GB2165782A - Sharpening device for secateurs, loppers and pruning knives - Google Patents

Abstract

The sharpening device (10) comprises a clamp (13) to hold the blade (11) to be sharpened, an elongate spade-shaped member (14) having a pad (16) of abrasive material attached to the broader end portion of member (14), and a support limb (15) provided with a series of apertures (17) along it, the rod-like end portion (18) of the elongate member (14) extending, with clearance, through a selected one of the apertures (17) so as to be supported by it for longitudinal reciprocal movement relative to the blade (11) held fast in the clamp (13) for grinding contact by said abrasive material (16). <IMAGE>

Description

SPECIFICATION Sharpening means This invention relates to sharpening means, particularly (but not exclusively) to blade sharpeners for sharpening the blades of secateurs (both long-handled secateurs for tow-hand operation and shorthandled secateurs for one-hand operation), loppers, and pruning knives.

The above-mentioned implements have blades provided with cutting edges of varying shape. For example, the shape may be straight following a straight line or may be curved, the curve following a single arcuate (circular or oval) path or following a double arcuate (or S-shaped) path. Furthermore, whatever the shape of the blade's cutting edge in the plane of the blade, the angle of inclination of that cutting edge normal to to the plane of the blade varies widely, e.g. from aproximately 25 to 60 .

Abrasive stones are available on the market which can be used to re-sharpen the cutting edge of a blade when it becomes blunt. However considerable skill is required in using such abrasive stones to effect re-sharpening to the correct angle originally provided by the manufacturer of the implement. This is especially so in the vicinity of the pivot pin (or hinge) interconnecting the two blades of the implement.

It is therefore considered desirable to provide blade sharpening means which can be used to resharpen blades, e.g. of the aforesaid implements, easily accurately and without the need for dismantling of the implement.

According to one aspect of this invention there is provided blade sharpening means comprising means to hold a blade to be sharpened, an elongate member having abrasive material at one end portion thereof, and support means to support the other end portion of the elongate member for longitudinal reciprocal movement of said member relative to a blade held in the first-mentioned means for grinding contact by said abrasive material.

Preferably said support means is fast with the holding means and in use supports the elongate member for longitudinal reciprocal movement relative to the support means.

Said support means may be adjustable in height, e.g. be telescopic or otherwise extensible in length.

Preferably said support means provides a plurality of support locations for the elongate member, said support locations being spaced perpendicularly away from the holding means by different distances to provide selectively different angles of inclination betwen the abrasive material and the blade held in said holding means.

Preferably said support means comprises a limb extending away from the holding means. Advantageously as said limb extends in use away from the holding means it also extends towards the edge of the blade held in said holding means.

Preferably said plurality of support locations are provided by a plurality of apertures spaced apart longitudinally of said limb. Advantageously said apertures are circular holes, Alternatively said apertures may be of oval or of slot-like form. In either case the apertures may be countersunk at least on the limb surface in use facing the blade held in the holding means.

Preferably said holding means comprises a clamp device.

Advantageously, the clamp device comprises two clamping elements pivotally interconnected at one end, the said limb being fast with one of said two clamping elements adjacent said one end.

By way of non-limiting example, embodiments of this invention will now be described with reference to the accompanying drawings, of which Figure 1 is a perspective view of sharpening means according to one embodiment of this invention in use with a pair of secateurs, Figure 2 is a side view of the sharpening means illustrated in Figure 1, Figure 3 is a front view of part of sharpening means according to another embodiment of this invention, and Figure 4 is a side view of the sharpening means of Figure 3.

The sharpening device 10 of Figures 1 and 2 is for sharpening the blade 11 of a pair of short-handled secateurs 12 that can be gripped in the hand for one-hand operation. The sharpening device 10 comprises a clamp 13, an elongate generally spade-shaped member 14, and a support limb 15.

The clamp 13 is to hold the blade 11 to be sharpened. The elongate spade-shaped member 14 has a pad 16 of abrasive material attached to its broader end portion. The support limb 15 is provided with a series of apertures 17 along it. The rod-like end portion 18 of the elongate member 14 extends, with clearance, through a selected one of the apertures 17 so as to be supported by it for longitudinal reciprocal movement relative to the blade 11 held fast in the clamp 13 for grinding contact by said abrasive material 16. Opposite the abrasive pad 16, the broader end portion of the elongate member 14 is provided with an upwardly projecting flat plate 20 of D-shaped outline. This plate 20 is gripped between the user's thumb and forefinger when the elongate member 14 is to be reciprocated (arrow A, Figure 1).

The clamp 13 comprises two clamping elements 21, 22 molded of plastics material. The upper element 21 is molded integrally or otherwise firmly attached to a block 23 forming the root of upstanding support limb 15, the limb 15 and element 21 preferably having an included angle between them of between 70 to 85 , e.g.77 . Thus, as limb 15 extends upwardly away from the clamp 13 it also extends towards the edge 1 1a of the blade 11 held in the clamp 13. This angled arrangement enables the limb 15 to withstand the increased pressure which may be required to resharpen a blade of hard, high quality steel. Preferably said limb 15 and the block 23 from which it projects are molded integrally with one another of plastics material.Thus the elongate member 14 is in use supported for longitudinal reciprocal movement relative both to the supporting limb 15 and to the clamp 13 of the sharpening device 10.

The bottom of block 23 is shaped to provide snap-fit connector means for a circular-section transverse bar 22a molded integrally with the lower clamping element 22. This snap-fit connector means serves to interconnect pivotally the two clamping elements 21,22 at their ends remote from the intended blade clamping region of clamp 13. A threaded fastener 24, comprising a nut and bolt, is located between the opposite ends of the clamp 13 and extends across the two clamping elements 21,22 for effecting mutual approach and separation of the two elements to achieve clamping and release of the blade 11.

In the embodiment of Figures 1 and 2, the apertures 17 are circular holes, successive holes increasing in size, i.e. diametric extent, as the limb 15 extends upwardly away from its root block 23 and from the clamp 13. The apertures 17 are each of greater diameter than the diameter of rod-like portion 18, and may be countersunk at least on the limb surface in use facing the blade 11 held in the clamp 13. Preferably such countersinking is provided on both surfaces.

In use, the secateurs 12 are opened wide and, by means of clamp 13, the device 10 is clamped onto the rear edge of the blade 11 to be sharpened, the device being positioned approximately mid-way along the blade and such that the blade's cutting edge 1 lea projects out of the clamp. The rod-like portion 18 of the elongate member 14 is then inserted into the topmost and largest one of the circular apertures 17 in limb 15 and the abrasive pad 16 rested lightly against the cutting edge 11a.

Viewing the arrangement from the side will enable the user to determine whether the angle between the blade and the abrasive pad is correct or appropriate. Alternatively, the user can effect a trial sharpening over a small area and then check if the blade angle over this newly-sharpened area matches up with that of the remainder of the blade. In either case, if the angle is too great, the member can be withdrawn from the uppermost aperture 17 and inserted selectively into a lower one before the checking procedure is repeated.It will be noted in this regard that the grinding angle 6 may be varied selectively in this way and is given by the formula: tan (3 = HID where D is the distance from the blade edge 11a to a point perpendicularly below the selected location of support for member 14 provided by limb 15, and H is the perpendicular distance from the said point to the said selected support location.

Preferably the grinding angle 6 is thus selectively 28 or 37 or 47" or 57 . These angles are believed to cover the vast majority of secateurs currently on the market in the United Kingdom.

With the grinding angle appropriately selected, the plate 20 of member 14 is gripped and the member longitudinally reciprocated to re-sharpen the edge. The reciprocal motion is executed not only in the vertical plane containing limb 15 and clamp 13, but also in vertical planes at varying angles thereto but still containing the same support location. In this way the whole length of the blade's cutting edge 11a may be re-sharpened.

It will be appreciated that, where the shape of that edge is not curved in a circular arc concentric with the support location (i.e. is not of radius D), reciprocal grinding motion in the vertical planes away from that containing limb 15 and clamp 13 will tend to increase the distance D and thus tend to decrease the grinding angle 6. However, by providing the apertures 17 as circular holes - of progressively increasing size - the rod-like portion 18 of member 14 tends to ride laterally up the curved edge of the hole through which it passes as the vertical plane of the member's reciprocal motion moves away from coincidence with limb 15 and clamp 13.This upward movement of the support location in effect increases the distance H which tends to compensate for the increase in distance D such that the grinding angle 6 remains largely unaffected by such angular movement of the grinding plane, i.e. the selected grinding angle 6 remains substantially constant.

Preferably the pad 16 is maintained moist during grinding operations.

In a number of experiments, it has been found that, in general, a blade can be quickly resharpened by the above-described device and method, e.g. in just a few minutes. This is readily determined as soon as a slight burr appears on the underneath face of the blade. This slight burr may be removed by withdrawing the member 14 from the limb 15 and wiping the abrasive pad 16 just once or twice in face-to-face abutment over this underneath surface to conclude the sharpening procedure.

It will be noted that due to the narrow width and depth dimensions of the spade-shaped member 14, it is possible to effect grinding right in towards the pivot pin of the secateur blades. Furthermore it will be appreciated that if the blades are particularly long, the sharpening device 10 may be initially clamped in position say one-third of the way along the blade and, after sharpening the blade edge in the vicinity of this clamping position, the sharpening device is unclamped and then re-clamped in a new position to enable sharpening of one or more further stretches of the blade.

The embodiment illustrated in Figures 3 and 4 is substantially similar to that described above but differs therefrom primarily in the following respects. The two elements 31,32 of the clamp device 33 function similarly but the lower element 32 is now molded integrally with the base of the upr standing and forwardly inclined support limb 35, the angle between them being preferably about 75 . The limb 35 is provided near its base with a rectangular cut-out 39 to receive a tongue 36 that projects rearwardly from the upper clamping element 31. This tongue-and-cutout arrangement 36,39 provides for the pivotal interconnection of the clamping elements 31,32. Apertures 37 in limb 35 are selectively to receive therethrough, and provide support for, the rod-like portion 38 of the elongate spade-shaped member 34. These apertures 37 have the form of horizontally extending slots which allow for wide lateral movement of the member 34 and thus facilitate re-grinding of the whole length of the blade 10 in one (or at most two) grinding operations. Preferably, said slot-like apertures 37 have rounded (e.g. oval or semi-circular) ends to provide the angle compensation tendency referred to above in connection with the embodiment of Figures 1 and 2. Optionally these apertures 37 may alternatively or additionally be countersunk on at least the limb surface facing the clamp's jaws.

Claims (16)

1. Blade sharpening means comprising means to hold a blade to be sharpened, an elongate member having abrasive material at one end portion thereof, and support means to support the other end portion of the elongate member for longitudinal reciprocal movement of said member relative to a blade held in the first-mentioned means for grinding contact by said abrasive material.

2. Blade sharpening means according to Claim 1, wherein said support means is fast with the blade holding means and in use supports the elongate member for longitudinal reciprocal movement relative to the support means.

3. Blade sharpening means according to either preceding Claim, wherein said elongate member is supportable by said support means in any one of a plurality of differing angular attitudes to a blade held in said holding means

4. Blade sharpening means according to any preceding Claim, wherein the said support means is adjustable in height.

5. Blade sharpening means according to Claim 4, wherein the said support means is telescopic or otherwise extensible in length.

6. Blade sharpening means according to any one of Claims 1 to 3, wherein said support means provides a plurality of support locations for the elongate member.

7. Blade sharpening means according to any preceding Claim, wherein said support means comprises a limb extending away from the holding means.

8. Blade sharpening means according to Claim 7, wherein said limb is positioned such that as it extends in use away from the holding means it also extends towards the edge of the blade held in said holding means.

9. Blade sharpening means according to either of Claims 7 and 8 when dependant from Claim 6, wherein said plurality of support locations are provided by a plurality of apertures spaced apart longitudinally of said limb, the said elongate member being insertable selectively into any one of said apertures.

10. Blade sharpening means means according to Claim 9, wherein the bottom boundary of each of said apertures rises progressively towards the sides thereof.

11. Blade sharpening means according to Claim 9 or Claim 10, wherein said apertures are circular holes.

12. Blade sharpening means according to Claim 9 or Claim 10, wherein said apertures are of oval or of slot-like form.

13. Blade sharpening means according to any one of Claims 9 to 12, wherein each of the apertures is countersunk at least on the limb surface in use facing the blade held in the holding means.

14. Blade sharpening means according to any preceding Claim, wherein said holding means comprises a clamp device.

15. Blade sharpening means according to Claim 14 when dependant (directly or indirectly) from Claim 7, wherein the clamp device comprises two clamping elements pivotally interconnected at one end, the said limb being fast with one of said two clamping elements adjacent said one end.

16. Blade sharpening means substantially as herein described with reference to and/or as ill use trated in Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.