Elastic deformation

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Elastic Deformation

The interesting events of lock picking happen over distances measured in thousandths of an inch. Over such short distances, metals behave like springs. Very little force is necessary to deflect a piece metal over those distances, and when the force is removed, the metal will spring back to its original position.

Deformation can be used to your advantage if you want to force several pins to bind at once. For example, picking a lock with pins that prefer to set from front to back is slow because the pins set one at a time. This is particularly true if you only apply pressure as the pick is drawn out of the lock. Each pass of the pick will only set the frontmost pin that is binding. Numerous passes are required to set all the pins. If the preference for setting is not very strong (i.e., the axis of the plug holes is only slightly skewed from the plug's center line), then you can cause additional pins to bind by applying extra torque. Basically, the torque puts a twist in the plug that causes the front of the plug to be deflected further than the back of the plug. With light torque, the back of the plug stays in its initial position, but with medium to heavy torque, the front pin columns bend enough to allow the back of the plug to rotate and thus cause the back pins to bind. With the extra torque, a single stroke of the pick can set several pins, and the lock can be opened quickly. Too much torque causes its own problems.

When the torque is large, the front pins and plug holes can be deformed enough to prevent the pins from setting correctly. In particular, the first pin tends to false set low. Excess torque can deform the bottom of the driver pin and prevent the key pin from reaching the sheer line. This situation can be recognized by the lack of give in the first pin. Correctly set pins feel springy if they are pressed down slightly. A falsely set pin lacks this springiness. The solution is to press down hard on the firstpin. You may want to reduce the torque slightly, but if you reduce torque too much then other pins will unset as the first pin is being depressed.

It is also possible to deform the top of the key pin. The key pin is scissored between the plug and the hull and stays fixed. When this happens, the pin is said to be false set high.