GB2023390A - Blade assembly for rotary trimmer - Google Patents

Abstract

A cutter blade assembly for a rotary trimmer, comprises a circular hub 11 formed with a central opening 13 for mounting it on the drive shaft of a rotary trimmer and three blades 15, 16, 17 integral therewith, and extending outwardly from said hub in equiangularly spaced relation. Each blade is formed with a convex cutting edge 18, the inner end portion 19 of which is tangential to the hub and a comparatively short straight cutting edge 20 on the side of the blade opposite to that having the curved cutting edge. Either of these cutting edges is adapted to be effective when it is the leading edge as determined by the direction of rotation of the trimmer drive shaft and the position of the blade assembly relative thereto. The blade assembly is of rubber which may be reinforced by plastic fibres or layers of fabric. <IMAGE>

Description

SPECIFICATION Blade assembly for rotary trimmer This invention relates to a blade assembly for a rotary trimmer.

Rotary trimmers of the type with which the instant invention is concerned may be classified in three categories. One of these classes is for brush cutters, a second is for long grass or weeds and the third is for short grass ordinarily encountered by a lawn mower.

United States Patent Number 3,781,991 discloses a brush cutter. Brush is heavy material as compared to weeds or grass and because of this the blade 15 comprises a flat plate of steel. While other suitable materials are suggested, it is submitted that a flexible material such as rubber or reinforced rubber would not be suitable. It simply would not cut through the heavy brush. Thus, the safety factor inherent in a flexible blade is lost and this is of the utmost importance when it is considered that these trimmer blades rotate at high speed which, in present day times reach 6400 r.p.m.

While this patent discloses a blade assembly comprising a central portion and hub from which three equiangularly spaced blades extend with each blade having oppositely disposed cutting edges. The edges on each blade are alike in contour and dimension. There is no hint or suggestion that the cutting edge on one side is particularly adapted for cutting foliage of a certain type and the edge on the opposite side for cutting foliage of a different character.

United States Patent Number 3,343,350 relates to a lawn mower blade. The blade is of an elastomeric material such as rubber or reinforced rubber and thus, provides the safety factor which is so important in a high speed rotary mower. Moreover, Figure 5 depicts a blade assembly comprising a central portion or hub from which extend three equiangularly spaced blades 32. Each of these blades has a leading edge that is bevelled (Figure 5), whereby it is constituted a cutting edge. While not illustrated in the drawings, lines 48,49, and 50 of column 2 of the specification state that both the leading and trailing edges may be bevelled to permit the blade to be turned upside down and used in the opposite direction.

This patent does not disclose a blade having a long convex cutting edge nor a blade having a cutting edge on one side of the blade which is adapted to perform a particular cutting operation and that on the opposite side, a different cutting function.

United States Patent Number 3,343,355 discloses another example of lawn mower blade of a flexible elastomeric material and thus, provides the safety factor discussed. The blade assembly comprises a central portion or hub 18 from which extend two arms or blades 20 and 21. Arm 20 has a leading edge 22 and arm 21, a leading edge 23. The leading edges 22 and 23 are curved in the plane of cutting and are bevelled whereby they are constituted cutting edges.

The trailing edges, that is the edges opposite to bevelled edges 22 and 23, are not bevelled or otherwise formed to impart to them the ability to function as cutting edges.

Other known mower blades are made of an elastomeric material such as rubber or rubber reinforced by plastics fibres or fabric layers.

The known art of safety cutter blades for rotary trimmers is singularly lacking in a blade assembly comprising a hub from which a plurality of equiangularly blades extend and which are integral with the hub, with each blade having cutting edges on its opposite sides with one cutting edge being particularly designed to cut long grass or weeds with a negative cutting action which throws the cut foliage outwardly away from the hub and trimmer drive shaft, while the cutter edge on the opposite side of the blade is designed to cut short grass with a positive cutting action.

With the foregoing conditions in mind, the present invention has in view the following objectives: 1. To provide a safety blade assembly for a rotary trimmer comprising a circular hub, from which outstand a plurality of blades which are integral with the hub, with each blade having opposite side edges, either of which may be the leading edge when the assembly is mounted on the drive shaft of a rotary trimmer and in which one side edge is designed to perform one cutting function and the opposite side edge is designed to carry out a different cutting action; 2. To provide, in a safety blade assembly of the type noted, a plurality of blades each of which has a comparatively long cutting edge curved in the cutting plane and a relatively short straight cutting edge opposite to the curved edge; 3.To provide, in a safety blade assembly of the character aforesaid, three blades, equiangularly spaced apart and each blade of which has bevelled edges on opposite sides, constituting cutting edges; 4. To provide, in a safety blade assembly of the kind described, blades having convex cutting edges, the inner ends of which are tangential to the circular hub; 5. To provide, in a safety blade assembly of the type noted, a hub having a central aperture and a bushing positioned in said aperture whereby the hub is adapted to be mounted on the drive shafts of rotarytrimmers of different diameters; 6. To provide, in a safety blade assembly of the character aforesaid, a hub and a plurality of blades, outstanding therefrom, which are of a flexible elastomeric material; and 7.To provide, in a safety blade assembly of the kind described, a plurality of blades, each of which has scored lines in parallel spaced relation on its outer end portion, which facilitate breaking off a portion of the blade to achieve a required length thereof.

Various other more detailed objects and advantages of the invention will in part, become apparent and in part be hereinafter stated as the description of the invention proceeds.

The foregoing objectives are achieved by providing a safety blade assembly of a flexible elastomeric material such as rubber, which may be reinforced by plastic fibres or fabric fibres, and which comprises a hub in the form of a circular disc having a central aperture for mounting the hub on the drive shaft of a rotary trimmer. A bushing may be detachably positioned in this aperture to adapt the hub to fit on drive shafts of different dimensions.

Integral with and extending outwardly from the hub and coplanar therewith, are a plurality of, pref erably three, blades equiangularly spaced apart.

Each of these blades has a comparatively long convex cutting edge on one side, the inner end portion of which is tangential to the hub. This cutting edge is intended to operate on long grass or weeds with a negative cutting action, which throws foliage outwardly and away from the drive shaft of the trimmer.

A relatively short straight cutting edge is formed on the opposite side of the blades. This cutting edge functions with a positive cutting action on short grass such as is ordinarily found on lawns.

Both of the cutting edges may take the form of bevelled surfaces on the respective side edges. In one embodiment, these bevelled surfaces are parallel to each other while in another embodiment they converge to define a frusto-conical blade structure.

Each blade may be scored along parallel lines in the region adjacent to its outer end to define sections which may be easily broken off to achieve a required length of the blades.

Four a full and more complete understanding of the invention, reference may be madeto the following description and accompanying drawing, wherein: Figure lisa perspective view of a safety blade assembly for a rotary trimmer embodying the precepts of the present invention; Figure 2 is a plan view taken on a large scale of the blade assembly; Figure 3 is a section taken about on the plane of the lines 3-3 of Figure 2; Figure 4 is a transverse section through the end of a blade, being taken about on the plane of line 4-4 of Figure 2; Figure 5 is a sectional view similar to Figure 4 of a modified blade structure; and Figure 6 is a perspective view depicting a portion of the hub and the bushing which is movably positioned relative thereto in exploded relation.

In Figures 1 and 2, a safety blade assembly 10 includes a hub 11 in the form of a disc having a circular periphery 12, and a central aperture 13. The latter constitutes a means for mounting the hub 11 on the drive shaft of a rotary trimmer. Inasmuch as rotary trimmers of the type with which this invention is concerned are well known and include drive shafts, it is deemed unnecessary to encumber the drawing and specification with an illustration and description of the trimmer and its rotary shaft.

Drive shafts for trimmers ordinarily comes in two diametric sizes. To adapt the hub 11 for mounting on drive shafts of two different diameters a bushing 14, is removably positioned in aperture 13.

Three blades, 15, 16 and 17 are formed integrally with hub 11 and are coplanar therewith. They are equiangularly spaced about hub 11 from which they outstand. Moreover, hub 11 and blades 15,16 and 17 are of a flexible elastomeric material such as rubber which may be reinforced by plastic fibres and fabric layers. As these blades 15, 16 and 17, are all alike, only one of them is herein described in detail. Thus, blade 16 has a comparatively long convex cutting edge 18, the inner portion of which is tangential to the periphery 12 of hub 11, as shown at 19. The opposite side of blade 16 is formed with a relatively short straight cutting edge 20.

In one embodiment, cutting edges 18 and 20 are defined by bevelled surfaces 21 and 22, which are substantially parallel to one another as illustrated in Figure 4. In the modified embodiment of Figure 5, they are defined by bevelled surfaces 23 and 24, which converge and as illustrated in Figure 5, cooperate with the body of blade 16 to define a frustoconical blade structure.

Trimmers of different sizes require blades of various lengths. As produced by the manufacturers, they will all be of the same standard length as shown in Figure 2. However, each blade 15, 16 and 17, is scored along lines 25 in the region adjacent to its outer end to define sections 26, any of which may be removed by breaking off along a weakened score line 23.

While the manner in which the subject safety blade assembly operates is believed to be obvious from the illustration of the drawing and description of parts set forth above, it is briefly outlined as follows: The drive shaft in which blade assembly 10 is mounted will always rotate in the same direction.

Assuming this direction is anti-clockwise, speaking with reference to Figure 2 and with the assembly 10 mounted on the drive shaft as illustrated, cutting edge 18 is the leading edge. It is designed to cut long grass and weeds with a negative action. This means that not only is the edge 18 engaged with the foliage with a wiping or slicing action which not only facilitates cutting but the cut foliage is thrown outwardly and away from hub 11 and the drive shaft on which it is mounted. Thus, wrapping or winding of the cut foliage about the drive shaft or any part of the trimmer is obviated.

When short grass such as is usually present on lawns is to be cut, the assembly 10 is removed from the drive shaft, its position thereon reversed whereupon it is again mounted on the drive shaft in a position in which cutting edge 20 becomes the leading edge and cuts the grass with a positive action; as the cut foliage in this case is short, there is no danger of it becoming entanged in the trimmer.

Claims (10)

1. A blade assembly for a rotary trimmer, including a drive shaft that rotates in one direction, a hub in the form of a disc and of a flexible material, a plurality of blades integral and coplanar with said hub and extending outwardly therefrom in equian gularlyspaced relation, means on said hubfor mounting it on said drive shaft, a comparatively long.

convex cutting edge on one side of each of said blades, and a comparatively short straight cutting edge on the side of each blade opposite to the side having the convex edge, whereby the hub may be mounted on the drive shaft in one position to render it with the convex cutting edge effective to cut long grass and weeds with a negative action and in a reversed position to bring said short straight edge into effective position to cut short grass with a posi tive action.

2. A blade assembly according to Claim 1, which has three blades.

3. A blade assembly according to Claim 1 or 2, in which the convex cutting edge of each blade has an inner end portion tangential to the periphery of the hub.

4. A blade assembly according to Claim 1,2 or 3, in which the means on the hub for mounting it in a drive shaft takes the form of an aperture at the centre of the hub.

5. A blade assembly according to Claim 4, together with a bushing removably positioned in said aperture, whereby one hub is adapted to be mounted on drive shafts of different diameters.

6. A blade assembly according to any preceding Claim, in which the cutting edges are defined by bevelled surfaces.

7. A blade assembly according to Claim 6, in which the bevelled surfaces are parallel to each other.

8. A blade assembly according to Claim 6, in which the bevelled surfaces converge to provide a frusto-conical structure.

9. A blade assembly according to any preceding Claim, in which each of the blades has a plurality of parallel scored lines in the region adjacent to its outer end with the scored lines identifying sections which may be removed by breaking off at a scored line.

10. A blade assembly for a rotary trimmer, substantially as described with reference to Figures 1 to 4 and 6, or Figures 1 to 4 and 6 as modified by Figures.