Patent Description:
Rotary disc saws, typically, comprise a carrier disc defining a circular outer periphery. A plurality of cutting elements are secured to and extend radially outwardly from the outer periphery of the carrier disc and are spaced apart circumferentially around the periphery thereof. A shaft accommodating bore extends co-axially centrally through the carrier disc for accommodating a drive shaft for rotating the rotary disc saw. Typically, such disc saws range in nominal diameter from <NUM> to <NUM>, where the nominal diameter is measured to include the carrier disc and the cutting elements. In a disc saw of nominal diameter of <NUM>, the carrier disc, typically would be of diameter in the range of <NUM> to <NUM>, and would carry thirteen to sixteen cutting elements, with each cutting element extending a radial distance from the carrier disc in the range of <NUM> to <NUM>. The cutting elements would be circumferentially spaced apart from each other around the carrier disc a circumferential distance in the range of <NUM> to <NUM>, and each cutting element would typically extend a circumferential distance around the periphery of the carrier disc of approximately <NUM>. In general, the cutting elements are impregnated with diamonds or synthetic diamonds, and are of thickness greater than the carrier disc, in order to avoid jamming of the carrier disc in the workpiece when the carrier disc extends into a slot in the workpiece cut by the rotary disc saw. In general, the carrier disc of such rotary disc saws is of steel material.

A problem with such rotary disc saws relates to the noise which they generate when cutting or grinding metal, stone and other masonry materials. It has been found that some rotary disc saws when cutting masonry materials can generate excessive noise which can damage the hearing of an operator. In such a rotary disc saw cutting a concrete block, the noise generated at one metre from the rotary disc saw was measured at 107dB(A). At three metres from the rotary disc saw the noise generated by the same rotary disc saw cutting the same concrete block was measured at <NUM>. 5dB(A), while at five metres from the same rotary disc saw cutting the same concrete block the noise was measured at <NUM>. Such noise levels can be seriously injurious to the hearing of an operator, particularly if an operator is exposed to such noise over long time periods. In order to minimise hearing damage, it is known for operators of such rotary disc saws to wear protective ear covers, which deaden the sound somewhat. However, such protective ear covers do not prevent some of the generated noise entering the ear, and thus over prolonged exposure to noise generated by such rotary disc saws an operator may suffer significant deterioration of hearing, to the extent that hearing is damaged irreversibly. There is therefore a need for a rotary disc saw which addresses this problem.

The present invention is directed towards such a rotary disc saw.

Korean Patent Specification <CIT> discloses the preamble of claim <NUM>, in particular a cutting tool with reduced vibration and noise which comprises a carrier disc, and a damping disc of a viscoelastic material. The damping disc is pre-coupled to a cover of metal or hard plastics material. The damping disc with the cover adhered thereto is attached to the carrier disc. The ratio of the area of the damping disc to the carrier disc may be in the range of <NUM>% to <NUM>% and preferably <NUM>%.

According to the invention there is provided a rotary disc saw comprising.

Preferably, the adhesive of the adhesive layer comprises an elastic adhesive, and more preferably, the adhesive of the adhesive layer comprises a rubberlike adhesive.

In one embodiment of the invention the adhesive of the adhesive layer when cured forms a rubberlike adhesive layer, and preferably, forms an elastic adhesive layer.

Ideally, the adhesive layer extends over the entire area of the corresponding major surface of the noise damping disc.

In another embodiment of the invention the adhesive of the adhesive layer is temperature stable at temperatures up to <NUM>, and preferably, up to <NUM>, and in another embodiment of the invention the adhesive is temperature stable at a temperature of <NUM> for a period of up to <NUM> minutes.

In one embodiment of the invention the adhesive layer is of thickness in the range of <NUM> to <NUM>, and preferably, the adhesive layer is of thickness in the range of <NUM> to <NUM>, and advantageously, the adhesive layer is of thickness of approximately <NUM>.

In another embodiment of the invention the maximum diameter of the noise damping disc lies in the range of <NUM>% to <NUM>% of the diameter of the outer periphery of the carrier disc. Preferably, the maximum diameter of the noise damping disc lies in the range of <NUM>% to <NUM>% of the diameter of the outer periphery of the carrier disc, and advantageously, the maximum diameter of the noise damping disc lies in the range of <NUM>% to <NUM>% of the diameter of the outer periphery of the carrier disc, and ideally, the maximum diameter of the noise damping disc is approximately <NUM>% of the diameter of the carrier disc.

In one embodiment of the invention the thickness of the noise dampening disc between the major surfaces thereof lies in the range of <NUM> to <NUM>, and preferably, the thickness of the noise dampening disc between the major surfaces thereof lies in the range of <NUM> to <NUM>, and advantageously, the thickness of the noise dampening disc between the major surfaces thereof is approximately <NUM>.

In another embodiment of the invention the outer periphery of the noise damping disc is substantially circular.

In one embodiment of the invention a plurality of circumferentially spaced apart noise damping slots extend inwardly into the noise damping disc from the outer periphery thereof. Preferably, the noise damping slots of the noise damping disc extend substantially radially inwardly into the noise damping disc from the outer periphery thereof.

Advantageously, each noise damping slot of the noise damping disc terminates adjacent its inward end in an arcuate slot, which preferably, is of partly circular shape, and advantageously, is of partly spiral shape. Preferably, the partly circular part of each noise damping slot of the noise damping disc terminates in a partly circular shape part, which in turn terminates in a partly spiral shape part.

In one embodiment of the invention each noise damping slot of the noise damping disc is of width in the range of <NUM> to <NUM>. Preferably, each noise damping slot of the noise damping disc is of width in the range of <NUM> to <NUM>. Advantageously, each noise damping slot of the noise damping disc is of width of approximately <NUM>.

In another embodiment of the invention each noise damping slot of the noise damping disc extends into the noise damping disc from the outer periphery thereof a radial distance from the outer periphery of the noise damping disc not greater than <NUM>% of the diameter of the noise damping disc.

Preferably, each noise damping slot of the noise damping disc extends into the noise damping disc from the outer periphery thereof a radial distance from the outer periphery of the noise damping disc in the range of <NUM>% to <NUM>% of the diameter of the noise damping disc.

Preferably, each noise damping slot of the noise damping disc extends through the noise damping disc from one of the major surfaces thereof to the other one of the major surfaces thereof.

In another embodiment of the invention the diameter of the shaft accommodating bore extending through the noise damping disc is greater than the diameter of the shaft accommodating bore extending through the carrier disc.

In another embodiment of the invention the noise damping disc comprises steel material.

In another embodiment of the invention a plurality of cutting elements are provided spaced apart circumferentially around the outer periphery of the carrier disc. Advantageously, each cutting element extends radially from the carrier disc, and preferably, each cutting element extends radially from the outer periphery of the carrier disc.

Preferably, the carrier disc defines a circular outer periphery.

In a further embodiment of the invention the carrier disc comprises steel material.

The invention will be more clearly understood from the following description of some preferred embodiments thereof which are given by way of example only with reference to the accompanying drawings, in which:.

Referring to the drawings and initially to <FIG> thereof, there is illustrated a rotary disc saw according to the invention indicated generally by the reference numeral <NUM> of the type which is typically used in an angle grinder, and is suitable for cutting and grinding metals, such as steel, cast iron and other metals and alloys, as well as ceramics, stone and other masonry materials, although, it will be readily apparent to those skilled in the art that the rotary disc saw <NUM> may be used for cutting and grinding other materials. The rotary disc saw <NUM> comprises a carrier disc <NUM> of steel having a pair of major surfaces, namely, a major surface 5a and a major surface 5b, and terminates in an outer periphery <NUM>, which in this embodiment of the invention is circular. The carrier disc <NUM> defines a geometric central axis <NUM>.

A plurality of circumferentially spaced apart cutting elements <NUM> are secured to the carrier disc <NUM> around the outer periphery <NUM> thereof. Each cutting element <NUM> defines opposite side faces <NUM> and extends radially outwardly from the outer periphery <NUM> of the cutting disc <NUM>. In this embodiment of the invention, each cutting element extends a circumferential distance s<NUM> around the outer periphery <NUM> of the carrier disc <NUM> of approximately <NUM>, and the circumferential spacing s<NUM> between adjacent ones of the cutting elements <NUM> is approximately <NUM>. However, it is envisaged that the circumferential distance s<NUM> around the outer periphery <NUM> of the carrier disc <NUM> along which each cutting element extends may lie in the range of <NUM> to <NUM>, and the circumferential spacing s<NUM> between adjacent ones of the cutting elements <NUM> may lie in the range of <NUM> to <NUM>. The cutting elements <NUM> are of steel impregnated with hard cutting particles, which in this embodiment of the invention are diamond particles. Alternatively, the cutting elements <NUM> may be impregnated with synthetic diamond particles, or the cutting elements <NUM> may comprise a sintered carbide material.

The cutting elements <NUM> are of thickness t<NUM> which is greater than the thickness t<NUM> of the carrier disc <NUM> in order to avoid jamming of the carrier disc <NUM> in a slot cut in a workpiece by the rotary disc saw <NUM>. In this embodiment of the invention the thickness t<NUM> of each cutting element <NUM> is approximately <NUM>, and the thickness t<NUM> of the carrier disc <NUM> is approximately <NUM>. However, it is envisaged that the thickness t<NUM> of each cutting element <NUM> may lie in the range of <NUM> to <NUM>, and the thickness t<NUM> of the carrier disc <NUM> may lie in the range of <NUM> to <NUM>.

A circular shaft accommodating bore <NUM> extends centrally and axially through the carrier disc <NUM> for in use engaging a drive shaft on which the rotary disc saw <NUM> is rigidly secured in order that the rotary disc saw <NUM> rotates with and is driven by the drive shaft. The shaft accommodating bore <NUM> defines a central axis (not shown) coinciding with the central axis <NUM> of the carrier disc <NUM>.

Such carrier discs and cutting elements of rotary disc saws as the carrier disc <NUM> and the cutting elements <NUM> of the rotary disc saws <NUM>, will be well known to those skilled in the art, and further description should not be required.

A noise damping disc <NUM> of steel having a pair of major surfaces 16a and 16b, and terminating in a circular outer periphery <NUM> is attached coaxially to the major surface 5a of the carrier disc <NUM> by a layer of adhesive <NUM> which bonds the major surface 16a of the noise damping disc <NUM> to the major surface 5a of the carrier disc <NUM> as will be described below. The noise damping disc <NUM> defines a central geometric axis <NUM>, which when the noise damping disc <NUM> is attached to the carrier disc <NUM>, coincides with the central axis <NUM> of the carrier disc <NUM>. A circular shaft accommodating bore <NUM> extends centrally and axially through the noise damping disc <NUM>, and defines a central axis (not shown), which when the noise damping disc <NUM> is attached to the carrier disc <NUM>, coincides with the central axis <NUM> of the carrier disc <NUM>. The shaft accommodating bore <NUM> of the noise damping disc <NUM> is of diameter slightly greater than the diameter of the shaft accommodating bore <NUM> extending through the carrier disc <NUM>, and is axially aligned with the shaft accommodating bore <NUM> of the carrier disc <NUM>. In this embodiment of the invention the diameter d of the outer periphery <NUM> of the noise damping disc <NUM> is of length equal to approximately <NUM>% of the diameter D of the outer periphery <NUM> of the carrier disc <NUM>. In this embodiment of the invention the diameter D of the outer periphery <NUM> of the carrier disc <NUM> is approximately <NUM>, and the diameter d of the outer periphery <NUM> of the noise damping disc <NUM> is approximately <NUM>.

In this embodiment of the invention the noise damping disc <NUM> is of thickness t<NUM> between the major surfaces 16a and 16b of <NUM> approximately, and when bonded to the carrier disc <NUM>, the major surface 16b of the noise damping disc <NUM> extends proud of a plane <NUM> defined by the side faces <NUM> of the cutting elements <NUM> on the adjacent side of the carrier disc <NUM>. The noise damping disc <NUM> is bonded to the major surface 5a of the carrier disc <NUM>, which in use is the major surface of the carrier disc <NUM> remote from the drive motor and gear box of the angle grinder driving the drive shaft on which the carrier disc <NUM> is rigidly secured. It is envisaged that the thickness t<NUM> of the noise damping disc may range from <NUM> to <NUM>.

Turning now to the adhesive bonding of the noise damping disc <NUM> to the carrier disc <NUM>, in this embodiment of the invention the adhesive <NUM> comprises an adhesive, which when cured forms a resilient, elastic, rubberlike layer <NUM> bonding the noise damping disc <NUM> to the carrier disc <NUM>. Ideally, the adhesive is temperature stable up to <NUM>. However, it is envisaged that an adhesive which is temperature stable up to <NUM> would be adequate, and it is also envisaged that an adhesive which is temperature stable at <NUM> for up to twenty minutes would also be suitable. The adhesive <NUM> is applied continuously over the entire surface area of the major surface 16a of the noise damping disc <NUM>. The adhesive <NUM> is applied to the major surface 16a of the noise damping disc <NUM> to a depth so that when the adhesive <NUM> is fully cured with the noise damping disc <NUM> securely bonded by the adhesive <NUM> to the carrier disc <NUM>, the adhesive <NUM> forms the rubberlike adhesive layer <NUM> between the noise damping disc <NUM> and the carrier disc <NUM>. The rubberlike adhesive layer <NUM> is of thickness t<NUM> of approximately <NUM>, although, it is envisaged that the thickness of the rubberlike adhesive layer <NUM> could lie in the range of <NUM> to <NUM>, although, preferably, the rubberlike adhesive layer <NUM> would be of thickness lying in the range of <NUM> to <NUM>.

Returning now to the carrier disc <NUM>, the carrier disc <NUM> is provided with a plurality of circumferentially spaced apart heat expansion compensating slots <NUM> which extend inwardly from the outer periphery <NUM> of the carrier disc <NUM> between adjacent pairs of the cutting elements <NUM>. In this embodiment of the invention each slot <NUM> extends inwardly into the carrier disc <NUM> from the outer periphery <NUM> thereof at an angle α less than <NUM>° to a tangent to the outer periphery <NUM> adjacent the slot <NUM>. In this embodiment of the invention the angle α of each slot <NUM> to the corresponding tangent is approximately <NUM>°. The slots <NUM> extend inwardly into the carrier disc <NUM> in a leading direction relative to the normal rotational direction of the rotary disc saw <NUM>. The normal rotational direction of the rotary disc saw <NUM> is indicated by the arrow A in <FIG>. In this embodiment of the invention each slot <NUM> extends a distance of approximately <NUM> into the carrier disc <NUM> from the outer periphery <NUM> thereof.

A plurality of perforations, in this embodiment of the invention cooling bores <NUM> of circular transverse cross section extend through the carrier disc <NUM> in a circumferential area <NUM> extending around the carrier disc <NUM> between the outer periphery <NUM> of the noise damping disc <NUM> and the outer periphery <NUM> of the carrier disc <NUM>. The bores <NUM> are arranged in circumferentially spaced apart groups <NUM>, and the bores <NUM> of each group <NUM> are spaced apart from each other and define a straight line <NUM>. In this embodiment of the invention, the straight line <NUM> defined by the bores <NUM> of each group <NUM> thereof are aligned with a centreline <NUM> defined by an adjacent corresponding one of the slots <NUM>. Although while it is desirable that the straight line <NUM> defined by the bores <NUM> of each group <NUM> thereof is aligned with the centreline of an adjacent corresponding one of the slots <NUM>, it is not essential, and the straight lines <NUM> defined by the bores <NUM> of the respective groups <NUM> need not be aligned with the centrelines of the corresponding slots <NUM>, for example, they could be parallel to the centrelines of the corresponding adjacent slots.

In use, the rotary disc saw <NUM> is secured to a drive shaft of a rotary disc saw apparatus, neither of which are shown, of the type which will be well known to those skilled in the art, and is operated in a normal manner as a conventional rotary disc saw. However, in this embodiment of the invention, since the major surface 16b of the noise damping disc <NUM> extends proud of the plane defined by the adjacent side faces <NUM> of the cutting elements <NUM>, the rotary disc saw <NUM> is not advanced into the workpiece to an extent that the noise damping disc <NUM> would engage the workpiece.

Referring now to <FIG> there is illustrated a rotary disc saw according to another embodiment of the invention indicated generally by the reference numeral <NUM>. The rotary disc saw <NUM> is substantially similar to the rotary disc saw <NUM>, and similar components are identified by the same reference numerals. The main differences between the rotary disc saw <NUM> and the rotary disc saw <NUM> lies in the noise damping disc, which in this embodiment of the invention is indicated by the reference numeral <NUM>. In this embodiment of the invention a plurality, namely, five circumferentially spaced apart noise damping slots <NUM> extend inwardly into the noise damping disc <NUM> from the outer periphery <NUM> of the noise damping disc <NUM>. Each noise damping slot <NUM> is of width w of approximately <NUM> and extends through the noise damping disc <NUM> from the major surface 16a to the major surface 16b, and extends substantially radially inwardly from the outer periphery <NUM> of the noise damping disc <NUM>. Each noise damping slot <NUM> terminates at its inner end in an arcuate slot <NUM> having a circular portion <NUM> which in turn terminates in an inner spiral portion <NUM>. Each damping slot <NUM> extends substantially radially into the noise damping disc <NUM> from the outer periphery <NUM> thereof a radial distance r of approximately <NUM>, which in this embodiment of the invention is approximately <NUM>% of the diameter d of the noise damping disc <NUM> which is approximately <NUM>.

The diameters of the carrier disc <NUM> of the rotary disc saw <NUM> and the carrier disc <NUM> of the rotary disc saw <NUM> are identical, and the diameters of the noise damping disc <NUM> and the noise damping disc <NUM> are also identical. The thicknesses t<NUM> of the carrier disc <NUM> of the rotary disc saw <NUM> and the rotary disc saw <NUM> are identical, and the thicknesses t<NUM> of the noise damping disc <NUM> and the noise damping disc <NUM> are also identical. The thickness t<NUM> of the adhesive layers <NUM> of the disc saws <NUM> and <NUM> are identical, and the shape, size and thicknesses t<NUM> of the cutting elements <NUM> of the disc saws <NUM> and <NUM> are also identical.

In the rotary disc saw <NUM>, the heat expansion compensating slots <NUM>, which are circumferentially spaced apart around the carrier disc <NUM> and extend inwardly from the outer periphery <NUM> thereof, are similar to the slots <NUM> of the carrier disc <NUM> of the rotary disc saw <NUM> described with reference to <FIG>, with the exception that in the rotary disc saw <NUM> each slot <NUM> adjacent its inner end terminates in a through-bore <NUM> extending through the carrier disc <NUM>. Additionally, the arrangements of the cooling bores <NUM> in the carrier disc <NUM> of the rotary disc saw <NUM> is slightly different to the arrangement of the cooling bores <NUM> in the carrier disc <NUM> of the rotary disc saw <NUM>, although the cooling bores <NUM> in the carrier disc <NUM> of the rotary disc saw <NUM> are arranged in groups <NUM> which define respective straight lines <NUM>, which are also aligned with a centre line <NUM> of the corresponding slot <NUM>.

Otherwise, the rotary disc saw <NUM> and its use is similar to that of the rotary disc saw <NUM>.

Comparative tests have been carried out on the rotary disc saw <NUM> of <FIG> according to the invention, and a control rotary disc saw. The control rotary disc saw was identical to the rotary disc saw <NUM> but without the noise damping disc and without the rubberlike adhesive layer <NUM>. It was found that the acoustic noise produced by the rotary disc saw <NUM> according to the invention was significantly less than the acoustic noise produced by the control rotary disc saw when the rotary disc saw <NUM> and the control rotary disc saw were cutting similar concrete blocks. In the comparative tests, similar concrete blocks were cut for fifteen minutes by the rotary disc saw <NUM> and the control rotary disc saw. Acoustic sound measurements were taken at distances of one metre, three metres and five metres from the rotary disc saw <NUM> and the control rotary disc saw. The table in <FIG> sets forth the results of the tests.

As can be seen from the table of <FIG>, the control rotary disc saw at one metre therefrom produced acoustic noise of <NUM>. 0dB(A), while at one metre from the rotary disc saw <NUM>, the rotary disc saw <NUM> produced acoustic noise of <NUM>. At three metres from the control rotary disc saw and the rotary disc saw <NUM>, the corresponding acoustic noise values were <NUM>. 5dB(A) and <NUM>. 0dB(A), respectively. At five metres from the control rotary disc saw and the rotary disc saw <NUM>, the corresponding acoustic noise values were <NUM>. 5dB(A) and <NUM>. 5dB(A), respectively.

These results show that the provision of the noise damping disc <NUM> bonded by the rubberlike adhesive layer <NUM> to the carrier disc <NUM> produces a significant reduction in the noise produced by the rotary disc saw <NUM>. At one metre from the respective rotary disc saws, the reduction in noise relative to that produced by the control rotary disc saw was 10dB(A), while at three metres from the respective rotary disc saws, the reduction in noise was <NUM>. 5dB(A), and at five metres from the respective discs, the noise reduction achieved by the rotary disc saw <NUM> according to the invention was 10dB(A).

During these comparative tests, the vibration values for the two disc saws <NUM> and <NUM> were also recorded in acceleration units, which is a conventional way of measuring vibration in hand tools. As can be seen from the right-hand most column of <FIG>, while the vibration was slightly higher in the disc saw <NUM> than the vibration generated by the control disc saw, the slight increase in vibration of the disc saw <NUM> is only marginal with respect to the vibration of the control disc saw.

While the rotary disc saws according to the invention have been described as comprising heat expansion compensating slots <NUM> and cooling bores <NUM>, while the provision of the slots <NUM> and the bores <NUM> is desirable, it is not essential. It will also be appreciated that the noise damping disc <NUM> of the rotary disc saw <NUM> may be provided with noise damping slots, and the number of noise damping slots in the noise damping discs of both the rotary disc saws <NUM> and <NUM> may be more or less than the number of noise damping slots described in the noise damping disc <NUM> of the rotary disc saw <NUM>, and additionally, the shape of the noise damping slots may be different to that of the noise damping slots of the noise damping disc <NUM>. In some embodiments of the invention it is envisaged that the noise damping slots may extend solely radially inwardly from the outer peripheries of the noise damping discs, and the width of the noise damping slots may be greater or less than that described with reference to the noise damping slots <NUM> of the noise damping disc <NUM>.

It is also envisaged that the noise damping slots of the noise damping disc may extend at an angle less than <NUM>° to a tangent to the outer periphery of the noise damping disc adjacent the noise damping slot, and in which case, it is envisaged that the noise damping slots would extend inwardly from the outer periphery of the noise damping disc in a trailing or leading direction relative to the normal rotational direction of the rotary disc saw. Indeed, it is envisaged in some embodiments of the invention that the angle to the tangent at which the noise damping slots would extend would be similar to the angle to the corresponding tangent at which the slots <NUM> extend from the outer periphery of the carrier disc.

It will also be appreciated that any desired and suitable number of cutting elements may be provided around the carrier disc, and it will also be appreciated that other sizes and shapes of slots <NUM> may be provided extending inwardly from the outer periphery of the carrier disc.

While the rotary disc saws <NUM> and <NUM> have been described as being of specific dimensions, it will be readily apparent to those skilled in the art that the disc saws may be of different dimensions, for example, it is envisaged that the disc saws may be of nominal diameter in the range of <NUM> to <NUM>, where the nominal diameter is measured to the outer periphery of the cutting elements. Additionally, it will be appreciated that any number of cutting elements may be provided around the periphery of the disc saws, and the number of cutting elements will depend firstly, on the diameter of the disc saw, and secondly, on the use to which the disc saw is to be put. It will also be appreciated that the circumferential distance which each cutting element will extend along the outer periphery of the carrier disc will also be different from disc saw to disc saw, again depending on the use to which the disc saw is to be put, and also depending on the diameter of the disc saw. Additionally, it will be appreciated that the spacing between adjacent cutting elements may also be different from disc saw to disc saw. Further, it is envisaged that the radial distance each cutting element extends from the outer periphery of the carrier disc will be different from disc saw to disc saw, again depending on the diameter of the disc saw and the use to which the disc saw is to be put.

The diameter of the noise damping disc will also vary, depending on the diameter of the disc saw. However, in general, it is envisaged that the diameter of the noise damping disc will not exceed <NUM>% of the diameter of the carrier disc, and preferably, it is envisaged that the diameter of the noise damping disc will range from <NUM>% to <NUM>% of the diameter of the carrier disc, although in some cases, the diameter of the noise damping disc may be as much as <NUM>% of the diameter of the carrier disc.

Claim 1:
A rotary disc saw comprising
a carrier disc (<NUM>) having a pair of major surfaces (<NUM>) and a shaft accommodating bore (<NUM>) extending therethrough from one of the major surfaces (<NUM>) to the other one of the major surfaces (<NUM>), the carrier disc (<NUM>) terminating adjacent its outer periphery (<NUM>) in one or more cutting elements (<NUM>),
a noise damping disc (<NUM>, <NUM>) having a pair of major surfaces (<NUM>), and a shaft accommodating bore (<NUM>) extending therethrough from one of the major surfaces (<NUM>) of the noise damping disc (<NUM>, <NUM>) to the other one of the major surfaces (<NUM>) thereof, the noise damping disc (<NUM>, <NUM>) being attached to one of the major surfaces (<NUM>) of the carrier disc (<NUM>) and being coaxial with the carrier disc (<NUM>),
characterised in that
the noise damping disc (<NUM>, <NUM>) is of maximum diameter not greater than <NUM>% of the diameter of the outer periphery of the carrier disc (<NUM>), and is attached to the carrier disc (<NUM>) by a layer of a resilient adhesive (<NUM>) located between adjacent ones of the major surfaces (<NUM>, <NUM>) of the carrier disc (<NUM>) and the noise damping disc (<NUM>, <NUM>) and extending continuously over substantially the entire adjacent major surface (<NUM>) of the noise damping disc (<NUM>, <NUM>).