Abstract:
An adapter for operating a keyhole saw ( 10 ) on a driving machine includes a driving section ( 17; 117 ) for absorbing torque and a threaded section ( 18; 118 ) screwed into a threaded hole ( 20 ) in the keyhole saw ( 10 ). A driving segment ( 16; 116 ) is offset radially relative to the adapter axis and is inserted in a form-fit manner into a receiving hole ( 21 ) present in the keyhole saw ( 10 ). The driving segment ( 16; 116 ) is located in an axially extending manner on the end of a driving element ( 12; 112 ) which includes the driving element section ( 17; 117 ). The threaded section ( 17; 117 ) is formed on a threaded mandrel ( 13; 113 ) which is situated in the driving element ( 12; 112 ) and is non-detachably connected thereto. The threaded mandrel ( 13; 113 ) is held in the driving element ( 12; 112 ) in a rotatable manner to be axially displaceable to a limited extent.

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2008/053315, filed on Mar. 19, 2008 and DE 10 2007 022 186.1, filed on May 11, 2007. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to an adapter for operating a keyhole saw on a driving machine, in particular an electric hand-held drill. 
     A known part of an adapter which forms a “power change system” for receiving a keyhole saw (EP 1 193 014 A1 and DE 601 04 177 T2) has the shape of a hollow hexagonal prism which is provided, at one end, with a threaded section around its circumference, and, close to the other end, it is provided with a circumferential, concave detent groove. The threaded section is screwed into a central threaded hole of the keyhole saw, and the adapter—having the keyhole saw attached thereto—is slid via its hexagonal prism into a drive sleeve having an inner, hexagonal sleeve wall until a detent ball which is held in a radial bore in the sleeve wall drops into the detent groove and holds the adapter in a non-displaceable manner. A sliding sleeve which is displaceable against the restoring force of a compression spring is situated on the drive sleeve for locking and unlocking the adapter. In the locking position, the sliding sleeve closes the radial bore to the outside, thereby blocking the detent ball which has dropped into the detent groove of the adapter and preventing it from being displaced in the radial direction. In the unlocking position, which the sliding sleeve assumes after following a displacement path against the restoring force of the compression spring, the radial bore is congruent with a recess in the inner wall of the sliding sleeve, thereby allowing the detent ball to escape radially outwardly when one of the groove flanks of the detent groove in the adapter strikes the detent ball when the adapter is pulled out of the drive sleeve, or when the adapter is slid into the drive sleeve. The drive sleeve includes a hexagonal receiving shank which is placed in the chuck of an electric hand-held power tool. When drilling is performed using the keyhole saw, a “pilot bit” is typically used to guide the keyhole saw in an exact manner. The pilot bit includes a hexagonal shank and a circumferential detent groove in the hexagonal shank, and it is held in a bit-connecting piece in a non-rotatable manner via the hexagonal shank and via a detent ball which drops into the detent groove in the hexagonal shank of the pilot bit, the detent ball being held in an axially non-displaceable manner in the bit-connecting piece in a radial bore. The bit-connecting piece is accommodated in the adapter and extends via a hexagonal segment part into the similarly formed hollow interior of the shank of the drive sleeve. 
     Given large diameters of the keyhole saw, to prevent the thread from stripping when high torques are transferred, two diametrically opposed driving holes are provided in the keyhole saw, and two axially extending driving pegs which extend into the driving holes are situated on the end face—which faces the keyhole saw—of the drive sleeve. The transfer of torque from the electric hand-held power tool via the drive sleeve to the keyhole saw therefore takes place via the driving pegs and the driving holes, and the load is relieved from the threaded connection between the keyhole saw and the adapter. The connection between the keyhole saw and the electric hand-held power tool is established by screwing the adapter via its threaded section tightly into the threaded hole of the keyhole saw, and then inserting the adapter into the drive sleeve until the driving pegs strike the keyhole saw. After the driving pegs are aligned with the driving holes, the adapter is slid completely into the drive sleeve, and the driving pegs enter the driving holes; the sliding sleeve must be pushed back against the force of the restoring spring until the detent groove of the adapter moves under the detent ball, then the detent ball drops into the detent groove. After the sliding sleeve is released, the restoring spring forces the sliding sleeve back, and the adapter is locked in place in the drive sleeve in an axially non-displaceable manner. After the pilot bit is inserted, the drive sleeve is inserted via its hexagonal shank into the chuck of the electric hand-held drill. 
     In the case of a known adapter, which is of a “standard design” and may be inserted directly into the chuck of an electric hand-held power tool, the driving pegs and threaded section are also situated on two separate components which are placed on the keyhole saw individually, while being joined together, and are then detachably connected to one another. The hollow component which includes the threaded section, into which the pilot bit is also inserted, includes a hexagonal clamping shank which is inserted into the chuck of the electric hand-held power tool, while the component on which the driving pegs are mounted is attached via a radial screw to the threaded section and the component on which the clamping shank is mounted. 
     SUMMARY OF THE INVENTION 
     The adapter according to the present invention for receiving a keyhole saw having the features mentioned in claim  1  has the advantage that the adapter is a single piece, and it is possible to perform these two procedures in one working step: via rotation, align the driving pegs which are located on the adapter with the driving holes which are present in the keyhole saw after the threaded mandrel is screwed into the threaded hole, then insert the driving pegs into the driving holes as required, using a linear motion; a play-free connection is then established between the keyhole saw and the adapter. In contrast to the known adapters, in the case of which the threaded section and the driving pegs are distributed on components which are separable from one another, are installed separately with the keyhole saw and must then be connected to one another, in this case, the threaded section and the driving pegs are combined to form one assembly and are not separable from one another, thereby ensuring that none of the components may become lost. 
     When the driving section is designed accordingly, the adapter according to the present invention may be clamped directly in the chuck of an electric hand-held power tool, and it may be clamped directly in the chuck of an electric hand-held power tool using the known, above-described drive sleeve of the “power change system”. 
     Via the measures mentioned in the further claims, advantageous developments and improvements of the adapter described in claim  1  are made possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail in the description that follows, with reference to embodiments depicted in the drawings. 
         FIG. 1  shows a side view of a keyhole saw and an adapter for receiving the keyhole saw, 
         FIG. 2  shows an exploded view of the adapter in  FIG. 1 , 
         FIG. 3  shows a longitudinal sectional view of a coupling part of a “power change system” with the adapter shown in  FIGS. 1 and 2  installed, 
         FIG. 4  shows a longitudinal sectional view of an adapter according to a second embodiment, 
         FIG. 5  shows a perspective view of the adapter in the direction of arrow V in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Adapter  11  for receiving a keyhole saw  10 , which is shown in an exploded view and a side view in  FIGS. 1 and 2 , is designed to be part of a “power change system” which may be operated in various configurations using an electric hand-held power tool, while adapter  111  shown in  FIGS. 4 and 5  is designed to be inserted into the chuck of an electric hand-held power tool. 
     Adapters  11  and  111  both include a driving element  12  and  112  and a hollow cylindrical threaded mandrel  13  and  113  which is situated in driving element  12  and  112  in a rotatable and axially displaceable manner. Driving element  12  and  112  includes a driving element body  14  and  114 , and a driving flange  15  and  115  which extends thereon as a single piece, the flange surface—that faces away from driving element body  14  and  114 —of which forms a mating surface for keyhole saw  10 . Two driving pegs  16  and  116  are situated diametrically to the driving axis on driving flange  15  and  115 , and they extend past the exposed flange surface—which forms the mating surface—parallel to the driving axis. Driving pegs  16  and  116  are designed as single pieces with driving flange  15  and  115 , as shown in the top part of  FIGS. 3 and 4 , or they are inserted as separate components into related axial bores  19  and  119 , and are pressed or staked therein, as illustrated in the bottom part of  FIGS. 3 and 4 . Driving element body  14  and  114  includes a driving section  17  and  117  via which driving element  12  and  112  absorbs a torque which is derived from the electric hand-held power tool. 
     Threaded mandrel  13  and  113 , which is rotatably situated in driving element  12  and  112 , extends on the flange side of driving element  12  and  112  out of driving element  12  and  112 , and it is provided in the end region with a threaded section  18  and  118  which is screwed into a central threaded hole  20  present in keyhole saw  10 . Two diametrically opposed receiving holes  21 —into which driving pegs  16  and  116  of driving element  12  and  112  may enter—are provided in keyhole saw  10  at the same radial distance from one another that exists between driving pegs  16  and driving element body axis  14 . The displacement path of threaded mandrel  13  and  113  is limited by two axially interspaced stops  22  and  122  on threaded mandrel  13  and  113 , and by two counter-stops  23  and  123 —which interact with stops  22  and  122 —on driving element  12  and  112 . Stops  22  and  122 , and counter-stops  23  and  123  are situated such that the displacement path of threaded mandrel  13  and  113  in driving element  14  and  114  is designed to be so great that the end—on which threaded section  18  and  118  is provided—of threaded mandrel  13  and  113  may be pulled back behind the exposed front ends of driving pegs  16  and  116 , so that driving pegs  16  and  116  may be inserted into receiving holes  21  in keyhole saw  10  before threaded section  18  and  118  is screwed into threaded hole  20  of keyhole saw  10 . A central recess  50  and  150  which leads into the flange surface which is used as the mating surface for keyhole saw  10  is provided in driving flange  15  and  115 . Threaded mandrel  13  and  113  includes, on the end of its threaded section  18  and  118 , a circumferential radial collar  51  and  151  which extends into recess  50  and  150 . Radial collar  51  and  151  forms stop  22  and  122 , and the base of recess  50  and  150  forms counter-stop  23  and  123  which interacts with stop  22  and  122  in order to limit the displacement path of threaded mandrel  13  and  113  in driving element  12  and  112 . 
     In the case of adapter  11  depicted in  FIGS. 1 through 3 , driving section  17  is designed as an external hexagon  24  for insertion, in a form-fit manner, into a coupling piece  25 —which is also referred to as a base mechanism—of a power change system. Coupling part  25  is known, and it is described in detail in EP 1 193 014 A1 which is documented above, and will therefore be described only briefly below. 
     Coupling part  25  includes a drive sleeve  26  which includes a hexagonal shank  27  for insertion into the chuck of an electric hand-held power tool, and a sliding sleeve  28  which may be displaced on drive sleeve  26  against the force of a compression spring  29 . Coupling part  25  also includes a bit-connecting piece  30  which is inserted in adapter  11  and extends via a hexagonal shank  31  into a similarly designed hexagonal hollow cavity in hexagonal shank  27  of drive sleeve  26 . Bit-connecting piece  30  includes a central recess  32 , the interior wall of which has a hexagonal design, and a radially displaceable detent ball  33 . A pilot bit  34  for guiding keyhole saw  10  using a hexagonal shank  35  is inserted into bit-connecting piece  30 , and it is locked in an axially non-displaceable manner via a detent ball  33  which drops into detent groove  36  in hexagonal shank  35 . 
     The inner wall of drive sleeve  26  is also hexagonal in design; adapter  11  with outer hexagon  24  on driving element  12  is therefore held in drive sleeve  26  in a form-fit manner in the direction of rotation. In order to hold adapter  11  in an axially non-displaceable manner, a detent ball  38  is held in a radially displaceable manner in a radial bore  37  of drive sleeve  26 , detent ball  38  extending radially outwardly from inner wall of drive sleeve  38  and being secured against falling out of radial bore  37  by sliding sleeve  28 . A recess  39  which extends to the end of sliding sleeve  28  is formed in the inner wall of sliding sleeve  28 . A radial flange  40  which is formed on drive sleeve  26  extends into recess  39 . A compression spring  29  is situated in recess  39 , and bears against radial flange  40  and against a ring  41  which is inserted on the end side in recess  39  and is attached to sliding sleeve  28 . When sliding sleeve  28  is slid to the left as shown in  FIG. 3 , and compression spring  29  is compressed, a part of recess  39  extends over detent ball  38  so that detent ball  38  may move radially outwardly into recess  39 , thereby enabling it to move behind the inner wall of drive sleeve  26 . 
     As shown in  FIGS. 1 through 3 , threaded mandrel  13  which is accommodated in driving element  12  extends via an end section  42 —which faces away from threaded section  18 —beyond driving element body  14 . A holding ring  43  is attached, e.g. via pressing or shrink-fitting, on end section  42 , and a spring element  44  designed as a snap ring having an axially-acting spring force is installed, spring element  44  bearing against the end surface of driving element body  14  and against holding ring  43 . Holding ring  43  includes, on its free end, an annular section  45  which is knurled, and, on its end facing driving element body  14 , it includes a hexagonal annular section  46  which is matched to outer hexagon  24  of driving element body  14 . A circumferential, concave detent groove  47  is situated between annular sections  45 ,  46 , and is used, in combination with detent ball  38  of drive sleeve  26  of coupling part  25 , to lock adapter  11  in coupling part  25 . Two radial stops  48  ( FIG. 2 ) which extend axially outwardly are diametrically opposed on the end surface—which faces driving element body  14 —of holding ring  43 , radial stops  48  interacting with two counter-stops  49 —which are situated on the end surface of driving element body  14 —in such a manner that radial stops  48  and counter-stops  49  engage in one another—at the end of the procedure to screw threaded section  18  into central threaded hole  20  of keyhole saw  10 —when the hexagon on annular section  46  of holding ring  43  becomes aligned with outer hexagon  24  of driving element body  14 . Spring element  44  ensures that this orientation of holding ring  43  and driving element body  14  is retained during assembly. 
     In the embodiment shown in  FIGS. 1 through 3 , the other stop  22  which is used to limit the displacement path of threaded mandrel  13 , is located on threaded mandrel  13 , and prevents threaded mandrel  13  from falling out of driving element  12 , is formed by holding ring  43  and the other counter-stop  23  of driving element body  14 , which interacts with stop  22 . 
     To assemble keyhole saw  10  and adapter  11 , complete adapter  11 —as shown, assembled, in FIG.  1 —is placed on keyhole saw  10  in a manner such that driving pegs  16  enter receiving holes  21  in keyhole saw  10 . Threaded section  18  of threaded mandrel  13  is then screwed into threaded hole  20  of keyhole saw  10 ; to do this, threaded mandrel  13  is rotated manually using knurled annular section  45 . Spring element  44  becomes increasingly loaded as threaded section  18  is screwed in further. When the end of the screw-in procedure has been reached, radial stops  48  on holding ring  43  bear against counter-stops  49  on driving element body  14 , and hexagonal annular section  46  of holding ring  43  is simultaneously aligned with outer hexagon  24  of driving element body  14 . Bit-connecting piece  30  with pilot bit  34  inserted is now introduced into threaded mandrel  13 , and adapter  11  is slid into drive sleeve  26 . Sliding sleeve  28  is thereby displaced manually to the left—as shown in FIG.  3 —until recess  32  lies over detent ball  33 . Entire adapter  11  is slid inward until detent ball  33  drops into detent groove  47  in holding ring  43 . If sliding sleeve  28  is now released, it is returned via the action of compression spring  29  to its locking position shown in  FIG. 3 , in which detent ball  33  extends into detent groove  47  in a radially non-displaceable manner and locks adapter  11  in drive sleeve  26  in an axially non-displaceable manner. 
     In the case of adapter  111  which is shown in  FIGS. 4 and 5  and is clamped directly in the chuck of an electric hand-held power tool, driving element section  117  on driving element body  114  of driving element  112  is formed by a stub chuck  152  which extends as a single piece on the end—which faces away from driving element flange  115 —of driving element body  114 . Driving element body  114  includes a radially continuous recess  153 , through which hollow threaded mandrel  113  passes. A manually grippable rotation aid in the form of a knurled wheel  154  is attached to threaded mandrel  113  in the region of recess  153 . Via knurled wheel  154 , threaded mandrel  113  may be rotated in order to screw threaded section  118  into threaded hole  20  of keyhole saw  10 . Bit-connecting piece  130  is inserted into threaded mandrel  113  and extends via hexagonal shank  131  into a corresponding blind hole  155  in stub chuck  152 , thereby being carried along in the direction of rotation in a form-fit manner. Bit-connecting piece  130  also includes a recess  132  having a hexagonal inner wall for receiving the hexagonal shank of the pilot bit, as shown in  FIG. 3 . 
     Threaded mandrel  113  includes, on its end which faces away from threaded section  118 , an end section  156  having a reduced inner diameter. Cylindrical bit-connecting piece  130  includes a cylindrical section  157  which has a reduced diameter and is inserted through section  156  of threaded mandrel  113 . The radial shoulders which are formed at the transitions of sections  156  and  157  form the other stop  122  on threaded mandrel  113  and counter-stop  123 —which interacts with stop  122 —on driving element  112  to limit the axial displacement path of threaded mandrel  113  in driving element  112 , thereby also preventing threaded mandrel  113  from falling out of driving element  112 . Cylindrical section  157  is much larger in its axial length than is section  156  on threaded mandrel  113 , thereby ensuring that threaded mandrel  113  may be displaced axially.