"MACHINE FOR CUTTING LEATHER AND SIMILAR MATERIALS FOR THE MANUFACTURE OF FOOTWEAR PARTS AND SIMILAR USES" DESCRIPTION The present invention refers to a machine for cutting natural leather, regenerated leather, synthetic materials for manufacturing footwear parts and the like. To be more precise, the invention refers to a machine for cutting butts of natural leather, sheets of regenerated leather or synthetic materials without the aid of a cutting die. Two kinds of machine for this type of process exist on the market. One type of machine is the so-called travelling head clicking press, wherein the operator brings a steel cutting die of the required shape over the material to cut, which is placed on a worktop; by subsequently moving a plate that is solidly attached to a hydraulic cylinder, which can be moved into position above the aforementioned cutting die with a motor-driven carriage, he governs the downstroke of the die to cut the material. Alternatively, the operator can hold the cylinder still and bring the material and the cutting die into position underneath it. Another type of machine is the so-called numerical control cutting bench, on which the operator places the material, flattening it with the aid of a vacuum system incorporated in the machine, and subsequently uses a projector to define the shapes of the soles (or other items) one at a time until the whole area of the material to cut has been covered; then the operator enables the cutting process and the machine performs the work, cutting out the various previously-arranged shapes. In the case of the traditional travelling -head clicking press, the production rate is relatively low because - although the cutting movement itself is quick - positioning, changing and then removing the cut piece from the cutting die all take time. Moreover, the operator has to cope with far from negligible physical fatigue because the cutting dies come in various sizes, but are always relatively heavy and consequently tiring to handle. In the case of the numerical -control cutting bench, on the other hand, working without a cutting die means that the fatigue is reduced to a minimum, but the production rate is virtually the same as with the machine using cutting dies because positioning the shapes all over the surface of the material to cut takes several minutes and the actual cutting operation is not as fast as with a cutting die. Moreover, when working on natural materials such as leather, operators have to allow for surface defects (cuts, wrinkles and imperfections due to injuries, Caesarean section and prior processing) and for differences in thickness, which oblige them to inspect and measure the butt before each cutting action; these procedures are normally required even when the traditional clicking press is used, of course, but these steps cannot be taken at the cutting bench because the material has to be held onto the worktop by the suction system and cannot be moved without losing the previously-arranged sole shape positions, so the operator has to inspect the material before fixing it in place and remember the variations in its features between one part and another during the positioning procedure. After several cuts have been made, moreover, the suction pressure holding the material on the table tends to diminish, so it is no longer held perfectly still and the butt and/or sheets tend(s) to move, with consequent inaccuracies in the cut pieces and frequent tool damage. Last, but not least, the cost of the numerical-control machines is far greater (up to 5 times more) than that of conventional machines, with the sole advantage of not having to use cutting dies. In addition, it poses some adaptation problems for operators who were used to working with travelling-head clicking presses. Hence the idea to produce a substantially numerical-control machine, that cuts the material without using a cutting die, but that retains the same working method as the conventional clicking press. These and other objects and advantages become evident from the following text. The machine according to the invention - for cutting natural or regenerated leather, synthetic or other similar materials for the manufacture of footwear parts or the like - substantially includes a combination of: a worktop whereon the material to cut is supported and retained; optic means for projecting images of the shapes to cut onto the material lying on said worktop; means for supporting and moving a cutting tool over said worktop; and means for controlling the displacement of said cutting tool in accordance with the data provided by said optics. Basically, the cutting tool is a head suitable for controlling the high-speed reciprocating axial movements at progressively orientable angles of a cutting tool ataπg the contour of the shaped pieces to cot out of tine mate riaL A cutting head of the aforesaid type is described in the Italian patent n0 (application FI2003/A/000176 of 02.05.2003 by the present applicant). The tool can be of the type described in the Italian patent n° (application FI2003/A/000127 of 02.05.2003). To be more specific, the machine in question can comprise a frame providing a worktop for supporting and anchoring the material to cut combined with: - a guide assembly lying on a plane parallel to the worktop; - a fixture on said guide assembly for carrying a tool for cutting the material; - an optic unit some distance above said worktop for projecting an image of the shape of the piece to cut out of said material onto the material to cut; - a system for orienting the optic unit to enable the operator to position said image on the material to cut; and - means for deriving data from the optic unit's orientation data to enable the positioning of said fixture and cutting tool, and the consequent cutting of the material in the places selected by the operator and at the operator's command. In practical terms, the guide assembly may comprise a carriage moving on crosswise guides and, on said carriage, longitudinal guides carrying a beam-like member or saddle capable of extending with one end over said worktop; said end being fitted with said cutting tool. The worktop is surrounded by structures for supporting the portions of material surrounding the portion ready to be cut that lies on the worktop. The optic unit is complete with a memory of several shapes of pieces to cut, which can be selected by the operator by means of a mouse control. The invention is easier to understand by following the description and attached drawing, which illustrate a non-restrictive practical embodiment of the invention. In the drawing: Figs. 1 and 1 A show a front view and an enlarged detail thereof; Figs. 2 and 2A show a side view and an enlarged detail thereof; Figs. 3 and 3A show an overhead view and an enlarged detailed thereof; Figs. 4 and 5 show partial longitudinal sections with the cutting tool in the withdrawn position and in the forward working position, respectively; and Fig. 6 shows an enlarged partial cross-section. As illustrated in the attached drawing, the numeral 1 indicates a base, at the front of which there is a worktop with a suction system 3, which forms the surface on which a part of the material is supported and retained while the required pieces are cut from the material. Said worktop 3 is surrounded by supporting surfaces 5 and 6 that form structures on which to place the remainder of the material around the part of material resting on the worktop 3. Said worktop 3 is complete with a suction system for creating a negative pressure suitable for stabilizing and anchoring the material to cut on said worktop 3, thus preventing it from either lifting away from or moving along the worktop. Also behind to the worktop 3, there is an area 7 for resting any excess material lying beyond the worktop 3, serving the same purpose as the supporting surfaces 5 and 6. Numeral 9 indicates the crosswise sliding guides supported by the base 1 and designed to enable the sliding of the carriage 11 , which can thus move in a horizontal crosswise direction Y. The carriage 11 can be driven by means of a servomotor 13, which drives a screw 15 coupled to a recirculating-ball worm screw 17, which consequently enables the movement of said carriage 11. The carriage 11 in turn provides longitudinal sliding guides 19 orthogonal to the sliding guides of the carriage 11 , for a longitudinal and horizontal beam or saddle 11 , designed to slide in a direction X, covering a stroke whose amplitude substantially coincides with the dimensions of the worktop 3 in the direction X. The sliding of the saddle 21 is induced by a motor 23, that drives a screw 25, coupled to a recirculating ball or equivalent worm screw 27 carried by the saddle 21. The saddle can thus be displaced along X so that the front end 21 A of said saddle or beam 21 can be displaced above the worktop 3, also projecting beyond its longitudinal dimension. The end 21 A of the saddle 21 carries the head 30 which forms the cutting tool, complete with a pneumatic cylinder 32, which enables the downstroke and upstroke of the cutting head 30 so as to cut the material lying on the worktop 3 and to lift the tool above said worktop. The tool, indicated generically by the numeral 34, can be advantageously of known type and is already described in the previously-mentioned Italian patent, and it is capable of a vertical movement determined by the cylinder-piston system 32, and can be oriented at any angle around the vertical axis to perform the cut according to the embodiment illustrated in the previously-mentioned patent. By means of a support 36 the base 1 supports the optic unit 40 that occupies a position coinciding with the central area of the worktop 3, but wsli above said worktop and consequently also above the saddle 21 and the parts associated therewith. The optic unit 40 includes a projector suitable for projecting images of shapes, which can be selected from a set of shapes memorized in the optic unit 40, and can be selectively projected at the operator's command for the purposes explained herein. The numeral 42 indicates a panel for the controls situated in front of the machine and readily accessible to operators coming into the vicinity at the front of the worktop 3; the numeral 44 indicates a mouse associated with said control panel 42 for the actions that operators must take to arrange the shapes of the pieces to cut on the material lying on the worktop 3 and enable the subsequent cutting procedure implemented by the head 30 and the tool 34, which can be moved on a horizontal plane in the vicinity of the worktop 3, according to coordinates that, in the solution illustrated, are Cartesian coordinates in the directions X and Y obtained by means of the guides 90 and the guides 19. Each cutting action involves the head 30 and the tool 34 being lowered by means of the cylinder-piston system 32. The fixture comprising the carriage 11 and the saddle 21 , that carries the head 30 with the tool 34, is connected to the optic unit 40, which can project a shape, or a plurality of successive shapes, onto the material lying on the worktop 3, as a result of the preliminary actions taken by the operator to establish the position (s) of the piece(s) to cut from the portion of material that has been placed on the worktop 3 and is retained thereon by the pneumatic suction system. Governed by the operator via the control panel 42 and the mouse 44, the interaction between the projection system in the optic unit 40 and the cutting system in the head 30 and tool 34 enables the cuts to obtain to be arranged by the optic unit 40 projecting images of the shapes required onto the material lying and retained on the worktop 3, and subsequently to cut the piece(s) in the position the operator has established by means of said preliminary procedure. The positioning and forward feed of the tool along the contour of the shapes to cut is done by means of the Cartesian system of the carriage. 11 and saddle 21 (or also by means of another suitable system, e.g. a polar system, equivalent to the one illustrated and described). The positions of the shapes and the choice of said positions case by case as a function of the characteristics of the material placed on the worktop 3 are made easy for tna operator who, ."©Eying en his own expertise and with the aid of the control panel, can easily establish the position for the cut(s) to ensure a rational and cost-effective production of the parts required with a minimum wastage of material and a maximum quality of each of the pieces obtained from the material (which is not always smooth and blemish -free). After the preliminary arrangement procedure, subject to the operator's consent, the machine proceeds to move the head 30 and the tool 34 to cut the one or more pieces from the material supported and retained on the worktop 3. After completing this operation and collecting the cut pieces, the operator can move the material lying on the worktop 3 and on the other supporting surfaces 5 and 7, to repeat the procedure for choosing the positions for the images of the shapes and then cutting other areas of the same material, moved as necessary at the end of each cutting cycle into the area over the worktop 3. In this way, the operator can easily use up all of their material, which sometimes has a relatively large surface area, adopting procedures that are very flexible and easy to perform using the control system available. It will be clear to a person skilled in the art from the above description what advantages can derive from a machine of the kind described above and as defined in the following claims. In particular, the machine in question offers the following advantages: 1. a smaller working field and a consequently limited area being affected by the cutting procedure, that is nonetheless held very firmly thanks to the suction system (provided with the machine); 2. the opportunity for operators to memorize defects and differences in thickness more easily and consequently to position the soles or other parts to cut without fear of error; 3. a projector and software that enable a quick and easy positioning of one or more soles on the material; 4. the opportunity to choose between cutting the entire area of material without moving it, or moving it each time; the operator can decide whether to fill the whole working field with the aid of the mouse and then cut the material without moving it, or to place the required part of the butt under the projector and then cut the pieces one at a time; 5. a minimum toss of time spent unloading the material; 6. nz cutting dies; 7. minimal operator fatigue; 8. a high production rate of the cutting head; 9. a more limited cost (up to three times less); 10. a simple and effective accident prevention barrier, as illustrated by the numeral 50. Using the machine described herein, depending on the features of the material to cut (any presence of defects and/or damage, differences in thickness, etc.), the operator can choose between: - positioning the material to cut just one piece at a time in the working field created by the worktop with the suction system 3, then moving and repositioning the material for a subsequent cutting step; or - positioning the shapes of several pieces to completely fill the working field (which is always smaller than the area of the material to cut) and then taking action to complete the cutting of the various pieces, then moving the material on the worktop 3 to start further cutting procedures on other parts of the material. Clearly, the drawing only shows one embodiment, given simply as a practical example of the invention, which may vary in shapes and arrangement without departing from scope of the concept underlying the present invention.