|Pictures of Thumbwheels and Cams in Disassembled Lock|
|In the picture above, the four
thumbwheels and four cams, one to the right of each thumbwheel, are
visible. The flat edges of all four cams are toward the bottom of the
lock, in the positions where the feeler inserts deepest.|
Normally, the cams are tight against the thumbwheels, as is the cam next to the leftmost thumbwheel is in the picture. The spring which pushes the cams against the thumbwheels is missing from this lock, allowing the cams to move to the right. The cam next to the rightmost thumbwheel has pulled away furthest from its thumbwheel.
The combination change tool pushes the cams to the right, disengenging them from the thumbwheels. The thumbwheels can then be moved to the new combination while the cam flat edges remain aligned under the pawl. When the combination change tool is removed, a spring pushes the cams back, re-engaging them with the thumbwheels. The cams again move when the thumbwheels are turned. The new combination now aligns the flat edges of the cams under the pawl, allowing the lock to open.
|In this picture, the flat edges of the
cams are visible next to the two thumbwheels on the left. The round edges
of cams are visible next to the two thumbwheels on the right. The cam for
the tens digit thumbwheel is pulled away from the thumbwheel. The cam for
the ones digit is close to the thumbwheel. (Since a spring pushes the cams
tight against the thumbwheels, the feeler won't ordinarily slip between
the cam and thumbwheel.)|
The feeler is used to line up the cam flat edges toward the bottom of the lock. To open the lock, each thumbwheel must be turned a quarter turn up to move the corresponding flat edge under a tong on the pawl. The ends of the tongs are the bright squares above each cam.
Return to method.