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What is a Master Key System?
A Master Key System is a mathematically based system of unique number values for pinning locks. Each pattern represents the cuts in a key that will open any lock keyed to that pattern. The system also has a Master Key Pattern that when cut as a key will open all the unique patterns in the system, so no matter which pattern is used, the Master Key will also open that lock. An algorithm for creating a master key system will produce every possible pattern, even though every (Change) pattern may not be viable, it will exist within the master key system. Whether a pattern is used is up to the locksmith designing or pinning the locks.
Designing a master key system begins with the Master Key, from there a standard master key system uses a two point difference for the progression of pin patterns. Pin patterns and key patterns are the same value. A key cut with a 15343 will open a lock keyed to pins 15343. A master key 31525 will open a lock that is master keyed to 15343 and 31525. In order to pin such a lock, one must calculate the bottom pins, and the master pins needed. First we use all the lowest pins in both patterns, 11323 then we calculate the difference between the lowest pin and the tallest pin in each position, we end up with 24222 for our master pins.
To calculate a complete system we start with the Master Key Cuts, then using the two point difference that is the standard, we calculate first the lowest possible pin in each position of the pattern. This is the initial change pattern for the The rule is that if a pin is used in the master, it cannot be used in any of the pinning patterns. We also have to determine the smallest and largest pin sizes we will be using. Some lock companies use very fine tolerances which result in the ability to have a large range of cut depths, locks that have larger tolerances have to restrict the number of cut depths because when the lock begins to wear out, the wrong key can be forced to open a lock. When new locks are keyed to 15631 and 15632 they are exclusive. The key for one will not open the lock of the other, but after years of use, the keys wears down, the pins in the lock wear down, the lock cylinder wears down, the lock cylinder housing wears down and each of these keys can end up opening the other lock, by wiggling the key, or forcing the key to turn, where the 1 pin on the key is forced to become close to a 2 and will then open the lock, with effort.
This is why the standard progression of a master key system is a two point progression. This ensures that every lock pattern has at least one cut that is two depths different from the patterns around it and throughout the system. Then with time, as the keys, locks and cylinders wear down, they are unlikely to be able to be forced by a neighbor with the wrong key. As the locksmith doing the work on Master Key Systems it is important that you do not implement a system that reduces security for the end user, as you could be liable depending on the laws in your state. Turning a system of min/max difference of 6 into one using 9 depths and cuts instead will severely limit the life of the security of the locks.
This is of course relative, since you can find locks made from very inexpensive materials, these locks are more likely to wear out quickly, allowing the wrong keys to open the lock. On the other hand there are lock manufacturers that use very high quality metal, the pins are made of nickel-silver instead of soft brass, the cylinders and housing have tolerances of .002 inches, and even after many years of abuse will still only open with the proper keys.
Because each pattern in the system is unique, and because no Change pattern has a pin that matches a master pin, every lock keyed to a master key system will open with a number of what are referred to as sub-masters. In a properly defined master key system all the sub masters are listed as well. There are sub masters that will open 25% of the change patterns, there are sub masters that will open only 4 change patterns, these sub masters can all be represented in a properly laid out master key system, allowing a good locksmith to use the various levels of master keys to design a fully integrated and departmentalized master key system, where department heads carry a single key, in most cases, to open every lock in their department but not any that they should not have access to. Their underlings in turn should normally only need one key to open the areas that they are responsible for. When you take advantage of the entire master key system, you can easily maintain an institution or facility by being able to rekey only areas affected by lost keys, and not the entire master key system, unless the lost key is a Top Level Master Key, then of course you would rekey the entire facility.
Gerald Howell, Lead Locksmith for The Key Wizard
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