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You are here: Home > For The Home > All Door Hardware > Lock Bumping

Lock Bumping

Lock bumping has recently gotten a lot of news coverage on local news stations as well as social video networks such as You Tube.  What is scary to many people is that any motivated thief can learn how to bump open a lock with a little practice and instuctions from the various lock bumping videos on the internet.  Bump keys are even sold online to locksmiths, but almost anyone can order one.  Owning and using a bump key with criminal intent is illegal in most communities.  Lock bumping is a locksmiths technique to open locks, which, according to the Associated Lockmiths Of America (ALOA), has been one method used by locksmiths for the past 75 years for which there is a key or cylinder malfunction. By using a key that fits in a lock, but does not necessarily open the same lock, and filing the grooves in the key to their maximum depth, one can open most pin tumbler locks as well as dimple locks, whether they are 'pin in pin' or not.  One does not necessarly have to obtain an uncut key blank to make a bump key.  Any key that fits that particular lock can be made into a bump key. By appling a little torque to the bump key and tapping it with a screwdrive or hammer, one can successfully bump a lock open. But before we get too far into the subject of lock bumping, lets first take a look at how a typical residential lock works.

Network News Report On Lock Bumping And Lock Jaw

Why Publish This Information?

We feel that since this infomation is readily available to thieves and criminals who can easily seek it out on the internet, it should also be made available to the general public so they can have enough information to take the necessary steps to protect themselves. 

How Pin Tumbler Locks Work

To fully understand the techique of lock bumping, one must first understand how pin tumbler locks work.  In 1848, inventor Linus Yale, Senior, patented a cylindrical pin tumbler lock, which was improved and patented again in 1861 by his son Linus Yale, Junior.

A pin tumbler lock consists of an outer casing, or "shell" ( green ) into which a cylindrical hole has been drilled and into which a "plug" ( yellow ) is inserted.  The shell also has a series vertical holes, called the "bore" or "chamber" drilled into it into which the "tumblers" are ( red and blue ) are inserted. Tumblers are comprised "key pins" ( red ) and "driver pins" ( blue). Driver pins have a spring on one end of them to create a downward load on the pin.

Lock Shell ( green ), with Plug ( yellow ),
Driver Pins ( blue ) & Key Pins ( Red )
Without the key inserted, the driver pins
are pushed down, thus preventing the plug
from turning in the shell.

The plug has a straight slot called the keyway at one end to allow the key to enter the plug, the other end might have a lever or cam which activates a mechanism to retract a locking bolt.  Five or six holes are drilled vertically into the plug.  Key pins ( red ) of different length are then inserted into these holes. The drive pins and key pins are collectively referred to as the "pin stack". The key pins are rounded on one end to allow a key to easily slide over them when entering the lock.

When the proper key is inserted, the
point at which the driver pins ( blue ),
meet the key pins ( red ) aligns with the
shear line ( that point at which the
plug ( yellow ) and shell ( green )
meet. )

The whole "key" to opening a pin tumbler lock is dependent upon the alignment of the shell, plug, the driver pin ( blue ), and a "key pin" ( red ), aligning. The point at which the plug and shell meet is called the "shear point".  When the shell and plug are assembled, the springs push the driver pins down into the plug. When the key is inserted into the keyway, the teeth in the key will slide under the rounded ends of the key plugs, thereby forcing the key plugs and the driver plugs to rise up so the point at which the top of the key plug meets the driver plug also aligns with the shear point.   The key is then turned and the plug rotates which opens the lock.  Locks that also have master keys, such as those used in an apartment building, or office building,  will have an extra driver pin called a "spacer pin".  The spacer pin creates a second set of shear points that are identical to all of the locks that the master key will fit, yet is different from shear point for that particular lock.

When the bottom of the driver pins ( blue )
meet the top of the key pins ( red ) align
with the shear line

Why Lock Bumping Works

Most of us are familiar with Newton's third law, which says that for every action, there is an equal and opposite reaction.  The best device that represents Newton's law as it applies to lock bumping is probably Newton's Cradle, pictured below. As you can see from the photo, when one ball on the far end of the cradle swings into it's neighbor, energy is transferred to the last ball in the cradle.

Lock bumping and lock picking guns work on a similar principle. When the bump key is rapped by a small hammer, energy is transferred from the bump key to the key pins, which in turn transfer energy to the drive pins. When the pin stack aligns properly with the shear point while the bump key has torque applied to it and is being tapped with the hammer, the lock will open.

Problems With Lock Bumping

It is fairly easy to damage the bump key or lock by bumping it.  Bumping can also cause deformation of the lock, thus causing the key to get stuck in the lock it is trying to open.

Preventing Lock Bumping

As strange as it seems,  some of the more expensive locks are easier to bump.  One of the reasons is that the more expensive locks have more precise machining tolerances, which allow for smoother operation of the pin stack and rotation of the plug. Also, more expensive locks are usually made from harder metal, which cause less deformations when the bump key is hit. Some expensive  locks also have narrower keyways, but in reality some bump keys do not require more room than normal keys and the smoother the lock is, the more efficiently the bumping force works. 

Much of the information for this article was derived from a white paper published in 2005 by Barry Wels & Rop Gonggrijp of TOOOL titled Bumping Locks, as well as Wikipedia.

Some locks have spool or mushroom security pins, which can generally make bumping more difficult but not impossible.

We highly recommend the use of bump proof locks, such as the Lock Jaw.

Permission is granted to copy distribute and or modify the drawings of lock shells and the photo of Newton's Cradle on this page under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.

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