(2) BACKGROUND TO THE INVENTION

The manual sharpening of blades is a common occurrence. It is often achieved by way of the cyclical reciprocation of a blade along a notched or forked formation defined between sharpening elements. Amongst knife specialists precision sharpening is normally required. To this effect the maintenance of the primary edge underscoring faces of a blade ending in its cutting edge at a fixed angle during a sharpening routine is of primary importance. It is an object of this invention to deal with this requirement. The invention is naturally not limited to only the sharpening of knife blades but can be used for any kind of blade that requires precision sharpening.

(3) FIELD OF THE INVENTION

This invention relates to a blade sharpener for sharpening the blade of blade carrying equipment. While not so limited the invention finds useful application in the field of precision knife sharpening.

(4) PRIOR ART DESCRIPTION

Equipment for the manual sharpening of blades by way of a manual cyclical reciprocation action of a blade along a notch or forked formation defined between sharpening elements is known in the art. U.S. Pat. Nos. 4, 550, 632 and 4, 440, 953 both define sharpening elements crossing one another in defining a sharpening notch. Both patents also include guiding means by means of which a blade is guided into a sharpening notch. The patents however do not address precision sharpening as the sharpening angle within the notch varies continuous during a sharpening routine. U. S Pat. No. 4,624,079 discloses elements that are mounted to maintain a fixed sharpening angle but does not include means defining an associated guide path thus failing in providing equipment of precision sharpening. U.S Pat. No. 7, 121 , 935 discloses elements that are mounted to maintain a fixed sharpening angle as well as including means defining an associated guide path. But the opening and closing action of the

sharpening edge providing means is by way of opposite to and fro linear displacements exposing the equipment to more extensive wear and tear than in the case of an inter- swivelling sharpening element action. (4) 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 blade sharpener, according to the invention, in the form of a precision knife sharpener in side elevation,

Figure 2 shows the knife sharpener in the direction of arrow A in figure 1 ,

Figure 3 shows in general exploded side elevation view the mechanism for limiting the extent of swivelling and for biasing cutting edge presenting carriers in the form of sharpening blades forming part of the sharpener toward a condition of minimum inter-blade swivelling,

Figure 4 explains the development of the curvature of a sharpening blade for achieving the maintenance of a constant sharpening angle along a sharpening path formed between the blades of the sharpener, and

Figure 5 shows the operation of the knife sharpener.

(5) DETAILED DESCRIPTION OF THE DRAWING

Referring to figures 1 , 2 and 5 of the drawings, a blade sharpener, according to the invention, in the form of a precision knife sharpener, is generally indicated by reference numeral 10.

The sharpener 10 comprises two cutting edge presenting carriers in the form of convexly extending cutting edge presenting sharpening blades 12 that are mounted to a carrier base 14 to swivel generally scissors type action in a contiguous relationship about a common axis 16 in forming an acute angle inter- carrier sharpening location 18 of which the positioning depends on the extent of inter blade swivelling, limiting means in the form of a stop layout 20 for limiting the extent of swivelling of the blades 12 and biasing means in the form of a spring configuration 22 by means of which the blades 12 are biased into extending away from the base 14 into a condition of minimum inter-blade flaring, as shown in figures 1 and 5(a).

The sharpener 10 further comprises carrier base mounted blade carrying equipment guiding means in the form of a swivelling zone bordering facility found along linear sections 24 extending along facing swivelling zone bordering formations in the form of base anchored loop shaped formations 26. A guide path, as bridging the spacing between the sections 24, is defined along the outer faces of the linear section 24 that in conjunction with the sharpening location 18 define a blade carrying equipment sharpening path 28. The blades 12 are at least substantially identical and are mounted in a mirror image symmetrical relationship with respect to a central axis 30 along which the blade carrying equipment sharpening path 28 also extends. The degree of curvature of the cutting edges 32 of the blades 12 are selected, as discussed below, to maintain a constant inter blade sharpening angle 34 along the sharpening path 28.

The blades 12 are constrained by the stop layout 20 to swivel between an outer inter-carrier sharpening angle location position as coinciding with the condition of minimum inter blade flaring, as again shown in figures 1 and 5(a), and an inner-inter carrier sharpening angle location position as coinciding with the condition of maximum inter-blade flaring as shown in figure 5(c). The sharpening path 28 thus extends between the conditions of minimum and maximum inter-blade flaring.

In more specifically referring to figures 2 and 3 the inner ends of the blades 12 end in hollow discs 36. The one disc 36.1 is formed with an outside boss 38 and an inside bush 40 mounted about the central axis 42 of the blade, disc, bush and boss unit 44. The other disc 36.2 is also formed with an outer shaft section 46 and an inner boss 48 that fits the bush 40 once the blades 12 are assembled into forming a blade assembly 50. The section 46 journals rotatably in a seat 52 forming part of a flange 54 by means of which the blade assembly 50 is anchored to the inside of the base 14 while the outside end of the boss 38 is accordingly journalled to the oppose side of the base 14. The assembly 50 also incorporates a spring configuration 22 in the form of a torsion type spring facility 56 fitted with radial pegs 58 that co-act with reaction points (not shown) within the discs 36 in urging the blades 12 into their condition of minimum flaring. The stop layout 20 incorporates a stationary stop formation 60 extending off centre from the flange 54 and through a slot in the disc 36.2 of which the length defines the extent of swivelling of its blade 12. Its free end is interspaced between suitably placed stop formations 64 within the other disc 36.1 in defining its extent of swivelling. The formation 60 also interacts with the torsion spring facility 56 to ensure that the blades 12 in addition to being urged into their conditions of minimum inter flaring are also urged into extending away from the base 14 about the central axis 30.

The overall effect of the assembly 50 once mounted is that the blades 12 are urged by the torsion type spring facility 56 into both their conditions of minimum inter flaring and extension about the axis 30 while the stop layout 20 limits each's extent of swivelling. While the way of regulating the urging and the extent of swivelling of the blades 12 are extensively discussed it will be appreciated that any suitable mechanism will suffice. The extent of swivelling of the individual blade units can for example be limited by end stops extending from the inner wall of the housing serving as stop points for a blade unit mounted stop while simple coil springs can be used to urge the blades 12 to a condition of extending about the axis 30.

In referring specifically to figure 4 the development of the curvature of the cutting edges 32 of the blades 12 for achieving the maintenance of a constant sharpening angle along a sharpening path 28 is achieved by developing a curved path 66 of which the angle 68 at any position there along between the radial line 70 and the tangential 72 is constant representing one half of the constant inter blade sharpening angle 34.

The sharpener 10 is of portable character being arranged for secure holding during a blade sharpening action by way of an integral handle 74 by means of which the sharpener 10 is held and urged against an operating base once in use during which action the axis 30 extends upright enabling the performance of an overhead blade sharpening action.

In more particularly referring to figure 5 a knife blade sharpening action commences by manually positioning the blade 76 of a knife within the outer sharpening location 8.1 along the sharpening path 28 as shown in figures 5(a) and 5(b) while holding the sharpener 10 by way of its handle 74 with the other hand against a working surface. The sharpening action proceeds conventionally by reciprocating the blade 76 and simultaneously moving it to and fro along the sharpening path 28, as shown through figures 5(c) and 5(d). A typical sharpening action will involve a cyclical routine involving the forward and downward motion of the blade 76 as indicated by arrows 78 and 80 in moving between figures 5(a), 5(b) on the one hand, and figures 5(c), 5(d), on the other hand, and a retraction and upward motion thereof between figures 5(c), 5(d), and figures 5(a), 5(b) along arrows 82 and 84.

Owing to the specific pre-selected curvature of the cutting edges 32 the angle of the inter carrier sharpening location 18 remains substantially constant between the outer and inner sharpening location positions 18.1 and 18.2 irrespective of its position along the sharpening path 28 ensuring the attainment of a very accurate blade sharpening effect in using the sharpener 10 of the invention.

It is an advantage of the invention as specifically described that a precision sharpening action is attained while using an inter-blade swivelling action effect.