Rotary disc tumbler cylinder lock

A cylinder lock of the rotatable disc tumbler type comprising a stationary lock casing having a cylindrical bore therein, a rotatable plug assembly in the bore of said casing including a shell member rotatable in said bore and a plurality of locking disc tumblers encircled within said shell member arranged in a stack along a common axis therein and rotatable about said axis, an elongated locking bar disposed outwardly adjacent the peripheries of said disc tumblers spanning the stack of tumblers and normally restrained by the tumblers at a position for locking said shell member against rotation relative to the casing, the disc tumblers having gates alignable with and adapted to receive said locking bar to permit rotation of the shell member relative to the casing and said tumblers having key openings therein collectively defining a forwardly opening keyway and shaped to be engaged and angularly moved by the bit of a key inserted therein for aligning the gates with the locking bar, pick barrier means projecting across each intertumbler space between each adjacent pair or tumblers flanking such space including a formation defining a generally cylindrical barrier surface concentric with said common axis and projecting axially from one face of one of the tumblers of each adjacent pair in a first direction and the adjacent tumbler of the pair having a recess in the face thereof confronting said one face and shaped to receive the cylindrical barrier surface in nested relation therein, the barrier surface having an axial extent greater than the space between adjacent disc tumblers in the stacked array and being disposed at a location radially outwardly encircling the keyway to prevent insertion of picking tool portions between tumblers from the keyway into the gate regions thereof, spacer means between each successive pair of disc tumblers in the stack resiliently biasing the tumblers away from each other, means restraining the forwardmost disc tumbler at a position inwardly adjacent the front of the lock against movement toward the front, and forward thrust means movable axially of the stack and bearing against the rearmost disc tumbler of the stack and including a manually operable threaded adjustment portion for adjusting the thrust means and said rearmost disc tumbler toward the front of the lock to vary compressive forces on the stack in the direction of said common axis and thereby adjust the spacing between the disc tumblers thereof.