Field of the Invention:

This invention concerns improvements relating to machine tools and more particularly relates to a novel machine tool for and a novel method of producing a turned or lathed article.

Background of the Invention:

The lathe is a well developed and understood machine tool for producing a surface of revolution on a workpiece. However, it has several limitations which makes its use complicated and expensive in some situations.

The workpiece or part needs to be held in a chuck which is rotated by the lathe. It is sometimes difficult to align the axis of rotation of the lathe with the desired axis of the part. This is especially true if the part is complex and does not have a convenient stub axle to grip it by. A mounting jug then needs to be made which increases the cost and complexity of the lathe.

Modern Computer Numerically Controlled (CNC) lathes have devices called bar feeds which permit new bar stock to be automatically fed into position. In

this case, a completed part is paired off and a new workpiece is introduced to make another part. If the part is complex such at it is not economic to produce it from a round bar, this automatic process is not possible. Whereas it is possible to design a flexible manufacturing cell featuring a robot to load parts into appropriate holding jigs on a lathe, this is very- expensive.

If the part is very large, it may not be possible to hold it such that it can be spun about the desired axis. In this case the part must currently be fabricated out of two or more components. This may not be desirable for the finished article.

If the part has several turned projections, perhaps along non parallel axes, the set up operation to get the axes into the various alignments can be very time consuming.

Summary of the Invention:

The present invention in its broadest aspect resides in the appreciation that at least some of the above described problems can be overcome or substantially reduced by keeping the article (workpiece) stationary and rotation the machine tool around it. This is a complete departure from the known methods of producing turned articles in which

the workpiece is rotated.

More particularly, according to one aspect of the present invention there is provided a machine tool for producing a turned or lathed article, the machine tool comprising a rotatable cutting head which is movable along its axis of rotation, the cutting head comprising cutting means for cutting the article, the cutting means being movable in a plane transverse to said axis of rotation. Preferably, the cutting head comprises a plurality of spaced apart arms extending parallel to the axis of rotation and the arms may be movable concurrently. Also the cutting may comprise sharpened projections at the ends of the arms. In this way, the tool can fit over and be moved along the workpiece to cut away portions to produce the turned article.

Preferably, the machine tool further comprises means for moving the cutting means in a plane transverse to the axis of rotation. In one embodiment of the invention, the moving means comprise a collapsible frame having two cross-members pivoted at their midpoints and the cutting means are connected to the ends of the cross-members. The frame is folded by a screw driven push rod which is movable along the axis of rotation and is connected to the frame by a radial bearing.

Alternatively, in another embodiment of the invention, the moving means comprises a tapered or reducing diameter retainer which is arranged to reduce the diameter of the cutting means when it is drawn into the retainer. The machine tool further comprises a screw driven push rod which is movable along the axis of rotation for drawing the cutting means into and pushing the same out of the retainer.

The invention also extends to a machine for producing a turned or lathed article, the machine including a machine tool according to the invention and a cutting head motor for rotating the cutting head about its axis. In addition, the invention also extends to a machine for producing a turned or lathed article, which includes a machine tool according to the invention which has a push rod as above entioned, and a push rod motor for driving the push rod along the axis of rotation.

According to another aspect of the present invention there is provided a method of producing a turned or lathed article, said method comprising: providing a cutting head having cutting means for cutting the article; rotating the cutting head about an axis of rotation; and moving the cutting means in a plane transverse to the axis of rotation so as to effect cutting of said article.

The above and further features are set forth with particularity in the appended claims and together with the advantages thereof will become apparent to those skilled in the art from consideration of the following detailed description of exemplary embodiments of the invention given with reference to the accompanying drawings.

Brief Description of the Drawings:

Figure 1 is a schematic, cross sectional view of a machine tool embodying the present invention; and

Figure 2 is a schematic cross sectional view of another machine tool also embodying the present invention.

Detailed Description f the Embodiments: Referring to Figure l of the accompanying drawings, there is shown a tool head 10 of a first embodiment of the present invention for use in a milling style machine. The tool head 10 comprises a holding frame 11 having a spindle portion 12. The tool head is held in a rotatable chuck 13 which is driven by a tool head electric motor 14.

The tool head 10 has two arms 15 mounted on a collapsible 'X' frame 16 (the 'X' frame comprises two cross-members 17 pivotally mounted together at their

midpoints) . The 'X' frame 16 is caused to fold in a closing motion by a screw driven push rod 18. The push rod 18 is connected to the frame 16 by a radial bearing 19 and runs through the hollow shaft of the spindle 12 that rotates the tool head 10. In this way a push rod electric motor 20 and the electric tool head motor 14 do not need to rotate. Parallel grooves 21 in the arms 15 of the tool head 10 mate with complementary ridge formations 22 in the holding frame 11 to promote parallel motion of the arms 15 and to improve stiffness.

The tool head 10 has two cutter tips 23 equidistant from the axis of rotation 24 and being arranged such that the offset from the axis for all tips 23 can be synchronously varied. In this way when the tool head 10 is spun around a workpiece projection

(not shown) , and the offset is reduced until the cutter tips 23 contact the workpiece, once any roughness is machined off, the cutting forces are substantially equal on all cutter tips. This minimises any net forces on the spinning head normal the axis of rotation 24.

Turning now to Figure 2 of the accompanying drawings, there is shown a second embodiment of the present invention. The tool head 10 of the second embodiment is similar to the first and equivalent

features of the tool head and machine have been labelled with equivalent reference numerals. To avoid unnecessary repetition, these equivalent features will not be described further hereinafter. In the second embodiment, the holding frame 11 comprises a tapered or decreasing diameter retainer 25 and the arms 15 have complementary shaped surfaces for engaging the tapered retainer 25. The closing motion of the arms 15 is caused by dragging the same into the tapered retainer 25 using the push rod 18. Additional tracks 26 and complementary formations 27 are provided on the surfaces of arms and tapered retainer to promote parallel motion of the arms and improve stiffness. In both of the above described embodiments the length of overhang of the arms 15 set a commensurate limit to the length of shaft or article that can be turned. The range of motion provided by the tapered retainer or the 'X' frame defines the maximum and minimum diameters that can be turned.

For CNC operations, the tool turning diameter is varied by a computer controlled servo. The tool mechanism then also contains a motor means to rotate it - preferably at variable speeds. In a typical application, several complex parts could be firmly retained in jigged positions on a work

pallet. The CNC machine tool then increments its position from part to part using its established positioning systems.

If the machine tool has a five or more axis capability, then the turning tool can be steered along any axis. It can even be steered along non linear axes to produce a turned part where the axis of revolution is a complex pathway.

Having thus described the present invention by reference to specific embodiments thereof, it is to be appreciated that the described embodiments are exemplary only and are susceptible to modification and variation without departure from the spirit and scope of the invention as determined by the appended claims. In particular, an autochange system could fit extensions or reducers to the movable arms 15 to expand the range of movement of the cutting tips 23 to accommodate various different tasks. In addition, the cutter tips can face outwards rather than inwardly so that the device can be used as a variable diameter boring machine. Furthermore, instead of adjusting the spacing between the arms 25 by employing a push rod 18 with a radial end bearing 19 the adjustment servo could be contained in the rotating part of the housing 11. in this case power to the motor 20 would have to be transmitted by brushes acting on annular tracks or

by inductive coupling between non contacting coils. Similarly control signals could be transmitted optically, inductively or by brushes on annular tracks.