Axial split-pin tumbler-type lock mechanism

In an axial split-pin tumbler-type lock mechanism including a lock cylinder having front an rear ends and a substantially smooth cylindrical inner wall surface, said inner wall surface having a longitudinal axis extending in a direction from front to rear in the cylinder, a barrel assembly secured within said cylinder and including a forwardly disposed operating part rotatable about said axis and a rearwardly disposed stationary part, said operating and stationary parts each including a portion having an outer surface adjacent to said inner wall surface and said portions adjoining each other at a transverse interfacial plane, a plurality of tumblers each having a forwardly disposed driver element carried by said operating part and a separate rearwardly disposed follower element carried by said stationary part, said driver and follower elements of respective tumblers being disposed in aligned adjoining relation and each tumbler being longitudinally reciprocally movable relative to said barrel assembly between positions wherein the joint between said elements is disposed respectively on opposite sides of said interfacial plane when the operating part is in a selected rotational position relative to the stationary part, said operating part being free to rotate when said joints coincide with said interfacial plane, said driver elements having front ends engageable with a key which when moved rearwardly moves said tumblers into positions wherein said joints coincide with said interfacial plane, and spring means disposed rearwardly of said follower elements to yieldingly urge said tumblers forwardly to positions wherein said interfacial plane is bridged by the follower elements to secure the operating and stationary parts against relative rotation, the improvement wherein said portions of said operating and stationary parts each include means providing a plurality of longitudinal grooves each extending for the full length of the portion in the outer surface thereof and having open opposite ends, said grooves in one portion being aligned respectively with said grooves in the other portion when the operating part is in said selected rotational position, said driver and follower elements being carried in said grooves, and the lock mechanism also includes discrete means disposed rearwardly of said portion of the stationary part for seating said spring means.