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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.

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