Fig. 11.
back, no sensible pressure on the levers is produced, but only just
enough to turn this protector lever, as Hobbs called it, on its pivot c,
and so bring down its end a in front of the square pin, and then the
bolt can no more be pushed back than when held by Chubb’s detector.
The protector is set free again by merely pushing the bolt forward
with the key, without reference to the
levers. However, the protector could
be prevented from acting by a method
used by the inventor himself for another
purpose, viz., by pushing a piece of
watch-spring through the keyhole, and
up behind the bolt, so as to reach the
protector at a, and keep it up while the
bolt was pushed back, or, again, by
pushing up the watch-spring between
any two of the levers, and holding
the end b of the protector with it, so as to press the stump against
the levers. Both these devices, however, are prevented now by
letting in a feather FF in a groove between the bolt and the back
of the lock, which no watch-spring can pass, and also bringing a
piece of the feather forward through the front gating of the levers
just under the stump. In this form the lock is safe against any
mode of picking known. A lock possessing valuable features was
invented in 1852 by Sir Edmund Beckett—afterwards Lord Grimthorpe—but
did not come into general use for commercial reasons.
All the locks containing many levers so far described have a common defect in that the levers are moved in one direction by the key and in the other by springs. But it not infrequently happens that dirt or grease gets between the levers and causes two or more to stick together, in which case one of them is lifted too high and the bolt is prevented from operating. To overcome this difficulty locks, especially those intended for safes, have been made so that alternate levers move in opposite directions, the key having two bits on opposite sides. This construction entails that the key enter the body of the levers instead of passing below them, an arrangement that had previously been in use to reduce the space into which gunpowder could be packed through the keyhole.
Fig. 12.
The key locks chiefly used in English safes have been the ordinary
lever lock with 6-8 or 10 levers, Chubb’s “detector,” Hobbs’s
“protector” or variants of these. In the Yale lock, which
reverts in some degree to the idea of the ancient Egyptian
lock, America has produced one key lock which has come into almost
Key locks.
universal use in that country and is certainly worthy of note. The
key of this lock, shown full size at ka in fig. 12, is remarkably small,
being stamped from a
piece of flat steel and
weighing only a small
fraction of an ounce. The
barrel abc has to turn, as
in the Bramah lock, in
order to move the bolt,
which is not shown in the
figure. That may be done
either as in Bramah locks
or by a tongue or bit
attached to the end ab of
the barrel as in several
other locks. The barrel
is prevented from being
turned, except by the
proper key, thus. The
(apparently) five plugs with spiral springs over them in fig. 12
are really all divided at the cross line bc, being all now lifted to the
proper height by the key. Consequently the barrel abc can turn
round, as there is no plug either projecting from it or projecting into
it. But when the key is out, all the plugs are pushed down by the
springs, and so the upper ones descend into the barrel and hold it
fast. And again, if any of the steps of a false key are too high, some
of the lower plugs will be pushed up beyond the barrel into the holes
above them, and so the barrel cannot turn. The bevelled end of the
key near a enables it to be pushed in under the plugs, though with
some friction and resistance.
It is frequently convenient to have a number of different locks so arranged that, whilst each has its own individual key, yet one special or “master” key will operate any of the series. In warded locks this is done by “differing” the wards of the individual locks so that each key will only pass its own lock, and then filing away the bit of an extra key so that it will pass all the wards; the objection to this method is that any of the individual keys can easily be filed away and so form a master key. A better method, which meets this objection, consists in making all the levers except one—or if need be two—of each lock alike and cutting another gating or widening the gating in the differing levers, so as to pass the master key which has one—or two—special steps.
The growth of safe deposits has called for special locks so that when a box changes tenants the outgoing tenant’s key shall be useless. In some cases the lock has been taken off and another substituted, but this is a clumsy makeshift now rarely employed, and has been superseded by the use of changeable key locks.
Fig. 13.
The first of these, invented by Robert Newell in 1841, was introduced into Great Britain from America by Hobbs in 1851. A simpler form, the construction of which is clearly shown by fig. 13, was brought out by Hobbs, Hart & Co. The bolt of this lock, instead of the ordinary main stump, carries a set of sliders, PPS, one corresponding to each lever and each carrying a projection S corresponding to a portion of the main stump. It will be seen that if any key having steps of certain lengths is inserted when the lock is unlocked and the bolt B thrown thereby, each slider will be raised to a height corresponding to that to which its lever is raised by the key, and the two fixed teeth CC will engage two of the teeth in the front of each slider, so that they will be held in place ready to enter the lever gatings when the same key is inserted.
A changeable key lock introduced by the Chatwood Safe Co. has no gatings in the levers, whose fronts are cut with teeth gearing into similar teeth cut in a set of disks carrying the gatings. The disks are mounted on a stud which can be moved by a key from the back of the lock in such a way that while the main stump is in the gatings—keeping the disks in position—the disks are carried forward out of gear with the levers; the key can then be removed and another having steps of suitable length inserted and turned so as to raise the levers, the disks being then brought back into gear.
Fig. 14.
Both the above locks require that the key steps should have certain definite lengths corresponding to the teeth, but a later lock resembling to some extent that brought out by Hobbs, Hart & Co. has been introduced by the Chatwood Co., in which it is sufficient after unlocking the lock to file any of the key steps and so alter the pattern of the key in any way. In this lock, which is illustrated in fig. 14, unlike all those that have been described, the levers are not pivoted but slide upon guide stumps; the main stump is divided as in Hobbs Hart’s lock, the various pieces being clamped together by a screw to form a solid stump. The sliders composing the main stump are not provided with teeth, the changing being effected as follows: when
