Abstract:
A folding tool such as a knife has an implement such as a blade pivotally attached to the handle with a pivot shaft, allowing the implement to be rotated from a closed to an open position. The invention allows the diameter of the pivot shaft to be varied, thereby allowing the diameter of the shaft to be effectively increased in the area where the implement rotates about the shaft so that the shaft extends to and makes contact with the interior surface of the bore through the implement, without restricting the ability of the blade to freely rotate about the shaft, minimizing or eliminating any tendency of the implement to wiggle relative to the handle.

Description:
FIELD OF THE INVENTION 
     This invention relates to hand tools such as knives and other hand tools that are equipped with blades and/or other implements that are pivotally attached to a handle, and more particularly to a method and apparatus for adjusting the diameter of the pivot shaft that attaches the blades and/or other implements to the handle to eliminate relative movement between the implement and the handle. 
     BACKGROUND 
     Folding tools such as knives have a handle with opposed halves that are held apart to define a blade-receiving space. A blade is pivotally attached to the handle with a pivot shaft or axle that has its opposite ends secured to the opposite handle halves, and which extends through a bore in the blade. The pivot shaft defines a strong and secure connection between the blade and the handle about which the blade may be pivoted between a closed position in which the blade is stowed safely in the handle, and an open position in which the blade extends away from the handle for normal use. 
     Although there are many different kinds of structures used for pivot shafts used to attach knife blades to knife handles, an inherent problem with pivoting knives (and other folding tools) is that there is almost always a certain amount of play between the blade and the handle. Thus, in order to enable the blade to pivot freely about the pivot shaft, there must be some tolerance between the outer diameter of the pivot shaft and the inner diameter of the bore in the blade through which the shaft extends. In high quality knives the amount of clearance between the blade bore and the shaft can be minimized, but there still must be enough tolerance to allow the blade to be pivoted relatively easily. This necessary tolerance results in rotational movement of the blade, which is perceived as wobble between the blade and the handle: this phenomena is often colloquially referred to as “tip wobble.” 
     Tip wobble is undesirable because it necessarily reduces the strength of the blade/handle connection. In extreme cases, tip wobble can result in an unsafe tool—this is sometimes a concern with lower quality folding knives. But tip wobble is often present even in the most highly engineered and expensive folding knives and can be both a bother and a structural limitation. 
     There are several common techniques utilized to eliminate, or at least minimize the amount of tip wobble. The most common approach is simply to reduce the tolerance between the blade bore and the pivot shaft—the closer the tolerance between the pivot shaft and the bore, the lesser the tip is able to wobble. The trade off with this approach is of course that a certain amount of spacing between the blade and the shaft is necessary to allow the blade to pivot freely. With automatic or semi-automatic style knives, an easily pivoting blade is a necessity. As such, this approach has its limitations. Another approach is to add a low-friction bushing around the pivot shaft so that the shaft—bore tolerance may be minimized. As with the other techniques just described, this is an effective way to help minimize tip wobble, but it does not eliminate wobble. Moreover, the bushings tend to wear and degrade over time and as they do so, tip wobble tends to increase. 
     Another solution relies upon a blade-locking mechanism to minimize relative movement between the blade and handle Some locking mechanisms utilize a 3 point-of-contact lock that forces out the play in the pivot bore. While this technique does help minimize blade movement, not all knife designs can incorporate these kinds of locking mechanisms. Other common locking mechanisms do not alleviate-tip wobble. 
     There is an ongoing need therefore for manufacturing techniques and methods that reduce tip wobble in folding tools such as knives. 
     The present invention relates to an apparatus and method for establishing a strong, secure interconnection between a folding tool implement and the handle of the folding tool, and which minimizes or eliminates tip wobble while insuring that the implement may be easily pivoted between the open and closed positions. The invention allows the diameter of the pivot shaft to be varied, thereby allowing the diameter of the shaft to be effectively increased so that the shaft extends to and makes contact with the interior surface of the bore through the blade, without restricting the ability of the blade to freely rotate about the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings. 
         FIG. 1  is a side elevation view of a folding knife of the type that incorporates the adjustable diameter pivot shaft according to the present invention, illustrating the blade of the knife in an open position. 
         FIG. 2  is a side elevation view of the folding knife shown in  FIG. 1  with a portion of the near-side handle removed to expose the near-side liner and other internal structures of the knife. 
         FIG. 3  is a cross sectional view taken along the line  3 - 3  of  FIG. 1 . 
         FIG. 4  is a cross sectional view taken along the line  4 - 4  of  FIG. 3 , showing only that portion of the knife and its structures around the blade/handle interconnection. 
         FIG. 5  is a perspective exploded view of the knife shown in  FIG. 1 . 
         FIG. 6  is a perspective exploded view of the adjustable diameter pivot shaft according to the present invention. 
         FIG. 7  is a perspective partial cross sectional view of a portion of the knife shown in  FIG. 1  where the blade interconnects with the handle, and with the blade shown in the open position. 
         FIG. 8  is a cross sectional view similar to the view of  FIG. 3 , illustrating an alternative embodiment of the adjustable diameter pivot shaft. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first illustrated embodiment of a folding knife  10  incorporating an adjustable diameter pivot shaft according to the present invention is illustrated in  FIGS. 1 through 7 . A first illustrated alternative embodiment of the folding knife that includes an adjustable diameter pivot shaft according to the present invention is illustrated in  FIG. 8 . It will be appreciated that the present invention is described herein as it is used in a folding knife, but that the invention is equally applicable to other kinds of folding tools that have implements other than the knife blades described herein. Thus, the principals of the invention and the structures that enable the invention may be used in many kinds of folding tools other than knives. Description of the invention as it is used with a knife should thus be considered a way of enabling the invention for those of skill in the art, but not as a limitation to the scope of the invention as defined in the claims. 
     Folding knife  10  includes an elongate handle  12 , and a blade  14  that is pivotally attached to the handle at one of its ends—referred to herein as the “forward” end  16  of the handle. Other relative directional terms correspond to this convention: the “rear” or butt end  18  of the handle is opposite the forward end; the “upper” part  20  of the blade is the dull, non-working portion and the “lower” part  22  of the blade is the sharpened, working portion; “inner” or “inward” refers to the structural center of the knife  10 , and so on.  FIGS. 1 and 2  show the knife  10  with the blade  14  in the open position. An X-Y-Z axis grid is shown in  FIG. 1 . The X-Y plane is defined as the plane parallel to the plane defined by the handle  12  and blade  14 —the blade travels in the X-Y plane as it is rotated between the closed and open positions. The Z plane is the plane transverse to the X-Y—as detailed below, the blade pivot shaft extends longitudinally in the Z-plane. 
     With reference now to  FIG. 5 , the various components of knife  10  will be described. Handle  12  of knife  10  comprises several components, including a pair of oppositely located handle halves, generally indicated at  24 ,  26 , that are parallel with each other and held spaced apart from one another by a spacer  28  that is attached between the handle halves along an upper edge thereof. Each of the handle halves  24  and  26  comprise an inner liner and an outer plate that are held parallel to one another. Specifically, handle half  24  is defined by liner  30  and an outer plate  32 . Likewise, handle half  26  is defined by liner  34  and outer plate  36 . It will be noted that each of the outer plates  32  and  36  includes a decorative center section ( 32   a  and  36   a , respectively) that is separately attached to the outer plate. It will be understood that the decorative sections  32   a  and  36   a  could be replaced by making the outer plates solid without the separable decorative sections. Moreover, it will be understood that the handle halves  24  and  26  may be unitary in construction—that is, there is no reason that the handle halves include a liner and an outer plate. 
     The handle  12  is assembled with blade  14  with various screws and spacers as best shown in  FIG. 5 . Thus, blade  14  is pivotally connected to handle  12  with a pivot shaft assembly  100 , which is described in much greater detail below, and which extends through aligned bores  38  in outer plate  32  and  40  in liner  30 , bore  102  in blade  14 , and bores  42  in liner  34  and bore  44  in outer plate  36 . As detailed below, the interior diameter of bore  44  is formed in a series of planar faces. A screw  46  extends through aligned bores in the rearward portion of the handle halves and the spacer and is threaded into a nut/spacer  48 , and a similar screw  50  and nut/spacer  52  are located midway along the length of handle  12  along the upper margin such that the screw spacer  42  extends through the handle halves and the spacer  28 . Additional screws may be used in a conventional manner to secure the handle components together and so that a blade-receiving groove  54  (see e.g.,  FIG. 3 ) is defined between the handle halves  24  and  26 . The blade receiving groove  54  defines a slot into which the blade  14  is received when it is moved to its closed position. When the blade is in the closed position, the sharp edge  22  of the blade is held safely within the confines of the handle. Spacers  48  and  52  are preferably cylindrical sleeves that have a threaded internal bore into which screws  46  and  50  are threaded. The screws thus secure the spacers between the handle halves  24  and  26  to maintain the handle  12  in a secure relationship with handle halves  24  and  26 , which are held in a spaced apart relationship. The handle halves  24  and  26  may be fabricated from any suitable material such as metal, a reinforced synthetic plastic; other suitable materials include metal, other plastics, wood, etc. The handle halves sections may be fabricated in singled or multiple pieces, as shown in  FIG. 5 . Decorative sections  32   a  and  36   a  may be any kind of material such as fine wood. As shown in  FIG. 5 , a loop  54  may be added to the rearward end of spacer  28  to define a location to attach a lanyard (not shown) to the knife  10 . 
     Continuing with  FIG. 5 , knife  10  is shown as including an optional blade locking mechanism  56 , which is formed as part of liner  34 . Locking mechanism  56  does not form a part of the present invention and is therefore not described in great detail. Nonetheless, the locking mechanism  56  is defined by a spring arm  58  formed in liner  34  that has a tooth  60  formed on the forward end  62  of the spring arm. Spring arm  58  is normally biased under spring force inwardly, toward blade  14  in the assembled knife so that when the blade is in the open position the tooth  60  cooperates with a notch  64  in the tang portion  66  of blade  14  to lock the blade in the open position. A stop pin  68  is secured between liners  30  and  34  and stops rotation of blade  14  in the open position by abutting a cooperatively formed notch  70  in the tang  66  of blade  14 . Thus, when the blade  14  is in the fully open position of  FIG. 1 , stop pin  68  is in an abutting relationship with notch  70  and locking mechanism  56  is locked such that tooth  60  is engaging notch  64 . 
     As noted, the blade  14  is pivotally attached to the handle  12  near the forward end of the handle with a pivot shaft assembly  100 . Blade  14  is attached to handle  12  such that the blade&#39;s working portion  22  extends away from the handle  12  when the blade  14  is in its open position ( FIG. 1 ), and tang portion  66  is located within the blade receiving groove  54  between the paired handle halves when the blade is in either the open or the closed position. That is, the tang portion  66  is always located between the handle halves  24  and  26  of handle  12 . The blade is pivotally attached to the handle with pivot shaft assembly  100 , which extends in the Z direction, transverse to the plane of the blade. 
     The pivot shaft assembly defines a blade pivot axis—the axis is the centerline through the pivot shaft that extends in the Z direction, transverse to the X-Y plane. Pivot shaft assembly  100  is shown in isolation in  FIG. 6  and includes a cylindrical sleeve or shaft  104 , a screw  106  that threads into first end  105  of the hollow, threaded interior  108  of shaft  104 , and a set screw  110  that threads into second end  107  of the threaded interior  108  of shaft  104 . As noted, shaft  104  has a hollow, threaded interior  108  so that the shaft defines a hollow cylinder. Second end  107  of shaft  104  has an oversized lip  112  and a series of planar faces  114  on the inner-facing side of the lip. The shaft has three bores formed approximately midway along its length, two of which are shown in  FIG. 6  and which are identified with reference numbers  120  and  122 . The third bore is identified with reference number  124 . The three bores  120 ,  122  and  124  are axially arranged and evenly spaced around the shaft. Three ball bearings, labeled with reference numbers  126 ,  128  and  130  are received into the bores  120 ,  122  and  124 , respectively. A fourth ball bearing  132  is received into the interior of shaft  104  and as detailed below, and is located between the interior end  134  of screw  106  and bearings  126 ,  128  and  130  in the assembled knife  10 . 
     The pivot shaft assembly is assembled with knife  10  by inserting the shaft  104  through bore  44  in outer plate  36  until the series of planar faces  114  rest in the cooperatively formed bore  44 . This cooperative geometric relationship between the planar faces  114  of shaft  104  and the planar faces of bore  44  prevents the shaft  104  from rotating relative to the outer plate  36 . The shaft  104  is inserted through bore  42  in liner  34 , bore  102  in tang portion  66  of blade  14 , bore  40  of liner  30  and bore  38  of outer handle  32 . The outer diameter of shaft  104  is slightly smaller than the diameter of bore  102 . Stated another way, there is some clearance between the outside of the shaft and the inner surface  103  of the bore  102 . 
     A first washer  136  is placed around shaft  104  between the inner-facing side of liner  34  and blade  14 , and a second washer  138  is similarly placed between the inner-facing side of liner  30  and blade  14 . With the shaft positioned with the handle components as just described, screw  106  is threaded into first end  105  of shaft  104  and is tightened. Again, shaft  104  is prevented from rotating as screw  106  is tightened because the series of planar faces  114  and the cooperative planar faces in bore  44 . As seen in  FIG. 3 , when screw  106  is tightened in place, bores  120 ,  122  and  124  are aligned in handle  12  with the centerline of blade  14 . At this point, ball bearing  132  is inserted into second end  107  of shaft  104 . Ball bearing  132  rests on the interior end  134  of screw  106 . Next, bearings  126 ,  128  and  130  are inserted into second end  107  of shaft  104 . Each of these bearings is received into the respective bores  120 ,  122  and  124  in shaft  104 . 
     Set screw  110  is next threaded into shaft  104 . The inner tip  140  of set screw  110  is smoothly tapered. As such, when the set screw is threaded into the interior of shaft  104 , the tapered tip  140  bears against the three bearings  126 ,  128  and  130  and these three bearings also bear against bearing  132 , which naturally assumes its position the center of the three bearings  126 ,  128  and  130  as pressure is applied to the bearings with set screw  110 . Optionally, a circularly concave divot  142  (see  FIG. 5 ) may be formed in the axial center of the interior end  134  of screw  106  to located and position bearing  132 , although as noted the bearing  132  will normally assume this position as set screw  110  is tightened. 
     It will be appreciated that as set screw  110  is threaded more tightly into shaft  104  and bears against the bearings, the three bearings  126 ,  128  and  130  are forced outwardly from the axial centerline through the shaft, through the bores  120 ,  122  and  124 , as illustrated with arrows A in  FIGS. 3 and 4 . This force is directed in the X-Y plane as set screw  110  is threaded inwardly in the Z direction. As set screw  110  is screwed more tightly against the bearings, the bearings are forced with greater pressure against the interior surface  103  of bore  102  through blade  14 , effectively increasing the diameter of the pivot shaft and similarly effectively decreasing to zero the clearance between the pivot shaft and the blade. And although the diameter of the pivot shaft  104  has in this manner been increased so that the tolerance between the blade and the shaft is zero, the blade is easily rotated about the shaft between the open and closed positions by virtue of the bearings, which rotate relatively freely as the blade is rotated between the open and closed positions—the inner surface  103  of the bore  102  through blade  14  rotates over the bearings as the blade is moved from open to closed, and from closed to open. 
     Optionally, the set screw  110  described above with the tapered end could be replaced with a set screw having a planar inner surface and using a fifth ball bearing between the planar end of the set screw and the axially arranged bearings. 
     The amount of pressure applied by the bearings against the blade may be adjusted by varying the position of set screw  110 . Because the bearings  126 ,  128  and  130  are bounded by the bores in which the bearings reside—that is, bores  120 ,  122  and  124 , the bearings are urged only in the direction of arrows A, in the X-Y plane. In other words, any tendency of the bearings to be driven in any direction other than in the X-Y plane When set screw  110  is tightened is eliminated because the bores define the only route that the bearings are able to move. Set screw  110  may optionally include means for fixing the position of the screw to prevent loosening, such as nylon locking materials or other conventional screw locking mechanisms. Moreover, the set screw shown in the drawings utilizes a hex-type head, but any kind of set screw adjustment head may be used. Furthermore, bearing  132  may be eliminated by fabricating the inner end of screw  106  so that it replicates the shape of bearing  132 . 
     Pivot shaft assembly  100  thus allows the effective diameter of the pivot shaft to be varied, and in the assembled knife  10  the diameter of the shaft is increased by screwing set screw  110  into shaft  104 . This forces bearings  120 ,  122  and  124  outwardly so that they bear against the interior surface  103  of the bore  102  through blade  14 . Because the bearings put pressure on the blade, tip wobble is eliminated. All of the bearings are preferably metallic or ceramic so that the blade  14  pivots smoothly and easily between the closed and open positions. 
     A first alternative embodiment of an adjustable diameter pivot shaft according to the present invention is shown in  FIG. 8 . There, pivot shaft assembly  200  includes a cylindrical sleeve or shaft  204 , a screw  206  that threads into first end  205  of the hollow, threaded interior  208  of shaft  204 , and a set screw  210  that threads into second end  207  of the threaded interior  208  of the shaft. Second end  207  of shaft  204  has an oversized lip  212  and is seated in outer plate  36  to prevent relative rotation between the shaft and the plate in the same manner described above with assembly  100 . The shaft  204  has three bores formed approximately midway along its length, two of which are shown in  FIG. 8  and which are identified with reference numbers  220  and  222 . Three ball bearings, two of which are shown in  FIG. 8  and labeled with reference numbers  226  and  228  are received into the bores  220  and  222 , respectively (and the third bearing, which is not visible, is received into the third bore in the manner described above—although the third bore is not visible in  FIG. 8 ). A first elastomeric pad  230  is located adjacent the interior end of screw  206  and a second elastomeric pad  232  is located adjacent the interior end of set screw  210 , the interior end of which is flat, unlike the interior end of set screw  110  which is smoothly tapered. Fourth ball bearing  234  is positioned between first elastomeric pad  230  and bearings  226 ,  228  and the third bearing, and fifth ball bearing  236  is positioned on the other side of the three central bearings ( 226 ,  228 , and the third bearing which is not visible in  FIG. 8 ), between the central bearings and the second elastomeric pad  232 . 
     The pivot shaft assembly  200  is assembled with knife  10  similarly to the process described above. Thus, shaft  204  is inserted through the bores in outer plate and inner plate, the blade, and the inner and outer plate on the opposite side of the blade. Washers  136  and  138  are placed around shaft  204  on opposite sides of the blade between the inner-facing side of the liners and the blade. With the shaft positioned with the handle components, screw  206  is threaded into first end  205  of shaft  204  and is tightened, thereby aligning bores  220  and  222  with the center of blade  14 . At this point, ball bearing  234  is inserted into second end  207  of shaft  204 . Ball bearing  234  rests on the first elastomeric pad  230  on the interior end of screw  206 . Next, bearings  226 ,  228  and the third bearing are inserted into second end  207  of shaft  204 . Each of these bearings is received into the respective bores in shaft  204 . Fifth bearing  236  is then inserted into the shaft. At this point the three central bearings are each received into the respective bores in the shaft and the fourth and fifth bearings  230  and  232  are located in the center of the axially arranged three central bearings,  226 ,  228  and the third bearing, occluded in the view of  FIG. 8 . 
     Second elastomeric pad  232  is then inserted into second end  207  of the shaft, and set screw  210  is threaded into the shaft. When the set screw is threaded into the interior flat face of the screw bears against the second elastomeric pad  232 , putting pressure on bearing  236 , which as noted is positioned in the center of the three central bearings as shown in  FIG. 8 . This compresses all of the bearings inwardly, causing bearings  226 ,  228  (and the third bearing, not visible) to be forced outwardly from the axial centerline through shaft  204  in the direction of arrows A, so that the bearings apply pressure against the inner surface  203  of the bore through the blade. As set screw  210  is threaded more tightly into shaft  204  and compresses the bearings, the three central bearings  222 ,  228  are forced in the X-Y plane, effectively increasing the diameter of the pivot shaft and similarly effectively decreasing to zero the clearance between the pivot shaft and the blade. 
     Those of skill in the art will readily appreciate that from a functional point of view, the pivot shaft assemblies  100  and  200  described above and shown in the drawings serve to vary the diameter of the pivot shaft, and as noted, in doing so as the diameter of the pivot shaft increased, decrease the clearance between the pivot shaft and the blade (or other implement) to zero. There are many equivalent structures to those described herein that may be employed to accomplish these functional objectives. For example, a cassette of needle bearings may be used with the pivot shaft, fitted with mechanisms to urge the needle bearings outwardly from the shaft. Roller bearings likewise may be utilized. These modifications illustrate that the number of bearings is not fixed at three, but can be as few as two bearings and include more than three. Thus, for example, the sleeve  104  could include more than three bearings if desired. 
     While the present invention has been described in terms of a preferred embodiment, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.