Flat plastic key with shortened key alignment groove

A flat plastic key for replacing a corresponding metal key having a longitudinal axis, a key alignment groove disposed in a side of the key at a location offset from the longitudinal axis by a first distance defining a first groove length where both the plastic and metal keys are configured to actuate a rotary cylinder lock having lock tumblers, an elongated key receptacle disposed along a lock longitudinal axis for receiving the key and a rotary lock face including substantially a rectangular lock entrance slot with spaced apart sidewalls, the longitudinal axis of the metal key being aligned with the longitudinal axis of the key receptacle when the key is inserted in the lock, the plastic key including:

• a. a head for receiving a lock actuating input torque within a force input area and having an end surface, a head thickness, a head width and a head length;
• b. a shank having a substantially rectangular cross section with substantially parallel sides defining a shank thickness, the shank further including a width, a length, a first end surface joined to the end surface of the head and a spaced apart second end surface;
• and
• c. a bit having an edge surface for receiving notches to actuate the lock tumblers and including a thickness, a width and a first end surface joined to the second end surface of the shank wherein the improvement comprises:
• a shortened key alignment groove disposed in a side of the key creating a decreased key thickness along the groove, where the groove is oriented parallel to but offset by the first distance from the key longitudinal axis and extends along the entire length of the bit but terminates at a groove termination point spaced well away from the first end of the shank, the shortened groove formed by decreasing the length of the key alignment groove from the first groove length of the metal key to a shorter second groove length to increase the volume and strength of the plastic key shank relative to the volume and strength of an exact plastic duplicate of the metal key shank by eliminating at least a part of the decreased key thickness created by penetration of the alignment groove into the shank of the exact plastic duplicate key to thereby increase the strength of the plastic key and its capacity to transfer the input torque to the lock.

A method for fabricating a plastic key suitable for replacing a metal key where both the plastic and metal keys are configured to actuate a rotary cylinder tumbler lock having lock tumblers, an elongated key receptacle for receiving the key and a rotary lock face having a substantially rectangular entrance slot with spaced apart side walls, the key and the lock including alignable longitudinal axes, where the metal key includes

• i. a metal head for receiving a lock actuating input torque, an end surface, a head thickness and a head width;
• ii. a metal shank having a substantially rectangular cross section with substantially parallel sides defining a shank thickness, the shank further including a width, a length and a first end surface joined to the end surface of the head and a spaced apart second end surface;
• iii. a metal bit for receiving notches to actuate lock tumblers and including a thickness, a width and a first end surface joined to the second end surface of the shank;
• and
• iv. a key alignment groove disposed in a side of the key creating a decreased key thickness along the groove, where the groove is oriented parallel to and offset by a first distance relative to the width longitudinal axis of the key and extends along the entire length of the bit and into the shank to define a first groove length;
• the plastic key fabricating method including the steps of:
• a. forming a plastic head for receiving a lock actuating input torque within a force input area, the head including an end surface, a head thickness, a head width and a head length;
• b. forming a plastic shank having a substantially rectangular cross section with substantially parallel sides defining a shank thickness, the shank further including a width, a length, a first end surface joined to the end surface of the head and a spaced apart second end surface;
• c. forming a plastic bit having a thickness, a width and a length geometrically compatible with the elongated key receptacle of the lock for receiving notches to actuate the lock tumblers and including a first end surface joined to the second end surface of the shank;
• and
• d. forming a key alignment groove in a side of the plastic key extending along the entire length of the bit at a location offset by the first distance relative to the key longitudinal axis but terminating at a groove termination point spaced well away from the first end of the shank to define a shortened groove having a length less than the first groove length of the metal key, wherein the shortened groove is formed by decreasing the length of the key alignment groove from the first groove length to a shorter second groove length to increase the volume and strength of the plastic key shank relative to the volume and strength of an exact plastic duplicate of the metal key shank by elimination of at least a part of the decreased key thickness created by penetration of the alignment groove into the shank of the exact plastic duplicate key to thereby increase the strength of the plastic key and its capacity to transfer the input torque to the lock.