Bypass keying, a masterkeying specialty, is a form of controlled cross keying, primarily used where there is an office suite with an external door and a number of offices within that suite. The front exterior door is operated by any of the interior door keys. This allows users to carry a minimum...
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Bypass keying, a masterkeying specialty, is a form of controlled cross keying, primarily used where there is an office suite with an external door and a number of offices within that suite. The front exterior door is operated by any of the interior door keys. This allows users to carry a minimum amount of keys to get into their space and may avoid confusion as to which key to use.
The basic principle works at the key bitting array stage of masterkeying. I will work one example to show how it operates.
Our example suite is a submaster of the overall building key system. If it is the latter, then you need to break it down to the submaster level and isolate the bittings that you will be using for this submaster and work with that block only.
As an example, the key bitting array is:
Top master: 105494
Submaster (usually the page master): 321494
Or block master if a smaller system: 321490
I will work with the block master for simplicity in explanation. See Chart 1 for a page of a progression array.
Start at the vary chamber (fourth chamber). The progression 0-2-6-8 for each small column-block determines the bitting that will work this particular bypass cylinder. How large a bypass will you need? One will need to size the overall number of keys meant to work this bypass, taking into account the number of rooms that are necessary for a rekeying. In my example there are 7 spaces in the suite, and some future capacity needs to be built in for future rekeying. The actual number of bittings used is determined by the keying that is used here, determined in advance by the keying meeting with the customer.
Normally, the most varied chamber is what is called the “stack.” In this case, it is the fourth chamber in the progression array that changes with every bitting. So in this example the stack is 0-2-4-6-8, and when mastered or “stacked” with the 0 bottom pin, and four two-step master pins, topped off with a top pin and spring, this chamber will work with keys cut to 0, 2, 4, 6, or 8. Even if all the rest of the cuts on the key remain constant, you will still have five possible keys operating this chamber, one master key and four change keys.
To increase the number of changes that can be applied to the bypass, move to the next most varied chamber in the progression. In this case, the next small column block in cue, which is the fifth chamber. The fifth chamber changes with every four-bitting block. This could be mastered for another four changes. This will then result in a total of 8 changes. As this continues, adding another master pin on top of the last will add four changes each time it is mastered, until it reaches a natural break point.
One break point where the limit could be hit is when the block master is exhausted. This will produce two fully stacked chambers. So using progression and probability math, this would be 4 times 4 = 16 changes that could be applied to the bypass. It is usually a good idea to set the bypass at the block master limit so that there is available capacity. But it could be set to be more selective too, that is to set the bittings in one small column block to be bypassed (a full stack and one master pin; four usable bittings), or two small column blocks (a full stack and two master pins stacked on each other; for 8 usable bittings), or even three small column blocks (a full stack and 3 master pins stacked on each other; for 12 usable bittings), leaving the rest in reserve, so long as those bittings are held in reserve too. This way one will selectively choose which bittings will operate a particular bypass.
Lastly as the most used option, we can supply all four small column blocks (a full stack in the 4th chamber and a second full stack in the 5th chamber). Thus we have isolated an entire block of this page master for this bypass to the intended suite. This should be an appropriate size submaster key system for this suite, with spares for rekeying and a suite master. Although I have set aside the entire block for bypass use, I did not lose any bittings for use in this submaster system. The bittings themselves can still be used for their intended rooms; however I did enable that bitting’s bypass capability, and if I so choose to pin it into the suite door, to activate that bitting’s bypass function for use, I can do so without impacting the office doors.
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