The invention relates to a machining apparatus as defined in the introductory part of claim 1. In previously known technology, there are devices designed for the cutting of objects of an essentially round shape, such as pipes, which devices cut the object by working it from the direction, of its periphery and in which the motion of the cutting tool is based on the use of centrifugal force. E.g, publi¬ cation DE 2 950 785 proposes an apparatus for cutting objects of a circular circumference which employs centrifugal force to produce the feed motion of the cutting tool. The cutting tool and its counterweight are attached to a bell-crank lever, which in turn is pivoted on a frame ring plate revolving around the object to be cut. As the frame ring plate rotates, the counterweight attached to one end of the bell-crank lever is driven outwards by the centrifugal force, and the cutting tool attached to the lever at a point on the other side of the pivot is moved fowards the pipe to be cut.

A drawback with the apparatus described in the above-mentioned publication is that the angle of the cutting ool in relation to the surface of the object being cut changes all the time during the cutting operation as the bell-crank lever turns. This means that the cutting tool has to be of an elongated shape and it must have either a knife-type or a saw-type cutter, whereas a shave-type cutter, which would produce the smoothest worked surfaces, cannot be used in this apparatus.

Furthermore, the apparatus described in the above-mentioned publication does not work satisfacto- rily in practice because the single-pivot lever mecha¬ nism employed in it is subject to vibrations that are impossible to eliminate. The vibrations of the working

cutter result in poor-quality worked surfaces and related problems.

A further problem with the apparatus referred to is that satisfactory cutting results can only be achieved when cutting objects of a size within very narrow limits. In practice the apparatus is only suited for the cutting of objects of a certain size, while objects having a smaller or larger diameter require a separate apparatus dimensioned for the diameter in question.

A problem with the previously known devices is that the worked surfaces obtained are rough, slanting or otherwise inaccurate. For example, in the case of plastic pipes the cut surfaces cannot be joined by welding unless the worked surfaces are straightened in some other way, which means more stages of operation in manufacture.

The object of the invention is to eliminate the drawbacks mentioned. The machining apparatus of the invention is characterized by what is presented in claim 1.

According to the invention, the machining ap¬ paratus is provided with a guide supporting a working cutter moving along it, and with a separate leverage element so engaged in power transmission contact with the working cutter that a centrifugal force acting on the leverage element counterweight causes the working cutter to move along the guide towards the object being machined. In an embodiment of the machining apparatus, a working device is mounted on an adjusting element allowing the position of the working device to be adjusted radially in relation to the axis of rotation to permit the machining of objects having different diameters.

In an embodiment of the machining apparatus, the working device is provided with a frame and the

adjusting elements consist of two arms linked to the frame at one end and fixed to the rim at the other end by means of a mortise-and-tenon joint, said arms engaging each other at one end via a non-slip trans- mission, e.g. a toothing, enabling the working device to be moved into different working positions without changing its attitude, thus permitting the machining of objects of different diameters.

In an embodiment of the machining apparatus, the working device is provided with a frame and the adjusting element consists of a series of different sized adjustment plates by means of which the frame of the working device can be detachably fixed to the rim, so that, by changing the adjustment plate, the working device can be moved into different working positions to permit the machining of objects of different diameters.

The adjusting element may naturally be any suitable element that enables the desired adjustment to be achieved, e.g. a guide-and-εlide mechanism. In an embodiment of the machining apparatus, the working cutter and the leverage element are linked via a tooth transmission or any other known type of non-slip transmission enabling the counterweight moment produced by the centrifugal force to be transmitted to the working cutter so as to produce a cutter feed motion and a cutter feed force.

In an embodiment of the machining apparatus, the apparatus is provided with two leverage elements and counterweights attached to them, arranged symmetrically on both sides of the working cutter.

In an embodiment of the machining apparatus, the working cutter is a shave-type cutter. The use of a shave-type cutter allows a desired cutting depth and an optimal quality of the cut surface to be achieved. Moreover, the apparatus will have a low noise level.

In an embodiment of the machining apparatus, the working cutter is a roller-type rotary cutter.

In an embodiment of the machining apparatus, the apparatus comprises a first working device and a second working device so placed on the rim that they work the same area of the workpieσe. In an embodiment of the machining apparatus, the working cutter of the first working device is a sharp-toothed wheel while the working cutter of the second working device is a shave-type cutter. The sharp-toothed wheel can be so placed on the rim that it will work the object surface before the shave, thus producing transverse grooves in the surface, so that the shave working this grooved surface will produce very short shavings.

The invention has the advantage that the apparatus can be so constructed that vibrations are eliminated.

Another advantage is that, with simple adjustments, the apparatus of the invention is capable of machining objects of a wide range of diameters and producing an excellent worked surface regardless of object diameter.

A further advantage of the invention is that the apparatus produces good-quality worked surfaces, thus eliminating the need for further working. A further advantage of the invention is that plastic pipes cut by the apparatus have a cut surface quality allowing direct plastic welding.

Furthermore, the apparatus of the invention is simple and cheap. Besides, the invention has the advantage that the machining apparatus is well suited for use as a component in an automated production process.

In addition, the invention allows very fast machining of objects. Moreover, the invention has the advantage that the machining apparatus has a low noise level and produces no detrimental dust particles.

In the following, the invention is described by referring to the appended drawing, in which

Fig. 1 presents a detail of an embodiment of the machining apparatus of the invention, Fig. 2 presents the detail in Fig. 1 as sectioned along line II - II,

Fig. 3 illustrates the operation of the adjusting elements of the working device in the embodiment shown in Fig. 1, Fig. 4a and 4b illustrate the working device and adjusting elements as used in another embodiment of the invention.

Figs. 5 and 6 show details of a third and a fourth embodiment of the machining apparatus of the invention.

Fig. 7 illustrates a third embodiment of the machining apparatus of the invention.

Fig. 8 presents the apparatus in Fig. 7 as sectioned along line VIII-VIII, and Fig. 9 illustrates a fourth embodiment of the machining apparatus of the invention together with auxiliary equipment.

Fig. 1 shows part of the apparatus of the invention, designed for machining the outside surface of objects of an essentially round shape, e.g. pipes, from the direction of the periphery, e.g. to make them thinner or to cut them. The machining apparatus com¬ prises a rim 1 revolving around the object (not shown) to be worked, and a working device 2 so mounted on the rim 1 that the feed motion of the working device 2 is produced by the centrifugal force. The working device 2 comprises a working cutter 3, a leverage element 4 and a counterweight 5, the leverage element 4 being connected to the working cutter 3 and the counterweight 5 and so pivoted that it is essentially immovable in relation to the rim 1, so that when the ^' rim is revolving, the centrifugal force causes the counter-

weight to turn outwards and the leverage element 4 to push the working cutter towards the object being worked. The cutter 3 belonging to the working device 2 is presented here schematically as a rectangular body. Placed symmetrically on either side of the cutter 3 are two counterweights 5, 5' , which are integral with the leverage elements 4, 4 ^! . The leverage elements 4, 4' are so pivoted that the centres of gravity of the counterweights are at a distance from the pivots about which the leverage elements turn when the centrifugal force acts on the counterweights 5, 5* . Between the working cutter 3 and the leverage elements 4, 4' are toothings 6, 6' enabling the torsion of the leverage elements to be converted into a cutter feed motion to- wards the object being worked and the centre of rota¬ tion of the apparatus. In the figure, the position of the leverage elements in a situation when the rim 1 is revolving and a centrifugal force is acting on the counterweights is indicated with dotted broken lines. The machining apparatus is provided with guides

24, along which the working cutter 3 moves. The leverage element 4 and the working cutter 3 are separate bodies so engaged in power transmission contact with each other that the centrifugal force acting on the counterweight 5 causes the cutter 3 to move along the guides 24 towards the object being worked.

In addition, the apparatus is provided with an adjusting mechanism enabling the same apparatus to be used for the machining of objects having different diameters. In this case, the working device 2 is mounted on an adjusting element 7 allowing the position of the working device to be adjusted radially in relation to the axis of rotation to permit the machining of objects of different diameters. In Figs. 1, 2 and 3, the working device 2 is provided with a frame 8. The adjusting elements 7 con¬ sist of two arms 9, 9' located symmetrically in rela-

tion to the working device 2. One end of each arm 9, 9' is connected to the rim 1 with a mortise-and-tenon joint which can be so fastened after adjustment that it becomes essentially fixed in relation to the rim 1. The arms are therefore fastened to the rim 1 e.g. by means of bolts going through the elongated slots in the arms

9, 9' . The other ends of the two arms engage each other via a non-slip transmission, e.g. a toothing, so that the working device 2 can be moved into different working positions without changing its attitude, thus permitting the machining of objects of different diameters. The elongated form of the slots also provides the advantage that when a shave-type cutter is used, the feed angle, i.e. the cutting depth, can be easily adjusted by varying the setting of the working device, supported by the arms 9, 9' .

In Fig. 3, the dotted broken lines indicate a different position to which the working device 2 has been set by adjusting the position of the arms 9, 9'. In the embodiment in Fig. 4b, the adjusting element 7 consists of a series of different sized ad¬ justment plates 7 ¹ , 7=, 7 ³ ... (in Fig. 4a), by means of which the frame of the working device can be de- tachably fixed to the rim. By changing the adjustment plate, the working device 2 can be moved into different working positions to allow objects of different diameters to be machined.

Fig. 5 illustrates an embodiment of the working device 2 employing a shave-type cutter 3, suited e.g. for the cutting of plastic pipes. The cutter 3 can be so designed that it has a certain cutting depth. The working cutter 3 can be connected to a returning means

10, e.g. a spring, which returns the cutter to its starting position when the rim stops rotating. Fig. 6 presents an embodiment of the working device which uses a roller-type rotary cutter 3.

Figures 7 and 8 illustrate a solution employ-

ing several working devices 2' , 2", 2"' and 2"" mounted on the rim 1 of the machining apparatus. The working devices are symmetrically arranged on the rim so that they counterbalance each other, thus eliminating undesirable vibrations of the rim during rotation. The cutters of the working devices are so arranged that they work the same area of the pipe. The cutter of the first working device 2' is a sharp-toothed wheel 11 and the cutter of the second working device 2" is a shave-type cutter 14.

If the sharp-toothed wheels 11 and 13 are placed on the rim 1 in the manner shown, the result is that the wheels work the object surface before the shave-type cutters, cutting transverse grooves in the working face. Thus, the shave-type cutters working the grooved surface will produce very small shavings that are easy to remove from the vicinity of the apparatus e.g. by means of a suction device.

The rim 1 revolves on bearings consisting of wheels 15 mounted on the frame 16. The wheels are flanged wheels which keep the rim 1 steady in the axial direction as well. The rim is provided with a groove 17 for a transmission belt 19 driven by a motor 18. The power transmission and the bearings of the rim 1 can naturally be implemented in any other known way.

Fig. 9 shows a lateral view of a general ar¬ rangement for the cutting of plastic pipes of a large diameter by using the apparatus 20 of the invention. The equipment comprises a frame 21 supporting the machining apparatus 20 and the holding means 22 and 23 used to keep the pipe in place during cutting.

The invention is not restricted to the em¬ bodiment examples described above, but instead several variations are possible within the scope of the idea of the invention as defined in the following claims.