Although this is a Chubb detent lock (circa September 1890), the lock was actually designed and patented by Gibbons on 18th May 1853, albeit in a slightly different form. The design is such that all the levers have to be lifted to the correct position simultaneously, before the bolt comes into full contact with the levers.
Chubbs made a number of different versions of this lock, after they dropped the detector from their safe lock design in favour of a more explosive resistant design. The example shown is the type usually seen.
The open ended levers have fine false notching, which serves two purposes, firstly as a prevention against picking and secondly for the detent to act upon, In the fully locked state the bolt cannot touch the top six levers. The bottom lever is connected to the detent which as the lever is lifted is moved into contact with the notching on the levers, effectively locking them in position. As shown below.
Here the lock is shown fully unlocked. As you can see the lever gating is very tight requiring a high degree of accuracy on the key. It is reported by a Chubb engineer who worked in the 1920’s that there were standing instructions to remove the detent from any lock they were to find it in as there were wear related problems which resulted in lock-outs in certain circumstances.
