Patent Publication Number: US-2013239415-A1

Title: Utility knife

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending U.S. Provisional Patent Application No. 61/610,144 filed on Mar. 13, 2012 and to co-pending U.S. Provisional Patent Application No. 61/656,196 filed on Jun. 6, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to knives and more particularly to utility knives. 
     BACKGROUND OF THE INVENTION 
     Utility knives typically include a housing, a blade carrier supported by the housing, and a blade coupled to the blade carrier for movement with the blade carrier between an extended position and a retracted position relative to the housing. During use, the blade may become dull or damaged. For some knives, this necessitates replacement of the entire blade. Other utility knives, often referred to as snap knives, incorporate a scored or segmented blade, allowing a user to break off the dull or damaged portion of the blade, to expose a new blade section for use. 
     SUMMARY OF THE INVENTION 
     The invention provides, in one aspect, a utility knife. The utility knife includes a frame defining a track and a blade carrier slidably received within the track. A blade is removably coupled to the blade carrier, and an actuator is operably coupled to the blade carrier to facilitate movement of the blade carrier along the track between an extended position and a retracted position. The utility knife also includes a first handle portion coupled to the frame and a second handle portion coupled to the first handle portion. The second handle portion is pivotable with respect to the first handle portion and the frame between a first position allowing movement of the blade between the retracted position and the extended position and a second position inhibiting movement of the blade between the retracted position and the extended position. 
     The invention provides, in another aspect, a utility knife. The utility knife includes a frame defining a track and a blade carrier slidably received within the track. The blade carrier includes a threaded bore. The utility knife also includes a blade removably coupled to the blade carrier. A double-lead fastener is received within the threaded bore of the blade carrier, and the fastener is rotatable relative to the blade carrier between a first position allowing movement of the blade carrier along the track and a second position inhibiting movement of the blade carrier along the track. 
     Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a utility knife according to one embodiment of the invention. 
         FIG. 2  is a perspective view of the utility knife of  FIG. 1  with a first handle of the knife removed. 
         FIG. 3  is a perspective view of the utility knife of  FIG. 1  with a second handle removed. 
         FIG. 4  is a perspective view of the utility knife of  FIG. 1  with the first handle removed. 
         FIG. 5  is a perspective view of the utility knife of  FIG. 1  with the first handle and a blade removed. 
         FIG. 6  is an end view of the utility knife of  FIG. 1  with the first handle removed. 
         FIG. 7  is a side view of a portion of the utility knife of  FIG. 1 . 
         FIG. 8  is a cross-section view of the portion of the utility knife of  FIG. 7  taken along lines  8 - 8  of  FIG. 7 . 
         FIG. 9  is a perspective view of a blade carrier of the utility knife if  FIG. 1 . 
         FIG. 10  is another perspective view of the blade carrier of  FIG. 9 . 
         FIG. 11  is a side view of the blade of the utility knife of  FIG. 1 . 
         FIG. 12  is a perspective view of a utility knife according to another embodiment. 
         FIG. 13  is an alternative perspective view of the knife of  FIG. 12 . 
         FIG. 14  is perspective view of the utility knife of  FIG. 12  with a handle of the knife removed. 
         FIG. 15  is a side view of the knife of  FIG. 12  with the handle removed. 
         FIG. 16  is a side view of a knife according to another embodiment. 
         FIG. 17  is a top view of the knife of  FIG. 16 . 
         FIG. 18  is a perspective view of the knife of  FIG. 16  with a portion of the handle removed. 
         FIG. 19  is a perspective view of the knife of  FIG. 16  with the handle removed. 
         FIG. 20  is a perspective view of the knife of  FIG. 16  with portions of the knife removed. 
         FIG. 21  is a perspective view of a carrier of the knife of  FIG. 16 . 
         FIG. 22  is a perspective view of a knife according to another embodiment. 
         FIG. 23  is a perspective view of the knife of  FIG. 22  with a handle removed. 
         FIG. 24  is a perspective view of an actuator of the knife of  FIG. 22 . 
         FIG. 25  is a perspective view of the actuator and a locking member of the knife of  FIG. 22 . 
         FIG. 26  is a perspective view of the knife of  FIG. 22  with the handle removed. 
         FIG. 27  is a perspective view of a carrier and the locking member of the knife of  FIG. 22 . 
         FIG. 28  is an enlarged side view of the knife of  FIG. 22  with the handle removed. 
         FIG. 29  is an alternative perspective view of the carrier and the locking member of the knife of  FIG. 22 . 
         FIG. 30  is a perspective view of a knife according to another embodiment of the invention. 
         FIG. 31  is a perspective view of the knife of  FIG. 30  with a handle removed. 
         FIG. 32  is a cross-sectional view of the knife of  FIG. 30  taken along lines  32 - 32  of  FIG. 30 . 
         FIG. 33  is an exploded view of a carrier and a locking assembly of the knife of  FIG. 30 . 
         FIG. 34  is a perspective view of the carrier and locking assembly of  FIG. 33  assembled. 
         FIG. 35  is a perspective view of a knife according to another embodiment of the invention. 
         FIG. 36  is a perspective view of the knife of  FIG. 35  with a handle removed. 
         FIG. 37  is a partially exploded perspective view of the knife of  FIG. 35 . 
         FIG. 38  is a side view of the knife of  FIG. 35 . 
         FIG. 39  is an enlarged, cross-sectional view of the knife of  FIG. 35 , taken along line  39 - 39  of  FIG. 38 . 
         FIG. 40  is a side view of a fastener of the knife of  FIG. 35 . 
         FIG. 41  is a rear perspective view of an actuator of the knife of  FIG. 35 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a knife  12 , which is a utility knife in the illustrated embodiment. The knife  12  includes a first handle  14 , a second handle  16  pivotally coupled to the first handle  14 , a frame  18 , a locking bar  20  ( FIG. 4 ), a blade carrier  22 , and a blade  24 . 
     With continued reference to  FIG. 1 , the first handle  14  includes a front end  28 , back end  30 , sidewalls  32  and  34  that extend from the front end  28  to the back end  30 , and a top wall  36  and a bottom wall  38  that both extend from the front end  28  to the back end  30 . The first handle  14  is generally hollow and includes an opening  40  in the front end  28  through which the frame  18  and the blade  24  extend. An elongated aperture  42  extends through the sidewall  32  between the front end  28  and the back end  30 . Also, an elongated aperture  44  extends through the bottom wall  38  between the front end  28  and the back end  30 . The second handle  16  pivots through the aperture  44 . Referring to  FIG. 3 , a post  46  extends between the sidewalls  32  and  34  adjacent the front end  28  of the first handle  14  and near the aperture  44  to pivotally couple the second handle  16  to the first handle  14 . 
     Referring to  FIGS. 2 and 3 , the second handle  16  includes a partially cylindrical recess  50  that receives the post  46  to pivotally couple the second handle  16  to the first handle  14  so that the second handle  14  can pivot about the post  46 . Although not illustrated, the knife  12  can include a biasing member, such as a spring, to rotationally bias the second handle  16  with respect to the first handle  14  about the post  46  generally in the direction of arrow  52  of  FIG. 2 . The second handle  16  includes a hook  54  that limits rotational movement of the second handle  16  with respect to the first handle  14  about the post  46  in the direction of the arrow  52  and inhibits the second handle  16  from rotating past the position illustrated and  FIG. 1  and uncoupling from the first handle  14 . The second handle  16  is also generally hollow and can be configured to retain spare blades  24 . The second handle  16  further includes a contoured grip surface  56  that is configured to provide an ergonomic grip for the user&#39;s fingers when the user grabs the knife  12  with the top wall  36  of the first handle  14  generally in the user&#39;s palm. 
     Referring to  FIGS. 5 and 8 , the frame  18  includes a front end  60  that includes an opening  62  and a back end  64  that includes an opening  66 . The frame  18  further includes a top wall  68  and a bottom wall  70  that both extend from the opening  62  at the front end  60  to the opening  66  at the back end  64 . A first sidewall  72  of the frame  18  extends from the top wall  68  to the bottom wall  70  and the first sidewall  72  includes an elongated aperture  74  between the openings  62  and  66 . A second sidewall  76  extends from the top wall  68  to the bottom wall  70  opposite the first sidewall  72  and the second sidewall  76  includes an elongated aperture  78  that extends from the opening  62  to the opening  66 . The aperture  78  extends through the opening  66  so that the blade carrier  24  can travel through the opening  66  to change the blade  24 . 
     With continued reference to  FIGS. 5 and 8 , the frame  18  defines a track  82  that extends from the opening  62  at the front end  60  of the frame  18  and through the opening  66  at the back end  64  of the frame  18 . The track  82  has a first portion  84  adjacent the back end  64  and a second portion  86  adjacent the front end  60  and the opening  62 . The first portion  84  of the track  82  has a width  88  defined as the distance between sidewalls  72  and  76  and the second portion  86  of the track  82  has a width  90  that is less than the width  88 . The reduced width  90  of the second portion  86  is created, at least in part, by an angled portion  92  of the first wall  72 . The width  88  is sized to guide movement of the blade carrier  22  in the direction of arrows  94  and  96  in  FIG. 8  and the width  90  is sized to guide movement of the blade  24  in the direction of the arrows  94  and  96 . The angled portion  92  of the wall  72  is positioned to act as a stop to limit movement of the blade carrier  22  past the stop  92  in the direction of arrow  94  and prevent the blade carrier  22  from traveling through the opening  62  at the front end  60  of the frame  18 . 
     Referring to  FIGS. 8-10 , the blade carrier  22  is received in the first portion  84  of the track  82  and the blade carrier  22  slides with respect to the frame  18  along the first portion  84  of the track  82  in the direction of the arrows  94  and  96  of  FIG. 8 . The blade carrier  22  includes a projection  98 , a friction member  100 , and an actuator  102 . The projection  98  extends through the blade  24  to couple the blade  24  with the carrier  22  for movement with the carrier  22  with respect to the frame  18 . The friction member  100  contacts the bottom wall  70  of the frame  18  to provide enough friction between the carrier  22  and the frame  18  to inhibit sliding movement of the carrier  22  along the track  82  caused by the force of gravity. Therefore, in the illustrated embodiment, a user must apply at least some force to the carrier  22 , via the actuator  102  in one method, to slide the carrier  22  along the track  82  and the force of gravity is insufficient to cause the carrier  22  to move in the direction of arrows  94  and  96  along the track  82 . 
     Referring to  FIGS. 1 and 2 , the actuator  102  extends through the aperture  42  of the first handle  14  and the aperture  78  of the frame  18  to provide the user with a place to grip the carrier  22 , such as with the user&#39;s thumb in one method, to slide the carrier  22  with respect to the frame  18  and the handle  14 . Referring to  FIG. 10 , the carrier  22  further includes a plurality of recesses  104  located on a side of the carrier  22  opposite the actuator  102 . As will be discussed in more detail below, the recesses  104  are engaged by the locking bar  20  via movement of the second handle  16  to inhibit movement of the carrier  22  and the blade  24  with respect to the handle  14  and the frame  18 . 
     Referring to  FIGS. 4-6 , the illustrated locking bar  20  includes a locking portion  106 , a first biasing member  108 , a second biasing member  110 , and an actuating surface  112 . The locking portion  106  includes projections  114  that face the blade carrier  22  and the projections  114  are sized to be received in the recesses  104  ( FIG. 10 ) of the carrier  22 . The locking portion  106  and the projections  114  are sized to extend through the aperture  74  of the frame  18  and the locking portion  106 , and the projections  114  extend along a great majority of the first portion  84  ( FIG. 8 ) of the track  82 . The biasing members  108 ,  110  are located at opposite ends of the locking portion  106  in the illustrated embodiment. The illustrated biasing members  108 ,  110  are leaf springs that bias the locking portion  106  generally in the direction of arrow  116  of  FIG. 6  and away from and out of engagement with the blade carrier  22 . As best seen in  FIG. 6 , the actuating surface  112  is angled or inclined away from the blade carrier  22 . The second handle  16  includes an actuating surface  118  that has an angle or inclination that matches the actuating surface  112  such that movement of the second handle  16  in the direction of arrow  120  causes the surface  118  to slide along the surface  112  to pivot the locking portion  106  in the direction of arrow  122  about pivot points  124 , which will be discussed in more detail below. 
     Referring to  FIG. 11 , the blade  24  includes a front end  130 , a back end  132 , and an aperture  134  adjacent the back end  132  that receives the projection  98  ( FIG. 9 ) of the carrier  22  to couple the blade  24  to the carrier  22 . A cutting edge  136  extends along the blade  24  from the front end  130  to the back end  132 . Parallel score marks  138 , which are parallel to the front end  130  and at an acute angle with respect to the cutting edge  136 , are located between the ends  130  and  132 . The score marks  138  allow the user to break the blade  24  along a score mark  138  if a portion of the cutting edge  136  between the score mark and the front end  130  becomes worn or dull. 
     In operation, referring to  FIGS. 1 ,  6 , and  8 , a user moves the blade carrier  22  in the direction of the arrow  94  by sliding the blade carrier  22  in the track  82  to extend a desired amount of the cutting edge  136  out of the opening  62  to cut a work-piece. When the desired amount of the cutting edge  136  has been exposed, for example, as illustrated in  FIG. 1 , the user pivots the second handle  16  with respect to the first handle  14  about the post  46  ( FIG. 3 ). The user pivots the second handle  16  by squeezing the second handle  16  and the first handle  14 , which causes the second handle  16  to move in the direction of the arrow  120  in  FIG. 6 . As the second handle  16  moves in the direction of arrow  120 , the actuating surface  118  of the second handle  16  slides along the actuating surface  112  of the locking bar  20 , which causes the locking portion  106  to move in the direction of the arrow  122  of  FIG. 6 . Continued movement of the locking portion  106  in the direction of the arrow  122  causes the projections  114  ( FIG. 8 ) to engage the recesses  104  ( FIG. 10 ) of the carrier  22 . Engagement between the recesses  104  and the projections  114 , as the user continues to squeeze the handles  14  and  16 , locks the blade  24  and the blade carrier  22  from movement along the track  82  and with respect to the handles  14  and  16  so that the user can use the cutting edge  136  to cut a work-piece. 
     After the work-piece has been cut, the user can release the force applied to the handles  14  and  16  that was caused by squeezing the handles  14  and  16 . This release causes the second handle  16  to pivot about the post  46  ( FIG. 3 ) with respect to the first handle  14  generally in the direction of the arrow  52  of  FIG. 2 . Referring to  FIG. 6 , such pivoting movement causes the second handle  16  to move in the direction of arrow  142 , which causes the actuating surface  118  of the handle  16  to slide down the actuating surface  112  of the locking bar  20  to allow the biasing members  108  and  110  to move the locking portion  106  and the projections  114  out of engagement with the recesses  104  ( FIG. 10 ) of the carrier  22 . Then, the user can retract the blade  24  via the actuator  102  of the carrier  22  to move the entire cutting edge  136  into the frame  18  so that the cutting edge  136  does not extend past the opening  62 . With the blade  24  in the desired position, the friction member  100  ( FIG. 7 ) of the carrier  22  provides enough friction against the bottom wall  70  of the frame  18  to prevent movement of the carrier  22  along the track  82  from the force of gravity. 
     Referring to  FIGS. 1 and 8 , although not illustrated, in one embodiment the back end  30  of the first handle  14  includes an aperture for removal and replacement of the blade  24 . In such an embodiment, the user slides the carrier  22  through the back opening  66  of the frame  18  and through the aperture in the back end  30  of the handle  14  to remove the carrier  22  and the blade  24  from the frame  18  and the handle  14 . The user can then attach a new blade  24  to the carrier  22  and insert the blade  24  and the carrier  22  back through the aperture at the back end  30  of the handle  14  and through the opening  66  in the back end  64  of the frame  18 . 
     Thus, the invention provides, among other things, a knife where the blade can easily be extended from the handle and refracted into the handle and can be securely held in a cutting position by squeezing the handle. 
       FIGS. 12-15  illustrate a utility knife  212  according to another embodiment of the invention. The knife  212  is similar to the knife  12  discussed above and only differences between the knives  12  and  212  will be discussed in detail below and like component have been given like reference numbers plus  200 . The knife  212  includes a link  244  that interconnects the second handle  216  and the locking bar  220 . The link  244  includes a first end  246  and a second end  248 . The first end  246  is pivotally coupled to the handle  216 . The second end  248  is pivotally and slidably coupled to the locking bar  220  via an elongated aperture  250  of the locking bar  220 . The handle  216  includes a front end  252  and a back end  254 . The link  244  is pivotally coupled to the handle  216  adjacent the back end  254  of the handle  216  and the second handle  216  is pivotally coupled to the first handle  214  ( FIG. 12 ) adjacent the front end  252  of the second handle  216 . Between the front end  252  and the back end  254 , a pin  255  pivotally and slidably couples the second handle  216  directly to the locking bar  220  via an elongated aperture  256  in the locking bar  220 . 
     In operation, to lock the blade carrier  222  in the desired position relative to the frame  218 , the user pivots the second handle  216  relative to the first handle  214  in the direction of arrow  320  about a pivot  258  until the second handle  216  moves from the position illustrated in  FIGS. 12-15  and is received in a recess  260  of the first handle  214 . When the second handle  216  is pivoted into the recess  260 , the link  244  locks the handle  216  in this closed position (open positions illustrated in  FIGS. 12-15 ). With the handle  216  in the closed position, the locking bar  220  moves to lock and hold the blade carrier  222  in the desired position as discussed above with regard to the knife  12  of  FIGS. 1-11 . Accordingly, the user does not need to squeeze the second handle  216  each time the user uses the knife, but rather only when the user desires to change the location of the blade carrier  222  relative to the frame  218 . 
       FIGS. 16-21  illustrate a knife  400  according to another embodiment of the invention. The knife  400  includes a handle  402 , a frame  404 , and a blade carrier  406  that positions a blade  408  relative to the handle  402  and the frame  404 . The knife  400  further includes an actuator and drive assembly  410  that positions the blade carrier  406 , and therefore the blade  408 , in the desired position. 
     The frame  404  includes a track  412 , and the carrier  406  slides within the track  412  to position the blade  408  in the desired position. The carrier  406  includes a first projection  414  that extends through the blade  408  to couple the blade  408  to the carrier  406  for movement relative to the track  412 . The carrier  406  further includes projections  416  that interact with the actuator and drive assembly  410  to move the carrier  406 , as will be discussed in more detail below. The carrier  406  further includes a friction member  417  that creates friction between the carrier  406  and the track  412  to inhibit undesired movement of the carrier  406  relative to the track  412  when the carrier  406  is not being moved by the actuator and drive assembly  410 . 
     The actuator and drive assembly  410  includes an actuator  418  and a drive shaft  420 . The actuator  418  includes a dial portion  422  that allows the user to rotate the actuator  418  using their thumb and index or forefinger. The actuator  418  further includes an internal ring gear  424 . The drive shaft  420  includes a spur gear  426  that meshes with the ring gear  424  such that rotation of the actuator  418  rotates the drive shaft  420 . The drive shaft  420  further includes a helical recess  428  that extends along the length of the shaft  420  and rotation of the shaft  420  rotates the recess  428 . The projections  416  of the blade carrier  406  are received in the helical recess  428  such that rotation of the recess  428  causes linear movement of the blade carrier  406  along the track  412 . 
     In operation, the user rotates the dial portion  422  of the actuator  418  in the direction arrow  430  ( FIG. 19 ), which causes the blade carrier  406  to move along the track  412  in the direction of arrow  432  to extend the blade  408  from the handle  402  so that the blade  408  can be used to cut a work-piece. When the user is finished using the blade  408 , the user rotates the actuator  418  in the direction of arrow  434 , which causes the carrier  406  and the blade  408  to move in the direction of arrow  436  and into the handle  402 . In the illustrated embodiment the gears  424  and  426  and the helical recess  428  are sized such that ¼ revolution of the dial portion  422  results in the carrier  406  translating ½ inch along the track  412 . The illustrated arrangement of the actuator and drive assembly  410  allows the blade  408  to be centrally positioned between sides  438 ,  440  ( FIG. 17 ) of the handle  402 . 
       FIGS. 22-29  illustrate a knife  500  according to another embodiment of the invention. The knife  500  includes a handle  502 , a frame  504 , and a blade carrier  506  that positions a blade  508  relative to the handle  502  and the frame  504 . The knife  500  further includes an actuator  510  that positions the blade carrier  506 , and therefore the blade  508 , in the desired position. 
     Referring to  FIG. 23 , the frame  504  includes a track  512  and recesses  514  evenly spaced along the track  512 . The carrier  506  slides within the track  512  to position the blade  508  in the desired position. The carrier  506  ( FIG. 29 ) includes a projection  516  that extends through the blade  508  to couple the blade  508  to the carrier  506 . The carrier  506  further includes an elongated aperture  518  having a length  520 . Projections  522  are located at each end of the aperture  518 . As best seen in  FIGS. 27 and 29 , a locking member  524  is coupled to the carrier  506  for movement with the carrier  506  along the track  512 . The locking member  524  includes a biasing member  526 , which is a leaf spring in the illustrated embodiment, and a projection  528  coupled to the spring  526 . 
     Referring to  FIGS. 24 and 25 , the actuator  510  includes a button  530  and a lock  532  that is rotatably coupled the button  530 . The button  530  includes a friction surface  534  that is engaged by a user&#39;s finger to both push and slide the button  530  relative to the frame  504 . The button  530  includes a post  536  that rotatably couples the lock  532  to the button  530 . The button  530  further includes a forward facing cam surface  538  and a rearward facing cam surface  540  that are used to move the projection  528  of the locking member  524  out of the recesses  514  of frame  504 , as will be discussed in more detail below. The lock  532  includes an aperture  542  that receives the post  536  of the button  530  to rotatably couple the lock  532  and the button  530 . The lock  532  further includes apertures  544  that are space approximately 180 degrees from each other around the aperture  542 . The lock  532  further includes a lever  546  that allows the user to rotate the lock  532  relative to the button  530 . 
     In operation, referring to  FIGS. 26 ,  28 , and  29 , the carrier  506 , and therefore the blade  508 , is held in position relative to the frame  504  by the locking member  524 . The projection  528  of the locking member  524  is received and held in two opposed recesses  514  of the frame  504  by the bias of the spring  526  of the locking member  524  to hold the carrier  506  in the desired position. With the carrier  506  in the desired position, as discussed above, the blade  508  is either extended for use or retracted for storage. In the illustrated embodiment, to move the carrier  506 , and therefore the blade  508 , relative to the track  512 , the user pivots the lever  546  of the lock  532  relative to the button  530  from a locked position ( FIGS. 26 ,  28 , and  29 ) in the direction of arrow  548  to an unlocked position. The lever  546  is rotated until it reaches the unlocked position and stops rotating. In the unlocked position, the apertures  544  are aligned with the projections  522  of the carrier  506 . In this position, the button  530  is allowed limited movement in the direction of arrows  550  and  552  relative to the carrier  506  because the projections  522  are allowed to move into the apertures  544 . Movement of the button  530  in the direction of arrows  550  and  552  is limited by the projections  522 . With the lever  546  in the unlocked position, to extend the blade  508  from the frame  504 , the user slides the button  530  in the direction arrow  552 . This causes the forward facing cam surface  538  ( FIG. 24 ) to push the projection  528  of the locking member  524  against the bias of spring  526  and out of the recesses  514  in which the projection  528  was held. Then, the user can continue to slide the carrier  506  in the direction of arrow  552  to extend the blade  508  from the frame  504  and the handle  502 . When the blade  508  is in the desired position, the user releases the button  530  which causes the projection  528  to automatically travel into adjacent opposed recesses  514  to hold the carrier  506  in the desired position. The user can move lever  546  back to the locked position ( FIG. 28 ) by rotating the lever  546  in the direction of arrow  554  ( FIG. 28 ) to inhibit unintentional movement of the carrier  506 . 
     To retract the blade  508 , the user rotates the lever  546  in the direction of arrow  548  to the unlocked position and moves the button  530  in the direction of arrow  550  ( FIG. 28 ). Movement of the button  530  in the direction of arrow  550  causes the rearward facing cam surface  540  ( FIG. 24 ) to move the projection  528  of the locking member  524  out of the recesses  514  in which the projection  528  was held, which allows the user to retract the blade  508  into the handle  502 . 
       FIGS. 30-34  illustrate a knife  600  according to another embodiment of the invention. The knife  600  includes a handle  602 , a frame  604 , and a blade carrier  606  that positions a blade  608  relative to the handle  602  and the frame  604 . The knife  600  further includes a locking assembly  610  that retains the blade carrier  606 , and therefore the blade  608 , in the desired position. 
     Referring to  FIG. 31 , the frame  604  includes a track  612  and the carrier  606  slides within the track  612  to position the blade  608  in the desired position. The carrier  606  includes a projection  614  ( FIG. 30 ) that extends through the blade  608  to couple the blade  608  to the carrier  606 . 
     The locking assembly  610  is coupled to the blade carrier  606  for movement with the carrier  606  along the track  612 . Referring to  FIG. 33 , the illustrated locking assembly  610  includes an actuator  618 , a bolt  620 , a nut  622 , a washer  624 , a first biasing member  626 , and a second biasing member  628 . In the illustrated embodiment, the biasing members  626  and  628  are spring washers or Belleville washers. 
     In operation, to position the carrier  606 , and therefore the blade  608 , relative to the frame  604 , the user moves the locking assembly  610  from a locked position ( FIG. 32 ) to an unlocked position. The move the locking assembly  610  to the unlocked position, the user rotates the actuator  618  in the direction of arrow  632 , which causes the bolt  620  to rotate relative to the carrier  606  because the nut  622  is held from rotation with the respect to the carrier  606 . As illustrated in  FIG. 34 , the nut  622  is held from rotation with respect to the carrier  606  because the nut  622  is received in a hex-shaped recess  634  of the carrier  606  that limits movement of the nut  622  relative to the carrier  606 . Rotation of the bolt  620  in the direction of arrow  632  causes the bolt  620  to move away from the frame  604  and in the direction of arrow  636  of  FIG. 32 . This movement of the bolt  622  releases a clamping pressure that was being exerted on the washer  624  by the springs  626 ,  628  and the actuator  618 . With the clamping pressure released, the user can move the carrier  606  and the blade  608  relative the frame  604  to a desired position. 
     When the blade  608  is in the desired position (e.g., extended or retracted), the user rotates the actuator  618  in the direction of arrow  640 . Such rotation of the actuator  618  also rotates the bolt  620 , which cases the actuator  618  to move in the direction of arrow  642  of  FIG. 32  to exert a clamping pressure on the spring washers  626  and  628 . The spring washers  626  and  628  then exert a clamping pressure on the washer  624 . The friction between the washer  624  and the frame  604  caused by the clamping pressure in the direction of arrow  642  retains the carrier  606  and the blade  608  in the desired position. 
       FIGS. 35-41  illustrate a knife  700  according to another embodiment of the invention. The knife  700  includes a handle  702 , a frame  704 , and a blade carrier  706  that positions a blade  708  in a desired position relative to the handle  702  and the frame  704 . The knife  700  further includes a locking assembly  710  that retains the blade carrier  706 , and therefore the blade  708 , in the desired position. 
     With reference to  FIG. 35 , the handle  702  includes a front end  712 , a back end  714 , sidewalls  716  and  718  that extend from the front end  712  to the back end  714 , and a top wall  720  and a bottom wall  722  that both extend from the front end  712  to the back end  714 . The handle  702  is generally hollow and includes an opening  724  in the front end  712  through which the frame  704  and the blade  708  extend. The handle  702  also includes an opening  725  in the back end  714  through which the blade carrier  706  and the blade  708  may be removed to facilitate replacement of the blade  708 . An elongated aperture  726  extends through the sidewall  716  between the front end  712  and the back end  714 . 
     With reference to  FIG. 36 , the frame  704  includes a front end  728  that includes an opening  730  and a back end  732  that includes an opening  734 . The frame  704  further includes a top wall  736  and a bottom wall  738  that both extend from the opening  730  at the front end  728  to the opening  734  at the back end  732 . A first sidewall  740  of the frame  704  extends from the top wall  736  to the bottom wall  738 , and the first sidewall  740  includes an elongated aperture  742  between the openings  730  and  734 . The aperture  742  extends through the openings  730 ,  734 . A second sidewall  744  extends from the top wall  736  to the bottom wall  738  opposite the first sidewall  740 . 
     The frame  704  defines a track  746  that extends from the opening  730  at the front end  728  of the frame  704  and through the opening  734  at the back end  732  of the frame  704 . The track  746  has a first portion  748  adjacent the back end  732  and a second portion  750  adjacent the front end  728  and the opening  730 . The first portion  748  of the track  746  has a width  752  defined as the distance between sidewalls  740  and  744 , and the second portion  750  of the track  746  has a width  754  that is less than the width  752 . The reduced width  754  of the second portion  750  is created, at least in part, by an angled portion  756  of the first sidewall  740 . The width  752  is sized to guide movement of the blade carrier  706  in the direction of arrows  758  and  760 . The angled portion  756  of the first sidewall  740  is positioned to act as a stop to limit movement of the blade carrier  706  past the angled portion  756  in the direction of arrow  758  and prevent the blade carrier  706  from traveling through the opening  730  at the front end  728  of the frame  704 . 
     Referring to  FIG. 37 , the blade carrier  706  is received in the first portion  748  of the track  746  and the blade carrier  706  slides with respect to the frame  704  along the first portion  748  of the track  746  in the direction of the arrows  758  and  760 . The blade carrier  706  includes opposing sides  762  and  764 , a projection  766 , a friction member  768 , a leaf spring  770 , and a threaded bore  772  extending through the blade carrier  706 . The projection  766  extends from the side  764  and through the blade  708  to couple the blade  708  with the carrier  706  for movement with the carrier  706  with respect to the frame  704 . The friction member  768  contacts the bottom wall  738  of the frame  704  to provide enough friction between the carrier  706  and the frame  704  to inhibit sliding movement of the carrier  706  along the track  746  caused by the force of gravity. Therefore, in the illustrated embodiment, a user must apply at least some force to the carrier  706 , (e.g., via the locking assembly  710 ) to slide the carrier  706  along the track  746 , and the force of gravity is insufficient to cause the carrier  706  to move in the direction of arrows  758  and  760  along the track  746 . 
     With continued reference to  FIG. 37 , the locking assembly  710  includes a fastener  774  and an actuator  776 . With reference to  FIG. 39 , the fastener  774  is received within the threaded bore  772 . The fastener  774  is rotatable relative to the blade carrier  706  to axially advance the fastener  774  in the direction of arrow  778 , until a distal end  780  of the fastener  774  bears against the track  746 , developing a clamping force between the fastener  774  and the track  746  to lock the blade carrier  706  in place. Similarly, the fastener  774  is rotatable relative to the blade carrier  706  to axially withdraw the fastener  774  in the direction of arrow  782  to disengage the distal end  780  of the fastener  774  from the track  746 , permitting the blade carrier  706  to slide within the track  746 . The actuator  776  is fixed to a proximal end  784  of the fastener  774  to facilitate rotation of the fastener  774  without the use of tools. Referring to  FIGS. 35 and 38 , the actuator  776  extends through the aperture  726  of the handle  702  and the aperture  742  of the frame  704  to provide the user with a place to grip the carrier  706  to slide the carrier  706  with respect to the frame  704  and the handle  702 . In addition, with reference to  FIGS. 39 and 41 , the actuator  776  includes a rear side  786  having a plurality of ridges  788  that engage with the leaf spring  770  of the carrier  706  as the actuator  776  rotates. This engagement provides the user with a tactile sensation (e.g., clicking) when the user rotates the actuator  776 . 
     Illustrated in  FIG. 40 , the fastener  774  defines a pitch distanced  790  (referred to hereafter as “pitch”) and a lead distance  792  (referred to hereafter as “lead”). The pitch  790  is the axial distance between adjacent crests  794  of the fastener  774 . The lead  792  is the axial distance that the fastener  774  is advanced for each complete rotation of the fastener  774 . A conventional threaded fastener (not shown) includes a single thread wrapped helically around the fastener. The pitch and the lead of the conventional fastener are equal; therefore the conventional fastener advances an axial distance equal to the pitch for each complete rotation. In the illustrated embodiment, the fastener  774  is configured as a double-lead screw (also referred to as a double-start screw or a double-threaded screw). The illustrated fastener  774  includes two separate threads  795   a,    795   b  offset 180 degrees and wrapped helically around the fastener  744 . As such, the fastener  774  advances twice the pitch  790  per rotation (i.e., the lead  792  is twice the pitch  790 ), thereby requiring less rotation to lock or unlock the blade carrier  706  than if a conventional fastener were used. In the illustrated embodiment, the fastener  774  is rotatable from the locked position to the unlocked position with an angular displacement of about 135 degrees or about ⅜ of a full rotation. In contrast, the conventional fastener would require an angular displacement of about 270 degrees, or about ¾ of a full rotation. 
     With reference to  FIG. 37 , the blade  708  includes a front end  796 , a back end  798 , and an aperture  800  adjacent the back end  798  that receives the projection  766  of the carrier  706  to couple the blade  708  to the carrier  706 . A cutting edge  802  extends along the blade  708  from the front end  796  to the back end  798 . Parallel score marks  804 , which are parallel to the front end  796  and at an acute angle with respect to the cutting edge  802 , are located between the ends  796  and  798 . The score marks  804  allow the user to break the blade  708  along a score mark  804  if a portion of the cutting edge  802  between the score mark and the front end  796  becomes worn or dull. 
     In operation, to position the carrier  706 , and therefore the blade  708 , relative to the frame  704 , the user moves the locking assembly  710  from a locked position ( FIG. 39 ) to an unlocked position. To move the locking assembly  710  to the unlocked position, the user grips and rotates the actuator  776 , which causes the fastener  774  to rotate relative to the carrier  706  and move away from the frame  746  in the direction of arrow  782 . This movement of the fastener  774  releases a clamping pressure that was being exerted on the track  746  by the distal end  780  of the fastener  774 . Because the fastener  774  is a double-lead fastener, the user need only rotate the actuator  776  by an angular displacement of about 135 degrees in a first direction (e.g., counterclockwise) to reach the unlocked position. This allows the user to move the locking assembly  710  from the locked position to the unlocked position in a single motion, without releasing the fastener  774 . With the clamping pressure released, the user can grip the actuator  776  to move the carrier  706  and the blade  708  relative the frame  704  to a desired position. 
     When the blade  708  is in the desired position (e.g., extended or retracted), the friction member  768  ( FIG. 37 ) of the carrier  706  provides enough friction against the track  746  to prevent movement of the carrier  706  along the track  746  from the force of gravity. The user then moves the locking assembly  710  to the locked position by gripping and rotating the actuator  776 , which causes the fastener  774  to move in the direction of arrow  778  of  FIG. 39 . This movement of the fastener  774  develops a clamping pressure. The clamping pressure, developed by the engagement of the distal end  780  of the fastener  774  with the track  746 , retains the carrier  706  and the blade  708  in the desired position. Because the fastener  774  is a double-lead fastener, the user need only rotate the actuator  776  by an angular displacement of about 135 degrees in a second direction (e.g., clockwise) to reach the locked position. This allows the user to move the locking assembly  710  from the unlocked position to the locked position in a single motion, without releasing the fastener  774 . 
     To replace the blade  708 , the user slides the carrier  706  through the back opening  734  of the frame  704  and through the aperture  725  in the back end  714  of the handle  702  to remove the carrier  706  and the blade  708  from the frame  704  and the handle  702 . The user can then attach a new blade  708  to the carrier  706  and insert the blade  708  and the carrier  706  back through the aperture  725  at the back end  714  of the handle  702  and through the opening  734  in the back end  732  of the frame  704 . 
     Various features of the invention are set forth in the following claims.