Abstract:
A tool holder for a tool drive with an outer and an inner concentric drive shaft. A first adapter is detachably held by a conventional clamping system in a receptacle of the outside drive shaft. A second adapter is concentrically mounted in the first tool receptacle of the first adapter so as to rotate with respect to the first adapter. The second adapter has a tool receptacle which can be inclined by a pivoting element. Thus, a tool can be eccentrically inserted and concentrically driven. This makes possible certain machining modes, for example the machining of a hollow shaft, since inner threads can now be turned rather than cut.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tool holder for a tool drive device. 
     2. Description of Prior Art 
     Interior threads, for example, have been produced by drilling and subsequent cutting, or respectively turning, of an interior thread which requires two work steps in succession. The cut threads are machine-cut threads. With the production of exterior threads it is possible to achieve a faster production speed, for example if the thread is generated by milling. Larger threads and exterior threads are produced by turning or milling on three-axis machines in three operations, and often have unacceptable tolerances in the geometry of roundness. 
     SUMMARY OF THE INVENTION 
     This invention has one object of creating a tool holder for clamping and operating a milling tool or a thread rolling die so that an inner thread can also be milled or rolled. In this case it should be possible to avoid unacceptable geometry tolerances. 
     This object is attained by this invention as described in the specification and outlined in the claims. 
     According to one advantage of this invention, it is possible with the tool holder of this invention to mill interior blind bores, also called pocket hole bores, even into a hollow shaft, for example. This provides completely new constructions, since a blind bore can have a larger diameter in the back in an area of its closed end than in an area which is open toward the outside. 
     A further advantage of this invention is that the clamped tool can be displaced and adjusted during the operation. 
     A tool holder with two concentric shafts is known from German Patent Reference DE-A-25 16 775. A tool receptacle for a thread milling cutter is pivotably arranged on an arm which is pivoted out by a worm gear by a defined amount. The tool, such as a thread milling cutter, is rotated about its own axis in the tool receptacle via this gear. The entire tool holder is simultaneously rotated around its axis. Thus the milling cutter actually describes a circular path in the course of the milling work which, with the simultaneous coordinated feeding, allows milling of a thread. The two concentric shafts in the gear are connected with each other by a gear with a fixed gear ratio. The tool holder is driven by a common driveshaft of a tool driving device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A tool holder in accordance with preferred embodiments of this invention will be described in connection with the drawings wherein: 
     FIG. 1 is a longitudinal cross section of a tool holder, namely in accordance with the prior art; 
     FIG. 2 is a sectional view of the tool holder shown in FIG. 1, taken along line A—A, as shown in FIG. 1; 
     FIG. 3 is a sectional view of the tool holder in another deflection direction; 
     FIG. 4 is a cross section showing a possible pocket hole bore; 
     FIG. 5 is a sectional view of a further embodiment of the tool holder, with increased functional possibilities; and 
     FIG. 6 is a plan view of the tool holder shown in FIG. 5, with a section taken along line A—A, as shown in FIG.  5 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The basis for the tool holder  1  of this invention is clearly shown in FIG. 1, namely a suitable drive device for a machine tool. The drive device comprises an exterior, hollow driveshaft  2  and an interior driveshaft  4 , which is concentrically arranged in the exterior driveshaft  2 . The exterior driveshaft  2  has, in a customary manner, a receiver for a first adapter. The interior driveshaft  4  is concentrically conducted through the hollow exterior driveshaft  2 . The interior drive shaft  4  can be operated synchronously or a synchronously to the exterior driveshaft  2  with respect to its number of revolutions. The interior driveshaft  4  can also be a hollow shaft. In that case, a hollow space of the interior driveshaft  4  can be used as a supply line for coolant, lubricant and/or compressed air. 
     Electric motors with concentric shafts are suitable as the driving means, thus the driveshaft of a first electric motor is concentrically passed through a hollow driveshaft of a second electric motor. Such motors are also known by the term cascade motors. Similar drive devices are also known in the form of a pure gear with two concentric driveshafts. 
     Examples of drives with two concentric driveshafts are, for example, a dual-shaft drive, described in the journal  Schweizer Maschinenmarkl  No. 20/1995, pages 94, 95 (Ellen-Christine Reiff). Another version of such a drive is represented by the coupling of two electric motors seated one behind the other. This is described in Swiss Patent Reference CH 682891 (Garu AG). Both have an exterior driveshaft and an interior driveshaft, which can be driven dependently or independently of each other. They can also be coupled with each other by means of a gear. 
     A tool holder  1  in accordance with this invention has a first adapter  10 , which has a first concentric tool receptacle  3 . The first adapter  10  is releasably held by means of a clamping system  15  with a clamping element  16  in a tool receptacle  3  of the exterior driveshaft  2 . A second adapter  20  is concentrically located inside the first tool receptacle  3  of the first adapter  10  and is rotatably seated in relation to the latter. The second adapter  20  contains a second tool receptacle  25 , which is seated, deflectable about a pivot shaft  31  seated eccentrically and parallel with the concentric driveshafts  2 ,  4 , on the first adapter  10  by means of a pivot element  30 . In this case the second adapter  20  is in releasable connection with the interior concentric driveshaft  4 , which passes through the clamping element  16 . Here, a connection is suitable, for example by means of an Oldham coupling, or also simply by means of an interior hexagon on the second adapter  20  for engagement with an exterior hexagon  5  on the interior concentric shaft  4 . 
     The second tool receptacle  25  by means of a gear, comprises gear wheels  22 ,  23 ,  34  and the adapter  20 , which is designed as a radial gear wheel  21  on the exterior. A second gear wheel  22  is fixedly connected with a third gear wheel  23  and with the third ear wheel  23  is eccentrically seated on a rotary shaft on the first adapter  10 , and is driven by the gear wheel  21 , wherein the third gear wheel  23  in turn drives a fourth gear wheel  34 . The fourth gear wheel  34  is fixedly connected with the second tool receptacle  25 . The rotary shaft of the second and third gear wheels  22 ,  23  simultaneously form a pivot shaft  31  for the pivot element  30 . The pivot element  30  in turn provides the guide and holder for the second tool receptacle  25 . Therefore the pivot shaft  31  is parallel with and at a distance from the two concentric shafts  2 ,  4 . 
     The second tool receptacle  25  can therefore be driven by the inner concentric shaft  4 . The drive is performed via the second adapter  20  by means of the gears  21 ,  22 ,  23 ,  34 . The gear comprises a toothed rim on the second adapter  20 , which in this way forms a first gear wheel  21  that engages with a second gear wheel  22 . The second gear wheel  22  is fixedly connected with a third gear wheel  23  on the same shaft. The third gear wheel  23  in turn is in engagement with a fourth gear wheel  34 , which is fixedly connected with the second tool receptacle  25 . It is apparent that, in place of this gear with the different gear wheels, the force transfer can take place by other means, for example a toothed belt. In any case, to this extent the second tool receptacle  25  can be driven by the interior driveshaft  4  independently of the state of deflection. 
     In order to perform and to limit the position of t he pivot element  30 , means for deflection are provided. In the embodiment shown in FIG. 2, the pivot element  30  has stops  35  on both sides in the area located opposite the pivot shaft  31 . Displacement elements  24  are arranged on and in the housing of the first cylindrical body  11  of the first adapter in such a way that with their ends they cooperate with the stops  35  and in this way define and limit the deflection of the pivot element  30  and arrest the pivot element  30  in the desired position. These displacement elements  24  can usually comprise screws with threads. Alternatively a threaded bolt is used, which at least partially projects through the pivot element. 
     An embodiment with a worm drive for deflecting the pivot element  30  is shown in FIG. 3. A controllable micro motor  38  or step motor can be installed in the first adapter  10 . In this case the micro motor  38  or step motor drives a helical shaft  36 , which engages radially on the outside of the pivot element with corresponding teeth  37  on the pivot element. This embodiment makes possible a controlled pivoting without interruption during the processing of a workpiece. The required electrical supply lines can be passed through the hollow shaft, for example, and transmitted by means of slip rings. Thus, the deflection is controllable and adjustable even during operation. 
     An example for a millable pocket hole bore is shown in FIG.  4 . It can be clearly seen that, following the penetration of a smaller diameter through the surface, the pocket hole bore can be downwardly widened. In the process it is possible, depending on the milling head used, to produce approximately any arbitrary profile. The only limitation here results from the diameter and the shape of the milling head. 
     Another function, or one expanded in the possibilities of its functioning, is shown in longitudinal section in FIG. 5, and in FIG. 6 in a plan view in section along line A—A, as shown in FIG.  5 . The second tool receptacle  25 , together with the first tool receptacle, is also driven via the first adapter  10  by the exterior concentric shaft  2 . Thus, a tool clamped into the second tool receptacle  25  rotates at the speed of the first adapter  10 . Normally the drive of the second adapter  20  rotates synchronously. This embodiment has no displacement elements  24  for deflecting the pivot element  20  and therefore for setting the eccentricity of the second tool receptacle  25 . This now takes place via the gear wheels  21  to  23 ,  34 . As long as the exterior concentric drive  2  and the interior concentric drive  4  rotate synchronously, for example at the same rotary speed in the same direction, the deflection state remains constant. If now the rotary speed of the inner concentric drive  4  is briefly, slightly reduced or increased, the pivot element  30  is deflected by means of the gear, since the difference in the rotary speeds, such as the relative movement of the two drives with respect to each other, drives this gear. Therefore the means for deflecting the pivot element  30  include the second adapter  20  and the gear itself, comprising the gear wheels  21 ,  22 ,  23 ,  34 , and no further elements are thus needed. It is thus possible to adjust the eccentricity of the second tool receptacle in a controlled manner during the processing of a workpiece. This can be very easily achieved with one of the cascade motors mentioned, since their driveshafts can be individually and independently controlled. It is apparent that the housing  11  of the first adapter is not drawn forward over the pivot element  30 . It is thus possible for the pivot element  30  to rotate by 360° around the pivot shaft  31  in the directions B to B′. For example, it then takes up the represented positions  30 ,  30 ′,  30 ″,  30 ′″. This rotating movement can take place during the actual processing of a workpiece, such as during operation, simultaneously and continuously, as described above.