Abstract:
A utility knife includes an elongaged handle having an internal cavity, two opposing ends and a side having at least one locking opening. A shuttle is sized to slide within the cavity and has a side surface. The shuttle has a spring-loaded locking button projecting from the side surface and into the handle. The button is sized and shaped to selectively project into the at least one locking opening. The shuttle is bonded to a conventionally shaped utility knife blade of the type which includes two opposing cutting regions. The shuttle can slide within the handle between the two opposing ends so that both cutting regions of the blade can be easily used as necessary. This utility knife is meant to be lost cost and disposable, but offers the user TWO cutting edges, doubling its effective use.

Description:
CLAIM FOR PRIORITY 
     Applicant hereby claims priority to US provisional patent application entitled “Utility Knife”, Ser. No. 61/279,076, filed Oct. 14, 2009, the entire application of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention generally relates to cutting devices of the type commonly referred to as utility knives and more particularly, to improvements to such knives. 
     2) Discussion of Related Art 
     So-called utility knives have been around for several decades. Each are usually simple in construction usually including a handle, a slidable blade holder and a trapezoidal blade. The trapezoidal blade is conventional and includes a long sharpened edge and two sides that form an acute angle with respect to the sharpened edge and a top edge that includes locking notches. This blade fits snugly within the blade holder and the blade holder fits within the handle. The conventional handle is usually made up of two halves that may lock together and further includes a slot through which a portion of the blade holder may pass (in the form of a finger purchase) and provide access to the user so that the user may selectively slide the blade holder as desired within a restricted range of displacement. The blade may selectively be displaced between a fully retracted position wherein the blade is safely positioned within the housing and a fully extended position wherein one side of the trapezoidal blade protrudes from the handle so that useful cutting work may be performed. 
     Although the blades of such conventional utility knives can be replaced as required, there is a growing demand to provide simple, safe and easy to use disposable utility knives that can be used and then thrown away when the blade becomes dull. In some cases, these disposable utility knives may require automatically activated covers or shields that move to cover and protect the otherwise exposed sharpened edge when the blade is not being used to cut, yet remains on “standby” with the blade protruding from the handle. 
     It is a first object of the invention to overcome the deficiencies of the prior art. 
     It is another object of the invention to provide a useful, low cost disposable utility knife that is made up of few parts. 
     It is another object of the invention to provide a low cost disposable utility knife that is made up of few parts and includes an integral automatically activated safety cover that covers the sharpened edge of the exposed blade when the blade is not in use. 
     It is yet another object of the invention to provide a utility knife that is easy to use and that uses both sides of the conventional utility blade without opening the handle assembly. 
     SUMMARY OF THE INVENTION 
     A utility knife includes an elongaged handle having an internal cavity, two opposing ends and a side having at least one locking opening. A shuttle is sized to slide within the cavity and has a side surface. The shuttle has a spring-loaded locking button projecting from the side surface and into the handle. The button is sized and shaped to selectively project into the at least one locking opening. The shuttle is bonded to a conventionally shaped utility knife blade of the type which includes two opposing cutting regions. The shuttle can slide within the handle between the two opposing ends so that both cutting regions of the blade can be easily used as necessary. This utility knife is meant to be lost cost and disposable, but offers the user TWO cutting edges, doubling its effective use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a utility knife, according to the present invention including a handle having locking openings, a shuttle and a blade; 
         FIG. 2  is a perspective assembly view of the knife of  FIG. 1 , including the blade, the shuttle, and the handle having two halves, according to the invention; 
         FIG. 3  is a perspective assembly view of the knife of  FIG. 1 , including the blade secured within the shuttle and the shuttle positioned within one half of the handle, according to the invention; 
         FIG. 4  is a front perspective view of the shuttle showing the blade secured therein and also showing a spring-biased locking button located in a rest position, and a finger-gripping pad, according to the invention; 
         FIG. 5  is a front perspective view of the shuttle shown without a blade and having the spring-biased locking button located in a fully depressed position, according to the invention; 
         FIG. 6  is a rear perspective view of the shuttle shown without a blade, according to the invention; 
         FIG. 7  is a partial sectional view of the knife of  FIG. 8  showing details of the locking tab, according to the invention; 
         FIG. 8  is a side view of the knife according to the invention showing the shuttle and blade locked in a “Box” cutting position; 
         FIG. 9  is a side view of the knife according to the invention showing the shuttle and blade locked in a “SAFE” position; 
         FIG. 10  is a side view of the knife according to the invention showing the shuttle and blade locked in a “Full” position exposing the blade on the opposing side of the handle; 
         FIG. 11  is a perspective partial view of a knife according to a second embodiment of the invention including a handle, a blade, and a shuttle including a blade guard; 
         FIG. 12  is a perspective view of the shuttle of  FIG. 11  showing details of the blade guard, according to the second embodiment of the invention; 
         FIG. 13  is a perspective view of one handle half showing the shuttle and blade in position within the handle, according to the second embodiment of the invention; 
         FIG. 14  is a perspective view of the shuttle with a blade secured thereto, according to the second embodiment of the invention; 
         FIG. 15  is a perspective partial view of a knife according to a third embodiment including a handle, a shuttle having an integrally formed guard and a blade wherein the guard is shown in BOTH the guarded position AND the exposed position, according to the third embodiment of the invention; 
         FIG. 16  is a shaded view of  FIG. 15 , according to the third embodiment of the invention; 
         FIGS. 17 and 18  are both perspective views of the knife of  FIGS. 15 and 16 , showing how the guard remains outside the handle, according to the third embodiment of the invention; 
         FIG. 19  is a perspective view of a knife according to a fourth embodiment of the invention, showing a handle assembly having a gripping bulge, two handle halves and a lock-release button; 
         FIG. 20  is a perspective assembly view of the knife of  FIG. 19 , showing a shuttle, a blade, and a blade cover, according to the fourth embodiment of the invention; 
         FIG. 21  is an opposing perspective view of  FIG. 20 ; 
         FIG. 22  is a perspective view of a shuttle blade assembly, according to the fourth embodiment of the invention, showing details of how the blade and blade cover are secured to the shuttle; 
         FIG. 23  is an opposing perspective view of  FIG. 22 ; 
         FIG. 24  is a perspective view of the shuttle, according to the fourth embodiment of the invention; 
         FIG. 25  is an opposing perspective view of  FIG. 24 ; 
         FIG. 26  is a cross-sectional view of the shuttle assembly of this fourth embodiment, showing details of how the blade cover locks to the split posts of the shuttle (blade is not shown) and showing details of a locking arm and engagement tab; 
         FIG. 27  is a plan view of the knife, according to the fourth embodiment of the invention without one handle half so that the shuttle can be viewed in the center “safe mode” position; 
         FIG. 28  is the same view of  FIG. 27 , showing the shuttle (and blade) in a full RIGHT position so that a portion of the blade projects from the handle; 
         FIG. 29  is the same view of  FIG. 27 , showing the shuttle (and blade) in a full LEFT position so that a portion of the blade projects from the handle; 
         FIG. 30  is a sectional view of the knife of  FIG. 19 , according to this fourth embodiment with the shuttle and blade in the central safe mode location, showing details of the two locking features of the invention; and 
         FIG. 31  is a plan side view of the knife according to the fourth embodiment showing details of the gripping bulge. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a knife  10  according to the invention is shown having a handle assembly  12  including a locking handle half  13  and a cover handle half  14 , a shuttle  16  and a blade  18 . The construction of this present knife  10  is very simple with few parts and is meant to be disposable by the user, but of course may be made so that blade  18  can be accessed by the user and replaced with a new blade, as can be appreciated and understood by one of ordinary skill in the art. However, according to the preferred embodiment of this invention, blade  18  is permanently bonded to shuttle  16  and cannot be removed from between handle halves  12 ,  14  once secured therein, as described below. 
     As shown in  FIGS. 3 and 4 , shuttle  16  includes a grip plate  20  and two opposing bonding plates  22  and  24  which define a blade channel  26  therebetween. Blade channel  26  is sized to snugly accommodate blade  18  so that blade  18  may be positioned within blade channel  26  during assembly and bonded therein using an appropriate adhesive and/or heat (using an ultra-sonic welding process, for example) and/or a mechanical fastener, such as a rivet or screws. Blade  18  may include appropriate openings (not shown) for assisting in the bonding process to receive fasteners, adhesive, or plastic, as is well known to those of ordinary skill in the art. Regardless how it is secured, blade  18 , according to the preferred embodiment of this invention, is firmly bonded to shuttle  16  during manufacture and cannot be removed during normal use of knife  10 . 
     Bonding plate  22  includes a slot  28  that defines a flexible platform  30  which is pivotally connected to plate  22  by an attached portion  32 , about a hinge axis  34 , as shown in  FIG. 4 . As is understood by those skilled in the art, the flexible characteristics of flexible platform  30  is controlled by the material used to make shuttle  16 , the shape and size of slot  28  and the thickness, shape and area of the attached portion  32  of platform  30 . 
     As shown in  FIGS. 4 and 5 , a locking button  36  is integrally formed to flexible platform  30  so that button  36  may pivotally displace about hinge axis  34  from a rest position shown in  FIG. 4  and a fully depressed position shown in  FIG. 5 . As described below, as button  36  is depressed, it will pivot against the inherent spring bias of the attached portion  32  in such a manner that will cause button  36  to automatically return to rest position, shown in  FIG. 4 . 
     As shown in  FIG. 2  and according to this preferred embodiment of the invention, blade  18  is made with a large opening  38  generally centrally located. This opening is sized and shaped to accommodate displacement of flexible platform  30  and button  36  when it moves from the rest position to the fully depressed position. Button  36  is preferably made pretty large so that the user may easily depress the button during use of the knife, as described below, however, button  36  may be any size and any shape depending on the design particulars of the knife to which the present invention is applied. 
     Referring to  FIGS. 5 and 6 , shuttle  16  further includes guide rails  40  which are parallel and spaced from grip plate  20  a predetermined distance. As shown in  FIG. 1 , grip plate  20  is positioned above and outside handle assembly  12  and may slide along handle assembly  12  within a slot  42  so that shuttle  16  and blade  18  may be displaced along the full length of knife  10 . The linear displacement of shuttle  16 , grip plate  20  and blade  18  is restricted by the length of slot  42 . Guide rails  40  are spaced so that they reside and slide smoothly within handle assembly  12  along the underside of slot  42 . Guide rails  40  and grip plate  20  work together to ensure that shuttle  16  and the attached blade  18  move evenly and smoothly within handle assembly  12  along its length, as desired and controlled by the user. 
     Referring to  FIGS. 1 ,  2 ,  8 ,  9  and  10 , locking handle half  13  includes preferably five locking openings, a left “full” opening  48 , a left “box” opening  50 , a centrally located “safe” opening  52 , a right “box” opening  54 , and a right “full” opening  56 . The purpose of these openings  48 ,  50 ,  52 ,  54 , and  56  is to receive and hold button  36  when the button aligns with any one of the openings. Button  36  is shaped and sized to snugly fit within any one of the openings  48 - 56  when in its rest position so that once button enters within any one of openings  48 - 56 , it will remain there by spring-bias of flexible platform  30  until button  36  is depressed to its fully depressed position. 
     During manufacture, blade  18  is registered and positioned within blade channel  26  of shuttle  16  and bonded thereto during any appropriate process, as described above. Applicant contemplates blade  18  being co-molded or over-molded with shuttle  16  during an injection process known by those in the art so that blade  18  becomes bonded to shuttle  16  as shuttle  16  is made through injection molding. In this over-molding process, blade  18  is precisely positioned within an injection mold of shuttle  16  so that as an appropriate plastic is injected into the mold, the plastic will flow around and bond to the inserted metal blade. When the part is cooled and ejected, the metal blade would effectively be bonded to the plastic shuttle. 
     Regardless, once blade  18  and shuttle  16  are formed, shuttle  16  is then positioned within slot  42  of handle assembly  12  so that grip plate  20  is positioned outside handle assembly  12  and guide rails  42  is positioned just within handle assembly  12 , as shown in  FIG. 7 . Handle halves  13  and  14  are then bonded together using any appropriate method, such as ultra-sonic welding or an adhesive. Shuttle  16  can then slide within handle assembly  12  along the length of slot  42  until button  36  aligns with any one of openings  48 - 56  and enters therein by spring bias of flexible platform  30 . Once button  36  enters any one of openings  48 - 56 , its engagement will lock shuttle  16  in position and will prevent any linear displacement of shuttle  16  and attached blade  18 . Once the user depresses button  36  into handle assembly  12 , grip portion  20  may be used to slide shuttle  16  (with blade  18 ) to a different position within slot  42  along handle  12  until button  36  again “finds” another opening  48 - 56 .  FIG. 7  shows (in section) button  36  in a rest position and locked within left “box” opening  48 . Since openings  48 - 56  are positioned at different locations along handle assembly  12 , either side of blade  18  may protrude a prescribed distance from either respective end of handle  12  for useful cutting work. For example, a fully exposed blade  18  at the left side of knife  10  is shown in  FIG. 1 . This arrangement is useful for general cutting of materials such as sheetrock, paneling, or carpet and other applications where a long cutting edge is required.  FIG. 8  shows button  36  locked within left “box” opening  48  and left side of blade  36  shown exposed a shorter distance from handle  12  which is appropriate for cutting boxes. The user may slide shuttle  16  and blade  18  so that it resides in the middle of handle assembly  12  in a safe position so that no portion of the blade is exposed or accessible to the user (or anyone). This arrangement is shown in  FIG. 9 . 
     Finally,  FIG. 10  illustrates that the user may further displace shuttle  16  and blade  18  to the right so that the right side of blade  18  may be used on the opposing (right) side of handle assembly  12 . This allows the user to quickly and easily use both sides of a single blade  18 . 
     Referring now to  FIGS. 11 and 12 , knife  10  is shown including a shuttle  60  that includes an integral blade guard  62 , according to a second embodiment of the invention. The purpose of blade guard  62  is to provide temporary protection against a person contacting the sharpened edge of blade  18  and causing injury while blade  18  resides outside handle  12 . As shown in  FIG. 12 , blade guard  62  is preferably formed integral with shuttle  60  and is made from a strong but resilient plastic that retains memory. Guard  62  includes a slot  64  that is sized to receive blade  18 . As shown in  FIGS. 11 and 12  and  14 , guard  62  includes a closed end  66  that prevents guard  62  from moving across the sharpened edge. Closed end  66  can only move upwardly along blade  18  during use to expose the sharpened edge when knife  10  is being used. The tip of blade  18  will engage with closed end  66  of guard  62  and prevent any downward movement beyond the sharpened edge. 
     In use of this second embodiment, as the user slides shuttle  60  using the same method as in the above described first embodiment of the invention so that the blade extends to a fully exposed position, as shown in  FIG. 11 , the guard  62  moves with the blade so that the sharpened edge of the blade is always protected, always covered. That is until the user presses the blade into a cutting surface at which point the cutting surface will force the guard  62  away from the blade and allow the sharpened edge of the blade to penetrate the cutting surface. Once removed from cutting surface, the flexible guard will spring back to its covering position over the sharpened edge. 
     According to this second embodiment, blade guard  62  is sized and shaped to slide freely within handle assembly  12  following the linear movement of blade  18 , as shown in  FIG. 13 . Referring to  FIGS. 15 ,  16 ,  17  and  18 , a third embodiment of the invention is shown wherein a similar blade guard  70  to guard  62  is provided, again integrally formed with a shuttle  72 , however in this embodiment, guard  70  always resides outside the handle  12 , regardless of where the blade  18  is located. 
     As in the second embodiment, described above, this guard  70  includes a slot  74  for receiving blade  18  and also includes a closed end  76 .  FIGS. 15 and 16  illustrates how the closed end  76  can move upwardly against the spring bias of the resilient plastic guard and cannot move downwardly beyond the sharpened edge of the blade  18  because the tip of the blade will engage with the closed end and prevent further movement. This movement is illustrated by arrows  78  in the figures. According to this embodiment, the sharpened edge of blade  18  actually resides outside handle assembly  12  even when blade  18  is moved back into a “safe” position within the handle. Guard  70  is designed to move with blade  18  and protect the sharpened edge regardless of where the shuttle is located with respect to handle  12 . The guard is allowed to be displaced to expose the useful sharpened edge of the blade only when the blade is located in the extended position. When blade  18  is located within the handle  12  in the safe position, the guard abuts against the lower edge of handle  12  and is thereby forced into a fixed position tightly covering the sharpened edge of the blade. 
     Since the blade guard  70  of this embodiment is always exposed and always accessible to the user, the guard is used as a grip plate  80  which allows the user to use the guard to slide the shuttle  72  linearly with respect to the handle  12 . 
     As mentioned above, in each of the embodiments described, all parts are preferably made from an appropriate plastic, such as: PVC, Polypropylene, Nylon®, Delrin®, Zytel®, any of the class of phenolics, including Micarta®, reinforced composites, such as “epoxy G-10”, and other thermoplastics. The blade is preferably made from heat-treated steel, as understood by those skilled in the art. The plastic parts are preferably made using a high-pressure plastic injection molding process. Various sections of the plastic parts (e.g., the handle) may include a rubber overmold to provide a select cushioning and improved grip. 
     As shown in some of the figures, the openings  48 - 56  may include appropriate indicia, such as “FULL”, “BOX” and “SAFE”. 
     Also, although not shown, a spring or rubber band may be included within handle  12  to bias shuttle  16  to the safe position regardless of the direction the shuttle moves (left or right). 
     Also not shown is a tether for helping secure the blade to the user&#39;s wrist, if desired. 
     Also, cover handle half  14  is preferably without openings, but may include at least one opening that aligns with at least one of the openings  48 - 56  of locking handle half  13 . These aligned openings may be used to hang the knife up when not in use. 
     Referring to  FIGS. 19 through 32 , a fourth embodiment of knife  100  is shown including a handle assembly  101  having a “cover” handle half  102 , a “button” handle half  104 , a shuttle  106 , a blade cover  108 , and a razor blade  110 . This embodiment is similar to the previous three embodiments described above, but the overall shape of handle assembly  101  (combined handle halves) is generally arcuate with a gripping bulge  190 , as described below. Also, shuttle  106  which slides within handle assembly  101  includes integrally molded snap fasteners that allow a blade cover  108  to securely snap to the shuttle  106  and thereby hold a metal razor blade  110  therebetween. Another difference is that a locking release button  112  is integrally formed to button handle half  104  along a “living hinge” so that the button  112  can pivot slightly when depressed. The button  112  in this fourth embodiment remains in place within the handle assembly  101  whereas in the above described previous embodiments, button  36  is integrally molded to shuttle  16  so that it moves with the shuttle when shuttle  16  is slid within the handle. 
     In explaining this fourth embodiment of the invention in greater detail, first refer to  FIGS. 22-26  to show how razor blade  110  is secured to shuttle  106 . In earlier embodiments, the razor blade was preferably secured to the plastic shuttle assembly using an appropriate adhesive or bonded to the plastic directly using co-molded techniques during molding or ultrasonic welding after molding. As can be seen in  FIGS. 22-26 , razor blade  110  of this fourth embodiment can be a standard utility blade in size and shape and thickness, but instead of having two notches along the upper edge, it preferably includes three holes  114  cutout in a triangular pattern in its body with two holes located along the top edge and one centrally located near the sharpened bottom edge  116 . Holes  114  are sized, shaped and positioned to fit onto three split posts  118  that have been integrally molded on one side of shuttle  106 . 
     Once the blade is fitted to shuttle  106  so that each of the three split posts is located within one of the three holes  114  of blade  110 , blade cover  108  can then be positioned adjacent the blade, opposite the shuttle. As can be seen in  FIGS. 22 and 26 , blade cover  108  also includes three bores  120  that are sized and positioned to receive split posts  118  of shuttle  106 . Each bore  120  includes at least one integrally molded locking ramp  122  that is designed to automatically lock onto the projected structure of each split post  118  in a one-way snap locking arrangement that is well known to those skilled in the art. The gap  124  located along the central axis of each split post  118  allows the each post structure to deflect and lock onto each respective locking ramp  122  as the two are forced together. The spring resiliency of the plastic allows each post structure to return to the original shape and thereby “lock” onto the ramp structure. This locked position is illustrated in  FIG. 26  as a cross section view. 
     So, to lock blade  110  onto shuttle  106 , blade cover  108  is pressed firmly against blade and shuttle until each locking ramp  122  engages with each respective split post  118  of shuttle  106 . To help increase the lateral compression force (the squeeze force) by the shuttle and the blade cover against the interposed blade, applicant has included small ridges  126  located on the inside surface  128  of blade cover  108 , shown in  FIG. 23 . Ridges  126  are located along edges of blade cover  108  relatively remote from bores  120 . During assembly of the blade to the shuttle, ridges  126  will contact the surface of the blade before locking ramps can lock onto the respective split post structure. The center of blade cover must be forced into blade and shuttle so that blade cover deforms between ridges  126 . The deformation resembles a kind of inwardly cupping. This cupping allows each split post to lock into each respective bore. Once the compression force is released, the engagement to each of the three split posts  118  will keep blade cover  108  cup-shaped and the spring resiliency of blade cover  108  will continue to apply a strong compression force towards shuttle  106 —resulting in firmly holding the blade therebetween. 
     Referring to  FIGS. 24 and 25 , shuttle  106  is generally triangular in shape and further includes an integrally formed bridge structure  130  along its upper edge  132 . Bridge structure  130  defines an opening positioned along upper edge  132 . Owing to the plastic material, bridge structure is meant to have a resilient spring bias so it can be pressed downward against the spring bias. When released, the bridge preferably returns upwardly to its original rest shape and position. A sliding control button  134  is formed to bridge structure  130 , preferably at a central location. Button  134  includes a contact pad portion  136 , a neck  138  and a locking shoulder  140 . Locking shoulder  140  is larger than neck  138  but smaller than contact pad portion  136 . 
     Also located on shuttle  106  is a transverse locking arm  142  and an engagement tab  144 . As shown in  FIG. 25 , engagement tab  144  extends outward from shuttle  106 . Shuttle  106  also includes a slide  146  that is sized and shaped to slide along an upper surface  147  of a guide rail  148  formed in button handle half  104 . Shuttle  106  also includes a flat contact surface  150  located along the lower portion of the triangular shuttle. 
     As shown in  FIG. 22 , blade cover  108  includes an integrally formed slide  152  that is sized and shaped to slide along an upper surface  153  of a guide rail  154  formed within cover handle half  102 . Slides  146  and  152  are preferably formed so that they align with each other, although this is not necessary for the shuttle to operate effectively within handle assembly  101  in according with this embodiment of the invention. Blade cover  108  also includes a flat contact surface  156  located at a lower point of blade cover  108 . 
     As shown in  FIG. 27 , shuttle  106  (with blade  110  secured thereto by a blade cover, not shown in the figure) is shown positioned in a central locking position within cover handle half  102 . As mentioned above, cover handle half  102  includes a slightly curved guide rail  148 . Shuttle is sized and shaped so that an upper surface  158  of bridge structure  130  becomes in sliding contact with an upper wall surface  160  of handle  102  while slide  146  comes into sliding contact with upper surface  147  of guide rail  148 . Contact flat surface  156  is position so slide along an outside surface  162  of a lower guide ridge  164  of cover handle half  102 . As shown in  FIG. 21 , a locking cutout  149  is provided within guide rail  148 , preferably at a central location, aligned with button  112 . The purpose of this locking cutout  149  is described below in explaining the “lateral locking” feature. 
     When button handle half  104  is secured to cover handle half  102  as shown in  FIGS. 31 and 19 , slides  146 ,  152  engage respective upper surfaces  147 ,  153  of respective guide rails  148 ,  154  of respective handle halves  102 ,  104 . Meanwhile, upper surface  158  of bridge structure  130  comes into sliding contract with upper wall surface  160  of handle half  102  and upper wall surface  166  of handle half  104 . All these structural features and relationships allows shuttle  106 , blade cover  108  and blade  110  to slide (once unlocked) within the handle halves  102 ,  104 , as desired from a central position, shown in  FIG. 27  to a usable position to the RIGHT, shown in  FIG. 28 , wherein one section of the cutting edge of the razor blade  110  projects from the handle halves  102 ,  104 , AND to a usable position to the LEFT, shown in  FIG. 29 , wherein an opposing section of the cutting edge of the razor blade  110  projects from the handle halves  102 ,  104 . The preferred use of this knife is disposable wherein blade  110  cannot be replaced, nor can handle halves  102 ,  104  be separated to provide any meaningful access to within the knife structure. Therefore, an important feature of the present invention (all embodiments) is to provide the user with access to two cutting edges. This should extend the useful life of this knife by a factor of two. This can only benefit the user. 
     As described above, the shuttle and blade moves right to center to left to center to right again, as desired and follow a curved path. The curved handle shape provides a more comfortable orientation for the user during cutting because it allows the user to penetrate a cutting surface with an exposed blade without having to rotate the wrist downwardly as much as one would with a conventional straight knife. 
     Referring to  FIGS. 19 and 31 , when handle halves  102 ,  104  are secured to each other, using an appropriate adhesive, fasteners, or ultrasonic welding, a common slot  170  is defined along the upper outside surface  172 . Slot  170  is sized to receive neck  138 . Slot  170  preferably includes a widened cutout  174  located at least at each end of the slot. Widened cutout  174  is sized to accommodate locking shoulder  140 . The relative height of locking shoulder on top of bridge structure  130  is such that when bridge structure is at its rest position (not depressed downward), locking shoulder  140  is of sufficient height to engage with either widened cutout  174  if shuttle is positioned within the knife so that locking shoulder aligns with either widened cutout. When the locking shoulder  140  engages widened cutout  174 , shuttle  106  and blade  110  and blade cover  108  will not be able to move with respect to either handle half, i.e., it will be locked. This is very useful during cutting so the widened cutouts  174  are preferably positioned to lock shuttle  106 , blade cover  108  and blade  110  when they are in the usable position at either end (LEFT AND RIGHT). Additionally, a central widened cutout  176  is preferably provided along slot  170  so that shuttle, blade and blade cover can be safely locked deep within the handle, i.e., the middle of the knife. 
     The above described widened cutouts  174 ,  176  make up vertical locking for holding the shuttle at prescribed locations with respect to the handle. The above described button  112  located in the middle of button handle half  104  works with the locking arm  142  and engagement tab  144  to form a “lateral locking” feature for further locking shuttle and blade with respect to the handle halves. This lateral locking feature is described in greater detail below. 
     As shown in  FIG. 30 , button  112  of button handle half  104  includes a hinge member  180  that allows the button to pivot when pressed a predetermined amount. Positioned opposite the hinge member  180  on button  112  is a release member  182 . Release member is sized and shaped to contact and depress a portion of locking arm  142  sufficiently to displace engagement tab  144  from a locked position wherein it is located within locking cutout  149  of guide rail  148  to an unlocked position thereby laterally unlocking shuttle  106  from button handle half  104 . 
     Each handle half  102 ,  104  can include registration pins and sockets to help align and hold the two handles halves together. 
     As shuttle  106  moves within handle assembly  101 , it is strongly guided by guide rails  148 ,  154  and slides  146 ,  152  AND is also stabilized by flat contact surfaces  150 ,  156  of shuttle  106  and blade cover  108  to engage lower guide ridges  164  of both handle halves  102 ,  104 . 
     Also, it is to be understood that an appropriately sized and shaped opening is provided at each end of handle assembly  101  (matching cutouts  192  of each handle half,  102 ,  104 ) that will accommodate selective passage of blade  110  as shuttle  106  moves blade  110  to a fully extended cutting position. 
     In use, when the user first receives the present knife, according to this fourth embodiment, the user must depress button  112  located along the side of button handle half  104  AND simultaneously press down button  134  and slide shuttle to either the LEFT or the RIGHT. Upon pressing button  112 , release member  182  will come into contact with a portion of locking arm  142  of the adjacently located shuttle  106  and will eventually push arm  142  sufficiently so that engagement tab  144  displaces out of engagement with locking cutout  149  of guide rail  148 . The user holds the button in and as the user presses down on the button  134  against the spring bias of the bridge structure  130  sufficiently so that locking shoulder  140  displaces from engagement with the centrally located widened cutout  176 . When both these locks are released, the user may then slide the shuttle to the left or the right by pushing or pulling on the button  134  so that neck  138  slides along slot  170  of the handle halves  102 ,  104 . 
     Once unlocked, the shuttle will move into a “safe usable” position which is located between the fully LEFT or full RIGHT position AND the center position. In this position, the blade is not exposed, but the user may quickly and easily push button  112  to the full LEFT or RIGHT position until locking shoulder pops up into engagement with either widened cutout  174  by the spring bias of bridge structure  130 . Once locked, the shuttle will be stable and one side of the cutting edge of the blade will be exposed and the knife can be used to cut something. When finished with a cut, the user can simply push the button  112  down against the spring bias of the bridge structure  130  of the shuttle  106  until the locking shoulder  140  exits the widened cutout  174  and the shuttle  106  and blade  110  can then be slid back into the “safe usable” position within the knife so that the blade will no longer be exposed. A simple metal or plastic spring (not shown) can be included to force the shuttle to the “safe usable” position either automatically after the blade leaves the cutting surface, or when the user releases the button  112 . Regardless, friction of the engagement tab  144  sliding against the guide rail  148  AND the friction of the locking shoulder sliding along the inside surface of the combined knife handles  102 ,  104  will help prevent accidental movement of the shuttle when it is located between widened cutouts (in the safe usable position). 
     When the user slides button  134  so that shuttle  106  slides across the center of handle assembly  101 , engagement tab  144  (which is spring biased into contact with guide rail  148 ) by the flexed locking arm  142 , will eventually align and fall “into” engagement with locking cutout  149 . This action will effectively lock the shuttle and the blade into a very safe central location within the knife. As this happens, the locking shoulder  140  will align with and move up into engagement (by the spring bias of the bridge structure  130 ) with the central widened cutout  176 . When locked in this “safe mode”, no portion of the blade can be accessed. The user would have to follow the above steps to again release both locking mechanisms to again be able to move the shuttle side to side. 
     Of course, although TWO safe locking features are preferred here, the above described disposable knife can be provided with only the lateral locking mechanism or the vertical locking mechanism, or neither, depending on the particular intended application or marketing strategy of the knife. 
     Cover handle half  102  preferably includes a flat section  191  (see  FIG. 21 ) that will allow for advertisement or other information printed on the handle). 
     The handle thus described in this fourth embodiment and shown in  FIGS. 19-31  includes a central “bulge”  190  that allows the user to better grip the handle assembly  101 . As is understood by those skilled in the art, rubber overlay or other gripping material may be applied to any portion of the handle assembly  101  to increase the grip by the user. 
     The handle halves  102 ,  104  can be made from metal or plastic, but are preferably made from an appropriate strong plastic that can be injection molded.