To pick a lock with modified drivers, use a lighter torque and heaveier pressure. you want to error on the side of pushing the key pins too far into the hull. In fact, another way to pick these locks is to use the flat side of your pick to push the pins up all the way, and apply very heavy torque to hold them there. Use a scrubbing action to vibrate the key pins while you slowly reduce the torque. Reducing the torque reduces the binding friction on the pins. The vibration and spinrg force cause the key pins to slide down to the sheer line.

The key to picking locks with modified drivers is rocognizing incorrectly set pins. A mushroom driver set on its lip will not have the springy give of a correctly set driver. Practive recognizing the difference.

Master Keys

Many applications require keys that open only a single lock and keys that open a group of locks. the keys that open a single lock are called change keys and the keys that open multiple locks are  called master keys. To allow both the change key and the master key to open the same lock, a locksmith adds an extra pin called a spacer to some of the pin columns. See Figure 9.8. The effect of the spacer is to create two gaps in the pin column that could be lined up with the sheer line. Usually the change key aligns the top of the spacer with the sheer line, and the master key aligns the bottom of the spacer with the sheer line (the idea is to prevent people from filing down a change key to get a master key.) In either case the plug is free to rotate.

In general, spacers make a lock easier to pick. They increase the number of opportunities to set each pin, and they make it more likely that the lock can by opened by setting all the pins at about the same height. In most cases only two or three positions will have spacers. You can recognize a position with a spacer by the two clicks you feel when the pin is pushed down. If the spacer has a smaller diameter than the driver and key pins, then you will feel a wide springy region because the spacer will not bind as it passes through the sheer line. It is more common for the spacer to be larger than the driver pin. You can recognize this by an increase in friction when the spacer passes through the sheer line. Since the spacer is larger than the driver pin, it will also catch better on the plug. If you push the spacer further into the hull, you will feel a strong click when the bottom of the spacer clears the sheer line.

Thin spacers can cause serious problems. If you apply heavy torque and the plug has beveled holes, the spacer can twist and jam at the sheer line. It is also possible for the spacer to fall into the keyway if the plug is rotated 180 degrees. See section 9.11 for the solution to this problem.

Figure 9.7: Mushroom, spool, and serrated driver pins

Figure 9.8: Spacer pins for master keying

Driver or Spacer Enters Keyway

Figure 9.9 shows how a spacer or driver pin can enter the keyway when the plug is rotated 180 degrees. You can prevent this by placing the flat side of your pick in the bottom of the keyway before you turn the plug too far. If a spacer or driver does enter the keyway and prevent you from turning the plug, use the flat side of you pick to push the spacer back into the hull. You may need to use the torque wrench to relieve any sheer force that is binding the spacer or driver. If that doesn't work try raking over the drivers with the pointed side of your pick. If a spacer falls into the keyway completely, the only option is to remove it. A hook shaped piece of spring steel works well for this, though a bent paperclip will work just as well unless the spacer becomes wedged.

Figure 9.9: Spacer or driver can enter keyway

Vibration Picking

Vibration picking works by creating a large gap between the key and driver pins. The underlying principle is familar to anyone who has played pool. When the queue ball strikes another ball squarely, the queue ball stops and the other ball heads off with the same speed and direction as the queue ball. Now imagine a device that kicsk the tips of all the key pins. The key pins would transfer their momentum to the driver pins which would fly up into the hull. If you are applying a light torque when this happens, the plug will rotate when all the drivers are above the sheer line.

Disk Tumblers

The inexpensive locks found on desks use metal disks instead of pins. Figure 9.10 shows the basic workings of these locks. the disks have the same outline but differ in the placement of the rectangular cut.

These locks are aesy to pick with the right tools. Because the disks are placed close together a half-round pick works better than a half-diamond pick (see Figure A.1}. you may also need a torque wrench with a narrower head. Use moderate to heavy torque.

Figure 9.10: Workings of a disk tumbler lock

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