Cutters – for shaping – Including tool having plural alternatively usable cutting edges
Reexamination Certificate
2002-08-26
2004-11-02
Fridie, Jr., Willmon (Department: 3722)
Cutters, for shaping
Including tool having plural alternatively usable cutting edges
C407S114000
Reexamination Certificate
active
06811360
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cutting plate for a ball race milling cutter and to an appropriate ball race milling cutter per se. In particular, such a cutting plate is provided with an upper and a lower surface that are substantially parallel to one another, wherein circumferential (continuous) edge surfaces connect the upper surface and the lower surface to one another, and wherein cutting edges are configured at least in part along the lines of intersection between the edge surfaces and the upper and/or lower surfaces. The feature that the upper and the lower surface are substantially parallel to one another clearly does not exclude deviation from parallel configuration or contouring with chip-guiding and chip-breaking structures.
The present invention also relates to a corresponding ball race milling cutter that is provided with a shank, a cutting head and a milling cutter axis, wherein at the forward free end of the cutting head there is provided at least one seat for an appropriate cutting plate.
Lastly, the present invention also relates to a method for manufacturing ball races with the aid of ball race milling cutters equipped with cutting plates, wherein active main and auxiliary cutting edges of the cutting plates are engaged respectively.
Corresponding ball race milling cutters and associated cutting plates have been known for a long time in the prior art, and are used in order to manufacture so-called ball races by cutting at a camber angle &agr;, that is to say grooves with a round, but nevertheless generally not exactly circular cross-section. The groove cross-section is instead configured such that the radius of curvature at the base of the groove is smaller than the radius of the balls that will roll along this race. The depth of this groove is also generally less than the radius of the balls, wherein in cross-section, the lateral flanks of the groove have a radius of curvature that is somewhat greater than the radius of the balls rolling along it, so the balls rolling in the ball race substantially touch only the flank areas of the ball race and engage neither with the base of the groove nor with the upper edges of the groove. This makes possible a very exactly defined position for the balls at the same time as low rolling resistance, so by means of such ball races, different machine parts can be connected that have to move easily against one another, even when they are relatively heavy and/or large amounts of force have to be transmitted between these machine parts (and via the balls lying in between them). Ideally, the cross-section of the ball race is substantially elliptical with an eccentricity of 1.01 to 1.1, and a large semi-axis symmetrically dividing the ball race, wherein the small semi-axis is slightly larger than the radius of the balls that will roll in the race, and the eccentricity is matched to the radius of the balls such that the points of contact of the balls on the race, seen from the cross-section of the balls, lie approximately 70° to 90° apart, that is on the flanks of the ball race at approximately 35° to 45° from the base thereof.
FIG. 1
shows by way of an example a cross-section through a so-called pivot pin in the form of a more or less cylindrical bush on the internal surface of which there are several ball races axially or slightly inclined towards the axis, which in cross-section appear approximately the shape of a segment of a circle.
FIG. 2
shows in an enlarged detail view that the cross-section of the corresponding ball race is not circular, but instead elliptical, and is substantially characterised by a radius of curvature at the base of the ball race that is somewhat smaller than the radius of the balls, and by a radius of curvature in the flank area of the groove or respectively the ball race, that is larger than the radius of the balls. In the upper area, the groove width generally exceeds the ball diameter, at least the diameter of the ball at the height of the groove edges.
Corresponding ball races are, as already described, produced in the prior art with special ball race milling cutters that are arranged at a so-called camber angle &agr; to the surface of the work piece, and in the end face area of which at least one specially formed cutting plate is located with which the desired groove shape is milled. The so-called camber angle is the angle between the milling cutter axis and the axis of the ball race or respectively the tangent on the axis in the section of the ball race that is currently being worked. Such a camber angle is typically in the range between 10° and 40°.
The cutting plates that are used in the end face area of the milling cutter generally have a shape that is approximately circular, sometimes slightly flattened in plan view, or more or less oval. They cut both with a main cutting edge arranged on the end face of the milling cutter, that has a directional component both in the axial direction as well as in a plane perpendicular to the milling cutter axis, and an auxiliary cutting edge that has a directional component more strongly parallel to the axis of the milling cutter. When using oval or respectively approximately circular cutting plates, the main and auxiliary cutting edges are obviously rounded and the transition from the main cutting edge to the auxiliary cutting edges is practically continuous without there being a clear differentiation between main and auxiliary cutting edges. Generally, however, this prior art can be characterised in that in the cutting edge section referred to as the “main cutting edge”, the radial component of the cutting edge predominates, whereas the auxiliary cutting edge is defined by a stronger axial component.
The setting of the milling cutter axis in the camber angle, described hereinabove, with respect to the surface of the work piece is implemented in that the base of the groove is cut by a part or respectively a section of the cutting edge of the cutting plate that lies relatively far forward in the axial direction, and is at a shorter distance from the axis of the milling cutter than parts of the auxiliary cutting edge set further back axially. This means that the base of the groove is formed by a cutting edge section rotating on a smaller orbit, and thereby a smaller radius of curvature (if additionally dependent on the camber angle) than the flank sections of the groove or respectively the ball race that are cut by the auxiliary cutting edge areas that are further to the rear axially and further away radially from the axis of the milling cutter, that, because of the inclined adjustment of the milling cutter with respect to the surface of the work piece, cannot however reach the base of the groove.
The result is the at least approximately elliptical cross-sectional shape of the groove shown in principle in FIG.
2
.
A disadvantage of the known cutting plates and ball race milling cutters is nevertheless in that for each ball diameter that necessitates a correspondingly dimensioned ball race, a cutting plate or respectively a cutting plate matched solely to the corresponding ball race has to be used with a milling cutter that has the appropriate diameter. As corresponding ball bearings or respectively ball joints are used and designed with widely differing diameters of balls, that are typically between 10 and 30 mm, a large number of different cutting plates have to be stocked in order to be able to correctly mill the proper ball race for every ball diameter. This means that the cutting plates for each individual ball diameter are used in comparatively small numbers, and nevertheless the manufacturer of such ball races must stock a large number of such cutting plates in order to be able to produce any desired dimension of ball race. In this way both the individual cutting plates and the manufacturing of such ball races are very expensive.
With respect to this prior art, the object of the present invention is to provide a cutting plate and a corresponding ball race milling cutter that make it possible to produce ball races for d
Fridie Jr. Willmon
Sandvik AB
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