Patent Publication Number: US-2005139396-A1

Title: Fixing arrangement

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a securing arrangement for retaining a cutting tooth on a drill bit, wherein the cutting tooth has a tool head and a shaft, the shaft is accommodated in a shaft receiver of the drill bit or of a holder which is connected to the drill bit, and the cutting tooth rests on support faces of the drill bit with one or a plurality of contact faces.  
      2. Discussion of Related Art  
      A securing arrangement is known from European Patent Reference EP 0 439 821 A 1. In this case, the drill bit includes pocket-shaped notches, into which each base part is welded. The base part has a shaft receiver, which is tapered. The shaft of the cutting tooth can be inserted into the shaft receiver. To create a cone connection, the shaft has a conical outer outline. A spring cotter is used to secure the cone connection and connects the base part to the shaft.  
      In operation, particularly where the loads are jerky and intermittent, the cone connection can become worn. The cutting tooth is then no longer retained without play and this leads to a heavy increase in wear until the tool finally breaks.  
     SUMMARY OF THE INVENTION  
      It is one object of this invention to provide a securing arrangement of the type mentioned above but where the cutting tooth is retained on the drill bit in a secure manner.  
      This object is achieved with support faces and contact faces that are set to be inclined in a circumferential direction. The drill bit includes a shoulder which is offset relative to the contact faces in the direction of the axis of the drill bit and is associated with and spaced from the cutting tooth. The cutting forces occurring during the cutting operation can be absorbed mostly via the inclined support faces. This type of supporting, in interaction with the space, makes it possible for the shaft of the cutting tooth to be substantially free of the cutting forces and reduces the danger of the tool breaking. Also, the space also makes it possible for the cutting tooth to be adjusted if the support face of the drill bit and/or the contact face of the cutting tooth becoming worn.  
      According to a preferred embodiment of this invention, the shaft receiver is admitted partially into the shoulder face, which is formed by the shoulder and faces the cutting tooth. A particularly sturdy support of the cutting tooth is produced when the drill bit provides two contact faces for each cutting tooth, and the two contact faces are set opposite one another. When the securing arrangement is developed so that the cutting tooth includes a threaded portion, which is mounted on the shaft, a nut is screw-connectable to the threaded portion, and the cutting tooth is pressed onto the support faces via the contact faces in a pre-tensioned manner by the nut, so that the shaft can then build up an initial tensioning, which absorbs even intermittent, jerky tool loads in a secure manner without loosening of the threaded connection.  
      The securing arrangement is configured advantageously so that, at least over a portion of its longitudinal region, which extends in the direction of the axis of the drill bit, the shaft of the cutting tooth is surrounded around the circumference completely by the shaft receiver. At the same time, a lateral deviation of the cutting tooth is prevented in a secure manner. In this case, the shaft of the cutting tooth includes at least one calibrating receiver, which is set back relative to the inner wall of the shaft receiver. In this case, the cutting tooth can then be produced true to measurement in the region of its shaft. Superfluous material can be used in the region of the calibrating receiver.  
      In one embodiment of this invention, the shaft of the cutting tooth is tapered at least over a portion of its longitudinal extension in the direction of its free end. The shaft receiver is also tapered at least in a regional manner, and an outside cross-section of the shaft is smaller than the inside cross-section of the shaft receiver. This arrangement simplifies the mounting of the cutting tooth into the shaft receiver. If the tool head of the cutting tooth includes one or a plurality of radial recesses in its region directed radially inwards, then material pockets are formed on the cutting tooth. Residue material collects in the pockets and forms a layer for protection against wear.  
      An improved cutting performance is provided if the tool head is closed at its circumferential end region with triangular, convexly curved shaped faces. In addition, the hard material elements are admitted into a web, which is disposed in a region of the cutting tooth lying radially outwards and which extends in the direction of the axis of the drill bit and protrudes above a base part of the cutting tooth. The hard material elements protrude in a regional manner in the radial direction above the web. The hard material elements form calibrating pins, which constantly free-cut the cutting tooth in the drill hole.  
      To improve the cutting performance even further, at a region remote from the shaft, the tool head of the cutting tooth includes a top face, into which a hard material insert, such as a hard metal insert, is inserted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      This invention is described in detail in view of an embodiment represented in the drawings, wherein:  
       FIG. 1  is a side view of a drill bit;  
       FIG. 2  is a perspective view of the drill bit in  FIG. 1 ;  
       FIG. 3  is a vertical section view of the drill bit;  
       FIG. 4  is a detailed representation taken from the view shown in  FIG. 3 ;  
       FIG. 5  is a side perspective view of a cutting tooth;  
       FIG. 6  is a rear perspective view of the cutting tooth shown in  FIG. 5 ; and  
       FIG. 7  is a section view taken through the shaft of the cutting tooth as shown in  FIGS. 5 and 6 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIGS. 1 and 2  show a drill bit  10 , produced in one piece from a casting that is annular and has a base body  11 . On a lower edge, the base body  11  has a securing ring  19 , which is in the form of a mounting. On a side remote from the securing ring  19 , mounting projections  21  are integrally formed around the circumference on the base body  11 . The mounting projections  21 , in this case, are spaced equally from one another so that a space  16  is produced. The base body  11  has webs  15  between the mounting projections  21 . The webs  15  each form an end face, which extends in the radial direction. All end faces of the webs  15  rest on a common plane. Inclined faces  18  proceed from the end faces at angle. The inclined faces  18 , in this case, are facing the interior, which is surrounded by the drill bit  10 . The end faces and the inclined faces  18  pass over at their circumferential ends into deflecting faces  26  of the mounting projections  21 . The deflecting faces  26  project above the end faces in the direction of the axis of the drill bit. The deflecting faces  26  each pass over into a roof portion  25  that passes over into a support face  24 . The support face  24 , in this case, is disposed at an angle to the horizontal. The two support faces  24  of one mounting projection  21 , in this case, are aligned opposite one another and are part of a tool receiver  20 . The tool receiver  20  has a shaft receiver  22 , which has an oval cross-section, with an insertion channel  22 . 1  between the two support faces  24 . The insertion channel  22 . 1  ends in an opening  12  and is machined into the base body  11  in the shape of a window. The opening  12 , in this case, is developed so that it widens outwardly in a continuous manner proceeding from the inner wall  17 . 1  of the base body  11 .  
      The disposition and development of the insertion channel  22 . 1  and of the opening  12  is shown in  FIGS. 2 and 4 . As shown in  FIG. 2 , cutting teeth  30  can be inserted into the tool receiver  20 . The development of the cutting teeth  30  is shown in FIGS.  5  to  7 . According to these Figures, the cutting teeth  30  have a tool head  31 , on which a shaft is integrally formed. The tool head  31  has hard metal inserts  35 . At its free end the shaft  32  has a threaded portion  33 .  
      The cutting tooth  30  is inserted with its shaft  32  into the insertion channel  22 . 1 . In the installed state, the cutting tooth  30  rests with corresponding mating faces on the support faces  24 .  
      The threaded portion  33  extends into the region of the opening  12 , so that a nut  34  can be screw-connected. The cutting tooth  30  can be tensioned on the support faces  24  with the nut  34 . As the cross-sectional geometry of the shaft  32  of the cutting tooth  30  is adapted to the outline of the insertion channel  22 . 1 , it is retained in a non-rotatable manner. As shown in  FIG. 1 , the cutting tooth  30  has two shaped faces  36 , which pass over into the deflecting faces  26  of the support parts  25  in a seamless manner.  
      To calibrate the drill bit  10 , projections  13  are disposed on the outer face of the base body  11  and have elements  14  produced from hard metal for protection against wear.  
      In the region of the inner wall  17 . 1 , the base body  11  also has projections  17 . 2  which extend into the interior of the drill bit  10  and optimize protection against wear at that location.  
      FIGS.  5  to  7  provide a more detailed representation of one embodiment of a cutting tooth  30 . The cutting tooth  30  has a tool head  31 , on which a shaft  32  is integrally formed via a rounding transition. The shaft  32  ends at the end remote from the tool head  31 , in a threaded portion  33 . The tool head  31  has an upper top face  31 . 1 , into which a hard metal insert  35  is admitted. To form a receiver for the hard metal insert, which is in the form of a straight pin, a web  37 . 1 ,  37 . 2  proceeds from the top face  31 . 1  at both the front and the rear.  
      As shown in  FIG. 5 , the top face  31 . 1 , near or in the region of the inside of the cutting tooth  30 , passes over into a steeply descending concavely curved wall  38 . 2  which is divided longitudinally by two ribs  38  and the web  37 . 1 . The ribs  38  and the web  37 . 1  form recesses  38 . 1 , which serve as material pockets for accommodating residue material. As shown in  FIG. 6 , at the rear the top face passes over into a wall  38 . 3 , which extends parallel to the axis of rotation of the drill bit  10 . The wall  38 . 3  supports the web  37 . 2 . The web  37 . 2  has hard material elements  39 . 3  that protrude above the web  37 . 2 . The walls  38 . 2  and  38 . 3  pass over into one another at the sides of the cutting tooth  30  by shaped faces  36  that are triangular and are convexly curved.  
      The shaft  32  is adjacent to a base part  39  of the tool head  31 . The shaft  32  has an oval cross-section, as shown in  FIG. 7 . The shaft  32  forms calibrating receiver  31 . 1  on the two longitudinal sides. Flat regions  32 . 2  are provided at the side of the shaft  32  and serve the calibration. Consequently, four true to measurement shaft regions can be forged between the calibrating receiver  31 . 1  and the flat regions  32 . 2 . The shaft regions prevent the shaft  32  from jamming when inserted into the shaft receiver  22 .