GB2272624A

GB2272624A - Rotary cutters

Info

Publication number: GB2272624A
Application number: GB9320736A
Authority: GB
Inventors: Henry John Bessinger
Original assignee: BESSINGER DIANA JACQUELINE
Current assignee: BESSINGER DIANA JACQUELINE
Priority date: 1992-11-24
Filing date: 1993-10-08
Publication date: 1994-05-25
Also published as: ZA938743B; GB9320736D0; GB9224631D0

Abstract

A rotatable head for a rotary cutter comprises a circular base plate 7 which is rotatable about its axis. Arranged about the upper surface of the base plate are retainers having holes 7 or channels passing therethrough in a direction radial to the axis of rotation. Culling elements 11 having an elongate filament 12 and an enlarged end portion (13) (Figure 2) are mounted in respective ones of the retainers by insertion of the filament through the hole or channel, the elements being retained during rotation of the head by the abutment of the enlarged end portion (13) against the radially inner side of the hole or channel. The holes or channels are so formed that during rotation the elements can pivot with respect to the mounting portions. <IMAGE>

Description

ROTARY CUTTERS The present invention relates to rotary cutters and is applicable in particular to rotary cutters known as filament trimmers.

According to a first aspect of the invention there is provided a rotatable head of, or for attachment to, a rotary cutter for use with a cutting element having an elongate cutting portion and an enlarged retaining portion, the head comprising a mounting portion for the cutting element, the mounting portion having a hole or channel passing therethrough in a direction having a component of rotation of the head, the arrangement being such that in use the cutting element can extend through and project beyond the hole or channel whilst the element is retained by the abutment of surface portions of the retaining portion against surface portions of the mounting portion at the radially inner end of the hole or channel, the hole or channel being so formed that the element can pivot bodily with respect to the mounting portion.

According to a second aspect of the invention there is provided a cutter for use with a head according to the above first aspect and comprising an elongate filamentary portion and a retaining portion for abutting the end of the hole or channel opposite the end from which the filamentary portion projects, wherein the filament has a larger cross-sectional area in the region proximal to the retaining portion than in the region distal to the retaining portion.

It will thus be appreciated that embodiments of the present invention may provide filament trimmers having a number of advantages over prior art trimmers.

It thus becomes possible to avoid the problem of a filament jamming or breaking whilst in use, problems which are inherent in many known types of trimmer due to the use of filament spools. Moreover, a trimmer may be provided which has filamentary cutting elements which can be easily fitted, not requiring the use of any tools, and which is less prone to breakage. The number of cutting elements usable with certain embodiments may also be large.

For a better understanding of the present invention and to show how the same may be carried out into effect reference will now be made, by way of example, to the following drawings, in which: Fig. 1 shows a partial section of a head unit for a filament trimmer according to a first embodiment of the present invention.

Fig. 2 shows a sectional view of Fig. 1 taken on the line A-A; Fig. 3 shows an enlarged view of a mounting portion of Figure 2; Fig. 4 shows a head unit for a filament trimmer according to a second embodiment of the invention.

Fig. 5 shows a sectional view of the mounting portion of Fig. 4 taken on line B-B; Fig. 6 shows a sectional view of the mounting portion of Fig. 4 taken on the line C-C; and Fig. 7 shows a sectional view of a modification of the head unit shown in Fig. 4.

With reference to Figures 1 and 2, there is shown a portion of a filament trimmer or, as it is more commonly known, a strimmer, having a head unit 1. The head unit 1 is arranged to be engaged through the shaft 2 by a rotary motor of the strimmer, thus enabling the head unit 1 to be rotated bodily by the motor.

The head comprises a circularly cylindrical cuplike holder 3 which is closed at its upper end by a wall 4 but open at its lower end. A threaded shaft 5 passing through the centre of the wall 4 connects the holder 3 to the motor drive. Alternative embodiments could utilize a bayonet type coupling to connect the head unit to the motor. Moreover, the head unit can be designed so that it can be a replacement for a conventional head unit of a known type of trimmer.

The holder 3 has a flange 6 at its open end and two holes or channels 7, spaced apart by 1800, through the cylindrical side wall of the holder to receive cutting elements 11. As will become apparent one or three or more such holes may be provided, one being adequate for a small trimmer. Projecting downwardly from the centre of the interior of the holder is an internally threaded mounting cylinder 8 with which is threadably engaged the stem 9 of a ground engaging support 10 of part spherical form.

This head unit is designed to be used with a cutting element 11 comprising an elongate filament 12, an enlarged retaining portion 13, an intermediate strengthening portion 14 and a handling stem 15. These cutting elements are preferably formed as a single piece from a mouldable material although, in an alternative embodiment, the enlarged retaining portion may be formed separately and be crimped, or otherwise secured, to the cutting element before use. In either case, the cutting element 11 preferably comprises a durable material such that the filament is resistant to wear and exhibits an appropriate degree of flexibility.

A suitable material is, for example, Nylon.

To mount the cutting element 11 in one of the retaining holes the filament is inserted through the or one hole 7 from the radially inner side until the enlarged retaining portion contacts the inner side of the wall of the holder thereby preventing further insertion. Access for this operation is gained through the lower, open end of the holder 3.

Figure 3 shows an enlarged, cross-sectional view of the cutting element mounted in a retaining hole.

The enlarged, spherical, retaining portion fits into a suitably shaped recess in the inner surface of the wall surrounding the hole. The diameter of the emerging portion 14 is sufficiently small that, when fully inserted, the cutting element can pivot about the centre of the enlarged portion by sliding between the abutting surfaces of the enlarged portion and the recess. This pivoting helps reduce the risk of the filament breaking when it is forced against the outer edge of the hole, for example when the rotating head strikes a rigid object such as a stone, by reducing the breaking force between the filament and the outer edge of the hole. The angle e through which the cutting element can pivot is preferably greater than 5 , for example 400.

Whilst Figure 3 illustrates pivoting in a plane perpendicular to the axis of rotation, it will be clear that the cutting element is free to pivot in any direction about its pivot point.

In use, the motor rotates the head unit at high speed and the resulting high speed rotation of the projecting ends of the filaments provides the required cutting action. The centrifugal force acting on the cutting elements causes them to be forced radially outwards, the enlarged end portion being pushed firmly against the bush. Thus, in use, the cutting elements are more firmly retained by the mount than is the case when the head is stationary.

The risk of the cutting element breaking is reduced further by the incorporation into the cutting element 11 of the intermediate strengthening portion 14. The diameter of this portion may be at least twice that of the filamentary portion 12.

Figure 1 illustrates a further feature which is included in order to reduce the risk of the filament breaking when the head strikes a rigid object. This involves the flange 6 which projects outwardly from the lower circumferential surface of the holder 3. In use, if a rigid object is encountered by the head unit it is struck firstly by the flange 6. As the head rotates, the filament can bend sufficiently to pass inside the object thus reducing substantially the breaking force exerted by the outer edge 36 of the retainer on the filament 12. The width of the flange need not be great, for example 5 mm is sufficient for a nylon filament.It is preferable that the filament emerges from the retaining hole in a plane relatively close to the plane of the upper surface of the guard rim, as a large spacing between the two planes will increase the risk that a rigid objet may jut over the rim and make contact with the emerging portion of the cutting element. The two planes are preferably less than 8 mm apart. It will be appreciated that the rim is equally effective if it is situated above, rather than below, the emerging filament.

Two further features which also help to reduce filament breakage are the smoothing of the outer edges of the holes 7, as shown in Fig. 3, and the smoothing of the upper, peripheral, edge of the flange 6 as shown in Fig. 1.

In order to prevent the cutting element 11 from disengaging itself from the hole, a retaining wall 16 is arranged adjacent the inside edge of the hole 7.

The retaining wall extends behind and below the enlarged retaining portion 13 of a cutting element when the element has been loaded. Access for loading and unloading of the cutting element is obtained by rotating the retaining wall about the pivot point 25.

The embodiment of Figure 1 includes a ground engaging support or "balance ball" 10 attached to the end of a column 9 which projects downwardly from the housing 3. Due to the smooth lower surface of the ball it tends not to dig itself into the ground and allows for smooth trimming. The trimmer may not therefore require a support strap.

The embodiment described above may be modified by relocating the housing 3 to a lower position on the column 9 and inverting it so that access to remove and load cutting elements can be obtained through the open upper end.

Figure 4 to 6 show a further embodiment of the invention which comprises a head unit 17 which may be moulded as a single piece. Figure 5 and 6 show closeup cross-sectional views of the mounting portion of Figure 4 taken on the lines B-B and C-C respectively.

The mounting portion 18 comprises a member 19 projecting upwardly from a circular base portion 20 and, formed in the mounting portion, a key-hole shaped slot 21, the width of the slot being greatest towards its lower end. The dimensions of the slot are arranged to be such that the elongate filament 12 of a cutting element of the type described with reference to Figure 3 can be inserted into the slot through the upper opening. Once inserted, by pulling the projecting filament radially outwards the intermediate portion 14 of the filament can be drawn through the enlarged portion of the slot until the enlarged retaining portion 13 of the cutting element engages the rear wall of the slot.As described above, the shape of the slot is arranged to allow the cutting element to pivot about the centre of the enlarged portion by sliding between the abutting surfaces of the enlarged portion and the slot. It will be apparent that when the cutting element is fully inserted however it cannot be removed without first being reinserted. Such a configuration therefore prevents the cutting element being accidentally removed either when the strimmer is in use or when it is being transported.

Figures 4 and 5 also show a guide channel 22 which is formed on the outer surface of the central column 23, directly behind the mounting portion 18. The channel has two side walls 24 which confine the retaining portion of the cutting element between them when the element is pushed radially inward by the user.

The element is thus forced upwards by the curved section 26 lying between the two side walls and can be grasped by the operator and removed. As an alternative to the construction shown in Figures 4 to 6, the guide channel may be recessed into the central column 23.

The unit 17 may have the form generally of a cylinder with the key-hole slot 21 formed to open at the peripheral cylindrical face of the cylinder, their being a hole extending behind the slot 21 and parallel to the rotational axis to provide a retaining wall for the cutting element. The slot and main channel of the key- hole slot 21 opening into that axially extending hole.

Figure 7 shows an axial diagrammatic crosssectional view of a modification of the embodiment shown in Figures 4 to 6 in which is included a ground engaging support 10. The ground engaging support comprises a retaining plate 31 attached to a part spherical base portion 33 by screws 28, and a bearing portion 30. The ground engaging support is coupled to a shaft 27 by means of a circlip or locknut 29 with the shaft in turn engaging the head 1 by means of a screw thread 32. As described above with reference to Figure 1, the ground engaging support prevents the trimmer from digging itself into the ground.

Modifications of the above described embodiments may provide means, integral with the head unit, for storing spare cutting elements. For example, with reference to Figs. 1 and 2, spare cutting elements may be stored within the housing 3 or within the balance ball.

Similarly, it will be apparent that such integral storage means can be provided in the embodiment described with reference to Figures 4 to 7.

Claims

1. A rotatable head of, or for attachment to, a rotary cutter for use with a cutting element having an elongate cutting portion and an enlarged retaining portion, the head comprising a mounting portion for the cutting element, the mounting portion having a hole or channel passing therethrough in a direction having a component at right angles to the direction of rotation of the head, the arrangement being such that in use the cutting element can extend through and project beyond the hole or channel whilst the element is retained by the abutment of surface portions of the retaining portion against surface portions of the mounting portion at the radially inner end of the hole or channel, the hole or channel being so formed that the element can pivot bodily with respect to the mounting portion.

2. A head according to claim 1 wherein the hole or channel is a hole defined by a passage through which the flexible portion needs to be threaded to load the cutting element.

3. A head according to claim 1 wherein the hole or channel is an open-sided channel.

4. A head according to claim 3, wherein the channel in cross-section is key-hole shaped.

5. A head according to any one of the preceding claims comprising a hollow cylinder having its axis substantially aligned with the axis of rotation of the head, wherein the or each mounting portion is a portion of the wall of the cylinder and the hole or channel of the or each mounting portion passes through the wall.

6. A head according to any one of claims 1 to 4 comprising a body portion providing a surface arranged to be substantially perpendicular to the rotational axis of the head, the or each mounting portion projecting from said surface.

7. A head according to any one of the preceding claims comprising at least one flange for rotation with the head, the or each flange projecting radially beyond the outer edge of the or each hole or channel.

8. A head according to any one of the preceding claims comprising, for the or each mounting portion, a retaining wall adjacent the radially inner end of the associated hole or channel.

9. A head according to claim 8, wherein the or each retaining wall is spaced radially inwardly of the radially inner end of the associated hole or channel to allow the cutting element to be loaded but is sufficiently close thereto to prevent the cutting element from being accidentally removed.

10. A head according to claim 9, wherein the or each retaining wall is curved in a radial plane from a radially inner location to a radially outer location to assist in loading and unloading of cutting elements.

11. A head according to claim 10, comprising two side walls extending on either side of and substantially parallel to said radial plane to guide the cutting element in its movement along the curved retaining wall.

12. A head according to any one of the preceding claims wherein the flexible cutting portion is a filament.

13. A rotatable head substantially as hereinbefore described with reference to Figs. 1 to 3 or Figs. 4 to 6 of the accompanying drawings.

14. A head according to any one of the preceding claims in combination with a cutting element having an elongate cutting portion and an enlarged retaining portion.

15. A cutting element for use with a head according to any one of claims 1 to 13 and comprising an elongate filamentary portion and a retaining portion for abutting the end of the hole or channel opposite the end from which the filamentary portion projects, wherein the filament has a larger cross-sectional area in the region proximal to the retaining portion than in the region distal to the retaining portion.

16. A cutting element substantially as hereinbefore described with reference to Figs. 1 to 7 of the accompanying drawings.

17. A cutting element according to claim 15 or 16 in combination with a head according to any one of claims 1 to 13.