fig. 61.
Hence a person putting a false bit into one of these locks will not only infallibly lose it at the very first trial, but will do so without gaining any information as to the nature of its inaccuracy; for as the gatings of the levers cannot be seen or felt, all that can be told about the action of a false bit is, that it has failed to open the lock. In fact, a counterfeit bit passes under the levers, and through the lock, just like the true bit; and it is only the stoppage afterwards met with of the bolt that indicates the failure of the false bit, which is by that time gone beyond recovery. Whatever amount of labour, therefore, may have been spent on the fabrication of a counterfeit bit, this bit can only be tried once, so that no alteration can afterwards be made in it.
Nothing that can be inserted into the radial slot of the cylinder C through the aperture in the front plates can do any injury to the lock; and a charge of gunpowder inserted in that way would only blow out again at the orifice without damaging the lock, both the apertures for the key being merely blind holes with parallel sides.
fig. 62.
fig. 63.
For the manufacture of the bits for the keys of this lock a self-acting machine is employed, in which the height and width of the several steps in the bit are regulated by adjustments of very great accuracy, and admitting of an almost endless variety of figure for the bits. This key-cutting machine is shown in [figs. 62] to [64], and consists of a small circular saw A running vertically, of the same thickness as each step in the bit I, which is brought up to the saw by the slide-rest B. The bit I is fixed in the holder C, which rocks upon a centre, so as to give the required curvature to the edge of each step in the bit when cut by the saw, as shown in the full-size section of the bit-holder, [fig. 63]. The adjustment of the depth of cut is effected by the set screw D upon the slide-rest coming up against the eccentric ring E upon the bed of the slide-rest; this ring is turned round by hand, and set to sixteen different positions by means of the catch-pin F and the sixteen holes on the circumference of the ring, allowing of sixteen different depths of cut. The lateral adjustment for the pitch between the successive steps of the bit is effected by the two bed-screws G G acting on the slide-rest B, having a dividing plate on the head, and such a pitch of thread that one turn of the screws traverses the slide-rest through the exact distance of one step in the bit. The occurrence of any play or backlash is entirely prevented by having the screws placed one at each end of the slide-rest; so that by slacking back one screw through one or more turns, and then advancing the other through the same number of turns, the slide-rest is always held with perfect steadiness between them, filling exactly the space between the ends of the two screws.
The number of changes admissible in this key-cutting machine, if used for making keys for locks having six levers, is the number of permutations that sixteen terms are capable of when taken six together, which is upwards of sixteen millions. Some of these changes are so slight that too great accuracy of workmanship would be required to make the locks accordingly; but of those changes that differ from one another so far that no lock could be opened by any other than its own key, more remain than could be used up by all the locks in the world.
