Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02590676 2007-05-17
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Tumbler Lock Mechanism Improvement to prevent break-in by "Bumper Key"
2. Background of the invention
The technique of opening a locked tumbler lock with a "Bumper Key" has long
been known
to locksmiths. In recent years the method has become known to many, due to the
popularization of the technique on the Internet.
The technique is based on the principle discovered by Newton that when a force
is applied to
a line of hard objects in close contact with each other, the force will be
transmitted down the
line to the object at the end of the line and that object will then act on the
force received and
fly off. The principle is demonstrated by the popular toy where 5 steel balls
hang on threads
and are touching each other. When one end ball is pulled away and allowed to
hit the line of
balls, the other end ball flies away, leaving the other 4 balls motionless in
place.
A Pin Tumbler Lock has in each chamber 2 pin tumblers pressed together by a
spring. There
are 4, or 5, or 6 chambers in line, each one holding 2 pins and a spring. See
Drawing #1.
When no key is inserted, the 2 pins in each chamber are aligned so that the
top pin crosses
the Shear Line (between the cylinder and the housing) and prevents the Plug
(The inner
cylinder which holds the key) from turning. When the correct key is inserted,
it lifts the lower
pin up to the shear line, pushing the upper pin above the shear line. This
position of the pins
permits the plug to turn. All the first pins are cut to a different length,
depending on the depth
of the cut in the key at that point. When all cuts in a key match the height
of the lower pins, it
allows all lower pins to reach the Shear Line, the plug turns and the lock
opens.
See drawings #1, #2 & #3.
The 'Bumper Key" is a key that fits the keyhole profile of the plug, but has
all its cuts filed
down to the lowest point. When this key is inserted into the lock, the plug
would not turn,
since all top pins are crossing the shear line. Then the key is held a
fraction out of the lock
and is hit with a hard object. The sloping angles of the cuts in the key bump
all lower pins
upward. However, the force exerted on the lower pins is immediately
transmitted to the
upper pins and they fly up, pushing the springs above them, leaving the lower
pins in place.
This action moves the upper pins out of the shear line for a moment, and that
is the moment
the operator turns the key and opens the lock. See drawing #4.
Clubs have sprung up around the world, where amateur locksmiths compete with
each other
to open various makes of locks by this method, for sport. Once learned, it
takes 5 seconds to
open a lock with a "Bumper Key".
The key has to fit the Keyway of the lock and the Bitting (the actual cuts in
the key) are filed
down to the lowest possible level, known in the trade as Position 9. Hence the
other name
for this technique is known as the 999 Method. See drawing #4.
This method of opening a lock works with almost all makes of common Tumbler
Locks, as
used in homes and post boxes and padlocks, and is now common knowledge. It is
to be
expected that not only sport enthusiasts would use this method. Not only is
the home and
office vulnerable to a break-in - there will be no evidence that forced entry
was used.
Insurance companies may refuse to pay when it is possible that the owner had
left the door
open and thus has contributed to the resulting loss.
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CA 02590676 2007-05-17
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Tumbler Lock Mechanism Improvement to prevent break-in by "Bumper Key"
There are locks produced by industry that are not vulnerable to this
technique, but they are
much more expensive and their numbers used are modest when compared to the
"Standard"
lock used everywhere.
Not only would it be desirable to change the present locking devices so they
would not be
vulnerable to this method of illegal entry, but it would be desirable to leave
evidence that an
attempt has been made to open the lock with a "Bumper Key".
Totally redesigning locks to prevent 'Bumping" would be very costly to the
industry.
The invention here requires only a modest change to the tooling to achieve
both objectives:
1. Prevent 'Key Bumping" as a method to open the lock
2. Prevent removal of the "Bumper Key" when an attempt to use it is made,
thus leaving evidence of attempted break-in.
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Tumbler Lock Mechanism Improvement to prevent break-in by "Bumper Key"
3. Description of prior art
See drawing #1.
A Pin Tumbler lock has in each chamber 2 pin tumblers pressed together by a
spring. There
are 4, or 5, or 6 chambers in line, each one holding 2 pins and a spring. See
Drawing #1.
When no key is inserted, the 2 pins in each chamber are aligned so that the
top pin crosses
the Shear Line (between the cylinder and the housing) and prevents the Plug
(The inner
cylinder which holds the key) from turning. When a key is inserted, it lifts
the lower pin up to
the shear line, pushing the top pin above the shear line. See drawing #2. This
position of the
pins in all chambers permits the plug to turn (drawing #3). All first pins are
cut to a different
length, depending on the depth of the cut in the key at that point. When all
cuts in a key
match the height of the lower pins, all lower pins reach the shear line, the
plug turns and the
lock opens (drawing #3).
The above described principle has been the basis of tumbler lock design for
over 150 years.
Some refinements are made to this design by allowing for Master Keys and
Individual Keys in
the same lock. A Master Key will open many locks, each of which has a
different Individual
key. This is achieved by replacing the top pin with a pair of pins, allowing
for 2 positions of
the key cut to reach the shear line - one position with the lower pin itself
reaching the shear
line, the other, Master Key cut position, allowing the lower plus the middle
pins to remain in
the plug and reach the shear line. Thus 2 keys of different cut are able to
open the same
lock, and the Master Key shares its setting with many locks, while the
Individual Key opens
only its own designated lock.
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CA 02590676 2007-05-17
Tumbler Lock Mechanism Improvement to prevent break-in by "Bumper Key"
4. Summary and description of the invention
The invention consists of adding 2 rows of radially directed additional holes
in the Plug (The
rotating cylinder of the lock), at a 30 angle from the center line in both
directions, and of a
diameter smaller than the regular chambers. See drawing #5. The regular top
pin in each
chamber is replaced by 2 pins: the top one has the lower end of its diameter
reduced to fit
into the added holes drilled at 30 from the centre line in the plug, and a
second pin with
standard diameter below that. The length of both upper pins together is equal
to the total
length of the single top pin it replaced. The angle of 30 is a suggested
position, but is not a
critical factor and may wary by up to 100 up or down.
When a regular key is inserted in the lock, the 2 upper pins are lifted above
the shear line
(See drawing #6) and the lock opens. Note that the middle pins slide over the
additional
holes in the plug as it turns, since their diameter is larger than the
diameter of these
additional holes.
When a "Bumper Key" is inserted to attempt an illegal entry and is hit sharply
with a hard
object, all lower pins feel the sudden upward force exerted on them. The force
is transmitted
up the column of 3 pins and the top pins, being the last in the column, fly up
against the
springs (See drawing #7), permitting the Plug (cylinder) to turn 30 in either
direction, at
which point these top pins fall into the added holes and lock up the cylinder
in that 30
position (See drawing #8). The lock becomes inoperable and the "Bumper Key"
cannot be
extracted, leaving evidence of an attempted break-in.
The middle pin, when the correct key is used, would normally stay above the
shear line and
permit opening of the lock. When the "Bumper Key" is used, that middle pin
remains below
the shear line, in the plug. The upper pin, with its narrower end, fits into
the extra narrower
holes and locks up the plug at 30 .
The 'Bumper key" remains trapped in the plug and cannot be extracted, as it is
held in place
by the two lower pins in the plug.
The description above deals only with one set of pins, but all 4, 5, or 6,
chambers and sets of
pins act in the same fashion. The number of chambers in locks varies between 4
and 6.
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Tumbler Lock Mechanism Improvement to prevent break-in by "Bumper Key"
5. Detailed Description of the Invention
This invention permits the manufacturer of the locks to retain all the tooling
and assembly
devices for the production of the locks.
The only addition in the usual tooling for the production of the plug is the
drilling of the 2 rows
of radially directed holes at 300 in both directions from the centerline.
These holes are 100 Th. Diameter and 200 Th. Deep. (Th. = 1/1000 of an Inch).
The top pin normally placed in each chamber is replaced by 2 pins, whose total
length is
equal to the single pin being replaced.
The upper pin has dimensions as shown in drawings #5 to #8.
The new replacement pins are manufactured from the same materials as the pin
being
replaced - usually brass.
The normal operation of the lock with the aforementioned additions remains the
same as
before the additions suggested by this invention.
When an attempt at illegal entry by means of a "Bumper Key" is made, the added
upper pins
fly up into the chamber, the lock turns up to 30 either side, but then the
springs in the
chambers push these upper pins to drop into the holes in the side of the plug
and prevent
further turning of the plug. The lock does not open and the "Bumper Key"
remains captured
inside the plug as evidence that tampering took place.
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