by Evan » 14 Sep 2013 15:21
Hi everyone:
The answer to why Gordon's Kaba Micro having only four pins is because of the three possible key pull positions... At each of those positions there have to be properly located upper chambers to allow for the key to be removed... Possible to do that with the offset rows of pins? Yes... But way more complex and expensive to do that in such a tiny housing...
With Kaba dimple locks you will not find a pin inside the lock at each dimple on the key, let's throw out some fancy vocabulary to understand why:
positive locking: the condition brought about when a key cut which is too high forces its tumbler into the locking position. This type of locking does not rely on gravity or spring pressure
positional master keying: a method of master keying typical of certain binary type disc tumbler key-in-knob looks and of magnetic and dimple key cylinders. Of all possible tumbler positions within a cylinder, only a limited number contain active tumblers. The locations of these active tumblers are rotated among all possible positions to generate key changes. Higher level keys must have more cuts or magnets than lower level keys
Kaba dimple keys are basically very complicated looking convenience keys... Just like double-bitted automotive keys which have the same cuts on each side, they can be inserted either way (right side up or upside down) into the locks that they operate and they will function because it has the same bitting groups cut on it twice... With the older Kaba locks like the 8 and 20 the lock is only reading the key in three locations, one row of pins off of each face side of the key and along the "top" edge...
Those Kaba keys are actually "handed" based on holding the key up like it was hanging from a hook and seeing which side of the key has the row of dimples which is longest from the bow of the key, either the right side or left side... "Right" handed keys will not operate "Left" handed locks and vice versa... As the pin chambers in the plugs are machined in different locations... There are "composite" keys which look like target practice because they have all the dimples from a "Left" and a "Right" key all of which are repeated twice... Those "composite" keys are used where maison keyed systems are provided...
So why aren't there pins in every chamber of the lock ? With positional master keying the conventional rules of how locks are keyed go out the window, the "Top Master Key" is the only real key in the system having all the cuts -- every lower level key has some of those cuts replaced with the shallowest #4 cut in a rotating constant pattern where the cylinders for which those change keys should operate have no pin in that chamber of the lock so that the change key with the #4 cut and the TMK which has the real bitting can operate without using master pins... This doesn't seem to make much sense, leaving pins out of a lock makes it possible to make more than one key operate but not allow any of the other keys in the keying system to work by mistake... How is that ?
The concept of positive locking where those shallow #4 cuts on the keys is what makes it work, because when a key which isn't supposed to operate another cylinder is inserted, there is a pin in the chamber in the lock above it which creates positive locking, the pin is pushed up into the bible by the shallow bitting on the unintended key as the only lock(s) which will allow each key to operate it are the ones which have the empty pin chamber(s) in the exact same positions as the #4 cuts on the keys...
Those are the basic rules for the realm in which Kaba dimple locks exist... I hope that what I have explained sheds some light onto how and why those locks operate...
~~ Evan
