AU624336B2 - Pivoted cutting blade - Google Patents

Description

A

FORM COMMONWEALTH OF AUST'-ALQI PATENTS ACT 1952 S F Ref: 33340 C rzBT COMPLETE SPECIFICATION

(ORIGINAL)

a a (Q1 FOR OFFICE USE: Class Int, Class Application Number: Lodged: P13607 7 August 1987 Ae A a *a in a A A* Accepted: Published: Priority: Related Art: Name and Address of Applicant: A A Sunbeam Corporation Limited Wade Street Campsie New South Wales 2194

AUSTRALIA

Peter Gordon Toms Actual Inventor; Address for Service: Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia Complete Specltcation for the invention entitled: Pivoted Cutting Blade The following statement Is a full description of this invention, Including the best method of performing It known to me/us 5815/2 r 1 1 i PIVOTED CUTTING BLADE This invention relates to cutting blades for rotary lawn mowers, and more particularly to the pivoted blades utilised on such machines.

Ideally, both from safety and efficiency view points, in the production of a rotary lawn mower the operative cutting plane of its blades with respect to the baseplate should be confined to close tolerances. Difficulty in maintaining these tolerances principally originates in the production of the blades themselves, which frequently results in an unacceptably high rejection rate. The problem has its roots in the requirement for a blade to be light-weight to avoid excessive centrifugal forces when operating, and thin for continued effective grass cutting In service. However, during the necessary heat treatment, for tempering purposes, a light-weight formed blade is liable to unpredictable distortion because of variation in composition of the metal raw stock.

It is the main object of the invention to provide a lawn mower cutting blade of a construction capable of repetitive production within S' acceptable tolerances with a low incidence of rejection.

0.oo To this end, the invention in one general form provides an 20 elongated pivoted cutting blade for a rotary lawn mower, the blde having raised apertured mounting portion near one end part, a leading edge cutting portion near the other end part, a central part extending from S, said mounting portion toward said cutting portion, an inclined part joining said central part and said cutting portion, said inclined part S 25 slopes away from said central part in the opposite direction to said mounting portion, and an upturned trailing marginal edge portion also near said other end part, a longitudinally extending reinforcing impression formed In said central part so as to extend from adjacent said mounting to a portion terminating at and merging with said inclined part, and for at least part of its length tapering with respect to the width of Y the blade, said apertured mounting portion further comprises an opening located centrally of a dome shaped formation, the opening having two recesses opposite one another.

This invention will be described in more detail with "eference to the accompanying drawings, in dhich: Fig. 1 is a perspective view of a pivoted cutting blade constructed according to the present invention; and, Fig, 2 shows a side elevation the same cutting blade, S-2- J R i669m The cutting blade 3 shown in the drawings consists of a generally rectangular strip of spring steel having near one end a mounting portion 4 which includes a bolt hole 5 and a surrounding dome-shaped impression 6. Near the outer end 7 of the blade 3 a chamfered cutting edge 8 is provided in a leading edge 9 while an inwardly tapering upwardly swept flange 10 is provided at the trailing edge 11 of the blade 3 and extends from the outer end 7 to an intermediate point 12 of the blade 3. The flange 10 at the outer end portion 7 of the blade 3 is provided with a notch 13 and a 04.9 ft f f #0 ft 4.

ft ft 49 *c ft ft ft 404 4I ##ftft ft 0 ft ft .4 4 ft *4 0 40 4 *4 f .44, ft 4,1 0ft 'ft ft. 40 ft. f 4 ft 4*rL ft 9 -2A- RLF/1669m t, S- U chamfered corner 14 for the purpose of noise reduction during operaticn.

The blade 3 between the intermediate point 12 and the mounting portion 4 lies in a first plane with the outer end portion 7 containing the cutting edge 8 lying in a lower but not necessarily parallel plane, and an inclined step 15 is provided as a transition between the point 12 with the end portion 7. The description in this specification relates to the blade 3 when disposed in its normal operating condition.

The cutting blade 3 may be mounted either to the lower or upper surface of a cutter disc (not shown). In the former instance the domed-shaped formation 6 protrudes from the upper face of the blade 3, but from the underface of the blade 3 in the latter instance.

The production o" a blade 3 is usually achieved through the us, of a progressive die to which raw stock of spring steel is delivered and wherein o^ various stages of processing occur. A fully formed blade is provided at ,o the output from the die. It has been found that, due to the tempering o oo process within the die, distortion or deflection, frequently occurs in the 'a portion 16 of the blade 3 lying between the point 12 and the mounting portion 4.

By this invention the progressive die (not shown) is constructed to create a longitudinally extending Impression, or recess, 17 principally in the body portion 16. In the instance where the blade 3 is intended for underside mounting to the cutter disc the impression 17 may be formed as a recess within the upper surface of the blade 3. The impression 17 may be oppositely directed if the blade 3 is intended for topside mounting upon its cutter disc.

Very little distortion of the blade 3 occurs during processing either in the step 15 or the oluter end portion 7 due to the reinforcing effect of the upswept flange 10 and the step 15, Itself, A very satisfactory form of impression 17 has been found to be one which extends '"rom the mounting portion 4 and tapers, in plan, towards the step 15 while maintaining an even depth. The depth of the impression 17 decreases as the outer end of the tapered impression 17 blends into the step 15, Best results have been obtained where the outer end of the tapering impression 17 extends a short di;tance beyond a transverse alignment with the Inner end 18 of the upswept flange 10. It has also been found that, In the case of the impression 17 providing a recess In the upper surface of the blade 3, considerably less abrasion at its out-r end occurs during service than if the Impression 17 were provided in a non-tapering form, Further more, the re-inforcing effect of the sides 19 and 20 of the Impression 17 is distributed more IA)/33o 3-

I_

uniformly over the body portion 16 for improved retardation of distortion during heating in the tempering process.

Whereas a preferred embodiment has been describied in the foregoing passages it should be understood that other forms, modifications and refinements are feasible within the scope of this inveontion.

04 4 304

Claims (6)

1. An elongated pivoted cutting blade for a rotary lawn mower, the blade having raised apertured mounting portion near one end part, a leading edge cutting portion near the other end part, a central part extending from said mounting portion toward said cutting portion, an inclined part joining said central part and said cutting portion, said inclined part slopes away from said central part in the opposite direction to said mounting portion, and an uptur,d trailing m-rginal edge portion also near said other end part, a longitudinally extending reinforcing impression formed in said central part so as to extend from adjacent said mounting to a portion terminating at and merging with said inclined part, and for at least part of its length tapering with respect to the width of the blade, said apertured mounting portion further comprises an opening locati'd centrally of a dome shaped formation, the opening having two recesses opposite one another.

2. A cutting blade according to claim 1, wherein tapering of said impression occurs over most of the length of said impression,

3. A cutting blade according to claim 1 or 2, wherein said upstanding trailing marginal edge portion extends from said other end S 20 part of the blade to an intermediate point thereof, and said impression extends longitudinally along said blade from near said apertured mounting portion to a position beyond said intermediate point of the blade.

4. A cutting blade according to any one of the preceding claims, wherein in the disposition of the blade In its normal working position the opening in said mounting portion is provided in an upwardly extending domed formation on the blade, and said impression is formed to provide a recess within the upper surface of the blade, so as to project in the opposite direction to said mounting, A cutting blade according to any one of claims 1 to 3, wherein 30 in the disposition of the blade 'n its normal working position the opening in said mounting portion is provided in a downwardly extendIng domed formation on the blade, and said impression is formed as a recess within the under surface of the blade.

6. A cutting blade according to any one of the preceding claims, wherein said impression is of uniform depth over the majority of its length. L-- RLF/1669m 1 il I n

7. A pivoted cutting blade for a rotary lawn mower substantially as hereinbeforp described with reference to the accompanying drawings. DATED this NINTH day of MARCH 1992 Sunbeam Corporation Limited Patent Attorneys for the Applicant SPRUSON FERGUSON S S S a. 4 *5 a Is S S S 4 St 5,44 .4 S SI 4 S Si 44 t~ 4 4 a S 444 S4~ 4 111544 4 9 'I RLF/1 669m