Developing Floor Master Keys Within Existing Master Key Systems

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 Many times records relating to these systems are outdated, unclear, or incomplete.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 Many times records relating to these systems are outdated, unclear, or incomplete.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).


Traditional Method

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.

In Figure 5, these cuts are recorded (in black). The cut entered was a 4 in the second column.

After examining third floor change keys, there was nothing new to add to the KBA but all third floor change keys had the first, fifth, and sixth cuts in common with the third floor master: 7 _ _ _ 5 0.

At this point, all keys have been either gauged or callipered.

The customer has verified that there were no other types of keys used.

The empty cells in the KBA can be filled in and used to develop key combinations that were never used and therefore safe to use.

The rest of the cells in the KBA will be filled in with a red marker to later identify what was added. The numbers will be select using proper master key procedures. Each column in a two-progression bitting array will use either the subset of numbers: {0,2,4,6,8} or {1,3,5,7,9}.

In Figure 6, the rest of the KBA is filled in. The KBA is almost completed all that is needed is to enter the sequence of progression. This is important as it shows which column will progress first.

When reviewing the change keys for each floor, it looked like the second, third, and fourth cuts differed and was used to generate the changes under the floor master. Two cuts in the second column were filled in as new. Because these columns are used to generate change keys, they were designated as: 3, 1, and 2 sequences.

It is noted that the cut that distinguished the difference between floor masters was in the fifth position; therefore that column will receive a number 4 sequence.

The remaining columns (first and sixth) will be designated either 5 or 6. There isn't much that can be determined to their original intent so the columns will be arbitrarily designated 5 and 6 (rather than 6 and 5).

The sequence will be entered (in red) into the KBA as: 5 3 1 2 4 6

Getting back to the first part of the request, rekeying several areas on the second floor, the completed KBA can be useful to obtain “fresh” key combinations that have never been used.

All second floor change keys will have the first, fifth, and sixth cuts in common with the second floor master: 701870. To guarantee that change keys have never been used, each change key generated must have at least one “red” cut from the second column.

In Figure 8, all the new key bittings are listed. Note they make use of the red numbers in the second column of the KBA.

The second part of the request is to generate a new master key for the third floor and to rekey all areas on the third floor. The first, second and third floor masters are: 701810, 701870, and 701850. The next key in progression and one that uses a new (in red) cut is: 701830.

To generate more floor masters, progress keys in the next sequential column (sequence 5). That is the first column. Figure 9 progresses other possible floor masters using this column in the KBA.

This method gets the job done but gauging keys can be tedious and time-intensive.


“Guerilla” Method

The method is called “guerilla” because it is unconventional, designed to get maximum results from minimum resources. All that is needed is the TMK.

Twenty-four “diagnostic” keys are cut based upon the key bitting of the TMK: 501892. The diagnostic keys are grouped into six sets; one set for each pin stack in the lock cylinder. Each set includes four keys; each key tests a cut in a chamber.

For example, the first cut of the TMK is 5. Standard master key practice dictates that if a 5 is used as a TMK cut, the other cuts in that position must be either: 1, 3, 7, 9. Each of the keys in the first set of diagnostic keys will have all cuts in common with the TMK except for the first cut.

The cuts of each key in the first set of diagnostic keys are: 701892, 101892, 301892, and 901892.

Each key in the first set will be stamped with two numbers: the first is a 1 representing the chamber it is used for and the second the change cut for which it is testing. The keys are in the first set would relatively be stamped: 17, 11, 13, and 19.

Note: One of the keys in the set (19) has a key bitting of 901892. It isn't possible to cut this key using a standard cutter. Be prepared to fit your code machines with a special cutter designed to overcome the normal “safety factor.”

Figure 10 demonstrates how to develop diagnostic keys.


The advantages of diagnostic keys are:

1. The keys do not have to be prepared in the field.

2. The keys take out all the guess work as to how a cylinder is keyed

3. The keys will be used later on for other services.

4. The time allotted to cutting these keys is predictable, taking the guesswork out of how to bill for them.


\Once the keys are cut, the process involves walking the floors and trying the keys in the locks. One key in a set will turn the cylinder, thus revealing the change cut in that position. This part of the method can be carried out by a layman since all that is being recorded is cuts that turn the cylinder.

As added value, the keys will reveal when a chamber is empty, master keyed, void of master wafers, loaded with extra master wafers, or defective.

Once all cylinders have been evaluated, a more precise understanding of how the floors are keyed is available.

Instead of just reverse-engineering the KBA to determine new change and master keys, each key that operates a cylinder can be matched to the lock.

The processes are the same in regards to developing a complete KBA. Both processes take about the same time. The guerilla method yields all information and does a more thorough job.

Another advantage is how the method is perceived to the customer. Checking each lock with a system the customer understands is preferable.

Many times locksmiths will turn down requests because of the condition that the existing system be left intact. The customer should be willing to invest the time for the locksmith to properly research the system to make sure that continuance is viable.

Locksmiths can better serve their customers by learning different methods on how to reverse engineer the KBA and recreate missing master key records.