Several design features in wafer locks can aid the fitting of keys without disassembly. With very few exceptions, all wafer lock plugs are made of die-cast material. In order to assure 100 percent compatibility when housing and plug parts are assembled, a tolerance gap is purposely designed into each part.
Popular utility lock manufacturers typically used .015" depth increments. As example, the height of most cam lock keys is approximately .250". .250 represents a "1" cut.T next depth of cut, ("2"), would be .235", a difference of .015". When tolerance gaps are taken into account, a wafer lock may be able to be easily operated by several different key combinations. As example, a key with cuts of 13131 may operate a lock even though the lock was set to a combination of 12121.
In an effort to prevent widespread interchanges, manufacturers often use key codes having two increments between cuts. In the example above, the manufacturers would only use cuts of 1, 3 or 5 and not use any 2 or 4 depths in their code series. Each cut would be two numbers, or .030" apart and much less likely to allow interchanges. Utility lock companies such as Fort Lock and Pundra, plus vehicles such as older Honda cars often use this three depth principle. Honda cycles using the HD74 and HD75 keyways and Hudson locks using depths of 1, X & 4 are other current examples.
The design of wafers can also be an aid in visual key fitting. While there are a few unusual wafer designs, most wafers are rectangular in shape and contain a cutout (window) section which allows the key to pass through (photo 1). The placement of the window depends on the depth of cut which will operate that tumbler. When the window is placed very high in the tumbler, a very high cut is required on the key in order to lift the tumbler into the unlocked position. When the window is placed very low in the tumbler, a deep cut is required on the key in order to align the tumbler at the unlocked position (photo 2).
With few exceptions (such as BMW and Mercedes sidewinders), spring pressure pushes the bottom of the wafer tumblers level within the spline groove. As a result, the window in each wafer tumbler comes to rest in the same general up and down contour as the cuts on the operating key. By use of a scope, or even with good eyesight, the general up and down contour of the key can usually be determined by looking into the keyway.
Preparation is an important part of success. First, determine what blank fits into the lock. Second, try to determine the lock manufacturer. While hand filing a key is always possible, wafers can often be distorted by filing and impressioning. Use of a code machine can save time, energy and the cost of a new lock if the wafer tumblers become unusable.
If you know the proper blank and your code machine is ready, key fitting can often be accomplished in a few short minutes. Wafer locks with five or six wafers can usually be easily picked open. Once the lock is picked, turn the plug approximately 1/8 turn. The wafers are now held in a rigid position. Using a diamond-shaped or ball-shaped pick, insert the pick to the far end of the plug. Exert a slight pressure against the wafer tumblers and slowly pull the pick out of the plug.
As the pick is retracted, it will 'ride' up and down across the rigid tumblers. Repeat the pick reading several times and observe the movements of the pick until you are sure of the up and down contour. Knowing the manufacturer will help you in knowing if there are 3, 4 or 5 depths being used. Then use your code machine to originate a key. Make higher cuts for any spaces you are not sure of.
If the key does not immediately turn, resort to impressioning. Insert the key into the lock and exert a light turning pressure. With light turning pressure applied, lift up and down on the key to obtain impressioning marks. Using your code machine, make the cuts one depth number deeper wherever a mark is showing. With any luck your key should operate with very few trips to the code machine.
A second key fitting method is by sight. Several companies make specialized scopes for looking into the keyway. An alternative method is a new miniature camera system by Keedex which can copy a magnified view of the tumbler positions onto a computer screen. As already described, wafer tumblers come to rest in the same general contour as the cuts on an operating key. The scope or camera will allow you to view each tumbler and determine the general height. Once the contour is determined, a code machine can be used to originate a key.
Always look for the easiest way to complete your job. Many new desk locks use a removable core system. If the lock is designed for plug removal, it must first be picked to the unlocked position. With few exceptions, the retainer is located at the rear of the plug. Insert a straight pick to the rear of the plug and raise the retainer for plug removal.
If all else fails then impressioning is the answer. Speed your impressioning by studying the tumbler contour first. You will then at least know what your final key cuts should look like. Use as little force as possible during impressioning. Some import locks use very thin wafer material and undue turning force can quickly twist a rectangular tumbler into an unusable 'S' shape. Even if you make a smooth operating key by impressioning, it is best to make the final customer key with a code machine. Correct spacing can be lost to the point where wafers may be not resting on the level valley of the hand filed cut. While the impressioned key operates well, it may be impossible to make duplicates of the key in the future.
While this article centered on wafer lock, many of the procedures can also be used for pin tumbler locks. As example, Ford pin tumbler locks can often be easily picked to an unlocked position. A ball pick can then be used to determine the contour and the key cuts can be made on a code machine. Once the general contour is completed, impression marks will be readily identifiable and a operating key can be completed in minutes.