Gear cutting – milling – or planing – Milling – Cutter spindle or spindle support
Reexamination Certificate
2001-07-31
2003-09-02
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Milling
Cutter spindle or spindle support
C279S002030, C279S002120, C408S23900A, C409S234000
Reexamination Certificate
active
06612791
ABSTRACT:
The invention deals with the rotationally true clamping of rotating machine elements, in particular in a balancing machine.
Modern material-removing machine tools often use high-speed drills, mills or grinders (with rotational speeds in the range from 10,000 to 20,000 revolutions per minute, sometimes even up to 40,000 revolutions per minute or more), the cutting capacity of which is based not so much on a high cutting force and cut depth but rather on the high rotational speeds. On account of the high centrifugal forces which are generated at such rotational speeds, even a slight unbalance of the tools and their holders may have pronounced negative consequences. Firstly, the spindle bearings in which the drive spindle of the machine tool is mounted are exposed to nonuniform loads and become worn more quickly. Secondly, the cutting result deteriorates, which may become obvious, by way of example, through an increased surface roughness of the cut surface. Where the present text speaks of tool holders, this term is understood as meaning all possible holding means in which the actual milling, drilling or grinding tools can be clamped and which in turn can be coupled to the drive spindle of the machine tool. The term is aimed in particular at commercially available tool holders with standardized steep-taper or hollow steep-taper coupling shanks.
For the above reasons, the tool holders are first balanced on a balancing machine before being used in the machine tool. Conventional measures for balancing are fitting additional weights or introducing weight-reducing bores. To allow a measured inbalance to be unambiguously ascribed to the tool holder, extremely high demands are imposed on the unbalance freedom of the rotating parts of the balancing machine. This is because if the measured unbalance were to emanate at least in part from the balancing machine itself, the balancing measures taken on the basis of the results of the measurement on the tool holder could in the worst possible scenario even increase the unbalance of the tool holder. The clamping of the tool holder in the balancing machine has proven to be a problem area. A clamping device which is provided in a known balancing machine for clamping the tool holder comprises a base body unit which is attached to a machine spindle which is driven about an axis of rotation and a receiving opening which is central with respect to the axis of rotation and into which a coupling shank of the tool holder can be inserted axially from one end. The receiving opening passes all the way through the base body unit in the axial direction. A chuck is arranged in the receiving opening, which chuck engages on the coupling shank of the tool holder and can be actuated by a chuck-actuating unit which is guided on the base body unit in such a manner that it can be displaced in the axial direction relative to the latter. The chuck-actuating unit has double guidance on the base body unit from two pairs of sliding surfaces. To achieve highly accurate guiding, these pairs may be designed as transition fits, but this means that the chuck-actuating unit can only be displaced with very great difficulty with respect to the base body unit. Greater tolerances allow easier adjustment of the chuck-actuating unit. However, it has been found that these tolerances led to true-running faults making their presence felt in the measurement results, which in view of the high demands imposed on the true-running accuracy of the balancing machine, considerably impair the reproducibility of the measurements. This effect is intensified further by the double guidance of the chuck-actuating unit on the base body unit. However, reproducible unbalance measurements are necessary for high-precision fine balancing of the tool holder.
Accordingly, it is an object of the invention to provide a clamping device which is easy to operate, in particular for a balancing machine, with a high level of true-running accuracy.
In achieving this object, the invention is based on a clamping device for clamping a machine element, in particular a tool holder for a drilling, milling or grinding tool or the like, which rotates about an axis of rotation, comprising a base body unit which has a receiving opening which is central with respect to the axis of rotation and into which a coupling shank of the machine element can be fitted axially from one end, a chuck which is arranged in the receiving opening, and a chuck-actuating unit, which is guided on the base body unit in such a manner that it can be displaced in the axial direction relative to the latter, for actuating the chuck.
According to the invention, it is provided that the chuck-actuating unit is axially guided by means of a rolling body arrangement on the base body unit, the rolling bodies of which arrangement roll along rolling surfaces of the base body unit and of the chuck-actuating unit. The rolling body arrangement allows easy yet precise axial guidance of the chuck-actuating unit, in particular if the rolling bodies are fitted with prestress between the base body unit and the chuck-actuating unit. Tolerances which may impair the reproducibility of the measurements only have to be accepted to a significantly lesser extent, if at all, than is the case with the sliding fits of the known solution. Moreover, the guidance of the chuck-actuating unit by rolling bodies is distinguished by a reduced cost.
Although in principle it is conceivable to use rolling bodies designed in other ways, it will be expedient to use balls which are held in a cage inserted between the base body unit and the chuck-actuating unit. Ball cages of this type are commercially available at low cost. In order to keep the weight of the components of the clamping device which move relative to the base body unit low, the cage is expediently made from plastic. A small number of balls are still sufficient to achieve highly accurate guiding if the balls are held individually, offset from one another in the circumferential direction, in each case in one recess in the cage.
A compact structure of the clamping device results from the fact that the rolling body arrangement and the chuck are arranged at least partially inside one another in the axial direction. At the same time, it is in this way possible to use a chuck with a relatively great axial length and with a correspondingly high flexibility of its tongues without the overall space taken up being subject to restrictions from the rolling body arrangement.
The rolling body arrangement may be accommodated radially between a cylindrical inner lateral surface section of the receiving opening and a cylindrical outer lateral surface section of a shank part, which extends axially in the receiving opening, of the chuck-actuating unit. In this case, it is expedient for smooth running if the shank part is formed integrally with a chuck-engagement head, which engages on the chuck, of the chuck-actuating unit.
It is possible to provide for the shank part to extend out of an end of the receiving opening which is remote from the machine element, for, at that location, a force-introducing body, which serves to introduce the actuating force, to adjoin the shank part, and for this force-introducing body to be approximately in the form of a disk.
In a variant of the known solution discussed in the introduction, the chuck is held on the base body unit and is supported, by means of a clamping section, on the outer lateral surface of a cone head, which is substantially enclosed by this unit and tapers away from the machine element, of the chuck-actuating unit. In this arrangement, the chuck engages, by means of a radially projecting holding flange in the region of its end which is remote from the machine element, in an annular recess which has been machined from the receiving opening radially into the base body unit, where it is held with clearance to move.
By contrast, in the clamping device according to the invention, it is preferably provided that the chuck, in the region of its end which is axially remote from the machine element, is mounte
Franz Haimer Maschinenbau KG
Howell Daniel W.
Rothwell Figg Ernst & Manbeck
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