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A knife includes a handle enclosing one or more of a blade, a blade shuttle, a transmission, and a trigger, where the handle includes a blade aperture. The blade shuttle is longitudinally moveable relative to the handle from a rest position to a first extended position and the blade shuttle is movea

A knife includes a handle enclosing one or more of a blade, a blade shuttle, a transmission, and a trigger, where the handle includes a blade aperture. The blade shuttle is longitudinally moveable relative to the handle from a rest position to a first extended position and the blade shuttle is moveable longitudinally from the first extended position to a cutting position when the blade is engaged in a workpiece. The blade shuttle is automatically retracted from the cutting position to the rest position when the blade is disengaged from the workpiece. The blade is detachably secured within the blade shuttle and protrudes a first distance through the blade aperture at the first extended position. The blade is extended from the first distance a substantially fixed length when engaged in the workpiece. The blade is adapted to automatically retract within the handle when disengaged from the workpiece.

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1. A knife, comprising: a handle enclosing at least a portion of one or more blades, a blade shuttle, a transmission, and a trigger, the handle comprising a blade aperture;the blade shuttle longitudinally moveable relative to the handle from a rest position to a first extended position and from the

1. A knife, comprising: a handle enclosing at least a portion of one or more blades, a blade shuttle, a transmission, and a trigger, the handle comprising a blade aperture;the blade shuttle longitudinally moveable relative to the handle from a rest position to a first extended position and from the rest position to a second extended position, the first extended position differentiated from the second extended position, the blade shuttle moveable longitudinally from the first extended position and the second extended position to a cutting position when the blade is engaged in a workpiece, the knife configured such that the blade shuttle is automatically retracted from the cutting position to the rest position when the blade is disengaged from the workpiece;the blade secured within the blade shuttle, a distal end of the blade protruding a first distance from the blade aperture at the first extended position and a second distance from the blade aperture at the second extended position, the first distance differentiated from the second distance, the knife configured such that when the distal end of the blade protrudes the first distance from the blade aperture, the distal end of the blade moves to a distance from the blade aperture greater than the first distance from the blade aperture when the blade is engaged in the workpiece, and when the distal end of the blade protrudes the second distance from the blade aperture, the distal end of the blade moves to a distance from the blade aperture greater than the second distance from the blade aperture when the blade is engaged in the workpiece, the knife configured such that the blade is automatically retracted to a safe position within the handle when the blade is disengaged from the workpiece; andthe trigger adapted to drive the blade shuttle from the rest position to the first extended position and from the rest position to the second extended position via the transmission,wherein the blade shuttle is in a fully extended position relative to the rest position in both the first and second extended positions,wherein the trigger is coupled to the handle at a fulcrum for pivotal movement to drive the blade shuttle from the rest position to the first extended position and from the rest position to the second extended position via the transmission, the trigger rotatably coupled to the blade shuttle through the transmission, andwherein the transmission comprises a pin coupled to the trigger such that a distance from the fulcrum to the pin remains substantially fixed as the trigger pivots to drive the blade shuttle between the rest position and the first extended position or between the rest position and the second extended position. 2. The knife of claim 1, the transmission comprising: a lever;a first spring operatively coupled to the trigger, the first spring adapted to: direct the lever to engage the blade shuttle in the first extended position and the second extended position; androtate the lever to disengage the lever and the blade shuttle in the cutting position;a second spring operatively coupled to the handle and the blade shuttle, the second spring adapted to automatically retract the blade shuttle from the cutting position to the rest position. 3. The knife of claim 2, wherein the second spring exerts no force on the blade shuttle in the rest position. 4. The knife of claim 2, wherein the knife further comprises at least a third spring adapted to act between the handle and the trigger and cooperate with the first and second springs to maintain a substantially constant force magnitude required to actuate the trigger and maintain the trigger in the actuated position. 5. The knife of claim 4, wherein the third spring is adapted to act between the handle and the trigger and cooperate with the first and second springs to maintain a substantially constant force magnitude required to actuate the trigger and maintain the trigger in the actuated position upon the blade engaging the workpiece. 6. The knife of claim 4, the force magnitude being between approximately 4 ounces and approximately 10 ounces. 7. The knife of claim 1, the knife further configured such that the blade shuttle is automatically refracted from the cutting position to the rest position when the blade is disengaged from the workpiece with the trigger in the actuated position. 8. The knife of claim 1, wherein the distance from the distal end of the blade to the blade aperture is approximately 0.028 inches greater than the first distance from the blade aperture when the blade is engaged in the workpiece. 9. The knife of claim 1, the blade shuttle moveable longitudinally from the rest position to a third extended position, the third extended position differentiated from the first and second extended positions, the blade shuttle moveable longitudinally from the third extended position to the cutting position when the blade is engaged in the workpiece. 10. The knife of claim 9, wherein the blade shuttle is in the fully extended position relative to the rest position in the third extended position. 11. The knife of claim 1, wherein the handle further comprises a longitudinally coupled two-piece handle assembly. 12. The knife of claim 1 further comprising a handle clip. 13. A knife, comprising: a handle enclosing at least a portion of one or more blades, a blade shuttle, a transmission, and a trigger, the handle comprising a blade aperture;the blade shuttle longitudinally moveable relative to the handle from a rest position to a first extended position and from the rest position to a second extended position, the first extended position differentiated from the second extended position, the blade shuttle moveable longitudinally from the first extended position and the second extended position to a cutting position when the blade is engaged in a workpiece, the knife configured such that the blade shuttle is automatically retracted from the cutting position to the rest position when the blade is disengaged from the workpiece;the blade secured within the blade shuttle, a distal end of the blade protruding a first distance from the blade aperture at the first extended position and a second distance from the blade aperture at the second extended position, the first distance differentiated from the second distance, the knife configured such that when the distal end of the blade protrudes the first distance from the blade aperture, the distal end of the blade moves to a distance from the blade aperture greater than the first distance from the blade aperture when the blade is engaged in the workpiece, and when the distal end of the blade protrudes the second distance from the blade aperture, the distal end of the blade moves to a distance from the blade aperture greater than the second distance from the blade aperture when the blade is engaged in the workpiece, the knife configured such that the blade is automatically retracted to a safe position within the handle when the blade is disengaged from the workpiece;the trigger adapted to drive the blade shuttle from the rest position to the first extended position and from the rest position to the second extended position via the transmission; andthe transmission comprising: a lever;a first spring operatively coupled to the trigger, the first spring adapted to: direct the lever to engage the blade shuttle in the first extended position and the second extended position; and rotate the lever to disengage the lever and the blade shuttle in the cutting position; anda second spring operatively coupled to the handle and the blade shuttle, the second spring adapted to automatically retract the blade shuttle from the cutting position to the rest position. 14. The knife of claim 13, wherein the second spring exerts no force on the blade shuttle in the rest position. 15. The knife of claim 13, wherein the knife further comprises at least a third spring adapted to act between the handle and the trigger and cooperate with the first and second springs to maintain a substantially constant force magnitude required to actuate the trigger and maintain the trigger in the actuated position. 16. The knife of claim 15, wherein the third spring is adapted to act between the handle and the trigger and cooperate with the first and second springs to maintain a substantially constant force magnitude required to actuate the trigger and maintain the trigger in the actuated position upon the blade engaging the workpiece. 17. The knife of claim 15, the force magnitude being between approximately 4 ounces and approximately 10 ounces. 18. The knife of claim 13, the knife further configured such that the blade shuttle is automatically retracted from the cutting position to the rest position when the blade is disengaged from the workpiece with the trigger in the actuated position. 19. The knife of claim 13, wherein the distance from the distal end of the blade to the blade aperture is approximately 0.028 inches greater than the first distance from the blade aperture when the blade is engaged in the workpiece. 20. The knife of claim 13, the blade shuttle moveable longitudinally from the rest position to a third extended position, the third extended position differentiated from the first and second extended positions, the blade shuttle moveable longitudinally from the third extended position to the cutting position when the blade is engaged in the workpiece.