Cutters – for shaping – Gear cutting tool – Hob
Reexamination Certificate
1999-12-23
2001-12-04
Tsai, Henry (Department: 3722)
Cutters, for shaping
Gear cutting tool
Hob
C407S025000, C407S030000, C082S158000
Reexamination Certificate
active
06325573
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an arrangement comprising a bore-type hobbing cutter and a holding arbor.
As far as the receptacle is concerned in a hobbing machine, a distinction is made between a hole type and a shank type. The cutter body, when of a bore-type design, has a centric hole with a longitudinal groove for positive torque transfer. In this case, a key is disposed in a groove of the holding arbor to interact with the longitudinal groove of the cutter hole. It is also known, however, to cause the cutter hole to intersect a transverse groove at its front-end face to obtain positive torque transfer. In the end, it is also known to obtain positive torque transfer via the front-end face.
The shank-type design has both the cutter body and conical or cylindrical shanks integrally formed at the ends of the cutter body. As a rule, a tool of such a sturdy structure features very high concentricity in running. It is unnecessary to pre-align it on the cutter arbor. A disadvantageous feature, however, is the high expenditure, particularly when the cutter is completely made of cemented carbide. Cutters made from hard material are extremely sensitive to shocks and bumps. When the cutter is damaged it frequently needs to be exchanged.
The most widespread type of hobbing cutters is the bore-type design having a longitudinal groove. These are accommodated by a standard-type holding arbor. The bore has ground centering surfaces, e.g. cylindrical surfaces, in the two end regions, each of which extends over approximately one third of the cutter body length. (It is also known to precisely grind them across the entire wall of the bore, but it requires more machining expenditure). The holding arbor has matching cylindrical, ground seating surfaces. Since the cutter body is slid onto the holding arbor minimal looseness is required between components. This will naturally interfere with concentricity in running. After assembly, there is a need to verify concentricity in running on testing collars of the cutter body which are provided for this purpose. If it does not exist below the tolerance limit prescribed it is common for an operator to align the tool and to effect radial relative displacement between the cutter body and holding arbor for a time until the desired concentricity in running is achieved. In any case, however, the concentricity in running of conventional bore-type hobbing cutters is significantly lower than that of a shank-type design.
It is an object of the invention to create an arrangement of a hobbing cutter and a holding arbor which enables concentricity in running which is as high as that of shank-type hobbing cutters, but avoids the disadvantages of this design.
BRIEF SUMMARY OF THE INVENTION
The inventive design provides a sleeve or cage which is disposed between the centering surface of the hobbing cutter and the seating surface of the holding arbor. In an aspect of the invention, two separate cages may be provided each of which is disposed in the region of centering surfaces, or a continuous sleeve-shaped cage which extends through the entire bore of the hobbing cutter. The thickness of the cage is smaller than the radial distance between the centering surface and seating surface. The cage accommodates, in a circumferential direction, at least a number of prechucking members, which are preferably metallic and are in contact with the associated centering surface and seating surface. The contact may be punctiform or line-like, but also circular or elliptical. At this point, the diameter or the distance between the contacting points or contacting lines of prechucking members is slightly larger than the radial distance between the centering and seating surfaces.
The design of the cage must be such as to meet the requirements described, namely to ensure accommodation of prechucking members. It is particularly advantageous to use a sleeve, preferably a metallic one.
When inserting the sleeve-shaped cage in between the holding arbor and hobbing cutter a relatively slight elastic deformation will occur on the prechucking members. Since a number of prechucking members are circumferentially disposed on the cage in a spaced relationship, preferably at equal circumferential spacings, the hobbing cutter will undergo automatic centering on the holding arbor. There is no need to test the cutter body for concentricity in running and, perhaps, to align it in a radial direction subsequently. Hence, the inventive arrangement makes possible a hobbing cutter the characteristics of concentricity are as good as those of a shank-type hobbing cutter, but which avoids the disadvantages thereof. Thus, the hobbing cutter of the inventive arrangement is considerably smaller in weight than a shank-type hobbing cutter. Hence, the hobbing cutter according to the invention is easier to handle. In addition, it is considerably less expensive with regard to material use than shank-type hobbing cutters are.
The prechucking members are preferably formed by spheres or rollers. When rollers are used there is a line-like contact, for example, between the cylindrical surfaces of the hobbing cutter and holding arbor.
Furthermore, the inventive arrangement has the advantage that the ground centering surfaces disposed at the ends of the bore need a relatively small axial extension which is clearly shorter than a third of the hobbing cutter length as it is known for conventional bore-type hobbing cutters. The undercut, which preferably joins the ground centering surface in an inward direction, may be kept considerably longer in the inventive arrangement than is the case for the known design. Accordingly, the manufacture of the inventive hobbing cutter is also easier and requires less expenditure than that of conventional bore-type hobbing cutters.
Alternatively, in lieu of a sleeve-shaped cage having prechucking members, a chucking sleeve may be provided which is hydraulically expandable in a radial direction and, when unchucked, has a thickness which is smaller than the radial distance between the centering and seating surfaces. The chucking sleeve may have a circularly extending toroidal chamber or a plurality of circumferentially disposed, spaced-apart chambers into which a hydraulic medium may be passed under a pressure, which will cause the sleeve to expand inwardly and outwardly in a radial direction. It yields the same centering effect as the described sleeve-shaped cage does which has prechucking members.
It is particularly advantageous in the inventive arrangement to machine the hobbing cutter on an equal-system arbor. After forming the bore and the above-mentioned cylindrical centering surfaces at the ends of the bore the hobbing cutter will be mounted, for further manufacture, on a machining arbor which, in turn, has cylindrical seating surfaces. The hobbing cutter is then centered on the machining arbor by means of the sleeve-shaped cage which was described earlier. All the subsequent machining steps up to the final manufacture of the hobbing cutter may then be carried out on this arbor. The mounting of the hobbing cutter on the machining arbor may be effected in a way similar to that for the holding arbor in the milling machine, i.e. by means of a hydraulic chucking nut which is screwed onto the arbor. Applying a hydraulic pressure to a hydraulic medium will cause a section of the nut to be forced against the hobbing cutter's front-end face directed to the nut, preferably via an intermediate ring, in order to axially hold the hobbing cutter against an abutment surface on the arbor. As mentioned earlier, it is unnecessary to perform a concentricity test.
The fact that the hobbing cutter is manufactured on the machining arbor described also helps decisively improve the milling result. The possibility of an exchange between different hobbing cutters and arbors is ensured while concentricity in running is maintained.
The inventive arrangement permits to internally cool or preheat the hobbing cutter with a view to leveling out stresses and changes to dimensions that result from
Carmincke Wolfgang
Davids Christian
Ebert Andreas
Hinzpeter Jurgen
Kolker Werner
Tsai Henry
Vidas Arrett & Steinkraus P.A.
Wilhelm Fette GmbH
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