IMPROVEMENTS RELATING TO CUTTING APPARATUS

Abstract: The present specification describes a cutting apparatus comprising at least one fixed cutting blade (1) having a cutting edge which extends generally radially from an axis of rotation (4), and at least one movable blade (3) which is mounted to be rotatable about the axis of rotation (4), said at least one movable blade (3) and/or said at least one fixed cutting blade (1), having an arcuate cutting edge which extends outwardly from the axis of rotation (4) and which is concave in the direction of the other of said blades.

Description: DESCRIPTION I MP R OVEME NT S R E L AT I N G TO C UTT I NG AP P AR ATU S The present invention relates to a cutting apparatus. More particularly the present invention relates to a cutting apparatus of the rotary type comprising a stationary or fixed cutting blade and a movable blade which follows a rotary path. Such rotary cutting apparatus is suitable for use in the hedge cutting device of the Applicants own British Patent No.2,266,648, or in other rotary cutting apparatus such as, for example, rotary cutting head electric razors. According to the present invention there is provided a cutting apparatus comprising at least one fixed cutting blade having a cutting edge which extends generally radially from an axis of rotation, and at least one movable blade which is mounted to be rotatable about the axis of rotation, said at least one movable blade and/or said at least one fixed cutting blade having an arcuate cutting edge which extends outwardly from the axis of rotation and which is concave in the direction of the other of said blades. According to a further feature of the present invention there is provided a cutting apparatus comprising at least one fixed cutting blade having a cutting edge which extends generally radially from an axis of rotation, and at least one movable blade which is mounted to be rotatable about the axis of rotation, said at least one movable blade having an arcuate cutting edge which extends outwardly from the axis of rotation and which is concave in the direction of rotation of the movable blade. Thus by virtue of the construction of the present invention a region of the curved cutting edge remote from the centre of rotation first contacts the cutting edge of the fixed cutting blade as the movable blade rotates about the axis of rotation, with contact being made at a point on the fixed blade which is likewise remote from the centre of rotation. Then as the movable blade continues to rotate the point or region of contact between the fixed and movable blades moves towards the axis of rotation. As a result of the above operation of the present invention any material extending between the blades, which is difficult to cut, tends to be moved towards the centre of rotation where the force available to cut material is the greatest. In a preferred embodiment of the present invention the cutting edge of either or both of the fixed and movable cutting blades is flexible. This can be effected by the blades being resiliently mounted or by the section of the blades incorporating the cutting edge being resiliently supported in the remainder of the respective blades. Preferably the fixed blade is rigidly mounted with a rigid cutting edge, and the cutting edge section of the movable blade is flexibly mounted on the remainder of the movable blade, which is mounted rigidly on a thrust bearing for rotation about the axis of rotation. Thus by virtue of the flexible mounting of at least the cutting edge of the movable blade, the blades are spring loaded together so that in the absence of any load they press against each other as the movable blade rotates. The resultant friction therebetween sharpens the cutting edges of both blades. Further, each blade preferably has two parallel planar surfaces with the cutting edge being formed by an acutely chamfered edge. The blades are then preferably arranged so that the acutely chamfered edges are substantially parallel to each other when in interengagement, and generally perpendicular to the surface of the material being cut. Thus, due to the planar surface of the blades being at an angle to the surface of the material being cut, as the blades cut the angle with which the blades penetrate the material creates more pressure on the outside of the blades than the inside, tending to press the blades together. This is advantageous as it tends to prevent any separation of the blades which would allow the material to twist and allow the material to pass between the blades without being cut. Alternatively the chamfered edges of the respective blades may be arranged such that the planar surface of the chamfered edge of the movable blade is peφendicular to the axis of the material to be cut and parallel to the side face of the fixed blade commencing at the apex or cutting edge of the blade, with the chamfered surface of the movable blade sliding over the said side face of the fixed blade during a cutting action. In a further alternative the respective side faces of the movable and fixed blades, commencing at the apex or cutting edge of the respective blades, are parallel to each other and, in use, peφendicular to the axis of the material being cut with said side faces then engaging and sliding over each other. Further the angled outer surfaces of the respective blades are preferably continued in a blade support which is part of a screw transport mechanism. In this way cut material is transported from the cutting apparats in one continuous movement. In a preferred embodiment of the present invention there are a number of fixed blades extending generally radially of the said axis of rotation and equi- angularly spaced apart from each other, around the centre of rotation, with the radially outer end regions of each fixed blade being formed so as to gently curve in the direction of the axis of rotation, and being secured to a first annular member which is coaxial with the axis of rotation, to thus form a crown-shaped fixed blade assembly. Two movable blades mounted on an elongate shaft, extend generally radially in opposite directions from the shaft which is coaxial with the axis of rotation, within the crown-shaped fixed blade assembly, with the respective cutting edges of the movable blades sweeping over the cutting edges of the fixed blades. Whilst the radially inner end regions of the movable blades are supported in a bearing, the radially outer end regions are fixedly secured to a further annular member located within said first annular member, coaxially with said axis of rotation. The outer periphery of this further annular member is preferably provided with a series of teeth by means of which the movable blades can be driven. Alternatively said elongate shaft may be connected to a drive motor for rotating the shaft and movable blades. The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: - Fig. 1 is a perspective view of the outside of a preferred embodiment of a cutting apparatus constructed according to the present invention; Fig. 2 is an axial elevational view of the inside of the embodiment of Fig. 1; Fig. 3 is a diagrammatic partial view of the fixed blade arrangement of Figs. 1 and 2; Fig. 4 is a diagrammatic illustration of the mode of operation of the cutting assembly of Figs. 1 to 3; Fig. 5 is a diagrammatic cross-sectional view of the bearing connection between the fixed and movable blades; Fig. 5a diagrammatically illustrates a cross-section of a modified construction with an axially adjustable drive coupling; Fig. 6 is a diagrammatic illustration of the cutting blade interengagement; Fig. 7 is a diagrammatic partial view of a modified construction in which the fixed blades have a concave cutting edge and the movable blades have a straight cutting edge; Fig. 8 is a diagrammatic illustration of an alternative cutting blade interengagement taken along line x-x in Fig. 7; and Fig. 9 is a diagrammatic illustration of a further alternative cutting blade interengagement. Figs. 1 and 2 of the accompanying drawings illustrate a preferred embodiment of the present invention comprising a number of fixed cutting blades 1 and two movable cutting blades 3 arranged to rotate about an axis of rotation 4. The fixed cutting blades 1 extend generally radially from a central hub 5 which is coaxial with the axis of rotation 4 for the movable blades 3. The fixed blades 1 are equi-angularly spaced apart from each other, around the central hub 5 , and the free end region 7 of each fixed blade 1 , is deformed in a gentle curve so as to lie parallel to the axis of rotation 4 with the respective end regions of each fixed blade being secured to a first annular member 9, to form a crown- shaped fixed blade assembly generally designated 11. This crown-shaped fixed blade assembly 11 is secured to, or integrally formed with, a drive guard 13 referred to herebelow. The two movable blades 3 are mounted for rotation in the central hub 5 , the construction of which is described herebelow with reference to Fig. 5 of the accompanying drawings . The movable blades 3 extend from the central hub 5 , generally radially therefrom in substantially opposite directions. Each movable blade 3 comprises a fixed section 15 and a cutting edge section 17, with the cutting edge section 17 being secured to the fixed section 15 by two resiliently flexible hinge members 19. Thus the cutting edge section 17 and hence the cutting edge 21 of each movable blade 3 is resiliently movable, the puφose for which is described hereinbelow. Further whilst the radially inner end of the fixed section 15 of each moveable blade 3 is secured to the central hub 5, the radially outer end region of each fixed section 15 is secured to a further annular member 23 which is coaxially located within said first annular member 9. The outer periphery of the further annular member 23 is provided with a series of teeth 25 which engage with a complimentarily toothed drive belt (not shown) which extends within the drive guard 13 and connects with a suitable drive gear or motor (not shown). Fig. 3 of the accompanying drawings illustrates the rigid attachment of each fixed blade 1 to the central hub 5 by a single bolt 27 and the rigid attachment thereof to the first annular member 9 by two further bolts 29, with Fig. 4 diagrammatically illustrating the mode of operation of the blades 1 and 3. Fig. 5 of the accompanying drawings is a diagrammatic cross sectional view of the central hub 5 , from which it will be seen that the portion 31 of the central hub 5 , which is fixedly connected to the inner end regions of the fixed blades 1 , carries a thrust bearing in the form of a ball race 33 which rotatably carries a shaft 35 which extends coaxially with the said axis of rotation 4, and which is fixedly connected to the inner end regions of said movable blades 3. The shaft 35 is threaded as at 37 and can, when installed in, for example, a hedge cutter as per the Applicants British Patent No. 2,266,648 be connected to a screw impeller (not shown) for entraining cut waste material to a collection receptacle (not shown). Further, as an alternative to a drive via teeth 25, the shaft 35 can be connected to a drive motor. In an alternative embodiment (not illustrated) the movable blades are of integral and rigid or relatively rigid construction i.e they do not have resilient cutting edge regions as per the embodiment of Figs, 1 and 2, and to allow the movable and fixed blades to move relatively to each other should this be necessary to avoid jamming, an axially adjustable spring loaded coupling is provided in the drive shaft for resiliently maintaining pressure between the rotatable ie said movable, blades and the fixed blades. This can take any desired form, one particular embodiment shown in Fig. 5a, providing a region of axial splines 45 on one end region of a section of the shaft 35, which splined region 45 is axially movable in a bearing 47 against a spring 49, which bearing 47 is axially secured to another section of the drive 51. As evident from both Figs. 1 and 2 of the accompanying drawings, each fixed blade 1 has a cutting edge 2 which extends radially from the central hub 5. However, the cutting edge 21 of each movable blade 3 is arcuate and curves concavely in the direction of rotation 'A' (Fig.l). Thus the outer end region 21' of the cutting edge 21 of each movable blade 3, will initially interengage with a particular fixed blade 1, and as the movable blades 3 rotate in direction 'A' , the point or region of contact between the blades 1 , 3 will move inwardly towards the central hub 5. Thus any material between the blades 1, 3, which is difficult to cut, will tend to be moved inwardly towards the central hub 5, where the force available to cut material is greater than that available at the periphery . Cutting performance is therefore optimised. In an alternative embodiment (not illustrated) the fixed blades also have a concave cutting edge which is directed towards the cutting edges of the movable blades, this enabling the concavity of one or both cutting edges to be reduced, if desired, to still attain the desired effect. In a still further alternative embodiment (see Fig. 7) the fixed blades 1 have a concave cutting edge 53 and the movable blades 3 have a straight cutting edge 55 when viewed along the axis of rotation, this arrangement being basically equivalent to the preferred construction of Figs. 1 and 2. Further, as shown in Fig. 6 of the accompanying drawings, each blade 1, 3 has parallel planar surfaces 39 with the cutting edges 2, 21 being formed by acutely chamfered edges 41, 43. The blades 1, 3 are so arranged that the acutely chamfered edges 41, 43 interengage parallel to each other and generally peφendicular to the material to be cut. Due to the resiliently flexible cutting edge 21 of the movable blade 3, the acutely chamfered edges 41, 43 are spring biassed together, enhancing cutting, and shaφening both blades 1, 3 as the acutely chamfered edges 41 , 43 move over each other due to the friction therebetween. Also, with the acutely chamfered edges 41, 43 generally peφendicular to the surface to be cut, the planar surfaces 39 are at an angle to the said surface of the material being cut. Thus as the blades cut, the angle with which the blades 1 , 3 penetrate the material creates more pressure on the outside of the blades than the inside, tending to press the blades 1, 3 together. This is advantageous as it tends to prevent any separation of the blades 1 , 3 which could allow the material to twist and enable the material to pass between the blades 1 , 3 without being cut. Further, the angled outer surfaces 39 of the respective blades 1 , 3 are contained in a blade support (not shown) which is part of the screw impeller (not shown) previously mentioned, whereby cut material is transported from the cutting apparatus in one continuous movement. In an alternative construction shown in Fig. 8, the chamfered edges 41,43 of the respective blades 3,1 may be arranged such that the planar surface 41 of the chamfered edge of the movable blade 3 is peφendicular to the axis of the material to be cut and parallel to the side face 39 of the fixed blade 1 commencing at the apex or cutting edge 2 of the blade 1, with the chamfered surface 41 of the movable blade 3 sliding over the said side face 39 of the fixed blade 1 during a cutting action. In a further alternative construction shown in Fig. 9, the respective side faces 39 of the movable end fixed blades 3, 1 commencing at the apex or cutting edge 21,2 of the respective blades 3,1 , are parallel to each other and, in use, peφendicular to the axis of the material being cut, with said side faces 39 then engaging and sliding over each other. The present invention thus provides a simple though advantageous cutting apparatus for use in a variety of situations such as, for example, hedge cutting and shaving.

Claims: CLAIMS 1. A cutting apparatus comprising at least one fixed cutting blade having a cutting edge which extends generally radially from an axis of rotation, and at least one movable blade which is mounted to be rotatable about the axis of rotation, said at least one movable blade and/or said at least one fixed cutting blade having an arcuate cutting edge which extends outwardly from the axis of rotation and which is concave in the direction of the other of said blades. 2. A cutting apparatus comprising at least one fixed cutting blade having a cutting edge which extends generally radially from an axis of rotation, and at least one movable blade which is mounted to be rotatable about the axis of rotation, said at least one movable blade having an arcuate cutting edge which extends outwardly from the axis of rotation and which is concave in the direction of rotation of the movable blade. 3. Apparatus as claimed in claim 1 or claim 2, in which the cutting edge of either or both of the fixed and movable cutting blades is flexible. 4. Apparatus as claimed in claim 3, in which the region of the cutting edge of the or each flexible cutting blade, is resiliently secured to the remainder of the blade. 5. Apparatus as claimed in claim 4, in which the or each fixed blade is rigidly mounted with a rigid cutting edge, the cutting edge section of the or each movable blade being flexibly mounted on the remainder of the movable blade which is mounted on a thrust bearing for rotation about the axis of rotation. 6. Apparatus as claimed in any one of claims 1 to 5, in which the cutting edges of the or each fixed and movable blades are spring loaded against each other. 7. Apparatus as claimed in any one of claims 1 to 6, in which the or each movable blade is mounted for rotation about the axis of rotation on a drive which includes an axially resilient coupling by means of which the or each movable blade can move along the axis of rotation away from the or each fixed blade whilst being spring biased towards the or each fixed blade. 8. Apparatus as claimed in claim 1 or claim 2, in which the or each fixed blades has an arcuate cutting edge which extend outwardly from the axis of rotation and which is concave in the direction of the cutting edges of the or each movable blade. 9. Apparatus as claimed in claim 1, in which the or each movable blades has a straight cutting edge when viewed along the axis of rotation, and the or each fixed blade has an arcuate cutting edge which extends outwardly from the axis of rotation and which is concave in the direction of the cutting edge of the or each movable blade. 10. Apparatus as claimed in any one of claims 1 to 9, in which each blade has a planar surface which merges with an acutely chamfered edge surface to form a cutting edge. 11. Apparatus as claimed in claim 10, in which the chamfered edge surfaces of the fixed and movable blades are arranged to be substantially parallel to each other when interengaged and generally peφendicular to the surface of the material being cut therebetween. 12. Apparatus as claimed in claim 10, in which the chamfered edges of the respective blades are arranged such that the planar surface of the chamfered edge of the movable blade is peφendicular to the surface of the material to be cut and parallel to the said planar surface of the fixed blade commencing at the cutting edge of the blade, so that the chamfered surface of the movable blade slides over the said side face of the fixed blade during a cutting action. 13. Apparatus as claimed in claim 10, in which the respective planar surfaces of the movable end fixed blades, commencing at the cutting edge of the respective blades, are parallel to each other and, in use, peφendicular to the surface of the material being cut with said planar surfaces then engaging and sliding over each other.

Inventors: WILSON GRAHAM JOHN, WILSON, GRAHAM, JOHN
Applicants: WILSON GRAHAM JOHN, WILSON, GRAHAM, JOHN
Application year: 1999
Main classification: A01G3
IPC codes: A01G3