BACKGROUND TO THE INVENTION Machines in accordance with the above are used, for example, to bore channels and bearing points in engine blocks and/or cylinder heads in the manufacture of internal combustion engines. In modern engines, the tolerance demands are high, and it is desirable to reduce the numbers rejected because said work pieces are labor-intensive and are expensive to produce.

Machines of this type are used, for example, to bore camshaft bearings in the cylinder heads of automobile diesel engines. The production rate in these situations is relatively high with a cycle time of ca. 1 to 2 minutes and a bore length of ca. 800 to 1000 millimeters.

Existing machines use a fixture which is connected rigidly to the machine frame and is used to fix the work piece. The bore spindle is usually moved by means of feed screws along a guide track which is arranged in the machine frame parallel to the longitudinal axis of the bore spindle. Heat from the machining is generated at the boring bit and is spread via the bore spindle to the guide track.

The guide track can be adjusted and oriented in

relation to the bore spindle when the machine is shut off, i. e. cold. When the machine has then reached its normal working temperature, the bore spindle working in a reciprocating movement along the guide track conveys the heat farther outward in the guide track. This results in an uneven deformation of the machine, which has a negative influence of the quality of the machining. Normal clearances in the guide track and in the bearing of the bore spindle also have a negative influence on the quality of the machining, and the effect of a directional error is amplified by the lever arm created in the case of a long bore spindle.

Given that it is necessary to take these problems into account when determining the machine dimensions, said machine is expensive to manufacture and takes up a large amount of space. It is also difficult to screen such a machine off from electromagnetic disturbance, which can affect the machine's digital control system.

For example, the cabling which runs between the machine support frame and the drive motor of the bore spindle forms an antenna whose radiation characteristics vary depending on the movement of the bore spindle along the guide track.

TECHNICAL PROBLEM The object of the present invention is to make available a machine for boring elongate holes in work pieces, which machine avoids the problems described above.

SOLUTION To this end, the invention is characterized in that the feed device is designed to receive the work piece, and in that the bore spindle is mounted securely in the support frame.

A number of variants of the invention are set out in the attached subclaims.

DESCRIPTION OF THE FIGURES Illustrative embodiments of the invention will now be described in more detail with reference to the attached drawings, in which: Fig. 1 is a perspective view which shows, in schematic representation, a machine configured according to a first illustrative embodiment of the invention, and Fig. 2 is a perspective view showing a machine configured according to a second illustrative embodiment of the invention.

DESCRIPTION OF PREFERRED ILLUSTRATIVE EMBODIMENTS The machine shown in Fig. 1 is used for horizontal boring of elongate holes, for example for boring oil channels in a cylinder head, and comprises a support 10 which bears a first electric motor 11 used for driving a feed screw 12. The thread of the screw engages with a nut element 13 which is connected to a holder 14 for a work piece 15. Together with the screw and the nut element, the holder 14 forms a feed device which rests on, and is guided on, guide track rails 16. The work piece 15 is held securely on the holder 14 by means of coupling members 17 of the quick-coupling type, for example pneumatically controlled. The working pressure to these coupling members is conveyed via supply cables 18.

The support 10 also bears a second electric motor 19 which is connected via a transmission 20 to a bore head which has a pair of bore spindles 21, the free end of which receives a boring bit 22. The longitudinal axis of the bore spindle is parallel to the guide track rails 16. The length of the bore spindle and the feed movement of the holder 14 are adapted to the desired feed depth. A steady rest 23 on the holder 14 is used

as a support bearing for the free end of the bore spindle before boring is started.

By means of the configuration of the machine as described above, heat can be conveyed away from the boring bit without deformation occurring in the machine frame. The fixed position of the bore spindle in the support frame makes it easy to attach lines for boring medium, for example cutting fluid. The screening of the machine from electromagnetic disturbance is also simplified. Because there is less clearance-related leverage effect on the bore spindle, the machine can be dimensioned more simply and at less cost and takes up less space. Machine wear and maintenance can also be reduced.

Fig. 2 shows a second illustrative embodiment of the invention in which the boring is carried out vertically, i. e. the spindle with cutting head is vertically suspended and the work piece is moved vertically. The intrinsic weight affords advantageous freedom from clearance in feeding. In addition, the steady rest 23 is not loaded by the weight in this embodiment of the invention. Moreover, chips from the machining work can fall downward and be washed away.

Since the bearings of the bore spindle can be dimensioned for lesser stresses, two parallel bore spindles can also be placed nearer each other, i. e. with a smaller center-to-center distance than in conventional machines. The reduced clearance makes it possible to bore elongate holes with very high precision.

The invention is not limited to the illustrative embodiments described above, and instead a number of variants are possible within the scope of the attached claims. For example, the machine according to the invention can be used for boring purposes other than those indicated.