by rphillips52 » 31 May 2012 15:34
Curtain
I might just clarify the definition of curtain.
A curtain is a shield in many types of lever lock which, when the tey turns, is turned to close the keyhole. This obstruction is intended to prevent the insertion of any more instruments for picking, as soon as any key-like instrument turns. Alone, it was not an effective obstacle.
Some locks had been fitted with a barrel, a slotted tube which surrounds the key stem, and frustrates the independent movement of the separate steps of the original Hobbs-type 2-in-1 pick.
When the barrel and curtain were fixed together they became a more effective obstacle. The initial turning of any implement closes the keyhole, and the barrel frustrates using separate key steps.
Usually, the curtain was fitted on the side which would be outside and so most at risk of attack. Many cabinet and safe loccks were fitted with barrel-and-curtain in the past.
Subsequently, Hobbs fitted a bolt-thrower to the barrel of some locks to prevent a worn key leaving a bolt half-shot; it also allows a small key to achieve a longer throw. In many modern two-sided locks, the thrower is integral with the curtain. This allows an increase in the number of differs possible, as a high-lift lever is no longer essential to allow a full-height step to operate the bolt when the key is inserted from either side. The bolt step may now be any height.
The term 'barrel-and-curtain' is now commonly abbreviated to 'curtain'.
Picks have now been designed to defeat the barrel.
