Lever

Lever

A lever (or lever tumbler) is a lock design that uses flat pieces of metal (also known as levers) and a bolt as locking components. In most designs, the position of the levers prevents the bolt from retracting. When positioned properly, a slot cut in the lever allows the bolt to retract. Lever locks are historically one of the most popular lock designs, but use has dwindled as less expensive pin-tumbler locks gained popularity. Lever locks are popular in Europe (specifically the UK) as residential and commercial door locks and on safes. Safe-deposit boxes in banks around the world use lever designs almost exclusively.

History

One of the first recognized lever lock designs were the Banbury lock created by the turn of the 18th century. This design did not use fences and gates like later lever locks but rather a simple hinged lever that the key had to lift out of the way in order for the bolt to retract. Security were still provided by traditional wards in the keyway.

Barron lock

In 1778 Robert Barron patented the first true lever lock which used fences and gates to provide security. The levers utilized a technique called double action in order to provide increased security. This technique is still in use to this day and is requires that individual levers be lifted to a precise height at which the fences can pass through the gate. Overlifting a lever would cause it to block the fence, whereas older locks' levers could just be lifted to any height as long as they cleared the obstacles.

Chubb lock

In 1827 the Chubb brothers, Charles and Jeremiah patented a new lock design based on Barron's work but with a twist; they reversed the placement of the fence and gates. The fence were now attached to the bolt and the levers contained the gates. This is the design still in use today in many locks. They also added a device called the detector, an extra lever that when triggered by overlifting one of the main levers would lock the bolt permanently and work as an indication of tampering. The detector could only be reset with a special key. The company added another security measure in 1837 to their locks that still sees use today: serrations on the gate levers to cause them to jam up if lifted improperly. A further refinement was patented 1883 by Chubbs to prevent decoding of their locks. This was a simple rotating barrel that closed off the keyway when the key was turned.

Tucker and Reeves

In 1851 a new design surfaced with a bolt that was not rigidly fixed but could shift in one end. This invention was patented by Tucker and Reeves to thwart picking attempts involving putting back pressure on the bolt. The shifting bolt made it harder to feel the gates inside the lock as it shifted. Two years later the design was refined to include a rotating barrel that prevented the bolt to move at all until a key was inserted.

Parsons lock

In 1832 the Parsons lock was created. This new design had seven levers that were symmetrical and pivoted around their midpoint whereas traditional levers are usually hinged at one endpoint. The key lifted the levers at one end, and the bolt had notches at both ends. Overlifting any lever would cause it to engage the notch in the bolt and lock it at that end even if the other end had cleared the bolt.

Principles of Operation

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Vulnerabilities

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See also

• Lock
• Key
• Lockpicking

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