To eliminate these drawbacks it is suitable to use a known bushing which has not previously been used for tool holders in turrets.

The known bushing is described in the following.

The known holder is intended to form part of a processing machine and constitute the holder for a machining tool such as a lathe shaft. The holder is secured in the machine by a tool attachment which may either be permanent or be located on a unit containing several tool holders in order to enable several machining operations to be carried out one after the other. Frequently the machining tool must be rather long so that machining can be performed in the hollow interior of a work piece. With long machining tools there is a considerable risk of the tool being subjected to vibration, thus resulting in a poorer quality of ^' machining. Several attempts have been made to reduce the occurrence of vibration. The tool shaft has, for instance, been arranged in a cradle with several screw joints pressing the shaft against the cradle. The vibration was not reduced as desired and wear occurred at the mouth of the holder, giving rise to further vibration. The problem of vibration is troublesome as is evident, for instance, from Sandvik Coromant's publication entitled 'Turning with dampened lathe shafts" HV-5300.008-SWE.

One method of reducing the undesired vibrations in the case of long machining tools is to replace mechanical attachment means by a hydraulic retention arrangement. This is achieved by providing a tool holder with an aperture to receive the shaft of the machining tool. Inside the wall of the aperture is a tubular space which can be filled with a medium such as oil or fat. If this medium is subject to pressure, the walls of the aperture will be forced inwards, thereby clamping the shaft of the machining tool extremely firmly. The force achieved in this wav exceeds anv force which can be achieved bv mechanical

SUBSTITUTE SHEET

means. Inner sleeves or bushings having the same outer diameter as the inner diameter of the aperture, but with different inner diameters can be inserted into the aperture, thereby enabling the tool holder to be used for machine tools of different thicknesses.

A suitable embodiment is a bushing provided with a through-hole and a tubular part. An annular space of the type described above is arranged in the bushing and inside the wall of the aperture. The sleeve is inserted into the holder aperture and medium in the annular space is thus subjected to pressure so that the tool inserted is firmly clamped, as well as the outer wall of the sleeve being firmly clamped against the wall of the aperture.

The bushing described is usually provided with a peripheral ring or flange which is located at the outer end of the bushing and designed to be located outside the holder aperture. The flange includes means to influence the medium.

Problems arise in cooling the machining part of the machining tool. These are solved by arranging one or more nozzles for coolant within the area normally covered by a flange and located in the unit containing the holder aperture. The flange is so designed that parts thereof located opposite a nozzle have been removed. Suitably a sector-shaped part of the flange is removed. The remaining part preferably encompasses an angle of up to 300°.

The known design will be described in more detail with reference to the six figures of the accompanying drawings and the design according to the invention with reference to the fourth sheet, in which

Figure 1 shows the end view of a bushing intended for insertion into the aperture of a tool holder,

Figure 2 shows the bushing seen from the side,

Figure 3 shows the bushing during insertion into a tool holder,

Figure 4 shows a tool holder together with a machining tool in operation, Figure 5 shows the bushing according to the invention, and

Figure 6 shows the latter bushing together with a tool holder.

Figures 1 and. 2 show a sleeve or bushing 1 with tubular part 2 and an annular end portion 3. Inside the sleeve is a space 4 which communicates with a conduit 5 for the supply of medium. The conduit communicates with a means 6 for regulating the pressure

of the medium inside the space 4. The pressure is regulated by a screw which can be tightened or loosened. The inner sleeve or bushing shown in Figures 1 and 2 is intended to be inserted in a tool holder 7 by way of the through-hole 8 in the holder 7. The tool holder is secured to a tool attachment 9 which may either be permanently secured and immovable or may be mounted on a movable member provided with several machining tools. In Figure 4 the inner sleeve or bushing is fully inserted into the tool holder 7. A lathe shaft 10 is also inserted into the aperture in the inner sleeve or bushing. The means 6 is now actuated, thereby subjecting the lathe shaft 10 to an inwardly directed pressure which may be in the order of 2000 bar. At the same time as the shaft is subject to an inwardly directed pressure, the outer wall of the space 4 is also subjected to an outwardly directed pressure. A high clamping force is thus obtained in the tool holder itself. The front end of the shaft 10 is provided with a machining tool for machining a work piece 11.

Another way of firmly clamping a machining tool is for each machining tool to be provided with a sleeve 2 having a peripheral space 4. Each tool may be provided with such a sleeve which is permanently built in. After insertion into the aperture 8 the medium in the space 4 of the built-in sleeve in the tool is subjected to pressure and the tool is thus firmly clamped in the tool holder 7.

Figures 5 and 6 show a bushing 2 and 12 having a flange 12 in sector form. Below the flange 12 shown in Figure 6, in the front transverse wall of the tool holder 7, is/are one or more nozzles in the area which would have been covered by removed flange parts. The nozzles communicate with a pressure medium source and can be directed towards the tip of the lather shaft 10.

The nozzles mentioned above may also be placed on the front side of the flange 3 or 12. Sealing O-rings are arranged at the inner and outer edges on the rear of the flange, to form a peripheral channel for coolant The nozzles at the front of the flange are connected to this peripheral channel.

The arrangement 6 may be directed either radially or tangentially in Figure 1 and also in the other figures.

The Italian company, Officine E. Biglia & C.S.p.A in Italy, has issued a prospectus designated S 89/3. The first page of this prospectus shows a turret with a number of tool attachments. The idea is that before tools are inserted into the tool attachments, the hollow in each tool holder shall be provided with a bushing of the type shown in Figures 1 and 2 or in Figures 5 and 6. These bushings may also cooperate with insert sleeves or various inner diameters. If such a sieeve is placed in the aperture of the tool holder attached to the turret, a tool inserted therein will be retained with considerable force along the entire inner surface of the bushing. Furthermore, the outer envelope surface of the bushing will retain the bushing firmly in the aperture of the tool holder.

The advantage of using the described bushing in the tool holders for a turret is that the vibration of the tool inserted will be greatly reduced and a considerable projection can be tolerated without vibrations occurring. The use of the bushing described also means that the number of tool holders can be greatly reduced. The use of a bushing of the type described above facilitates the adjustment of a tool and also enables first-class tool centering. Tools can also be exchanged considerably more quickly when a hydraulic bushing is used.