Patent Publication Number: US-2009217720-A1

Title: Rapid-change lock

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. Ser. No. 10/708,658 filed Mar. 17, 2004, now U.S. Pat. No. 7,533,550, which claims the benefit of U.S. Provisional Application No. 60/469,025, filed May 8, 2003 and U.S. Provisional Application No. 60/481,298, filed Aug. 27, 2003 the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates generally to cylinder locks, and more particularly to a programmable cylinder lock which allows for adapting the lock to operate upon insertion of a key having a different configuration than a key to which the lock was originally adapted. 
     In many organizations, such as businesses, apartment buildings, hotels, schools, etc., it is generally desirable to customize the locks to the particular organization. There are two general methods by which keys and locks may be customized. The first involves reconfiguring the drivers and tumblers in the lock so that a key with a particular top edge contour may operate the locks of the organization. The second involves configuring the keyways in the locks to accept keys having a unique pattern of longitudinal contours formed in their sides. The purpose of the exclusivity generated by these methods is to prevent unauthorized entry into the organization. When keys and locks formed by the second method are involved, it is not sufficient for opening the lock that one have a key having a top edge contour appropriate to the lock; the key must also include an appropriate longitudinal contour of grooves and/or ridges. 
     In general, standard, conventional locks include a housing that has a cylindrical bore therein. An elongated generally cylindrical plug is rotatably mounted within the bore. A plurality of cylindrical apertures or holes extend through the housing and can be aligned with corresponding cylindrical holes in the plug. Paired sets of drivers and tumblers are positioned within these holes (i.e., the drivers within the holes in the housing, the tumblers within the holes in the plug) and are capable of moving within the plug and housing in such a manner as to allow for rotational movement of the plug in response to a main key inserted in the lock. The arrangement and construction of the lock also causes one or more of these sets of drivers or tumblers to be positioned in the interface between the plug and housing to prevent relative rotation between the plug and the housing when the wrong main key or no main key is inserted in the lock. However, the relative positioning of the sets of drivers and tumblers, plug, and housing is such that, when the proper key is inserted, the drivers are substantially wholly within the holes in the housing and the tumblers are substantially wholly within the holes in the plug, such that the plug can be rotated without interference to an unlocking position. 
     Many locks or sets of locks also include two types of keys: tenant keys and master keys. In general, each tenant key will only open one lock of a particular subset of locks, whereas a master key may open all the locks of the subset. Over the course of time, the security of an organization may become compromised by the loss of control of one or more of the tenant keys. For example, in apartment buildings, hotels, or motels, a guest or renter may leave and inadvertently or intentionally retain a key. When this occurs, subsequent occupants or tenants cannot be secure in their persons and property. Thus it would be desirable to easily and quickly reprogram the locks to accept a new key or set of keys. 
     Locks that can be easily changed are also desired by businesses where several employees are in possession of keys to fit the locks. In such situations, an employee may be discharged or quit, but retain possession of a key. Further, an employee may lose a key, thus placing the security of the locked area in doubt. Locks that can be easily changed are also desired in matters of personal security. One example of such a situation is a school where teachers and/or administrators may wish to quickly change the configuration of locks on classroom doors to secure students inside the classroom and safely set apart from the hallways in the event that an undesirable or dangerous individual breaches the security of the school. 
     When keys are lost or are possessed adversely, the general response is to change the locks fitting the lost key to require a key with a new top edge contour to correspond to different length tumblers. Generally, the shape of the longitudinal inner walls of the keyway that confront the longitudinal contour on the side of the key is not changed due to the generally exorbitant cost of such a change. 
     There are several generally known methods in the prior art for changing the configuration of drivers and tumblers in standard cylinder locks. Some of these methods involve removing the drivers and tumblers from a lock and replacing them with a different set of drivers and tumblers. However, there are many disadvantages to these prior methods of changing locks. First, these methods are tedious and time consuming. Second, they generally require the presence of a locksmith. And finally, they require disassembly and reassembly of the actual lock structure along with removal and replacement of the lock in a door. 
     Thus, it would be desirable to provide and construct a lock that permits rapid change in the positioning of drivers and tumblers to accept a key of a different design or configuration. It would further be desirable to provide a lock that allows the operative key to be changed without removal of the plug from the lock, and/or other disassembly of the lock structure. It would be further desirable to provide a lock wherein such change could be effected in a more rapid fashion than is currently available in locks of the prior art. 
     SUMMARY OF INVENTION 
     The present invention relates to a changeable lock assembly comprising: a) a housing having a bore therein; b) a plug rotatably mounted in the bore, the plug having a longitudinal axis, and a first passage parallel to the longitudinal axis, and configured to receive a key selected from a subset of keys, said subset of keys comprising at least a first key and a second key, each key having at least one contour position; and c) a change member movable within the lock between a first position in the lock and a second position in the plug, the change member being movable from the first position to the second position solely in response to rotation of the plug by the operation of the second key; wherein when the change member is in the first position, the first key operates the lock, and wherein when the change member is in the second position, the first key does not operate the lock. 
     The present invention also relates to a changeable lock assembly that can be reconfigured to operate with different keys of a set of user key, without disassembling the lock, comprising: a) a housing having a generally cylindrical bore with an inner surface and a plurality of generally cylindrical driver chambers intersecting the bore surface; b) a plurality of generally cylindrical drivers, each driver being positioned and movable within one driver chamber and being urged toward the bore surface; c) a plug having a generally cylindrical periphery and rotatably mounted within the bore so as to form a shear line at the interface of the bore surface and the plug periphery, the plug further having: a longitudinal axis; a keyway intersecting the periphery and parallel to the longitudinal axis and configured to receive a key selected from a subset of keys, the subset of keys including at least a first key having a first contour edge that operates the lock in a first lock configuration but does not operate the lock in a second lock configuration, and a second key having a second contour edge that operates the lock in the second lock configuration but does not operate the lock in the first lock configuration, wherein the first contour edge and the second contour edge have at least a first contour position and a second contour position that are differently configured; a plurality of generally cylindrical tumbler chambers intersecting the periphery and the keyway and generally orthogonal to the longitudinal axis, each tumbler chamber being aligned with a driver chamber when the plug is at a first rotated position with respect to the housing so as to form a pin chamber; and a plurality of retainer cavities intersecting the periphery, each retainer cavity being spaced apart from a corresponding tumbler chamber and aligned with a corresponding driver chamber when the plug is at a second rotated position with respect to the housing; and a change tool slot configured parallel to the longitudinal axis, that extends from the front face of the plug and intersects a portion of each of the retainer cavities; d) a plurality of tumblers, each tumbler being positioned and movable within one tumbler chamber; e) a plurality of lock configuration change balls, each change ball being associated with one pin chamber, having a first position within the pin chamber between the driver and tumbler, and a second position within the retainer cavity, and being movable from the second position within the retainer cavity upon insertion of a change tool into the change tool slot. 
     The present invention further relates changeable lock assembly comprising: a) a housing having a bore therein; b) a plug rotatably mounted in the said the bore, the plug having: i) a longitudinal axis; ii) a first passage parallel to the longitudinal axis, and configured to receive a key selected from a subset of keys, said subset of keys comprising at least a first key and a second key, each key having at least one contour position; iii) a second passage configured in the plug to receive a change tool, and c) a change member movable within the lock between a first position in the lock and a second position in the plug, the change member being movable from the first position to the second position solely in response to rotation of the plug by the operation of the second key; wherein when the change member is in the first position, the first key operates the lock, and wherein when the change member is in the second position, the first key does not operate the lock. 
     The present invention further relates to a changeable lock assembly comprising: a) a housing having a bore therein; b) a plug rotatably mounted in the bore, the plug having a longitudinal axis, the plug further including a first passage parallel to the longitudinal axis, the first passage adapted to receive at least a first key and a second key; and c) first and second subsets of pin chambers, wherein each pin chamber of the first subset of pin chambers lies in a first plane perpendicular to the longitudinal axis, and wherein each pin chamber of the second subset of pin chambers lies in a second plane perpendicular to the longitudinal axis, and wherein the first plane and the second plane are not coplanar. 
     The present invention relates also to a changeable lock assembly, comprising a) a housing having a generally cylindrical bore with an inner surface and a plurality of generally cylindrical driver chambers intersecting the bore surface; b) a plurality of generally cylindrical drivers, each driver being received by and movable within one driver chamber and being urged toward the bore surface; c) a plug having a generally cylindrical periphery and rotatably mounted within the bore so as to form a shear line at the interface of the bore surface and the periphery, the plug further having: 1) a longitudinal axis; 2) a keyway configured parallel to the longitudinal axis and configured to receive a key selected from a subset of keys, the subset of keys including at least a first key and a second key, the first and second key each having an edge with at least one contour position that is differently configured; 3) a plurality of generally cylindrical tumbler chambers intersecting the periphery and the keyway and generally orthogonal to the longitudinal axis, the tumbler chambers being equal to the number of driver chambers and being aligned therewith when the plug is at a first position with respect to the housing so as to form a pin chamber, such that when the plug is in the first position and at least one of the drivers is urged so as to intersect the shear line, the plug cannot be rotated within the housing; 4) a plurality of retainer cavities intersecting the periphery and spaced apart from a corresponding tumbler chamber, the retainer cavities being aligned with a corresponding driver chamber when the plug is at a second position with respect to the housing; d) a plurality of tumblers, each tumbler being received by and movable within one tumbler chamber; e) a plurality of lock configuration change members, at least one change member being positioned in the each pin chamber between a driver and tumbler, at least one of the change members being responsive to the at least one contour position when the second key is inserted into the keyway such that the change member is disposed wholly within the driver chamber and can be moved within the lock to one of the retainer cavities when the plug is rotated from the first to second position; f) the plug being rotatable after insertion of: (1) the first key when the one change member is within tumbler chamber; and (2) the second key when the change member is in the one retainer cavity. 
     The present invention also relates to a method for reprogramming a lock, the method comprising: a) providing an adaptable lock assembly comprising a housing having a bore therein, a plug rotatably mounted in the bore, the plug having a longitudinal axis, the plug further including a first orifice parallel to the longitudinal axis, the first orifice adapted to receive a key selected from a subset of keys, the subset of keys including at least a first key and a second key, and a change member movable within the lock between a first position in the lock and a second position in the plug, the change member being movable from the first position to the second position solely in response to rotation of the plug by operation of the second key, wherein when the change member is in the first position, the first key operates the lock, and wherein when the change member is in the second position, the first key does not operate the lock; b) providing a subset of keys, the subset of keys including at least a first key and a second key, each of the first key and the second key including a top contour, the second key having a different top contour than the first key, the first key being operable to operate the lock; c) inserting the second key into the first orifice; and d) moving the change member from the first position to the second position such that the first key is inoperable to operate the lock. 
     The present invention relates also to a method of making a changeable lock plug by machining a standard lock plug, comprising the steps of: a) providing a standard lock plug having a keyway, an axial centerline and a circumferential surface, the standard plug further having a plurality of tumbler chambers extending through the circumferential surface along a first line extending parallel to the axial centerline, wherein each tumbler chamber extends into the keyway and has a centerline that is spaced apart by a first distance from an adjacent tumbler chamber; and b) machining a plurality of retainer cavities into the standard plug through the circumferential surface along a second line extending parallel to the axial centerline, wherein each retainer cavity extends into the plug body is displaced radially from a corresponding tumbler chamber by an arc angle along the circumferential surface. 
     The present invention also relates to a method of machining a plug for a variable change lock, comprising: a) providing a plug body having a keyway, an axial centerline, and a circumferential surface; b) machining a plurality of tumbler chambers through the circumferential surface along a first line extending parallel to the axial centerline, wherein each tumbler chamber extends into the keyway and has a centerline that is spaced apart by a first distance from an adjacent tumbler chamber; c) machining a plurality of retainer cavities through the circumferential surface along a second line extending parallel to the axial centerline, wherein the retainer cavities extend into the plug body, and each retainer cavity is displaced radially from a corresponding tumbler chamber by an arc angle along the circumferential surface; and d) machining a slot through the circumferential surface and along the second line. 
     The present invention also relates to a lock kit, comprising: A) a subset of keys including at least a first key having a first contour edge that operates the lock in a first lock configuration but does not operate the lock in a second lock configuration, and a second key having a second contour edge that operates the lock in the second lock configuration but does not operate the lock in the first lock configuration, wherein the first contour edge and the second contour edge have at least a first contour position and a second contour position that are differently configured; B) a change tool; C) a changeable lock assembly that can be reconfigured to operate with different keys without disassembling the lock, comprising: a) a housing having a generally cylindrical bore with an inner surface and a plurality of generally cylindrical driver chambers intersecting the bore surface; b) a plurality of generally cylindrical drivers, each driver being positioned and movable within one driver chamber and being urged toward the bore surface; c) a plug having a generally cylindrical periphery and rotatably mounted within the bore so as to form a shear line at the interface of the bore surface and the plug periphery, the plug further having: 1) a longitudinal axis; 2) a keyway intersecting the periphery and parallel to the longitudinal axis and configured to receive a key selected from the subset of keys; 3) a plurality of generally cylindrical tumbler chambers intersecting the periphery and the keyway and generally orthogonal to the longitudinal axis, each tumbler chamber being aligned with a driver chamber when the plug is at a first rotated position with respect to the housing so as to form a pin chamber; and 4) a plurality of retainer cavities intersecting the periphery, each retainer cavity being spaced apart from a corresponding tumbler chamber and aligned with a corresponding driver chamber when the plug is at a second rotated position with respect to the housing; and 5) a change tool slot configured parallel to the longitudinal axis, that extends from the front face of the plug and intersects a portion of each of the retainer cavities; d) a plurality of tumblers, each tumbler being positioned and movable within one tumbler chamber; e) a plurality of lock configuration change balls, each change ball being associated with one pin chamber, having a first position within the pin chamber between the driver and tumbler, and a second position within the retainer cavity, and being movable from the second position within the retainer cavity upon insertion of the change tool into the change tool slot; D) instructions for use; and E) a means for securing the keys, lock assembly, change tool, and the instructions. 
     The present invention solves the problems and eliminates the drawbacks of locks as described above in the background of the invention. The present invention does so by providing both an adaptable or changeable lock and a method of using the lock in order to reprogram the lock to accept a second key having a different top contour than a first key. The present invention provides a lock that permits rapid change in the positioning of drivers and tumblers to accept one or more keys of a different design or configuration, without removal of the plug from the housing of the lock, and without disassembly of the lock assembly. The present invention provides a lock that allows the operative key to be changed without removal of the plug from the lock, or other disassembly of the lock assembly. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a perspective, disassembled view of the components of one embodiment of a lock assembly of the present invention. 
         FIG. 2A  is a cross-sectional view of the housing with a side view of the plug of a lock assembly of the present invention, depicting a series of change members and retainer cavities when a first operable key is inserted in the keyway. 
         FIG. 2B  is a cross-sectional view of the housing and plug taken along line  2 B- 2 B of  FIG. 2A . 
         FIG. 3A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the positioning of the change members and retainer cavities when a second key is inserted into the keyway. 
         FIG. 3B  is a cross-sectional view of the housing and plug taken along line  3 B- 3 B of  FIG. 3A . 
         FIG. 4A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the second key inserted and rotated one-quarter turn clockwise. 
         FIG. 4B  is a cross-sectional view of the housing and plug taken along line  4 B- 4 B of  FIG. 4A . 
         FIG. 5A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated back to an originating position with the second key still inserted in the keyway. 
         FIG. 5B  is a cross-sectional view of the housing and plug taken along line  5 B- 5 B of  FIG. 5A . 
         FIG. 6A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the first key, now inoperable, inserted into the keyway. 
         FIG. 6B  is a cross-sectional view of the housing and plug taken along line  6 B- 6 B of  FIG. 6A . 
         FIG. 7A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the positioning of the change members and retainer cavities when a third key is inserted into the keyway. 
         FIG. 7B  is a cross-sectional view of the housing and plug taken along line  7 B- 7 B of  FIG. 7A . 
         FIG. 8A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the third key inserted and rotated one-quarter turn clockwise. 
         FIG. 8B  is a cross-sectional view of the housing and plug taken along line  8 B- 8 B of  FIG. 8A . 
         FIG. 9A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated back to its original position with the third key still inserted in the keyway. 
         FIG. 9B  is a cross-sectional view of the housing and plug taken along line  9 B- 9 B of  FIG. 9A . 
         FIG. 10A  is a cross-sectional view of the housing with a side view of the plug of the lock assembly showing the second key, now inoperable, inserted into the keyway. 
         FIG. 10B  is a cross-sectional view of the housing and plug taken along line  10 B- 10 B of  FIG. 10A . 
         FIG. 11A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the third key inserted in the keyway and the plug rotated one-quarter turn with a change tool inserted in a change slot. 
         FIG. 11B  is a cross-sectional view of the housing and plug taken along line  11 B- 11 B of  FIG. 11A . 
         FIG. 12A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated to its original position and the first key inserted in the keyway with the change tool now removed from the change slot to make the first key operable again. 
         FIG. 12B  is a cross-sectional view of the housing and plug taken along line  12 B- 12 B of  FIG. 12A . 
         FIG. 13A  is a perspective side view of a fourth key to operate the lock assembly depicting a top contour to raise certain of the change members of the lock assembly. 
         FIG. 13B  is a perspective side view of a fifth key to operate the lock assembly depicting a top contour to raise certain of the change members of the lock assembly. 
         FIG. 13C  is a perspective side view of a sixth key to operate the lock assembly depicting a top contour to raise certain of the change members of the lock assembly. 
         FIG. 13D  is a perspective side view of a seventh key to operate the lock assembly depicting a top contour to raise certain of the change members of the lock assembly. 
         FIG. 14A  is a cross-sectional view of the housing, with a side view of the plug of one embodiment of the lock assembly with a master key inserted in the keyway. 
         FIG. 14B  is a cross-sectional view of the housing and plug taken along line  14 B- 14 B of  FIG. 14A . 
         FIG. 15A  is a cross-sectional view of the housing, with a side view of the plug of one embodiment of the lock assembly rotated one-quarter turn with a master key inserted in the keyway. 
         FIG. 15B  is a cross-sectional view of the housing and plug taken along line  15 B- 15 B of  FIG. 15A . 
         FIG. 16A  shows a second embodiment of a lock assembly, showing a cross-sectional view of the housing, with a side view of the plug, depicting a series of change members and retainer cavities when a first operable key is inserted in the keyway. 
         FIG. 16B  is a cross-sectional view of the housing and plug taken along line  16 B- 16 B of  FIG. 16A . 
         FIG. 17A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the first key inserted in the keyway and the plug rotated one-quarter turn with a change tool inserted in a change slot. 
         FIG. 17B  is a cross-sectional view of the housing and plug taken along line  17 B- 17 B of  FIG. 17A . 
         FIG. 18A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated to an original position with a second key inserted in the keyway and the change tool still inserted in the change slot. 
         FIG. 18B  is a cross-sectional view of the housing and plug taken along line  18 B- 18 B of  FIG. 18A . 
         FIG. 19A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the second key inserted in the keyway and the plug rotated one-quarter turn with the change tool inserted in the change slot. 
         FIG. 19B  is a cross-sectional view of the housing and plug taken along line  19 B- 19 B of  FIG. 19A . 
         FIG. 20A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated to its original position with the second key inserted in the keyway and the change tool now removed from the change slot. 
         FIG. 20B  is a cross-sectional view of the housing and plug taken along line  20 B- 20 B of  FIG. 20A . 
         FIG. 21A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the second key removed from the keyway and a first key, now inoperable, inserted in the keyway. 
         FIG. 21B  is a cross-sectional view of the housing and plug taken along line  21 B- 21 B of  FIG. 21A . 
         FIG. 22A  is a perspective side view of a third key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22B  is a perspective side view of a fourth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22C  is a perspective side view of a fifth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22D  is a perspective side view of a sixth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22E  is a perspective side view of a seventh key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22F  is a perspective side view of an eighth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22G  is a perspective side view of a ninth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22H  is a perspective side view of a tenth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22J  is a perspective side view of an eleventh key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22K  is a perspective side view of a twelfth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22L  is a perspective side view of a thirteenth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22M  is a perspective side view of a fourteenth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 22N  is a perspective side view of a fifteenth key to operate the lock assembly depicting a top contour to raise certain of the change members. 
         FIG. 23A  is a cross-sectional view of the housing, with a side view of the plug of another embodiment of a lock assembly of the present invention further depicting a memory block in a closed position and a first key, which is operable, inserted into the keyway. 
         FIG. 23B  is a cross-sectional view of the housing and plug taken along line  23 B- 23 B of  FIG. 23A . 
         FIG. 24A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting a first key inserted and rotated one-quarter turn clockwise with a change tool inserted and the memory block moved back from the retainer cavities. 
         FIG. 24B  is a cross-sectional view of the housing and plug taken along line  24 B- 24 B of  FIG. 24A . 
         FIG. 25A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the plug rotated back to its original position with a second key inserted and a change tool inserted in the change slot thereby opening the memory block. 
         FIG. 25B  is a cross-sectional view of the housing and plug taken along line  25 B- 25 B of  FIG. 25A . 
         FIG. 26A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly with the second key and change tool both inserted and the memory block open and the plug rotated one-quarter turn. 
         FIG. 24B  is a cross-sectional view of the housing and plug taken along line  26 B- 26 B of  FIG. 26A . 
         FIG. 27A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the second key inserted in the plug and the plug rotated one-quarter turn with the change tool now removed from the change slot. 
         FIG. 27B  is a cross-sectional view of the housing and plug taken along line  27 B- 27 B of  FIG. 27A . 
         FIG. 28A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated back to its original position with the change tool removed and the second key, now operable, inserted in the keyway. 
         FIG. 28B  is a cross-sectional view of the housing and plug taken along line  28 B- 28 B of  FIG. 28A . 
         FIG. 29A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug in an original position with no key inserted and having a series of radial tumblers and change members. 
         FIG. 29B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  29 B- 29 B of  FIG. 29A . 
         FIG. 30A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the positioning of the radial tumblers and change members when a first key is inserted into the keyway. 
         FIG. 30B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  30 B- 30 B of  FIG. 30A . 
         FIG. 31A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly depicting the first key inserted and rotated one-quarter turn counterclockwise. 
         FIG. 31B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  31 B- 31 B of  FIG. 31A . 
         FIG. 32A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly the first key inserted and rotated one-quarter turn counterclockwise with a change tool inserted in a change slot. 
         FIG. 32B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  32 B- 32 B of  FIG. 32A . 
         FIG. 33A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated back to an original position with the first key removed and change tool still inserted in the change slot, with a new second key inserted in the keyway. 
         FIG. 33B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  33 B- 33 B of  FIG. 33A . 
         FIG. 34A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the second key inserted in the keyway and the plug rotated one-quarter turn counterclockwise with the change tool inserted in the change slot. 
         FIG. 34B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  34 B- 34 B of  FIG. 34A . 
         FIG. 35A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the second key inserted in the keyway and the plug rotated one-quarter turn counterclockwise with the change tool now removed from the change slot. 
         FIG. 35B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  35 B- 35 B of  FIG. 35A . 
         FIG. 36A  is a cross-sectional view of the housing, with a side view of the plug of the lock assembly showing the plug rotated to its original position with the second key still inserted and the change members reset to a new configuration. 
         FIG. 36B  is a cross-sectional view of the housing and plug with a plan view of the radial tumbler taken along line  36 B- 36 B of  FIG. 36A . 
         FIG. 37  is a perspective, disassembled view of the components of an embodiment of the lock assembly of the present invention having two sets of pin chambers to hold two sets of driver/tumbler stacks. 
         FIG. 38  is an end cross-sectional view of the plug and housing of the lock assembly of the embodiment having two separate sets of pin chambers and driver/tumbler stacks. 
         FIG. 39A  is a side perspective view of a key having a top edge contour and a longitudinal contour adapted for a lock of the present invention. 
         FIG. 39B  is an end view of the key taken from line  39 B- 39 B of  FIG. 39A . 
         FIG. 39C  is a cross-sectional view of the key taken along line  39 C- 39 C of  FIG. 39A . 
         FIG. 40A  is a side perspective view of a key having a Y-shape to fit a keyway of a plug having two separate sets of pin chambers, the key having top edge contours and longitudinal contours adapted for a lock of the present invention. 
         FIG. 40B  is an end view of the key taken from line  40 B- 40 B of  FIG. 40A . 
         FIG. 40C  is a cross-sectional view of the key taken along line  40 C- 40 C of  FIG. 40A . 
         FIG. 41A  is a cross-sectional view of a housing, with a side view of the plug of an embodiment of a lock of the present invention having an anti-tamper pin. 
         FIG. 41B  is a cross-sectional view of the housing and plug with a plan view of the anti-tamper pin, taken along line  41 B- 41 B of  FIG. 41A . 
         FIG. 42  shows a perspective, disassembled view of the components of an embodiment of the lock assembly of the present invention having a plug positioning means. 
         FIG. 43A  shows a cross-sectional view of a plug and housing through line  43 - 43  of  FIG. 42  of an embodiment of a lock of the present invention having a plug positioning means, with the plug in a key insertion position. 
         FIG. 43B  shows a cross-sectional view of a plug and housing through line  43 - 43  of  FIG. 42  of an embodiment of a lock of the present invention having a plug positioning means, with the plug in a lock programming position. 
         FIG. 44A  shows an end view of the plug of an embodiment of a padlock of the present invention having a latch with a lazycam, in an initial position. 
         FIG. 44B  shows the end view of the plug of  FIG. 44A , in a reprogramming position. 
         FIG. 44C  shows the end view of the plug of  FIG. 44A , in a second unlock position. 
     
    
    
     DETAILED DESCRIPTION  
     The lock includes a housing with a bore disposed through the housing and a plug (or lock core) rotatably mounted within the bore. The plug has a longitudinal axis and a first orifice or passage parallel to the longitudinal axis to provide a keyway that is adapted to receive a key. The housing and plug also each include a plurality of paired sets of radially extending apertures or holes, respectively, which are adapted to receive, respectively, the drivers and tumblers of the lock. The radially extending holes in the housing form driver chambers. The radially extending holes in the plug form tumbler chambers. When the lock is in a first position wherein the drivers and tumblers can move in a vertical direction (in the Figure), the vertical apertures of the plug are aligned with the vertical apertures of the housing. In this first lock position or first rotated position, the tumbler chambers are aligned with the respective driver chambers, each resulting pair of extended apertures or holes forms a pin chamber. The drivers and tumblers can move within the aligned set of pin chambers. The lock can also include a change member, for example, a change ball in the form of a ball bearing, that is adapted to be disposed within the pin chamber as part of the paired driver/tumbler stack or set, or alternatively can be disposed within a separate retainer recess or cavity located in or otherwise associated with the plug. This change member can have a size smaller than that of the other members of the driver/tumbler stack or set. By moving a change member or change members between one or more of the pin chambers and the retainer cavities, one may alter the driver/tumbler configuration such that the lock will accept and operate with a second key having a differing top contour, but will not operate with the originally operable first key. 
     With the lock of the present invention, a subset of keys can be provided, each key configured such that it can be the operable key for the lock. In one embodiment of the present invention, as an operator progresses through each key of the subset of keys for a particular lock, at least one additional change member is displaced from a pin chamber and into a retainer cavity. As this occurs, any keys of the subset of keys that are configured to move less than the current number and configuration of change members that are displaced will no longer operate the lock. Using any key of the subset of keys that is configured to move more than the current number and configuration of change members that are displaced can displace at least one additional change member, and thus change the driver/tumbler configuration of the lock to match that new key. For example, if a lock includes six driver/tumbler stacks or sets, then there can be up to seven keys in an operable subset, with each successive key displacing at least one more change member than the previous key. Thus, each key will have a nearly identical top contour to the previous key in the set, with the exception that at least one additional contour location will be raised, as will be explained in greater detail below. This embodiment of the lock of the present invention thus allows for reconfiguring driver/tumbler stacks or sets in the absence of a change tool, thereby allowing for rapid, automatic rekeying, simply by using a new key of the subset of keys. 
     Once all the change members have been displaced into retainer cavities, thus reaching the end of a key set, the lock can be reset to the first key in the set through the use of a change tool. In order to effect this change, the plug includes a second orifice or passage to provide a change slot, which is configured in the plug in a direction parallel to the longitudinal axis thereof, and intersects each of the retainer cavities. When the retainer cavities are aligned in a plane with the driver chambers of the housing, and the change tool is inserted in the change slot, any change members in the retainer cavities will be displaced there from and into the driver chambers, thus returning the change members to the driver/tumbler stack and resetting the lock to operate with a subsequently-inserted key from the set of keys. 
     The method of using this embodiment of the lock of the present invention involves inserting a first key to which the lock is programmed to operate into the keyway of the lock. This key then can be used to rotate the plug within the housing of the lock. The first key is then removed from the longitudinal slot. A second key, having a different though complementary top edge contour than the first key, is then inserted. The second key is complementary to the first key in that each raised contour position of the first key is found on the second key. The second key is different in that it has at least one additional contour position or location raised, which the first key does not have; the top edge contour of the second key otherwise matches the top edge contour of the first key. As this happens, the driver/tumbler stack associated with that raised contour location is lifted such that the change member of that driver/tumbler stack is raised above the shear line of the lock and is disposed in the respective driver chamber of the housing. As the plug rotates by rotating the second key, the retainer cavities will come into alignment with the respective driver chambers of the housing. As this occurs, the force of a spring or other biasing mechanism disposed or positioned above the driver in the respective driver chamber forces any change member raised above the shear line of the lock down into a corresponding retainer cavity. As the second key and plug are rotated back to the original position, the additional change member is then disposed in a retainer cavity offset from the tumbler chambers of the plug, whereby the lock has been reset to operate with the second key. The first key is now inoperable due to its inability to lift the now additionally changed driver/tumbler stack sufficiently to allow rotation of the plug. 
     Alternate embodiments of the invention can include an embodiment that involves the use of a change tool with each reconfiguration of the drivers and tumblers of the lock. This embodiment can expand the number of keys in a particular set of keys, since instead of moving change members from the tumbler chamber, via the driver chamber, into the retainer cavities as one progresses through a set of keys, one may shift change members back and forth between the tumbler chambers and retainer cavities. This embodiment of the invention can also include keys having at least two raised contour locations, which prevent automatic lock changing. However, more keys can be provided to a key set. For example, by staggering two raised contour locations over a total of six contour locations, 15 different key combinations can be achieved. Similarly, a subset of keys having four raised contour locations over a total of six contour locations provides for 15 different key combinations. 
     Yet another alternate embodiment of the present invention can include a memory block that is disposed in the plug of the lock and is adapted to intersect the change slot and the openings to the retainer cavities. This memory block prevents different keys from being inserted into the lock in an unauthorized fashion by partially blocking the openings to the retainer cavities. Thus any change members raised above the shear line cannot fit through the openings and into the retainer cavities as they are rotated into alignment with the driver chambers, unless an authorized user inserts a change tool which displaces the memory block away from the change slot such that the full breadth of the opening to each of the retainer cavities is exposed to receive a change member. 
     Yet another alternate embodiment can include at least one radial tumbler disposed in a radially extending slot in the plug. The radial slot is disposed in or associated with a sidewall of the plug radially outwardly from the longitudinal axis of the plug. These radial tumblers can include notches to accept a sidebar which is disposed between the housing and plug of the lock. This sidebar and radial tumbler configuration adds extra security to the lock in that a user will need a key not only having a proper top edge contour but also a proper longitudinal contour in order to move the radial tumblers to a proper position to allow the sidebar to move inwardly from the housing of the lock into the plug, thereby allowing the plug to rotate to operate the lock. 
     The method of reconfiguring the lock of the present invention as described above can be used to reconfigure the drivers and tumblers in order to change tenant keys that can properly operate the lock. The method involves the use of a change tool when an authorized or operable user key is inserted into the lock, re reset the lock to allow another user key of the subset of keys to become the operable user key. 
     Yet another embodiment of the present invention allows for master keys that can operate the lock properly without reconfiguring the driver and tumbler arrangement. In particular, in one embodiment, this alternate embodiment includes at least one master shim or pin, preferably with at least one master shim being disposed in each tumbler chamber of the plug. These master shims are disposed in the driver/tumbler stack directly beneath the change member. The master shims are each sized larger than the change members and are also sized larger than the openings to the retainer cavities. Thus, when a master key is inserted into the keyway of the plug, all of the driver/tumbler stacks are raised so that the bottom tumbler lies beneath the shear line and within the tumbler chamber of the plug, while each of the master shims lies directly above the shear line of the lock and in the driver chamber of the housing. When the plug is rotated in the lock such that the retainer cavities come into alignment with the driver chambers of the housing, the master shims can not fall through the opening and into the retainer cavities due to their larger size. The master shims also prevent any change members from moving into the retainer cavities, because the master shims are disposed between the retainer cavities and any change member in a driver chamber, and will block the opening to the retainer cavities through which the change members could enter. Thus, there is no pathway for the change member to enter the retainer cavities. As such, one may operate a master key to open any lock in a particular facility system without reconfiguring the driver/tumbler stack of the lock. In an embodiment of the present invention that includes a memory block, there is no need for the driver/tumbler stack to include master shims, since the change members can be prevented from entering the retainer cavities by the memory block. 
     Referring to  FIG. 1 , an embodiment of the lock  10  includes a housing  12  with a generally cylindrical bore  14  through the housing  12  for receiving a generally cylindrical plug  16 . The plug  16  has a periphery that is sized to rotate within the housing  12 . The housing and plug of the lock include vertical apertures within which drivers and tumblers are disposed. The housing  12  has a plurality of generally cylindrical driver chambers  40  that intersect with the inner surface of the bore, while the plug  16  has a plurality of correspondingly generally cylindrical tumbler chambers  42  When the driver chambers  40  of the housing and the tumbler chambers  42  of the plug are aligned, a plurality of pin chambers  18  are formed. Each pin chamber  18  has disposed therein a plurality of generally cylindrical drivers  20  and a plurality of generally pencil-shaped tumblers  22 , consisting of a cylindrical body with a tapered end. The tumblers  22  are positioned in the tumbler chambers  42  such that the tapered end extends into a first passage of the plug  16  in the form of a keyway  24 . The drivers  20  are positioned and movable within the pin chambers  18  above corresponding tumblers  22 . A biasing means in the form of driver spring  26  is located within each driver chamber  40  between a rectangular top plate  28  removably secured or attached to the housing  12 , and the respective driver  20  to bias or urge the paired driver  20  and tumbler  22  stack in a downward fashion such that the tapered end of the tumbler  22  projects into the keyway  24  when no key is inserted therein. The driver spring  26  is typically a tempered, stainless steel to prevent material deformation upon multiple cycles of compression and extension. Preferably, the spring material is a made of non-metallic stainless steel wire of about size 008, and is available as part number C108.times.008.times.520 from W. B. Jones Spring Co., Inc., of Wilder, Ky. Typically, the driver chambers  40  and tumbler chambers  42  have a generally circular cross section. 
       FIG. 2A  shows a cross-sectional view of the housing  12  and a plan view of the drivers  20  and plug  16  disposed within the housing.  FIG. 2B  is a sectional view of the lock through line  2 B- 2 B of  FIG. 2A , which shows the plug  16  and housing  12  in sectional view, and the hardware (driver  20 , biasing means  26 , change member  56 , master shim  60  and tumbler  22 ) in plan view. To improve the understanding of the invention, the retaining cavities  58  and change slot  88  shown in  FIG. 2A  (and in similar subsequent figures) have been displaced from the longitudinal centerline  54  of the plug  16  (see  FIG. 2B ) so that the tumblers  22  and contour positions  68 , 70 , 72 , 74 , 76  and  78  of key  30 , shown in phantom lines, can be viewed. 
     In  FIGS. 2A and 2B , when a first key  30  of a subset of user keys is inserted into the keyway  24 , the paired stacks of tumblers  22  and drivers  20  are raised to a height consistent with a top edge contour  32  of the key. If a proper (or operable) key has been inserted, a lower end  34  of the respective driver  20  or an upper end  36  of the respective tumbler  22  is disposed along a shear line  38  of the lock  10 . The shear line  38  is located at the interface of where the outer circumference or periphery of the plug  16  confronts or opposes the inner surface of the bore  14 . Thus, the proper or operable key will raise the respective tumblers  22  and drivers  20  to allow for rotation of the plug  16  within the housing  12 . As the plug  16  rotates, each driver  20  will be disposed substantially wholly within the respective driver chamber  40  of the housing  12 , while each tumbler  22  will be disposed substantially wholly within the respective tumbler chamber  42  of the plug  16 . The first key  30  can have a longitudinal contour  44  configured at least along one side of the key and a top edge contour  32 . Alternatively, longitudinal contours  44  can be configured on both sides of the key. 
     More specifically, and as shown in  FIG. 1 , the body  46  of the lock  10 , of the illustrated embodiment, is generally cylindrical in configuration and is provided with a generally circular flange  48  at one end thereof to abut a door or other member in which the lock  10  may be installed. A portion of the body  46  can be threaded (not shown) near the end opposite of the flange  48  to permit the lock  10  to be secured to an object (not shown) requiring locking. The bore  14  is formed in and extends through the housing  12  about and along a longitudinal axis  50  and passes through both ends of the housing  12 . The plug  16  of the illustrated embodiment includes a cylindrical body  52  configured such that in the assembled lock  10 , the periphery of the plug  16  confronts or opposes the surface of the bore  14  of the lock  10 , with the longitudinal axis  50  of the bore  14  and a longitudinal axis  54  of the plug  16  being substantially coaxial. Latch end  15  of the plug  16  extending from the housing  12  can be provided with threads  67 , with which a mating lock nut (not shown) can be threaded to secure the plug  16  within the bore  14  of the housing  12 . A latch member (not shown) can be secured on the latch end  15  of the plug  16  to engage a recess or bolt (also not shown) to lock the object in which the lock  10  is installed. 
     When the respective driver chambers  40  of the housing and the tumbler chambers  42  of the plug are aligned, a plurality of pin chambers  18  are formed, extending from the keyway  24  in the plug to and through the top end of the housing. The pin chambers  18  extend in a manner substantially orthogonal with respect to the longitudinal axis  54  of the plug  16 . The portion of the pin chambers  18  represented by the tumbler chambers  42  intersect the bore  14  and extend through a portion of the plug  16  to intersect the keyway  24 , while the portion of the pin chamber  18  represented by the driver chambers  40  extend into and through the housing  12  of the lock  10 . Thus, the driver chamber  40  portion of each pin chamber  18  intersects the housing  12  and the bore  14 , while the tumbler chamber portion  42  of each pin chamber  18  intersects the periphery of the plug  16  and the keyway  24 . Biased by the driver spring  26  between the top plate  28  and each driver  20 , driver  20  disposed within each driver chamber  40  is urged generally toward the bore  14 . When no key is inserted into the keyway  24 , the force of the driver spring  26  can cause at least a portion of each driver  20  to project into the tumbler chamber  42  portion, of the pin chamber  18  within the plug. 
     Each tumbler chamber  42  is axially aligned with a respective driver chamber  40  when the plug  16  is in an initial or first position shown in  FIGS. 2A and 2B , and has not been rotated. A portion of each tumbler  22  within tumbler chamber  42  can extend into the keyway  24  due to the biasing or urging force created by the combination of the respective driver  20  and driver spring  26 . Additionally, the upper end  36  of each tumbler  22  can contact and engage the lower end  34  of each driver  20 . While the illustrated embodiment of the lock  10  of the present invention is depicted as having a particular number or plurality of paired stacks or sets of drivers  20  and tumblers  22 , alternate embodiments of the lock  10  may include one pair of driver and tumbler  20 ,  22 , or multiple pairs of drivers and tumblers  20 ,  22  of lesser or greater number than that depicted in the illustrated embodiment. 
     The lock  10  of the present invention also includes a lock configuration change member  56 , which, as in the illustrated embodiment, can be in the form of a generally spherical change member or change ball, such as a ball bearing. Change member  56  is configured to be disposed within the pin chamber  18  and incorporated as part of each paired stack or set of drivers  20  and tumblers  22 . Alternatively, the change member  56  can be disposed in a separate retainer cavity  58  configured in or otherwise associated with the plug  16 . Each change member  56  is movable such that it can be displaced from a first position in the pin chamber  18 , more specifically in tumbler chamber  42 , to a second position within the respective retainer cavity  58 . Conversely, change member  56  can be displaced from the second position within the retainer cavity  58  to the first position in the pin chamber  18 . By moving a change member  56  between one or more of the pin chambers  18  and the respective retainer cavities  58 , one can alter the configuration of one or more of the paired stacks or sets of drivers  20  and tumblers  22  to accept and render operable keys having a differing top contour  32 . Thus, when a change member  56  is in a first position, it can be incorporated as part of a paired stack or set of drivers  20  and tumblers  22 . In a driver/tumbler stack having a change member  56 , the driver  20  and tumbler  22  can each contact and engage a respective side of the change member  56  when it is disposed between the driver  20  and the tumbler  22 . In a driver/tumbler stack where the change member  56  has been displaced to the second position, the driver  20  and the tumbler  22  can contact and engage one another. Alternatively, as will be explained in more detail below, the driver/tumbler stack can include a generally circular master shim  60  disposed amongst or between the driver  20 , tumbler  22 , and change member  56  of the respective stack or set. A lock  10  of the present invention can be provided with a subset of keys that can operate the particular lock, and are adapted to displace one or more change members  56 , as will be described in greater detail below. 
     Each retainer cavity  58  has an opening having a circular cross section for receiving change members  56 . Typically, the change member  56  has a diameter smaller, more typically just slightly smaller, than the cross section of the retainer cavity  58 . The spherical shape of the change member  56  allows rolling movement within the cavity  58  and driver/tumbler chambers  40  and  42  of the lock, and to project the same cross-sectional shape regardless of its orientation. Also, the spherical shape of the change member  56  has no corners or edges which can obstruct its free movement. A barrel- or cylindrical-shaped change member can be used in a lock of the present invention, although it may have a tendency to tilt or tumble within a chamber, and increase the potential of becoming lodged within the chamber and jamming the lock. For the purpose of describing succeeding embodiments of the present invention, the change member  56  will hereinafter be referred to as the change ball  56 . 
     Referring now to  FIGS. 2A-13D , a first embodiment of the lock  10  of the present invention is illustrated. This illustrated embodiment of the present invention allows an operator to change the configuration of drivers  20 , tumblers  22 , and change balls  56  of a lock that operates with a first user key  30 , to accept and render operable a second user key  62 , and render inoperable the first key  30 , without the use of a change tool  64  (see  FIG. 1 ). Thus, the second key  62  is used to change the configuration of drivers  20 , tumblers  22 , and change balls  56  in the lock  10  in order to foreclose the use of the first key  30 , without removal and disassembly of the lock itself A subset of user keys can be provided wherein the use of each subsequent operating key can reconfigure or re-key the lock  10  to foreclose any previous operating key from operating the lock  10 . This progression can be determined by the differing top edge contours  32  of each of the keys. As an operator progresses through using each key of the subset of keys for a particular lock  10 , at least one additional change member of ball  56  is displaced from one of the pin chambers  18  into the respective retainer cavity  58 . As this occurs, any key of the subset of keys that is configured to displace less than the current number and configuration of change balls  56  that are displaced will no longer operate the lock  10 . Using any key of the subset that is configured to displace one or more additional change balls than the current number and configuration of change balls  56  that are displaced, will change the corresponding configuration of driver  20 , tumbler  22 , and change ball  56  to match that key. For example, if a lock includes six pin chambers  18  having drivers  20 , tumblers  22 , and/or change balls  56 , then there can be up to seven keys in an operable set, with each successive key displacing at least one more change ball  56  than the previous key. One key of the seven key set would displace none of the change balls  56 . This key can be termed the null or base key. Each successive key will have a nearly identical top contour to a previous key in the set, with the exception that at least one additional contour location  66  will be raised, as will be explained in greater detail below. 
     In the illustrated embodiment of  FIGS. 2A-12B , the lock  10  of the present invention is shown as having first, second, third, fourth, fifth, and sixth pin chambers identified, respectively, as  19 ,  21 ,  23 ,  25 ,  27 ,  29 , each adapted to house a set of a driver  20 , a tumbler  22 , and a change ball  56 . A key inserted into a keyway  24  is shown as having first, second, third, fourth, fifth, and sixth contour locations identified, respectively, as  68 ,  70 ,  72 ,  74 ,  76 ,  78 . When a key is fully inserted into keyway  24 , these first, second, third, fourth, fifth, and sixth contour locations  68 ,  70 ,  72 ,  74 ,  76 ,  78  register with the corresponding first, second, third, fourth, fifth, and sixth pin chambers  19 ,  21 ,  23 ,  25 ,  27 ,  29 , respectively. Each of these contour locations  68 ,  70 ,  72 ,  74 ,  76 ,  78  can be a raised contour location or a lowered contour location. With particular reference to  FIG. 2A , one can see that the first key  30  has no raised contour locations  66 , such that no change balls  56  are raised above the shear line  38 . 
     When a key is inserted in the keyway  24 , a raised contour location  66  will raise the upper end  36  of the respective tumbler  22  flush with the shear line  38  of the lock  10 , such that any change ball  56  disposed in a first position will be raised above the shear line  38  and into the driver chamber  40  of the housing  12 . Referring to  FIG. 3A , a second user key  62  is shown as having a first contour location  68  that is raised. The second key  62  can rotate the plug  16  and operate the lock since, when it raises the respective drivers  20 , tumblers  22 , and change balls  56  of the pin chambers  18 , the junction between any two of those components proximate to the shear line  38  is flush therewith. None of these components, and particularly neither the driver  20  nor the tumbler  22 , spans across the shear line. In particular, the raised first contour location  68  of the second key  62  raises change ball  56  disposed within the first pin chamber  19 , above the shear line  38 . Once the plug  16  has been rotated to displace the change ball  56  of the first pin chamber  19  into its corresponding retainer cavity  58 , the first key  30  is rendered inoperable due to its lowered first contour location  68  (see  FIG. 6A ). Referring to  FIG. 7A , a third key  63  has raised first and third contour locations  68 ,  72 . Raised third contour location  72  displaces an additional change ball  56  that is disposed in the third pin chamber  23 . Thus, a subsequent key, having at least one additional raised contour location  66 , will render inoperable any other previously-operable key that has a lowered contour position corresponding to a raised contour position  66  of the subsequent key. The set of keys can include a fourth key  80  (shown in  FIG. 13A ) having raised first and third, and an additional raised fifth contour location  76 , a fifth key  82  (shown in  FIG. 13B ) having raised first, third, and fifth contour locations  68 ,  72 ,  76  and an additional raised second contour position  70 , a sixth key  84  (shown in  FIG. 13C ) having raised first, second, third, and fifth contour locations  68 ,  70 ,  72 ,  76  and an additional raised fourth contour position  74 , and a seventh key  86  (shown in  FIG. 13D ) having raised first, second, third, fourth, and fifth contour locations  68 ,  70 ,  72 ,  74 ,  76 , and an additional raised sixth contour position  78 . It is to be understood that the set of six keys shown is simply illustrative, and can be any number of similarly configured keys, with a maximum number equal to one more than the number of pin chambers  18  in the lock  10 . 
     Once all the change balls  56  have been displaced into respective retainer cavities  58 , thus reaching the end or having used the last of the subset of user keys, the lock  10  can be reset to the first key  30  in the subset through the use of the change tool  64 . Alternatively, the lock  10  can be reset any time an operator desires, not just when all of the keys of a set have been used. In order to effect this change, the plug  16  includes a second orifice or passage in the form of change slot  88 . Change slot  88  is typically configured in the plug  16  in a direction parallel to the longitudinal axis  54  of the plug  16 , and typically extends from the front face of the plug and intersects a portion of each of the retainer cavities  58 . When the plug  16  has been rotated to a position where the retainer cavities  58  are aligned with the driver chambers  40  of the housing  12 , and the change tool  64  is fully inserted in the change slot  88 , any change balls  56  disposed in the retainer cavities  58  will be displaced out of the retainer cavities  58  and into the driver chambers  40 . When the plug  16  is then rotated back to its original position, the change balls  56  are returned to the corresponding stack or set of drivers  20  and tumblers  22 , and the lock  10  is reset. 
     The change slot  88  is preferably configured into the plug  16  along the longitudinal line passing through the centers of the retainer cavities  58 . This configuration allows the change tool  64  inserted into the change slot  88  to raise a change ball  56  contained therein at its center of weight and to its maximum height. Additionally, the change slot  88  is configured to minimize the width thereof to that necessary to accommodate a change tool  64  that can effectively raise the change balls  56  out of the retainer cavities  58 . In a typical door lock, having six or so pin chambers, the width of the change slot is typically about 0.020 inches (about 0.50 mm) or less. If the width of the change slot  88  is too large, a member such as a master shim  60  (discussed herein after) might catch the corner  188  of the opening to the retainer cavity  58  at the intersection with the change slot  88  (see  FIG. 2A ). With time, the repeated impact of the master shim against the corner  188  can cause wear at the corner  188 , which could eventually permit a shim to twist and jamb into the opening. 
     The method of using the lock  10  of this embodiment of the present invention involves inserting a first key  30  to which the lock  10  is programmed to operate into the longitudinal keyway  24  of the lock  10 . This key then can be used to rotate the plug  16  within the housing  12 . The first key  30  is then removed from the longitudinal keyway  24 . The second key  62  has a different though complementary top edge contour  32  than the first key  30 . The top edge contour  32  of the second key  62  also has raised contour locations  66  that match the top edge contour  32  of the first key  30 , to raise any paired stacks or sets of drivers  20  and tumblers  22  in like manner as would also be raised by the first key  30 , and at least one additional raised contour  66 . As the second key  62  is inserted, the additional raised contour  66  on the second key causes at least one change ball  56  to be raised above the shear line  38  of the lock  10  and disposed in the respective driver chamber  40  in the housing  12 . 
     When the second key  62  and plug  16  are rotated clockwise, the retainer cavities  58  will come into alignment with the driver chambers  40 . As this occurs, the spring force of the driver spring  26  disposed above each driver  20  in the driver chamber  40 , forces the change ball  56 , situated above the shear line  38 , down into its corresponding retainer cavity  58 . When the second key  62  is rotated along with the plug  16  back to its original position, the additional change ball  56  is now disposed in a retainer cavity  58  offset from the pin chamber  18 , and thus the lock  10  has been reset to operate with the second key  62 . 
     While only one change ball  56  at a time is being described moving from a tumbler chamber  42  to the retainer cavity  58 , the invention provides that more than one change ball  56  at a time can be moved from the tumbler chambers  42  to the retainer cavities  58 . 
     Referring now to  FIGS. 2A and 2B , the illustrated embodiment of the lock  10  is depicted with an operable first key  30  inserted into the keyway  24 . The first key  30  has a top edge contour  32  with no contour location  66  raised. All six contour locations  68 ,  70 ,  72 ,  74 ,  76 ,  78 , have a lowered position. The Figures show that these lowered contour locations  68 ,  70 ,  72 ,  74 ,  76 ,  78  keep the change balls  56  disposed within the tumbler chambers  42  when the first key  30  is inserted. Since the drivers  20 , tumblers  22 , and change balls  56  in each of the pin chambers  18  are raised such that no driver or tumbler spans or straddles the shear line  38 , the first key  30  operates the lock by rotating the plug  16  within the housing  12 . 
     It should be recognized that when the lower portion of a change ball  56 , below its centerline, spans the shear line, the rotation along the shear line of the plug within the housing will cause the ball  56  to be forced into the drive chamber  40 . If the centerline or the upper portion of the change ball lies along the shear line, the plug will not rotate in the bore of the housing, and may become jammed. 
     Referring now to  FIGS. 3A and 3B , the plug  16  and housing  12  are depicted with the first key  30  removed and a second key  62  now inserted in the keyway  24  of the lock  10 . This second key  62  has a top edge contour  32  that differs from that of the first key  30 , particularly in that the first contour location  68  is raised. The first key  30  has a first contour location  68  that is lowered. The raised first contour location  68  of the second key  62  causes the change ball  56  in the first pin chamber  19  to be raised above the shear line  38 . Since the drivers  20 , tumblers  22 , and change ball  56  of each of the series of pin chambers  18  are positioned with no driver, tumbler, or change ball spanning or straddling the shear line  38 , this second key  62  can operate the lock  10 . 
     Referring now to  FIGS. 4A and 4B , the lock  10  of the present invention is depicted with the second key  62  inserted in the plug  16  and rotated one-quarter turn clockwise, which brings the retainer cavities  58  into alignment with the driver chambers  40  in the housing. The driver spring  26  disposed above the driver  20  in the first driver chamber  40  of first pin chamber  19  then forces the change ball  56  that was disposed above the shear line  38  down into a corresponding retainer cavity  58 . 
     Referring now to  FIGS. 5A and 5B , the plug  16  with the second key  62  inserted in the keyway  24  has been rotated back to its original position. The change ball  56  associated with the first pin chamber  19 , when in its first position, is now been displaced into its second position within one of the retainer cavities  58  disposed in or associated with the plug  16 . The various drivers  20 , tumblers  22 , and change balls  56  are disposed within the pin chambers  18  such that the lower ends  34  of all the drivers  20  are positioned along and flush with the shear line  38  and within the driver chambers  40 . Thus, the second key  62  operates the lock by rotating the plug  16  within the housing  12 . 
     Referring now to  FIGS. 6A and 6B , the second key  62  has been removed from the keyway  24  and the first key  30  has been reinserted. The Figures illustrate that the first key  30  now is foreclosed from operating or cannot operate the lock  10 . The differing first contour location  68 , which is a lowered position in this first key  30 , cannot sufficiently raise the driver  20  and tumbler  22 , such that the driver  20  is disposed partially within the driver chamber  40  and partially within the tumbler chamber  42  of the first pin chamber  19 . Since the driver  20  of the first pin chamber  19  spans the shear line  38  of the lock  10 , the plug  16  will not rotate within the housing  12 , and thus first key  30  is foreclosed from operating the lock  10 . 
     Referring now to  FIGS. 7A and 7B , the plug  16  and housing  12  are depicted with the second key  62  removed and a third key  63  now inserted in the keyway  24 . This third key  63  has a top edge contour  32  that differs from that of the second key  62 . The third contour location  72  of the third key  63  is raised, whereas in the second key  62 , the third contour location  72  is lowered. Like the second key  62 , the third key  63  includes a raised first contour location  68 . With the third key  63  inserted, this third raised contour location causes the change ball  56  of the third pin chamber  23  to be raised above the shear line  38 . Since the drivers  20 , tumblers  22 , and change balls  56  of each of the pin chambers  18  are aligned such that no member is spanning or straddling the shear line  38 , this third key  63  can now operate the lock  10 . 
     Referring now to  FIGS. 8A and 8B , the lock  10  of the present invention is depicted with the third key  63  inserted and rotated one-quarter turn clockwise, which brings the retainer cavities  58  into alignment with the driver chambers  40 . The driver spring  26  disposed in the third driver chamber  40  of the third pin chamber  23  then forces the change ball  56  that was disposed above the shear line  38  down into a corresponding retainer cavity  58 . 
     Referring now to  FIGS. 9A and 9B , the plug  16  with the third key  63  inserted in the keyway  24  has been rotated back to its original position. The change ball  56 , associated with the third pin chamber  23  when in its first position, is now been displaced into its second position within one of the retainer cavities  58  disposed in or associated with the plug  16 . The various drivers  20 , tumblers  22 , and change balls  56  are disposed within the pin chambers  18  such that the lower ends  34  of all the drivers  20  are positioned along and flush with the shear line  38 , and all drivers  20  are disposed fully within the driver chambers  40  of the housing  12 . Thus, the third key  63  operates the lock by rotating the plug  16  within the housing  12 . 
     Referring now to  FIGS. 10A and 10B , the third key  63  has been removed from the keyway  24  and the second key  62  has been reinserted. The Figures illustrate that the second key  62  now cannot operate the lock  10 . The differing third contour location  72 , which is a lowered position in the second key  62 , cannot sufficiently raise the driver  20  and tumbler  22  of the third pin chamber  23  such that the driver  20  is disposed partially within the driver chamber  40  and partially within the tumbler chamber  42  of the third pin chamber  23 . Since the driver  20  of the third pin chamber  23  spans the shear line  38 , the second key  62  will not rotate the plug  16  within the housing  12 , and thus second key  62  is foreclosed from operating the lock  10 . 
     Referring now to  FIGS. 11A-12B , the resetting of the lock  10  to again accept the first key  30  is shown. The lock  10  is shown with the third key  63  (an operable user key) inserted and with plug  16  rotated one-quarter turn clockwise to bring the retainer cavities  58  into alignment with driver chambers  40  of the pin chambers  18 . A change tool  64  is inserted into the change slot  88  of the plug  16 , causing any change balls  56  disposed in their second position in the retainer cavities  58  to be displaced out of the retainer cavities  58 , and into the driver chambers  40 . 
     With the change tool  64  still inserted in the change slot  88 , the plug  16  is then rotated back one quarter turn counterclockwise to an original position (not shown) wherein the driver chamber  40  and the tumbler chambers  42  are now aligned. The change balls  56 , which have been isolated in the driver chamber  40  by the change tool  64 , remain disposed in the driver chambers  40  in the housing  12  just above the shear line  38 . 
     Referring now to  FIGS. 12A and 12B , when each change ball  56  is within its respective pin chamber  18  and the plug  16  is in its first rotated position, the lock has been reset. After the third key  63  has been removed from the keyway  24 , the first key  30  can be reinserted. The first key  30  cannot and does not raise any of the change balls  56  above the shear line  38  of the lock  10 . Thus, the lock  10  has been reset by use of the change tool  64  to enable the first key  30  to operate the lock  10 . 
     The embodiment of the lock  10  depicted in  FIGS. 2A-12B  also allows for a master key which can properly operate the lock  10  without reconfiguring the arrangement of drivers  20 , tumblers  22 , and change balls  56 . In particular, and referring now to  FIGS. 14A-15B , the illustrated embodiment includes a plurality of master shims  60 , with at least one shim being disposed in each pin chamber  18  of the lock  10 . These shims  60  are disposed in the pin chambers  18  beneath the change ball  56  in the stack. The master shims  60  are each sized larger (in the embodiment illustrated, of a larger diameter) than the change balls  56 . The master shims  60  are also of a larger size or diameter than the openings to the retainer cavities  58 , such that a master shim  60  cannot pass into a retainer cavity  58 . Typically, the master shims  60  have a cylindrical diameter larger than that of the change ball  56 , and of the retainer cavities  58 . For the same reason, the size of the drivers  20  positioned in the driver chambers  40  are typically sized larger than the opening of the retainer cavity  58  to prevent the respective driver from entering through the opening and into the retainer cavity when the plug  16  is rotated within the housing  12  to align the retainer cavities  58  and the driver chambers, which would jamb the lock. 
     Referring to  FIGS. 14A-14B , a master key  87  is configured such that, when inserted into the keyway  24  of the plug  16 , all of the drivers  20 , tumblers  22 , change balls  56 , and master shims  60  are raised so that the tumblers  22  lie below the shear line  38  and are disposed within the tumbler chamber  42 , while each of the master shims  60  lie directly above the shear line  38  and in the driver chambers  40 . Referring to  FIGS. 15A-15B , when the plug  16  is then rotated one quarter turn clockwise within the housing  12 , such that the retainer cavities  58  come into alignment with the driver chambers  40 , a master shim  60  cannot be biased by spring force into the retainer cavities  58  because the diameter is larger than that of the opening to the retainer cavity  58 . At the same time, the master shim  60 , positioned between the retainer cavity  58  and the change member  56 , can block the pathway of and prevent the change ball  56  from being displaced from within the driver chamber  40  into the retainer cavities  58 . As such, one may operate or use a master key to open any lock  10  in a particular facility system without reconfiguring the drivers  20 , tumblers  22 , and change balls  56  of the lock  10 . 
     The illustrated embodiment shown in  FIGS. 2A-12B , depicts the tumblers each having the same length, which assists in illustrating the principles of operation of the invention. However, in an alternative embodiment, the length of the various tumblers in the set of tumbler chambers can differ and vary. For a given set of selected tumblers in a lock, a first key  30  will have a top edge contour  32  having contour positions that are configured, or machined, with either higher or lower contour heights, to raise the top of each change ball  56  to the shear line  38  when the first key  30  is inserted into the keyway, so that no change members are disposed in a retainer cavity. A second key  62  in this alternative embodiment has a different though complementary top edge contour  32  that is otherwise similar to the top edge contour  32  of the first key  30 , except that at least one contour position  66  is raised. As the second key  62  is inserted, the additional at least one raised contour  66  on the second key  62  causes at least one change ball  56  to be raised above the shear line  38  of the lock  10  and disposed in the driver chamber  40  of the housing  12 . 
     The subset of keys is made to accommodate the tumbler and driver combinations used in the pin chambers of the particular changeable lock. With a typical key, the height of any contour position can be cut to accommodate the height of the corresponding tumbler selected for use in each pin chamber. Generally, a longer tumbler  22  requires a lower contour cut, and a short tumbler requires a higher contour cut. When cutting the key contour positions, the landing width of the position should be sufficiently wide to prevent a tumbler from beginning to descend prematurely off the end of the contour landing in any one of the pin chambers if the key is withdrawn slightly from the keyway. 
     A second embodiment of the invention is depicted in  FIGS. 16A-22N  wherein like numbers designate like components. The second embodiment illustrates the use of a change tool  64  for reconfiguring the drivers  20 , tumblers  22 , and change balls  56  of the lock  10 . This embodiment can expand the number of keys in a particular subset of user keys compared to the first embodiment. Instead of moving additional change balls  56  from the pin chambers  18  into the retainer cavities  58  as one progresses through a subset of user keys, as described in the first embodiment, the second embodiment enables one to move change balls  56  back and forth between the first position in the pin chambers  18  and the second position in the retainer cavities  58 . Typically, the movement of change balls  56  to and from the retainer cavities  58  and the pin chambers  18  permits the reconfiguration of the lock to operate with a different user key of the subset of user keys. The movement of the change balls to and from also typically involves, at some point in the process, a resetting of the lock, wherein all the change members are returned back into their respective pin chambers. The lock is in a reset configuration when all the change members  56  are in the pin chambers, with an authorized or an operable user key inserted in the keyway, or with no key inserted. The contour locations  66  used in this second embodiment also prevent the “automatic” change described above for the first embodiment with respect to  FIGS. 2A-12B , as explained in greater detail below. 
       FIG. 16A  shows that a first key  30   a  has raised first and third contour locations  68 ,  72 , while the remaining contour locations  70 ,  74 ,  76 ,  78  are lowered. Upon a first use of the first key  30   a  after the lock has been reset, the change balls  56  in the first and third pin chambers  19 ,  23  will be raised above the shear line  38  and, upon rotation of the plug, deposited or displaced into the second position in their respective retainer cavities  58 , as shown in  FIGS. 16A and 16B . 
     The lock  10  may be reset to operate with a second key  62   a  in the key set through the use of the change tool  64 . In order to effect this change, the plug  16  includes a second passage, shown as change slot  88 . The change slot  88  is configured in the plug  16  in a direction parallel to the longitudinal axis  54 , and is positioned to intersect each of the retainer cavities  58 . When the plug  16  is rotated to align the retainer cavities  58  with the driver chambers  40 , and the change tool  64  is inserted in the change slot  88 , any change balls  56  disposed in the retainer cavities  58  are displaced out of the retainer cavities  58  and into the driver chambers  40  in the housing  12 . This facilitates the return of the change balls  56  to the stack of drivers  20  and tumblers  22 , and the resetting of the lock  10 . 
     The method of using the lock  10  of this embodiment of the present invention provides a means for rapidly changing the internal configuration of the drivers, tumblers and change members of the lock to reconfigure the lock to operate exclusively with one of many different keys in a set of keys. The method of using the rapid change lock does not require disassembly, or removal of the plug from the housing. The method involves inserting a first key  30   a  into the longitudinal keyway  24  of a lock  10  that is programmed or configured to operate with the first key  30   a . This first key  30   a  then can be used to rotate the plug  16  within the housing  12 . After the plug  16  is rotated one-quarter turn clockwise(that is, about 90° in the illustrated embodiment) to bring the change slot  88  into alignment with the driver chambers  40 , the change tool  64  can be inserted into the change slot  88 , forcing any change balls  56  disposed in the retainer cavities  58  into the driver chambers  40 . With the change tool  64  in the inserted position, the plug  16  is then rotated back one-quarter turn counter-clockwise to its original position. The first key  30   a  is then removed from the keyway  24 . Removal of the first key  30   a  from the keyway allows the driver springs  26  disposed above the drivers  20  force any change balls  56  from the driver chambers  40  into the tumbler chambers. This resets the lock, or said another way, places the lock into a reset configuration. A second key  62   a  is then inserted. The second key  62   a  has a different though complementary top edge contour  32  to the first key  32   a ; that is, it is otherwise similar to the top edge contour  32  of the first key  30   a  except that a different two of the contour positions  66  are raised. When key  62   a  is inserted, at least two change balls  56  are raised above the shear line  38  and are disposed in the driver chambers  40  of the housing  12  as shown in  FIGS. 18A and 18B . As the second key  62   a  and plug  16  are rotated onequarter turn clockwise, the retainer cavities  58  will come into alignment with the driver chambers  40  of the housing  12 . The change tool  64  is then removed from the change slot  88 , whereby the driver springs  26  disposed above the drivers  20  force the change balls  56  located above the shear line  38  down into the corresponding retainer cavities  58 . As the second key  62   a  is rotated along with the plug  16  back to its original position (see  FIGS. 20A and 20B ), the disposed change balls  56  remain deposited in the retainer cavities  58 , offset from the pin chambers  18 , thereby reconfiguring the lock to operate with the second key  62   a.    
     The illustrated second embodiment will now be described in additional detail. In  FIGS. 16A and 16B , the lock  10  of the second embodiment is depicted with the first key  30   a  inserted into the keyway  24  and with the first and third change balls  56  disposed in the respective retainer cavities  58 . The first key  30   a  can operate the lock  10  since its insertion causes none of the driver or tumbler members of any of the pin chambers  18  or any of the change balls  56 , to span the shear line  38 . The first key  30   a  has a top edge contour  32  having first and third contour locations  68 ,  72  in a raised position, and with the remaining four contour locations  70 ,  74 ,  76 ,  78 , in a lowered position. The Figures show that the lowered contour locations  70 ,  74 ,  76 ,  78  keep the change balls  56  disposed within their respective tumbler chambers  42  when the first key  30   a  is inserted. The raised first and third contour locations  68 ,  72  lift the drivers  20  and tumblers  22  such that the lower ends  34  of the drivers  20  are positioned along the shear line  38  with the drivers  20  disposed entirely in the first and third driver chambers  40 . The change balls  56  associated with the first and third pin chambers  19 ,  23  have been displaced into and are disposed in the corresponding retainer cavities  58  in the plug  16 . 
     Referring now to  FIGS. 17A-21B , the lock  10  can be reset and reconfigured to accept a second key  62   a,  without disassembling the lock  10 . In  FIGS. 17A and 17B , the lock  10  is shown with the first key  30   a  inserted and the plug  16  rotated one-quarter turn clockwise to bring the retainer cavities  58  into alignment with the driver chambers  40 . The change tool  64  is inserted into the change slot  88 , causing change balls  56  to be displaced out of the retainer cavities  58  and into the driver chambers  40  associated with the first and third pin chambers  19 ,  23 . 
     With the change tool  64  still inserted in the change slot  88 , the plug  16  is rotated back one-quarter turn counter-clockwise to the original position. The change balls  56  remain disposed in the driver chambers  40  in the housing  12  as the plug  16  is rotated back to its original position. Referring now to  FIGS. 18A and 18B , the first key  30   a  has been removed from the lock  10  and a second key  62   a  has been inserted. The second key  62   a , as seen in the illustrated embodiment, has raised first and fifth contour locations  68 ,  76 , which raise the change balls  56  in the first and fifth positions (corresponding to pin chambers  19 ,  27 ) above the shear line  38 . 
     Referring now to  FIGS. 19A and 19B , the plug  16  with second key  62   a  inserted is then rotated one-quarter turn clockwise to bring the change slot  88  into alignment with the driver chambers  40 . The change tool  64  is then removed from the change slot  88 , allowing the driver springs  26  disposed above the drivers  20  in the first and fifth positions to force the respective change balls  56  into the retainer cavities  58 . When the second key  62   a  is then rotated back to the original position, shown in  FIGS. 20A-20B , the lock  10  has been reset and reconfigured to enable the second key  62   a  to operate the lock  10 .  FIGS. 21A and 21B  show that the first key  30   a  cannot operate the lock since the driver  20  of the fifth pin chamber  27  will span the shear line  38  and prevent rotation of the plug  16 . 
       FIGS. 22A-22N  show various other keys of the subset of keys that can operate the second embodiment of the lock of the present invention. Each of the keys in  FIGS. 22A-22N  is configured to raise only two of the change balls above the shear line  38  of the lock  10 . All of the keys are unique. That is, the keys are configured whereby the any two raised contour locations  66  are staggered, such that no two keys exhibit the same staggered pattern of two raised contour locations  66 . This configuration prevents the lock  10  from being automatically changed without employing a change tool  64 , as is the case with the first embodiment of the lock  10 . It can be recognized that a key will not operate in a lock  10  when a lowered contour location  66  is present on the key in a position corresponding to a pin chamber  18  in which a change ball  56  has been displaced into its second position in a retainer cavity  58 . When a lowered contour location  66  registers with a change ball  56  in its second position in its respective retainer cavity, the driver  20  in the corresponding pin chamber  18  will span across the shear line  38  of the lock  10 , and the plug  16  cannot rotate. By staggering two high contour locations  66  on the key, as shown with the subset of keys in  FIGS. 22A-22N , it is always assured that, for any key that is used with the exception of the operable key, a lowered contour location  66  will associate or register with a pin chamber  18  that has its change ball  56  displaced to the retainer cavity  58 . This can be seen more particularly with reference to  FIGS. 20A and 21A . In  FIG. 20A , a second key  62   a  which is operable is inserted into the lock  10 . This second key  62   a  has raised first and fifth contour locations  68 ,  76 . The change balls  56  corresponding to those first and fifth contour locations  68 ,  76  have been displaced into corresponding retainer cavities  58 . No driver or tumbler member in the pin chambers  18  spans the shear line  38  of the lock  10 . This second key  62   a  can operate the lock by rotating the plug  16  within the housing. In  FIG. 21A , the second key  62   a  has been removed and a first key  30   a  is inserted. First key  30   a  has at least one lowered contour location  66  corresponding to a pin chamber  18  having a change ball  56  that has been displaced into a retainer cavity  58 . In particular, the fifth contour location  76  is lowered, and registers with the fifth pin chamber  27  where the change ball  56  has been displaced into its corresponding retainer cavity  58 . The first key  30   a  cannot raise the driver  20  and tumbler  22  in the fifth pin chamber  27  high enough, causing that driver  20  to span the shear line  38 . As such, the first key  30   a  cannot operate the reconfigured lock  10  shown in  FIGS. 21A and 21B . 
     The illustrated embodiment shown in  FIGS. 16A-22N  depicts the tumblers each having the same length, which assists in illustrating the principles of operation of the invention. However, in an alternative embodiment, the length of the various tumblers in the set of tumbler chambers can differ and vary. For a given set of selected tumblers in a lock, a first key  30   a  will have a top edge contour  32  having contour positions that are configured, or machined, with either higher or lower contour heights, to raise the top edge  36  of any two tumblers  22  to the shear line  38  when the first key  30   a  is inserted into the keyway. The two contour positions corresponding to the two tumblers  22  are configured to raise and displace two change members into the respective retainer cavities. A second key  62   a  in this embodiment will have a different though complementary top edge contour  32  that is otherwise similar to the top edge contour  32  of the first key  30   a , except that a different pair of two contour positions  66  are configured to raise and displace the corresponding two change members  56  into the respective retainer cavities  58 . 
     In another alternative of the second embodiment of the invention, the subset of keys can be configured so that each user key in the subset can raise four of the change balls above the shear line  38  of the lock  10  when inserted into the keyway  24 . Each user key of the subset of user keys is configured with four raised contour locations  66 , wherein no two keys exhibit the same staggered pattern of four raised contour locations  66 . The maximum number of keys in the four-raised-contour subset is the same as that number for the two-raised-contour subset of keys described herein before. The four-raised-contour key has an added advantage of reducing the possibility of “incidental keying”. This situation can occur when a lock is opened with a key from outside the subset of keys having one or more contour positions with a slightly different height. The slightly different contour height can cause the centerline of a change ball to be unintentionally raised above the shear line  38  when that key is inserted into the keyway. When the centerline of a change ball is just slightly above the shear line, the rotation of the plug within the bore of the housing will force the change ball into the driver chamber, from where it is then deposited into the retainer cavity upon rotation of the plug. When the legitimate user key is inserted into the lock, the absence of the unintentionally-displaced change ball in the pin chamber prevents the key from raising the driver  20  above the shear line, thus rendering the legitimate key inoperable. 
     In yet another alternative of the second embodiment, the subset of operable keys can be configured so that the individual user keys raise different numbers of the change balls above the shear line of the lock upon insertion into the keyway and rotation of the plug. In this alternative embodiment, each key in the subset must be configured to avoid allowing any one key from having all of the raised contour positions of any other key in the subset, since having such would enable the former key to change automatically the configuration of the lock that is operated by the latter key without requiring use of the change tool. Using a subset of keys that can raise different number of change balls typically limits the total number of keys in the subset of keys requiring a change tool. For example, a six-chamber lock with a subset of keys that can raise some combination of two change members, three change members, or four change members, is typically limited to less than 10 possible combinations. By comparison, a six-chamber lock with a subset of keys that only have two raised contour positions to move two change members, or only have four raised contour positions to move four change members, has 15 possible combinations, and a six-chamber lock with a subset of keys that only moves three change members has 10 possible combinations. 
     To lock out all user keys of the subset from operating the lock  10 , an operator may have a “lockout” key having all contour locations  66  raised (shown as key  86  in  FIG. 13D ) or at least having each contour location  66  raised where any one of the subset of user keys has a raised contour. Use of the lockout key (which can also be termed a programming or configuration key) would raise any remaining change balls  56  above the shear line  38  upon insertion into the keyway, regardless of which user key could previously operate the lock. By simply rotating this lockout key one-quarter turn clockwise (in the illustrated embodiment), such that the retainer cavities  58  come into alignment with the driver chambers  40  of the housing, any and all change balls  56  are forced by spring  26  from the driver chambers  40  down into the retainer cavities  58 . This renders the lock  10  operable only for the “lockout” key. If an operator tried to use any other user key of the subset, the lowered contour locations  66  would not raise one or more of the drivers  20  sufficiently high enough, causing that driver  20  to span the shear line  38 . 
     In a preferred embodiment, the lock is provided with a means for signaling to the user that the key and plug are in the first rotated position (or the key insertion position). A typical plug positioning means is a detent and pin. As shown in  FIG. 42 , the periphery of the plug  16  is provided with a first detent cavity  160 , typically a rounded or cylindrical hole. A detent pin, shown as a detent ball  164 , is disposed in the first detent cavity  160 , and is biased radially outward toward the shear line or periphery of the plug by a biasing means, shown as a detent spring  162 . A second detent cavity  166  is disposed in the inner surface of the bore  14  of the cylindrical portion  11  of housing  12 , and is shown in  FIG. 42  as a hole formed in the cylindrical portion  11  of the housing  12 . The detent means is configured such that the first detent cavity  160  and the second detent cavity  166  align and register with one another when the tumbler chambers in the plug  16  are aligned with the drive chambers  40  of the housing  12 . The second detent cavity  166  has a size or diameter less than the size or diameter of the detent ball  164 , such that when the first and second detent cavities are aligned, the detent ball is retained substantially within the first detent cavity  160 . Typically, the first detent cavity  160  is formed on the side of the plug  16  opposite the retainer cavities  58 . The first detent cavity  160  is also typically disposed in the plug  16  longitudinally displaced from any of the retainer cavities  58 . This ensures that the first detent cavity  160  cannot register or align with any of the retainer cavities  58  or drive chambers  40  when the plug  16  is rotated fully within the housing  12 . Interference between the operation of the plug positioning means with the movement of a change ball  56  between a driver chamber  40  and a retainer cavity  58  is thereby avoided. 
     In operation, when the plug is in its first rotated position shown in  FIG. 43A , the first detent cavity  160  and the second detent cavity  166  align, and the detent ball  164  rests partially out of the first detent cavity  160  and partially into the second detent cavity  166 , biased in place by the detent spring  162 . 
     When an operable key  30   a  is inserted into the lock and rotated toward its second rotated position shown in  FIG. 43B , the inner surface of the bore  14  forces the detent ball  164  fully within the first detent cavity  160 , where it is retained by the inner surface of the cylindrical portion  11  of the housing  12 . After the lock has been reprogrammed, as discussed herein, and the lock is rotated back toward its first rotated position. When the plug returns to the first rotated position, the first detent and the second detent cavities  160  and  166  again align. The user may hear and feel in the fingers, through the key, the impact of the detent ball  164  when driven by the detent spring  162  against the inside rim of the second detent cavity  166 . This signals that the plug has been returned to the key inserted and removal position, and is properly aligned in the housing for removal of the operating key from the lock. 
     A typical way of forming the detent means during the making of the lock is described. While restraining the plug  16  from movement within the housing  12  and with the tumbler chambers  42  aligned with the drive chambers  40 , a hole is drilled through the cylindrical portion  11  of the housing, forming the second detent cavity  166 , and partially into the plug  16 . A small flat surface can be machined onto the outer surface of the cylindrical portion  11  to facilitate the drilling. The plug is then removed and a larger-diameter hole is drilled into the plug, centered on the smaller partial hole, to form the first detent cavity  160 . A detent ball  164  on top of a detent spring  162  are then inserted and restrained in the first detent cavity  160  as the plug  16  is inserted into the bore  14  of the housing  12 . A preferred detent spring has a stainless steel wire of about size 013, and is available as part number C090.times.013.times.190 from W. B. Jones Spring Co., Inc., of Wilder, Ky. 
     Optionally the lock of the present invention can be configured with a second plug positioning means to provide a signal to the user that the plug has been rotated to the second rotated position within the housing for inserting the change tool and resetting the lock. 
     Referring now to  FIGS. 23A-28B , wherein like components are referenced by like numbers, an illustrated third embodiment of the present invention is shown comprising at least one memory block associated with a retainer cavity. The memory block  90  is disposed in the plug  16  of the lock  10  and is configured to intersect the change slot  88  and retainer cavities  58 . The memory block  90  prevents a user key other than the currently operable user key from being used to alter the driver, tumbler, and change ball configurations in the lock  10  in an unauthorized fashion. The memory block  90  accomplishes this by partially blocking the openings to the retainer cavities  58 , so that change balls  56  cannot fit past the opening and into the retainer cavities  58 . An authorized user may then insert a change tool  64  to move the memory block  90  away from the change slot  88  and expose the full diameter of the openings of the retainer cavities  58 . 
     The lock  10  having a memory block  90  is shown in  FIGS. 23A-23B  having an inserted first key  30   b  that can operate the lock  10 . The memory block  90  comprises a single block member associated with a plurality of memory block springs  92  that have a first end  94  operatively connected to a side edge  96  of the memory block  90 , and a second end  98  operatively connected to an inner wall  100  located in the plug  16 . The memory block springs  92  bias the memory block  90  in a direction toward the retainer cavities  58  such that the memory block  90  overlaps with and thereby reduces the size of the opening to the retainer cavities  58 . As can be seen in  FIG. 23A , a change ball  56  associated with the first pin chamber  19  is disposed in its second position within the corresponding retainer cavity  58 . Each driver  20  in the pin chambers  18  is positioned such that its lower end  34  is flush with, and does not span, the shear line  38 , thus allowing the plug  16  to rotate within the housing  16 . 
     Referring now to  FIGS. 24A and 24B , the lock  10  is depicted with the first key  30   b  inserted and with the plug  16  rotated one-quarter turn clockwise in the lock  10 . A change tool  64  is shown inserted into the change slot, which results in two occurrences: (1) the change tool  64  displaces the memory block  90  away from the retainer cavities  58 , thus exposing the openings to the retainer cavities  58  to their fullest size (diameter) and (2) the change tool  64  displaces any change ball  56  that had been disposed in the retainer cavities  58 , into the respective driver chamber  40 . In the embodiment shown in  FIG. 24A , the change tool  64  has displaced the change ball  56  back up into the first driver chamber  40 . 
     The memory bar  90  is configured with a bevel  93 , shown in  FIG. 23A , positioned along the change slot  88  near the entry opening on the change slot  88 , illustrated as the indicator mark  114  in  FIG. 1 . As the change tool  64  is inserted into the change slot  88 , the tool  64  engages the bevel  93 , biasing the memory bar  90  radially toward the inner wall  100  sufficiently to expose the full diameter of the openings of the retainer cavities  58 . 
     With the change tool  64  still inserted, the plug  16  has been rotated back one-quarter turn counter-clockwise to its original position. The first key  30   b  has been removed and a second key  62   b  has been inserted, as shown in  FIGS. 25A and 25B . The second key  62   b  has a different top edge contour  32  than the first key  30   b.  The illustrated embodiment, the third contour location  72  is raised in the second key  62   b,  whereas it was lowered in the first key  30   b . As shown in  FIG. 25A , the second key  62   b  raises the change balls  56  associated with the first and third pin chambers  19 ,  23  above the shear line  38 . The driver  20  in each remaining pin chamber  18  is disposed within the driver chamber  40  of the housing  12  with its bottom edge  34  positioned along the shear line  38 . In this configuration, the plug  16  can rotate within the housing  12 . The change tool  64  is still inserted in the change slot  88 , thus keeping the memory block  90  disposed away from the openings to the retainer cavities  58  such that the memory block  90  does not reduce the diameter of the openings. 
     Referring now to  FIGS. 26A and 26B , the plug  16  with the second key  62   b  inserted has been rotated one-quarter turn clockwise to bring the retainer cavity  58  and the change tool  64  (which is still inserted in the change slot  88 ) into alignment with the driver chambers  40 . The inserted change tool  64  has engaged the bevel  93  and biases the memory block  90  away from the opening to the retainer cavities  58 . The change balls  56  of the first and third pin chambers  19 ,  23  are still disposed within the respective driver chambers  40  above the shear line  38  and directly above the retainer cavities  58 . 
     The change tool  64  is then pulled from the change slot  88 . So long as at least some portion of the length of the change tool  64  remains in the entry to the change slot  88  and engaged with the bevel  93 , the memory block  90  remains biased away from the opening to the retainer cavities  58 . Thus, as the distal end of the change tool  64  is withdraw past each driver chamber  40 , any change ball  56  disposed within the driver chamber  40  above the shear line  38  is forced by the driver spring  26  through the opening and into the corresponding retainer cavity  58 . 
     After the change tool  64  is completely withdrawn from the change slot  88 , and any change ball  56  disposed in the driver chamber  40  has been driven into its retainer cavity  58 , the spring force of the memory block springs  92  biases the memory block  90  back toward the retainer cavities  58  as shown in  FIGS. 27A and 27B . This again reduces the size of the openings to the retainer cavities  58  such that the operable size for the opening to the retainer cavity  58  is too small for a change ball  56  to pass into or out from the retainer cavity  58 . 
     With the change tool  64  removed, the plug  16  is rotated in the housing  12  back one-quarter turn counter-clockwise to the original position. As seen in  FIGS. 28A and 28B , the memory block  90  remains biased by the spring force of the bias springs  92  toward the openings of the retainer cavities  58 . When a subsequent key with a raised contour location  66  at one of the remaining second, fourth, fifth, or sixth contour locations  70 ,  74 ,  76 ,  78  (or any combination of those locations) is inserted, at least one additional change ball  56  will be displaced above the shear line  38 . However, if the lock  10  is rotated without inserting a change tool  64  to open the memory block  90 , the change balls  56  cannot be forced out of the driver chambers  40  and down into the retainer cavities  58 . Thus, with a memory block  90 , additional keys cannot change the configuration of the drivers  20 , tumblers  22 , and change balls  56  unless a change tool  64  is used. Likewise, reinsertion of the first key  30   b  will not operate the lock  10 , since the driver  20  of the third pin chamber  23  would be disposed across the shear line  38  of the lock  10 . 
     The illustrated embodiment uses a single unitary memory bar  90  that covers and uncovers all of the retainer cavities. Alternatively, a separate memory bar can be provided for each retainer cavity, or for a plurality of retainer cavities. 
     The housing  12  and the plug  16  of the lock  10  can each include an indicator mark  114  and  144 , respectively, to be used in conjunction with the change tool  64  in reprogramming the lock  10 . 
     Referring to  FIGS. 1 and 37 , in order to change the lock  10 , the change tool  64  is provided for insertion into the longitudinal change slot  88 . The change tool  64 , suitably configured for use with the lock  10  as described, has a handle portion  136  and a blade portion  138 . The blade portion  138  has a beveled edge end  141  to facilitate movement of the blade portion  138  past the retainer cavities  58  during insertion. As described above, with this change tool  64 , the driver mechanism of the lock  10  can be readily changed to facilitate operation of the lock  10  with a different second key  62   a.  The blade portion  138  has a linear edge  143  that is configured to raise each change ball  56  out of its respective retainer cavity  58  when fully inserted into the change slot  88 . The change tool  64  can also include a change tool notch  140  that is adapted to insert into a change tool notch groove  142  that can be disposed circumferentially in the housing  12  (see  FIG. 11A ). The notch  140  can register with the groove  142  to prevent the change tool  64  from being withdrawn and removed from the change slot  88  unless the retainer cavities  58  or the tumbler chambers  42  are aligned with the driver chambers  40 . 
     The plug  16  of the embodiment illustrated in  FIGS. 23 through 28  can be made by machining the plurality of tumbler chambers  42 , the plurality of retainer cavities  58 , and the change slot  88  into a metal cylinder, typically a cylindrical bar stock material. Alternatively, an existing conventional plug having only the plurality of tumbler chambers can be retrofitted by machining the plurality of retainer cavities and the change slot  88  therein. 
     In a first method of making a changeable lock plug, a standard lock plug is provided and machined. This step typically comprises disassembling an existing standard lock, by removing the plug from the lock housing, and removing the hardware, such as springs and pins (the drivers, tumblers and any master shims) from the lock plug, thereby recovering the standard lock plug. 
     The standard lock plug has as a keyway, an axial centerline and a circumferential surface The standard lock plug further has a plurality of tumbler chambers  42  extending through the circumferential surface along a first line extending parallel to the axial centerline. Each tumbler chamber extends into the keyway and has a centerline that is spaced apart by a first distance from an adjacent tumbler chamber. Typically adjacent tumbler chambers are separated by the same first distance. 
     In the next step, the standard lock plug is machined to provide a plurality of retainer cavities  58 , into the standard lock plug. The retainer cavities are formed through the circumferential surface along a second line extending parallel to the axial centerline, and hence parallel to the line of the tumbler chambers  42 . Each retainer cavity extends partially into the plug body. The second line is positioned whereby the retainer cavities are displaced radially from the first line of tumbler chambers by an arc angle along the circumferential surface. Typically, the arc angle is about 30° to about 160°, more typically about 45° to about 135°, offset from the first line. 
     In a typical embodiment, the retainer cavities are machined to a depth into the plug body of at least its diameter, more typically at least 105% of its diameter. Typical retainer cavity diameters are from about 0.050 inches (about 1.3 mm) to 0.090 inches (about 2.3 mm), and are typically of a size, or diameter, less than the diameter of the driver and any master shim positioned within the driver chambers of the housing. More typically, the diameter of the retainer cavities are drilled to a diameter of about 95% and less than the size (diameter) of the driver. Typically, the retainer cavities are formed with a standard drilling machine. 
     In a next step, a slot is cut along the axial direction in the outer surface of the plug along the same line as the second bores. The slot is illustrated as the change slot  88  in the embodiments. The slot is generally formed as a u-shaped or rectangular cross section, penetrating the circumferential surface of the plug and extending radially inward toward the center axis. The slot is typically formed having a depth of approximately the same depth as the retainer cavities, and having a width of about 0.04 inches (1.0 mm) or less, and more typically of about 0.02 inches (0.5 mm) or less. The slot typically extends longitudinally completely from the front face  13  of the plug to the latch end  15  of the plug, passing through the centers of each retainer cavity. The slot can be cut by any well known means, such as a circular saw. 
     After forming the retainer cavities and the slot, the lock is then reassembled by reinstalling the drivers, tumblers, springs, and change balls in a programmed arrangement. The change ball is typically a spherical change ball, sized to fit within the depth of the retainer cavity, as described herein above. 
     In a typically method, the plug body is secured, such as by clamps, for rotational movement about its center axis. The plug is first secured in a first position whereby the tumbler chambers register with a reference point. The reference point is registered with a drilling machine. The drilling machine operates a drilling bit that is rotated at a cutting speed, and can move the drilling bit along the axis of the drill bit from a first position outside the plug surface to a second position that penetrates a depth into the plug. The plug is then rotated about its axis to a second position, which is offset radially from the first position by the arc angle. The drilling machine is then operated to drill the retainer cavity to its depth. The drilling machine is also configured for movement along the longitudinal axis of the plug, whereby successive retainer cavities can be drilled along the second line of the plug to form the plurality of retainer cavities. More typically, the drilling machine comprises a plurality of drilling bits that are configured spaced apart, whereby the plurality of retainer cavities can be machined simultaneously. 
     In a second method of making a changeable lock plug, a base lock plug is provided and machined. The base plug is typically a cylindrical body configured with a keyway. In this method, both the tumbler chambers and the retainer cavities, and the change slot, are machined into the circumferential surface for plug body. The plurality of tumbler chambers are machined, typically by a drilling machine, through the circumferential surface along a first line extending parallel to the axial centerline, wherein each tumbler chamber extends into the keyway. Typically, the tumbler chambers penetrate the plug surface at a position opposite (180°) from the base of the keyway. The plurality of retainer cavities are then machined through the circumferential surface along a second line as described above for the first method. 
     In a typically method, the base plug body is secured, such as by clamps, for rotational movement about its center axis. The base plug is first secured in a first position whereby a drilling machine registers with a reference point representing the axial centerline of a first retainer cavity. The drilling machine operates a drilling bit that is rotated at a cutting speed, and can move the drilling bit along the axis of the drill bit from a first position outside the plug surface to a second position that penetrates a depth into the plug. The drilling machine is configured for operation to drill the first tumbler chamber through the circumferential surface of the plug and into the keyway. The drilling machine is then moved along the longitudinal axis of the plug to a next position, corresponding to the axial centerline of the second tumbler chamber. The drilling machine is again operated to drill the second tumbler chamber. Successive tumbler chambers can thus be machined. Alternatively, the drilling machine can comprise a plurality of drilling bits that are configured spaced apart, whereby all required retainer cavities can be machined simultaneously along the first line. 
     The plug is then rotated about its axis to a second position, which is offset radially from the first position by the arc angle. The drilling machine is then operated to drill each retainer cavity to its depth, as described above. 
     Alternatively, the set of tumbler chambers and retainer cavities can be machined into the base plug by separate drilling machines, sequentially or simultaneously, without requiring rotational movement of the plug body. 
     A change slot is also formed along the second line, passing through the plurality of retainer cavities. The change slot is typically secured in placed and machined with a rotating saw. The step of forming the change slot can be performed while the plug is in the same position as for the drilling of the retainer cavities. 
     Referring now to  FIGS. 29A-36B  and  39 A- 39 C, in another illustrated alternate embodiment wherein like components are referenced by like numbers, the plug  16  of the present invention can optionally include at least one first groove in the form of a radial slot  102  disposed in the circumference of the plug  16  extending radially and outwardly from the longitudinal axis  54  of the plug  16 . This radial slot  102  forms a cavity through and within the outer periphery of the plug  16 . The keyway  24  allows for the insertion of a first key  30   c  having a longitudinal contour  44  of grooves and/or ridges and a top edge contour  32 . A radial tumbler  104  can be disposed in the radial slot  102 , the radial tumbler  104  including a distal end  106  that extends into the keyway  24 . 
     The radial tumbler  104  can be configured for circumferential movement within the radial slot  102  around the longitudinal axis  54  of the plug  16 . The radial tumbler  104  is biased toward the keyway  24  of the plug  16  by a radial tumbler spring  108 . As a result, the distal end  106  of the radial tumbler  104  projects into the keyway  24  when no key is present. Thus, not only must the top edge contour  32  of the first key  30  be of correct shape to raise the drivers  20  and tumblers  22  and any change ball  56  to match the shear line  38  of the lock  10 , but the longitudinal contour  44  on the first key  30  must be a configuration that allows the first key  30  to confront distal end  106  of the radial tumbler  104  that extends into the keyway  24 , and to properly position the radial tumbler  104  to allow the plug  16  to be rotated. 
     A plurality of radial tumblers  104  can be disposed within a plurality of radial slots  102  in the sidewall of the plug  16 . For purposes of illustration, only one radial tumbler  104  will be described. Also alternatively, a secondary radial tumbler or secondary set of radial tumblers (not shown) can be provided on the opposite side of the plug  16 , such that the distal ends  106  of the radial tumblers project into each side of the keyway  24 . 
     A radial tumbler spring  108  is positioned in confronting relationship with the radial tumbler  104 , between a top edge  110  of the radial tumbler  104  and an upper sidewall  112  of the plug  16 . This spring  108  biases the radial tumbler  104  away from the upper sidewall  112  and toward the keyway  24 . The distal end  106  of the radial tumblers  104 , as shown in the illustrated embodiment, can be beveled such that a key being inserted into the keyway  24  can move past the radial tumblers  104 . 
     The lock  10  of the illustrated embodiment can further include a sidebar  116  disposed in a longitudinal sidebar slot  118  formed in the periphery of the plug  16 . Both the sidebar  116  and sidebar slot  118  extend along a line substantially parallel to the longitudinal axis  54  of the plug  16 . At least one sidebar spring  120  is disposed within the plug  16  and confronts the sidebar  116  in order to bias the sidebar  116  radially outwardly from the longitudinal axis  54  of the plug  16 . 
     The sidebar  116  of the illustrated embodiment extends substantially along the length of the plug  16  and includes a projection  122  on a first side thereof. The projection  122  is adapted to mate with a second groove  122  which is configured in the bore of the housing  12 . At least one lug  126  extends radially inwardly from a second side of the sidebar  116 , toward the radial tumbler  104 . The lug  126 , in the illustrated embodiment, is disposed substantially opposite from the projection  122  of the sidebar  116 . The sidebar spring  120  biases the sidebar  116  away from the radial tumbler  104 , such that the projection  122  of the sidebar  116  is disposed within the second groove  124  when the plug  16  is in an original position as shown in  FIG. 9B . In the illustrated embodiment, two sidebar springs  120  are used to bias the sidebar  116 . 
     The radial tumbler  104  further includes a sidebar groove  128 , which allows for circumferential movement of the radial tumbler  104  even while the sidebar  116  is held in position with projection  122  in the second groove  124 . The sidebar groove  128  in the radial tumbler  104  is only of a radial depth sufficient to house the length of the sidebar  116  when the projection  122  is disposed in the second groove  124 . The radial tumbler  104  further includes a sidebar notch  130  that extends from the sidebar groove  128  in a direction orthogonal to and substantially toward the longitudinal axis  54  of the plug  16 . 
     With no key or an inoperative key inserted in the keyway  24 , the radial tumbler  104  can be disposed within the radial slot  102  such that the sidebar  116  is not aligned radially with the sidebar notch  130 . Thus, any attempted rotation of the plug  16  will also be prevented by the location of the projection  122  in the second groove  124  of the housing  12  (see  FIG. 29B ). When a proper first key  30  is inserted in the keyway  24  (as shown in  FIG. 30B ), the sidebar lug  126  will align radially with the sidebar notch  130  to allow displacement of the sidebar  116  out of the second groove  124  and into the sidebar notch  130  upon rotation of the plug  16 . 
     At the time of insertion of a proper first key  30   c  and prior to the turning of the plug  16 , each of the tumblers  22 , drivers  20  and change balls  56  will be lifted by the top edge contour  32  of the first key  30   c  such that the junction between any two of the drivers  20 , tumblers  22 , and change balls  56  proximate to the shear line  38  is flush with shear line  38 . Also, to enable rotation of the plug  16 , the first key  30   c  must have a longitudinal contour  44  that matches the pattern of the keyway  24  formed by the distal end  106  of the radial tumbler  104 . An operable first key  30   c  can operate the lock  10  having a radial tumbler on one side of the plug  16 , or a lock  10  with matched radial tumblers  104  disposed on each side of the plug  16 . However, hereinafter, only one radial tumbler  104  on one side of the plug  16  will be discussed in order to illustrate the principles of the present invention. 
     As the proper first key  30   c  is inserted, the radial tumbler  104  will move circumferentially such that the lug  126  of the sidebar  116  is positioned in radial alignment with a sidebar notch  130  disposed in the first radial tumbler  104 . The sidebar lug  126  then has suitable space for movement radially (inwardly) toward the radial tumbler  104  and into the sidebar notch  130  upon turning of the first key  30   c.  When the first key  30   c  is turned, the sidebar projection  122  cams out of the second groove  124 , causing the sidebar  116  to move radially inward to a position wherein the lug  126  of the sidebar  116  is accommodated by the sidebar notch  130  in the first radial tumbler  104 . 
     With a proper first key  30   c  inserted in the lock  10  and the above-described disposition of the drivers  20  and tumblers  22 , the plug  16  can be rotated to disengage the latch member (not shown) from the doorjamb slot or other recess so that the door or other member can be opened. If the top edge contour  32  of a key is inappropriate for operating the lock  10 , a portion of one or more of the drivers  20  will project into a tumbler chamber  42  of the pin chambers  18 , and/or a portion of one or more of the tumblers  22  will project into a driver chamber  40 , to fix the plug  16  at the locking orientation so that the door or other member in which the lock  10  is installed cannot be opened. Additionally, a change ball  56  or master shim  60  could span the shear line  38 , thus blocking rotation of the plug  16 . Additionally, a key, even a key with a proper top edge contour  32 , will be unable to operate the lock  10  if the key does not have a pre-selected design of the longitudinal contour  44  running along its length to match the contour of the keyway  24  provided by the distal ends  106  of the radial tumbler  104  projecting into the keyway  24 . Such a proper longitudinal contour  44  establishes the proper alignment of sidebar lug  126  with sidebar notch  130 . 
     With reference to  FIGS. 29A-36B , the keyway  24  in the plug  16  is substantially rectangular in shape, and intersects a portion of the periphery of the plug  16 . The limits of the keyway  24  are formed by a first internal side wall  132  and a second internal sidewall  134  of the plug  16 . As described above, the distal end  106  of the radial tumbler  104  extends into and through a projection of at least one of the first and second internal sidewalls  132 , 134  of the keyway  24 . This distal end  106  projects a pre-selected distance into the keyway  24 . In alternate embodiments, distal ends  106  of multiple radial tumblers  104  can project through both the first and second internal sidewalls  132 ,  134 . 
     To reprogram the lock  10 , the first key  30   c,  which is the proper key to originally operate the lock  10 , is inserted into the keyway  24  (see  FIGS. 30A and 30B ), and the plug  16  is rotated relative to the housing  12  (one-quarter turn counter-clockwise) until a first indicator mark  114  on the face  115  of the plug  16  is aligned with a second indicator mark  144  on the face of the housing  12  (see  FIGS. 1 ,  31 A and  31 B). Alignment of the indicator marks  114 ,  144 , ensures that the retainer cavities  58  are aligned with the driver chambers  40 . Referring now to  FIGS. 32A and 32B , the change tool  64  is then fully inserted into the change slot  88 . As the change tool  64  is inserted into the change slot  88 , each successive change ball  56  located in a retainer cavity  58  is displaced from its second position in the retainer cavity  58  to its first position into the driver chamber  40  in the housing  12 . The plug  16  can then be rotated back to the starting position, where the first key  30  removed from the keyway  24 , and a second key  62   c  is inserted into the keyway  24  (see  FIGS. 33A-33B ). With the change tool  64  still inserted in the change slot  88 , the plug  16  is again rotated (one-quarter turn counter-clockwise) relative to the housing until the indicator marks  114 ,  144  are again aligned (as shown in  FIGS. 34A and 34B ). The change tool  64  is then removed from the change slot  88 , and a change ball  56  disposed in a driver chamber  40  is forced down into its corresponding retainer cavity  58  by to the force of driver spring  26  (see  FIGS. 35A and 35B ). When the plug  16  is rotated back to its originating position (see  FIGS. 36A and 36B ), the second key  62   c  can now operate the lock  10 , but the first key  30   c  cannot. 
     Referring again to the sequence of Figures in to  FIGS. 29A-36B , each of key  30   c  and  62   c  has been configured, when inserted into the keyway, to displace the radial tumbler  104  circumferentially into a position wherein the lug  126  of the side bar  116  is aligned radially with the side bar notch  130  in the radial tumbler  104 . In this position, the projection  122  of the sidebar  116  can be displaced out of the second groove  124  so that the plug  16  can be rotated within the housing  12  of the lock  10 . 
     Referring now to  FIGS. 37 ,  38 , and  40 A-C, in an alternate embodiment of the present invention, a lock  10   c  can have a plurality of rows  146 ,  148  of pin chambers  18   a  and  18   b . A first row  146  of pin chambers  18   a  is disposed in the housing  12  and plug  16  along in a first plane  150  passing through the longitudinal axis  54  of the plug  16 . A second row  148  of pin chambers  18  is disposed in the housing  12  and the plug along a second plane  152  passing through the longitudinal axis  54  of the plug  16 . The second plane  152  is angularly offset from the first plane  150 . The housing  12  has a plurality of rows of driver chambers  40   a  and  40   b,  with driver chambers  40   a  forming a portion of the pin chambers of row  146 , and the driver chambers  40   b  forming a portion of the pin chambers of row  148 . 
     The plug  16  has a plurality of rows of tumbler chambers  42   a  and  42   b,  each configured to align with a corresponding row of the drive chambers  40   a  and  40   b  when the lock is in its neutral or first rotated position shown in  FIG. 38 . The plug also has a plurality of rows of retainer cavities  58   a  and  58   b,  and a plurality of change slots  88   a  and  88   b.    
     Each of the pin chambers  18  is adapted to receive at least a driver  20 , a tumbler  22 , optional, though preferably, a change ball  56 , and optionally, though preferably, a master shim  60 . 
     The lock of the illustrated embodiment operates as desirable scribed hereinbefore for the first and second embodiments of the invention having a single row of pin chambers, with the added requirement that operation of the illustrated lock requires both sets of change members to move between the respective pin chambers,  18   a  and  18   b,  and retainer cavities,  58   a  and  58   b.    
     The provision of a second row of pin chambers, which increases the number of stacks of drivers  20 , tumblers  22 , and change balls  56 , increases the number of lock change combinations, thereby increasing the security and utility provided by the lock  10   c . Although the illustrated embodiment depicts two rows  146 ,  148  of a pin chamber  18  that contain driver/tumbler stacks, an additional row or more of such pin chambers  18  can be included in the lock  10  of the present invention. 
     Also, the embodiment of the lock  10  illustrated in  FIGS. 37 and 38  can include additional components such as a memory block  90 , radial tumblers  104 , and sidebars  116 , as described above with respect to alternate embodiments of the present invention. 
     In an alternate embodiment of the present invention depicted in  FIGS. 41A and 41B , the lock  10   d  includes at least one an anti-tamper pin  154  that rests and is movable within an anti-tamper orifice or passage  156  in the plug  16 . The anti-tamper pin  154  has a first position wherein a first end of the anti-tamper pin  154  blocks can intersect with and thereby block the longitudinal change slot  88 , whereby a change tool  64 , or any other object, cannot be fully inserted into the change slot  88 . A proper first key  30   d  comprises an anti-tamper groove  158  that registers with a second end of the anti-tamper pin  154  when the anti-tamper pin  154  is in a second position. With the key  30   d  inserted in the keyway, the change tool  64  can be inserted without impediment into the change slot  88 , to move the anti-tamper pin  154  to its second position. 
     The embodiments of a changeable lock assembly can be used in a variety of locking devices. These locking devices include both commercial and residential locks, and include by example, knob locks, deadbolt locks, and padlocks. The operation of a typical knob lock includes the use of the operable key both to unlock and lock the door knob by turning a latch that is secured to the latch end  15  of the plug. The latch typically unlocks the door knob, which can then turn or rotate by hand, and thereby operate an elongated bolt that engages and disengages the jamb of the door or other object that is being locked. The operation of a typical dead-bolt lock includes the use of the operable key to unlock and rotate a latch that drives an elongated bolt to engage and disengage the jamb of the door or other object that is being locked. These locks are well-known to one skilled in the art. 
     The operation of a typical padlock includes the use of the operable key to unlock a J-shaped shackle. In a typical padlock configured in a locked position, a bolt within the lock body (or a pair of bolts) is biased into a position within a groove in each leg of the shackle, to positively restrain the shackle from withdrawing from the body. The design and operation of a typical padlock is described in U.S. Pat. No. 3,710,603 (Miller) and U.S. Pat. No. 4,776,187 (Evans et al), both incorporated herein by reference. The padlock is typically configured whereby the rotation of the key with the plug causes the bolt(s) to be displaced from the grooves, thereby allowing the shackle to withdraw from the body. A typical, conventional padlock is configured whereby the inserted key will only rotate in one direction to unlock the shackle, and is typically provided with a spring or other means for biasing the bolt, as well as the plug and the key, back toward its initial or “key-insertion” position 
     The padlock of the present invention comprises a changeable lock assembly configured to rotate in both the first direction (generally clockwise, facing the keyway) and the second direction.  FIGS. 44A ,  44 B, and  44 C show an end view of the plug of the padlock in its initial position, and when rotated in both the first and second directions. Rotation of the plug in the first direction, from a first position shown in  FIG. 44A  to a second unlock position shown in  FIG. 44C , can unlock the padlock. As with conventional padlocks, the lock is typically configured with a spring or biasing means to return the rotated plug back to the initial “key insertion” position. Rotation of the plug in the second direction (generally, counterclockwise), from the first position shown in  FIG. 44A  to a reprogramming position shown in  FIG. 44B , can provide for reprogramming of the lock in accordance with the invention described hereinabove. Preferably, the rotation of the plug in the second direction will not unlock the padlock. To avoid unlocking the padlock when the plug is rotated in the second direction, the latch-rotating end  15  of the plug is provided with a tailpiece or latch  216  comprising a shaft  218  extending from a generally rounded base  217 . The base  217  is rotatably retained to the latch end  15  with a threaded nut  220 . The base  217  has a forward face  222  and a reverse face  224  defined by an opened wedge portion  219  (typically of about one-quarter to one-third of the circumference). A stop pin  226  that extends from the latch end  15  can restrict rotation of the latch  216  within the span of the opened portion  219  between the forward face  222  and the reverse face  224 . 
     When the key is operated in the lock, the clockwise rotation of the key in the plug turns the plug and forces the stop pin  220  against the forward face  222  of the latch  216 , which drives the latch to rotate in the clockwise direction (counter-clockwise when viewed from the rear of the plug, as shown in  FIG. 44C ). The rotation of the latch disengages the bolt(s) from the grooves in the shackle and unlocks the padlock. A spring or other biasing means (not shown) returns the latch, the plug, and the inserted key back to the initial position. 
     The latch  216  of a typical padlock is configured to prevent its rotation in the counterclockwise direction. When the key rotates the plug counterclockwise to the second rotating or programming position, (clockwise when viewed from the rear of the plug, as shown in  FIG. 44B , the stop pin  220  is free to move within the opened portion  219  of the restrained latch  216 . This arrangement is conventionally called a “lazy cam”, where the cam or tailpiece is configured to remain stationary while the cylinder plug is partially rotated. 
     Optionally, the rotation of the plug in the second direction can also unlock the padlock, although the process of unlocking the padlock can make the reprogramming of the changeable lock assembly more complicated. 
     In the padlock of the present invention, the plug can be placed into its second rotated position shown in  FIG. 44B  within the housing, wherein the retainer cavities and change slot align or register with the driver chambers. The lock configuration of the padlock can be reprogrammed using a change tool to operate with a different user key of a subset of user keys, as described herein before for the second embodiment of the changeable lock assembly. Alternatively, the lock configuration of the padlock can be configured to operate with a progression of different though complementary user keys, as described herein before for the first embodiment of the changeable lock assembly. Each of the user keys can reprogram the lock for use by displacing a change member from a pin chamber into a retainer cavity, which disables any user keys of the subset of keys from operating the lock which are configured to move less than the current number and configuration of change members. 
     While the invention has been disclosed by reference to the details of preferred embodiments of the invention, it is to be understood that the disclosure is intended in an illustrative rather than in a limiting sense, as it is contemplated that modifications will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.