GB2154115A

GB2154115A - Orbital cutting system

Info

Publication number: GB2154115A
Application number: GB8506401A
Authority: GB
Inventors: John Alexander Reynolds; Michael Rudd; John Samuel Cooper; Kevin Michael Fisher
Original assignee: BIRMID QUALCAST
Current assignee: BIRMID QUALCAST
Priority date: 1983-07-26
Filing date: 1985-03-12
Publication date: 1985-09-04
Also published as: GB8506401D0; GB2154115B

Abstract

An orbital cutting system for mowing or trimming vegetation has a cutter pivotally mounted on a rotary head (20), the pivot being displaced from the axis of the head such that the cutter orbits the axis when the head is rotated. The cutter is pivotally mounted on an eyelet projecting from the underside of a peripheral flange (11), the eyelet being protected by a ramped step (30) on the underside of the flange (11) immediately upstream of the eyelet in the direction of rotation. <IMAGE>

Description

SPECIFICATION Orbital cutting system This application is divided from our copending application 8418383 and the invention relates to an orbital cutting system for mowing or trimming vegetation, the system comprising at least one pivotally mounted cutter orbiting the axis of a rotary support head.

A known orbital cutting system consists of a rotary disc having one or more elongate blades pivotally mounted at its periphery. A cutting system of this type is shown, for example, in British Patent 1 570 252.

The device shown in Patent 1 570 252 is designed, however, for portable trimmer units which are used for cutting light growths of vegetation, and it would be inadequate for use in ground-supported lawnmowers where the cutting head is maintained in a fixed position close to the ground. In these circumstances air drag and grass drag on the rotary head can significantly affect performance.

One particular problem with prior devices of this type is that of the blade becoming detached from its mounting when under heavy load. This is at least partly due to the conflicting requirements of providing a blade which can be readily attached and detached while at the same time remaining securely in position when subjected to a heavy load in use.

Previous arrangements have also included those in which the blade must be precisely aligned in a predetermined direction before it can be fitted or removed from the head, the predetermined direction being outside the normal range of angular movement of the blade when in use. One such arrangement is shown, for example, in U.S. Patent 3 320 733. These arrangements may provide a more secure attachment but lack the ease of fitting and removal associated with rotary discs having snapfitted orbital cutters.

In accordance with the present invention there is provided an orbital cutting system comprising a cutter pivotally mounted on a rotary support head, the pivot being displaced from the axis of the head such that the cutter orbits the said axis when the head is rotated, and characterised by the cutter being pivotally mounted on the underside of the rotary head whereby the cutter orbits the said axis in a plane disposed beneath the head.

The underside of the head preferably includes means for guarding the pivotal mounting against the impact of stones or other solid obstacles during rotation of the head, the guard means being disposed immediately upstream of the pivot relative to the direction of rotation.

In a preferred embodiment of the invention the guard means comprises a step having a ramped leading edge.

By way of example only, an orbital cutting system embodying the invention will now be described with reference to the accompanying drawings, in which Fig. 1 is an underneath view of a cutter head for a ground-supported lawnmower; Fig. 2 is a section on line D-D of Fig. 1; Fig. 3 is a top plan view of the head shown in Figs.

1 and 2; Fig. 4 is a scrap section on line G-G of Fig. 1; Fig. 5 is a scrap section on line H-H of Fig. 1; Fig. 6 is a side view of a pivot mounting for the cutting element in the head of Figs. 1-5; Fig. 7 is a section on line A-A of Fig. 6; Fig. 8 is a plan view of a cutter blade for mounting on the pivot of Figs. 6 and 7; and Fig. 9 is a side view of the blade shown in Fig. 8.

Referring to these Figures, the cutter head 20 shown in Figs. 1-5 is formed of plastics material and generally has the shape of a truncated cone with a flat disc top 10 and a peripheral flange 1 lIThe centre of the head is moulded with a brass insert 12 for receiving a motor shaft (not shown). In use, the head 20 rotates about a substantially vertical axis, the flange 11 then being at a lower level than the central disc 10.

The upper surface of the central disc 10 has eleven equi-spaced fan blades 13 which draw a cooling flow of air over the motor when the head 20 is rotated.

The assembly is stabilised by means of six webs 14 located beneath the central disc 10. To prevent the resulting sector compartments formed by the webs from becoming clogged with grass cuttings, and to reduce both air and grass drag, a flat disc 15 is fitted beneath the webs 14 parallel to the central disc 10.

In practice, the flange 11 shown in Figs. 1-5 is provided with an eyelet for the pivoted mounting of either a plastic cutting blade or a length of flexible cutting line. Atypical eyelet is shown in Figs. and 7, the eyelet being riveted to the flange 11 through the small hole 16. When riveted in position, the enlarged head 17 of the eyelet is disposed beneath the flange 11 with the intermediate portion 18 bearing against the underneath surface of the flange, and the end portion 19 passing through the hole 16. Awasher (not shown) is fitted underneath the riveted head of the eyelet boss when it is attached to the flange, the washer nestling between the two ribs 35 (Fig. 3) and spreading the torque load on the plastic over a wider area.

A cutter blade for pivotal attachment to the eyelet is shown in Figs. 8 and 9. The blade consists of an elongate portion 21,the leading edge of which performs the cutting action, and an enlarged head portion 22 with a keyhole opening 23. The blade is reversible so that either edge can be used as the leading edge. The enlarged portion 24 of the keyhole opening 23 is a snap-fit over the head 17 of the eyelet. Once fitted, the blade can be pulled outwards until the intermediate portion 18 of the eyelet receives the reduced portion 25 of the keyhole opening 23. In this position the blade cannot be detached from the eyelet. The blade is retained in this non-detachable position by centrifugal force when the cutter head is subsequently rotated at high speed.

The blade also includes an opposed pair of "pips" 26, one of which enters a groove 27 (Fig. 1) in the underneath surface of the flange 11 whenever the blade is subjected to a heavy load. Such loads force the blade to pivot about the eyelet until a substantial portion of the blade lies within the periphery of the head 20. The pip 26 running in the groove 27 prevents the resulting reversal of centrifugal force on the blade from detaching the blade by preventing movement of the enlarged portion 24 of the keyhole opening 23 back into alignment with the head 17 of the eyelet.

The eyelet is protected from stones and other obstacles by a step 30 in the flange 11 immediately upstream of the eyelet in the direction of rotation.

The direction of rotation is anticlockwise as viewed in Fig. 1 and the step 30 is shown most clearly in the scrap section of Fig. 4. It can be seen from this section that the step 30 is itself protected by extending it back parallel to the flange 11 for a short length 31 and then providing a lead-in ramp 32. It can also be seen from Fig. 1 that the trailing edge of the step 30 is profiled to accommodate the head 22 of the blade should the blade swing forward of its radial position during cutting.

The opposite side of the cutter head 20 is weighted to counterbalance the eyelet and the blade, and the flange 11 is therefore similarly ramped at 33 as shown in Figs. 1 and 5.

Instead of attaching a blade to the eyelet of Figs. 6 and 7, an alternative cutting element in the form of a short length of nylon line can be connected to the eyelet. For example the line can be passed through the eyelet with a small blob at one end to prevent it running through the eyelet hole 34 when the head is rotated. The inside of the hole 34 is radiused to stop the nylon line chafing and, as shown in Figs. 6 and 7, the outer edge of the eyelet is also provided with a part-radius profile to prevent any possibility of the metal edge cutting the line. Alternatively the line might be connected to a keyhole loop which is snapped on to the eyelet in the same manner as the cutter blade.

Claims

CLAIMS 1. An orbital cutting system for mowing or trimming vegetation, the system comprising a cutter pivotally mounted on a rotary support head, the pivot being displaced from the axis of the head such that the cutter orbits the said axis when the head is rotated, and characterised by the cutter being pivotally mounted on the underside of the rotary head whereby the cutter orbits the said axis in a plane disposed beneath the head. 2. A system according to Claim 1 in which the underside of the head includes means for guarding the pivotal mounting against the impact of stones or other solid obstacles during rotation of the head, the guard means being disposed immediately upstream of the pivot relative to the direction of rotation. 3. A system according to Claim 2 in which the guard means comprises a step having a ramped leading edge. Amendments to the claims have been filed, and have the following effect: (a) Claims 1 to 3 above have been deleted or textually amended. (b) New or textually amended claims have been filed as follows:-

1. An orbital cutting system for mowing or trimming vegetation, the system comprising a plastic cutter blade with an opening for snap-fitting overthe head of a pivot pin on the underside of a rotary support head, the pin being displaced from the axis of the head such that the blade orbits the axis while being retained substantially in a radial position by centrifugal force when the head is rotated at a sufficiently high speed, the blade pivoting rearwardly from the radial position under a heavy load such that a substantial portion of the blade lies within the periphery of the head; and means disposed on the underside of the head upstream of the pivot relative to the direction of rotation for guarding the pivot against the impact of stones or other solid obstacles during rotation of the head, the guard means accommodating limited forward pivotal movement of the blade from its radial position.

2. A system according to Claim 1 in which the guard means comprises a step with a profiled trailing edge for accommodating the limited forward pivotal movement of the blade.

3. A system according to Claim 1 or claim 2 in which the rotary support head has a radiallyextending peripheral flange, the cutter blade being pivotally mounted on the underside of the flange.

4. A system according to any one of the preceding claims in which the cutter blade is displaceable outwardly from the axis of the rotary head between a detachable and a non-detachable position, the blade being retained in its non-detachable position by centrifugal force when the head is rotated at a sufficiently high speed.

5. A system according to claim 3 in which the pivot pin comprises an eyelet riveted to the flange, the eyelet having an enlarged head, an intermediate portion7 and a reduced diameter end portion, the intermediate portion bearing against the underneath surface of the flange and the end portion passing through a hole in the flange.

6. A system according to claim 5 further comprising a washer fitted underneath the riveted head of the eyelet to spread the torque load.