a first illustrated embodiment of a folding knife 10 incorporating an adjustable diameter pivot shaft according to the present invention is illustrated in fig1 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 fig8 . 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 . fig1 and 2 show the knife 10 with the blade 14 in the open position . an x - y - z axis grid is shown in fig1 . 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 fig5 , 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 fig5 . 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 ., fig3 ) 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 fig5 . decorative sections 32 a and 36 a may be any kind of material such as fine wood . as shown in fig5 , 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 fig5 , 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 fig1 , 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 ( fig1 ), 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 fig6 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 fig6 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 fig3 , 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 fig5 ) 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 fig3 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 fig8 . 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 fig8 and which are identified with reference numbers 220 and 222 . three ball bearings , two of which are shown in fig8 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 fig8 ). 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 fig8 ), 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 fig8 . 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 fig8 . 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 .