Abstract:
A utility knife having a quick release feature, whereby a resilient blade engaging member biased to the locked position engages an opening in the blade, and when the blade engaging member is pushed against the end of a guide slot it automatically releases from the blade allowing the blade to be removed from the knife handle. The knife handle structure reinforces the throat of the knife, by providing a double channel configuration comprising an outer channel with a blade retaining surface and an inner channel inverted relative to the outer channel and providing a blade supporting surface. The outer channel is tapered toward the inner channel about the throat of the knife, to reinforce the throat and prevent deformation under the stresses imparted by the knife blade when in use.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to knives. In particular, this invention relates to a retractable utility knife with improved blade support and blade replacement features.  
         BACKGROUND OF THE INVENTION  
         [0002]    Utility knives are used in a variety of commercial and domestic applications, including construction, household repairs, arts and crafts and many others. Utility knives provide the advantage of being extremely sharp, and are typically loaded with a blade which is scored into segments, so that as the tip of the blade becomes dull the end segment can be broken off and the user can continue using the knife by exposing the next successive segment, which is still sharp.  
           [0003]    However, utility knives present a number of disadvantages, particularly in heavy duty applications such as construction. Eventually, when the last segment has been broken off of the blade, the blade must be replaced. Conventionally, this requires removing the sliding body which retains the blade in the knife handle, attaching a new blade, and replacing the sliding body into the knife handle. This can be a difficult operation to perform without a surface to rest the knife on (for example while on a ladder), and increases opportunities for injury because of the manipulation required in order to hold the blade on the sliding body while inserting it into the knife handle.  
           [0004]    Moreover, in heavy duty applications there is a considerable amount of force experienced by the blade, for example when cutting wallboard and other surfacing materials, which tends to deflect the blade laterally. The primary resistance to deflection of the blade within the handle is provided by the throat of the handle, which conventionally provides a single layer of supporting surface (generally metallic) on each side of the blade. Accordingly, over time the cutting force on the blade tends to widen the throat of the knife handle, which in turn allows the blade to deflect more when in use. This results in inaccurate cuts and the blade segments breaking off prematurely.  
           [0005]    It would accordingly be advantageous to provide a utility knife with a quick release feature which allows the blade to be changed without removing the sliding body from the knife handle and with minimal manipulation. It would further be advantageous to provide a knife structure which reinforces the throat of the knife, thereby reducing deflection of the blade during use and thus minimizing opportunities for inaccurate cuts and premature breakage of the blade.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a utility knife having a quick release feature, whereby forcing the sliding body toward the throat of the knife handle releases the blade, so that a new blade can be inserted easily and without removing the sliding body from the knife handle.  
           [0007]    The invention accomplishes this by providing a resilient blade engaging member, biased to the locked position, which engages an opening in the blade in normal use. When the blade engaging member is pushed against the end of the guide slot in which the sliding body travels, it automatically releases from the blade allowing the blade to be removed from the knife handle and a new blade positioned and engaged therein.  
           [0008]    The present invention further provides a knife handle structure which reinforces the throat of the knife, to better restrain the knife blade against deflection and thus to prolong the life of the knife blade and facilitate the accuracy of cutting with the knife.  
           [0009]    The invention accomplishes this by providing a knife handle having a double channel configuration, comprising an outer channel providing a blade retaining surface and an inner channel inverted relative to the outer channel and providing a supporting surface for the blade. In the preferred embodiment the outer channel is tapered toward the inner channel about the throat of the knife, to reinforce the throat and prevent deformation under the stresses imparted by the knife blade when in use.  
           [0010]    The present invention thus provides a knife, comprising a handle, comprising an outer channel having a back surface, side surfaces and retaining flanges depending inwardly from the side surfaces, an inner channel comprising blade supporting surface and sides, the sides abutting the side surfaces of the outer channel and the blade supporting surface being spaced from the retaining flanges for slidably receiving a blade therebetween, and a sliding body for engaging the blade trapped between the retaining flanges and the blade supporting surface, the sliding body having a locking member for locking a position of the sliding body within the handle.  
           [0011]    In further aspects of the invention, the inner channel is disposed in inverted relation to the outer channel; a portion of the back surface of the outer channel tapers toward the blade supporting surface and abuts the blade supporting surface at a throat of the knife; the locking member comprises a locking bolt extending through the sliding body and through a guide slot in the blade supporting surface and into a nut trapped between the sides of the inner channel; the blade engaging member comprises a blade engaging member for engaging the blade to the sliding body, the blade engaging member comprising a body portion and a resilient blade engaging arm projecting from the body portion, the blade engaging arm having a blade engaging projection for extending through an opening in the blade, and a cam finger extending through the guide slot disposed between the blade engaging projection and an end of the guide slot adjacent to a throat of the knife, whereby when the sliding body is moved so that the blade engaging finger is pressed against the end of the guide slot the blade engaging projection recedes from the opening in the blade to disengage the blade from the sliding body; the back surface of the outer channel comprises an opening through which the cam finger extends when the blade engaging projection recedes from the opening in the blade; and/or a pocket clip is affixed to an opening in the blade supporting surface and covers an end of the handle opposite the throat of the knife.  
           [0012]    The present invention in a further embodiment provides a knife, comprising a handle, comprising an outer channel having a back surface, side surfaces and retaining flanges depending inwardly from the side surfaces, a blade supporting surface having a guide slot, spaced from the retaining flanges for slidably receiving a blade therebetween, and a sliding body trapped between the retaining flanges and the blade supporting surface, the sliding body having a locking member disposed through the guide slot for locking a position of the sliding body within the handle, and comprising a blade engaging member for engaging the blade to the sliding body, the blade engaging member comprising a body portion, and a resilient blade engaging arm projecting from the body portion, the blade engaging arm having a blade engaging projection for extending through an opening in the blade, and a cam finger extending through the guide slot, disposed between the blade engaging projection and an end of the guide slot adjacent to a throat of the knife, whereby when the sliding body is moved so that the blade engaging finger is pressed against the end of the guide slot, the blade engaging projection recedes from the opening in the blade to disengage the blade from the sliding body.  
           [0013]    In further aspects of the further embodiment of the invention, a portion of the back surface of the outer channel tapers toward the blade supporting surface and abuts the blade supporting surface at a throat of the knife; the back surface of the outer channel comprises an opening through which the cam finger extends when the blade engaging projection recedes from the opening in the blade; the blade supporting surface is part of an inner channel is disposed in the outer channel; the inner channel is disposed in inverted relation to the outer channel; the locking member comprises a locking bolt extending through the sliding body and through a guide slot in the blade supporting surface and into a nut trapped between the sides of the inner channel; and/or a pocket clip is affixed to an opening in the blade supporting surface and covers an end of the handle opposite the throat of the knife. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    In drawings which illustrate by way of example only a preferred embodiment of the invention,  
         [0015]    [0015]FIG. 1 is a perspective view showing the utility knife according to the invention in a partially opened condition;  
         [0016]    [0016]FIG. 2 is a front elevational view of the utility knife of FIG. 1;  
         [0017]    [0017]FIG. 3 is a rear elevation of the handle in the utility knife of FIG. 1;  
         [0018]    [0018]FIG. 4 is a cross sectional side elevation of the utility knife of FIG. 1;  
         [0019]    [0019]FIG. 5 is an enlarged partial cross section of the utility knife of FIG. 1 showing the sliding body position for release of the blade;  
         [0020]    [0020]FIG. 6 is an enlarged partial cross section of the utility knife of FIG. 1 showing the blade engaging member in a release position;  
         [0021]    [0021]FIG. 7 is a plan view of the blade engaging member; and  
         [0022]    [0022]FIG. 8 is an elevational view of the blade engaging member. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    [0023]FIG. 1 illustrates a preferred embodiment of the utility knife  10  according to the invention. The utility knife comprises a handle  20 , a blade support  30 , a sliding body  40  for retaining the blade  2  and locking the blade  2  at a desired position within the handle  20 , and a locking element  50  which engages the blade  2  to the sliding body  40 .  
         [0024]    In the preferred embodiment, the handle  20  comprises an outer channel  22  having a back face  24 , side faces  26  and inwardly depending flanges  28  which retain the blade  2  in the handle  20  and conceal the cutting edge  2   a  and spine  2   b  of the blade  2  when the blade  2  is retracted into the handle  20 .  
         [0025]    Disposed within the outer channel  22  is a blade support surface  30 , spaced from the retaining flanges  28  with sufficient clearance to allow the blade  2  and blade engaging member  50  (described below) to slide freely within the space defined between the retaining flanges  28  and the blade support surface  30 , while providing substantial support for the blade  2  against lateral shimmying and deflection while in use. In the preferred embodiment the blade support surface  30  is formed by an inner channel  32  having a front face  34  and sides  36  which can be welded, soldered or otherwise suitably affixed to the outer channel  22 . The blade supporting surface  30  further comprises a guide slot  38  defining a path of travel for the sliding body  40 , and optionally an opening  39  for receiving a pocket clip  70  (omitted from FIG. 1 for clarity, shown in FIG. 4).  
         [0026]    The sliding body  40  comprises a blade engaging member  50 , described below, and a locking member comprising a locking bolt  42  having a rotary knob  42   a  and stem  42   b  (seen in FIGS.  4  to  6 ) extending through the guide slot  38  into a nut  44  trapped within the sides  36  of the inner channel  32  or otherwise suitably trapped within the outer channel  22  to prevent rotation of the nut  44 . The stem  42   b  of the locking bolt  42  extends through the body  52  of the blade engaging member  50 , through the guide slot  38  and into the nut  44 , to restrict movement of the sliding body  40  to within the limits of the guide slot  38 .  
         [0027]    The blade  2  is engaged to the sliding body  40  by the blade engaging member  50 , illustrated in FIGS. 7 and 8. A body portion  52  is provided with an opening  54  through which the stem  42   b  of the locking bolt  42  extends. Preferably spring flanges  56  are provided on either side of the opening  54 , splayed slightly away from the body  52  so as to push against a hub  42   c  of the rotary knob  42   a  and thus force the body portion  52  against the blade supporting surface  30 , to prevent the sliding body  40  from shimmying within the handle  20 . The body portion  52  is formed wide enough to be trapped between the flanges  28  and the blade supporting surface  30 , and is preferably approximately the same thickness as the blade  2 .  
         [0028]    A locking arm  60  which fits through the slot  38  extends forwardly of the body portion  52 , and provides an engaging projection  62 , for example in the form of a loop. The engaging projection  62  projects in the direction of the blade  2 , and projects beyond the body portion  52  to bias the blade engaging member  50  to the locked position in which the engaging portion  62  extends through an opening  4  in the knife  2 . The engaging projection  62  also preferably extends from the arm  60  in a direction away from the throat  80  of the knife  10 , so as to resist a longitudinal force pulling the blade  2  out of the handle  20 . The engaging portion  62  terminates in a cam finger  64 , for releasing the blade  2  in the manner described below. Preferably the entire blade engaging member  50  is stamped as an integral piece from spring steel, or another suitable resilient material  
         [0029]    The throat  80  of the utility knife  10 , best seen in FIG. 2, comprises the inwardly depending blade retaining flanges  28  of the outer channel  20 , the blade supporting surface  30  and a tapered portion  24   a  of the rear surface  24  of the outer channel  20 , which tapers toward the throat  80  and abuts the blade supporting surface  30 , as at  82 . This provides additional reinforcement to the front face  34  of the inner channel  32  along the portion which experiences the most lateral stress when the knife  10  is in use, and thus resists widening of the throat  80  (i.e. deformation of the blade supporting surface  30  which increases its spacing from the blade retaining flanges  28 ), which tends to lower the useful life of the blade  2  by causing premature breakage, and reduces the accuracy of cutting. The tapered portion  24   a  of the outer channel provides an opening  24   b  through which the locking arm  60  and cam surface  64  project when the blade engaging member  50  is in the unlocked position shown in FIG. 6, as described below. The front face  34  of the inner channel  32  may extend beyond the throat  80  to provide additional support against deflection of the blade  2 , and to provide an edge which facilitates breaking off of dull the blade segments.  
         [0030]    In a storage condition, the sliding body  40  is locked at a position where the blade  2  is retracted into the handle  20 . To use the utility knife  10  the user grasps the rotary knob  42   a  and turns it to loosen the bolt  42  and release the sliding body  40 , and slides the sliding body  40  toward the throat  80 . Edge  58  of the blade engaging member  50  pushes against the concealed end of the blade  2 , to force the blade  2  out of the handle  20  and expose the end segment of the blade  2 . The user rotates the rotary knob  42   a  in the other direction to tighten the bolt  42  and lock the sliding body  40 , and can then use the knife  10  with the blade  2  locked in position. The reinforcing strength provided by the tapered portion  24   a  of the outer channel  22  against the blade supporting surface  30  at the throat  80  of the knife  10  helps to maintain the blade  2  secure against shimmying and lateral deflection while the knife  10  is in use.  
         [0031]    As the outer segment of blade  2  dulls, the user can break off the dull segment, unlock the sliding body  40  and further extend the blade  2  to expose the next segment of blade  2 , which has been protected by the handle  20  and is thus still sharp. When the last segment of the blade is dull, the user must replace the blade  2 . The user rotates the rotary knob  42   a  to loosen the bolt  42  and forces the sliding body  40  toward the throat  80 . As can be seen in FIG. 5, as the sliding body  40  approaches the end of the slot  38 , the cam finger  64  engages the end of the slot  38 . As the sliding body  40  is moved closer to the throat  80 , cam finger  64  draws locking arm  60  inwardly until engaging projection  62  has receded from the hole  4  in the blade  2 , as shown in FIG. 6. At this point, the blade  2  is disengaged from the sliding body  40  and can be removed from the handle  20 . A new blade  2  is inserted in its place, lining up the opening  4  over the engaging projection  62 . By pushing the blade  2  into the handle  20 , the sliding body  40  is forced away from the throat  80  and as the cam finger  64  slides up the end of the slot  38  the resilient locking arm  60  returns to the engaging position in which the projection  62  extends through the opening  4  of the blade  2 . At the point shown in FIG. 5, the new blade  2  is locked to the sliding body  40  and can be retracted into the handle  20  for use or storage.  
         [0032]    Advantageously, the engaging projection  62  is angled away from the throat  80  (i.e. toward the sliding body  40 ), so that a longitudinal force pulling the blade  2  away out of the knife  10  actually draws the engaging projection  62  further through the hole  4 , as the blade is pulled into the inflection portion  63 , to prevent dislodgement of the blade  2 .  
         [0033]    Various embodiments of the present invention having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention. The invention includes all such variations and modifications as fall within the scope of the appended claims.