GB1574926A - Lawn mower sharpening attachment - Google Patents

Description

(54) LAWN MOWER SHARPENING ATTACHMENT (711) ) I, PETER DAVID SPRINGALL, a British Subject, ob Tweedmouth Industrial Estate, Berwick-upon-Tweed, Northumberland, TD15 2XF, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an implroved lawn mower sharpening attachment and to a lawn mower including such an attachment.

In British Patent No. 1,369,219 there is describbed and claimed a sharpening attachment for a grass cutting machine of the rotary cylinder type comprising an abrasive element, two arms secured to the abrasive element, one part of each arm being formed in two parts one angularly adj,usrahle to the other, each arm adapted for pivotal engagement with a tie bar on the machine, positioning means adapted for connection to the tie bar d the machine, and spring means associated with the positioning means such that the abrasive element can be held in a desired spring biassed position adjacent the blades of the machine.

Whilst the arrangement disclosed in British Patent No. 1,369,219 is perfectly satisfactory the sharpening attachment disclosed therein may only be used with lawnmowers provided with a tie bar. Thus that attachment is not suitable for all types of rotary cylinder lawnmowers.

An object of the present invention is to provide an improved lawnmower sharpening attachment suitable for all types od rotary cylinder lawnmowers.

According to the present invention there is provided a lawnmower sharpening attachment for lawnmowers of the rotary cylinder type in which grass is cut between a rotary blade and a fixed blade, the sharpening attachment comprising an abrasive element, and means for mounting the abrasive element on the fixed blade of a rotary cylinder lawnmower, the mounting means including one or more projections adapted to engage on the inside d the fixed blade and spring means for biassing the abrasive element so as to engage and sharpen the cutting edges of the moving blades on rotation thereof.

Preferably the abrasive element comprises a rigid backing member and a replaceable sheet of abrasive material. The spring means pre ferably are adapted to engage a rear edge of the fixed blade.

The invention also includes a lawnmower comprising a plurality ob movable blades arranged cylindrically about a horizontal shaft, a fixed blade with which the movable blades cm operate to cut grass and sharpening means on the fixed blade adapted to be arranged so as to engage and sharpen the cutting edges of the movable blades on rotation thereof, the sharpening means including one or more pro sections engaging on the inside of the fixed blade, and spring means biassing the sharpening means into sharpening engagement with the movable blades.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows part of a cylinder lawnmower on its side; Figure 2 is a perspective view from above of a preferred attachment; Figure 3 is a perspective view from below of the attachment of Figure 2; Figure 4 is an underneath view of a cylinder lawnmower showing a first fitting step; Figure 5 is an underneath view of a cylinder la'nnmower showing a second fitting step; and Figure 6 is a diagrammatic side elevation showing the sharpening action.

In Figure 1 of rhe drawings a part of a conventional cylinder lawnmower is shown on its side. The lawnmower consists of a large rear roller 1 a small front roller 2, a rotary cylinder carrying blades 3 and a fixed bottom blade 4. The cylinder mower cuts grass by a scissor action between the rotating cylinder blades 3 and the fixed bottom blade 4. In the present invention there is provided a sharpening attachment which is designed to be fixed onto the fixed blade 4 of rhe mower to sharpen the rotating blades 3.

The preferred form of attachment is shown in figures 2 and 3 which shows a sharpening attachment 5 comprising an abrasive element consisting of a backing member 7 and a replaceable sheet of abrasive material 8 secured to the front face thereof by adhesive. The backing member 7 has two spaced protruding tabs 9 and a bent spring element 10. The spring element 10 passes through two openings 11 in a flange 12 on the backing member 7 and terminates in hooks 13 at its free ends. The openings 11 as seen from figure 3, are formed as Shaped slots having a longitudinal portion and a transverse portion to facilitate fitting as explained below and the backing member 7 has a longitudinal bend 14 so that in use the abrasive element is angled into engagement with the movable blades of the mower.

In use the sharpening attachment operates as follows: as explained in relation to Figure 1 the blades of a cylinder mower work on a scissor action so that in a correctly adjusted mower there should be no gap between the fixed and moving blades. In order to fit the attachment the gap is increased by releasing adjustment screws (not shown) provided on all cylinder mowers and this allows the abrasive member to be secured in position.

Once the gap has been enlarged the attach ment is taken and the spring element 10 engaged in the transverse portions of the openings 11. The attachment is then slid onto the fixed bottom blade 4 with the tabs 9 on the inside and the hooks 13 on the outside as shown in figure 4. As shown in figure 5 the spring element 10 is then moved into the longitudinal portions of openings 7 and the hooks 13 engaged behind the back edge of the bottom blade 4 to secure the attachment in position.

In this position the blades are ready for sharpening but final adjustment of the adjustment screws may be necessary to ensure that the cylinder blades on rotation rub against the abrasive and not the tabs 9. Rotation of the cylinder blades will then sharpen them as indicated diagrammatically in Figure 6.

Once the blades have been sharpened the attachment is removed by reverse procedure and the cylinder adjusted so that the movable cylinder blades and fixed blade just touch.

The backing member 7 may be an extrusion of plastics material or aluminium for example and may include a further arm (not shown) that clamps the attachment to the bottom blade to restrict movement of the extrusion, thus providing a means of grinding the blades truly concentric with the horizontal spindle in the event of misalignment.

An advantage of the attachment disclosed herein is that it will fit all cylinder lawnmowers without adjustment apart from ensuring that the length of the attachment is suitable for the machine on which it is to be used.

Although the abrasive is preferably a sheet d silicon carbide or fused aluminium oxide it is understood that the abrasive may be of any suitable type and in block form if desired.

WHAT I CLAIM IS: 1. A lawnmower sharpening attachment for lawnmowers of the rotary cylinder type in which grass is cut between a rotary blade and a fixed blade, the sharpening attachment comprising an abrasive element, and means for mounting the abrasive element on the fixed blade of a rotary cylinder lawnmower, the mounting means including one or more projections adapted to engage on the inside of the fixed blade and spewing means for biassing the abrasive element so as to engage and sharpen the cutting edges of the moving blades on rotation thereof.

2. A lawnmower sharpening attachment according to claim 1 wherein the abrasive element comprises a rigid backing member and a replaceable sheet of abrasive material.

3. A lawnmower sharpening attachment according to claim 1 or 2 wherein the spring means is adapted to engage a rear edge of the fixed blade, for biassing the abrasive element so as to engage and sharpen the cutting edges of the moving blades.

4. A lawnmower sharpening attachment according to claims 2 and 3 wherein the spring means comprises an elongate spring element which passes through openings in a flange on the backing member of the abrasive element and the free ends of which are hooked to engage the rear edge of the fixed blade.

5. A lawnmower sharpening attachment according to claim 4 wherein the openings are L-shaped slots.

6. A lawnmower sharpening attachment according to claim 2, 4 or 5 wherein the backing member is of a substantially elongate rectangular shape and includes a longitudinal bend iine so that in use the abrasive is angled into engagement with the movable blades of the mower.

7. A lawnmower sharpening attachment according to any one of the preceding claims and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A lawnmower comprising a plurality of movable blades arranged cylindrically about a horizontal shaft, a fixed blade with which the movable blades co-operate to cut grass and sharpening means on the fixed blade adapted to be arranged so as to engage and sharpen the cutting edges of the movable blades on rotation

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. in figures 2 and 3 which shows a sharpening attachment 5 comprising an abrasive element consisting of a backing member 7 and a replaceable sheet of abrasive material 8 secured to the front face thereof by adhesive. The backing member 7 has two spaced protruding tabs 9 and a bent spring element 10. The spring element 10 passes through two openings 11 in a flange 12 on the backing member 7 and terminates in hooks 13 at its free ends. The openings 11 as seen from figure 3, are formed as Shaped slots having a longitudinal portion and a transverse portion to facilitate fitting as explained below and the backing member 7 has a longitudinal bend 14 so that in use the abrasive element is angled into engagement with the movable blades of the mower. In use the sharpening attachment operates as follows: as explained in relation to Figure

1 the blades of a cylinder mower work on a scissor action so that in a correctly adjusted mower there should be no gap between the fixed and moving blades. In order to fit the attachment the gap is increased by releasing adjustment screws (not shown) provided on all cylinder mowers and this allows the abrasive member to be secured in position.

Once the gap has been enlarged the attach ment is taken and the spring element 10 engaged in the transverse portions of the openings 11. The attachment is then slid onto the fixed bottom blade 4 with the tabs 9 on the inside and the hooks 13 on the outside as shown in figure 4. As shown in figure 5 the spring element 10 is then moved into the longitudinal portions of openings 7 and the hooks 13 engaged behind the back edge of the bottom blade 4 to secure the attachment in position.

In this position the blades are ready for sharpening but final adjustment of the adjustment screws may be necessary to ensure that the cylinder blades on rotation rub against the abrasive and not the tabs 9. Rotation of the cylinder blades will then sharpen them as indicated diagrammatically in Figure 6.

Once the blades have been sharpened the attachment is removed by reverse procedure and the cylinder adjusted so that the movable cylinder blades and fixed blade just touch.

The backing member 7 may be an extrusion of plastics material or aluminium for example and may include a further arm (not shown) that clamps the attachment to the bottom blade to restrict movement of the extrusion, thus providing a means of grinding the blades truly concentric with the horizontal spindle in the event of misalignment.

An advantage of the attachment disclosed herein is that it will fit all cylinder lawnmowers without adjustment apart from ensuring that the length of the attachment is suitable for the machine on which it is to be used.

Although the abrasive is preferably a sheet d silicon carbide or fused aluminium oxide it is understood that the abrasive may be of any suitable type and in block form if desired.

WHAT I CLAIM IS: 1. A lawnmower sharpening attachment for lawnmowers of the rotary cylinder type in which grass is cut between a rotary blade and a fixed blade, the sharpening attachment comprising an abrasive element, and means for mounting the abrasive element on the fixed blade of a rotary cylinder lawnmower, the mounting means including one or more projections adapted to engage on the inside of the fixed blade and spewing means for biassing the abrasive element so as to engage and sharpen the cutting edges of the moving blades on rotation thereof.

2. A lawnmower sharpening attachment according to claim 1 wherein the abrasive element comprises a rigid backing member and a replaceable sheet of abrasive material.

3. A lawnmower sharpening attachment according to claim 1 or 2 wherein the spring means is adapted to engage a rear edge of the fixed blade, for biassing the abrasive element so as to engage and sharpen the cutting edges of the moving blades.

4. A lawnmower sharpening attachment according to claims 2 and 3 wherein the spring means comprises an elongate spring element which passes through openings in a flange on the backing member of the abrasive element and the free ends of which are hooked to engage the rear edge of the fixed blade.

5. A lawnmower sharpening attachment according to claim 4 wherein the openings are L-shaped slots.

6. A lawnmower sharpening attachment according to claim 2, 4 or 5 wherein the backing member is of a substantially elongate rectangular shape and includes a longitudinal bend iine so that in use the abrasive is angled into engagement with the movable blades of the mower.

7. A lawnmower sharpening attachment according to any one of the preceding claims and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A lawnmower comprising a plurality of movable blades arranged cylindrically about a horizontal shaft, a fixed blade with which the movable blades co-operate to cut grass and sharpening means on the fixed blade adapted to be arranged so as to engage and sharpen the cutting edges of the movable blades on rotation

thereof, the sharpening means including one or more projections engaging on the inside of the fixed blade, and spring means biassing the sharpening means into sharpening engagement with the movable blades.