WO2009112960A1

WO2009112960A1 - Method for sawing blocks of stone material using a diamond-blade frame and associated machine

Info

Publication number: WO2009112960A1
Application number: PCT/IB2009/050640
Authority: WO
Inventors: Luca Toncelli
Original assignee: Luca Toncelli
Priority date: 2008-02-19
Filing date: 2009-02-17
Publication date: 2009-09-17
Also published as: ITTV20080028A1

Abstract

Method for sawing blocks of stone material by means of a multi-blade machine, comprising a blade-holder frame (20) provided with straight cutting blades, in which said frame is brought into contact with the block (50) to be cut with a relative oscillating movement of said blade-holder frame and said block to be cut so as to produce a cutting movement, said blade-holder frame being made to perform a gradual advancing movement towards the surface of the block so as to produce a so- called penetrating movement; characterized in that said relative oscillating movement of the blades and block to be cut is a composite pendular movement comprising an oscillating movement about a first centre of rotation situated, with respect to the plane in which the blade-holder frame lies, on the opposite side to said block to be sawn and a rotational movement about a second centre of rotation lying in the plane of said blade-holder frame, such that the cutting movement is a relative rotary translational movement of each blade and block being sawn, and when the oscillating movement with respect to said first centre of rotation is reversed, the rotational movement about said second centre of rotation also reverses its direction of rotation, such that said two movements are synchronized with each other, the cutting profile generated on the block is a substantially circular profile and the contact between said cutting blades and the block is a theoretically point-like contact.

Description

Method for sawing blocks of stone material using a diamond-blade frame and associated machine

*** The present invention relates to the technology of cutting blocks of hard, typically siliceous, stone of a natural or composite nature, using diamond blades.

It is known that the cutting of blocks of hard stone, such as granite or other siliceous materials, both of a natural and composite nature, is usually performed using pendulum sawing machines which have steel (not diamond) blades spray-coated with an abrasive mixture. Alternatively, diamond wire cutting machines are used.

Instead, the cutting of blocks of softer materials, such as marble or other calcareous stones for example, is performed with sawing machines in which the blade- holder frame moves with a reciprocating rectilinear movement and the blades of which are provided with diamond segments. To perform the cutting of hard stones with diamond blades it is necessary to achieve an area of contact between blades and block to be cut which is very short, so that the diamond blades exert a pressure on the block sufficient to cut into the stone and at the same time avoid excessive overall loading of the blade which would cause the deformation thereof with a consequent deviation of the cut. Over the years various solutions for cutting blocks of hard stone using diamond blades have been proposed, all of which involved a relative sliding movement of diamond tool and stone.

Summarised very briefly, the known methods envisaged that the blade-holder frame performed a high-frequency reciprocating movement and at the same time was displaced or moved forwards along a predetermined trajectory with respect to the block to be sawn, so that, in each position occupied in succession by the frame, the blades carried out a plurality of sawing cycles or strokes acting on the same (practically point-like) block portion.

With progression of the cutting action the blade-holder frame was also imparted downward movement (or so-called "lowering movement") so that the blades gradually moved closer to the bottom of the groove formed with sawing.

For a more detailed description, reference should be made to the following patents:

- Italian patent No. 1,247,055 in the name of Dario Toncelli filed on 12 April - Italian patent No. 1,275,946 in the name of Luca Toncelli filed on 21 March 1995.

In these patents it can be noted that, while the blade-holder frame performs reciprocating rectilinear movements, there is a simultaneous relative oscillating/rotational movement of the blade-holder frame and block to be cut, so that the cutting profile on the block is curvilinear or circular. The combination of the reciprocating rectilinear movement and the oscillating/rotational movement forms the cutting movement. In addition, there is the already mentioned lowering movement.

Essentially the combination of the cutting and advancing movements produces a succession of relative positions of the blade-holder frame and block, as indicated in the accompanying Figure 1.

The blades remain in contact with the block only along a very short section which in theory is even point-like.

In the first cited patent (Italian patent No. 1,247,055) rotation may involve both the block and the blade-holder frame. In the first case, rotation of the block about a movable centre is obtained by causing rolling of the block-holder carriage to- and-fro along a curved guide, while the blade-holder frame performs only a slow lowering movement (in addition to the to-and-fro, reciprocating, rectilinear movement). In the second case, rotation of the blade-holder frame (together with the lowering movement) is performed by lowering and raising alternately the blade-holder pendulum supports by means of a jig connected to the said supports.

In the second cited patent (Italian patent No. 1,275,946) the block remains stationary and the blade-holder frame, in addition to the cutting movement, also performs the rotational and lowering movement. These latter two movements are performed by means of controlled actuation of the parallel pendulum supports and, therefore, the screws and nut screws which control the lowering movement of the blade-holder frame.

It should be noted that the to-and-fro reciprocating movement of the blade holder is performed at a high speed and therefore with a relatively high frequency, while the rotational and lowering movements are performed slowly.

Also worth mentioning is Italian Patent No. 1,253,660, in which cutting of the granite blocks is performed using diamond blades (for use in normal granite pendulum sawing machines) with a cutting profile which is not straight, but is curved and substantially coincides with the profile of a worn blade. The patents described above during their industrial application have proved unsuitable for achieving the predefined object, namely that of effectively cutting hard stone without deviations in the cut.

Also all the other various attempts and various solutions tested hitherto during the past decades have produced totally unsatisfactory results, so that hitherto it has not been possible to perform industrially the cutting of hard stone such as granite using diamond blades.

The main object of the invention is therefore to provide an industrially advantageous solution to this problem and need.

This object is achieved with a method for sawing blocks of hard, natural or agglomerate, stone material using a multi-blade sawing machine, comprising: a blade-holder frame provided with straight cutting blades having a substantially continuous diamond cutting edge, where said frame is brought into contact with the block to be cut, starting from its initial sawing surface with a relative oscillating movement of said blade-holder frame and said block to be cut so as to produce a cutting movement, said blade-holder frame being made to perform a gradual advancing movement towards the surface of the block opposite said initial sawing surface so as to produce a so-called penetrating movement, each blade being longer than the maximum dimension of the block to be sawn by an amount at least equal to the stroke of said blade-holder frame during said oscillating movement, characterized in that said relative oscillating movement of blades and block to be cut is a composite pendular movement comprising an oscillating movement about a first centre of rotation situated, with respect to the plane in which the blade-holder frame lies, on the opposite side to said block to be sawn and a rotational movement about a second centre of rotation lying in the plane of said blade-holder frame, such that the cutting movement is a relative rotary translational movement of each blade and the block being sawn, said composite pendular movement also being characterized in that, when the oscillating movement with respect to said first centre of rotation is reversed, the rotational movement about said second centre of rotation also reverses its direction of rotation, such that said two movements are synchronized with each other and the cutting profile generated on the cutting block is a substantially circular profile and the contact between said cutting blades and the block is a theoretically point-like contact, and this point during each oscillating cycle moves along the entire cutting profile in one direction and then in the opposite direction, returning to the starting point.

In essence in the method according to the present invention the blade-holder frame is made to perform a reciprocating oscillating movement about a centre of rotation, outside the blade-holder itself and situated in relation to the plane of the blade-holder on the other side of the block to be sawn, and at the same time a rotational movement, also of a reciprocating nature, about a centre of rotation situated in the plane of the blade-holder frame, this second movement being synchronized with said oscillating movement so that, during the time taken by the blade-holder frame to perform a complete oscillation, it performs a complete translational movement between the two ends of said block.

It should be noted that "penetrating movement" is intended to mean a, preferably continuous and constant, relative approach movement of the blade-holder frame and the block to be sawn, regardless of the direction of this movement (e.g. horizontal or vertical) or the object which is moving (the frame, block or both). The penetrating movement coincides with the lowering movement when the blade-holder frame moves downwards towards the block, which is stationary.

Preferably the first centre rotation is not fixed relative to the absolute reference system of the sawing machine, but is fixed in relation to a reference system integral with the system/mechanism for translation of the blade-holder frame and movable relative to the (absolute) reference system of the sawing machine.

If said first centre of rotation were fixed during the penetrating/lowering movement, the radius of rotation of the centre of mass of the sawing machine would increase; since the length of the cord travelled must be kept constant (twice the radius of the crank), the height of camber is reduced and consequently the cutting efficiency of the sawing machine is reduced.

Although this is a possible variant of the invention, preferably the first centre of rotation is designed movable and integral with the lowering/penetrating mechanism. Therefore the radius of the centre of rotation of the centre of mass of the blade-holder remains constant, as does the cutting efficiency of the sawing machine during its penetration into the block.

These considerations are also clearly applicable to the means and mechanisms constructed according to the invention in order to implement the method thereof.

The greater lengths of the blade and its continuous diamond edge in relation to the size of the block produces relative sliding contact between diamond tool and stone material, which gives rise to the phenomenon of abrasive cutting.

When operation of the blade-holder frame during its oscillating movement is obtained with a conventional connecting rod and crank mechanism, then the greater length of each blade in relation to the maximum dimension of the block to be sawn is equal to twice the length of the crank.

Conceptually, the cutting movement is obtained starting from a first end position, where the blade-holder frame is inclined on one side in relation to the surface of the block with a maximum value of inclination and one end of the diamond edge of the blades is in contact with one end of the block. Then the blade-holder frame is made to perform a rotary translational movement so as to move towards the opposite end of the block and rotate so as to cause the blade-holder frame to assume firstly an intermediate position, where the blades are arranged parallel to the surface of the block and the middle of the diamond cutting edge is in contact with the middle of the block, and then reach a second end position where the blade-holder frame is inclined in an opposite manner to that of the first end position, so that the envelope curve of the points of contact between diamond cutting edge and block which forms the cutting profile has a substantially circular shape.

In this way the rectilinear reciprocating movement of the blade-holder frame and the oscillating movement of the blade-holder frame (which in this case is substantially a rotational movement), similar to those described in prior art patents cited above, are now synchronked so that the resulting cutting movement is a rotary translational movement of the blades about a centre of rotation which is fixed (in the sense described above) in relation to the blade-holder frame.

In particular, the cutting movement is imparted to said blade-holder frame, while the lowering/penetrating movement may be imparted to the blade holder itself or to the block to be cut.

It can be noted that, by superimposing the various positions assumed by the blade-holder frame during the various instants, a figure similar to Figure 1 is obtained. However, the difference is substantial because, while in the case of the known machines this figure represents only the middle positions assumed by the blade-holder frame (it should be remembered that the blade-holder frame is moved to-and-fro at high speed), here instead the positions shown are the only positions assumed in that, for each point of contact between blades and block, the blade-holder frame assumes a single position. The contact between diamond cutting edge and stone is in theory "point-like", except where there are deformations of the blade under the cutting pressure.

It is very important to note that, with the movement described above, the path followed by the end of the blades is a curved line, which is very similar to a circumferential arc in the case where the camber of the cutting profile is small and is less than about 1% of its length.

Therefore, the kinematic system/mechanism which performs the movements described above must impart to the ends of blades, and therefore to the corresponding points of engagement with the blade holder, displacement trajectories which are curvilinear and in particular similar to a circumferential arc in the cases where it is required to provide circular cutting profiles in which the camber of the profile is small and in particular less than about 1% of its length.

Obviously the kinematic system can assume any arrangement, so the blades may have a substantially horizontal arrangement or a substantially vertical arrangement. The advantageous characteristic features of the invention will emerge more clearly from the following detailed description of a particular kinematic embodiment of the sawing machine, capable of providing cutting profiles consisting of a circumferential arc having a small camber less than about 1% of its length, provided with reference to the following figures in which: Figure 2 is a schematic view of a sawing machine with a horizontal blade- holder frame which implements the method according to the invention;

Figures 3, 4, 5, 6 are schematic views of the sawing machine according to Figure 2, in which the different relative operating positions of blade-holder frame and block to be cut are shown; Fig. 7 is a schematic view of the blade-holder frame and the block, showing the trajectory of the points of attachment of the blade-holder frame to the pendulums or oscillating arms during the movement of the sawing machine; and

Fig. 8 is a schematic view of an alternative embodiment of a sawing machine with a blade-holder frame which implements the method according to the invention. In Figure 2, 10 denotes in its entirety a horizontal machine for sawing a block

50 of hard, natural or agglomerate, stone placed on a carriage. The sawing machine 10 comprises a blade-holder frame 20 arranged horizontally and provided with a plurality of straight blades, for example 80 - 100 in number, with a continuous diamond cutting edge. The length of each blade is greater than the maximum dimension of the block to be sawn by a length at least equal to the translational stroke of the blade-holder frame. In the case of operation with connecting rod and crank, the length of each blade is equal to the maximum dimension of the block plus twice the length of the crank. The blade-holder frame is constrained at its ends by means of two non-parallel oscillating arms or pendulums 22 and 24, so that it can be moved with a pendular motion.

The top ends 22a and 24a of the pendulums 22 and 24, opposite to the ends 22b and 24b hinged with the blade-holder frame 20, are fixed to supports (not shown in the figures).

The two arms or pendulums 22 and 24 are not parallel to each other, but inclined so as to converge towards a common centre of rotation, so that in combination with the blade-holder frame and with a straight line which ideally connects together the top ends 22a, 24a, they define a trapezium which during each oscillation changes from the right-angled trapezium configuration to an isosceles trapezium configuration and finally a new right-angled trapezium configuration which is an opposite mirror image (these configurations can be seen in Figures 3 to 5, respectively).

The blade holder 20 is also made to perform a reciprocating movement by means of a connecting rod/ crank mechanism 30 consisting of a crank 32 hinged with a connecting rod 34 by means of a crank pin 36. The connecting rod is in turn hinged with the blade-holder frame 20 by means of a connecting-rod pin 38.

The mechanism 30 also includes a flywheel 40 integral with the crank 32 for ensuring a uniform movement of the blade-holder frame 20. The cutting method is performed in the manner described below with reference to Figures 3, 4, 5 and 6 which show the different operating positions which the blade-holder frame 20 is able to assume during a cutting cycle.

Starting from the position shown in Figure 3, where the blade-holder frame 20 is inclined on one side so that the left-hand portion of its blades is in contact with the left-hand end of the block to be cut 50, by means of the connecting rod/ crank 30 mechanism the frame 20 moves towards the left (looking at the figure), while, at the same time, owing to the configuration of the non-parallel pendulums 22 and 24, it rotates clockwise so as to straighten and reach the position shown in Fig. 4 In the position of Fig. 4, the blade-holder frame 20 is arranged horizontally and the central portion of the blades is in contact with the middle of the block to be cut. In this position the pendulums 22 and 24 are arranged symmetrically and are splayed apart with an angle of amplitude such as to ensure the desired movements.

Continuing with the cutting operation, the blade-holder frame 20 moves towards the left and at the same time continues to rotate clockwise, being inclined on the opposite side to the configuration shown in Figure 3, reaching then the configuration shown in Figure 5 where the right-hand portion of the blades is in contact with the right-hand end of the block to be cut.

From the end configuration shown in Figure 5, both the translational movement and the rotational movement of the blade-holder frame 20 reverse their direction. The blade-holder frame is advanced towards the right and at the same is rotated in an anti-clockwise direction, so that the frame assumes firstly the configuration shown in Figure 6, where the blade-holder frame is arranged horizontally and in contact with the middle of the block (similar to Figure 4) and then, continuing, the starting configuration shown in Figure 3 is reached, where the blade- holder frame is inclined with the left-hand portion of the blades in contact with the left-hand end of the block 50. This completes a cutting cycle and at the same time an oscillating movement cycle of the blade-holder frame.

The resultant movement performed by the blade-holder, which passes from the position shown in Figure 3 to that of Figure 4 and then to that of Figure 5, is a rotary translational movement in which the centre of rotation is situated in the middle of the blade-holder frame and is therefore a moving centre of rotation. During this movement the blades with which the blade-holder frame 20 is provided, since they are longer than the block to cut 50, make sliding contact along its surface, thus cutting into the top of the block. Essentially, the reciprocating, rectilinear, translational movement of the blade- holder frame is combined with a simultaneous rotational movement of the blade holder synchronized with the translational movement. In the figures it can be noted that with each pass, i.e. with each stroke of the blade-holder frame, each blade passes from a position where it is cutting a top end of the block and is inclined in one direction (see Fig. 3) into an opposite position where it is cutting the opposite end and is inclined symmetrically with respect to the previous position (see Fig. 5). Between the position shown in Fig. 3 and that shown in Fig. 5 there is an intermediate position (see Fig. 4) where the blade in its middle part is cutting the middle of the block at the top of the cutting profile. The blades are therefore subject simultaneously to two movements: a translational movement during which they advance and a rotational movement during which the blades rotate about a centre of rotation moving along a trajectory. Therefore the relative movement of the blades and block is a rotary translational movement and the blades rotate and simultaneously slide along the block to be cut. The cutting profile consequently generated on the block is a substantially circular profile and the contact between the cutting edge of each cutting blade and the block is a theoretically point-like contact (basically extending along a short line section): said point of contact for each oscillating cycle of the sawing machine and therefore the blade moves along the entire cutting profile first in one direction and then in the opposite direction, returning to the original position, resulting in a relative sliding movement of the diamond cutting edge and block being sawn equivalent to the oscillating stroke of the blade-holder.

It should be noted that, as ready mentioned, each blade has a length greater than the maximum length of the blocks to be cut and the difference in length is equal to twice the length of the crank of the connecting rod and crank operating mechanism.

In this way it is ensured, on one hand, that the entire diamond edge of the blade participates in the sawing action and, on the other hand, that there is the possibility of relative sliding contact between the blade and fore-lying surface of the block during the rotary translational movement which is the movement which ultimately produces the cutting action.

In other words, assuming that the maximum dimension of the block to be sawn is 3.5 m and that the length of the crank is 35 cm, then the length of the blade will be about 4.2 m. Assuming, for example, that the oscillating frequency of the blade-holder frame is 60 cycles per minute (i.e. one cycle per second), then the sliding speed or the relative speed of the blade and block will be 1.4 m per second.

As the blade-holder frame 20 is moved in the manner indicated, the cutting blades are gradually moved towards the block, generating the so-called lowering (or penetrating) movement such as to allow cutting of the block into slabs.

In this case, the supports to which the ends 22a and 24a of the pendulums 22 and 24 are fixed may be movable and, while the blade-holder frame is moved as described, the pendulum supports are gradually moved towards the block and therefore both the lowering/penetrating movement and the cutting movement are imparted to the blade-holder frame 20. Alternatively, it is possible to keep the supports of the pendulums 22 and 24 fixed and raise the block so that the blade-holder frame 20 is imparted only the cutting movement, while the relative approach movement of block and blades, or lowering movement as defined above, is imparted to the block. Essentially, compared to the prior art solutions commented upon initially, the rotational movement is fast and, while the two (translational and rotational) movements previously differed in terms of speed, now the two movements are synchronized with each other so that with each translation cycle there is a corresponding simultaneous rotational cycle. In the kinematic system described above, when the pendulums have a particularly significant length, greater than half the length of the cutting profile, the circular path described by the end of the blades comes very close to being the ideal path necessary for achieving the desired circular cutting profile where the camber of the said profile is small and less than about 1% of its length. '' The cutting profile consists of the envelope curve of the points of contact between cutting blades and block and this profile corresponds substantially to a circumferential arc, and the contact between diamond profile and stone is in theory "point-like", except where there are deformations of the blade under the cutting pressure. It should be noted that, during practical construction of a horizontal sawing machine based on the kinematic system described above, with cutting profiles 3.5 m long, corresponding to the maximum length of the blocks used in the market, and with pendulums more than 1.5 m long, the difference between the actual trajectory of the blade ends and the ideal trajectory necessary for providing a perfectly circular cutting profile is less than about 2 mm, an amount comparable to the deformation of the blade caused by the cutting forces.

Consequently, in practice, with a machine thus constructed it is possible to achieve a cutting profile fairly close to a circumferential arc, thus ensuring a small zone of contact, relative to the length of the blade, between diamond tool and stone. It is thus possible to perform the cutting of hard stone using diamond tools having a thickness of about 3-5 mm. As a result, it is possible to reduce by nearly half the cutting waste compared to the present-day cutting methods which use metal grains or diamond wires, with a consequent considerable saving in terms of material and energy. The sawing machine which implements the cutting method described above may also be constructed using different kinematic systems; for example, as an alternative to the pendulums, in order to achieve a circular trajectory of the blade ends, the means for guiding and supporting the blade-holder frame may be formed by means of a curved guide for each of the four corners of the blade-holder frame, while movement of the frame could be achieved by means of the conventional connecting rod and crank mechanism.

In this way, by providing guides with a specially designed curved profile, it is possible to move the blade-holder frame with a rotary translational movement which generates a perfectly circular cutting profile. In Figure 7 the reference number 60 denotes the curve which the point of attachment (22b, 24b) of the blade-holder frame to the corresponding pendulum 22, 24 should describe in order to obtain the desired effect.

It is important to point out that in horizontal sawing machines in which the kinematic system envisages a connecting rod and crank system for the movement of the blade holder, if the advancing movement is imparted to the blade-holder frame, namely if the blade-holder frame is subject to a lowering or downward movement, then the phenomenon of displacement of the connecting rod base along a circumferential arc must also be considered.

In fact, if the block remains stationary, as the cut progresses, the classic problem of a virtual elongation of the connecting rod arises, since the horizontal projection of the path of the connecting rod base varies with a variation in the heightwise position of the blade-holder frame.

More precisely, if we assume that the dimension of the centre of rotation of the crank coincides with the middle point heightwise of the block to be cut, at the start and at the end of the cut the connecting rod is oriented upwards and downwards, respectively. This causes a minor oscillation of the blade-holder frame, but in particular the combination of the reciprocating movement of the blade-holder frame together with the lowering movement of the blade-holder causes an asymmetrical movement. In order to overcome this problem, the sawing machine should have one of the following alternative characteristics:

(i) the columns are provided with curved guides for the downward movement of the centres of oscillation of the pendulums, so as to maintain always the same distance between the cutting zone and centre of the crank, (ii) a connecting rod which is adjustable lengthwise depending on the height of the centres of oscillation of the pendulums is provided; in this connection see the patent application No. 1,210,554 in the name of Luca Toncelli entitled: "Device for automatically and continuously compensating for the virtual elongation of the connecting rod in a pendulum sawing machine for cutting marble, granite and hard stone".

Alternatively, in order to eliminate this problem, it is sufficient to impart the advancing movement not to the blade-holder frame, but to the block to be cut which is thus raised. The optimum solution therefore appears to be that of a sawing machine with a short connecting rod with raising of the block. According to an alternative embodiment, the use of a curved profile blade 60 as shown in fig. 8 is provided.

Said blade 60 presents a cutting edge which has a substantially concave profile.

The camber radius of the cutting edge of the blade 60 is larger than the cutting profile radius generated on the sawing block. In particular said blade 60 has preferably a symmetrical shape with respect to its longitudinal axis 61.

The curved profile generates variable stiffening on the blade 60 along the longitudinal axis 61 direction.

The stiffening generated by an initial pretension of the blades 60 provides for the central cutting surface to oppose more effectively to the lateral forces so that the blades remain rectilinear and the cut doesn't deviate from the vertical direction.

The above description refers to a substantially horizontal arrangement of the blades, but the principle is equally valid for a substantially vertical arrangement, so that a variant of the invention consists in providing a vertical instead of a horizontal sawing machine in which the blade-holder frame is arranged vertically. likewise the description refers to the conventional situation of a multi-blade sawing machine, but it may also apply in an identical manner to a sawing machine also with a single blade.

Claims

1. Method for sawing blocks of hard - natural or agglomerate - stone material, using a multi-blade sawing machine, comprising: a blade-holder frame (20) provided with straight cutting blades having a substantially continuous diamond cutting edge, where said frame is brought into contact with the block (50) to be cut, starting from its initial sawing surface with a relative oscillating movement of said blade-holder frame and said block to be cut so as to produce a cutting movement, said blade-holder frame being made to perform a gradual advancing movement towards the surface of the block opposite to said initial sawing surface so as to produce a so-called penetrating movement, each blade being longer than the maximum dimension of the block to be sawn by an amount at least equal to the stroke of said blade-holder frame during said oscillating movement, characterized in that said relative oscillating movement of blades and block to be cut is a composite pendular movement comprising an oscillating movement about a first centre of rotation situated, with respect to the plane in which the blade-holder frame lies, on the opposite side to said block to be sawn and a rotational movement about a second centre of rotation lying in the plane of said blade-holder frame, such that the cutting movement is a relative rotary translational movement of each blade and block being sawn, said composite pendular movement also being characterized in that, when the oscillating movement with respect to said first centre of rotation is reversed, the rotational movement about said second centre of rotation also reverses its direction of rotation, such that said two movements are synchronized with each other, the cutting profile generated on the block being a substantially circular profile and the contact between said cutting blades and the block being a theoretically point-like contact, so that this point during each oscillating cycle of said blade-holder frame moves along the entire cutting profile in one direction and then in the opposite direction, returning to the starting point with relative sliding of said diamond cutting edge and block by an amount equivalent to the oscillating stroke of the blade-holder frame.

2. Method according to Claim 1, characterized in that said rotational movement about said second centre of rotation is obtained starting from a first end position where the blade-holder frame (20) is inclined on one side with respect to the surface of the block (50) with a maximum inclination value and the end of the blades is in contact with one end of the block, the blade-holder frame (20) is made to perform a rotary translational movement so as to move towards the end of the blade- holder frame (20) opposite to the block (50) and is rotated so as to cause the blade- holder frame (20) to assume firstly an intermediate position where the blades are arranged parallel to the surface of the block and their middle is in contact with the middle of the block (50) and then reach a second end position where the blade-holder frame (20) is inclined in an opposite manner to that of the first end position such that there is relative sliding of the diamond edge and the block by an amount equal to the movement stroke and the envelope curve of the points of contact between cutting blades and block which forms the cutting profile has a substantially circular shape.

3. Method according to Claim 1 or 2, in which the first centre rotation is (i) designed fixed relative to a reference system integral with the mechanism for translation of the blade-holder frame and (ii) movable relative to the reference system of the sawing machine.

4. Method according to Claim 3, characterized in that said oscillating movement about said first centre of rotation is imparted to said blade-holder frame

(20).

5. Method according to Claim 4, characterized in that said oscillating movement is obtained by means (22, 24) for constraining the blade-holder frame, designed to impart a pendular movement to the said blade-holder frame (20).

6. Method according to Claim 5, characterized in that said constraining means are oscillating arms or pendulums (22, 24) which are not parallel with each other and which in the middle oscillating position are arranged symmetrically and splayed apart so as to form an isosceles trapezium together with the blade-holder frame (20).

7. Method according to Claim 6, characterized in that said oscillating arms or pendulums (22, 24) have a length close to or greater than half the length of the cutting profile.

8. Method according to Claim 4, characterized in that said cutting movement is obtained by means of curved guiding means of the blade-holder frame.

9. Method according to any one of the preceding claims, characterized in that said penetrating movement is imparted to said blade-holder frame (20).

10. Method according to Claims 6 and 9, characterized in that said penetrating movement is obtained by means of movement of said oscillating arms or pendulums (22, 24).

11. Method according to Claims 8 and 9, characterized in that said penetrating movement is obtained by means of movement of said curved guiding means of the blade-holder frame.

12. Method according to any one of Claims 1 to 8, characterized in that said penetrating movement is imparted to said block to be cut (50).

13. Method according to Claim 1, 2 or 3, characterized in that said cutting movement and said penetrating movement are imparted to said block to be cut, while said blade-holder frame remains fixed.

14. Method according to any one of the preceding claims, characterized in that said cutting movement and said penetrating movement are performed with the blade-holder frame lying in a substantially horizontal position.

15. Method according to any one of the preceding Claims 1 to 13, characterized in that said cutting movement and said penetrating movement are performed with the blade-holder frame lying in a substantially vertical position.

16. Method according to any one of the preceding Claims characterized in that said sawing is performed by blades (60) having a concave cutting edge profile, said profile having a camber radius larger than the cutting profile radius generated on the sawing block (60).

17. Method according to Claim 16 characterized in that said sawing is performed by blades (60) wherein the edge opposite to said cutting edge is also concave.

18. Sawing machine for cutting blocks of hard - natural or agglomerate - stone materials, comprising a blade-holder frame (20) and means (22, 24, 30) for relative movement of said frame (20) and block to be cut (50), characterized in that said movement means (22, 24, 30) impart a relative oscillating movement, about a first centre of rotation situated, in relation to the plane in which the blade-holder lies, on the opposite side to said block to be sawn (50), and a relative rotational movement, about a second centre of rotation situated in the plane of said blade-holder frame, of the blade-holder (20) and the block to be cut (50), said two movements being -., synchronized so as to produce a rotary translational movement such that the cutting profile generated on the block (50) as a result of the sliding contact between the diamond edge and block being sawn has a substantially circular form and the contact between said cutting blades and block is a theoretically point-like contact.

19. Machine according to Claim 18, characterized in that said movement means (22, 24, 30) impart an oscillating movement about the first centre rotation so this centre of rotation is (i) fixed relative to a reference system integral with the mechanism for translation of the blade-holder frame and (ii) movable relative to the reference system of the machine.

20. Machine according to Claim 18 or 19, characterized in that said movement means comprise means (22, 24) for oscillation of said blade-holder frame (20) and a connecting rod and crank mechanism (30) for imparting a reciprocating movement to said blade-holder frame (20).

21. Machine according to Claim 20, characterized in that said oscillating means comprise at least two pendulums (22, 24) which are fixed in the vicinity of each of the two ends of the blade-holder frame (20) and said two pendulums (22, 24), in the position where the blade holder (20) is arranged parallel to the surface of the block to be cut, are arranged symmetrically and splayed apart so as to form an isosceles trapezium with the blade-holder frame.

22. Machine according to Claim 21, characterized in that said at least two pendulums (22, 24) have a length very close to or greater than half the length of the cutting profile.

23. Machine according to Claim 18 or 19, characterized in that said movement means comprise curved guides for said blade-holder frame.

24. Machine according to anyone of Claims from 18 to 23 characterized in that said blades (60) have a concave cutting edge profile, said profile having a camber radius larger than the cutting profile radius generated on the sawing block (60).

25. Machine according to the preceeding Claim 24, characterized in that said blades (60) have the edge opposite to said cutting edge also concave.