WO1990013220A1 - Bottom blade for grass cutting unit - Google Patents

Abstract

A wedge-shaped blade/block assembly for a reel-type grass cutter has a tongue (56) in the blade (50) engaging a groove (68) in the bottom block. Abutments (58, 60, 70, 72) above and below the tongue (56) resist vertical forces on the cutting edge (54). A series of generally horizontal bolts acting through the tongue (56) and groove (68) hold the blade firmly in engagement with the bottom block yet permit ready replacement of the blade when worn.

Description

Accordingly, the present invention consists in a bottom block assembly for a grass cutting unit having a rotating cutter reel, the assembly comprising an elongate bottom block adapted for mounting horizontally in the grass cutting unit and an elongate blade secured to the bottom block and adapted in use to present a transverse cutting edge for cooperation with the rotating reel; wherein the blade comprises a thickened mounting portion remote from the cutting edge, said portion providing first and second blade abutments spaced in a generally vertical direction and each extending along the length of the blade, wherein the bottom block is provided with first and second block abutments positioned for engagement with the respective blade abutments and wherein fastener means are provided which act along a line extending between the blade abutments to draw together the blade and the bottom block.

Preferably, the blade and the bottom block are provided with respective comple entarily engaging parts serving to prevent relative displacement in a generally vertical direction.

Suitably, said complementarily engaging parts comprise respectively a tongue and a groove.

Advantageously, the blade and the bottom block present smooth upper surfaces which are contiguous.

The invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 is a perspective view of a first bottom block assembly according to the prior art,

Figure 2 is a perspective view of a second bottom block assembly according to the prior art.

Figure 3 is a perspective view of a bottom block assembly according to the present invention and,

Figure 4 is a transverse section on the bottom block assembly of Figure 3.

There is shown in Figure 1 a conventional bottom block assembly having a bottom block 10 of substantial angle cross section and a bottom blade 12 in the form of a relatively thin strip. The blade is secured to a bottom block through screws, rivets or other suitable fastening devices at the locations shown at 14. The forward portion of - 1 - BOTTOM BLADE FOR GRASS CUTTING UNIT

This invention relates to grass cutting units of the type having a rotating cutter reel and is more particularly concerned with a bottom blade for use in such a cutting unit.

A common bottom block assembly comprises a substantial bottom block of angle section to which is bolted a bottom blade in the form of relatively thin strip. Typically, the blade is bolted to the bottom block from beneath and extends forwardly to an upturned lip which provides the cutting edge. This arrangement, although common, has a number of significant drawbacks. With a portion of the relatively thin blade effectively cantilevered forwardly of the bottom block, there is a tendency for the blade cutting edge to deflect vertically. Upward deflection can lead to premature wear of the bottom blade and cutter reel whilst downward deflection causes the cutting unit to jam more easily. It has been proposed to add stiffening pieces to the bottom block assembly, but this has not been totally satisfactory. It has further been proposed to form the bottom blade integrally with the bottom block, but since the bottom blade requires periodic replacement on wear, an integral arrangement is too costly unless very thin sections are used for the bottom block, in which case the problem of lack of rigidity is exacerbated.

It is a further problem with certain known designs that the bolts securing the bottom blade to the block are positioned flush with the bottom surface of the blade. It is accordingly difficult to achieve a good purchase on the bolt for removal, and unfastening the bolts can be a tedious process, particularly if significant wear has occurred. It is an object of this invention to provide an improved bottom block assembly for a grass cutting unit in which deflection of the cutting edge is considerably reduced.

It is a further object of this invention to provide an improved bottom block assembly in which the blade and bottom block are held rigidly together in use but can be readily separated when a worn bottom blade has to be replaced. the blade is formed with a lip serving to produce a transverse cutting edge 16 for cooperation with the cutter reel. In alternative constructions, a cutting edge of appropriate land width can be defined in a generally flat blade by a transverse groove spaced a short distance from the blade edge.

An alternative known construction is shown in Figure 2. In this case, the assembly is formed integrally of relatively thin material defining a blade 18 having a cutting edge 20 and a block 22 of triangular section. To provide stiffness, a filler plate 2k is sometimes inserted at the base of the block 22.

Both the described known constructions suffer from the disadvantage that the cutting edge is provided on a relatively thin blade which is cantilevered from a transverse line of support. In the Figure 1 construction, it will be recognised that the blade 12 can be deflected upwardly about the toe 26 of the bottom block and downwardly about the line defined by fastening locations 14. In the case of the Figure 2 arrangement, upward and downward deflection can occur about the transverse line 28 separating the blade 18 and the block 22.

As has been mentioned previously, vertical deflection of the cutting edge can seriously reduce cutting performance.

Turning now to Figures 3 and 4, there is illustrated an improved bottom block assembly according to this invention.

The bottom blade 50 is of generally triangular section having at the apex an upturned lip 52 providing a cutting edge 54. The base of the triangular section is formed with a tongue 56 extending longitudinally of the blade and delimiting an upper blade abutment surface and a lower blade abutment surface 60. These abutment surfaces are generally co-planar and are inclined at a slight angle to the vertical. At intervals along the length, the bottom blade is provided with threaded blind apertures 62 which extend through the tongue 56.

The bottom block 64 has a truncated triangular section with a central void 66. The forward edge of the block is provided with a groove 68 separating upper and lower block abutment surfaces 70 and 72 respectively. As is shown in the drawings, the groove 68 and block abutment surfaces 70, 72 are shaped and dimensioned so as to provide a complementary engagement with the tongue 56 and blade abutment surfaces 58, 60, of the bottom blade.

Pairs of apertures 7 and 76 are provided in the bottom block and aligned with the respective blind apertures 62 in the bottom blade. A series of bolts 78 extend through these apertures and threadily engage the bottom blade so as to draw together the blade and bottom block. It will be noted that in the region of the head of bolt 78, the bottom block 64 is recessed to provide ready access to the bolt.

As the thickness of the blade increases progressively from the cutting edge 5^ towards the bottom block 64, the rigidity of the blade is significantly increased. Moreover, the vertical spacing of the mating abutment surfaces on the blade and bottom block together with the tension in the bolt 78 acting generally horizontally, provide substantial resistance to vertical deflection of the blade relative to the block. Thus a downward force W at the cutting edge 54 will be resisted by tension in the bolt 78 and engagement between abutment surfaces 60 and 72 whilst an upward force P will be resisted by the bolt tension and engagement between abutment surfaces 58 and 70.

Because the bottom block assembly according to this invention is generally wedge shaped, optimum use can be made of the available space between the cutting reel and ground so as to give maximum rigidity in the assembly both torsionally and in bend. The smooth and continuous upper surfaces of the blade and of the block also promote efficient discharge of cut grass.

Maintenance procedures are simplified in a number of respects. Since the bottom blade is of increased inherent stiffness as compared to blades, for example, as shown in Figure 1, it becomes possible to use fewer fastener devices. Since the fastener devices extend generally horizontally, that is to say at an angle to the horizontal of less than 45 and preferably 30 or less, they do not need to be finished flush with the underside of the assembly. A more positive purchase can therefore be provided. Moreover, there is no possibility of the head of the bolt or other fastener being worn through contact with the ground, thereby further increasing the difficulties of removal. The tongue and groove formations on the blade and bottom block serve the useful purpose of providing a positive key. This prevents any displacement during use in the vertical direction and can also serve on assembly of the blade and bottom block to straighten out any minor distortions in the bottom blade. It will be understood that the positions of the tongue and groove can be reversed, whilst other complementary formations could be employed. Thus a series of projecting dowels could serve the same purpose or, with appropriately close tolerences, the bolts 7 could serve additionally as locating elements. In appropriate cases, there need be no such complementarily engaging parts serving to prevent vertical displacement, with the two blade abutments then being contiguous and similarly the two block abutments.

Claims

1. A bottom block assembly for a grass cutting unit having a rotating cutter reel, the assembly comprising an elongate bottom block adapted for mounting horizontally in the grass cutting unit and an elongate blade secured to the bottom block and adapted in use to present a transverse cutting edge for cooperation with the rotating reel; wherein the blade comprises a thickened mounting portion remote from the cutting edge, said portion providing first and second blade abutments spaced in a generally vertical direction and each extending along the length of the blade, wherein the bottom block is provided with first and second block abutments positioned for engagement with the respective blade abutments and wherein fastener means are provided which act along a line extending between the blade abutments to draw together the blade and the bottom block.

2. A block assembly as claimed in Claim 1, wherein the blade and the bottom block are provided with respective complementarily engaging parts serving to prevent relative displacement in a generally vertical direction.

3- A block assembly as claimed in Claim 2, wherein said complementarily engaging parts comprise respectively a tongue and a groove.

4. A block assembly as claimed in Claim 3. wherein said line of action of the fastener means passes through said tongue and said groove.

5. A block assembly as claimed in any one of the preceding claims, wherein said fastener means comprise a plurality of screw threaded fasteners spaced longitudinally of the assembly and each acting along a line inclined at less than 45 to the horizontal.

6. A block assembly as claimed in Claim 6, wherein said line is inclined at 30 or less to the horizontal.

7. A block assembly as claimed in any one of the preceding claims, being of wedge form.

8. A block assembly as claimed in any one of the preceding claims, wherein the blade and the bottom block present smooth upper surfaces which are contiguous.