Patent Publication Number: US-8978254-B1

Title: Exchange blade knife

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 12/968,042 filed on Dec. 14, 2010, which is incorporated herein by reference. 
     Application Ser. No. 12/968,042 was a continuation of U.S. application Ser. No. 11/895,906 filed on Aug. 28, 2007, now U.S. Pat. No. 7,900,363 which is incorporated herein by reference. 
     U.S. application Ser. No. 11/895,906 claimed the benefit of U.S. Provisional Patent Application No. 60/840,541 filed on Aug. 28, 2006 which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a knife having a blade that can be removed and replaced. 
     BACKGROUND 
     A knife of the finest quality and craftsmanship with a dull cutting edge is less useful than the cheapest knife having a sharp cutting edge. Yet, a significant amount of skill is needed to properly sharpen a knife. Professionals who use knives in their work, such as professional chefs, often invest the effort needed to learn the skill of knife sharpening and honing, and, they maintain that skill through frequent practice. This is usually not the case with the general public. Consequently, most knives in general use are not properly honed. It is often the case that a consumer buys an expensive, high quality knife and is initially impressed with its fine sharp cutting edge. Yet, after a few months of use, the formerly proud knife owner is disappointed with a knife which “can&#39;t seem to hold its edge”. The knife owner may try to sharpen the knife with a sharpening stone or the like. But more often that not, the knife owner cannot seem to regain that original “factory edge”. The knife owner may even give up and buy a new knife. What is needed is a knife that has a replaceable blade which in all important respects functions as typical knife 
     SUMMARY 
     The above stated need is met by a replacement blade knife which includes a handle, a blade holder mounted to the handle, a replaceable blade and a blade lock for fixing the replaceable blade to the blade holder. The replaceable blade includes an opening adjacent to its base edge. The blade holder includes a blade recess for receiving the replaceable blade and a boss corresponding to the opening in the blade which projects from the surface of the blade recess. The boss has a thin portion that is no thicker than the replaceable blade and a thick portion that is thicker than the replaceable blade. The blade lock is pivotably mounted to the blade holder for pivoting between an opened position for receiving the replaceable blade and a closed position for retaining the replaceable blade. The blade lock also includes an opening corresponding to the boss of the blade holder. The blade holder boss is oriented so that the edge of the blade lock first encounters the thin portion of the boss as the blade lock is pivoted from the opened position toward the closed position. As the blade lock continues to pivot, the blade lock rides up on the thicker portion of the boss until the blade lock opening receives the thick portion of the boss and thus retains the blade lock in the closed position. When the blade lock opening receives the thick portion of the boss, the blade lock springs back into contact with the blade holder and the blade. The blade lock is opened to remove a replaceable blade by applying opposite pressure to the distal end of the blade lock. In order for the blade lock to open, the portion of the blade lock adjacent to the blade lock opening must pop back up onto the blade holder boss. If one or both of the edges of the blade holder boss or the blade lock opening which make contact when opposite opening pressure is applied are slightly rounded or beveled, then the blade lock can pop back up onto the blade holder boss when sufficient opening pressure is applied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of the replacement blade knife shown with the replaceable blade removed. 
         FIG. 1A  is a side view of the removable blade of the replacement blade knife shown removed from the replacement blade knife of  FIG. 1 . 
         FIG. 2  is a side view of the replacement blade knife shown with the replaceable blade in place and the blade lock in the opened position. 
         FIG. 2A  is a cross section view of the blade lock of the replacement blade knife taken from plane A-A of  FIG. 2 . 
         FIG. 3  is a side view of the replacement blade knife shown with the replaceable blade in place and the blade lock in the closed position. 
         FIG. 3A  is a cross section view of the replacement blade knife taken from plane A-A of  FIG. 3 . 
         FIG. 3B  is a cross section view of the replacement blade knife taken from plane B-B of  FIG. 3 . 
         FIG. 4  is a magnified top view of the proximate portion of a blade lock. 
         FIG. 4A  is a cross section view taken from plane A-A of  FIG. 4 . 
         FIG. 5  is a magnified top view of the proximate portion of a blade holder. 
         FIG. 5A  is a cross section view taken from plane A-A of  FIG. 5 . 
         FIG. 6  is a magnified top view of the proximate portions of a blade holder and a blade lock with the blade lock in a fully opened position with the blade removed for clarity. 
         FIG. 6A  is a cross section view taken from plane A-A of  FIG. 6  showing a cross section of the blade lock with the blade holder removed for clarity. 
         FIG. 6B  is a cross section view taken from plane B-B of  FIG. 6  showing a first cross section of the blade holder with the blade lock removed for clarity. 
         FIG. 6C  is a cross section view taken from plane C-C of  FIG. 6  showing a second cross section of the blade holder with the blade lock removed for clarity. 
         FIG. 7  is a magnified top view of the proximate portions of a blade holder and a blade lock with the blade lock shown between the opened position and the closed position with the blade removed for clarity. 
         FIG. 7A  is a cross section view taken from plane A-A of  FIG. 7  showing a cross section of the blade lock and the blade holder shown with the blade holder between the opened position and the closed position. 
         FIG. 8  is a magnified top view of the proximate portions of a blade holder and a blade lock with the blade lock approaching the closed position with the blade removed for clarity. 
         FIG. 8A  is a cross section view taken from plane A-A of  FIG. 8  showing a cross section of the blade lock and the blade holder with the blade holder approaching the closed position. 
         FIG. 9  is a magnified top view of the proximate portions of a blade holder and a blade lock with the blade lock in the closed position with the blade removed for clarity. 
         FIG. 9A  is a cross section view taken from plane A-A of  FIG. 9  showing a cross section of the blade lock and the blade holder with the blade holder in the closed position with the blade removed for clarity. 
         FIG. 10  is a magnified top view of the proximate portions of a blade holder with the blade removed for clarity showing an alternate boss which is biased in a locked position. 
         FIG. 10A  is a cross section view taken from plane A-A of  FIG. 10  showing a cross section of the blade holder with the blade removed for clarity showing an alternate boss which is biased in a locked position. 
         FIG. 11  is a magnified top view of the proximate portions of a blade holder with the blade removed for clarity showing an alternate thumb flange extending from the thumb holder. 
         FIG. 11A  is a cross section view taken from plane A-A of  FIG. 11  showing a cross section of the blade holder with the blade removed for clarity showing an alternate thumb flange extending from the thumb holder. 
         FIG. 12  is a plan view of a blade holder fashioned in accordance with an embodiment of the replacement blade knife adapted for receiving standard box cutter blades. 
         FIG. 12A  is a magnified cross section view of the blade holder shown in  FIG. 12  taken from plane A-A of  FIG. 12 . 
         FIG. 12B  is a cross section view of the blade holder shown in  FIG. 12  taken from plane B-B of  FIG. 12 . 
         FIG. 13  is a cross section view of the blade holder shown in  FIG. 12  shown receiving a standard box cutter blade. 
         FIG. 14  is a cross section view of the blade holder shown in  FIG. 12  shown receiving a modified replaceable knife blade. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 1A , an example replacement blade knife  10  is shown to include a handle  11 , a replaceable blade  12 , a blade holder  40  and a blade lock  70 . As can be seen in  FIG. 1 , blade holder  40  is mounted to handle  11  and blade lock  70  is pivotably mounted to blade holder  40  at pivot joint  72 . 
     As can be seen in  FIGS. 1 and 1A , replaceable blade  12  includes a cutting edge  14 , an opposite back edge  16  and a base edge  18 . Cutting edge  14  and back edge  16  preferably meet at the tip of the knife. Base edge  18  extends between the base of back edge  16  and the base of cutting edge  14 . Replaceable blade also has an opening  20  adjacent to base edge  18 , which in this example is elongated and oriented generally parallel to base edge  18  as is shown in  FIG. 1 . One of the benefits of this replacement blade knife is that replaceable blade  12  may be replaced by a variety of blades, saw blades or even tool elements. Replaceable blade  12  may be discarded when removed or perhaps more preferably returned to the manufacturer for re-sharpening. 
     Blade holder  40  is mounted to handle  11  and includes a blade recess  42  for receiving replaceable blade  12 . Blade holder  40  may be fixed to handle  11  or optionally may be pivotably mounted to handle  11 . If blade holder  40  is pivotably mounted to handle  11 , then handle  11  would be slotted to accommodate blade holder  40 , blade lock  70  and blade  12  in the same well known way the handle of a typical folded blade knife accommodates a pivoting blade. Blade holder  40  is generally “L” shaped. Blade holder  40  includes a relatively short base portion  44  at its proximate end for supporting the portion of the replaceable blade adjacent to replaceable blade&#39;s base edge  18  and a relatively long back edge portion  46  which extends to its distal end. Back edge portion  46  supports the back edge  16  of replaceable blade  12 . Blade holder  40  includes a back surface which is preferably generally flat and a front surface which includes a blade recess  42  for receiving replaceable blade  12 . Blade recess  42  of the blade holder  40  preferably extends over most of back edge portion  46  and base portion  44  of blade holder  40 . Blade recess  42  is bounded on its upper edge by a back surface  42 A which has a width corresponding to the thickness of blade  12  and which is located to receive back edge  16  of blade  12 . Blade recess  42  is bounded at its base edge by a base surface  42 B which also has a width corresponding to the thickness of blade  12  and is located to receive base edge  18  of blade  12 . 
     Blade recess  42  of base portion  44  is also interrupted by a projecting boss  48 . Boss  48  provides two functions in this example. First, boss  48  is received by opening  20  of blade  12  to further secure the position of blade  12  relative to blade holder  40 . Second, boss  48  provides a means for locking blade lock  70  in the closed position. In this example, the upper surface of boss  48  varies in its offset from the surface of blade recess  42  from a relatively low portion  48 A adjacent to back surface  42 A of blade recess  42  to a relatively high portion  48 B generally opposite from back surface  42 A. Low portion  48 A of boss  48  preferably does not extend above the upper surface of replaceable blade  12  when replaceable blade  12  is received by blade recess  42 . High portion  48 B of boss  48  is preferably at least sufficiently raised above the upper surface of replaceable blade  12  to cause boss  48  to be securely captured by a corresponding boss opening  74  in blade lock  70  as will be described in greater detail below. It is preferable that blade holder  40  be fashioned from a hard, strong material such as stainless steel. 
     Blade lock  70  secures and fixes replaceable blade  12  to blade holder  40 . Blade lock  70  is pivotably mounted to blade holder  40  at pivot joint  72  and pivots between an opened position shown in  FIGS. 2 and 6  and a closed position shown in  FIGS. 3 and 9 . The opened position shown in  FIGS. 2 and 6  accommodates the removal and replacement of replaceable blade  12 . Replaceable blade  12  is held in place when blade lock  70  is in the closed position shown in  FIGS. 3 and 9 . Pivot joint  72  is preferably located outside the perimeter of blade holder blade recess  42  and preferably proximate to corner of blade recess  42  corresponding to back edge  16  and base edge  18  of replaceable blade  12 . As can be seen in  FIGS. 3A and 3B , blade lock  70  is a channel shaped member adapted for fitting around blade holder  40 . As can be seen in  FIGS. 3A and 3B , channel shaped blade lock  70  includes a back flange  70 A which generally covers the back surface of blade holder  40  and a front flange  70 B which generally covers the front surface of blade holder  40 . It is preferable that the shape of blade lock  70  generally corresponds to the shape of blade holder  40  and that blade lock  70  fits securely around blade holder  40  when in the closed position shown in  FIGS. 3 and 9 . When in the closed position, the front flange  70 B of blade lock  70  extends over a portion of replaceable blade  12  adjacent to back edge  16 . Also, when in the closed position a base edge  76  of blade lock  70  extends past boss  48  which projects from blade holder  40 . Front flange  70 B of blade lock  70  includes a boss opening  74  which corresponds to blade holder boss  48  projecting from blade holder  40 . 
     As noted above, back edge portion  46  of blade holder  40  as well as the portion of blade recess  42  of blade holder  40  which extends into back edge portion  46  are preferably elongated and preferably extend most of the length of the straight portion of back edge  16  of blade  12  in order to support blade  12 . Similarly, as noted above, when blade lock  70  is in the closed position and when blade  12  is mounted in blade holder  40 , back flange  70 A and front flange  70 B of blade lock  70  surround back edge portion  46  of blade holder  40  as well as the portions of blade  12  adjacent to its back edge  16 . Accordingly, because back edge  16  of blade  12  is extensively supported, blade  12  may be relatively thin, flexible and inexpensive and still function as a conventional knife blade. Because of this it is possible to produce, a sharp, high quality blade  12  which has a length comparable to the length of conventional knife blades, which when installed as described above functions in a way comparable to the knife blade of a conventional knife and which is sufficiently low in cost to allow economical removal and replacement. 
       FIGS. 6-9A  provide detailed views of blade lock  70  and blade holder  40  showing how blade lock  70  engages blade holder  40  to hold blade  12  in place and also shows how blade lock  70  may be disengaged from blade holder  40  to allow the removal of a blade. More particularly,  FIGS. 6-9  show how boss opening  74  in front flange  70 B of blade lock  70  reacts to boss  48  as blade lock  70  is rotated from the opened position shown in  FIG. 6  to the closed position shown in  FIG. 9 . The skilled reader should note that blade  12  has been omitted from  FIGS. 6-9A  for clarity. The distal ends of both the blade lock and the blade holder have also been broken away and removed in  FIGS. 6-9A  for clarity. 
     In  FIG. 6 , blade lock  70  is in the opened position. Blade recess  42  is completely uncovered allowing the removal or placement of a blade (not shown).  FIG. 6  also corresponds to  FIG. 2 .  FIG. 6A  shows a cross section of blade lock  70  alone taken from plane A-A which longitudinally bisects opening  74 .  FIG. 6B  shows a cross section of blade holder  40  only taken from plane B-B which bisects boss  48 . As can be seen in  FIG. 6B , boss  48  gently slopes from a low portion  48 A to a high portion  48 B. 
     If all of the edges of boss opening  74  and boss  48  were perfectly square, the initial force required to open blade lock  70  from a closed position might be unacceptably large. Accordingly, one or both of the edges of boss opening  74  and boss  48  should be rounded or beveled in those areas which initially engage as blade lock  70  begins to rotate away from the closed position. As can be best seen in  FIGS. 6B and 6C , in this example embodiment, the upper outside edge  48 C of boss  48  is beveled to allow the corresponding lower inside edge of boss opening  74  to ride up onto boss  48 . This action makes it possible to further rotate blade lock  70  toward the opened position shown in  FIG. 6 . Thus an operator wishing to pivot blade lock  70  from the closed position as shown in  FIG. 9  to the opened position shown in  FIG. 6 , would exert a clockwise force on the end of blade lock  70  most distant from pivot joint  72 . The beveled portion of boss  48  should be configured so that blade lock  70  may be opened with a moderate manual force but also so that blade lock  70  will not open during normal use of knife  10 . As with blade holder  40 , blade lock  70  should be fashioned from a strong, tough material such as stainless steel. 
     Beveling or rounding the proximate edge of boss  48  as shown and described above or the proximate inside edge of boss opening  74  of blade lock  70  or beveling or rounding both edges is merely one method for providing a means for allowing passage of blade lock front flange  70 B over boss  48  to allow opening of blade lock  70 .  FIGS. 10 and 10A  show an alternate method for providing a means for allowing passage of blade lock front flange  70 B when pivoting blade lock  70  from the closed position to the opened position. In  FIGS. 10 and 10A , boss  148  is fashioned as a resilient prong which is fixed to blade holder  40  at a base  148 A. This arrangement is sufficiently flexible to permit boss  148  to deflect under moderate manual pressure from the locked position shown in  FIG. 10A  with solid lines to the unlocked position shown in  FIG. 10A  with dashed lines. Blade holder  40  now includes an cavity  140 A for allowing boss  148  to deflect towards the back surface of blade holder  40 . As can be seen in  FIG. 10 , cavity  140 A is sized to provide clearance for the downward flexure to boss  148  in response to finger pressure applied at arrow P shown in  FIG. 10A . Boss  148  may be an integral part of blade holder  40  as shown in  FIG. 10A  or boss  148  may be a separate part which is fixed to blade holder  40  by welding or fasteners. Boss  148  should be fashioned from a tough, elastic material such as stainless steel. At a minimum, boss  148  should be fashioned from a tough material having an elastic range sufficient to allow enough deflection of prong  148  to permit an operator to open blade lock  70  without causing the plastic deformation of boss  148 . 
       FIGS. 11 and 11A  show yet a second alternate method for disengaging blade lock  70  from blade holder  40 . In  FIG. 11A , manual pressure P is applied to an alternate thumb catch flange  70 B 1  projecting from the outside edge of blade lock front flange  70 B adjacent to boss opening  74  to cause front flange  70 B to deflect sufficiently to clear high portion  48 B of boss  48  as shown with the superimposed dashed lines in  FIG. 11A . This approach could eliminate the need for rounding or beveling either the edges of boss  48  or corresponding inside edges of boss opening  74 . 
     Pivot joint  72  may also include a hinge pin which extends beyond the surfaces of the back and front flanges of blade lock  70 . Such a hinge pin would be useful if blade holder  40  were in turn pivotably mounted to handle  11  for retracting within handle  11 . A skilled user could manipulate a hinge pin at pivot joint  72  with one hand in order to open the knife with one hand. Thus pivot joint  72  may be a dual use part. 
     Replacement blade knife  210 , which is another embodiment of the replacement blade knife is shown in  FIGS. 12-14 . Replacement blade knife  210  is generally identical to knife  10  shown in  FIGS. 1-9A . The skilled reader should consider that in all important respects blade lock  70  and handle  11  are unchanged from that which is shown in  FIGS. 1-9A . For the purposes of understanding replacement blade knife  210 , only blade  12  has been changed to blade  212  and blade holder  40  has been changed to blade holder  240  as will be described in greater detail below. 
     As can be seen in  FIG. 12 , blade holder  240  of knife  210  includes generally the same features as blade holder  40  of knife  10 , except the upper shoulder surface  242 A of recess  242  presents two projections  242 A 1  and  242 A 2 . Still further, the shape of recess  242  is altered so that a triangular indentation  248 A intrudes into boss  248 . Taken together, the purpose of projections  242 A 1  and  242 A 2  and triangular indentation  248 A can be easily understood by referring to  FIG. 13 . As can be seen in  FIG. 13 , a standard box cutter blade  312  has a standard Isosceles Trapezoid shape with a sharp cutting edge  312 B along its longest side, and two spaced notches  312 A 1  and  312 A 2  in the edge opposite the sharp cutting edge. As can be seen in  FIG. 13 , projections  242 A 1  and  242 A 2  of blade holder  240  are arranged to receive notches  312 A 1  and  312 A 2 . Further, when notches  312 A 1  and  312 A 2  receive projections  242 A 1  and  242 A 2 , indentation  248 A of boss  248  receives a corner  312 C of box cutter blade  312 . Once a blade lock like blade lock  70  shown in  FIG. 3  is rotated into position, box cutter blade  312  is secured in the position shown in  FIG. 13 . 
     As can be seen in  FIG. 14 , blade holder  240  knife  210  is fully capable of receiving a replaceable knife blade  212  which is substantially identical to blade  12  shown and described above. However, blade  212 , although nearly identical to blade  12  (in terms of its interfaces with blade holder  240  and blade lock  70 ) has two notches  232 A and  232 B defined in back edge  232 . The location and placement of these notches  232 A and  232 B is such that when opening  220  of blade  212  receives boss  248 , notches  232 A and  232 B also receive protrusions  242 A 1  and  242 A 2  of blade holder  240 . Thus blade holder  240  is adapted for holding standard box cutter blades as shown in  FIG. 13  and is also adapted to hold a knife blade very similar to blade  12  shown and described above—but only with the very minor alteration of adding two notches in the back edge of the blade. 
     As can be seen from the above detailed description, replacement blade knife  10  and replacement blade knife  210  satisfy the objectives of the invention. Replaceable blade  12  can be removed and replaced with a fresh, factory sharp blade when blade  12  becomes dull. Moreover, as noted above, replaceable blade  12  may be removed and replaced with either an identical replacement blade or any one of a multitude of specialized knife blades, saw blades or tool elements. This capability greatly increases the versatility of the knife. 
     It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims and allowable equivalents thereof: