An improved cylinder lock with a key operated removable plug comprising, in combination:
- a first key means for operating the cylinder lock;
- a second key means for allowing removal of the plug;
- a cylinder having a longitudinal axis and defining a passage including a cylindrical portion of substantially constant diameter said cylinder also including tumbler recess means in a longitudinal direction along one side of the passage, and a longitudinal recess having an arcuately shaped cross section at the opposite side of the passage from the one side, said longitudinal recess having parallel sides extending parallel to the longitudinal axis;
- an outwardly extending circumferential flange at one end of the passage, a groove in the inside surface of the passage through the flange to the longitudinal recess;
- a plug rotatably mounted for rotation about the longitudinal axis in the cylindrical portion of the passage, said plug having an outside diameter substantially equal to the diameter of the cylindrical portion and rotatably mounted in the cylindrical portion, said plug including front face plate means of greater diameter than the plug to limit translation of the plug into the cylinder from the front of the passage, said plug including:
- a plurality of tumbler passages generally transverss to the longitudinal axis;
- an associated, longitudinal key slot mateable with the first and second key means and interconnecting the tumbler passages, and
- a control tumbler passage mateable with the first and second key means, said control tumbler passage positioned at least in part longitudinally spaced from the front face plate means and beyond the circumferential cylinder flange when the plug is in the cylinder;
- a plurality of combinating tumblers in the tumbler passages configured to engage both the first and second key means, each tumbler defining a dimension transverse to the longitudinal axis greater than the plug diameter, biasing means for the combinating tumblers in each tumbler passage, to bias the combinated tumblers beyond the plug diameter to engage the tumbler recess means on the one side of the passage in the cylinder and prevent plug rotation, said tumblers being translated against the force of the biasing means by either the first key means or the second key means to align the tumblers projecting beyond the diameter of the plug into the longitudinal recess on the opposite side of the passage whereby the plug may be rotated with the tumblers rotatable in the longitudinal recess:
- an unbiased control disc tumbler in the control tumbler passage configured to engage both the first and second key means, said control disc tumbler defining a dimension transverse to the longitudinal axis greater than the plug diameter, said control disc tumbler defining means engaging the flange and preventing movement of the plug in a longitudinal direction out of the cylinder (1) when the first key means is placed in the key slot to engage the control tumbler and (2) when no key means is in the key slot;
- said control disc tumbler also defining means disengageable from the flange to release the plug when the second key means are engaged with the tumblers to align the combined tumblers within the longitudinal recess of the cylinder and the control tumbler disc is also translated to align one end with the groove through the flange, said one end shaped to slide in the groove, the opposite end of said control disc tumbler having a width greater than the width of the groove and tumbler recess means.