NZ237682A - Shearing hand piece: tension pin loading resultant acts in, or forwardly of, cutting zone - Google Patents

Description

Z1768Z Priority U:.,. .v .. | a. n:5to ; ■7i: Complex i-'.-.v C!sr-: 2 5 J UN Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION SHEARING HAND PIECE I, ALASTAIR MACKENZIE, an Australian citizen of RMB 3138, Ararat, Victoria 3377, AUSTRALIA hereby declare the invention, for which We pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: "SHEARING HAND PIECE" The present invention relates to shearing hand pieces for use in shearing sheep or other animals. More particularly, the invention relates to an improved cutter head of a shearing hand piece.

Conventionally, a cutter head of a shearing hand piece comprises a comb mounted on the body of the hand piece and a cutter mounted for oscillatory movement in a plane parallel to the comb, the cutter being in close contact with the comb and being moved across the comb by a cantilever drive member known as the fork. In order to achieve clean cutting of the fleece, it is necessary to apply a force to hold the cutter against the comb in order to resist the tendency for the soft wool fibres to fold over and move the cutter away from the comb. Shearing hand pieces conventionally comprise means for adjusting the loading between the cutter and the comb and this is known as setting the "tension" of the cutter. The cutter tension necessary to achieve clean cutting also results in the generation of friction between the comb and cutter resulting in heat generation and wear. A significant aspect of the shearer's art is involved in setting the tension to a sufficient level to obtain a pressure adequate to achieve satisfactory cutting but without generating - -excessive friction leading to overheating and wear. o Q Conventional cutter heads as discussed above utilise a scissors type cutting action between the teeth of the cutter and comb. It has been proposed to provide a guillotine type cutting action in which the cutter is rigidly supported so as to move in a plane extremely close to the plane of the comb so that cutting can occur without friction between the cutter and comb. However, such an action requires the use of a heavy and precise mechanism in order to achieve the necessary rigidity and close spacing between the cutter and comb. In practise, it is extremely difficult to achieve a true guillotine type action and most practical forms of mechanism will contain elements of a scissors type mechanism with some flexibility and loading between the cutter and comb and a guillotine type mechanism which is rigid without any loading between the cutter and comb.

It has been determined that the more rigid is the mechanism, the lower will be the tension required for clean cutting and hence heat generation and wear will be lower.

Existing hand pieces are also subject to significant vibration generated by the out-of-balance masses of oscillating or rotating components and it is desirable to reduce the vibration.

*T & According to the invention, there is provided a shearing hand piece comprising a cutter assembly having a comb, a cutter mounted for oscillatory movement in a plane parallel to the comb, drive means for driving the cutter, and means for applying pressure to the teeth of the cutter to provide a pressure necessary to cut wool in a cutting zone in which cutting can occur by co-operation between the teeth of the cutter and comb, said pressure-applying means comprising pressure distributing means mounted above the cutter and engaged with the teeth of the cutter to substantially equalise the pressure between the respective teeth of the cutter, and a strut device comprising at least one rigid strut for applying load to the pressure distributing means, the resultant of the load applied by the strut device acting along an axis in a direction forwardly of the hand piece and inclined towards the plane of movement of the cutter, said axis intersecting said plane of movement substantially in, or forwardly of, the cutting zone.

The application of load to the pressure distributing means along an axis which intersects, or is forwardly of, the cutting zone minimises the bending moment applied to the pressure distributing means about a transverse axis parallel to the plane of movement of the cutter. This means that the structure does not need to be of such high mass in order to provide the requisite degree of rigidity. This, in turn, leads to a reduction in the vibration of the cutter assembly, and also permits a decrease in the tension which needs to be applied to the cutter.

In one preferred form of the invention, the cutter is constrained to move in an arc by one or more links swinging from a pivot or pivots mounted in the body of the hand piece in a position at or adjacent to the location of the centre post in a conventional hand piece, the pressure distributing means being at the forward end of the link(s) and acting to transmit the drive to the cutter. The strut or struts are analogous to the traditional "tension pin" and when loaded apply a downward force on the cutter via the pressure distributing means and generate a tension in the link or links. The or each strut and the or each link are so positioned that they intersect at a point substantially on a plane normal to the comb and extending through the approximate centres of resistance of the cutting edges of the cutting teeth whereby the applied load does not generate any bending moment on the pressure distributing means or in the link(s) or in the strut(s). This configuration permits a lightweight construction of high rigidity. r The link(s) may be formed in a thin plate-like construction in a plane substantially parallel to the plane of the comb, with the strut(s) being simply supported at each end and being directed symmetrically with respect to the cutter teeth. The link(s) can twist or rotate by a small amount to permit deflection of the pressure distributing means about a longitudinal axis to equalise the pressure on the cutter teeth. However the link(s) is still rigid enough to transmit the drive. This configuration permits the elimination of certain pivotal joints incorporated in prior constructions to obtain pressure equalisation and leads to a further reduction in the oscillating mass.

Advantageously, the drive means is located at or behind the pivotal mounting of the link(s) leading to a reduction in the out of balance mass.

The pressure distributing means may comprise a so-called "chicken's foot" comprising one or more pairs of divergent legs each engaged with a respective one of the cutter teeth and in a preferred embodiment the chicken's foot is rigidly mounted at the forward end of the link(s).

Advantageously, the drive means comprises a crank having an axis which is inclined to and which at least approximately intersects the axis of crank rotation, and a swivel joint linked to the crank and mounted for oscillatory movement about a swivel axis at right angles to the plane of the cutter and comb, the link(s) being interposed between the swivel joint and the pressure-distributing means such that rotation of the crank results in oscillation of the link(s) in a plane substantially parallel to the plane of the cutter and comb.

Advantageously, the strut device is so arranged that the resultant of the load applied by the device acts along an axis which intersects the plane of movement of the cutter substantially in, or forwardly of, the cutting zone. The cutter is constrained to move in an arc by at least one link pivotal about the axis oscillatory movement, the link(s) carrying the pressure distributing means at its forward end in order to transmit the drive to the cutter. This configuration permits a lightweight construction of high rigidity. The link(s) may be formed in a thin plate like construction in a plane substantially parallel to the plane of the comb with the strut device being simply supported at each end.

Embodiments of the invention will be described by way of example only with reference to the accompanying drawings in which:- Figure 1 is a fragmentary longitudinal section of an embodiment of the shearing hand piece in accordance with the invention and showing the forward end of the hand piece; Figure 2 is a schematic plan view of a cutter of the cutting head of the hand piece; Figure 3 is a schematic plan view showing a swivel housing and sleeve of a swivel drive-transmitting joint of the hand piece; Figures 4 to 6 are schematic perspective views showing alternative configurations; Figure 7 is a section similar to Figure 1 and showing another embodiment; and Figure 8 is a section similar to Figure 1 and showing yet another 5 embodiment.

As shown in the accompanying drawings, a shearing hand piece comprises a tubular housing 2 which forms the handle of the hand piece and having at its forward end a cutter head comprising a comb 4 and a cutter 6 10 which oscillates in the plane parallel to the comb 4. The tubular housing 2 encloses a drive motor which may be a pneumatic motor as described in my Australian patent application 67781 /90 or an electric motor. Alternatively, the tubular housing 2 may contain a drive gear which is powered by a conventional down-tube from a remote electric motor. An output shaft 8 of the 15 motor or drive gear extends axially of the housing 2 and is linked by a drive system to the cutter head to cause oscillatory movement of the cutter 6 across the comb 4. The embodiments to be described primarily provide an improved cutter assembly which results in a lighter and simpler construction without substantial out-of-balance masses which could create significant vibration in the 20 forward end of the hand piece.

The cutter 6 comprises at least two teeth 10 (see Figure 2) extending forwardly from a body 12. The axis A-A shown in Figure 2 extends through the approximate centres of resistance of the cutting edges of the two teeth 10. A 25 pressure-distributing member 14 which is known as a "chicken's foot" is of bifurcated form to provide two divergent legs each of which lies above and applies pressure to one of the two cutter teeth 10 by engagement of the forward end of the leg with the tooth. The forward end of each leg includes a downwardly-extending point 16 which engages in an aperture 18 in the upper 30 surface of the respective tooth so that the points engage the teeth and transmit drive to the cutter. The chicken's foot 14 also includes downwardly projecting lugs 20 engaged in recesses 22 in the cutter body 12 to prevent the cutter 6 r &■ d3 76 u2 from flying loose if the points 16 happen to break. The chicken's foot 14 is rigidly mounted at the forward end of a flexible arm 24 of plate-like form extending in a plane substantially parallel to that of the cutter 6 and comb 4, the arm 24 being oscillated in that plane by the drive system to thereby cause 5 the cutter 6 to oscillate across the comb 4. The chicken's foot 14 includes a spherical socket 26 which receives a ball 28 at the lower end of a tension pin 30 which extends downwardly and forwardly along an axis B-B at approximately 45 ° to the plane of the comb 4. The tension pin 30 includes at its upper end a ball 32 which swivels within a part-spherical bearing surface 34 10 formed within a sleeve 36 located within a tubular spigot 38 at the forward end of the housing. A cap 40 is threadedly mounted on the spigot 38 such that rotation of the cap 40 applies movement to the sleeve 36 to displace the tension pin 30 along the axis B-B and this results in adjustment of the pressure between the cutter 6 and the comb 4. This adjustment is known as setting the 15 "tension" of the cutter.

The flexible arm 24 which carries the chicken's foot 14 at its forward end is mounted at its rear end to the base of a swivel housing 42 mounted via a spherical joint 44 from the housing 2 of the hand piece. The swivel housing 20 forms part of a swivel drive-transmitting joint between the output shaft 8 and the arm 24. The spherical joint 44 comprises a ball 46 mounted on the shank of a pin 48 secured to the housing of the hand piece and lying on an axis C-C which intersects the axis B-B of the tension pin 30 at the centre of the ball 32 at the upper end of the tension pin 30. The ball 46 of the spherical joint 44 is 25 mounted for limited axial movement along the shank of the pin 48 and the swivel housing 42 includes at its base a spherical socket 50 which surrounds the ball 46. The swivel housing 42 is thus mounted for limited universal movement about the axis of the pin 48 and also for limited rectilinear displacement along the axis of the pin 48. The swivel housing 42 is of yoke-like form comprising 30 above its base two parallel spaced arms 52 (see Figure 3). A sleeve 54 is supported in the space between the two arms 52 for oscillatory movement about an axis D-D at right angles to the plane of Figure 1 and to the axis C-C. 2^ 7 682 n - ii - The axis C-C, the axis of movement D-D of the sleeve 54 relative to the arms 52, and the axis E-E of the sleeve 54 intersect at a common point O.

Preferably, the sleeve 54 is mounted on the arms 52 of the swivel housing 42 by opposed trunnion pins 56 extending between each arm 52 of the swivel 5 housing and the adjacent side of the sleeve 54. Each trunnion pin 56 may be inserted from outside the swivel housing 42 through an aperture in the arm 52 of the housing to be received in a socket in the adjacent side of the sleeve 54 or the trunnion pins 56 may be rigidly mounted on the sleeve 54 and engaged in apertures in the opposed arms 52 by deforming the arms inwardly after 10 insertion of the sleeve.

A crank 58 is journalled within the interior of the sleeve 54 by bearings 60. The crank 58 is mounted at the forward end of the output shaft 8 of the drive motor or drive gear, with the axis of the crank 58 being inclined relative 15 to the axis of the output shaft 8 so that the crank axis also passes through, or closely adjacent to, the point O. The output shaft 8 is itself capable of limited axial movement for reasons which will be explained hereinafter.

Upon rotation of the output shaft 8 the crank 58 will describe a conical 20 path due to its inclination relative to the axis of the output shaft. The crank 58 will rotate within the sleeve 54 and will cause the sleeve 54 to oscillate in a vertical plane relative to the swivel housing 42 about the axis D-D and will transmit to the swivel housing 42 via the trunnions 56 a horizontal component of movement so that the sleeve 54 and swivel housing 42 will oscillate in a 2 5 horizontal plane about the axis C-C to thereby drive the cutter 6 via the flexible arm 24. This drive configuration with the inclined crank and sleeve results in a smaller off-centre mass and moment of inertia than conventional crank and slide mechanisms for converting rotational movement of the output shaft into oscillation of the cutter and results in less vibration.

Pressure equalisation by the chicken's foot 14 at the points 18 on the cutter teeth 10 takes place by mea^.oLa-.tOFsionaHMsrrinlthe flexible arm 24. 237682 This twist will also serve to accommodate slight misalignments due to manufacturing tolerances between the axis D-D of the trunnion pins 56, the axis C-C of the pin 48 and the axis E-E of the sleeve 54 and crank 58. This misalignment will also be accommodated by slight up and down movement of the spherical joint 44 of the swivel housing 42 by slight movement of the ball 46 of the joint along the axis of the pin 48. The pressure equalisation of the chicken's foot on the cutter teeth by slight twisting of the flexible arm results in a simple construction without the need for complex joints on the chicken's foot.

In an alternative construction, the arm 24 may be torsionally rigid, with pressure equalisation taking place by slight longitudinal rotation of the arm, this being permitted by allowing for slight lateral movement along axis D-D between the sleeve 54 and the arms 52 of swivel housing 42.

In yet another alternative construction, the arm 24 may be torsionally rigid and may be pivotally mounted at its rear end for rotation about its axis to permit pressure equalisation.

The cutter 6 will wear during use, leading to a reduction in its thickness 20 and it is also necessary for the cutter 6 to be periodically sharpened which will result in a further reduction in cutter thickness. As the cutter wears or when the cutter is sharpened, the tension in the cutter 6 can be maintained by screwing down the tension cap 40 which acts on the tension rod 30. This will jttXi. o result in slight displacement of the centre of the upper ball 32 of the tension rod 30 forwardly from the axis C-C. The resulting slight misalignment is taken up by slight tilting of the swivel housing 42 about the ball 46 of the spherical joint 44, this movement in turn being permitted by slight axially forwards displacement of the output shaft 8. In other words, as the tension cap 40 is screwed down, the swivel housing 42 will tilt slightly forwardly. It is to be 30 noted, however, that the flexible arm 24 remains axially rigid due to the tensioning effect on the arm under the force applied by the tension pin 30, avoidance of bending (as opposed to twisting) of the arm being important to the operation for the reasons described below. 3 / 682 ( To achieve clean cutting of the wool with a minimum generation of heat due to frictional forces, the pre-loading of force between the cutter and comb 5 must be very small. However, the cutter assembly must have very high stiffness to ensure that the cutter cannot be separated from the comb by wool fibres. This not only requires that the parts must be sturdily built but also requires that the arm 24 remains rigid, and hence straight in an axial sense, as any resilient bowing of the arm will reduce the stiffness of the cutter assembly. 10 Under the tensioning effect of the arm, the arm 24 remains straight even when the cutter thickness is reduced through wear or sharpening, and this is, permitted by the slight tilting of the swivel housing and the slight axial movement of the output shaft as discussed above. It will be noted from Figure 1, that the axis B-B of the tension pin 30 and a plane at right angles to the 15 cutter through the axis A-A intersect at a point H, and the spherical joint 44 has a centre at point K which is able to displace linearly along the shank of the pin 48. A straight line joining the points H and K passes along the axis of the arm 24 at all positions of the arm including inclined positions which the ^ arm must adopt as the cutter thickness reduces. The axis B-B of the tension pin is symmetrical with respect to the points 16.

The tension pin 30 is directly connected to the chicken's foot 14 by means of the spherical socket 26 with the tension pin 30 being so positioned that the axis B-B of the pin intersects the cutter 6 substantially in the cutting 25 zone of the cutter teeth, and which extends between the tips and the roots of the teeth. This configuration substantially obviates the generation of bending moment of the cutter 6 and arm 24 about a transverse axis perpendicular to the plane of Figure 1 and this, in turn, permits the arm 24 to be of thin and lightweight construction leading to reduction vibration. It will also be seen 30 from Figure 1 that the tension pin 30 acts as a simply-supported strut which is not subject to any lateral forces, apart from inertia forces, intermediate its end. This enables the pin to be of lightweight construction, such as a thin-walled ? ] MAY 1391 237682 tube.

With the configuration described, the arm 24 remains rigid in an axial sense and the bending moment applied to the chicken's foot 14 is minimised.

The resulting mechanism has a relatively high degree of rigidity which permits clean cutting at a lower tension with consequent reduction in heat generation /~n and wear.

In a modification, the arm 24 is inclined downwardly by a few degrees 10 from the housing 42 so that the axis of the arm passes through or beneath a horizontal plane containing the points 16. With this configuration, the axis B-B of the tension pin 30 is inclined from that shown in Figure 1 so that the point H lies in or below the horizontal plane containing the points 16. The purpose of this configuration is to minimise the disturbance of equal 15 distribution of the closing force that is applied to the cutter teeth and which tends to occur when the cutter meets resistance to its motion across the surface of the comb. Additionally, the axis of the pin 48 may be inclined so as to be at right angles to the axis of the arm to reduce the vertical load on the bearings. In a practical form of this modification, the pin can be defined by 20 the shank of a grub screw held by a locking nut.

In another modification, the swivel housing is modified so that the arm 24 inclines downwardly from an intermediate part of the swivel housing 42 (as vjJ opposed to the base of the housing) with the axis of the arm lying on a line joining points O and H. A separate, light, flexible tension member extends between the base of the swivel housing and the chicken's foot in the position previously occupied by the arm 24 in the arrangement shown in Figure 1. This configuration permits the point H to be further lowered beneath the horizontal plane containing the points 16, even to the level of the cutting plane itself. 30 This configuration also facilitates construction of the swivel housing and arm as an integral unit in the form of a sheet metal pressing.

O ,c 237682 In the embodiment described, the cutter has only two teeth. The principles of the invention are, however, equally applicable to cutters with more than two teeth and embodiments will now be described in relation to a cutter with four teeth.

In Figure 4, the arm 24 is rigidly attached at its forward end to a rigid fork-like member 64 having divergent legs 66. A pressure-distributing member 68 is mounted at the forward end of each leg 66 by means of a pivot 70 for pivotal movement about a longitudinal axis parallel to the plane of the comb.

Each pressure distributing member 68 engages two of the teeth 72 of the cutter, with its pivot 70 being positioned midway between those two teeth as shown in drawing 4. The tension pin 30 is connected at its lower end to the fork-like member 64.

In this embodiment, pressure equalisation between the respective teeth of each pair of cutter teeth is achieved by pivotal movement about the pivot 70 of the pressure distributing member 68 associated with that pair of teeth and pressure equalisation between the two pairs of teeth is achieved by twisting of the arm 24.

The embodiment shown in Figure 5 is similar to that shown in Figure 4 except that pressure equalizing members 80 associated with each pair of teeth 72 are rigidly attached to the arms 66 of the fork-like member 64 whereby pressure equalisation between the two teeth associated with each pressure distributing member 80 is achieved by twisting of the associated arm 66.

Pressure equalisation between the two pairs of members 80 occurs by twisting of the arm 24.

In the embodiment shown in Figure 6, the arm 24 is forked at its forward end to provide two extensions 24a each of which carries a forked pressure distributing member 100 at its forward end. In this embodiment, pressure equalisation between the two teeth 72 associated with each member 237662 100 occurs by twisting of the associated forked extension 24a and pressure equalisation between the two sets of members 100 occurs by twisting of the arm 24. The tension pin 30 is connected to each of the pressure distributing members 100 by rigid struts 102 which diverge from a pivot 104 at the lower end of tension pin 30 and are themselves connected to the pressure distributing members 100 at respective pivots 106. The resultant of the forces acting in the rigid struts 102 and the tension pin 30 (which itself acts as a rigid strut) acts along an axis which is equivalent to the axis B-B of Figure 1. The arm 24, together with forked extensions 24a and the pressure distributing members 100 can be integrally formed from a single sheet metal blank pressed and folded in order to form the pressure distributing members at the end of the extensions 24a. Similar constructional techniques may be used for the arm 24 and chicken's foot 14 of the embodiment of Figure 1. The swivel housing 42 with arms 52 may also be constructed integrally with the arm 24 from the same single sheet metal blank.

In the embodiments described, the pressure distributing member(s) and cutter are driven along an arcuate path by a linkage having a single flexible arm. In alternative arrangements, the linkage may comprise two or more arms which may form either a parallelogram or a trapezoidal linkage.

In the preceding embodiments there is disclosed a shearing hand piece comprising a cutter assembly having a comb, a cutter mounted for oscillatory movement in a plane parallel to the comb, drive means for driving the cutter, and means for applying pressure to the teeth of the cutter to provide a pressure necessary to cut wool in a cutting zone in which cutting can occur by co-operation between the teeth of the cutter and comb, said pressure-applying means comprising pressure distributing means mounted above the cutter and engaged with the teeth of the cutter to substantially equalise the pressure between the respective teeth of the cutter, and one or more rigid struts for applying load to the pressure distributing means, the resultant of the load applied by the strut or struts acting..along-an-axis-iTr"a"?ri|ection forwardly of .y' ■4 i f) 237682 the hand piece and inclined towards the plane of movement of the cutter, said axis intersecting said plane of movement substantially in, or forwardly of, the cutting zone. The application of load to the pressure distributing means along an axis which intersects, or is forwardly of, the cutting zone minimises the 5 bending moment applied to the pressure distributing means about a transverse axis parallel to the plane of movement of the cutter. This means that the structure does not need to be of such high mass in order to provide the ) requisite degree of rigidity. This, in turn, leads to a reduction in the vibration of the cutter assembly, and also permits a decrease in the tension which needs 10 to be applied to the cutter.

The tension of the cutter is set by displacing the tension pin axially, such as by means of a screw threaded mounting for the socket which houses the upper end of the pin. Substantial variation in cutter thickness must be 15 accommodated by means of the adjustable mounting for the socket. The variation in thickness occurs because the cutter will wear during use and also because the cutter will be subject to several resharpening operations, each of which will have the effect of reducing the thickness of the cutter. The correct geometry of the cutting assembly is achieved when an axis through the centre 20 of the upper swivel mounting of the tension pin and the pivot point of the arm carrying the chicken's foot is perpendicular to the plane of the comb. In this condition the lower end of the tension pin and thus the chicken's foot will oscillate in an exact plane parallel to the plane of the comb. However, with the large range of adjustment necessary to accommodate the variations in 25 cutter thickness, this desired geometry will only be achieved at one point throughout the range of adjustment. Typically the geometry is such that the correct geometry will be achieved for a cutter approximately midway through its normal working life. For cutter conditions in which this geometry is not achieved, the lower end of the tension pin and hence the chicken's foot will 30 not oscillate within a true plane. When the cutter mechanism is relatively compliant, this out of plane movement can be accommodated by the flexibility of various parts of the mechanism. However, with more rigid mechanisms such vj & ^ 7682 as that described in the preceding embodiments, the out of plane movement cannot be easily accommodated and it is therefore desirable to provide a system which ensures that the planar movement is achieved substantially throughout the range of adjustment necessary to accommodate new and worn cutters. The embodiments shown in Figures 7 and 8 seek to provide such an effect.

As shown in Figure 7, the centre of the ball 32 and also of the part-spherical bearing surface 36C lies on the axis C-C. The part-spherical bearing 10 surface 36C is defined in the interior of a solid piston 60 mounted for displacement along the axis C-C, the bearing surface 36C being formed on the axis of the piston 60 which coincides with the axis C-C. The bearing surface 36C communicates with a conical bore 62 which opens onto the circumferential surface of the piston 60 to permit insertion of the upper end portion of the 15 tension rod 30 into the piston 60 and also to permit swivelling of the upper end portion of the tension rod 30 during oscillation of the cutter 6. The piston 60 is mounted for axial movement within a cylindrical sleeve 64 which is mounted within a tubular spigot 66 on the upper part of the housing 2 either by means of a coarse thread or by means of a press fit. The spigot 66 and 20 sleeve 64 are slotted to permit access of the upper end portion of the tension pin 30 to the conical bore 62. When the sleeve 64 is a threaded fit within the spigot 66, correct angular alignment between the slots in the sleeve and spigot is obtained by using a compressible washer (not shown) between the sleeve and spigot and tightening the sleeve against the washer. A cap 68 is threadedly 25 mounted on to the upper end portion of the sleeve 64 by means of a fine thread 70 and includes a central boss 72 which engages the upper end of the piston 60.

In order to set the tension of the cutter 6, the cap 68 is rotated in order 30 to drive the piston 60 axially within the sleeve 64 and hence to displace the part-spherical bearing surface 36C and ball 32 along the axis C-C. An annular friction spring 74 is interposed between the sleeve 64 and a depending skirt r> 267682 68a of the cap 68 in order to prevent unintentional loosening of the cap 68 by I vibrations within the hand piece during operation. Throughout the range of s adjustment, the centre of the ball 32 remains on the axis C-C and hence the lower end of the tension pin 30 and thus the chicken's foot 14 will oscillate in 5 a true plane parallel to the plane of the comb 4. Accordingly, despite the rigidity of the cutter mechanism substantially true planar movement of the cutter 6 can be achieved, with consequent uniform cutting, throughout the range of adjustment of the tension pin.

In the embodiment of Figure 7, slight rubbing friction will occur between the ball 32 at the upper end of the tension pin 30 and the part-spherical bearing surface 36C when the tension pin 30 oscillates with the chicken's foot 14. Such rubbing friction can avoided with the construction shown in Figure 8 as will now be described.

In the construction of Figure 8, the piston 60 is formed integrally with the cap 68 and comprises a head 80 which is a close fit within a cylindrical bore of a sleeve 82 press fitted into the tubular spigot 66 of the housing 2. A lower stem portion 84 of the piston 60 is provided with a fine thread 86 which 20 is engaged in a threaded bore in the base 82a of the sleeve 82 whereby rotation of the cap 68 and piston 60 will result in axial displacement of the piston 60 relative to the sleeve 82. A friction spring 74 is interposed between the skirt 68 a of the cap 68 and the sleeve 82 in order to prevent unintentional rotation of the cap 68 under the vibrations occurring during operation of the 25 hand piece. The head 80 of the piston 60 is undercut to define a frusto-conical bearing surface 90 which intersects the axis B-B of the tension pin 30 exactly at right angles to that axis, the surface 90 being ground in order to achieve this precise relationship and is also hardened. The axis of the frusto-conical surface 90 is coincident with the axis C-C. The tension pin 30 is formed at its 30 upper end with a head 92 having a flat end face which is held with engagement with the frusto-conical surface 90. In order to maintain the head 92 against C J / t locating collar 94 mounted within the sleeve 82 between the head 80 of the piston 60 and a circlip 96 on the stem portion of the piston. A key 98 is interposed between the sleeve 82 and the collar 94 in order to ensure that the collar 94 is held against rotation within the sleeve 82 whereby the aperture in the collar 94 for the head 92 of the tension pin 30 is retained on the axis B-B. In order to accommodate the oscillation of the head 92 of the tension pin 30 during oscillation of the chicken's foot and cutter, the head 92 is undercut and/or the aperture in the collar 94 is divergent toward the outside of the collar. During oscillation of the chicken's foot and cutter, the flat end of the head 92 of the tension pin will roll along the frusto-conical surface 90 substantially without sliding friction. This movement will occur about the point of intersection of axes B-B and C-C and this point moves along the axis C-C when the piston 60 (and hence the frusto-conical surface 90) is displaced along axis C-C to set the cutter tension. When the end surface of the head 92 of the tension pin 30 is a flat surface, there will be a very slight displacement of the axis B-B as the tension pin oscillates. Although displacement is so slight as to not affect the planar motion of the chicken's foot and cutter to any adverse extent, even this effect can be negated by rounding the end face of the tension pin head so that it forms a part-spherical or cylindrical surface centred at the centre of the ball 28 at the lower end of the tension pin.

In a modification of this embodiment which avoids the need for the locating collar 94 to hold the head 92 against the frusto conical surface, a conically tapered pin extending from the head is received within a bore extending from the surface and at right angles thereto. This simplifies the construction. The bearing surface on the piston may be defined by a part-conical surface in part of the periphery of the piston. This latter variation provides an increased surface area for the piston on the side thereof remote from the pin and hence reduced reactive pressure at that side of the piston.

In the embodiment of Figure 8, the conical surface of the piston centred on a vertical axis provides rolling contact with the.end of the tension pin which results in reduced friction, heat generation, and wear. Although for the reasons disclosed above, the adjustment of the piston preferably occurs along axis C-C, the concept of a conical bearing surface for the rolling contact of the end of the tension pin can also be used to advantage in a configuration in which adjustment of the tension takes place by movement of the piston (or other member having the conical bearing surface) in the general direction of the tension pin axis. It is however, to be noted that in such a configuration the conical bearing surface would still always be centred about a vertical axis and that vertical axis would displace laterally during tension adjustment.

Although this aspect of the invention has been described in relation to a cutter head having a swivel drive-transmitting joint as disclosed in the preceding embodiments, the principles disclosed herein are applicable to cutter heads having other types of drive.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention.

Claims (20)

WHAT I CLAIM IS:

1. A shearing hand piece comprising a cutter assembly having a comb, a toothed cutter mounted for oscillatory movement in a plane parallel to the comb, drive means for driving the cutter, and means for applying pressure to the teeth of the cutter to provide a pressure necessary to cut wool in a cutting zone in which cutting can occur by co-operation between the teeth of the cutter and comb, said pressure-applying means comprising pressure distributing means mounted above the cutter and engaged with the teeth of the cutter to substantially equalise the pressure between the respective teeth of the cutter, and a strut device comprising at least one rigid strut for applying load to the pressure distributing means, the resultant of the load applied by the strut device acting along an axis in a direction forwardly of the hand piece and inclined towards the plane of movement of the cutter, said axis intersecting said plane of movement substantially in, or forwardly of, the cutting zone.

2. A shearing hand piece according to claim 1, wherein the cutter is constrained to move in an arc by at least one link pivotally mounted for swinging movement about a rear pivot, the pressure distributing means being at the forward end of the link and acting to transmit the drive to the cutter.

3. A shearing hand piece according to claim 2, wherein the strut and link are so positioned that they intersect at a point substantially on a plane normal to the comb and extending through the approximate centres of resistance of the cutting edges of the cutting teeth.

4. A shearing hand piece according to claim 2 or claim 3, wherein the link is formed in a thin plate-like construction in a plane substantially parallel to the plane of the comb, with the strut being simply supported at each end and being directed symmetrically with respect to the cutter teeth, the link being capable of twisting or rotating to permit deflection of the pressure distributing'-• , y '\ t O means about an axis extending longitudinally of the hand piece to ec^frise the \ A -23- y ^ f / o fc pressure on the cutter teeth.

5. A shearing hand piece according to any one of claims 2 to 4, wherein the drive means is located at or behind the pivot mounting of the link.

6. A shearing hand piece according to any one of claims 1 to 5, wherein the pressure distributing means comprises a chicken's foot comprising one or more pairs of divergent legs each engaged with a respective one of the cutter teeth.

7. A shearing hand piece according to claim 6 when dependent on claim 2, wherein the chicken's foot is rigidly mounted at the forward end of the link.

8. A shearing hand piece according to any one of claims 1 to 7, wherein an end of the strut device remote from the pressure distributing means is mounted for swivel movement substantially about a point located substantially on an axis passing through a pivot centre about which the cutter oscillates and extending perpendicular to said plane of oscillatory movement, said cutter assembly further comprising means for varying the load applied by the strut device to the pressure distributing means by displacing the remote end of said strut device such that the swivel point remains substantially on said axis.

9. A shearing hand piece according to any one of claims 1 to 3, wherein the strut device comprises a tension pin simply supported at each end.

10. A shearing hand piece according to claim 2 or any claim dependent on claim 2, wherein the link is of a thin plate-like construction.

11. A shearing hand piece according to claim 10, wherein the link is inclined towards the plane of the comb to intersect the axis of action of the strut device at or below the zone of engagement of the pressure distributing ^ ' means with the cutter. .j/ *;i*29APR

12. A shearing hand piece according to any one of claims 1 to 11, wherein the drive means comprises a crank having an axis which is inclined to and which at least approximately intersects the axis of crank rotation, a swivel joint linked to the crank and mounted for oscillatory movement about a swivel axis generally at right angles to the plane of the cutter and comb.

13. A shearing hand piece according to any one of claims 1 to 12, wherein, an end of the strut device remote from the pressure distributing means being mounted for swivel movement substantially about a point located substantially on a swivel axis passing through a pivot centre of the cutter and extending perpendicular to said plane of oscillatory movement, said hand piece further comprising means for varying the load applied by the strut device to the pressure distributing means by displacing the remote end of said strut device such that the swivel point remains substantially on said swivel axis.

14. A shearing hand piece according to any one of claims 1 to 13, further comprising a bearing surface mounting an end of the strut device remote from the pressure distributing means for rolling movement along the surface, and means for varying the load applied by the strut device to the pressure distributing means by displacing the bearing surface, said bearing surface being an at least partly conical surface centred on an axis extending perpendicular to the plane of oscillatory movement of the cutter.

15. A shearing hand piece according to claim 2 or claim 3, wherein the link is substantially rigid.

16. A shearing hand piece according to claim 2 or claim 3, wherein the link is capable of torsional deflection.

17. A shearing hand piece according to claim 2 or claim 3 or claim 15 or claim 16, wherein the link comprises an elongate plate.

18. A shearing hand piece according to claim 2 or claim 3 or any one of claims 15 to 17, wherein the pressure distributing means is pivotally mounted at a forward end of the link.

19. A shearing hand piece according to claim 18, wherein the pressure distributing means comprises a fork member having divergent legs each engaged with a respective one of the cutter teeth.

20. A shearing hand piece substantially as hereinbefore described with reference to the accompanying drawings. ALASTAIR MACKENZIE lys BALDWIN, SON & CAREY 93033 In: \oDer\rah.harid-niece.SDe V