are held pressing down against the circumference of the cylinder C by their springs I bearing against the pin P. In this position also the bolt spring between the main bolt and the stump-bolt, [fig. 54], presses the stump S down into the notches of the levers, so that the levers are completely locked by the stump, as seen in [fig. 53].

In order to unlock the lock, which in [fig. 53] is shown with the bolt shot, it is necessary that all the gatings G in the levers should be brought precisely under the stump S. Through the centre keyhole F there is no communication possible at any time with the levers L; nor will any instrument, however slender, if passed into the radial slot through the aperture at N be able to reach them, whether the cylinder C be in the position shown in [fig. 53] or turned round into any other position. For the only difference made by turning the solid cylinder C is that the radial slot in it is carried away from the aperture in the external plates, and the solid part of the cylinder is brought opposite to the aperture, which is thereby completely closed against the insertion of a picking instrument. This construction accordingly not only precludes the possibility of opening this lock with an ordinary key, in which the part that acts on the levers is attached to the stem of the key, but it also renders it an absolute impossibility to introduce a pick of any form, as nothing can reach the levers L except a detached piece of such a size and shape as to be capable of travelling round in the vacant space left in front of the slide block R in the radial slot of the cylinder C.

fig. 57.

For the purpose of unlocking the lock the bit N, [fig. 57], is used. This bit is of such a size as to fit into the vacant space of ³⁄₈ × ³⁄₈ × ¹⁄₈ inch in the radial slot of the cylinder C; and the indent at V is merely for the purpose of ensuring the insertion of the bit in the right direction, the external aperture for the bit being made with a corresponding projection to fit the indent in the bit. This bit being inserted through the aperture in the door, is pushed in by means of the key stem M, which is flattened on two sides for that purpose, as shown in [fig. 55]; and the bit is thus pushed home into its place in the radial slot of the cylinder, as shown at N, [fig. 53].

The key stem M is now inserted into the centre keyhole F, and the cylinder is turned round by it in the direction shown by the arrow, carrying round the slide block R and the bit N. The slide block R, while moving through the concentric portion at the commencement of the guide grooves J J, does not affect the bit; but by means of the cam groove O in the tail of the stump-bolt, [fig. 54], it moves that bolt so far as to lift the stump S completely out of the notches in the levers L, which are thereby left free to be raised. On continuing to turn the cylinder C, the eccentric part of the guide grooves J J causes the slide block R to move outwards along the radial slot, pushing the bit N before it; and the bit is thus made to project beyond the circumference of the cylinder, which it can then do, being no longer confined by the guard A. The further projection of the bit as the cylinder revolves causes the steps in the bit to lift their respective levers; and the steps in the bit are so arranged that, when the cylinder arrives at the position shown in [fig. 58], all the gatings G are brought simultaneously opposite the stump S, which is instantly shot down through the distance of the ¹⁄₁₀th inch play by the bolt spring. The bit N remains in contact with the extreme part T of the levers while the stump S is entering the gatings, the action of the bolt spring being so rapid that the bit cannot move through any appreciable distance during the time.