Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

[10] Mr. Denison informs us that there is a further contrivance, which he will explain privately to any persons who wish to manufacture these locks, of which the object is, not to add any thing to the security of the lock under ordinary circumstances, but to provide against the unusual case of a very dexterous thief having occasional access to the lock when open; in which case (but for some such further provision) he might manage to construct a false key capable of opening the lock at any other time, by a method which, for obvious reasons, it is not advisable to publish.

It is true that iron safes have been made for some years in which any number of large bolts are shot by a handle and then locked by a very small key. But in such locks the key must be used in locking, and this leads to certain objections, viz. the key must occasionally at least be confided to some person whose duty it is to lock up the safe after the owner has left the place; there is also the temptation to leave the key in the lock, since it will be wanted in locking up; and thus there is the danger of some dishonest person taking an impression of the key. Besides this, the real strength and security of such safes is only that due to the small lock which locks into the main bolt; whereas in Mr. Denison’s lock the security and strength are those due to the lock itself, with its large and strong tumblers, and other provisions peculiar to its construction; and the key for a lock of the largest size, which was lately exhibited at the Society of Arts by Messrs. S. Mordan and Co., the makers, only weighs a little more than a quarter of an ounce. It may be mentioned that for large locks the key may be solid, although in the small ones it is more convenient to have a pipe-key, on account of the different construction of the curtain.

fig. 52. Mr. Denison’s small lock.

The arrangement of the small lock for drawers, &c. is somewhat different from that of the large ones, and will be understood by referring to [fig. 52]. The action of the handle H on the bolt B and on the tumblers T is sufficiently clear from the figure. The curtain in this case has no plug, but is only a flat plate held up by a thin spring behind it, and moving up and down on the drill-pin of the key, and kept from turning by having one edge against the side of the lock. The bolt has a kind of second stump, only coming up so high as to be able just to pass under the corner of the curtain when it is up, but not able to pass when the curtain is at all pressed down by any thing inserted in the key-hole. In a drawer lock the key has only to be turned a quarter round in order to raise the tumblers. In small locks, the friction of the tumbler-plates is quite enough to keep them in any position, without putting the pin in the middle so as to balance them, as in large locks with heavy tumblers.

In the making of these locks the key must be made first, with proper provisions to prevent the repetition of the same pattern; a kind of pattern or model for locks of each size should be made; the tumblers put on the pin with plates of the intended thickness between, and when raised by the key to the proper height they should be clamped down; and the jaws for the stump of the bolt may then be cut by a circular saw moving in a slit in the model corresponding to the place of the stump. The tumblers for large locks may be cut off from a strip of hoop-iron to the proper lengths by a stamping cutter, giving them the proper circular end, and a punch might at the same time make the pin-hole in the middle. The tumblers for small locks should be stamped out of sheet brass or iron.

It will thus be evident that from the general simplicity of construction, and the small amount of finish required in the working parts, this lock can be made at small cost. We may also add that this lock is as creditable to the public spirit as to the mechanical skill of the inventor; for the lock is not patented, patents being, in Mr. Denison’s estimation, obstructions to the progress of science.

The next result of the “lock controversy” which we have to notice is the production of not less than three improved locks by Messrs. Chubb. We thought it our duty to invite the attention of this celebrated firm to the preparation of this Rudimentary Treatise, and in answer to the application of our publisher we received the following communication from Messrs. Chubb, which we insert verbatim:—

“It will not be necessary to describe the lock as originally made, as a description of it will be found in Mr. Chubb’s paper read before the Institution of Civil Engineers.

“Lock No. 1.—The first of the improvements introduced consists of a barrel, to which a circular curtain is attached, revolving round the drill-pin in the lock; so that if any instrument is introduced to attempt to pick it, the curtain immediately closes up the key-hole, and prevents the introduction of any auxiliary instruments, there being several required in action at once to produce any effect.