Not all cam locks have four slots; some only have two: top and bottom. When you turn the key 90 degrees, the key is not removable from that position. The lock is key retaining. To remove the key, you first have to return the key to the start- ing position. But what would happen if we had a de- clining step key? If each of the cuts from bow to tip is the same or deeper than the previous cut, that means each of the wafers from front to back is the same or taller than the previous wafer. As we be- gin to withdraw the key, the wafers only need to move up and out of the way of the steeples. The lack of a slot may not be enough to prevent a declining step key from being removed. This is a reason for avoiding declining step keys. A Look at the RV Deadbolt Lock Now let’s look at this RV deadbolt lock. There are two cylinders. The one in the handle is an ordinary cam lock, and it’s usually master keyed. This one uses the MK9901 master key, in addition to the us- er’s key. The shell has four slots, so you can remove the key in either of two positions. The cylinder in the corner of the lock body operates the latch bolt. It’s a cam lock with a lazy cam. The shell has three slots instead of two or four. In normal operation of the lock, you only need two slots: top and bottom. This is the neutral position for the lock. To secure the door, you insert the key in the vertical position, rotate 90 degrees coun- terclockwise to the extend position, rotate back to the neutral position and remove the key. The key should not be removable in the extend position. Assuming that the manufacturers do not sell any declining step keys, we should be safe… theoretically. But remember that badly worn automotive key in an old ignition lock. It’s not supposed to pull out in the run position, but it does. We’ll come back to this in a minute. WWW.ALOA.ORG Figure 4. The shell has three slots. As I said, the third slot is not used in the normal operation of the lock. Its pur- pose is removing and replacing the plug. The plug uses a retainer in the 6th posi- tion, which is accessible from inside the keyway. To prevent removal of the plug while the door is secured (which would defeat the purpose of having a lock at all), the retainer can’t slide forward us- ing the top and bottom slots. It needs the third slot to slide forward. This allows the manufacturer to sell replacement plugs and keys to any customers who want to rekey their own lock. The new plug ar- rives with two black keys and a special blue key that’s longer than the operating key, designed to trip the retainer. The procedure is: Use the old key to turn the old plug to the retract position, remove the key in that position, insert the blue key, pull out the old plug, put the blue key into the new plug, insert the new plug into the lock, turn it to the neutral position, remove the blue key and test the lock with the new black key. It seems to me that this procedure is rather complicated for the customer to be expected to “do it yourself.” It would be much simpler if the retainer was only accessible from the back side of the lock and they simply told customers that to replace the plug, you have to remove the lock from the door, depress the retainer, slide out the old plug, slide in the new one and return the lock to the door. In my opinion, this procedure isn’t much more difficult, and it would eliminate the need for the third slot entirely. APRIL 2021 KEYNOTES 19
