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How Tumbler Pin Locks Work

Posted by Customer Support , 06 February 2009 · 496 views

How Tumbler Pin Locks Work

The most common type of lock in use today is the pin tumbler cylinder lock. Pin tumblers cylinder locks were invented in 1848 by Linus Yale and he patented his invention. His son Linus Yale, Jr. improved on his father's lock and applied for a second patent in 1861. This type of lock has been in common use for over one hundred and sixty years.

A spring is attached to the driver pin as shown in the picture to put a downward force on the driver pin that holds it tight against the key pin which prevents the plug from being turned and opening the lock unless the correct key is inserted into the keyway. The other end of the plug usually is connected to a cam that retracts the locking bolt from inside the door frame.

The key pins are rounded on the bottom so a key can slide over them when it is inserted into the lock.

If there is no key in the lock or the wrong key is inserted into the lock the misalignment of the driver and key pins will prevent the cylinder plug from turning and the lock will not open. When the correct key is inserted into a lock, the alignment between the key pins and the driver pins changes. This is called the shear line. The shear point is created when the key pushes the pins up until they line up straight in the middle.

When all the pins are aligned at the shear point, the lock plug can turn as shown below retracting the locking bolt and opening the lock.

A master key can be created by adding an extra pin called a spacer pin. This extra pin creates a second set of shear points that are identical to all of the locks that the master key will fit while still being different from the shear point of each individual lock.