Patent Publication Number: US-8539677-B2

Title: Utility knife

Description:
The invention relates generally to utility knives and more particularly to a utility knife with an improved locking assembly and blade carrier. 
     BACKGROUND OF THE INVENTION 
     Utility knives typically comprise a knife housing that is provided with an aperture that receives a blade such that the blade extends from the housing. A user can grasp the housing and use the blade for cutting or slicing. When the blade becomes worn, dull or breaks the housing may be opened to allow replacement of the blade. 
     SUMMARY OF THE INVENTION 
     A utility knife comprises a housing comprised of a first housing portion and a second housing portion movable relative to the first housing portion between a closed position and an open position. The first portion carries a strike plate and the second housing portion carries a locking member. An overlapping locking mechanism locks the first housing portion relative to the second housing portion to prevent relative movement in a first direction. The overlapping locking mechanism can be unlocked by moving the first housing portion relative to the second housing portion in a second direction. The locking member is movable between a first position in which it engages the strike plate to prevent the first housing from moving relative to the second housing in the second direction and a second position in which it does not engage the strike plate and allows the first housing to move relative to the second housing in the second direction. 
     The first housing portion may comprise a first perimeter edge that abuts a second coextensive perimeter edge on the second housing portion defining a seam where the overlapping locking mechanism extends across the seam. The first housing portion may carry a pin that extends through a slotted aperture formed in the second housing portion such that the first housing portion and second housing portion are rotatable relative to one another about the pin. The overlapping locking mechanism may be positioned remote from the pin. The locking member may be biased to the locked position and may comprise a resilient member such as a leaf spring. The locking member may have a fixed end and a movable free end such that when the locking member is in the first position the free end is positioned directly behind the strike plate. A button may be moveable between a locked position and an unlocked position where the button terminates in a distal end that is disposed opposite the free end of the locking member. The locking member may bias the button to the locked position and the button may be depressed to move the locking member to the second position. The locking member may bias the first housing portion away from the second housing portion. 
     A safety mechanism may prevent the second housing portion from moving in the second direction even when the locking member is in the unlocked position. The safety mechanism may include a blade carrier that holds a blade in an extended and a retracted position relative to the housing. The blade carrier may comprise a latch engageable with a first stop to fix the position of the first housing portion and the second housing portion relative to the latch. The latch may engage a second stop to fix the position of the first housing portion relative to the latch and allow movement of the second housing portion relative to the latch. The latch may comprise a resilient member comprising a tab engageable with the first stop and the second stop. An actuator button may extend through a slot formed in the housing and be connected to the carrier. The second housing portion may comprise a first plurality of recesses that are dimensioned such that the first tab can be located in any one of the first plurality of recesses and the first housing portion may comprise a second plurality of recesses that are dimensioned such that a second tab can be located in any one of the second plurality of recesses. At least one of the second plurality of recesses has a width that is greater than the width of the second tab to define a gap that allows the first housing portion to move rearward relative to the second housing portion. The gap is sized such that the housing portions are able to move relative to one another a distance sufficient to disengage the overlapping locking mechanism. 
     The utility knife may comprise a blade holder comprising a wireform having a first end secured to one of the first or second housing portions and a second free end where the wireform is bent such that the second free end clamps a spare blade against the fists or second housing portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an embodiment of the utility knife of the invention in the closed position. 
         FIG. 2  is a section view taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a front view of the utility knife of  FIG. 1  in an open position. 
         FIG. 4  is a section view taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a section view similar to that of  FIG. 4  with the housing portions in contact with one another. 
         FIG. 6  is a top view of the utility knife as shown in  FIG. 3 . 
         FIG. 7  is a bottom view of the utility knife as shown in  FIG. 3 . 
         FIG. 8  is a front view of the utility knife of  FIG. 1  in a completely open position. 
         FIG. 9  is a top view of the utility knife as shown in  FIG. 8 . 
         FIG. 10  is a section view similar to that of  FIG. 5  in the closed position. 
         FIG. 11  is a detailed front view of a housing portion. 
         FIGS. 12 and 13  are detailed views of an embodiment of the blade carrier. 
         FIGS. 14 and 15  are block diagrams illustrating methods of operating the knife. 
         FIG. 16  is a section view similar to that of  FIG. 2  showing an alternate embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The utility knife is shown generally at  1  in the figures and comprises a first housing portion  2  and a second housing portion  4 . The housing portions are releasably secured to one another to form the complete knife housing  6 . The knife housing  6  has a generally elongated profile that may be comfortably grasped by a user&#39;s hand with the front end or nose  6   a  of the knife extending from the user&#39;s hand. Toward the rear end or butt  6   b  of the housing  6  a hand grip  8  is formed that may be gripped during use of the knife. 
     The first housing portion  2  comprises a perimeter edge  10  that abuts a substantially coextensive perimeter edge  12  on the second housing portion  4  in the assembled housing  6  to define a generally open interior. A slot  11  is provided in the nose  6   a  between the first housing portion  2  and the second housing portion  4  through which a blade  9  extends during use of the knife. Near the rear end  6   b  the first housing portion  2 , raised projections  14  are formed that extend outwardly from the perimeter edge  10 . Raised projections  14  extend inside of the perimeter edge  12  of the second housing portion  4  to align the housing portions  2  and  4  in the assembled housing  6 . 
     At the rear end  6   b  of housing  6  housing portion  2  carries a pin  20  supported between spaced supports  22  and  24  in a generally fixed position. Pin  20  extends through a slotted aperture  26  formed in housing portion  4  such that the housing portions  2  and  4  can rotate relative to one another about pin  20  between the closed position of  FIG. 1  and the open position of  FIGS. 8 and 9 . Slotted aperture  26  is wider than the pin  20  such that the pin  20  can also move in aperture  26  toward and away from the nose  6   a . This axial movement allows housing portion  2  to move a limited distance along the length of housing portion  4  as will hereinafter be described. The term “axial” as used herein means generally along the long axis of the knife from nose  6   a  to rear end  6   b  as represented by arrow A in  FIG. 2 . 
     Overlapping locking mechanisms  37  and  39  are formed at the nose  6   a  of the knife to lock the housing portions  2  and  4  together. The overlapping locking mechanisms engage one another to prevent the housing portions  2  and  4  from separating from one another at the nose  6   a  due to the forces exerted on the housing  6  by the blade  9  during use of the knife. Referring to  FIG. 2 , overlapping locking mechanism  37  is located at the top end of the nose  6   a  and includes an engagement element  40  on housing portion  2 . Engagement element  40  extends across the seam S, where seam S is defined by the edges  10  and  12  when they abut in the closed housing  6 . Engagement element  40  defines a bearing surface  40   a  that faces seam S. Housing portion  4  includes a mating engagement element  42  that includes a bearing surface  42   a  that faces opposite to bearing surface  40   a.    
     To assemble the housing  6  the housing portion  2  is placed against housing portion  4  in a slightly offset position with the housing portion  2  offset toward the rear of housing portion  4 . Housing portion  2  is slid in the axial direction toward the nose of housing portion  4  until bearing surface  40   a  of engagement element  40  is disposed behind bearing surface  42   a  of engagement element  42 . The engagement of element  40  and element  42  prevents housing  2  from moving away from housing portion  4  along a transverse direction, represented by arrow B, that is disposed generally perpendicular to the axial direction. Because of the mechanical interlocking of the engagement elements  40  and  42  the nose  6   a  cannot be pried apart. 
     A similar overlapping locking mechanism  39  is formed on the bottom end of nose  6   a . Referring to  FIG. 4 , interlocking mechanism  39  is shown in the open position. Housing portion  2  includes an engagement element  46  that extends across the seam S when the housing portions  2  and  4  are in the closed position. Engagement element  46  defines a bearing surface  46   a  that faces the housing portion  2 . Housing portion  4  includes a mating engagement element  47  that includes a bearing surface  47   a  that faces opposite to bearing surface  46   a . To assemble the housing  6  the housing portion  2  is pushed against housing portion  4  in the slightly offset position. Housing portion  2  is slid forward in the axial direction relative to housing portion  4  until engagement element  46  is disposed behind engagement element  47 . The engagement of these elements prevents the nose of the knife from being pried open by forces exerted by the blade on the housing during use of the knife. 
     To lock the housing portion  2  to the housing portion  4  a locking member  48  is provided on one of the housing portions that engages a fixed strike plate  50  on the other housing portion. In the illustrated embodiment the locking member  48  is formed on housing portion  4  and strike plate  50  is formed on the housing portion  2  at a generally central location. The strike plate  50  is fixed to the housing portion  2  and extends therefrom toward housing portion  4 . The locking member  48  is mounted to the other housing portion  4  opposite to the strike plate  50 . 
     The locking member  48  comprises a member movable between a first locked position and a second unlocked position. The locking member is biased to the locked position. In the illustrated embodiment the locking member  48  comprises a resilient member in the form of a leaf spring. A first end  48   a  of the spring is fixed to housing  4  such as by fasteners  54  and the opposite free end  48   b  extends from the housing in a cantilevered fashion such that it may move toward and away from the housing portion  4  between the unlocked and locked positions respectively. The leaf spring is made of a resilient material such as steel such that it may be deformed to occupy the unlocked position and resiliently return to its original shape to occupy the locked position.  FIG. 4  shows the locking member  48  in the undeformed position.  FIG. 5  shows the locking member  48  in the deformed, unlocked position where it is moved from the locked position of  FIG. 4  toward housing portion  4 . Locking member  48  may alternatively be a rigid member movable between the locked and unlocked positions and biased to the locked position by a separate spring. 
     When locking member  48  is in the locked position and housing  6  is fully closed the distal end  48   b  of locking member  48  is positioned directly behind (toward rear end  6   b ) strike plate  50 ,  FIG. 10 . When locking member  48  is in this position and housing portions  2  and  4  are closed against one another, locking member  48  prevents housing portion  2  from sliding rearward relative to the housing portion  4  along axial direction A. The distal end  48   b  of locking member  48  abuts strike plate  50  and blocks axial movement of the housing portion  2  rearward relative to housing portion  4 . If the housing portions  2  and  4  are prevented from moving axially relative to one another, the overlapping locking mechanisms  37  and  39  remain engaged such that the housing portions  2  and  4  cannot be separated at nose  6   a  and cannot be opened. The rear end  6   b  of the housing  6  also cannot be separated due to the engagement of pin  20  with slot  26 . As a result, the housing portions  2  and  4  remain fixed to one another in the closed position. 
     Referring to  FIGS. 1 ,  4 ,  5  and  8 , a push button  56  extends through a hole  57  formed in the wall of the housing portion  2 . Push button  56  has a head  58  that is located on the outside of the housing portion  2  where it may be pressed by a user to move the push button relative to the housing  6  towards and away from housing portion  4 . Push button  56  moves between an extended locked position to a depressed unlocked position. The head  58  is larger than the hole  57  and may include raised areas or other topography to facilitate the user&#39;s grip on the head. The shaft  62  of push button  56  extends through hole  57  and terminates in a distal end  62   a  that is disposed opposite the free end  48   b  of locking member  48 . A fastener  64  or other device engages the shaft  62  to retain the push button  56  in the housing portion  2 . 
     The shaft  62  has a length such that when the locking member  48  is in the locked position, and the housing portions  2  and  4  are closed, the free end  48   b  of locking member  48  contacts the end  62   a  of shaft  62  and biases the push button  56  to the extended locked position,  FIG. 10 . When the push button  56  is depressed by the user, the shaft  62  is moved toward housing portion  4  against the bias of locking member  48  until the distal end  48   b  of the locking member  48  is not in blocking engagement with the strike plate  50 . The shaft  62  pushes against the locking member  48  until the end  48   b  of the locking member  48  moves beyond the end of the strike plate  50 . Because the locking member  48  is no longer in blocking contact with the strike plate  50  the housing portion  2  can slide in the axial direction relative to housing portion  4  toward the rear end  6   b  of the knife. 
     Moving housing portion  2  rearward relative to housing portion  4  disengages the overlapping locking mechanisms  37  and  39 . Once the overlapping locking mechanisms  37  and  39  are no longer engaged the nose end of housing portion  2  can move transversely away from the nose end of housing portion  4  allowing the housing portions to separate from one another as shown in  FIGS. 3 ,  5 ,  6  and  7 . The housing portions  2  and  4  can be rotated about pin  20  to the fully open position shown in  FIGS. 8 and 9 . 
     As the housing portion  2  is slid rearward relative to housing portion  4  to disengage locking mechanisms  37  and  39 , the locking member  48  is biased against the distal end of the strike plate  50 . Because locking member  48  is biased into contact with strike plate  50 , when the overlapping locking mechanisms  37  and  39  are disengaged, the locking member  48  biases the housing portion  2  away from housing portion  4  such that when the user releases housing portion  2 , the housing portions are separated slightly by locking member  48  as shown in  FIG. 4 . The separation of the housing portions  2  and  4  allows the user to easily grasp and separate the housing portions to the fully open position of  FIGS. 7 and 8 . 
     To prevent the housing  6  from inadvertently opening, the blade carrier  70  includes a safety feature that requires the user to properly position the blade carrier before the housing  6  can be opened. Referring to  FIGS. 11 ,  12  and  13 , the blade carrier  70  comprises a fixed rail  72  mounted to one of the housing portions, shown mounted to housing portion  4 . The rail  72  has a downwardly extending edge  72   a  that is spaced from the housing wall and that extends along the direction of travel of the blade between the blade&#39;s extended and retracted positions. A first support surface  74  and a second support surface  76  extend along the direction of travel of the blade to support the blade carrier as it moves along the rail  72 . 
     The blade carrier  70  comprises a relatively flat support plate  78  that rides on rail  72  and support surfaces  74 ,  76 . The plate  78  is dimensioned and shaped to hold a blade between the outwardly extending flanges  80  and  82 . A stop  84  is formed along the back edge of the plate  78  against which the back edge of the blade is positioned such that the blade is properly positioned and seated on the plate  78 . A positioning member  86  extends from the plate  78  along the top edge thereof. Positioning member  86  engages one of a plurality of notches  88  formed in the top edge of the utility blade to retain the blade on carrier  70  and to properly position the blade  9  on the carrier  70  in one of a plurality of positions. 
     A retention clip  90  extends from the back of the plate  78 . Clip  90  is positioned just below the edge  72   a  of rail  72  and is dimensioned such that it extends beyond edge  72   a . The end of clip  90  is formed with a retaining member such as an upwardly extending finger  92  that is disposed behind the rail  72  such that the edge  72   a  of rail  72  sits in the groove  94 . The clip  90  secures the carrier  70  to the rail  72  while allowing the carrier  70  to reciprocate along the length of rail  72 . When the housing is in the open position, the carrier  70  may be removed by sliding the carrier  70  toward the front of the knife such that the clip  90  is disengaged from the rail  72 . The carrier  70  may be removed for cleaning or maintaining the tool. 
     The carrier  70  also includes a latch  94  that locks the carrier in a fully retracted position, a fully extended position or one of a plurality of partially extended positions and also acts as a safety to prevent the inadvertent opening of the housing  6 . The latch  94  extends from the top of the plate  78  and comprises a resilient member that extends toward the rear of the knife. The latch  94  has a T-shape where the tabs  96  and  98  extend toward the first housing portion  2  and the second housing portion  4 , respectively. An actuator button  100  extends through a slot  102  formed in the housing  6  such that when the user moves the actuator button  100  in slot  102  the carrier  70  is reciprocated along rail  72 . The button  100  is connected to the latch  94  by neck  104  that is long enough to allow the button  100  to be depressed such that the latch  94  can be deformed from the locking position shown in the figures to a release position as will hereinafter be described. 
     A series of stops are provided in the housing portion to fix the position of the carrier  70  in housing  6 . Housing portion  4  includes a plurality of downwardly recesses  110   a ,  110   b ,  110   c  and  110   d  that extend along the length of the housing portion and are located along side of the latch  94 . The recesses  110   a ,  110   b ,  110   c  and  110   d  are dimensioned such that the tab  98  can be located in any one of the recesses. The walls of the recesses act as stops to limit motion of carrier  70  relative to housing portion  4 . Once the tab  98  is located in a recess the engagement of the tab  98  with the walls of the recess prevents the carrier  70  from moving along rail  72 . By depressing button  100  and deforming latch  94  downward the tab  98  is removed from locking engagement with the recess. 
     Housing portion  2  includes a plurality of recesses  112   a ,  112   b ,  112   c  and  112   d  that extend along the length of the housing portion  2  and are located along side of the latch  94  and are positioned opposite to recesses  110   a ,  110   b ,  110   c  and  110   d , respectively. The recesses  112   a ,  112   b ,  112   c  and  112   d  are dimensioned such that the tab  96  can be located in any one of the recesses. The recess  112   a  disposed closest to the nose of the knife is dimensioned like the recesses formed on housing portion  2  where the walls of the recesses act as stops such that engagement of the tab  96  with the walls of the recess  112   a  prevents relative movement between the carrier  70  and housing portion  2 . The remaining recesses  112   b ,  112   c  and  112   d  have a width that is greater than the width of the tab  96 . As shown in  FIG. 2  recess  112   b  is wider than recess  112   a  or any of recesses  110   a ,  110   b ,  110   c  and  110   d . Recesses  112   c  and  112   d  are sized and configured in the same manner as recess  112   b . When tab  98  is located in one of recess  110   b ,  110   c  or  110   d  tab  96  is located in the corresponding recess  112   b ,  112   c  or  112   d  (shown in dashed line position in  FIG. 2 ). Because recess  112   b ,  112   c  or  112   d  is wider than tab  96 , tab  96  sits at the back of the recess with a gap G between the tab  96  and the front of the recess. The length of the gap G is slightly longer than the axial distance the housing portion  2  must move relative to housing portion  4  to disengage the overlapping locking mechanisms  37  and  39 . 
     To move the carrier  70  and adjust its position in the housing  6 , the user pushes down on button  100  to depress the latch  94  and force tab  96  out of recess  110   a ,  110   b ,  110   c  or  110   d  and tab  98  out of recess  112   a ,  112   b ,  112   c  or  112   d . Once the tabs are removed from the recesses, and while the button  100  is depressed, the user can push on the button  100  to adjust the position of the carrier  70  in the housing  6  and the length of blade extending from the housing  6 . The carrier  70  can move the tabs  96 ,  98  from forward most recesses  110   a  and  112   a  where the blade is fully extended to rearward most recesses  110   d  and  112   d  where the blade is fully retracted. At least one pair of intermediate recesses is provided  110   b ,  112   b  and  110   c ,  112   c  where the blade is extended but is in less than the fully extended position. 
     When the carrier  70  is in the fully extended position tab  98  is closely received in recess  110   a  and tab  96  is closely received in recess  112   a . Because tab  96  is closely received in recess  112   a  carrier  70  is prevented from moving relative to the housing portion  2 . Likewise, because tab  98  is closely received in recess  110   a  carrier  70  is also prevented from moving relative to the housing portion  4 . Because carrier  70  is fixed relative to both housing portion  4  and housing portion  2 , housing portion  2  is fixed relative to housing portion  4 . Thus, when the carrier  70  is in the fully extended position, the housing portion  2  cannot move axially relative to housing portion  4 . As a result, the overlapping locking mechanisms  37  and  39  cannot be disengaged and the housing portions  2  and  4  cannot be separated from one another. Thus, when the blade is in the fully extended position, the housing  6  cannot be inadvertently opened even if button  56  is depressed. 
     When the carrier  70  is in any position except the fully extended position the housing  6  can be opened. For purposes of explanation assumed that the carrier  70  is moved to the first retracted position where tab  98  engages recess  110   b  and tab  96  engages recess  112   b . In this position, the position of the blade carrier  70  is fixed relative to housing portion  4  because tab  98  is closely received in recess  110   b  such that movement of the carrier  70  relative to the housing  6  is prevented. However, as previously explained, recess  112   b  is wider than the tab  96 . As a result, the gap G, provided between tab  96  and the front of recess  112   b , allows the housing portion  2  to slide rearward relative to housing portion  4  in the axial direction A far enough to disengage the overlapping locking mechanisms  37  and  39 . While the gap G allows the housing portion  2  to slide rearward relative to housing portion  4 , the housing portions cannot move relative to one another unless the push button  56  is depressed and the locking member  48  is disengaged from the strike plate  50 . This embodiment provides the safety when the blade is in the fully extended position and allows the device to be opened when the blade is in any other position. The recesses may be configured such that the safety action is provided in other than or in addition to the fully extended position if desired. 
     An alternate embodiment of the knife is shown in  FIG. 16  where like reference numerals are used to identify like components previously described with respect to  FIGS. 1 through 10 . The knife shown in  FIG. 16  is the same as that previously described except that the housing  6  may only be opened if the blade carrier is in the fully retracted position. Housing portion  2  includes a plurality of recesses  112   a ,  112   b ,  112   c  and  112   d  that extend along the length of the housing portion  2  and are located along side of the latch  94  and are positioned opposite to recesses  110   a ,  110   b ,  110   c  and  110   d  formed in housing portion  4 , respectively. The recesses  110   a ,  110   b ,  110   c  and  110   d  are dimensioned such that the tab  98  is closely received in any one of the recesses. The recesses  112   a ,  112   b  and  112   c  are also dimensioned like the recesses formed on housing portion  4  where the tab  96  is closely received by the walls of the recesses such that engagement of the tab  96  with the walls of the recesses  112   a ,  112   b  and  112   c  prevents relative movement between the housing portion  2  and carrier  70 . The last recess  112   d  (the fully retracted position) has a width that is greater than the width of the tab  96 . When tab  98  is located in  110   d , tab  96  is located in the corresponding recess  112   d  as shown in dashed line. Because recess  112   d  is wider than tab  96 , tab  96  sits at the back of the recess with a gap G between the tab  96  and the front of the recess such that the housing portion  2  can be slid rearward relative to housing portion  4 , as previously described as previously described with reference to  FIG. 2 . When the carrier  70  is in any position except the fully retracted position, tab  96  is closely received in recesses  112   a ,  112   b  and  112   c  and the housing portion  2  cannot move axially relative to housing portion  4  such that the overlapping locking mechanisms  37  and  39  cannot be disengaged and the housing portions  2  and  4  cannot be separated from one another. Thus, when the carrier  70  is in any position except the fully retracted position, the housing  6  cannot be opened even if button  56  is depressed. 
     A blade holder  120  is also provided in the housing. The blade holder  120  comprises a wireform clamp  124  having one end  124   a  secured to housing portion  4  such as by a screw and a second free end  124   b . The wireform is bent such that the free end  124   b  acts as a spring clamp to hold the blades. The wireform is slightly deformed when a blade or blades are located behind the wireform such that a clamping force is created on the blades to hold the blades in position. A platform may be provided against which that blades may be pressed by the wireform clamp. In the present embodiment the platform comprises a pair of supports  126  spaced such that the blades span the supports. Each support has a first end and a second end where the second end is disposed further away from the housing portion than the first end such that the blades are supported at an angle in the housing with the top ends of the blade projecting away from the housing. By angling the support surfaces  126  relative to the housing portion a space is provided between the top of the blades and the housing that allows the user&#39;s fingers to get behind the blades. The blades may be removed by grasping the top edge of the blades and slightly deforming the wireform  124  to release the blades. 
     Operation of the utility knife of the invention will be described with reference to the figures. Assume that the knife is in the assembled “use” configuration with the first housing portion  2  and the second housing portion  4  coupled together as shown in  FIGS. 1 and 2 . In this position edges  10  and  12  abut one another at seam S and the overlapping locking mechanisms  37  and  39  are engaged to prevent the housings  2  and  4  from separating. The locking member  48  is biased to the locked position where the locking member  48  is in blocking engagement with the strike plate  50  such that the housing portion  2  cannot move axially relative to housing portion  4  in the direction A. The locking member  48  is also biased into engagement with the distal end  62   a  of post  62  such that the locking member  48  biases push button  56  to the extended position. 
     The actuator button  100  can be depressed by a user to disengage the tabs  96  and  98  from the recesses and the blade carrier  70  moved along rail  72  to extend or retract the blade from the housing  6 . When the push button is depressed the tab  96  is forced out of recess  112   a ,  112   b ,  112   c  or  112   d  and tab  98  is forced out of recess  110   a ,  110   b ,  110   c  or  110   d . The button  100  can then be pushed forward or backward in the slot  102  to retract or extend the blade. When the button  100  is released the latch  94  resiliently returns to its undeflected position where tab  96  is enters one of recesses  112   a ,  112   b ,  112   c  or  112   d  and tab  98  is engaged with one of recesses  110   a ,  110   b ,  110   c  or  110   d.    
     Referring to  FIG. 14 , to open the housing  6 , the carrier  70  is moved to a non-safety position (block  1401 ). In the illustrated embodiment the carrier  70  may be moved to any position except for the fully extended position. The push button  56  is depressed forcing the end of post  62  against locking member  48  to move the free end  48   b  of locking member  48  away from and out of blocking engagement with the strike plate  50  (block  1402 ). While holding the button  56  in the depressed position, the user slides housing portion  2  rear ward relative to housing portion  4  (block  1403 ). The housing portion  2  is slid in the axial direction of arrow A toward the rear of the housing  6  as shown in  FIG. 4 . As the housing portion  2  is slid rearward, pivot pin  20  moves in slot  22  and the strike plate  50  rides over the locking member  48 . Simultaneously, the overlapping engagement mechanisms  37  and  39  are moved from the engaging positions shown in  FIGS. 1 and 2  to the non-engaged positions shown in  FIG. 4  (block  1404 ). When the user releases the housing portion  2 , the locking member  48  returns to its undeformed state forcing the housing portion  2  away from the housing portion  4  to the position shown in  FIGS. 3 ,  5 ,  6  and  7  (block  1405 ). The housing portions  2  and  4  can be completely separated from one another by rotating the housing portions  2  and  4  away from one another to the position of  FIGS. 8 and 9  (block  1406 ). The user can access the replacement blades to remove, replace and/or reposition the blade. 
     Referring to  FIG. 15 , the housing  6  may be reassembled by rotating the housing portions  2  and  4  back toward one another until they are in the position shown in  FIG. 5  where locking mechanism  48  is engaged by strike plate  50  (block  1501 ). The housing portions  2  and  4  are pushed toward one another until surface  10  abuts surface  12  and locking member  48  is pushed to the deformed position by strike plate  50  as shown in  FIG. 4  (block  1502 ). Housing portion  2  is slid forward in the axial direction relative to housing portion  4  until the housing portions are coextensive and overlapping locking mechanisms  37  and  39  are engaged as shown in  FIGS. 1 and 2  (block  1503 ). As housing portion  2  moves axially relative to housing portion  4  and approaches the fully closed position, strike plate  50  clears the end  48   b  of locking member  48  allowing locking member  48  to return to the locked position where is positioned behind and in blocking engagement with strike plate  50  (block  1504 ). When the strike plate  50  clears the end of locking member  48  and locking member  48  returns to its extended position, locking member  48  engages post  62  to bias button  56  to the extended locked position (block  1505 ). 
     Specific embodiments of an invention are disclosed herein. One of ordinary skill in the art will recognize that the invention has other applications in other environments. Many embodiments are possible. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described above.