Summary of the Prior Art It is recognised that resonance of circular saw blades effects saw blade noise levels and saw blade cutting performance, both surface finish and power consumption. These resonances occur in tooth saw blades, diamond saw blades, hole saws and other tools with rotating planar bodies. In toothed power blades these resonances are excited by the impact of the cutting teeth on a work piece.

A number of vibration suppressing features have been suggested for saw blades to alleviate these effects.

One example of a vibration suppressing feature is shown in US 4794835, Fujiyoshi. This publication shows a saw blade including tightly zigzagged laser cut slits. The slits follow a path between the edge of the saw blade and a stress relieving hole or a path between two stress relieving holes in the blade body. The tight zigzag of the slits leaves a pair of interleaving combs. The heat and subsequent cooling of the laser cutting deforms the interleaving fingers of the combs giving some residual contact points between the fingers. Vibration of the blade leads to rubbing of these point contacts and conversion of some of the vibration energy to heat.

This resonance damping feature has the disadvantage that laser cutting of extensive slits is a time consuming and expensive practice and would add considerably to the cost of manufacturing a blade.

Another example of a blade including laser cut slots is the Forrest Duraline HI-A/T. This blade includes five radial slots extending inwardly from the blade edge. These slots are laser formed and filled with an energy absorbing media. Damping performance of these blades is greatly impaired if the slots are cleaned or lose their energy absorbing media. The step of laser cutting slots adds significantly to the cost of manufacture.

Another prior art blade, the Checkmate type ZPQ has three radial slots extending 25mm with six millimetre diameter copper plugs inserted at the end of the slots. This blade performs poorly if the copper plugs are removed or dislodged. Manufacturing this blade would involve additional steps of forming close fitting copper plugs and placing and inserting those plugs at the correct location. This would add significantly to the cost of manufacture of the blade.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rotating tool with planar body which including damping features which go some way towards overcoming the above disadvantages.

In a first aspect the invention consists in a rotating tool including: a substantially planar body, a mounting arrangement at the centre of said planar body, a plurality of cutting elements at the periphery of said body, and at least one energy absorbing crack in said body, each said crack penetrating said body and having opposed crack faces, said faces of each said crack touching over at least substantially their entire length, each such crack ending at either itself, another such crack, an aperture in said blade, an edge of said blade or other crack arresting feature.

Preferably each said crack has been formed by a full or partial shearing action and forced back into alignment.

Preferably each said crack does not follow a radial line or a circular arc concentric with said body.

Preferably each said crack follows a curved or sinusoidal path between its ends.

Preferably one of said ends of each said crack is closer to said centre of said body than the other of said ends of said crack.

Preferably each said crack does not join at either end to another said crack (unless to itself) and there are an odd number said cracks spaced around said centre of said body.

Preferably there are three said cracks.

Preferably each said crack terminates at each end at an aperture in said body.

Alternatively said cutting elements are dispensed around the periphery of said body and at least a selection of said cracks terminates at one end at a said aperture and at the other end at an edge of said body, between adjacent said teeth.

In a further aspect the invention consists in a method of manufacturing a rotating tool with planar body including the steps of : placing a tool blank against a die having a cutting edge to form a crack of desired shape in the tool body, advancing a punch against said tool blank, said punch having a cutting edge matching said cutting edge of said die, the relative advancement of said punch relative to said die shearing said tool blank between said cutting edges, retreating said punch, bringing a support surface into place on one side of said tool blank and, pressing against the other side of said tool body forcing the sheared surfaces of said crack back into alignment.

Preferably said method includes, prior to the above, forming at least one pair of apertures through said tool body, and said desired crack shape ends at each end at a said aperture, and the cutting edges of said punch and of said die at configured such that in advancing said punch central regions of said crack are sheared before regions closer to the ends of said crack.

Preferably the regions closest to each end of said crack are fully sheared but displaced less than the full thickness of said blade body.

To those skilled in the art to which the invention relates, many changes in construction and

widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a portion of a saw blade, showing a damping crack formed in the blade body and a damping crack at the blade edge, both according to present invention.

Figure 2 is a cross sectional side elevation on line DD on Figure 1.

Figure 3 is a plan view of a portion of a slaw blade showing damping cracks formed in the blade body, with the damping cracks terminating at a selection of different crack arresting features.

Figures 4A-4C are cross sectional side elevations through a punch and die press machine performing a piercing operation on a blade body to form the stress relieving openings for either end of a blade body crack. Figures 4A, 4B and 4C follow one another in time sequence.

Figure 5 is a cross sectional plan elevation of the press tooling for initial shearing of a blade body crack according to the present invention. The upper tool is in cross section.

Figures 6A-6C are cross sectional side elevations through line CC in Figure 5, including some hidden detail, showing stages of the shearing operation for the blade body crack, using the tooling of Figure 5. Figures 6A-Figures 6C following one another in time sequence.

Figures 7A and 7B are cross sectional side elevations (on line AA in Figure 5) showing the tooling and blade body at two time instants. The time instants are immediately before shearing takes place and at the completion of the shearing operation respectively.

Figures 8A and 8B are cross sectional side elevations (on line BB in Figure 5) showing the

tooling and blade body at the same respective time instants as in Figures 7A and 7B.

Figures 9A and 9B are cross sectional side elevations showing a press performing the step of realigning the faces of the crack formed in the shearing operation of Figures 6A-6C.

DETAILED DESCRIPTION The present invention relates to rotating tools which include a body which at least substantially planar. The present invention primarily intended the use of saw blades where the cutting teeth produce particular resonance issues, in the preferred embodiment of the invention is described in relation to such blades. However the invention is also applicable to diamond saw blades, and to other rotating tools which are subject to vibration and resonance and have a comparatively thin sheet metal wall or body, such as hole saws.

Referring to Figure 1, in the preferred embodiment in the present invention a saw blade has a substantially planar saw body 1. The saw blade body 1 is of generally conventional form, comprising a substantially circular disc, usually of an appropriate metal such as steel. The blade includes a mounting arrangement 3 at the centre of the planar body. The mounting arrangement may be a simple arbor hole 3 for mounting on a saw spindle. The mounting arrangement may also include a diamond (or other) shaped knock out portion for accommodating other spindle forms or may be specifically formed for accommodating other spindle forms. The blade includes a plurality of teeth 2 spaced around it's periphery. These teeth 2 may number anywhere from sixteen to eighty depending upon the blade diameter, intended cutting media and/or cut finish. The number, spacing and form of blade teeth 2 are not important to the present invention.

In addition to these conventional features the saw blade of the preferred embodiment includes one or more vibration damping cracks 5,8. With reference to Figure 2 each vibration damping crack 5,8 has opposed crack faces 10,11 abutting and touching one another. As will be made more clear in the description of the forming process for these cracks, the abutment between the crack faces 10,11 is continuous along the full length of each crack.

Each vibration damping crack is preferably formed so that it terminates at each end at a crack arresting feature. For example, with reference to Figure 1, the crack may end at an aperture 6,7 or the crack may end at a blade edge. Alternatively, with reference to Figure 3, the crack 101 may end at another crack 102 (as at 105) or turn back upon itself (as at 103), to end at a crack by ending at itself (forming a closed loop with a slug remaining in place). All of these are effectively crack arresting features. Other crack arresting features known in the art may also be suitable.

In the preferred embodiment, the vibration damping features of the saw blade include a plurality of blade body cracks 5 and a plurality of blade periphery cracks 8 terminating at the blade edge.

Each blade body crack 5 preferably follows a path between a pair of spaced apart apertures 6.

These apertures 6 may, for example, have diameters approximately four times the saw blade thickness. Each blade body crack 5 preferably follows a curved path between the pair of apertures, for example a shallow sinusoidal path. The path of the crack 5 preferably has a significant radial extent over the course of its path. That is it intersects circles concentric with said saw blade over a range of radii, which range is a significant proportion of the overall radius of the blade body.

It has been found that waves of elastic strain travel around the saw blade during cutting, commonly referred to as the"mode of vibration". With the vibration damping cracks 5 having a significant radial extent they intersect the path of a substantial proportion of the travelling waves of strain. The waves of strain produce relative movement between the opposed and abutting crack faces 10,11. Rubbing of the crack faces 10,11 absorbs some of the energy of the travelling waves of strain. This energy is dissipated as heat producing the damping effect.

The sinusoidal crack path assists the damping effect by providing an increased length of abutting edges compared with a straight line, and varying angles of incidence between the wares of strain and the cracks. This increases the energy damping.

Each peripheral damping crack 8 preferably extends between an opening 7 at one end and the base of a heat expansion slot 4 at its other end. The heat expansion slot 4 and the vibration

damping crack together amount to a significant radial intrusion from the periphery of the saw blade, intercepting and dissipating further energy from the waves of strain travelling around the blade in the vicinity of its periphery.

It the case of both the body cracks 5 and the periphery cracks 8, the opposed faces 10,11 of the crack directly abut. This provides a frictional contact for dissipating energy during relative movement excited by vibration of the saw blade.

The vibration damping cracks 5 are preferably formed to intersect expected fundamental modes of vibration of the saw blade. Fundamental modes of vibration are capable of description by statement of the number of nodal diameters and the number of nodal circles.

Nodal diameters and nodal circles of a fundamental mode are lines of zero displacement when the blade is resonating at that fundamental frequency. Vibration of the blade will peak when the frequency of the exciting force coincides with one of the fundamental modes of vibration for the blade. Accordingly it is preferred that each vibration damping crack 5 follows a path that is neither directly radial nor circular and concentric with the blade body. This ensures that the vibration damping cracks 5 will interfere with most of the modes of vibration of the blade.

In the preferred form of the invention three of each of the blade body cracks 5 and blade periphery cracks 8 are provided, evenly spaced around the blade. However other selections might equally be used, particularly blade body cracks alone.

Manufacturing the blade preferably comprises a series of steps to initially manufacture the blade body, followed by additional operations to complete the blade teeth and blade surface finishing. Completion of the blade teeth and surface finishing does not form a part of the present invention and will not be specifically described. Manufacture of the blade body will be described in so far as it includes steps for forming the vibration damping cracks 5,8.

Additional steps in forming the blade body will generally include initially cutting the overall blade body shape, forming the central arbor hole 3 (and any associated adaptive knock outs) and forming the basic teeth profiles 2 around the periphery of the blade. These steps may be performed in advance of, simultaneously with, or interspersed with one of more of the steps involved in forming the vibration damping cracks 5,8. Most conveniently formation of at least

the overall shape of the 1 blade body and central arbor hole 3 are done in advance of any of the steps in producing the blade body cracks 5,8. Also, the basic teeth profiles 2 and heat slots 4 are formed prior to at least some of the steps in forming the peripheral damping cracks 5,8.

One preferred manufacturing sequence involves cutting the overall shape of the blade body 1 and central arbor hole 3 in a first punching operation, and cutting the basic tooth profiles 2 and heat slots 4 in a second. punching operation. The crack arresting apertures 6,7 at each end of the blade body cracks 5 and at the inner end of the peripheral cracks 8 are formed in a third punching operation. Shearing of the cracks 5,8 is performed in a fourth punching operation, together with shearing of any central arbor knock outs. Sheared faces 10, 11 of the cracks 5,8 formed in the fourth operation are realigned in a final pressing operation. Any arbor knock- outs are also realigned in this operation.

The first two operations are known in the art and do not need description in further detail.

Furthermore there are a variety of processes in use offering different advantages and disadvantages, and the preference for one over another will most probably depend on the particular expertise of the manufacturer and the type of blade being formed. These include laser cutting or mechanical cutting. However to integrate well with the preferred forming method for the cracks, the preferred blade body forming method would involve a punch and die pressing operation.

The third operation will be further described with reference to Figures 4A-4C. The fourth operation will be further described with reference to Figure 5, Figures 6A-6C, Figures 7A-7B and Figures 8A-8B. The fifth and final operation in forming the blade body will be described with reference to Figures 9A and 9B.

Referring to Figures 4A-4C a press includes a moving upper platen 20 and a stationary lower platen 21. A plurality of punch tools 22 are secured to the upper platen 20, positioned for cutting the desired apertures 6 in the blade body 1. A die 23 is positioned on the lower platen 21 to have complementary openings 24 in registration with the punches 22 of the upper platen.

Exit passages 25 for slugs 30 punched from the blade body 1 are provided below the cutting apertures 24 in the die 23. A central spindle (not shown) is preferably provided for locating

the blade arbor hole in a correct position over the die.

In operation, a blade body 1 is placed against the upper surface of the die 23. The upper platen 20 is brought down so that the punch tools 22 shear slugs 30 of the blade body 1 through the apertures 24 in the die 23. This is depicted by the sequence of Figures 4A-4C. In Figure 4A the upper platen 20 is travelling downward and has reached a position at which the punch tools 22 contact the upper surface of the blade body 1. In Figure 4B the punch tools 22 have penetrated the blade body 1, removing slugs 30 from the blade body 1, and have partially pushed these slugs through the openings 24 in the die 23. In Figure 4C the punch tools 22 have fully penetrated the die 23 releasing the slugs 30 into the waste channels 25 in the lower platen 21. From this point the upper platen 20 withdraws from the die 23 and blade body, 1 leaving the blade body 1 with a plurality of appropriately positioned openings 6-the crack arresting openings 6 for the crack ends 5.

In particular, in the drawings of Figures 4A-4C the formation of two holes 6, one for each end of a single blade body crack 5 is shown, but the further apertures 7 for the periphery cracks 8 may also be formed in this application.

With reference to Figure 5, in the fourth operation the cracks 5,8 are formed by at least partial shearing of the blade body 1. An upper tool 37 is carried by the upper platen. A lower tool 36 is carried by the lower platen 53. The upper and lower tools have at least substantially flat bearing surfaces 41, 38 respectively, for bearing against the blade body 1 in the vicinity of the shear line 35. Each tool 36,37 may also include buttressing 39,42 or other reinforcement to alleviate any deformative effect of the side forces that are produced during the punching process. The upper 37 and lower tools 36 each have a cutting edge, 43 and 40 respectively, following a matching sinusoidal path. These cutting edges 43,40 are preferably substantially coterminous and are placed so that with a blade body properly aligned between the upper and lower platen the cutting edges 43,40 terminate at tool ends 44,45 within the stress relieving openings 6 preformed in the blade body 1 in the third forming step, see Figures 6A-6C.

A particular feature of the preferred tooling is demonstrated by Figures 6A-6C, Figures 7A-7B and Figures 8A-8B. The tooling is configured so that the relative shearing of the blade body

1 is progressively reduced toward either end of the cut being formed. This progressive reduction in shear displacement reduces the deformation of material in the region surrounding the ends of the cut. If the dimensions of the crack and of the crack arresting apertures 6 and the curvature of the tooling are each carefully chosen, then all bending of the blade body 1 in this fourth forming step can be kept within the bounds of elastic deformation, and can be entirely recovered in the realignment step. This preserves blade body flatness in the eventual blade body.

The progressive shear is accomplished by providing either or both of the upper and lower tooling 37,36 with a convex cutting edge 43,40 in the vertical direction. That is, the bearing face or cutting edge of the respective tool (37 or 36) is progressively closer to its respective platen (54 or 53) in moving to the ends of the tool (50 or 51) from the middle of the tool (55 or 56). This is most clearly seen in Figures 6A to 6C. Preferably this progression leads to a continuous curve, such as an arc. This curvature of the tooling 37,36 is preferably at least limited so that bending of the blade body to that curvature remains fully elastic.

The curvature of the upper and lower tools 37,36 is depicted in Figures 6A-6C. The curvature of each tool is matching and opposed-both tools are slightly convex. The comparative effect of this is demonstrated by the cross sections of Figures 7A-7B and 8A-8B. The cross sections of Figures 7A-7B are taken on line AA in Figure 5. The cross sections of Figures 8A-8B are taken on line BB of Figure 5.

The cross sections of 7A and 8A are taken at a first time instant immediately prior to any shearing taking place on the blade body 1. At this time instant the upper and lower tooling 37, 36 both contacts the blade body 1 at the middle of the path (55,56 in Figure 6A) of the cut, see Figure 8A. As can be seen in Figure 7A at the ends (50,51 in Figure 6A) of the path of the cut the tooling has not yet closed on the blade body 1.

Figures 7B and 8B show the same cross sections at a later time instant at which the shearing has been completed. This time instant matches the time instant in Figure 6B. At this time instant the blade body 1 has been fully sheared all along the length of the cut, suffering total displacement of approximately 1 *4 blade body thicknesses at the centre of the cut (see Figure

8B) and approximately half a blade body thickness adjacent the ends of the cut (see Figure 7B). This leaves an overlap 60 between the shear faces 10, 11 adjacent the ends of the cut, and a complete separation 61 adjacent the centre of the cut.

Referring to Figures 7A-7B and 8A-8B, certain details of the tools 36,37 have been found particularly useful. With reference to Figure 2, a shearing operation will usually result in distinct characteristics appearing in the parted faces. These characteristics are known as the shear 10,11 and the break. In a typical shearing process the shear will account for 30% of the depth of the cut, while the break will account for the remaining depth. This is typically not of concern, and the tool parameters which lead to this ratio are chosen to maximise tool life and minimise cutting force. However in the present case it has been found desirable to have a greater shear to cut depth ratio. In fact shear to cut depth ratios greater than 50% and preferably greater than 90% have been found preferable. It is believed, that when realigned, the cut faces have greater contact area with higher shear ratios, and that the abutting pressure over that contacting area is conversely reduced (but still present). It is believed that this leads to better vibration damping performance and also to improved blade flatness with lower internal stresses. Therefore, in the preferred forming method of the present invention, tool parameters are chosen which have been found to increase the shear to cut depth ratio. These parameters are described with reference to Figure 7A. In particular two parameters are important. Firstly the die clearance angle 68 is set as 0 degrees. Secondly the punch face 65 to die face 66 clearance 67 is set as 4% of the material gauge of the blade body. Variations in these parameters are possible while achieving the equivalent result of a high shear to cut depth ratio.

Figures 6B and 7B clearly demonstrate that although the material of the blade body has been fully sheared, adjacent the ends of the cut the cut faces 10,11 still overlap and abut one another as overlap 60. This is somewhat useful in facilitating realignment of the cut faces 10,11 in the subsequent pressing step.

The forming process is further illustrated in Figures 6A-6C. Referring to Figure 6A the blade body 1 is inserted between the upper and lower tooling 37,36 in appropriate location. This location may be precisely controlled by locating the arbor hole 3 over a central spindle and by rotationally locating the blade body 1 by one of its peripheral teeth 2.

Referring to Figure 6B the upper platen 54 is lowered to bring the upper tooling 37 to a final cut position which is carefully controlled to ensure that the sheared surfaces 10,11 are not overly displaced. This control may be achieved by precise motion control of the upper platen 54, for example driving the platen using cams or eccentric linkages. Alternatively it may be achieved by physical motion limiters such as stops in between the upper and lower platens 54,53 which could be used with hydraulically or gravity actuated presses.

Referring to Figure 6C the upper platen 54 is then withdrawn. The frictional interface 60 between the faces 10,11 of the cut which still overlap and abut in the region adjacent the ends of the cut prevents the blade 1 returning flat under its own elastically.

Forming of a periphery crack 8 follows substantially the same pattern and is preferably conducted with the same platen movements that form the blade body cracks 5. In the case of the periphery cracks 8 the tooling is preferably progressive in its shearing displacement, growing from a partial blade body thickness adjacent the stress relieving or aperture 7 to a larger displacement radially further out. Appropriate tooling for forming this cut may approximate a portion of the tooling of Figure SA immediately adjacent one end (44 or 45) of that tool.

This fourth forming stage, which includes the carefully controlled upper and lower platen displacement, may also be used to partially shear any blade body knock outs (such as arbour knockouts) from the surrounding blade body.

The final stage in forming the blade body is realignment of the various cut faces. These cut faces include cut faces of blade body cracks 5, periphery cracks 8 and of any blade body knock outs that have been included. Referring to Figures 9a-9b this process of realignment involves placing the processed blade body 1 between upper and lower flat plates 70,71 carried by upper and lower platens of a press. The upper plate 70 is brought down to press the blade 1 between the upper and lower plates 70,71 as depicted in Figure 9B. This pushes the cut faces 10,11 back into realignment. The upper plate 70 is withdrawn, and (as depicted in Figure 9c) the blade body 1 remains flat. The cut faces 10,11 remain in alignment (including during and following use) because non-elastic deformation has been avoided in shearing the cracks 5,8

in the earlier forming stages.

As can be readily understood, the present invention provides vibration damping features for flat saw blades that fit well within the general scheme of blade manufacture. The manufacturing process is inexpensive and can be integrated with current manufacturing processes. The blade features have large contact surface areas leading to a good vibration reducing characteristic with minimal additional cost. Blade body flatness and appearance is largely unaffected.