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Pin Diameter
Some lock
manufacturers (e.g.,
Yale)
bevel the
edges of the plug holes and/or
round off the
ends of the
key pins. This tends to
reduce the
wear on the lock and it can both
help and hinder lock picking. You can recognize a lock with these features by the large
give in set pins. That is, the
distance between the height at which the
driver pin catches on the edge of the plug hole and the
height at which the key pin hits the hull is larger (sometimes as large as a
sixteenth of an inch) when the plug holes are beveled or the pins are rounded. While the
key pin is
moving between those two heights, the only
resistance to
motion will be the force of the spring. There won't be any
binding friction. This corresponds to the
dip in the force graph shown in Figure 5.1.
A lock with beveled
plug holes requires more
scrubbing to open than a lock without
beveled holes because the driver pins set on the
bevel instead of setting on the top of the plug. The plug will not turn if one of the
drivers is caught on a
bevel. The key pin must be scrubbed again to
push the driver pin up and off the bevel. The
driver is resting on the bevel, and the bottom
plate has moved enough to
allow the right driver to bind. After the right driver pin sets, the bottom plate slides further to the right and noe the left driver pin is scissored between the bevel and the top plate. It is caught on the bevel. To open the
lock, the left driver pin must be pushed up above the bevel. Once that driver is free, the
bottom plate can
slide and the righ driver may
bind on its bevel.
If you
encounter a lock with beveled plug holes, and all the pins
appear to be set but the lock is not
opening, you should reduce
torque and continue
scrubbing over the pins. The reduced
torque will make it easier to push the drivers off the
bevels. If pins
unset when you reduce the torque, try
increasing the torque and the
picking pressure. The problem with increasing the force is that you may
jam some key pins into the hull.