AU3915999A - Lawnmower blade - Google Patents

Description

S F Ref: 471930

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

r Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Sunbeam Corporation Limited Wade Street Campsie New South Wales 2194

AUSTRALIA

David Paul Seidel and Patrick Anthony Doyle Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Lawnmower Blade ASSOCIATED PROVISIONAL APPLICATION DETAILS [311 Application No(s) [33] Country PP4777 AU [32] Application Date 21 July 1998 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815 LAWNMOWER BLADE Technical Field The present invention relates to lawnmowers, and in particular relates to a lawnmower blade.

Background of the Invention Particular forms of current lawnmower blades are pivotally mounted to a blade mounting disc and extend outboard therefrom, with a cutting edge being disposed toward the outboard end of the leading edge of the blade. The trailing edge of such a blade is typically upturned toward the outboard end to form a grass deflecting portion aft of the cutting edge to deflect grass cut by the cutting edge into a grass catcher.

The junction between the grass deflecting portion and the flat portion of blade lying immediately aft of the cutting edge is typically a relatively sharp angle with a radius joining the two portions of only about 10 mm. During use, grass clippings which have been cut by the cutting edge are impacted heavily by the grass deflecting portion which acts as a bluff body, the impacted grass cuttings bouncing off the deflecting portion and being thrown into the catcher. Softer and wetter type grasses get reduced to a sticky mass as a result of this impact and get stuck to the underside of the mower base plate, further increasing the difficulty of catching such grasses. The bluff o body presented by the grass deflecting portion also effects the air flow over the blade reducing the airflow through the catcher which is relied upon to efficiently convey the grass cuttings.

The sharp radius at the base of the grass deflecting portion forming the grass deflecting portion as a bluff body also results in excessive wear on the blade, particularly when used under abrasive conditions such as with sandy soils. Sand particles impact heavily on the base of the grass deflecting portion which can eventually result in the grass deflecting portion breaking away from the remainder of the blade with potentially hazardous effect on the operator or any bystander.

[N:\LIBLL]01814:GJG:TCW 2 The trailing edge of known lawnmower blades typically extends from the inboard end flat along a plane on which the blade is mounted to a blade mounting disc before rising sharply at the inboard end of the grass deflecting portion from where it continues rising in a straight line toward the blade outboard end. The sharp juncture between the flat inboard section of the trailing edge and the rising outboard section can cause the blade to jam underneath the blade mounting disc if the blade is deflected rearwardly during use when it impacts a heavy object, such as a rock, in its path. The current configuration can also increase noise generated by the blade as a result of the increased height of the trailing edge which increases in height along a straight line to an apex at the outer end.

Known lawnmower blades generate high levels of noise, largely as a result of the interaction of air flow about the outboard end of the blade with the blade housing at the base of the lawnmower. Whilst attempts have been made to abate this source of noise, further improvements would be advantageous.

Current designs of pivoting blades typically provide for the cutting edge to extend generally parallel to a radius of the mounting disc passing through the blade pivot axis when the blade is in an equilibrium position under the action of centrifugal force acting on the blade alone. Any impact on the blade leading edge, be it minimal impact of grass being cut or larger impact forces generated when striking a heavy object 20 such as a rock, displaces the blade aft of this equilibrium position. Depending on the impact force, large displacements aft of the equilibrium position with the cutting edge parallel to the radius are incurred before the restoring moment generated by the centrifugal force moves the blade back toward the equilibrium position. As a result the o o blade may be aft of the desired parallel position during much of its period in use.

When lawnmower blades impact a hard object, such as a rock, in use, the blade, as well as being displaced rearwardly, is forced upward. As the blade is mounted underneath the blade mounting disc and the upper surface of the inboard end of the blade abuts the mounting disc, the blade tends to bend upwardly about the edge of [N:\LIBLL]01814:GJG:TCW the disc. Repeated bending of the blade about this point causes fatigue damage to the blade which may result in premature failure of the blade adjacent the edge of the disc.

Object of the Invention It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages.

Summary of the Invention There is disclosed herein a lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and a blade grass deflecting portion extending rearwardly and upwardly from said blade outboard leading portion to an outboard section of said trailing edge, wherein said blade outboard leading portion merges into said blade grass deflecting portion with a radius of at least 25 mm at all positions along a junction therebetween on said upper face.

Preferably, said radius is between 32 mm and 41 mm at all said positions along said junction.

Preferably said blade grass catching portion is inclined at an angle of between •50 and 60 degrees to said blade outboard leading portion at all positions on said grass deflecting portion at said trailing edge outboard section.

~There is disclosed herein a lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing 25 edge, said lawnmower blade including: •a cutting edge formed along an outboard section of said leading edge, a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and [N:\LIBLL]01814:GJG:TCW a blade grass deflecting portion extending rearwardly and upwardly from said blade outboard leading portion to an outboard section of said trailing edge, wherein an inboard length of the boundary of said upper face defined by said trailing edge lies in a mounting plane, said mounting plane being perpendicular to a pivot axis about which said blade is adapted to pivot, said boundary being smooth and continuous outboard of said inboard length, said inboard length smoothly merging with a concave length of said boundary disposed immediately outboard thereof, a convex length of said boundary being disposed outboard of said concave length.

Preferably said convex and concave lengths are separated by a straight intermediate length of said boundary.

Alternatively said convex and concave lengths are directly linked at a point of inflection.

Preferably said concave length extends at least partway along said outboard section of said trailing edge.

Preferably a straight outboard length of said boundary extends from said concave length to said outboard end.

Preferably said convex length has a radius in excess of 30 mm.

There is still further disclosed herein a lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and 20 a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, "a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and ooo• 999 ~a blade grass deflecting portion extending rearwardly and upwardly from said 9999 25 blade outboard leading portion to an outboard section of said trailing edge, and at least two notches provided in said grass catching portion at said outboard 9 96 end and extending inboard.

Preferably each of said notches is of a type configuration.

[N:\LIBLL]01814:GJG:TCW

M

Preferably each of said notches extends inboard from said outboard end a distance of approximately 4 mm.

Preferably each of said notches has a width measured along said outboard end of approximately 8 mm.

Preferably each of said notches is separated at said outboard end by a distance of between 3 and 6 mm.

More preferably each of said notches is separated at said outboard end by a distance of between 4 and 5 mm.

There is yet further disclosed herein a lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, a pivot axis disposed toward said inboard mounting end about which said blade is adapted to be pivotally mounted on a blade mounting disc, a mounting support region adapted to abut and thereby be supported by said mounting disc when said blade is in an equilibrium in use pivotal position, the remaining region of said blade outboard of said mounting support region being unsupported when said blade is in said equilibrium pivotal position, wherein the centre of mass of said unsupported region is disposed further S 20 rearwardly from said cutting edge than is said pivot axis, a line passing through said unsupported region centre of mass and said pivot axis subtending an angle of at least U degrees with said cutting edge.

Preferably said angle is between 5 and 10 degrees.

•There is further disclosed herein a method of enhancing the mean fatigue life of a batch of lawnmower blades formed from blanks cut from strips of metal, said strips having been slit from a sheet of metal, including the steps of: slitting a sheet of metal into a plurality of strips each having the width of a lawnmower blade blank with a shear slitting means engaging one side of said sheet, [N:\LIBLL]01814:GJG:Tcw feeding each said strip into a blank cutting die, ensuring said one side is arranged so as to form, in use, a lower face of each blade, cutting each said strip into a plurality of blanks with a shear cutting means engaging said one side of each said strip, forming each said blank into a lawnmower blade with said one side forming said lower face of each said blade.

There is also disclosed herein a lawnmower blade produced according to the above method.

Brief Description of the Drawings Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a lawnmower blade.

Figure 2 is a plan view of the lawnmower blade of Figure 1.

Figure 3 is a front elevation view of the lawnmower blade of Figure 1.

Figure 4 is a side view of the lawnmower blade of Figure 1 from the outboard end thereof.

~Figure 5 is a side view of the lawnmower blade of Figure 1 from the inboard mounting end thereof.

o S.o Figure 6 is a rear elevation view of the lawnmower blade of Figure 1.

Figure 7 is an inverse plan view of the lawnmower blade of Figure 1.

Figure 8 is a perspective view of a blade mounting disc and lawnmower blade S arrangement.

~Figure 9 is a fragmentary plane view of the arrangement of Figure 7.

des.

Figure 10 is a fragmentary cross section view of the arrangement of Figure 9 taken through section 10-10.

Figure 11 is a plan view of a lawnmower blank.

[N:\LIBLL]01814:GJG:TCW Detailed Description of the Preferred Embodiments The lawnmower blade 100 according to the preferred embodiment has upper and lower faces 101, 102 bounded by an inboard mounting end 110, an outboard end 120, a leading edge 130 and a trailing edge 140. A cutting edge 131 is formed along an outboard section of the leading edge 130. A blade outboard leading portion 132 extends rearwardly from the cutting edge 131 toward the trailing edge 140. A blade grass deflecting portion 142 extends rearwardly and upwardly from the blade outboard leading portion 132 to an outboard section 141 of the trailing edge 140.

The blade outboard leading portion 132 here merges into the blade grass deflecting portion 142 with a radius of at least 25 mm at all positions along a junction between the blade outboard leading portion 132 and the blade grass deflecting portion 142 on the blade upper face 101. The radius is preferably between 32 and 43 mm at all positions along the junction. Here the radius varies from approximately 34 mm at the outboard end 120 to approximately 39 at the inboard end of the blade outboard leading portion 132 and grass deflecting portion 142 immediately aft of the inboard end 13 la of the cutting edge 131. The intermediate trailing portion 143 of blade immediately inboard of the blade grass deflecting portion 142 is also turned up with respect to the remainder of the blade 100 and smoothly merges into the blade grass deflecting portion ooo 142 and the leading and inboard areas of the blade, the junction between the upturned o 20 intermediate trailing portion 143 and the leading and inboard areas of the blade here has a radius varying between 39 mm and 44 mm.

•The blade grass catching portion 142 is preferably inclined at an angle of between 50 and 60 degrees to the blade outboard leading portion 132 at all positions on V0°0 the grass deflecting portion 142 at the trailing edge outboard section 141. Here the blade grass catching portion 142 is inclined at approximately 55 degrees at the outboard end varying to about 52.5 degrees at its inboard end aft of the cutting edge inboard end 0:i 131a. Whilst the blade grass deflecting portion 142 is typically flat toward the trailing edge outboard section 141, it need not be, and may in particular be slightly concavely curved.

[N:\LIBLL]01814:GJG:TCW The preferred arrangement of the blade grass deflecting portion 142, particularly the generous radius merging with the blade outboard leading portion 132, provides for improved grass catching performance. Grass cuttings having been cut by the cutting edge 131 are relatively gently swept aft along the blade outboard leading portion 132, through the radius and up the face of the blade grass deflecting portion 142 to the trailing edge outboard section 141 from where it is thrown into the grass catcher.

The improved aerodynamic profile of this area of the blade, as compared to the generally bluff body arrangement of grass deflectors of prior art blades, provides a more streamlined airflow and greater lift to convey the grass cuttings into the catcher at a higher velocity and with lower noise generation, providing for increased capture of cuttings by mass, and increased compaction of the cuttings. The increased compaction of cuttings allows a greater mass of cuttings to be collected in the catcher prior to emptying. The grass catching improvements can be further enhanced by providing further venting in the catcher, allowing for increased airflow therethrough conveying the grass cuttings.

The generous radius between the blade grass deflecting portion 142 and the blade outboard leading portion 132 also reduces the impact load on the blade 100 of abrasive materials such as sand, thereby reducing the wear on the blade in abrasive ooooo environments.

20 A further advantageous preferred feature of the lawnmower blade 100 relates to the profile of the trailing edge 140, as perhaps best depicted in Figure 6. An inboard length 145 of the boundary 144 of the upper face 101 which is defined by the trailing edge, lies in a mounting plane MP. The mounting plane is perpendicular to a pivot axis P about which the blade 100 pivots when the blade is mounted on a blade mounting disc 200 as depicted in Figures 8 through 10. The inboard length 145 of the boundary 144 lies in the mounting plane MP so that it is not inhibited by the lower face of the blade omounting disc, against which the blade upper face 101 abuts in a mounting support region 111, as the blade 100 pivots during normal operation. The form of the inboard length 145 of boundary within the mounting plane is not of importance, and here is [N:\LIBLL]01814:GJG:TCW generally formed of two straight lines, 145a and 145b, formed obliquely to and parallel to the leading edge 130 respectively. The boundary 144 is smooth and continuous outboard of the inboard length 145. The inboard length 145 smoothly merges with a concave length 146 of the boundary disposed immediately outboard, gradually upturning the trailing edge 140. A convex length 147 of the boundary 144 disposed outboard of the concave length 146 curves the trailing edge 140 back downwardly. The convex 146 and concave lengths 147 of the boundary 144 may be separated by a straight intermediate length 148 of boundary, as depicted here, or they may be directly linked at a point of inflection. The concave length 147 here extends partway along the outboard section 141 of the trailing edge 140, but it may stop short of the outboard section 141 or alternatively extend up to the blade outboard end 120. If the concave length stops short of the outboard end 120, as in the depicted embodiment, a straight outboard length 149 of boundary is provided which extends beyond the concave length 147 to the blade outboard end 120. The convex length 146 should preferably have a generous radius in excess of 30 mm.

The preferred arrangement of the trailing edge 140, as described above in relation to the boundary 144 of the upper face 101 defined by the trailing edge 140, helps to prevent jamming of the blade 100 under the blade mounting disc 200 if the ooooo blade impacts a heavy object. The smooth merging of the inboard length 145 with the 20 concave length 146 allows the blade to readily pivot back upon impact without jamming a sharply rising length of the trailing edge of a prior art blade into the edge of the mounting disc 200. The convex length 147 of the boundary reduces the total height of the trailing edge 140, thereby reducing the noise generated thereby as airflow and grass Scuttings pass over.

To further reduce noise generated by the blade 100, particularly as a result of interaction between the blade outboard end 120 and the blade housing at the base of the a a..

lawnmower (not shown), two or more notches 121 may be provided in the grass catching portion 142 at the outboard end 120 and extending inboard. In the preferred embodiment depicted, two shaped notches 121 are provided. Each of the notches [N:\LIBLL]01814:GJG:TCW 121 extends inboard from the outboard end 120 by a distance of approximately 4 mm, and each has a width measured along said outboard end of approximately 8 mm. The notches 121 should preferably be separated at the outboard end 120 by a distance of between 3 and 6 mm, more preferably between 4 and 5 mm, to ensure an interaction therebetween effecting the airflow at the outboard end of the blade, breaking down the concentration of air shear and thereby reduce the noise generated by the blade interaction with the blade housing of the lawnmower. Here the notches 121 are separated by a distance of approximately 4.5 mm.

The overall blade length of 124 mm and thickness of 2 mm is typical for a standard 460 mm diameter cut of a domestic lawnmower, however the width of 57 mm is wider than prior art blades, and is approximately 12.5 mm wider than typical blades.

The increased width improves the rigidity of the blade 100 and reduces stresses generated by bending and impact loads.

A yet further advantageous preferred feature of the lawnmower blade 100 relates to the mass distribution of the blade. As discussed above, in use, the blade 100 is pivotally mounted on a blade mounting disc 200 as depicted in Figures 8 through about a pivot axis P disposed toward the inboard mounting end 110. A mounting support region 111 of the blade surrounding the pivot axis P abuts the lower face of the mounting disc 200 when the blade is in an equilibrium pivotal position (as depicted) 20 with respect to the mounting disc and is thus supported by the disc. The remaining region of the blade outboard of the mounting support region 111 is unsupported, extending from underneath the mounting disc 200 as a cantilever. This unsupported region of the blade has a centre of mass M. The depicted position of the unsupported 0 region centre of mass M as shown in the accompanying drawings is an approximation based on the centre of mass of the region of the blade outboard of the line shown in Figure 9, rather than the exact boundary of the unsupported region, marked as hidden detail in Figure 9, which is inboard of the absolute edge of the disc 200 as a result of the peripheral lip 201.

[N:\LIBLL]01814:GJG:TCW During operation, as the blade mounting disc 200 rotates, centrifugal force F acting on the blade 100 will act through the centre of mass M of the unsupported region. Without any load on the blade 200, the equilibrium position of the blade 200 will be with the unsupported region centre of mass M lying on a radial line passing through the axis of rotation R of the mounting disc through the blade pivot axis P. Any impact load acting on the leading edge 130 of the blade, be it a small impact load from grass being cut or a larger load from a heavy object, will tend to displace the blade 100 aft of this equilibrium position. The moment created by the centrifugal force F tending to bring the blade back to the equilibrium position will increase with increased displacement from the equilibrium position.

Here the centre of mass M of the unsupported region is disposed further rearwardly from the cutting edge 131 than is the pivot axis P, with a line passing through the unsupported region centre of mass M and the pivot axis P subtending an angle u. of approximately 7.6 degrees with the cutting edge as depicted in Figure 9. As a result, the equilibrium position of the blade 100 is with the cutting edge 131 leaning forward in the direction of rotation. Any impact load acting on the blade 100 will therefore tend to displace the blade aft toward a position where the cutting edge 131 is parallel to a radial line from centre R passing through the pivot point P, being a desired position of the blade for efficient cutting. At this position, a restoring moment is 20 created about the pivot axis P by the centrifugal force F tending to restore the blade 100 to its forwardly inclined equilibrium position, and inhibiting any further aftward 0a. displacement of the blade 100 beyond the desired parallel position.

For prior art blades with the equilibrium position corresponding to the desired o parallel position, impact can result in large aftward displacements of the blade away from the desired position before any sizeable restoring force is created driving the blade back toward the equilibrium position. The current design thus provides for a smaller range of angular displacement of the blade about the desired parallel position. The angle cx should preferably be between 5 and 10 degrees, and is here about 7.6 degrees.

The canting of the blade forward when in the equilibrium position enables more [N:\LIBLL]01814:GJG:TCW 0- 0 M effective use of more powerful engines which have recently come onto the market without suffering increased effects of impact on the blade displacing it aft of the desired parallel position.

The blade 100 is mounted on the blade mounting disc 200 by means of bolts 300 passing through a hole 112 provided in the blade 100 and centred about the pivot axis P. The area immediately surrounding the hole 112 is raised so as to provide a recess 113 about the hole 112 in the blade lower face 102. This recess 113 provides a housing for the bolt head 301, elevating it to or above the surrounding blade lower face 102, thereby protecting it from wear and damage.

The blade 100 is arranged such, when mounted on the mounting disc 200, the cutting edge 131 is the lowest portion of the blade, being lower than but parallel to the mounting plane MP. The cutting edge 131 is here approximately 30 mm long, but may be longer (or shorter) as desired.

With reference to Figure 10, the distance by which the cutting edge 131 is lower than the mounting plane MP, and the height of the blade grass deflecting portion 142 above the mounting plane MP should be designed such that the centre of mass M of the unsupported region of the blade lies on, or close to, the mounting plane. If the centre of mass M of the unsupported region does not lie on the mounting plane M, .•being the plane at which support of the blade on the mounting disc is effected as 20 described above, the centrifugal force F acting through the unsupported region centre of mass M will create a moment about the mounting plane MP. This moment will progressively bend the unsupported region (including the cutting edge 131) of the blade as the rotational speed of the mounting disc 200 increases. For example, if the centre of mass M is above the mounting plane MP, the cutting edge 131 will move downwards as the speed is increased and move upwards as the speed is decreased, providing an uneven cut finish on the surface of the lawn being mown. In the embodiment depicted, the centre of mass M of the unsupported region is disposed approximately 0.5 mm above the mounting plane MP.

[N:\LIBLL]01814:GJG:TCW The blades 100 are typically manufactured from sheet metal, preferably 2 mm thick cold rolled carbon steel, with sheets of metal first being slit into a plurality of strips each having the width of a single blade blank (depicted in Figure 11). The strips are then fed into a blank cutting die which cuts each strip into a plurality of blanks.

The blanks are then pressed into the final form of the lawnmower blades 100. The sheet material is slit by a shear slitting means, typically comprising one or more slitting rollers which engage one side of the sheet, the opposing side of the sheet laying on a flat surface. The slitting rollers engage the one side of the material and penetrate the surface by a shear action cutting partially through the thickness of the sheet, thus producing a shiny, relatively uniform "shear edge". When the slitting roller reaches a certain depth, the load developed in the remaining uncut thickness of the material exceeds the ultimate strength of the material, thereby breaking the material and producing a dull, ragged and irregular "break edge".

When the slit strips of material are fed into the blank cutting die, no attention is typically afforded to the orientation of the strips as they are fed into the die. The cutting operation in the blank cutting die also cuts the material from one side, creating a "shear edge" and a "break edge", which may or may not be on the same side as the respective "shear edge" and "break edge" created by the slitting means. No control is oaooo °currently placed on the orientation of the slit strips being fed into the blank cutting die 20 or of the design of the cutting means with respect to which face of the blank (ie upper or lower face of the final product) is engaged by the cutting means thereof.

The current applicant has found that the fatigue life of individual blades from a given batch can vary markedly, and has found that fatigue failures are often initiated in the lower face 102 of the blade 100 adjacent the edge of the mounting disc 200. It is believed that these failures occur as a result of the blade being bent upwardly about the edge of the mounting disc 200 when the lawnmower passes over a solid object and the blade impacts the same. This bending load produces a tensile stress in the lower face 102 of the blade and a compressive stress in the upper face 101 of the blade, concentrated adjacent the blade mounting disc edge. Repeated impacts and the [N:\LIBLL]01814:GJG:TCW consequent application of bending loads can initiate fatigue cracks in the tensile loaded lower face 102. Such cracks grow under repeated impacts, eventually resulting in fatigue failure of the blade with potential hazardous effects as the blade is thrown from the lawnmower.

The applicant has observed that these fatigue failures are more prevalent in blades which have the "break edge" disposed toward the lower, tensile loaded, face 102 of the blade. The rough surface of the "break edge" creates a stress concentration promoting the initiation of fatigue cracks. Such fatigue cracks do not occur in compressively loaded surfaces, and hence having a rough edge at the compressively loaded upper face 101 would not effect the blade fatigue life. Having discovered the root cause of the fatigue problem, the current applicant has undertaken to ensure that the "break edge" is always disposed toward the upper face 101 of the blade and the smooth, relatively stress concentration free "shear edge" is disposed toward the lower face 102 of the blade, to thereby enhance the mean fatigue life of a given batch of blades.

This is accomplished by ensuring the slit strips are fed into the blank cutting die with the one side which has been engaged by the slitting means being arranged so as to form the lower face of each blade and cutting the blanks in the blank cutting die with a shear cutting means which engages the same one side of each strip.

a.

20 The blank cutting die is designed such that the shear cutting means engages what will form the lower surface of the blank, and controls are put in place to ensure that the strips are consistently fed into the blank forming die in the correct orientation.

This may be achieved either by visual inspection of each strip being fed into the blank cutting die, which will be made easier if the strips are in the form of coils, or preferably by automated means whereby the strips are conveyed from the slitting means to the blank cutting die in a fixed orientation.

o A [N:\LIILL]01814:GJG:TCW

Claims (19)

1. A lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and a blade grass deflecting portion extending rearwardly and upwardly from said blade outboard leading portion to an outboard section of said trailing edge, wherein said blade outboard leading portion merges into said blade grass deflecting portion with a radius of at least 25 mm at all positions along a junction therebetween on said upper face.

2. The lawnmower blade of claim 1, wherein said radius is between 32 mm and 41 mm at all said positions along said junction.

3. The lawnmower blade of either of claims 1 and 2, wherein said blade grass catching portion is inclined at an angle of between 50 and 60 degrees to said blade outboard leading portion at all positions on said grass deflecting portion at said trailing :edge outboard section. *oe

4. A lawnmower blade having upper and lower faces bounded by an 20 inboard mounting end, an outboard end, a leading edge and a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and a blade grass deflecting portion extending rearwardly and upwardly from said blade outboard leading portion to an outboard section of said trailing edge, *aab.a wherein an inboard length of the boundary of said upper face defined by said trailing edge lies in a mounting plane, said mounting plane being perpendicular to a pivot axis about which said blade is adapted to pivot, said boundary being smooth and [N:\LIBLL]01814:GJG:TCW 16 continuous outboard of said inboard length, said inboard length smoothly merging with a concave length of said boundary disposed immediately outboard thereof, a convex length of said boundary being disposed outboard of said concave length.

The lawnmower blade of claim 4, wherein said convex and concave lengths are separated by a straight intermediate length of said boundary.

6. The lawnmower blade of claim 4, wherein said convex and concave lengths are directly linked at a point of inflection.

7. The lawnmower blade of any one of claims 4 to 6, wherein said concave length extends at least partway along said outboard section of said trailing edge.

8. The lawnmower blade of any one of claims 4 to 7, wherein a straight outboard length of said boundary extends from said concave length to said outboard end.

9. The lawnmower blade of any one of claims 4 to 8, wherein said convex length has a radius in excess of 30 mm.

A lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing edge, said "lawnmower blade including: S. a cutting edge formed along an outboard section of said leading edge, 20 a blade outboard leading portion extending rearwardly from said cutting edge toward said trailing edge, and O* °a a blade grass deflecting portion extending rearwardly and upwardly from said blade outboard leading portion to an outboard section of said trailing edge, and o.o. least two notches provided in said grass catching portion at said outboard end and extending inboard.

11. The lawnmower blade of claim 10, wherein each of said notches is of a type configuration.

12. The lawnmower blade of either of claims 10 and 11, wherein each of said notches extends inboard from said outboard end a distance of approximately 4 mm. [N:\LIBLL]01814:GJG:TCW

13. The lawnmower blade of any one of claims 10 to 12, wherein each of said notches has a width measured along said outboard end of approximately 8 mm.

14. The lawnmower blade of any one of claims 10 to 13, wherein each of said notches is separated at said outboard end by a distance of between 3 and 6 mm.

15. The lawnmower blade of claim 14, wherein each of said notches is separated at said outboard end by a distance of between 4 and 5 mm.

16. A lawnmower blade having upper and lower faces bounded by an inboard mounting end, an outboard end, a leading edge and a trailing edge, said lawnmower blade including: a cutting edge formed along an outboard section of said leading edge, a pivot axis disposed toward said inboard mounting end about which said blade is adapted to be pivotally mounted on a blade mounting disc, a mounting support region adapted to abut and thereby be supported by said mounting disc when said blade is in an equilibrium in use pivotal position, the remaining region of said blade outboard of said mounting support region being unsupported when said blade is in said equilibrium pivotal position, wherein the centre of mass of said unsupported region is disposed further rearwardly from said cutting edge than is said pivot axis, a line passing through said unsupported region centre of mass and said pivot axis subtending an angle of at least 20 degrees with said cutting edge.

17. The lawnmower blade of claim 16, wherein said angle is between and 10 degrees.

18. A method of enhancing the mean fatigue life of a batch of lawnmower blades formed from blanks cut from strips of metal, said strips having been slit from a sheet of metal, including the steps of: slitting a sheet of metal into a plurality of strips each having the width of a S" lawnmower blade blank with a shear slitting means engaging one side of said sheet, feeding each said strip into a blank cutting die, ensuring said one side is arranged so as to form, in use, a lower face of each blade, [N:\LIBLL]01814:GJG:TCW 18 cutting each said strip into a plurality of blanks with a shear cutting means engaging said one side of each said strip, forming each said blank into a lawnmower blade with said one side forming said lower face of each said blade.

19. A lawnmower blade produced according to the method of claim 18. A lawnmower blade substantially as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings. DATED this Seventh Day of July 1999 Sunbeam Corporation Limited Patent Attorneys for the Applicant SPRUSON FERGUSON t*oo *t 0 SI* o 900 a S i 0 a f [N:\LIBLL]01814:GJG:TCW