Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

CHAPTER X.
EFFECTS OF THE GREAT EXHIBITION OF 1851 IN IMPROVING ENGLISH LOCKS.

We have now to refer to the effects of the lock controversy. It was no doubt annoying to be told, on good authority, that the machines on which we so much prided ourselves were wrong in principle; and that our locks, in order to afford the degree of security which are expected of such contrivances, must be re-constructed. The grumbling with which the first part of this proposition was received would alone have sufficed to lead to a suspicion of its truth, if the large number of new locks that have actually appeared had not confirmed it. Whether the second part of the proposition has been fairly carried out, is a point which must now be considered.

One of the first locks produced during or immediately after the lock controversy was Mr. Parnell’s, to which the bold term of patent defiance lock is attached. This lock is said to depend for its security on a mode of arrangement which may best be described in the inventor’s own words: “Viewing the lock from its exterior, it presents nothing remarkable; but, upon removing the plate, it will be seen that all possible access to the mechanism with false or surreptitious keys is effectually prevented by a solid cylinder of hardened [?] brass, with protecting wards extending the whole depth of the lock, and having in the centre the aperture for the key, which fits to a mathematical nicety so exact as to preclude the possibility of any second instrument being used to open it.... This protecting cylinder must revolve with the key to get to the works; and the moment it passes from the key-hole in going round to lock or unlock, the solid portion moves into its place, and so completely closes that aperture that the point of a pin, or a fine steel-pen, has failed to be inserted between it and the outer plate or cap, to say nothing of the utter hopelessness of perforating the metal.

“The cylinder or protecting cap, though it revolves by the action of the key somewhat in the same way as the cylinder of the Bramah lock, appears to be intended rather for closing or protecting the key-hole than for governing the movements of the bolt. The internal arrangements of the lock are as follow: Supposing the bolt to be shot, and to be about to be unlocked, the key, by the time it has made about one-third of a rotation, meets with a forcible resistance in the shape of an upright spring-bolt or detector of strong steel acting on the revolving cylinder. The key passes this detector, and arrives at the levers or tumblers. In the bolt-stud which works in the slot of these tumblers there is a small deep serrated notch on one side, corresponding to similar notches on each of the tumblers; if, therefore, the bolt be forced, these notches would lock into each other in a similar manner to the catch on a ship’s windlass or a hoisting crane. There is also a double-action tumbler-bolt, so adjusted, that if any of the tumblers be overlifted, this little appendage becomes thrust down at one end into the bolt of the lock, where it wedges all fast until the tumblers become properly re-adjusted. The double-action tumbler-bolt also falls into the lock-bolt when the latter is locked or shut, thereby imparting an additional strength to the lock. The key has a power of expansion or enlargement while turning in the lock; it meets with an eccentric plate which draws out the bits somewhat; so that, at the moment of acting on the tumblers, they protrude farther from the pipe of the key than when the key entered the key-hole. The key is, in fact, larger when in than when out of the lock. There is connected with the works of the lock a ‘detention-cap,’ so formed that, in the event of a false key being used, a powerful bolt instantly locks into the revolving cylinder, and holds fast the surreptitious instrument.” Such is, in substance, the account which Mr. Parnell has given of his own lock. It must, however, be stated, that the points of security or novelty claimed by Mr. Parnell for his lock were patented by previous inventors. The revolving cylinder or curtain was claimed by Mitchell and Lawton in the patent of 7th March, 1815, as noticed at [page 52] ante. The expanding key-bit was claimed by Mr. Machin of Wolverhampton in 1827, as noticed at [page 61], and by Mr. Mackinnon ([page 62]); while the serrated notches in the tumbler were used by many lock-makers long before the date of Mr. Parnell’s patent. The detention-cap for catching and holding a false key when put into the lock was also patented by Mitchell and Lawton, as noticed at [page 53] ante.

We come now to notice a lock lately invented by Mr. E. B. Denison (the author of the Rudimentary Treatise on Clocks in this series), which has the merit of combining considerable novelty in construction with security. After the details given in the two preceding chapters, it will certainly be no small praise when we express our conviction that in the present state of the art of lock-picking, this lock may be considered as secure. Mr. Denison has furnished us with a description of his lock, which we insert almost in his own words. Mr. Denison claims for this lock the following advantages:—

1. That a very large and strong lock on this construction only requires a very small key. 2. That no key is required to lock it, although it is free from the inconvenience pertaining to spring-locks, viz. that the door cannot be shut without locking itself. Moreover this lock is more secure than any spring-lock can be. 3. That it cannot get out of order from the usual causes of the tumblers sticking together or their springs breaking, inasmuch as the action of the tumblers does not depend on any thing but the key and the handle, and there are no tumbler-springs. 4. That for the same reason, the parts of this lock do not require any polishing or delicacy of execution. 5. That the key-hole being completely closed by a curtain, except when the key is in, the lock is protected from the effects of the atmosphere and dust entering at the key-hole. 6. That this lock is secure against any known mode of picking; the smallness of the key-hole prevents the insertion of any instrument strong enough to open the lock by violence. 7. That this lock, from the simplicity of its construction, admits of being made at small cost.

These objects are accomplished as follows:—In the large-sized locks, such as would be used for safes and large doors, the tumblers T, [fig. 51], are made of pieces of hoop-iron, 6 or 7 inches long and 1¹⁄₂ inch wide: these tumblers are supported by and turn on a pin a, placed at about the middle of their length; so that being balanced on the pin, or nearly so, and having their separating plates P between them, which cannot turn, the tumblers will stand in any position indifferently; and in order to secure sufficient friction to keep them steady, one or more of the separating plates P is bent a little, so as to act as a spring when the cap of the lock is screwed down. The lock is shewn in [fig. 51] as locked, the bolt B having been shot by the fantailed piece f on the handle, and the tumblers sent down, so that the stump s cannot enter their jaws by the other piece of the handle; and it is evident that the handle cannot draw the bolt back again until the tumblers have all been raised by the key to the proper position to allow the stump s to enter their jaws. It will be observed that in the position shewn in the [figure], the stump does not touch the tumblers; and consequently, so long as the bolt is kept in the position represented, no pressure of the stump against the tumblers can be felt, although by means of a false key or pick-lock the tumblers be raised to any height. No implement, however, can be pushed into the key-hole without first pressing in the curtain K, which is held up against the cap of the lock by the two spiral springs c c on each side of the key-hole; and at the back of the curtain there is a square plug p, which goes through a hole in the back of the lock, and has a notch in it through which the bolt can pass when the curtain is up, closing the key-hole, but at no other time. In other words, the act of pushing in the key sends down the curtain plug, the effect of which is to hold the bolt fast in the position in which the stump cannot be made to touch the tumblers. If the proper key be used and turned about half round to the right, it will bring the tumblers to the proper height for the stump to pass. The key is then taken out; for so long as it is in the lock, the bolt cannot be moved; and then turning the handle to the right, the bolt is drawn and the door opened.

fig. 51. Mr. Denison’s large lock.

The handle H should be so made, that as soon as the fantailed piece f has sent the bolt just clear of the tumblers, the other arm to the right of H may begin to move the tumblers; but the fantail need not send the stump above one-sixteenth of an inch beyond the tumblers; and the curtain-plug and bolt must be so adjusted that the curtain cannot be pushed in until the bolt is so far out that the stump is this one-sixteenth of an inch beyond the tumblers. The curtain K need only be a thin piece of steel, and the bolt B must be thick enough for the curtain to go down just to the level of the thin plate P between the bolt and the first tumbler T. The curtain-plug p is made as long as the key-hole and rather broader, and of the shape represented, partly for the sake of steadiness in pushing in the curtain, and also for more completely protecting the key-hole; for if an attempt be made to pick the lock by drilling into the key-hole, the drill will pass into the inside of the door and not into the inside of the lock.[10]