Abstract:
A lock which is rekeyable or programmable to operate with a different key from the exterior thereof without disassembling it or removing it from a lock assembly in which it is assembled is disclosed. The lock is rekeyed by a change key through the keyway so that the lock appears from the exterior thereof to be a conventional lock. The change key which can not operate the lock adjusts a movable shear line formed by what is in effect an externally adjustable tumbler. The lock includes a plurality of pin tumbler sets and a plurality of cylinders disposed one in the other in the lock casing. The pin tumbler sets and the cylinders cooperate to from a plurality of common pin tumbler shear lines, i.e., shear lines formed by a number of individual shear lines of individual pin tumbler sets. In a given position of the adjustable shear line, only one of the keys will position the pin tumblers to form the proper common pin tumbler shear which is aligned with the adjustable shear line to operate the lock. The rekeying structure of the lock is passive and its presence is not noticed when operating the lock. The lock also includes structure which indicates that the adjustable shear line is in one of the position with which a common tumbler shear line may be aligned. The lock further includes structure which locks the adjustable shear line in a given position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a lock adjustable or programmable to operate with different keys and to methods of providing and operating such a lock. 
     There are many instances in which it is desirable to change the keying of a lock. For example, when one loses a key to a lock, particularly a door lock, the primary concern is often not with unlocking the lock since duplicate keys are usually left with relatives, neighbors, landlords, superintendents, building agents, etc., but that the finder of the key will be able to identify the location of the lock and unlock it. That concern becomes more serious when the key was lost or stolen under circumstances which permit an identification of the key owner, such as when a woman&#39;s handbag is lost or stolen, or when a set of keys is taken, for example, from an automobile. In such instances, the lock must either be rekeyed or changed to prevent the lost or stolen key from operating the lock. In either case, a locksmith was usually called to change the keying of the lock or to replace the lock itself. 
     Pin tumbler locks which may be rekeyed without removing the tumblers, and therefore rekeyed without a locksmith, are known. U.S. Pat. No. 1,565,556 of Fremon, issued Dec. 15, 1925, and U.S. Pat. No. 2,603,081, of Pelle, issued July 15, 1952 disclose locks which must be removed from the lock assembly in which they have been assembled in order to effect rekeying. Therefore, while those locks may not require a locksmith for rekeying, rekeying would not ordinarily be attempted by someone who is not mechanically inclined. 
     The U.S. Pat. No. 1,565,556 to Fremon discloses a pin tumbler lock which is selectively operable with two keys. In one condition of the lock it is only operable with one of the two keys, and in another condition of the lock it is only operable with the other of the two keys. The lock includes an annular ring which encloses a lock plug having a keyway therein. Both the ring and the plug are rotatable relative to the lock casing. A pair of radially extending pins engage either the ring and plug together so that both rotate relative to the casing, or the ring to the casing so that only the plug rotates relative to the casing. A bar is movable to cause the pins to engage the ring and plug together or the ring to the casing. In order to change the condition of the lock, i.e., rekey it, the lock has to be removed from a lock assembly in which it is assembled to gain access to the movable bar so that its position may be changed. 
     Pelle U.S. Pat. No. 2,603,081 discloses a rekeyable lock in which the longitudinal position of one of the tumbler assemblies is changed by a gear assembly to rekey the lock. However, access to the gear assembly which repositions that tumbler assembly is obtained from the rear of the lock which requires that the lock be removed from a lock assembly in which it is installed. 
     A lock which may be rekeyed from the exterior thereof without removing it from a lock assembly in which it is assembled is disclosed in U.S. Pat. No. 3,257,831 of Schlage, issued June 28, 1966. The lock disclosed in U.S. Pat. No. 3,257,831 to Schlage is selectively operable with primary and secondary keys, initially only with the secondary key, and rekeyable by the primary key to operate with the primary key instead of the secondary key. The lock can not be rekeyed from the exterior of the lock by the secondary key to operate again with the secondary key, but may be rekeyed by the primary key to operate with the secondary key. Thus, the same key which is used to operate the lock also rekeys the lock. As a result, the functions of rekeying and operating the lock can not be separated so that anyone authorized to rekey the lock can also operate it. Rekeying is accomplished in the U.S. Pat. No. 3,257,831 to Schlage by reconfiguring the keyway to limit the distance that the secondary key may be inserted, thereby preventing the secondary key from properly positioning the tumblers for operation of the lock. 
     A lock which may be rekeyed from the exterior by a reset key which adjusts the positioning of the tumblers is disclosed, for example, in U.S. Pat. No. Re. 28,319 of Kerr, which was reissued on Jan. 28, 1975 (original patent issued on Sept. 4, 1973). U.S. Pat. No. Re. 28,319 to Kerr discloses an axial pin tumbler lock which includes a number of pin tumbler sets that extend circumferentially about the lock, each of the tumbler sets including three axially-extending tumblers. One set of circumferentially-extending tumblers is rotated relative to the other two sets by the reset key to form new combinations of three tumblers for each tumbler set, thereby rekeying the lock. The reset key must be inserted into the lock in the same angular position relative to the lock that it was in when it was last withdrawn from the lock, otherwise the lock can not be rekeyed. In order to facilitate proper introduction of the reset key, U.S. Pat. No. Re. 28,319 to Kerr suggests that the front of the lock be marked with indicia to indentify the positions of the axial tumbler sets. However, such indicia may distinguish the exterior appearance of the lock from a non-rekeyable lock of the same type and thereby suggest that the lock may be rekeyed. 
     A lock commercially available from U-Change Lock Industries, Inc. of Oklaholma City, OK is rekeyable from the exterior thereof by adjusting the positioning of the tumblers. In order to rekey the lock, both a change tool which repositions the pin-tumblers that operate the lock and a key with which the lock is to operate must be inserted into the lock. While the key is inserted in the keyway of the lock, a slot is provided at the exterior of the lock adjacent the keyway through which the change tool is inserted. The slot, however, distinguishes the exterior of the lock from conventional locks and may suggest that the lock is rekeyable. 
     A lock commercially available from Winfield Locks, Inc. of Costa Mesa, CA is rekeyable from the exterior thereof to operate with different master keys. The lock includes one keyway for the usual unlocking key and a second keyway for an emergency or master key. The lock is rekeyed to accept a new master key by inserting the current master key into the second keyway, turning it a quarter turn, and then inserting the new master key and turning it back the quarter turn. The presence of two keyways is evident and distinguishes the exterior of the lock from a conventional lock. 
     There is thus a need for a lock rekeyable from the exterior thereof, which appears from the exterior thereof to be a conventional lock, and which permits rekeying with the capability of preventing operation of the lock during rekeying and/or by the person rekeying. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a lock which can be rekeyed or programmed to operate with a different key simply and quickly from the exterior of the lock without removing the lock from a lock assembly in which it is assembled. 
     It is another object of the present invention to provide a lock which is rekeyable from the exterior thereof and which from the exterior of the lock and a lock assembly in which the lock may be assembled appear conventional. 
     It is another object of the present invention to provide a lock which can be rekeyed from the exterior thereof through the same keyway used to operate the lock. 
     It is another object of the present invention to provide a lock which can be rekeyed from the exterior thereof from the interior side of a door or other object in which it is installed. 
     It is another object of the present invention to provide a lock which may be repeatedly rekeyed to selectively operate with different keys, i.e., rekeyed to prevent operation with a first key and permit operation with a second key and then rekeyed to operate again with the first key but not with the second key. 
     It is another object of the present invention to provide a lock which may be rekeyed from the exterior thereof without permitting the person rekeying the lock to operate it, unless it is specifically desired that the person rekeying the lock also be able to operate it. 
     It is another object of the present invention to provide a method of improving security in the use of rekeyable locks by providing a lock which may be rekeyed from the exterior thereof without requiring a key which operates the lock. 
     It is another object of the present invention to provide a rekeyable lock which may have a number of keyed positions, at least one of which may be used for permitting access on a limited security basis for short, selected periods of time, and at least one of which permits access on a higher security basis for longer periods of time. 
     It is another object of the present invention to provide a lock system including a plurality of locks each rekeyable from the exterior thereof in which one or more of the keys operable with each lock may act as a master key for the lock system. 
     It is another object of the present invention to provide such a lock system in which another key may operate as a sub-master key for a sub-group of the plurality of locks. 
     It is another object of the present invention to improve security in the use of master lock systems by providing a lock which must be activated to operate with a master key but which does not require the master key in order to activate the lock for master key operation. 
     It is another object of the present invention to provide a lock rekeyable from the exterior thereof which utilizes standard cut keys. 
     It is another object of the present invention to provide a lock rekeyable from the exterior thereof in which the lock may be locked against rekeying without disassembling the lock itself. 
     It is another object of the present invention to provide a lock which is rekeyable from the exterior thereof, which indicates during rekeying, for example by feel, audibly, etc., the position to which the lock is keyed, and which after rekeying appears from the exterior thereof to be a non-rekeyable lock. 
     It is another object of the present invention to provide a rekeyable lock which distinguishes keyed positions of the lock and visually indicates from the secure side of the lock the present keyed position of the lock, and which from the unsecured side of the lock appears to be a non-rekeyable lock. 
     It is another object of the present invention to provide a lock which may be rekeyed without changing the position or configuration of the pin tumblers which operate the lock. 
     Other objects of the present invention are to provide a lock referred to in the above objects from a commercially-available conventional lock which is modified in accordance with the invention, to manufacture the lock from scratch, and/or to manufacture the lock from both conventional, standard lock parts and specially-designed lock parts. 
     Other objects of the present invention are methods for providing a lock referred to in the above objects, and for providing the lock from a standard lock modified in accordance with the invention. 
     The above and other objects are achieved by the invention which provides a pin tumbler lock which is assemblable into a lock assembly, rekeyable from the exterior of the lock assembly to be selectively operable by each of a plurality of different keys, i.e., keys of different bit configurations, and which from the exterior of the lock and the lock assembly, at least from the unsecured side of the lock, appear as a conventional lock and conventional lock assembly. In a preferred embodiment, the lock is rekeyed through the lock keyway. 
     The lock comprises a pin tumbler system including a plurality of pin tumblers and a plurality of rotatable members which cooperate to define a plurality of common shear lines across which selected rotatable members may be rotated by selected keys, and means defining an adjustable shear line adjustable from the exterior of the lock, the lock being operable with only a selected key which positions the pin tumblers to form that common shear line aligned with the adjustable shear line. 
     The adjustable shear line after adjustment rekeys the lock to require a different one of the plurality of keys to operate the lock. The pin tumblers of the lock when positioned by respective ones of the plurality of keys which operate the lock define respective ones of a plurality of common tumbler shear lines. In order to operate the lock, the adjustable shear line and a common pin tumbler shear line must be aligned to form a lock shear line. Even though a number of common tumbler shear lines may be formed, the only one which permits operation of the lock is the one aligned with the adjustable shear line. The lock is thus operable along only one of the common tumbler shear lines at a time depending upon the position of the adjustable shear line; and once the adjustable shear line is adjusted to a given position, operation of the lock requires a key which will position the pin tumblers to form that common pin tumbler shear line which is aligned with the given adjustable shear line. 
     In a preferred embodiment, the adjustable shear line is adjusted, as mentioned, through the keyway of the lock by a change key insertable into the keyway, so that no additional slots or other entry or access structure is required to rekey, which enables the lock from the exterior thereof at least from the unsecured side of the lock to appear conventional. Once rekeying has been effected, the change key may be removed and the lock remains rekeyed. In another embodiment, the adjustable shear line is adjusted from an end of the lock opposite the end in which the keyway is disposed, for example in a door lock, from the inside of the door. 
     In a specific embodiment, the rotatable members referred to above are a plurality of cylinders, one disposed in the other, with which the pin tumblers when properly positioned define the plurality of common tumbler shear lines. The lock comprises a casing, the plurality of cylinders, which are rotatably disposed one in the other in the casing, structure closing one end of the lock in which the keyway is disposed, the plurality of pin tumblers and means in the casing and the plurality of cylinders for movably receiving the plurality of pin tumblers. The pin tumblers are positionable by respective keys inserted in the keyway and are configured to form first and second common tumbler shear lines when positioned by first and second properly configured but different keys, respectively. 
     Specifically, the first common tumbler shear line is formed between a first and a second of the plurality of cylinders when the tumblers are positioned by the first key inserted in the keyway, the first common tumbler shear line permitting rotation of the first cylinder relative to the second cylinder. The second common tumbler shear line is formed between the second cylinder and the casing when the pin tumblers are positioned by the second key inserted in the keyway, the second common pin tumbler shear line permitting rotation of the second cylinder relative to the casing. 
     The lock includes means for engaging selected cylinders and which defines the adjustable shear line selectively positionable between two selected cylinders and between a selected cylinder and the lock casing. The engaging means may also engage the casing and a selected cylinder or cylinders. In a first position, the adjustable shear line is positioned between the first and second cylinders, and the engaging means may engage the second cylinder and the casing independently of the positioning of the pin tumblers. In a second position, the adjustable shear line is positioned between the second cylinder and the casing, and the engaging means engages the first and second cylinders independently of the positioning of the pin tumblers. In the first position of the adjustable shear line, the first key but not the second key is operable to rotate the first cylinder relative to the second cylinder and the casing. In the second position of the adjustable shear line, the second key but not the first key is operable to rotate the first and second cylinders together relative to the casing. 
     In a specific embodiment, the engaging means defining the adjustable shear line includes at least one engaging member which is movable from the exterior of the lock and from the exterior of the lock assembly into preselected, fixed but readjustable positions. In a preferred embodiment, two movable engaging members are provided which are disposed adjacent to each other and form the adjustable shear line between the two members. In effect, the at least one engaging member or the two engaging members function as an externally adjustable tumbler which, however, when adjusted remains fixed until readjusted. In that specific embodiment, adjustment per se of the adjustable tumbler, i.e., the at least one or the two engageable members, does not change the positioning and configuration of the pin tumblers. 
     The engaging means includes structure engageable through the keyway and/or engageable through an end of the lock opposite the one end for operating the engaging means from the exterior of the lock assembly to position the adjustable shear line and selectively engage the cylinders and the casing. The first and second cylinders include means for movably receiving the at least one engaging member, and the engaging means includes structure for moving the at least one engaging member between the first position in which the adjustable shear line is between the first and second cylinders, and the second position in which the adjustable shear line is between the second cylinder and the casing. 
     According to a preferred embodiment, the structure in the means for engaging for moving the at least one engaging member comprises a pinion gear and the at least one engaging member comprises a rack positioned relative to the pinion gear to be moved between first and second positions defining the first and second positions of the adjustable shear line by rotation of the pinion gear. A second movable engaging member is provided in the form of a spring-loaded rack extension disposed adjacent the rack and moved by the rack. The rack and the rack extension meet to form the adjustable shear line. 
     The engaging means also comprises an actuating member which in one embodiment is removably couplable to the pinion gear through the keyway, and in another embodiment, extends when coupled to the pinion gear, beyond an end of the lock opposite the end in which the keyway is disposed, and is rotatable from the exterior of the lock assembly. The pinion gear and the actuating member include mutually engageable structure for engaging and rotating the pinion gear upon rotation of the actuating member. 
     In the illustrated embodiment, the lock includes three cylinders, one disposed in the other. In addition to the first and second cylinders referred to above, the lock includes a third cylinder. The first cylinder may be an inner cylinder, the second cylinder an intermediate cylinder and the third cylinder an outer cylinder, the first and second cylinders being rotatably disposed in the third cylinder. The third cylinder also includes means for movably receiving the pin tumblers. 
     The pin tumblers are configured to form the first common pin tumbler shear line between the first and second cylinders to permit rotation of the first cylinder relative to the second and third cylinders and the casing when the pin tumblers are positioned by the first key. The pin tumblers are also configured to form the second common pin tumbler shear line between the second and third cylinders to permit the first and second cylinders to rotate relative to the third cylinder and the casing when the pin tumblers are positioned by the second key. The pin tumblers are also configured to form a third common pin tumbler shear line between the third cylinder and the casing when the pin tumblers are positioned by a third key different from the first and second keys inserted in the keyway. The third common pin tumbler shear line permits rotation of the first, second and third cylinders relative to the casing. The engaging means also selectively engages the first, second and third cylinders independently of the positions of the pin tumblers. 
     The first key but not the second and third keys is operable to rotate the first cylinder relative to the second and third cylinders and the casing across the first common pin tumbler shear line when the engaging means positions the adjustable shear line in its first position; the second key but not the first and third keys is operable to rotate the first and second cylinders together relative to the third cylinder and the casing across the second common pin tumbler shear line when the engaging means positions the adjustable shear line in its second position; and the third key but not the first and second keys is operable to rotate the first, second and third cylinders together relative to the casing across the third common pin tumbler shear line when the engaging means positions the adjustable shear line in its third position while at the same engaging the first, second and third cylinders. 
     According to one aspect of the invention, the lock includes means operable from an end of the lock opposite the closed end for positively engaging the at least one engaging member to resist movement thereof and thereby lock the at least one engaging member in a selected position. In one embodiment, the means for positively engaging comprises a set screw and a threaded hole in the lock positioned to open adjacent the at least one engaging member, the set screw being selectively tightenable in the hole into engagement with the engaging member to prevent repositioning of the at least one engaging member. 
     According to another aspect of the invention, the lock includes means cooperating with the at least one engaging member for indicating at least when the at least one engaging member is in one of the positions. The indication may be visual, and/or audible and/or felt manually. In one embodiment, in which the rack and the rack extension are provided, the means for indicating comprises a detent arrangement including a spring-loaded detent member urged against the rack and structure on the rack which receives and seats the detent member in the positions of the rack. In that embodiment, the detent arrangement provides a manually sensible indication and/or an audible indication that the detent member is seated in the detent structure of the rack. In another embodiment, in which the rack and the rack extension are also provided, the means for indicating comprises a pointer and a scale which visually indicate the position of the rack, the pointer being moved to uniquely indicate positions corresponding to the positions of the rack. 
     According to another aspect of the invention, the rotatable member includes structure engageable by a specially-configured key inserted in the keyway. According to one embodiment, the specially-configured key comprises a bit having a specially-configured tip which engages mating structure in the rotatable member for rotating the rotatable member, the bit when engaged with the rotatable member not moving the tumblers from a rest position thereof. 
     According to the invention, a method is provided of increasing the security of a rekeyable lock which comprises; providing a lock which is rekeyable from the exterior thereof with an actuating device inserted in the keyway of the lock; keying the lock to a first keyed position to be operable with a first key; giving the actuating device to one person; and giving a second key which operates the lock in a second keyed position thereof to another person; whereby both the one and the other persons must be present to operate the lock in the second keyed position thereof. 
     According to another method of the invention, a lock which may be adjusted from the exterior thereof to operate with selected ones of a plurality of different keys is provided by: providing a pin tumbler lock having a plurality of cylinders and a plurality of sets of pin tumblers, each set being capable of forming a plurality of individual pin tumbler shear lines; providing structure which forms an adjustable shear line which is adjustable into a plurality of positions from the exterior of the lock either through the keyway thereof or from the end of the lock opposite the end having the keyway; configuring and arranging the cylinders and the pin tumblers to be capable of aligning the individual pin tumbler shear lines to form a plurality of common pin tumbler shear lines in alignment with respective ones of the plurality of positions of the adjustable shear line when the pin tumblers are positioned by respective ones of the plurality of keys, which common pin tumbler shear lines permit rotation of a selected cylinder or cylinders relative to another cylinder or other cylinders and a casing of the lock and prevent rotation of the another cylinder or other cylinders relative to the casing; providing an actuating device capable of adjusting the adjustable shear line from the exterior of the lock through the keyway thereof or from the opposite end mentioned above; whereby the lock may be operated by a given one of the plurality of keys only if the common pin tumbler shear line formed by that given key is aligned with a position of the adjustable shear line. 
     According to another method of the invention, a lock which may be adjusted to operate with selected ones of a plurality of different keys from a conventional radial pin tumbler lock having a casing which includes structure cooperating with a plurality of pin tumblers is provided by: providing a plurality of cylinders, one disposed in the other, an inner cylinder including a keyway therein, the cylinders being configured to cooperate with the structure in the casing to receive a plurality of pin tumbler sets in communication with the keyway for actuation by a key inserted in the keyway; providing structure defining an adjustable shear line which is adjustable into a plurality of positions from the exterior of the lock through the keyway thereof or through an end of the lock opposite the end having the keyway; providing a plurality of pin tumbler sets each capable of forming a plurality of individual shear lines and when installed in the lock and actuated by a respective key, further capable of forming a plurality of common pin tumbler shear lines aligned with respective ones of the plurality of positions of the adjustable shear line, the common pin tumbler shear lines permitting rotation of a selected cylinder or cylinders relative to another cylinder or other cylinders and to a casing of the lock and prevent rotation of the another cylinder or other cylinders relative to the casing; providing an actuating device capable of adjusting the adjustable shear line from the exterior of the lock through the keyway thereof or from the opposite end; whereby the lock may be operated by a given one of the plurality of keys only if the common pin tumbler shear line formed by that given key is aligned with a position of the adjustable shear line. 
     A lock according to the present invention includes a number of features, and may advantageously be used under a wide variety of circumstances and for a number of applications. Because the lock is rekeyable from the exterior thereof and is so easy to rekey, almost anyone including a child can effect rekeying. A locksmith or a mechanically-inclined person is not required. For example, a parent, with a child at home, who loses a key or has a key stolen while out of the home on an errand or at work, may simply telephone home and request that the child rekey the lock. As mentioned, the lock may be rekeyed quickly and easily, and may even be rekeyed from the secured side of the lock, i.e., from the inside of a locked door without opening the door. As a general matter, a person who loses a key or has it stolen may telephone a neighbor, friend, his landlord, the superintendent, etc., who was given a change key, and request that the lock be rekeyed. The lock may later be rekeyed to accept the previous key so that the person may reenter his home, or if the person was already carrying the new key which the lock had been rekeyed to accept, the lock may be left rekeyed. In accordance with a feature of the invention, the person having the change key does not also have access to the home (or car, office, room, etc.) unless he was also given a key which operates the lock. 
     Quite often, access is required to a person&#39;s home for making repairs or for accepting a delivery. One keyable position of the lock may be reserved as an &#34;access&#34; position to allow for such access while at the same time reserving another keyable position as a &#34;safe&#34; position. Prior to leaving the home, the person would rekey the lock to the access position and leave an &#34;access&#34; key for that position with a friend, neighbor, the landlord, the repairman, etc. Later, after the access key was returned, the lock would be rekeyed to the safe position in which the access key would not work. Thus, even if a copy of the access key had been made, or if the access key had not been returned or was lost, rekeying of the lock to the safe position ensured security. As long as there was no reason to suspect that security was compromised by giving out the access key, the access position of the lock and the access key could be used again in the future. 
     There are many other instances for employing safe and access positions. For example, an access key may be given to a housekeeper, or to a neighbor for entry to care for pets or plants during the day or during a vacation or business trip. Automobile owners often worry about parking attendants making copies of home keys attached to the key ring holding the car keys. Should an automobile owner become concerned, he simply has to telephone a person to whom he has given a change key and request that the lock be rekeyed to a position which the key on the key ring will not operate. A rekeyable lock according to the invention may also be advantageously in automobiles, particularly as an ignition lock. As an ignition lock, the lock would usually be keyed to the safe position and only rekeyed to the access position when the automobile is to be left with a parking attendant at a garage, restaurant, etc., or left with a repair facility. Since the lock may be rekeyed quickly and easily from the exterior thereof, the lock may be rekeyed to the access position immediately prior to reaching, or right at, the garage, restaurant, repair facility, etc., and then rekeyed back to the safe position as soon as the automobile is returned or driven away. The invention also has application to increasing security in vehicle leasing operations. For example, the ignition lock may be rekeyed after each vehicle is returned to prevent operation of the vehicle with an ignition key which was not returned or copied. 
     Still further uses of the rekeyable lock according to the invention utilizing access and safe positions are possible. For example, if more security is desired before the lock may be unlocked in the access position thereof, the lock may be left in the safe position, and the change key given to one person and the access key given to another person. With the lock in the safe position, security is assured since no one has a safe key except the owner. However, to unlock the lock in the access position, both the person having the change key and the person having the access key must be present before the lock may be rekeyed to the access position and unlocked. This may be of use where a person does not know his neighbors well, but must provide access to his home in his absence, or where it is desired that two people be present before entry is permitted. For example, a landlord may not wish to have access to an apartment without another person being present so as not to be be in a position of being suspect if anything is missing from the tenant&#39;s apartment. In that case, the landlord may be given the access key, a neighbor the change key, and the lock be left in the safe position. Such use may also have industrial or military applications with respect to entry into restricted areas. 
     A lock in accordance with the invention may be provided with three rekeyable positions, and used, for example, with a first position being the access position, a second position being the safe position and a third position being an ultra-safe position. The access and safe positions may be utilized as described above. The ultra-safe position may be utilized in instances in which the highest security against entry by an authorized or formerly authorized key is desired. That is accomplished by simply not giving out the ultra-safe key and rekeying the lock to the ultra-safe position whenever the highest security is desired. The ultra-safe position may be utilized when a person is to be away from his home for extended periods, as, for example, when on vacation or a business trip. In a two-position rekeyable lock, the safe position may also function as an ultra-safe position if access to the safe key is severely restricted. 
     There are instances in which multiple copies of the same key are distributed for use, for example, by employees. Should an employee upon termination either refuse or forget to surrender his key, the employer need only rekey the lock, and not change it, and distribute new keys to the remaining employees to prevent entry by the terminated employee while still permitting entry by the remaining employees. 
     Under some circumstances, a landlord may wish to lock a tenant out of his apartment. Using a lock according to the invention allows that to be done by the landlord by rekeying the lock from the exterior of the apartment, which does not require that the landlord enter the apartment. In addition, such rekeying does not provide a visual indication that the tenant has been locked out, as opposed to padlocking the door or changing the lock. 
     A lock according to the invention which may be rekeyed from the inside of a door in which it is installed provides other advantages. Should one in his home wish to prevent someone else having an access key from entering, he may do so without opening the door and without the other person knowing, even as that person approaches the door. 
     Since a lock according to the invention may be rekeyed a number of times to accept different keys, e.g., three, the lock provides a multiplication factor over conventional locks which are not rekeyable. Thus, where locks are changed often (as conventional interchangeable core locks are), a lock according to the invention could replace three locks, which would allow the purchase of a higher quality lock since it would last three times longer. 
     A system of locks may be configured so that one of the keyable positions is opened by the same master key. The other keyable positions may be used as described above and in other ways. The master lock system may be configured to operate with two different master keys. In that case, the locks may be configured so that in a first keyed position, all locks are operable with a first master key, and in a second keyed position, all locks are keyed to be operated with a second master key different from the first master key. If desired, the second master key may be a submaster key, which may operate only a sub-group of the system of locks. 
     Locks according to the invention may be used in door locks, car locks, mail box locks, locker locks, safety deposit boxes, padlocks, padlocks with interchangeable cores, and other locks. With respect to door locks, the lock may be used in mortise locks, rim cylinder locks, cylinder-in-knob locks, interchangeable core locks and other types of door locks. 
     As discussed above, the lock may be made from a standard commercially available lock which is modified as described herein, or the lock may be manufactured as a rekeyable lock at the factory from scratch, or manufactured from both specially-designed parts and standard lock parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate like parts, and in which: 
     FIG. 1 is a section view of a prior art pin tumbler lock taken axially through the lock depicting the lock in its locked condition without a key inserted therein and a portion of a door in which the lock is installed; 
     FIG. 2 is an axial section view similar to FIG. 1 depicting the lock of FIG. 1 with a key inserted therein which positions the lock pin tumblers to form a shear line for unlocking the lock; 
     FIG. 3 is a section view of the lock of FIG. 1 taken radially through the lock; 
     FIG. 4 is a radial section view similar to FIG. 3 of the lock and key of FIG. 2 with the key rotated to rotate the lock cylinder through a common pin tumbler shear line formed by the pin tumblers; 
     FIG. 5 is a perspective view of a lock according to the invention, assembled into a lock assembly installed in a door, and a change key for rekeying the lock to cause it to operate with a different key; 
     FIG. 6 is an enlarged perspective view of the change key depicted in FIG. 5; 
     FIG. 7 is an exploded perspective view of the lock according to the invention; 
     FIG. 8 is perspective view partially in phantom of a portion of the lock according to the invention depicting an inner cylinder, an intermediate cylinder and an outer cylinder of the lock, and a rack and pinion arrangement for forming a shear line adjustable from the exterior of the lock through the keyway by the change key, the rack being positioned in its first position to place the adjustable shear line in its first position between the inner and intermediate cylinders; 
     FIG. 9 is a view similar to FIG. 8 depicting adjustment of the adjustable shear line by rotation of the change key inserted in the pinion gear of the rack and pinion arrangement to position the rack in its second position which places the adjustable shear line in its second position between the intermediate and outer cylinders; 
     FIG. 10 is a section view of the lock according to the invention taken axially through the lock depicting the lock in its first keyed position in which the rack is in its first position and the adjustable shear line is in its first position between the inner and intermediate cylinders, the lock being depicted without a key inserted therein installed in a door, a portion of which is also depicted; 
     FIG. 11 is a view similar to FIG. 10 depicting the lock in its first keyed position, with a first key inserted in the keyway positioning the pin tumblers to form the first common pin tumbler shear line between the inner cylinder and the intermediate cylinder in alignment with the first position of the adjustable shear line, the first common pin tumbler shear line and the adjustable shear line in its first position together forming the first lock shear line; 
     FIG. 12 is a view similar to FIG. 11 depicting the lock rekeyed from the position of FIGS. 10 and 11 to its second keyed position in which the rack is in its second position and the adjustable shear line is in its second position between the intermediate and outer cylinders, and with the second key inserted in the keyway positioning the pin tumblers to form the second common pin tumbler shear line between the intermediate cylinder and outer cylinders in alignment with the second position of the adjustable shear line, the second common pin tumbler shear line and the adjustable shear line in its second position together forming the second lock shear line; 
     FIG. 13 is a view similar to FIG. 11 depicting the lock rekeyed from the position of FIG. 12 to its third keyed position in which with the rack is in its third position and the adjustable shear line is in its third position between the outer cylinder and the casing, and with the third key inserted in the keyway positioning the pin tumblers to form the third common pin tumbler shear line between the outer cylinder and the casing in alignment with the third position of the adjustable shear line, the third common pin tumbler shear line and the adjustable shear line in its third position together forming the third lock shear line; 
     FIG. 14 is a radial section view of the lock depicted in FIG. 10 taken along line 14--14 of FIG. 10; 
     FIG. 15 is a radial section view similar to FIG. 14 of the lock and first key depicted in FIG. 11 with the first key being rotated to rotate the inner cylinder across the first lock shear line relative to the intermediate and outer cylinders and the casing; 
     FIG. 16 is an axial section view of the lock depicted in FIG. 10 with the change key inserted therein for adjusting the rack and the position of the adjustable shear line through the keyway from the exterior of the lock; 
     FIG. 17 is a radial section view of the lock depicted in FIG. 16 taken along line 17--17 of FIG. 16; 
     FIG. 18 is a radial section view similar to FIG. 16 depicting the lock and first key of FIG. 11 with the pin tumblers and rack being positioned to form the first lock shear line and with the first key being rotated to rotate the inner cylinder; 
     FIG. 19 is a section view of the lock of FIG. 17 taken radially therethrough depicting the detent arrangement and the set screw which cooperate with the rack to indicate the position of the rack (and adjustable shear line) and lock the rack in a given position, respectively, partly broken away to expose pin tumbler structure in the lock; 
     FIG. 20 is an enlarged perspective view of the pinion gear and the change key of the lock of FIG. 5 depicting the specially-configured mating structure of the pinion gear and the change key; 
     FIG. 21 is a perspective view of the pinion gear and the change key of the lock according to another embodiment of the invention in which the specially-configured mating structure of the pinion gear and the change key differ from that of FIG. 20; 
     FIG. 22 is a rear perspective view of the lock depicted in FIG. 5 in its fully assembled condition outside of the lock assembly; 
     FIG. 23 is a partially exploded, rear perspective view of the lock depicted in FIG. 22 illustrating disassembly thereof; 
     FIG. 24 is a rear view of the lock depicted in FIG. 23 in a further disassembled state thereof showing the pinion gear; 
     FIG. 25 is a perspective view of a lock according to another embodiment of the invention in which the adjustable shear line is adjusted from the end of the lock opposite the end having the keyway entrance therein, the lock being assembled into a lock assembly installed in a door; 
     FIG. 26 is an enlarged perspective view of a portion of the assembled and installed lock depicted in FIG. 25 partially exploded to expose a dial used to adjust the position of the adjustable shear line; 
     FIG. 27 is an enlarged perspective view of a portion of the lock of FIG. 25 broken away and partially in phantom to illustrate adjustment of the rack by the dial, also depicting a pointer which indicates the position of the rack and the adjustable shear line; 
     FIG. 28 is a radial section view of the lock of FIG. 25 depicting the lock in its first keyed position in which the rack is in its first position and the first adjustable shear line is in its first position between the inner and the intermediate cylinders; 
     FIG. 29 is a view similar to FIG. 28 depicting the lock rekeyed from the position in FIG. 28 to its second keyed position in which the rack is in its second position and the adjustable shear line is in its second position between the intermediate and the outer cylinders; and 
     FIG. 30 is an exploded perspective view of the lock of FIG. 25. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIGS. 1-4 illustrate the construction and operation of a conventional single cylinder, single lock shear line, pin tumbler lock, and FIGS. 4-30 illustrate the construction and operation of presently preferred embodiments of the invention. The conventional lock of FIGS. 1-4 is described first as background, and as an aid to facilitate an understanding of the invention. 
     Conventional pin tumbler lock 40 in FIGS. 1 and 2 is depicted installed into a door 41 as part of a lock assembly that is not shown in the drawings. The lock assembly may be a conventional rim lock assembly or a conventional mortise lock assembly which are well known in the art. Lock 40 includes a casing 42, a single rotatable cylinder 44, six pin tumbler sets 46 and structure in the cylinder and the casing for receiving the pin tumbler sets. Each pin tumbler set 46 includes two pin tumblers 47, and a spring 48 to radially bias the pin tumblers of the respective set into a keyway 50 extending within cylinder 44 from end 52 of the lock. The two pin tumblers of each pin tumbler set 46 meet at a respective individual pin tumbler shear line 54. As depicted in FIG. 1, the individual pin tumbler shear lines 54 are offset one from the other so that a number of pin tumblers 47 extend across the adjacent circumferences of casing 42 and cylinder 44. As long as any one pin tumbler extends across the adjacent circumferences of cylinder 44 and casing 43 (see FIG. 3), rotation of cylinder 44 relative to casing 42 is prevented. The lock assembly in which lock 40 is assembled includes a mechanism for locking and unlocking a bolt or latch (not shown), only part of that mechanism being shown, as referenced generally by 56. Mechanism 56 is coupled to cylinder 44 to be rotated therewith and causes locking and unlocking of the bolt or latch of the lock assembly when cylinder 44 is rotated. Thus, lock 40 and the lock assembly in which it is installed can only be locked and unlocked by rotation of cylinder 44. 
     Referring to FIG. 2, the bit 58 of a suitably-configured key 60 inserted in keyway 50 positions the respective tumblers 47 of tumbler sets 46 so that the respective individual tumbler shear lines 54 of the respective tumbler sets extend along a common tumbler shear line 62 located between the adjacent circumferences of cylinder 44 and casing 42. In that position of the tumblers, no tumbler extends across the adjacent circumferences of cylinder 44 and casing 42 so that cylinder 44 may be rotated relative to casing 42 across common tumbler shear line 62 (which is also the lock shear line) by key 60, as shown in FIG. 4, to lock or unlock lock 40. In lock 40, each tumbler set 46 includes two tumblers, but as is conventional in the art, the tumbler sets 46 may include a different number of tumblers. 
     In the lock construction depicted in FIGS. 1-4, only a single common tumbler (or lock) shear line 62 can be formed which will allow rotation of cylinder 44 in casing 42, and the common shear line 62 can only be changed by changing at least one of the tumblers of the tumbler sets 46. Thus, rekeying can only be accomplished by changing the configuration of the pin tumblers, which requires disassembly of the lock, which in turn almost always requires the services of a qualified locksmith, as discussed above. As also discussed above, this precludes easy rekeying of such locks to reject unlocking with an old, formerly authorized key and accept unlocking with a new key. 
     A lock made in accordance with the invention, however, as summarized above, permits easy rekeying of the lock from the exterior thereof to reject operation with a formerly authorized key and permit operation with a new key. 
     Referring now to FIG. 5, lock 70 according to the invention is assembled into a conventional mortise lock assembly 71 installed in door 41. No changes need be made to lock assembly 71 to accomodate lock 70, which may be installed in lock assembly 71 conventionally in place of current mortise lock cylinders. Although the lock assembly into which lock 70 is installed is depicted as a mortise lock assembly, lock 70 may be assembled into a rim lock assembly as well. When assembled into a rim lock assembly, the casing of lock 70 will be modified accordingly, for example by removing exterior screw threads on the casing used to mount the lock in a mortise lock assembly. A change key 72 (actuating member) is provided to rekey lock 70 to reject operation with an old key and permit operation with a new key. To accomplish that, change key 72 is inserted in keyway 74, which is a conventional keyway, but need not be, and rotated to move the adjustable shear line referred to above in lock 70. Operation of lock 70 requires that one of the common pin tumbler shear lines referred to above be formed in alignment with the adjustable shear line to operate the lock. Each adjustment of the adjustable shear line to a new position requires that a different key be used to position the tumblers to form a common pin tumbler shear line aligned with the new position of the adjustable shear line to operate lock 70. Since the adjustable shear line is easily adjusted without disassembly of the lock from the exterior of lock 70 and lock assembly 71 by change key 72, lock 70 may easily and simply be rekeyed to require a new key to operate the lock by almost anyone in the household, including young children. As shown in FIG. 6, tip 76 of key 72 is specially configured, e.g., in the shape of &#34;Y&#34;, to engage a mating Y-shaped recess in lock 70 for effecting rekeying as described in more detail below. The use of a Y shape is illustrative, and other tip configurations may be used, as shown, for example, in FIG. 21. Since a change key alone can not lock or unlock lock 70, the particular tip configurations used are not critical. However, providing a number of different tip configurations which are mutually exclusive increases overall security in that someone with a formerly authorized key or an access key, etc., or a person who seeks to rekey the lock by tampering with it, will not be able to rekey the lock back to a keyed position which accepts the formerly authorized key or access key without a proper change key. 
     Referring to FIG. 7, lock 70 includes a plurality of cylinders which permit a corresponding plurality of common pin tumbler shear lines to be formed by different keys which position properly configured conventional pin tumblers. In the embodiment depicted in FIG. 7, lock 70 includes three cylinders, first inner cylinder 78, second intermediate cylinder 79 and third outer cylinder 80. Cylinders 78, 79 and 80 are concentrically disposed, but need not be, relative to each other and are disposed in a bore 82 of casing 84 which extends eccentrically of casing 84. Inner cylinder 78 includes an end 86 and casing 84 includes an end 88 which together form a closed outer end of lock 70. End 86 of inner cylinder 78 is of enlarged diameter compared to the diameter of cylinder 78 and forms a shoulder against which the edges of cylinders 79 and 80 abut to form the closed end of the lock. Keyway 74 is conventional and is disposed in end 86 of cylinder 78. Each of cylinders 78, 79 and 80, and casing 84 includes a series of holes 94, 95 96 and 97, respectively, respective ones of which are registered in the assembled condition of the lock and receive therein pin tumblers of respective tumbler sets referenced generally by 98, only one of which is shown in FIG. 7. Pin tumbler set 98 depicted in FIG. 7 and the other tumbler sets of lock 70 include three pin tumblers 99 which at adjacent ends thereof form three individual pin tumbler shear lines, which facilitate the formation of three common pin tumbler shear lines, as described in more detail below. Pin tumbler sets 98 may include more than three pin tumblers to increase the total number of key configurations which will form common pin tumbler shear lines and operate the lock. If desired, in a particular lock system, the size of one or more cylinders may be varied among locks or groups of locks to increase the total number of key configurations available in the system to operate the different locks. Pin tumbler sets 98 also include a spring 100 for urging the pin tumblers radially inwardly. Elongated plate 101 and elongated recess 102 in casing 84 are provided to maintain tumbler sets 98 in their respective holes. 
     In the embodiment depicted in FIG. 7, casing 84 and inner cylinder 78 were part of a conventional lock, such as lock 40 depicted in FIGS. 1-4. As compared to lock 40, casing 84 was bored out to receive additional cylinders 79 and 80, and casing 84 and cylinder 78 were further modified to accept a rack and pinion arrangement 103, which is described below. In order to accomodate rack and pinion arrangement 103, a slot 104 is formed in cylinder 78 where a tumbler hole was formerly located. As a result, cylinder 78 has five tumbler holes 94 while casing 84 has six tumbler holes 97 corresponding to the six tumbler holes in casing 44 of lock 40. While lock 70 may thus be fabricated from a conventional lock by modifying it and adding parts, lock 70 may also be specially manufactured as a unit. 
     As depicted in FIGS. 7-9, rack and pinion arrangement 103 (means for engaging) includes a rack 105 (at least one movable member), a rack extension 106 (another movable member), a spring 107, a screw 108, a pinion gear 110 (rotatable member) and structure in lock 70 for receiving those parts. Rack 105 and rack extension 106 abut and form a rack shear line 112 which is the adjustable shear line referred to above. Rack 105 and rack extension 106 function as a tumbler which, however, is not operated by a key, but rather is moved by pinion gear 110 to adjust the position of adjustable shear line 112. Pinion gear 110 in turn is rotated from the exterior of lock 70 by change key 72, as described above. Pinion gear 110 includes structure in the form of a specially-configured recess 114 which matingly receives and is engaged by the correspondingly shaped tip 76 of change key 72, as described above. As the sequence of FIGS. 8 and 9 illustrates, the tip 76 of change key 72 is inserted in keyway 74 into engagement with pinion gear 110 and rotated to rotate pinion gear 110 and move rack 105 and rack extension 106. 
     To accommodate rack 105, rack extension 106, spring 107 and screw 108, a slot 116 is formed in casing 84 adjacent an end 117 thereof opposite end 88. A cylindrical recess 118 is formed in end 119 of cylinder 78 communicating with slots 104 and with slot 116 of casing 84 in the assembled condition of the lock so that rack 105 and pinion gear 110 may mesh when assembled into slot 104 and recess 118, respectively. When constructing lock 70 from a conventional lock, care must be exercised in positioning slot 104 and recess 118 because of the limited space available in the cylinder supplied with the conventional lock. A suitable angle for slot 104 in cylinder 78 (and slot 116 in casing 84) has been found to be 15 degrees with respect to the vertical, i.e., with respect to the axis of the lock, with slots 104 and 116 extending to one side of the central axis of the lock. At that angle, slot 104 passes through a line running through or adjacent the tumbler holes of cylinder 78, which requires that the hole adjacent end 119 of cylinder 78 be slotted. Cylinders 79 and 80 are slotted at corresponding locations. Slot 104 is offset from the central axis of cylinder 78 to provide more space on one side of the central axis in which to position the recess 118, which is correspondinly offset. Other positions of slot 104 and recess 118 may be provided whether in a cylinder of a conventional lock or a specially manufactured cylinder. When rack and pinion arrangement 103 is assembled in lock 70, screw 108 and spring 107 urge rack extension 106 radially inwardly against rack 105 which is urged into meshing engagement with pinion gear 110. 
     Lock 70 operates as follows. Referring to FIGS. 10 and 14, which depict lock 70 itself fully assembled and in FIG. 11 assembled into lock assembly 71 as well, the pin tumblers 99 of tumbler sets 98 are urged by springs 100 radially inwardly into keyway 74. The individual pin tumblers 99 of tumbler sets 98 are configured so that the tumbler sets do not form a common tumbler shear line without a key inserted in keyway 74, as depicted in FIG. 10. The adjustable shear line 112 formed by rack and pinion arrangement 103 is adjusted to be positioned between two adjacent cylinders or between outer cylinder 80 and casing 84, depending on the last adjustment of rack 105 and rack extension 106. In the state depicted in FIGS. 8 and 10, the adjustable shear line 112 is positioned in its first position between the inner cylinder 78 and the intermediate cylinder 79. In that state of lock 70, with no key inserted, no common lock shear line is formed between tumbler sets 98 and rack 105/rack extension 106. Accordingly, the inner cylinder 78, to which the locking mechanism 56 is coupled, can not be rotated and lock 70 can not be operated. 
     Referring to FIGS. 11, 15 and 18, lock 70 is depicted in its first keyed position in which inner cylinder 78 may be rotated. In that first keyed position, a proper first key 120 inserted into keyway 74 positions pin tumblers 99 of the tumbler sets 98 to form the first common pin tumbler shear line 122 aligned with adjustable shear line 112, which together form the first common lock shear line, permiting inner cylinder 78 to be rotated (see FIGS. 15 and 18) by first key 120 to operate the lock. The pin tumblers engage intermediate cylinder 79, outer cylinder 80 and casing 84, and prevent rotation of cylinders 79 and 80 relative to casing 84. In addition, rack extension 106 may also engage cylinders 79 and 80 and casing 84, although that is not necessary. Any of the other authorized keys (the second and third keys) will not position tumblers 99 to form a common tumbler shear line which is alligned with shear line 112 in its first position, and accordingly will not operate lock 70. 
     As described above, lock 70 is rekeyed to operate with a different key by adjusting the position of adjustable shear line 112 with change key 72. As depicted in FIG. 11, key 120 is a standard key and extends in keyway 74 the full length thereof. Key 120 therefore underlies bore 123 in casing 84 which is from a standard lock which previously housed a tumbler set in bore 123. However, in lock 70, pinion gear 110 is positioned under bore 123, which would prevent key 120 from being fully inserted into lock 70. To permit standard key 120 to be fully inserted into lock 70 as depicted in FIG. 11, pinion gear 110 is spring loaded by spring 124 to be displaceable longitudinally of keyway 74. Alternatively, a shorter key may be used which when fully inserted does not contact pinion gear 110, or a longer casing may be used so that a standard key when fully inserted does not contact the pinion gear, in which cases pinion gear 110 need not be spring loaded. 
     Referring to FIG. 12, lock 70 has been rekeyed to its second keyed position in which the position of adjustable shear line 112 has been adjusted from the FIG. 11 position to place it in its second position between cylinders 79 and 80. See FIG. 9. To operate lock 70 in that state, pin tumblers 99 of tumbler sets 98 must be positioned to form second common pin tumbler shear line 125 which is aligned with adjustable shear line 112 in its second position. Second key 126 inserted in keyway 72 accomplishes that positioning of the pin tumblers which forms second common tumbler shear line 125 in alignment with the second adjusted position of adjustable shear line 112. In that state of lock 70, inner cylinder 78 and intermediate cylinder 79 are engaged by rack 103 and by pin tumblers 99 to rotate together across the second common lock shear line. Therefore, rotation of cylinders 78 and 79, and with them locking mechanism 56, by second key 126 operates lock 70. The pin tumblers prevent rotation of outer cylinder 80 and engage it to casing 84. In addition, rack extension 106 may also engage outer cylinder 80 and casing 84, although that is not necessary. Other authorized keys (first and third keys) will not operate lock 70 since they can not form a common tumbler shear line which is aligned with adjustable shear line 112 in its second position. 
     Referring to FIG. 13, lock 70 is depicted in its third keyed position in which rack 105 has been adjusted to position adjustable shear line 112 in its third adjusted position between outer cylinder 90 and casing 84. In order to operate lock 70 in that state, pin tumblers 99 must be positioned by a third proper key 132 to form third common pin tumbler shear line 134 aligned with adjustable shear line 112 in its third position between cylinder 80 and casing 84. In that state of lock 70, cylinders 78, 79 and 80 are engaged by rack 105 and also by pin tumblers 99 and rotate together across the third common lock shear line formed by third common pin tumbler shear line 134 and adjustable shear line 112 in its third position. 
     Because of the configuration and operation of pin tumblers 99, the relationship of the first, second and third keys is not a progressive one in which the bit configuration of the keys would include the same but progressively higher points for progressively moving the common tumbler shear lines. Such a progressive relationship of keys would not unlock lock 70 in its rekeyed positions described above. 
     FIGS. 16 and 17 illustrate adjustment of the position of adjustable shear line 112 by change key 72. Change key 72 is inserted in keyway 74 from the outside of lock 70 and lock assembly 71 until tip 76 engages recess 114 in pinion gear 110. Change key 72 includes two stops, stop 135 formed by a shoulder in shaft 136 at the transition to tip 76, and stop 137 formed by channel piece 138 connecting shaft 136 to bow 139, the distance between stops 135 and 137 along shaft 136 coresponding to the distance from pinion gear 110 to the outside end 86 of cylinder 78. Rotation of key 72 rotates pinion gear 110 to move rack 105 to thereby move the position of adjustable shear line 112. As depicted in FIG. 5, change key 72 is inserted in generally the center of keyway 74, i.e., in the curved central portion between the two generally straight portions. As can be seen in FIG. 14, Y-shaped recess 114 in pinion gear 110 is aligned with that curved portion of keyway 74. Centering recess 114 with respect to keyway 74 provides the maximum free space in the keyway to accommodate shaft 136 of change key 72 without contact between the shaft and the lock pin tumblers. However, other positioning of recess 114 with respect to keyway 74 may be provided. 
     A detent arrangement (means for indicating) for indicating the position of rack 105, and correspondingly the position of adjustable shear line 112, is illustrated in FIGS. 8, 9 and 19. Detent arrangement 140 includes a detent member 142, a detent spring 144, detent recesses or seats 146 and bore 148 in inner cylinder 78 to receive detent member 142 and detent spring 144. The tip of detent member 142 is beveled, as are the recesses 146, to facilitate seating and unseating of the the detent member in the recesses as rack 105 is moved. Seating of detent member 142 is perceptible in that a slight resistance to further rotation of change key 72 is provided. The higher the force of detent spring 144, the more perceptible the seating will be. For example, as pinion gear 110 is slowly rotated, one can feel detent member 142 riding up the inclined surface of one recess and then abruptly seating in the next recess as rotation continues. Once detent 142 is properly seated in a recess, one can feel the detent ride up one side of the recess as the change key is rotated in one direction, then feel the detent being seated in the recess when the change key is rotated in the opposite direction, and then feel the detent riding up the opposite surface of the recess as rotation in the opposite direction is continued. In addition, if the force of detent spring 144 is made large enough, seating of detent member 142 may create a sound which may be audibly detected. Other detent arrangements may also be used. For example, a bearing ball may be used as a detent member and correspondingly shaped recesses used to seat the ball. 
     To increase the security of lock 70 with respect to unauthorized attempts to change the position of adjustable shear line 112, rack 105 may be locked in a given position by set screw 150, as illustrated in FIGS. 8, 9 and 19. In the illustrated embodiment, a threaded bore 152, provided in inner cylinder 78 to receive set screw 150 (means for positively engaging), is positioned to provide access to set screw 152 (see FIGS. 22 and 23) from the exterior of lock 70 in its assembled condition. (Lock 70, however, must be disassembled from lock assembly 71.) Bore 152 is advantageousely coaxially aligned with bore 148 to simplify manufacturing. 
     In accordance with the invention, adjustment of the lock to require operation with a new key is effected from the exterior of lock 70 and lock assembly 71. That is accomplished by insertion of change key 72 (FIG. 6) into keyway 74, which appears conventional, as does the exterior of lock 70. Therefore, lock 70 is not distinguisible from a conventional lock from the exterior thereof. In order to permit change key 72 to be fully inserted into lock 70, the shaft 136 of key 72 must have a small cross section, which presents a problem in securely joining shaft 136 to bow 139. If shaft 136 is simply joined to bow 139 by welding, for example, or shaft 136 and bow 139 are made in one piece, the considerable torque which may be generated by bow 139 during roation of key 72 when tip 76 is engaged in recess 114 of pinion gear 110 could cause shaft 136 to be severed from bow 139. To prevent that, shaft 136 is mounted to bow 139 so as to rotate, rather than break off, when a predetermined torque is exceeded. Shaft 136 is attached to cylindrical plug 160 by welding, for example, or shaft 136 and plug 160 are formed as one piece. Plug 160 is in turn mounted in cylindrical recess 162 in bow 139. Set screw 164 locks plug 160 in recess 162 and prevents it from rotating upon the application of up to a predetermined torque determined by the sizes of shaft 136, plug 160 and set screw 164. When that predetermined torque is exceeded, set screw 164 permits plug 160 to rotate in recess 162. 
     As mentioned above, tip 76 of change key 72 may be specially-configured to improve security. FIG. 20 illustrates the presently preferred Y-shape, and FIG. 21 illustrates a semi-cylindrical shape. 
     FIGS. 22-24 illustrate removal of lock 70 from lock assembly 71 and disassembly of lock 70. Screws 176 are loosened in conventional manner to remove lock 70 from lock assembly 71. Pin 178 in the rear of lock 70 is pushed to release knurled nut 180, which is then loosened to remove locking mechanism 56 and expose the rear of cylinder 78, which may then be withdrawn and the remainder of lock 70 disassembled. As depicted in FIG. 24, set screw 150 is accessible from the rear of lock 70, after lock 70 has been removed from lock assembly 71, to lock rack 105 in a given position. 
     Referring now to FIGS. 25-30, a lock according to another embodiment of the invention is depicted in which the adjustable shear line 112 may be changed from the inside of a door 41 in which the lock is installed. Lock 182 internally is constructed similar to lock 70. Specifically, tumbler construction and the rack and pinion arrangement 103a of lock 182 are similar to those of lock 70. Pinion gear 110a is, however engaged from the end 184 of the lock opposite keyway end 86. Shaft 186 (actuating member) is fastened at one end thereof to pinion gear 110a and extends from end 184 of lock 182 to the exterior of the inside of door 41 where dial 188 is fastened to the other end of shaft 186. As depicted in FIGS. 25 and 26, dial 188 is recessed in lock plate 189 so that it may be covered by escutchen plate 190 which is fastened to plate 189 by screws. Dial 188 may be rotated to rotate shaft 186 and pinion gear 110a by a suitable implement such as a coin, screwdriver, etc. A knob may be attached to dial 188, if desired, particularly if recessing of the dial is important. Referring to FIG. 27, a scale 192 is provided adjacent dial 188 which includes pointer 194 to indicate the position of adjustable shear line 112 (means for indicating). Scale 192 and pointer 194 replace the detent arrangement 140 of lock 70, or may be provided in addition to the detent arrangement rather than in lieu of it. 
     Since lock 182 is rekeyed to operate with a different key from the interior of a door, it is not necessary to provide a set screw or other locking device to lock rack 105a in a given position. If desired, however, a set screw or other locking device to lock rack 105a may be provided for lock 182. 
     Slots 104a, 116a and recess 118a of the rack and pinion arrangement 103a in lock 182 are positioned slightly differently as compared to lock 70. In lock 182, recess 118a (FIG. 30) in cylinder 78a is located above the central axis of the lock and slot 104a in cylinder 78a and slot 116a in casing 84a extend at a greater angle with respect to the axis of lock 182 than in lock 70. As indicated above, positioning of recess 118a and slot 116a are dependant on the availability of space in inner cylinder 78a. 
     Lock 182 operates essentially in the same manner as described above for lock 70. 
     Embodiments of the invention illustrated in the drawings and described herein are meant to be exemplary rather than exhaustive. In addition, certain changes may be made to such embodiments which may be apparent to those of skill in the art. It is the intention of the applicants to cover by the claims herein all such changes which do not depart from the spirit and scope of the invention.