(3) FIELD OF THE INVENTION This invention relates to a manually operable blade sharpener at least employable for the precision sharpening of a blade. Although not so limited the sharpener of the invention finds useful application in the field of the sharpening of knife blades.

(4) PRIOR ART DESCRIPTION Equipment for the manual sharpening of blades by way of the manual cyclical reciprocation of a blade in a notch or forked formation defined between sharpening elements is known in the art. US patent numbers 4,550, 632 and 5,440, 953 both define sharpening elements crossing one another in defining a sharpening notch. Both patents also present guiding means for guiding a blade into a sharpening notch. None of the these patents, however, address the situation of precision sharpening as their sharpening elements are swivellably mounted to a base that thus gives rise to a continuously changing sharpening angle in the performance of a sharpening routine. While the subject matter of US patent number 4,624, 079 discloses sharpening elements that are mounted to maintain a fixed sharpening angle it does not present a guide path associated therewith. It also thus does not provide for the precision sharpening of a blade.

(6) BRIEF DESCRIPTION OF THE DRAWING The invention is now described, by way of example, with reference to the accompanying drawings. In the drawings Figure 1 shows a manually usable blade sharpener in the form of a knife blade sharpener, in side elevation, Figure 2 shows the blade sharpener of figure 1 though with a modification as regards the ability to alter the slope of a blade-sharpening path defined along the sharpener, Figure 3 shows the sharpener of both figures 1 and 2 in end elevation, Figure 4 shows the sharpener of the figure 1 in plan view, Figure 5 stepwise shows the operation of the sharpener though omitting the modification as regards the ability to alter the slope of the blade sharpening path, and Figure 6 shows in detail the operation of the sharpener as modified to also alter the slope of the blade-sharpening path.

(6) DETAILED DESCRIPTION OF THE DRAWINGS Referring to figures 1 to 5 of the drawings a blade sharpener in the form of a knife blade sharpener is generally indicated by reference numeral 10.

The sharpener 10 comprises two horizontally displaceably mounted sharpening strip providing carriers 12 and 14 respectively, each including an obliquely extending linear sharpening strip providing rod 16 and carrier movement non-interference guiding means in the form of a slot defining formation as providing a slot defining frame member layout formed by facing rail pairs 18,20 facing one another across a slot 22. The rail pairs 18 and 20 form part of a carrier support frame 24 to which the carriers 12,14 are mounted to be displaced in diametrically opposed directions once the sharpener 10 is used for blade sharpening purposes. The carrier 12 is thus mounted to be outwardly displaced in the direction of arrow 13 and the carrier 14 in the direction of arrow 15. The carriers 12,14, as mounted in snug adjacent displacing relationship relative to one another, are mounted to be displaced along the spacings 26 formed between the rails 18.1, 18.2 and 20.1, 20.2 of the rail pairs 18,20.

While the carriers 12,14 are freely displaceably mounted their respective ranges of displacement are limited to cause the rods 16 to maintain a forked crossover relationship by forming a randomly displaceable crossover point 28 defining a cutting angle 17 within which the cutting edge of the blade of a knife is in an abrasion incurring way moved during a sharpening action. The location of the crossover point 28 is naturally dependent on the relative positioning of the carriers 12,14 and thus the rods 16 but is limited to a uni-planar displacement in a plane parallel to the planes of displacement of the carriers 12,14. While the crossover point 28 is randomly displaceable within the relative operative ranges of the carriers 12,14, it is naturally constrained to move along a linear sharpening path extending along the slot 22 once the sharpener 10 is used for performing a blade sharpening action, as more fully discussed below.

The carriers 12,14 are limited to their ranges of displacement by way of limiting means in the form of adjustable stops that are provided, as regards outward displacement, by stop screws 30 adjustably fitting though threaded apertures in the end sections 24.1 of the frame 24 that constrains outward displacement by coming to abut against frame members 12.3, 14.3 respectively. As regards inward displacement the limiting means is provided by nuts 32 fitting adjustably onto threaded ends of upper sliding arms 12.1, 14.1 forming part of the respective carriers 12,14. To cause the return of the crossover point 28 to an inter-strip commencement crossover position in the region of the entrance to the slot 22 when not exposed to a sharpening action, the carriers 12,14 are biased by biasing means in the form of springs 36 each extending between the appropriate end section 24.1 of the support frame 24 and a hook formation 23 formed on the relevant carrier 12,14. To cushion inward displacement of the towards the nuts 32 as urged by the springs 36 when a blade is rapidly removed from the slot 22 the arms 12.1, 14.1 are fitted with cushioning springs 27. Although not shown the tensioning of the springs 36 can be adjustable by either replacement of springs of different tension or by providing a series of hook formations 23 for each spring.

The leading side surfaces 16.1 of the rods 16 are naturally abrasively formed for performing their combined abrasive sharpening effect once the sharpener 10 is in use.

The support frame 24 is constituted from its ends frame sections 24.1 and overhead sections 24.2 running into rail pair securing formations 25 or adjustment means as shown in figure 2 for the modified sharpener 10 and discussed in more detail further on. Thé rail pairs 18,20 in turn run from the formations 25 into a stand section 24.3 via which the frame 24 is anchored to a base 38 forming part of the sharpener 10. The rail pairs 18,20 flare outward at the inlet 34 to the slot 22 to facilitate location of a blade into the slot 22 : The carriers 12,14 are displaceably mounted to the support frame 24 via their upper sliding arms 12.1, 14.1 that pass slidably along apertures each formed at a high elevation through aperture blocks 42 forming part of the end sections 24.1 and lower sliding arms 12.2, 14.2 each supported at both ends in apertures 44 formed in aperture blocks 46 also forming part of the end sections 24.1. Each of the upper sliding arms 12.1, 14.1 is only supported in the end section side towards which it slides on the carriers 12,14 being caused to slide more out of overlap with respect to one another.

To accommodate a variety of primary edge blade angles the carriers 12, 14 make provision for adjustment of the slopes of the rods 16 and thus of their sharpening surfaces 16.1. This is achieved by having the rods 16 swivellably mounted at their upper ends 16. 2 to rod support carrier frame sections 48 while the lower end 16.3 of each rod 16 is releasably securable to one of a series of rod lower end positions of securing in the form of rod connecting apertures 50 that are suitably arcuately arranged to permit the registration and securing of a selected one of the apertures 50 with an aperture formed at the lower end of the rod 16. The apertures 50 are presented along aperture carriers 52 integrally formed above the lower sliding arms 12.2, 14.2.

As shown in figure 5 the use of the sharpener 10 involves conventionally cyclically reciprocatingly moving the blade of a knife along the blade-sharpening path that extends down the slot 22. As the object of the sharpener 10 is to achieve precision sharpening of the cutting edge of a blade, the path does not necessarily extend centrally down the slot 22.

A typical blade for which the sharpener 10 is useful in performing a precision sharpening action comprises primary edge underscoring faces ending in its cutting edge. Trailingly as regards the width of the blade the next part of the side faces of a blade is found in the secondary faces that in turn lead onto the broad trailing side faces. The typical blade is normally symmetrically formed with precision sharpening of the blade with the sharpener 10 thus involving the primary edge underscoring faces.

Such precision sharpening involves maintaining the position of the primary edge angle underscoring faces 54 of a blade 56, as shown in the detail to figure 5 (a), and as terminating in the cutting edge 58 of the blade 56, in a fixed and preferably symmetrical relationship with respect to the crossover point 28 throughout a cyclical and reciprocating blade sharpening action. This is achieved by maintaining the central plane through the blade 56 and consequently its broad side face areas 60, as trailing the secondary faces 63 in parallel with the central axis 62 down the slot 22 When the width of the blade 56, as defined between opposite faces 60, is such that a snug but free displacement of the blade 56 along the slot can be achieved, the blade-sharpening path is naturally defined down the slot 22 as such.

Cyclical to-and-fro reciprocation of the blade 56 along the slot 22 has the effect of maintaining the blade 56 in parallel with the axis 62 down the slot 22 in turn causing its primary edge angle underscoring faces 54 to maintain a fixed relationship relative to the crossover point 28.

When the blade width is however less than the width of the slot 22 the sharpening path is defined down one of the rail pairs 18,20 in that the blade 56 is maintained against the appropriate rail pair 18,20 during the sharpening action. This scenario is typically shown in figure 5. A manually applied cyclical reciprocating sharpening action has the effect of causing the blade 56 to move up and down the sharpening path and to and fro in the crossover point 28 according to figures 5 (a) to 5 (b) with the crossover point 28 following the cutting edge 58 of the blade 56 owing to the biasing effect of the springs 36. As the crossover point 28 is freely uniplanarly displaceable it automatically finds its position of blade sharpening edge bedding when the blade 56 is moved along its sharpening path.

A typical sharpening routine involves as first step the desirable setting of the slopes of the rods 16 and thus of their surfaces 16.1 as described above.

While blades are often constructed as explained above, other forms of blade design are also found. In again referring to figure 2 and also to figure 6 the modified sharpener also accommodates blades of which the broad side face areas do not extend in parallel with one another. Typically such broad side face areas run directly into their primary faces. Otherwise such blades may have secondary faces while the primary faces still extend in a non-parallel relationship with one another. To still achieve the desired sharpening action for such blades in maintaining their primary edge underscoring faces, as ending in their cutting edge, in the crossover point 28 during use of the sharpener, provision is made for adjusting the slope of at least one of the rail pairs 18,20. This is achieved by having the appropriate rail pair 18,20 swivellably mounted in its root as found in its point of connection to the stand section 24.3, as shown in figure 2, while its remote end is adjustably secured to the overhead section 24.2 by way of an adjustment facility (not shown in detail) including locking means enabling the re- lockable adjustment of the slope of the appropriate rail pair 18, 20. As shown in figure 2 the position of adjustable locking to the overhead section 24.2 provides an indicating scale 64 for indicating the extent of adjustment of the rail pair 18,20 relative to the vertical.

Use of the figure 2 embodiment of the sharpener 10 in conjunction with a blade 64 of which the broad side areas are not parallel to one another involves desirably pre-setting of the slope of the relevant rait pair 18,20 to the effect of ensuring that the centre line 66 of such blade 64, as shown in figure 6 (a), is parallel to the vertical. The sharpening path is in this case defined along the rail pair 18,20 of which the slope is suitably adjusted. This has the effect that the primary edge underscoring faces 68 still symmetrically fit the crossover point 28, as shown in more detail in figure 6 (b).

A sharpening routine performed with the modified sharpener 10 of figure 2 of which the rail pair slope is appropriately adjusted can thus be performed with the same extent of precision, as is the case for a blade of which the broad side areas are parallel to one another, as discussed with reference to figure 5. As shown in figures 6 (c) and 6 (d) the modified sharpener 10 can naturally also be used for blades having parallel broad side face areas. In such case the adjustable rail pair 18,20 is simply adjusted to cause the rail pairs 18,20 to extend parallel to one another thus effectively having a sharpener similar to that shown in figures 1 an 5. As a blade used in conjunction with the figures 6 (c) and 6 (d) embodiment is the same as that used in the figures 1 and 5 embodiment it carries the same nomenclature.

Once a blade has been sharpened by means of the sharpening rods 16 the final step in its preparation is often its steeling. This is normally done at a blade cutting edge underscoring angle of larger that the angle of sharpening. If this step is required the sharpener 10 can simply be arranged to enable replacement of the rods 16 by steeling rods (not shown in detail but implied by the figure 2 embodiment of the invention). Alternatively while not shown the sharpener 10 can include steeling rods fitted with appropriately arranged clips that automatically define the desired increased underscoring angle once clipped to the rods 16.