In the technical sector, grinding machines (or grinders) used to perform surface finishing of metal parts and the like are known.

Said grinders comprise in particular so-called "centreless"or"noseless"machines which are of the "through-operation"type in that the part to be machined, which normally extends in'a longitudinal direction parallel to a feeding direction, is not supported at its opposite ends by corresponding chucks/tailstocks and moves axially in the said feeding direction through the working tools with which it remains in contact during the pass.

It is also known that said working tools are composed of an operating wheel, which is made of material suitable for determining the surface finish of the workpiece and which rotates at a high speed (about 1,500 rpm), and a guide or feed wheel, which is made of friction material such as an abrasive combined with rubber or the like and which rotates at a low speed (about 30 rpm); said guide wheel has the function of retaining the workpiece in the direction transverse to the feeding direction'in order to avoid vibrations and loss of contact with the operating wheel and prevent the workpiece from assuming a rotational speed corresponding to that of the operating wheel.

All the machines must perform periodic operations for restoring the lateral surface of the guide wheel, which is subject to deformations resulting in imperfect

tangential contact with the workpiece during the passing movement of the latter axially through the wheels.

This irregular contact of the workpiece with the guide wheel essentially produces an instantaneous variation in the speed of rotation of the workpiece and displacement thereof from the feeding direction, which factors are the cause of imperfections in machining and therefore finishing of the workpiece.

In the technical sector apparatus able to perform said maintenance of the surface of the guide wheel are known, said apparatus being arranged on the opposite side to the latter relative to the workpiece to be machined.

These solutions, although performing their function, in addition to causing considerable complications in the design of the machine-particularly owing to the large number of controlled axes which must be provided in view of the fact that the guide wheel, in its practical embodiment, is also inclined with respect to the longitudinal axis-also produce a longitudinal profile (directrix) of the wheel which does not correspond precisely to the locus of the points of contact between wheel and workpiece, resulting in imprecise contact between the wheel and workpiece which, as mentioned, is the direct cause of corresponding machining defects.

The technical problem which is posed, therefore, is that of providing an apparatus able to allow machining of the guide wheel of grinding machines in order to restore the surface thereof and ensure that uniform contact between the guide wheel and workpiece is better maintained.

Within the scope of this problem a further requirement is that said apparatus may be applied to ready existing machines and is able to bring about a reduction in the

controlled axes necessary for a successful outcome of the operation.

These technical problems are solved according to the present invention by an apparatus for machining the lateral surface of guide wheels of grinding machines also comprising an operating wheel, which wheels rotate about respective longitudinal axes parallel to each other, said apparatus comprising a tool for working said surface of the guide wheel, said tool being mounted on an associated support element movable from a position of disengagement of the tool from the surface of the wheel to a position where the tool makes contact with the same surface, said position where the tool makes contact with the guide wheel being located in the space defined between the two wheels, i. e. guide wheel and operating wheel.

Further details may be obtained from the following description of a non limiting example of embodiment of the invention, provided with reference to the accompanying plates of drawings, in which: - Figure 1 shows a perspective view of a grinder with an apparatus for restoring the surface of the guide wheel according to the invention; - Figure 2 shows a front view of the machine according to Figure 1 ; - Figure 3 shows a schematic side view of the machine according to Figure 1 in the working condition with the apparatus at rest; - Figure 4 shows a section along the plane indicated by IV-IV in Figure 3; - Figure 5 shows a schematic side view of the machine according to Figure 1 in the stopped condition with the apparatus in operation; - Figure 6 shows a section along the plane indicated by VI-VI in Figure 5; and

- Figure 7 shows a cross-section of a variation of embodiment of the apparatus according to the invention.

As shown, the said grinding machine 100 (referred to as "grinder"below) is essentially formed by: - a base 101 on which a support 110 for the fixed operating wheel 111 is fixed; - a support 120 for the blade 121 on which the workpiece 1 rests, said workpiece being fed in a feeding direction X-X parallel to the longitudinal axis of the same workpiece; - a support 130 for the guide wheel 131, which is movable in a horizontal transverse direction Y-Y with respect to the feeding direction X-X.

The apparatus according to the invention for restoring the surface of the guide wheel is mounted on said grinder 100.

As can be seen more clearly in Figures 3 and 4, said apparatus essentially consists of two pairs of vertical columns 201 arranged at opposite front ends of the grinder 100 and connected at the top by a surface 202 extending parallel to the feeding direction X-X.

Said columns have, mounted on them, a cross-piece 203 movable in a vertical transverse direction Z-Z, upon actuation of associated means, in the example consisting of cylinders 204 which are fixed to the said horizontal surface 202 and the rods 204a of which are connected to corresponding supports 203a of the cross- piece 203.

The support for the tool for working the guide wheel is mounted on the cross-piece 203, said support in the example consisting of an arm 205 which is provided at its free ends with the diamonds 205a for machining (diamond-cutting) the surface of the guide wheel 131.

Said tool-holder support is movable translationwise on the cross-piece 206 in a direction parallel to the

direction of feeding X-X of the workpiece and upon actuation of associated controlled means indicated by 215 and for example consisting of a coupling of the type comprising female thread/ball screw (=screw with revolving ball bearings).

In this way the tool is able to come into contact with the lateral surface of the wheel along the whole of its extension in the axial direction X-X.

In a preferred embodiment it is envisaged that the said support for the tool for working the surface of the guide wheel also comprises a second arm 206 which has, mounted on it, a counter-blade 206a able to keep the workpiece 1 in the machining position so as to prevent it from escaping in the vertical direction Z-Z.

In this case it is envisaged that the cross-piece 203 is provided internally with a shaft 207 which may be rotationally driven by a corresponding actuating system which is conventional per se and therefore only schematically indicated by 207a in Fig. 3.

It is envisaged moreover that the cross-piece 203 may also have, formed in it, ducts 209a for supplying the fluid for cooling the tool and the wheel during restoration of the latter.

Said ducts 209a terminate in corresponding nozzles 209 mounted on the cross-piece 203 in the region of the arm 205 and/or the arm 206 for respectively supporting the diamonds 205a and the counter-blade 206a.

The operating principle of the apparatus is as follows: - when it is required to restore the contact surface of the guide wheel 131, the cross-piece 203 is lowered from the rest position in Figures 3, 4 into the working position shown in Figures 5,6, resulting in the diamonds 205a coming into contact with the lateral surface of the wheel 131 which is made to rotate at a suitable speed so as to cause machining of the said

surface; - at the same time delivery of the cooling fluid by the nozzles 209 is activated; - the tool 205a is fed in the feeding direction X-X so as to perform a pass along the whole surface of the guide wheel 131; - once the operation has been completed, the cross- piece 203 is brought back into the original position.

It is therefore pointed out how the tool for diamond- cutting the wheel is arranged essentially in the same position occupied by the workpiece during the pass and how, since the associated support means may be provided with a relatively high rigidity, it is possible to obtain a finish for the contact surface of the wheel 131 essentially corresponding to the actual extension, in the longitudinal direction, of the tangential contact between wheel and workpiece.

As can be seen from the figures, in a preferred constructional form the diamond-cutting tool may be provided symmetrically with respect to the feeding axis X-X, i. e. this means that-the diamonds 205a are also present on the side where the operating wheel 111 is situated, allowing simultaneous diamond-cutting of both the guide wheel 131 and the operating wheel 111.

It is pointed moreover how the apparatus according to the invention allows the control of only two axes of movement of the diamond-cutting tool, namely the vertical axis Y-Y and the longitudinal axis X-X.

Although described and illustrated with a translational movement, the apparatus may also be designed to perform rotational or rotary-translational movements able to bring the tool into the correct position for contact with the surface of the guide wheel.