Locksmiths are often called out to rekey areas where an existing master key system is in place. Many times records relating to these systems are outdated, unclear, or incomplete. When starting a new master key system is out of the question, it is up to the locksmith to either pass on the job...
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Locksmiths are often called out to rekey areas where an existing master key system is in place. Many times records relating to these systems are outdated, unclear, or incomplete.
When starting a new master key system is out of the question, it is up to the locksmith to either pass on the job or continue using it. Developing new sub-master keys, like floor masters, can be challenging but not impossible.
This article will cover two methods that can be applied to develop sub-master keys within an existing master key system. The first is a traditional method and the second is a “guerilla” approach.
Floor Master Key
Multiple-story buildings usually are masterkeyed so that there is a sub-master key for each floor, that is a key that can access all areas of the floor.
Floor master keys usually have between two to four cuts in common with the top master key. When dealing with a two-progression system, two cuts in common yield 16 change keys; three cuts in common yield 64 change keys; and four cuts in common yield 256 change keys.
The floor master keys that service high-rises (buildings with greater than six floors) traditionally have three cuts in common with the top master key as there are usually less than 64 change keys needed.
Some buildings having less than six floors have many hundreds of areas needing to be individually keyed and therefore the floor master keys would have four or five cuts in common with the top master key.
In Figure 1, the relationship of the number of floor masters to change keys is relative to the total number of chambers and how many chambers are dedicated to floor master activity.
Developing New Keys in the Existing System
It is necessary to develop a scenario that can best demonstrate the differences in the two mentioned methods used to work and develop floor master keys in an existing system.
In this example, a locksmith is called out to rekey several areas in a three-story building. There are several areas on the second floor to rekey. The third floor master key has been lost, so a new master key has to be generated and all areas on the third floor must be rekeyed.
There are no records, but there are copies of each master key and change key, along with a copy of the top master key (TMK).
The first task at hand is to develop a key bitting array and recreate enough records so that the requested rekey will be accomplished without having to repeat existing key bitting combinations.
Figure 2 is a blank “key bitting array” form. It will be used to generate key combinations once it has been completely filled out.
Use a key gauge or dial calipers to measure the depths of each key cut.
First, make sure the cuts of the furnished keys are within factory specifications. If they are out of tolerance you will not be able to get an accurate read when determining the key combinations.
If the keys are out of spec, you can take an extra lock cylinder and experiment with every chamber by dropping in different pins until you determine what the cuts should be.
If the keys are within spec, continue to determine the key combination for each key by either using the gauge or dial caliper.
For the example, the furnished top master key is determined to be: 501892. The first; second; and third floor masters respectively are determined to be: 701810, 701870 and 701850.
In Figure 3, the cuts of the TMK and the known floor master keys are entered (in black).
The existing change keys from the first floor are determined. All first floor change keys have the first, fifth, and sixth cuts in common with the first floor master: 7 _ _ _ 1 0. The second cut was always an 8.
The third cuts varied as either: 3, 5, 7, or 9.
The fourth cuts varied as either: 4, 6, 0, or 2.
In Figure 04, these cuts are recorded (in black) in the KBA.
All second floor change keys were gauged and the first, fifth, and sixth cuts were similar to the second floor master: 7 _ _ _ 7 0. The second cut was either an 8 or 4, and like the change cuts from the first floor the third and fourth cuts varied the same.
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