EP2437915B1

EP2437915B1 - Sharpener for cylinder lawnmower blades

Info

Publication number: EP2437915B1
Application number: EP10755217.6A
Authority: EP
Inventors: David Anthony Edgerley
Original assignee: Albrion Sales Ltd
Current assignee: Albrion Sales Ltd
Priority date: 2009-06-01
Filing date: 2010-05-28
Publication date: 2014-03-19
Anticipated expiration: 2030-05-28
Also published as: WO2010139986A2; WO2010139986A4; GB0909336D0; WO2010139986A3; EP2437915A2

Description

This invention relates to sharpeners for cylinder lawnmower blades.
A standard form of lawnmower cuts the grass by interaction between a series of helical blades which are mounted on a rotating member and which cooperate with a counterblade mounted on the underside of the lawnmower structure. As the set of helical blades rotates, a scissoring action occurs between each of the helical blades and the counterblade to cut the grass or lawn. The height of the cut is determined by the adjustment of the rollers supporting the mower, and the evenness of the cut depends on the spacing of the helical blades in a circumferential direction.
As the mower is used, the blades wear and the efficiency of cutting is correspondingly reduced.
It is accordingly desirable to provide means whereby the blades may be sharpened, and a number of devices have been disclosed for this purpose in the patent literature. GB-A-1514615 , GB-A-1588045 , GB-A-1588046 and GB-A-2029736 are examples of such disclosures. EP-A-1384551 discloses a sharpening attachment for a lawnmower of the cylinder type where the counterblade is of substantially J-shaped cross-section. The sharpening attachment consists of a T-section strip with an abrasive upper surface. Means are provided to hold the strip above the edge of the J-section bottom blade. This may be effected in particular by forming the vertical portion of the T-section as a C-shaped cross-section channel which can be engaged by fastening means which hold the abrasive-surfaced strip in the desired position.
A problem with the sharpening attachment disclosed in the specification referred to above is that it is not always easy to position it on the counterblade on a number of cylinder mower designs before sharpening.
In accordance with the present invention, apparatus for sharpening the rotatable blades of a cylinder mower where the rotatable blades co-act for cutting with a cutting edge of an elongate fixed counterblade of J- or L-shaped cross-section, wherein the cutting edge is formed on that portion of the counterblade projecting from a flat portion thereof to provide the J- or L-section comprises at least one clip and an elongate member, the elongate member having an abrasive surface on one side and, on the other side engagement means adapted to engage with the clip(s) in a fashion enabling the clips to hold the elongate member against the counterblade with an edge of the elongate member lying along the side of the counterblade from which the cutting edge projects, is characterised by location means as set out in the main claim.
Preferably the location means is a ridge extending along part or all of the elongate member.
Preferably the elongate member is an extruded section. Preferably the engagement means is a key-configuration cross-section extending from the side of the elongate member opposite the side provided with an abrasive surface. Preferably the key-configuration cross-section is configured to engage with the clip at two or more different positions.
Preferably the side of the elongate member having an abrasive surface is slightly convex. This assists in ensuring that as the cylinder with the helical blades rotates during sharpening, the blades contact the abrasive surface inboard of its edges, even if there is variation in the exact angle (measured about an axis running along the edge of the counterblade) between the sharpening apparatus and the edge of the counterblade against which it is mounted. However, if the width of the elongate member is sufficient to ensure the helical blades do not contact the edge of the elongate member, the abrasive surface may be flat or even slightly concave (but having a radius of curvature of any such concavity greater than the radius of the cylinder).
In use of the sharpener apparatus according to the invention, the ridge on the elongate member sits behind the cutting edge of the mower counterblade with the edge of the counterblade lying between it and the engagement means.
The invention is illustrated, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic cross-section of apparatus according to the present invention through the elongate member and through a clip;
Figure 2 is a perspective view of the apparatus seen from one side;
Figure 3 is a perspective view of the apparatus the other way up from the view in Figure 2;
Figure 4 is a diagrammatic cross-section analogous to Figure 1 but showing the apparatus engaged on the counterblade of a first type of cylinder mower, and
Figure 5 is a view like Figure 4 but showing a different design of counterblade.

Referring first to the device shown in Figures 1 to 3, this consists basically of three parts, an extrusion 1, and two clips 2 each of which fits into the extrusion 1. Each clip 2 has a tightening screw 3 which fits into a threaded hole in the body of the clip 2.
One side of the extrusion 1 carries a strip of abrasive material 4 while, on the side opposite strip 4, there is a key configuration channel 5 and a ridge 6- As can be seen, each clip 2 has a portion with an external key configuration which fits into channel 5 on the extrusion 1. The extrusion has open ends allowing the clips to be slid in and moved along the extrusion to a suitable location, for example a quarter and three quarters along the length of the extrusion.
Figure 4 shows how the apparatus may be fitted against a counterblade 8 of a cylinder mower. Figure 4 shows the orientation of the mower when the sharpening device is being fitted. This is upside down compared to the normal orientation of the mower in use. Before fitting, the screws 3 are loosened off and the counter blade itself moved away from the rotatable helical-bladed cylindrical member (raised as shown in Figure 4, where the mower is upside down to provide clearance for the edge of the extrusion remote from channel 5 to be inserted between the counterblade 8 and the helical blades on the cylindrical cutter of the mower. Insertion is continued until the edge of the counterblade 8, denoted 9 in Figure 4, comes to lie between the ridge 6 and one wall of the key configuration channel 5, with the edge of extrusion 1, denoted 10, lying against the generally flat portion of blade 8. The extrusion 1 is then held tightly against the end of the counterblade 8 by turning screws 3 in clips 2, with the abrasive surface 4 on the lower side of extrusion 1 as shown in Figure 4.
The path and direction travelled by the edges of the helical blades on the rotating cylindrical cutter forming part of the mower is denoted in Figure 4 by dashed line 11 and arrow 12. As can be seen, this is tangential to the abrasive surface 4 and accordingly, when the blade 8 is moved into a position which is close to its normal cutting position but slightly spaced therefrom (by the thickness of extrusion 1), as the helical blades rotate, they will be drawn across the surface of the abrasive strip 4 and accordingly sharpened. The convex shape of the abrasive surface assists the smooth running of the helical blades across it (the convex shape (tangent to tangent line of contact) means that the sharpener can sharpen a much greater variety of counterblade/cylinder arrangements than if the abrasive surface was flat - different counterblade sections means that the extrusion, located by two lines of contact, one on the cutting edge of the counterblade and one on the flat of the counterblade some distance behind the cutting edge, can be oriented at a range of angles in relation to the cutting cylinder whilst still offering up the abrasive to the rotating cylinder so that the line of contact between abrasive and rotating cylinder falls well within the width of the abrasive strip), and the pressure exerted by the blades on the strip pushes the extrusion 1 towards the counterblade 8 so that it sits tightly on the counter blade supported between the engagement means and ridge 6, with the lateral force caused by the blades passing across the abrasive surface being taken up by the wall of the key configuration channel of the extrusion itself and not transferred to the clips, which can accordingly be made of relatively weak mechanical strength material, e.g. plastics.
In order to effect sharpening, the rotating helical blade arrangement must be rotated. In the case of an electrically powered mower, this can be easily achieved by simply actuating the motor which turns the blades. In the case of a manually powered mower, where the rotation of the helical blades is derived usually using a gear driven by the rotation of a ground-engaging roller or side wheels in order to sharpen the blades, the mower is oriented in its customary mowing position and pushed along, so rotating the helical blades and sharpening them as they pass over the layer of abrasive located where they would normally engage against the blade 8 in a shearing action.
In such a case, it is important to ensure that the head of fixing screw 3 is not dragged along the ground, and in order to achieve this, the mower should be set, usually by lowering a rear roller assembly, to its highest cut setting. Additionally, the length of screw 3 can be kept to a minimum, while still enabling the apparatus to be fitted to a wide variety of models of cylinder mowers, by enabling clip 2 to be inserted into channel 5 at different depths. In Figure 4, clip 2 is fully inserted into channel 5. However, in the arrangement shown in Figure 5, the apparatus is fitted to a counterblade 19 which is set on a triangular spar 20, the assembly of blade 19 and spar 20 being of substantially greater depth than the simple bent counterblade 8 shown in Figure 4. To compensate for this, the clip 2 is only partly inserted into channel 5, enabling a screw 3 to be used of the same length as is shown in Figure 4.
At the end of sharpening, rotation of the helical blades is stopped, the counterblade lowered slightly, screws 3 loosened, the apparatus of the invention slipped off the counterblade, and the counterblade then raised until it cooperates with the helical blades with a smooth scissor action.
The length of the extrusion should be chosen to correspond with the width of the helical blades, i.e. the width of cut of the mower. Generally mower models come in a relatively small number of standard widths, so the apparatus of the invention may be made in a set of matching widths, or the extrusion may be long enough to cover the maximum axial blade length encountered on the cylindrical cutter, and instructions given to hacksaw off any extra before first use.

Claims

Apparatus for sharpening the rotatable blades of a cylinder mower where the rotatable blades co-act for cutting with a cutting edge (9) of an elongate fixed counterblade (8) of J- or L-shaped cross-section, wherein the cutting edge (9) is formed on that portion of the counterblade (8) projecting from a flat portion thereof to provide the J- or L-section, the apparatus comprising at least one clip (2) and an elongate member (1), the elongate member having an abrasive surface (4) on one side and, on the other side, engagement means (5) being adapted to engage with the clip(s) (2) in a fashion enabling the clip(s) (2) to hold the elongate member (1) against the counterblade (8) with an edge (10) of the elongate member (1) lying along the side of the counterblade from which the cutting edge projects, and characterised by location means (6) adapted to locate the elongate member (1) relative to the cutting edge (9) of the counterblade (8) with the location means (6) when the elongate member (1) is held against the counterblade (8) lying against the counterblade (8) to the rear of the cutting edge thereof and the cutting edge of the counterblade lying against the engagement means (5).
Apparatus according to Claim 1 wherein the location means (6) is a ridge extending along at least part of the elongate member (1).
Apparatus according to Claim 1 or 2 wherein the elongate member (1) is an extruded section.
Apparatus according to any one of Claims 1 to 3 wherein the engagement means (5) is a key-configuration cross-section extending from the side of the elongate member (1) opposite the side provided with an abrasive surface (4).
Apparatus according to any one of Claims 1 to 4 wherein the key-configuration cross-section (5) and the clip(s) (2) may be engaged with one another in two or more different positions.
Apparatus according to any one of Claims 1 to 5 wherein the abrasive surface (4) is slightly convex.