Abstract:
A tool is configured with a centering element and a fastening portion with form-locking elements for axial mounting and fastening onto a drive shaft of a hand-held power tool. The centering element and the form-locking elements are arranged in a first tool part. The form-locking elements are located radially outside the centering element and are configured with a quadrangular cross section that corresponds to a trapezoidal cross section, which is perpendicular to an axis of the drive shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is a Continuation application of U.S. patent application Ser. No. 10/574,463, filed in the US on Apr. 4, 2006 (“Parent Application”), which Parent Application was described in German Patent Application DE 10 2004 050 798.8, filed in Germany on Oct. 19, 2004 “the German Patent Application). The Continuation application derives its basis for priority under 35 USC §119(a)-(d) from the Patent Application and the German Patent Application, the subject matter of both of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention is based on a device for fastening an axially mountable tool to a drive shaft, drivable in oscillating fashion, of a hand-held power tool, as generically defined by the preamble to claim  1 . 
         [0003]    From European Patent Disclosure EP 1 213 107 A1, a device for fastening an axially mountable tool to a drive shaft, drivable in oscillating fashion, of a hand-held power tool, is known. This device includes a centering recess and six form-locking elements, which are embodied as tips in an outline of their centering recess and are therefore part of the centering recess. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention is based on a device having a centering element and at least one form-locking element for fastening an axially mountable tool to a drive shaft, which is drivable in an oscillating manner, of a hand-held power tool in which the centering element is provided for centering the tool relative to the drive shaft, and the form-locking element is provided for defining a rotary position of the tool relative to the drive shaft. 
         [0005]    It is proposed that the form-locking element is located radially outside the centering element. As a result, an advantageous separation of a centering function from a defining function and/or a torque transmission function can be achieved, so that a more-comfortable fastening process is attainable. Because the form-locking element is located radially on the outside, an advantageously long lever for transmitting torque can be achieved, with comparatively little material stress in the region of the form-locking element, without losing precision in a centering operation. 
         [0006]    The term “intended” is to be understood in this respect to mean “designed” and “equipped”. 
         [0007]    In an embodiment of the invention, it is proposed that the centering element has a circular cross section. As a result, it can be attained that after the centering operation, the rotary position is freely selectable and is independent of the centering operation. The centering element can be embodied either as a circular recess or as a bolt with a circular cross section. 
         [0008]    A sturdier and more secure form lock can be attained if the form-locking element is intended for engagement in a recess. However, embodiments of the invention are also conceivable in which the form-locking element is formed by a set of teeth, for instance, and is intended to mesh with a corresponding set of teeth. A more-secure hold of the form-locking element is attainable if the form-locking element has at least one axially extending bearing face. 
         [0009]    If the form-locking element is intended for fastening the tool in at least three rotary positions, then the device can advantageously be suitable for fastening a tool with three possible working positions, in particular a tool with triple symmetry, for instance a triangular grinding plate. 
         [0010]    If the form-locking element is intended for fastening the tool in at least four rotary positions, then the device can advantageously be intended for fastening a tool with four possible working positions, and particularly for fastening a tool with quadruple symmetry or with working positions that differ by 90°. As an example, a circular saw blade can be named. 
         [0011]    A device that can be used universally for many different kinds of tools can be attained if the form-locking element is intended for fastening the tool in at least twelve rotary positions. Especially if the rotary positions are distributed uniformly over an angular range, flexible adjustment with simultaneously more-secure torque transmission is attainable. 
         [0012]    A rotationally symmetrical device is attainable if the angular range amounts to 360°. Especially in the case of a twelve-fold rotational symmetry, a device that can advantageously be used for tools both with triple symmetry and with quadruple symmetry is attainable, which is suitable especially both for fastening a triangular grinding plate and a circular saw blade. 
         [0013]    Torque transmission with little material stress and simultaneously more-precise centering of the tool can be attained if a radius associated with one position of the form-locking element is more than twice as large as a radius of the centering element. If a plurality of form-locking elements is located on a circle, the radius of the circle can be associated with the form-locking elements, and otherwise, the radial spacing of the form-locking element or one edge of it, from an axis of rotation of the drive shaft can be associated with them. 
         [0014]    An economical, safe form-locking element is attainable if the form-locking element is embodied in pin-like form. 
         [0015]    If the device has a plurality of identically shaped form-locking elements, distributed uniformly over a circle around the centering element, then an asymmetrical load on the device upon torque transmission can be avoided. 
         [0016]    Point-wise stress on material can be avoided if the form-locking element has at least one slaving face, oriented substantially in the circumferential direction. The direction of the face is determined by the surface normal. A precise-fitting slaving face, or a bearing face corresponding to the slaving face, can be attained structurally simply if the slaving face is embodied as flat. Comfortable guidance into an engagement rotary position of the form-locking element is attainable if the form-locking element has at least one chamfer for reinforcing a slip-on operation. 
         [0017]    Play-free fastening can be attained and an overload on the device can be avoided if the device includes a spring element for generating a clamping force on the tool. A set-point torque of the device can be made clearer to a user if a blocking force of the spring element is associated with a rated torque of a fastening element, in particular a screw. 
         [0018]    A cost-saving device can be attained if the centering element is embodied as a fastening screw. 
         [0019]    If the spring element is embodied as a cup spring, it can advantageously be capable of being manufactured inexpensively, and the contact-pressure flange can be useful for axially pressing the tool against the drive shaft. 
         [0020]    Sufficiently precise centering with adequate stability is attainable if the diameter of the centering element amounts to between 4 and 8 mm. 
         [0021]    The invention is also based on a tool, having a centering element and a form-locking element for axial mounting and fastening onto a drive shaft, drivable in oscillating fashion, of a hand-held power tool, in which the centering element is intended for centering relative to the drive shaft and the form-locking element is intended for defining a rotary position relative to the drive shaft. 
         [0022]    It is proposed that the form-locking element is located radially outside the centering element. As a result, a tool can be attained that can be fastened in a fastening operation to the drive shaft, which operation includes an operation, independent of the centering operation, for determining the rotary position. 
         [0023]    A secure form-locking connection between the tool and the drive shaft is attainable if at least one corresponding form-locking element of the drive shaft is associated with the form-locking element. 
         [0024]    An especially economical replaceable tool can be attained if the form-locking element is embodied as a recess. However, embodiments of the invention are also conceivable in which the form-locking element is embodied as a raised bulge that engages a recess on the drive shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Further advantages will become apparent from the ensuing description of the drawings. In the drawings, exemplary embodiments of the invention are shown. The drawings, description and claims include numerous characteristics in combination. One skilled in the art will expediently consider these characteristics individually as well and put them together to make useful further combinations. 
           [0026]      FIG. 1  depicts a hand-held power tool with a centering element and a form-locking element for fastening an axially mountable tool; 
           [0027]      FIG. 2  depicts the hand-held power tool of  FIG. 1  in a configuration of a centering operation; 
           [0028]      FIG. 3  depicts a detail of the tool of  FIGS. 1 and 2 ; and 
           [0029]      FIG. 4  depicts a bearing flange of the hand-held power tool of  FIGS. 1 through 3 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0030]      FIG. 1  shows a hand-held power tool  28  with a drive shaft  16  which is drivable in oscillating fashion and is supported, via a ball bearing  30  and a needle bearing  32 , in a housing  34  of the hand-held power tool  28 , half of the housing having been removed in the drawing. The hand-held power tool  28  includes an electric motor, not shown here, which via a motor shaft drives an eccentric disk the inside of which is engaged by an arm  36 , connected to the drive shaft  16  in a manner fixed against relative rotation, so that a rotary motion of the eccentric disk generates an oscillatory motion of the arm  36  and thus of the drive shaft  16 . 
         [0031]    On an end of the drive shaft  16  protruding from the housing  34 , the hand-held power tool  28  has a device for fastening an axially mountable tool  14 , which device includes a plate-like bearing flange  38 , a fastening screw  42 , and a spring element  24  embodied as a cup spring. The device serves to provide a rotationally and axially fixed connection between the tool  14  and the drive shaft  16 , so that the oscillating motion of the drive shaft  16  is converted into an oscillating pivoting motion  40  of the tool  14 . 
         [0032]    The bearing flange  38  has a circular bearing face, which extends perpendicular to the drive shaft  16  and on which a total of twelve pin-like form-locking elements  12  of trapezoidal cross section are distributed uniformly over an angular range that is defined by the entire circumference of the circle. In the middle of the bearing flange  38 , a centering element  10  ( FIG. 2 ) embodied as a blind bore is mounted, with a female thread, not shown here, for receiving the fastening screw  42 . 
         [0033]    The form-locking elements  12  are located radially outside the centering element  10 . The radius  18  of the circle on which the form-locking elements  12  are located exceeds the radius  20  of the centering element  10  by a factor of four. The form-locking elements  12  have lateral slaving faces  22 , which extend radially outward, relative to the axis of rotation of the drive shaft  16 , as well as axially. On an edge facing away from the body of the hand-held power tool  28 , the form-locking elements  12  also have a chamfer  46  for reinforcing a slip-on operation of the tool  14  ( FIG. 4 ). 
         [0034]    The tool  14  is part of a large assortment of possible insert tools, which includes circular saw blades, milling cutters, grinding plates, and cutting tools. In a fastening portion  44 , which is identical in all the tools of the assortment, the tool  14  has twelve form-locking elements  12 ′, located in a circle and embodied as recesses or holes, which correspond to the form-locking elements  12  on the bearing flange  38 . The form-locking elements  12 ′ have a shape that corresponds to the trapezoidal cross section of the form-locking elements  12  ( FIG. 3 ). 
         [0035]    In an installed state of the tool  14 , the form-locking elements  12  reach through the form-locking elements  12 ′ and define a rotary position of the tool  14  relative to the drive shaft  16 . Because of the twelve-fold symmetry of the arrangement of form-locking elements  12 ,  12 ′, the device is suitable for defining twelve different rotary positions of the tool  14  relative to the drive shaft  16 , and these positions differ from each of their adjacent rotary positions by 30° each. Each rotary position corresponds to a different association between the form-locking elements  12  and the form-locking elements  12 ′. 
         [0036]    In the center of the fastening portion  44  and of the circle on which the form-locking elements  12 ′ are located, the tool  14  has a round hole, whose diameter amounts to 6 mm and thus corresponds to the diameter of a shaft of the fastening screw  42 . 
         [0037]    During an installation operation, a user pushes the fastening screw  42 , provided with the spring element  24 , through the round hole in the fastening portion  44  and introduces the fastening screw  42  into the centering element  10 , embodied as a blind bore, in the bearing flange  38 . A head  48  of the fastening screw  42  has a hexagonal recess for receiving a hex wrench. 
         [0038]    By screwing the fastening screw  42  into the centering element  11 , the tool  14  is displaced past the spring element  24 , acting as a contact-pressure flange, in the direction of the bearing flange  38 , until the tool  14  comes into contact with the form-locking elements  12 . By rotating the tool  14 , the user can now determine the rotary position relative to the drive shaft  16 . In the process, by a contact pressure generated by the spring element  24 , the tool  14  is automatically deflected past the chamfers  46  of the form-locking elements  12  into one of the twelve rotary positions in which the tool  14  can be fixed. Centering of the tool  14  is made more precise by the intermeshing of the form-locking elements  12 ,  12 ′, and especially by the contact of a radially inward-pointing side face of the form-locking elements  12  with a radially inner edge of the form-locking elements  12 ′. 
         [0039]    Once the form-locking elements  12  have entered into engagement with the form-locking elements  12 ′, the user tightens the fastening screw  42  further, until the tool  14  is pressed by the spring element  24  against the bearing face of the bearing flange  38 . The spring element  24  becomes fully compressed once a rated torque of the fastening screw  42  is attained, which is perceptible to the user from a sudden increase in a torque required to turn the fastening screw  42 . The spring element  24  then generates a clamping force, dictated essentially by the blocking force, with which clamping force the tool  14  is held without play on the bearing face of the bearing flange  38 .