Abstract:
A drill having end-face major surfaces, contiguous faces descending from the major cutting edges and flanks contiguous to the major cutting edges. Center cutting edges are formed by end-face taperings. A chisel cutting edge is between the center cutting edges. Shapes of the cutting edges are disclosed. First ones of the flanks are angled to create an outward apex angle so that the major cutting edges and the center cutting edges run at a constant taper angle.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a 35 U.S.C. §§371 national phase conversion of PCT/EP2008/006898, filed Aug. 21, 2008, which claims priority of German Application No. 10 2007 040 178.9, filed Aug. 25, 2007, the disclosure of which is incorporated by reference herein. The PCT International Application was published in the German language. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a drill according to the preamble of claim  1 . 
         [0003]    Drills of the type referred to here are known. They have on their end face at least two major cutting edges which merge into minor cutting edges provided on the circumferential region of the drills. The major cutting edges are formed by faces and flanks contiguous to one another, the faces descending in the direction of rotation of the drill and the flanks descending in the opposite direction. As a rule, the drill is set in rotation and is brought into engagement with a workpiece. It is also conceivable, however, to set the workpiece in rotation and hold the drill fixedly in terms of rotation. In this case, the faces point in the opposite direction to that in which the workpiece rotates. The chips removed by the at least one major cutting edge run off on the faces. In the region of the mid-axis of the drill, a chisel cutting edge is obtained, to which the two end-face major cutting edges are contiguous. Drills of the type referred to here are usually manufactured with a relative core diameter of 10% to 35% of the drilling diameter. In the case of a core diameter greater than 20%, it is necessary to shorten the chisel cutting edge, which connects the two major cutting edges, by means by what is known as tapering out. As a result of this tapering out, center cutting edges are formed which usually form an obtuse angle with the major cutting edge. The smaller this angle is, the shorter these center cutting edges are and, as a rule, the greater the cutting efficiency which these have. The result of the tapering out is that the faces assigned to the major cutting edges form an obtuse angle with the faces assigned to the center cutting edges. In conventional ground sections of drills with a continuous flank, a greater apex angle necessarily arises in the region of the center cutting edge than in the region of the major cutting edge. It became apparent that, in such a configuration of the drill, chips removed by the cutting edges may be compacted and may not flow off freely. The drilling performance is thereby reduced. Damage to the drill may also occur. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the invention, therefore, is to provide a drill which avoids the disadvantages mentioned here. 
         [0005]    To achieve this object, a drill is proposed which has the features mentioned below. This drill comprises at least two end-face major cutting edges with outer minor cutting edges which adjoin these and which are arranged in the region of the circumferential surface of the drill. Both faces and first flanks which are inclined in the opposite direction are contiguous to the major cutting edge. The faces are inclined in the direction of rotation of the drill and the first flanks in the opposite direction. The at least two major cutting edges of the drill are formed by the line of intersection of the faces with the first flanks. Moreover, at least two center cutting edges with faces which form an obtuse angle with the faces of the major cutting edges are provided. The drill is distinguished in that the first flanks also have segments which are arranged at an obtuse angle to one another, the number of segments of the first flanks corresponding to the number of segments of the faces. The at least two center cutting edges and major cutting edges descend, as seen from the chisel cutting edge, at a constant apex angle a outward in the direction of the circumferential surface of the drill, that is to say in the direction of the minor cutting edges. 
         [0006]    A preferred exemplary embodiment of the drill is distinguished in that the inner faces of the center cutting edges are inclined to a lesser extent than the further-out faces of the major cutting edge. The latter runs in a plane in which the mid-axis or axis of rotation of the drill also lies. The inner face preferably forms an acute angle with a plane on which the mid-axis stands perpendicularly. 
         [0007]    In a preferred exemplary embodiment of the drill, there is provision for the inner face of the center cutting edge to merge into the outer face of the major cutting edge via a bend or via an arc. The chip run-off can thereby be influenced in a wide range. 
         [0008]    In a further preferred exemplary embodiment, there is provision for the inner segment of the first flank to be inclined to a greater extent than the outer segment, that is to say, starting from the mid-axis of the drill, the inner first segment of the flank descends in the direction of the circumferential surface of the drill to a greater extent than the outer flank segment reaching up to the circumferential surface of the drill. 
         [0009]    A particularly preferred exemplary embodiment of the drill is distinguished in that the clearance angle of the first flanks becomes smaller outward, as seen from the center of the drill, that is to say from the mid-axis. The clearance angle preferably decreases continuously. 
         [0010]    In a further preferred exemplary embodiment of the drill, there is provision for the at least first flank, which is contiguous to the major cutting edge, to have adjoining it a second flank. This is inclined to a greater extent than the first flank, that is to say its clearance angle is greater than that of the first flank. 
         [0011]    An exemplary embodiment of the drill is particularly preferred in which the second flank has, in a similar way to the first flank, segments which are inclined differently, as seen in the radial direction of the drill, correspondingly to the segments of the first flank and which merge into one another via a bend or an arc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention is explained in more detail below by reference to the drawings in which: 
           [0013]      FIG. 1  shows an end view of a drill with a conventional ground section without tapering out; 
           [0014]      FIG. 2  shows an end view of a drill with a conventional ground section and with tapering out; 
           [0015]      FIG. 3  shows a drill with a ground section according to the invention both in an end view and in a side view; 
           [0016]      FIG. 3   a  shows a first side view of the drill illustrated in  FIG. 3 ; 
           [0017]      FIG. 3   b  shows a second view of the drill illustrated in  FIG. 3 ; 
           [0018]      FIG. 4  shows a different exemplary embodiment of a drill with an arcuate cutting edge in an end view and a side view; 
           [0019]      FIG. 4   a  shows a first side view of the drill illustrated in  FIG. 4 ; 
           [0020]      FIG. 4   b  shows a second side view of the drill illustrated in  FIG. 4 , and 
           [0021]      FIG. 5  shows a further modified exemplary embodiment of a drill according to the invention with an acute angle of 180°. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    A known drill  10 , illustrated in an end view in  FIG. 1 , has a first major cutting edge  3  and a second major cutting edge  3 ′ arranged point-symmetrically with respect to the mid-axis  5  of the drill. The two major cutting edges  3 ,  3 ′ are connected to one another by means of a chisel cutting edge running through the mid-axis  5 . The two major cutting edges  3 ,  3 ′ are arranged parallel to a diametral line  9  which in  FIG. 1  runs horizontally through the mid-axis  5 . The first major cutting edge  3  is assigned a face  11  running perpendicularly with respect to the image plane of  FIG. 1 , and the second major cutting edge  3 ′ is assigned a corresponding face  11 ′. 
         [0023]    The faces  11 ,  11 ′ are inclined in the direction of rotation of the drill, indicated by an arrow  13 . The major cutting edges  3 ,  3 ′ have adjoining them respective flanks  15 ,  15 ′ which descend in the opposite direction and are consequently inclined opposite to the direction of rotation indicated by the arrow  13 . 
         [0024]    The major cutting edges  3 ,  3 ′ merge into minor cutting edges  19 ,  19 ′ which are arranged in the region of the circumferential surface  17  of the drill and which in  FIG. 1  run perpendicularly with respect to the image plane. The minor cutting edges may be oriented parallel to the mid-axis  5  of the drill or else may run along an imaginary helix. 
         [0025]      FIG. 1  shows that the chisel cutting edge  7  forms an acute angle with a diametral line  21  running perpendicularly with respect to the diametral line  9 . In the region of this chisel cutting edge  7 , the cutting properties of the drill are poor, and therefore this chisel cutting edge should be as short as possible. This is achieved by means of a tapering out which is evident from  FIG. 2 . 
         [0026]      FIG. 2  shows a known drill  10 ′ in an end face view. Identical and functionally identical parts are given the same reference numerals, and therefore, to that extent, reference is made to the description relating to  FIG. 1 . 
         [0027]    The drill  10 ′ illustrated in  FIG. 2  is constructed basically in the same way as that explained with reference to  FIG. 1 . It differs solely in that, in its end face, flattenings  23 ,  23 ′ are introduced, which extend near to the mid-axis  5  of the drill and which include parts of the major cutting edge  3 ,  3 ′ and, in particular, of the chisel cutting edge  7 . The main cutting edge  3  no longer runs continuously in a straight line from the minor cutting edge  19  as far as the chisel cutting edge  7 . It descends, at a distance from the diametral line  21 , at an acute angle to the diametral line  9 . The same applies to the second major cutting edge  3 ′. 
         [0028]    The flattenings  23 ,  23 ′ result, therefore, in cutting edge regions of the major cutting edges, which cutting edge regions descend with respect to the diametral line  9  and are also designated as center cutting edges which run at an obtuse angle with respect to the major cutting edges  3 ,  3 ′. The smaller this angle is, the shorter these center cutting edges are, and, as a rule, the higher the cutting efficiency of these is. On the other hand, however, due to a tapering out of this kind, afforded by the flattening  23 ,  23 ′, an increase in the apex angle of the center cutting edges, as compared with the apex angle of the major cutting edges, is obtained. The increase in the apex angle in the center region has a highly adverse influence on the centering behavior of the drill, particularly during the spot-drilling phase, and this may cause the drill to run off-center. If a drill runs off-center as early as during spot-drilling, it can no longer be stabilized even during the subsequent full-drilling process, because its guide chamfers hold it in this position offset with respect to the axis of rotation. As a result, very high normal forces act upon the guide chamfers of the drill and also upon the cutting edge corners lying between the major and the minor cutting edges, thus greatly reducing the service life of the drill. 
         [0029]    Moreover, a compaction of the chips removed from a workpiece occurs at the bending point of the major cutting edge  3 ,  3 ′, and therefore these chips cannot flow off freely. 
         [0030]      FIG. 3  shows an end view of a drill  1  according to the invention. The front end of the drill  1  is illustrated in a side view in  FIG. 3   a . In terms of the end view,  FIG. 3   a  is a view from the right. 
         [0031]      FIG. 3   b  illustrates the front side of the drill  1  in a side view which, in terms of the end view according to  FIG. 3 , reproduces a view from below. Identical and functionally identical parts are given the same reference numerals, and therefore, to that extent, reference is made to the description relating to  FIGS. 1 and 2 . 
         [0032]    The drill  1  accordingly has a first major cutting edge  3  and a second major cutting edge  3 ′ which are arranged point-symmetrically to one another with respect to the mid-axis  5  of the drill. As seen in the direction of rotation illustrated by the arrow  13 , the major cutting edges  3  and  3 ′ have adjoining them the first and the second face  11 ,  11 ′. These are inclined in the direction of rotation. The drill illustrated in  FIG. 3  also has first flanks  15   a ,  15 ′ a  which adjoin the major cutting edges  3  and  3 ′ and which, starting from the first major cutting edge  3 ,  3 ′, descend opposite to the direction of rotation. 
         [0033]    As in the known drill  10 ′ according to  FIG. 2 , in the drill  1  flattenings  23 ,  23 ′, also designated as a tapering out, are provided, which reach near to the mid-axis  5  and therefore greatly shorten the chisel cutting edge  7 , as compared with the known drill according to  FIG. 1 . They also have the result that, starting from the minor cutting edge  19 , the first major cutting edge  3  first runs parallel to the diametral line  9  and then continues at an acute angle to this diametral line  9 . Here, too, therefore, a center cutting edge  25  is obtained. The same applies correspondingly to the second major cutting edge  3 ′ in which a center cutting edge  25 ′ is formed by means of the flattening  23 ′. 
         [0034]    The faces  11 ,  11 ′ assigned to the first major cutting edge  3 ,  3 ′ run perpendicularly with respect to the image plane of  FIG. 3 , while the faces assigned to the inner part of the major cutting edges, that is to say the faces  27 ,  27 ′ assigned to the center cutting edges  25 ,  25 ′, likewise descend in the direction of the direction of rotation indicated by the arrow  13 , but at a substantially flatter angle. The two segments of the face form an obtuse angle. 
         [0035]    It is clear from  FIG. 3  that the first flanks  15   a ,  15 ′ a  have two segments  29   a  and  31   a  which are inclined at an obtuse angle to one another. The first segment  29   a  adjoining the circumferential surface  17  extends over that region of the first major cutting edge  3  which runs essentially parallel to the diametral line  9 . The second segment  31   a  of the first flank  15   a  adjoins the first segment  29   a  inward and extends over the second part of the first major cutting edge, to be precise over the region of the center cutting edge  25 . The two segments  29   a  and  31   a  form an obtuse angle, the inner second segment  31   a  descending, as seen from the mid-axis  5 , more steeply outward to the circumferential surface than the outer first segment  29   a . The two segments  29   a  and  31   a  are separated from one another by a bending line  33   a . As regards the second major cutting edge  3 ′, the same conditions arise. Reference is therefore made to the explanations relating to the first major cutting edge  3 . 
         [0036]    The diametral line  9  separates the first flanks  15   a ,  15 ′ a  from second flanks  15   b ,  15 ′ b  which are inclined to a greater extent than the first flanks  15   a ,  15 ′ a  with respect to an imaginary plane on which the mid-axis  15  stands perpendicularly and which coincides with the image plane of  FIG. 3 . The clearance angle is therefore greater here than in the region of the first flanks. 
         [0037]    The second flanks  15   b ,  15 ′ b  are designed correspondingly to the first flanks  15   a ,  15 ′ a : the second flanks  15   b ,  15 ′ b  have in each case a first segment  29   b  and  29 ′ b  and also  31   b , and  31 ′ b . Correspondingly to the first and second segments  29   a ,  31   a ,  29 ′ a ,  31 ′ a , the second segments  29   b ,  29 ′ b  and  31   b ,  31 ′ b  are also inclined at an obtuse angle to one another, the segments  29   b ,  29 ′ b  which adjoin the mid-axis  5  descending in the direction of the circumferential surface of the drill  1  at a steeper angle than the further-out second segments  31   b  and  31 ′ b.    
         [0038]    The two segments  29   b ,  29 ′ b  and  31   b ,  31 ′ b  merge into one another via a bending line  33   b.    
         [0039]    If the drill  1  reproduced in  FIG. 3  is viewed from the right, the side view, reproduced in  FIG. 3   a , of the drill  1  is obtained. Identical parts are given the same reference numerals, and therefore, to that extent, reference is made to the description relating to  FIG. 3 . 
         [0040]    It is shown that the first major cutting edge  3  is arranged essentially parallel to the diametral line  9  running perpendicularly with respect to the image plane in  FIG. 3   a  and also parallel to a plane which runs at a distance from the mid-axis  5 . The first flank  15   a  with the first segment  29   a  and with the second segment  31   a  lies below the first major cutting edge  3 . These two segments merge into one another the bending line  33   a . The second flank  15   b  with the first segment  29   b  and with the second segment  31   b  can also be seen. These two segments merge into one another via the bending line  33   b . It is shown clearly that, with respect to a plane on which the mid-axis  5  stands perpendicularly, the second segment  31   b  descends more steeply outward to the circumferential surface  17  than the first segment  29   b.    
         [0041]      FIG. 3   a  also shows the flattening  23 , and also the minor cutting edge  19  which here runs along an imaginary helix, that is to say not parallel to the mid-axis  5 . The minor cutting edge  19  lags behind a guide chamfer  20  during the machining of a workpiece. 
         [0042]    If the drill  1  illustrated in an end face view in  FIG. 3  is viewed from below, the side view reproduced in  FIG. 3  is obtained, only the front part of the drill  1  being reproduced here. Identical parts have the same reference numerals, and therefore reference is made to the explanations relating to  FIGS. 3 and 3   a.    
         [0043]    The center cutting edge  25 ′ which adjoins the tip  35  of the drill  1  and is part of the major cutting edge of the drill  1  can be seen below the center line  5  in  FIG. 3   b . The associated face  27 ′ confronts the viewer. It is part of the flattening  23 ′, which constitutes the tapering out of the drill  1 , and merges into the face  11 ′ via a bending line  36 ′. However, an arcuate transition is particularly preferred. 
         [0044]    The second major cutting edge  3 ′ with the associated face  11 ′ adjoins the center cutting edge  25 ′. The second major cutting edge  3 ′ merges into the minor cutting edge  19 ′. An edge  37  can be seen here between the second major cutting edge  3 ′ and the minor cutting edge  19 ′. There may, however, also be provision for the major cutting edges to merge into the minor cutting edges via a radius. 
         [0045]    What has been said with regard to the second minor cutting edge  3 ′ and to the center cutting edge  25 ′ applies correspondingly to the point-symmetrically arranged first major cutting edge  3  and center cutting edge  25 . 
         [0046]    The first flank  15   a  and the second flank  15   b , with the associated segments  29   a ,  31   a  and  29   b ,  31   b , can be seen above the mid-axis  5 . The bending line  33   a  of the first flank  15   a  and the bending line  33   b  of the second flank  15   b  can also be seen. 
         [0047]      FIG. 3   b  shows very clearly that, starting from the tip  35  of the drill  1 , the center cutting edge  25 ′ and the second major cutting edge  3 ′ merge into one another and have the same constant angle of inclination, also designated as an apex angle, with respect to the center line  5 . 
         [0048]      FIG. 4  shows an end view of a modified exemplary embodiment of the drill  1  illustrated in  FIG. 3 . Identical parts are given the same reference numerals, and therefore, to that extent, reference is made to the description relating to the preceding Figures. 
         [0049]    The drill  1  reproduced in  FIG. 4  differs from that illustrated in  FIG. 3  only in that the segments  29   a ,  31   a  of the first flank  15   a  do not merge into one another via a bending line, but, instead, arcuately. There is therefore no sharply defined step between the two segments. 
         [0050]    The same applies correspondingly to the segments  29 ′ a ,  31 ′ a  of the first flank  15 ′ a  which lies opposite the first flank  15   a  point-symmetrically with respect to the mid-axis  5 . 
         [0051]    The same also applies to the second flanks  15   b  and  15 ′ b : the first segments  29   b  and  29 ′ b  merge arcuately into the second segments  31   b  and  31 ′ b , so that, here too, there is no bend formed, but, instead, a smooth transition. 
         [0052]    If the drill  1  illustrated in an end view in  FIG. 4  is viewed from the right, the side view illustrated in  FIG. 4   a  is obtained. Everything said with regard to  FIG. 3   a  applies correspondingly to this illustration. 
         [0053]    In a bottom view of the drill  1  reproduced in an end view in  FIG. 4 , the side view, illustrated in  FIG. 4 , of the drill  1  is obtained. Everything said with regard to  FIG. 3   b  applies correspondingly to the illustration according to  FIG. 4   b.    
         [0054]    It is also clear from the illustrations according to  FIGS. 4   a  and  4   b  that no bending lines are provided here, and that the segments of the flanks merge arcuately into one another. 
         [0055]    The bending lines  33   a  and  33   b  mentioned in  FIGS. 3 ,  3   a  and  3   b  are therefore absent in the drill illustrated in  FIGS. 4 ,  4   a  and  4   b  and are replaced by an arcuate transition of the flanks. 
         [0056]      FIG. 4   b  depicts the apex angle α which is formed by the major cutting edges  3 ,  3 ′ and the center cutting edges  25 ,  25 ′ and which is not illustrated in  FIG. 3   b  for the sake of clarity. 
         [0057]      FIG. 5  shows a side view of a further exemplary embodiment of a drill  1 . This view corresponds to the side views according to  FIGS. 3   b  and  4   b . Identical and functionally identical parts are given the same reference numerals, and therefore reference is made to the description relating to the preceding Figures. In the particularly preferred exemplary embodiment of the drill, as illustrated in  FIG. 5 , there is provision for the apex angle a to amount to 180°, that is to say that the two end-face major cutting edges  3  and  3 ′ and the center cutting edges  25 ,  25 ′ of the drill lie in a plane on which the mid-axis  5  stands perpendicularly. In this drill, contrary to known drills, a face correction is not necessary because, as is evident from  FIGS. 3 and 4 , the major cutting edges lie approximately 5% to 15% in front of the middle, that is to say arranged in front of the diametral line  9 , as seen in the direction of rotation indicated by the arrow  13 . In this case, the first flanks  15   a  and  15 ′ a  are configured so that an absolutely planar drillhole bottom is obtained even when the major cutting edge is curved, that is to say lies in front of the middle in the region of the center cutting edges  25 ,  25 ′. 
         [0058]    It was stated above with reference to  FIGS. 3 ,  3   a ,  3   b  and  4 ,  4   a  and  4   b  that the first and second segments  29   a ,  29 ′ a ,  29   b ,  29 ′ b  and  31   a ,  31 ′ a ,  31   b  and  31 ′ b  merge into one another via a bending line or an arcuate region. In addition, there is preferably provision for the clearance angle of the flanks to decrease, starting from the center, that is to say starting from the mid-axis  5 , toward the circumferential surface  17 . By virtue of this configuration, the cutting edge corners which are subjected to a particularly high load can be designed with higher stability. At the same time, so much latitude is afforded at the center of the drill that even very high feed motions are possible with this type of drill. 
         [0059]    A further relieving of the cutting edge corners may be achieved in that the edge  17  is avoided in the transitional region between the major cutting edges and minor cutting edges and a radius is formed. 
         [0060]      FIG. 5  therefore shows a drill in which the apex angle α amounts to 180°. A top view of the end face of a drill of this type corresponds to the top view reproduced in  FIG. 3 . To that extent, reference is made particularly to this illustration. 
         [0061]    In  FIG. 5 , the first flank  15   a  and the second flank  15   b  can be seen above the center line  5 , and also the first segment  29   b  and the second segment  31   b  of this second flank  15   b . The second major cutting edge  3 ′ and its segment and the center cutting edge  25 ′ can be seen below the center line  5 . The face  11 ′ assigned to the second major cutting edge  3 ′ and the face  27 ′ assigned to the center cutting edge  25 ′ can also be seen. These faces are separated by a bending line  36 ′ or merge into one another via an arc. 
         [0062]    In this illustration, too, as in  FIGS. 3   b  and  4   b , it becomes clear that the second major cutting edge  3 ′ and its associated cutting edge segment, to be precise the center cutting edge  25 ′, are inclined, starting from the center line  5 , at the same, preferably continuous, apex angle, a continuous transition being present between the center cutting edge  25 ′ and the second segment  3 ′. In  FIG. 5 , the center cutting edge  25 ′ and the second major cutting edge  3 ′ are arranged at an angle of 90° to the mid-axis  5 . The same applies correspondingly to the point-symmetrical first major cutting edge with the associated cutting edge segment, the center cutting edge  25 . The apex angle α of  180 ° is consequently obtained. 
         [0063]    When the drill  1  illustrated in  FIG. 5  is used, a completely planar drillhole bottom is obtained. On account of the special configuration of the tapering out, which is implemented by the flattening  23 ′ and the flattening  23 , not evident here, a compaction of the chips removed the center cutting edges  25  and  25 ′ is reliably avoided. These can flow off freely via the face  27 ,  27 ′. 
         [0064]    It is therefore shown that a drill which avoids the disadvantages known in the prior art is provided in a simple way. The exemplary embodiments according to  FIGS. 3 and 4  ensure that the drill is centered very accurately especially in the spot-drilling phase. This is achieved by means of the tapering out, that is to say by the faces  23  and  23 ′ which lead to an increase in the apex angle in the center region, as will be evident from  FIGS. 3   a  and  3   b . At the same time, a compaction of the chips removed here is avoided. 
         [0065]    The avoidance of chip compaction is also obtained in the exemplary embodiment of the drill  1 , as illustrated in  FIG. 5 . 
         [0066]    A summary of the elements of all the embodiments follows. 
         [0067]    This disclosure concerns a drill with at least two end-face major cutting edges  3 ,  3 ′, with faces  11 ,  11 ′ contiguous to these cutting edges and the faces descending in a first direction. First flanks  15   a ,  15 ′ a  are contiguous to the at least two major cutting edges  3 ,  3 ′ and descend in the opposite direction to the faces  11 ,  11 ′. At least two end-face taperings out, by means of each of which is formed a center cutting edge  25 ,  25 ′ which is contiguous to the major cutting edges  3 ,  3 ′ and faces  27 ,  27 ′ descend in the first direction are contiguous to the major cutting edges. A chisel cutting edge  7  runs between the at least two center cutting edges  25 ,  25 ′. Minor cutting edges  19 ,  19 ′ are provided in the region of a circumferential surface  17  of the drill  1 . Each major cutting edge  3 ,  3 ′ is associated with a minor cutting edge  19 ,  19 ′. The at least two major cutting edges  3 ,  3 ′ are formed by the line of intersection of the faces  11 ,  11 ′ with the first flanks  15   a ,  15 ′ a . The faces  11 ,  11 ′ of the major cutting edges  3 ,  3 ′ and the faces  27 ,  27 ′ of the center cutting edges  25 ,  25 ′ are arranged at an obtuse angle to one another. This drill is distinguished in that the first flanks  15   a ,  15 ′ a  have segments  29   a ,  29 ′ a ;  31   a ,  31 ′ a  which are arranged at an obtuse angle to one another. The segments of the first flanks  15   a ,  15 ′ a  are associated with the face  27 ,  27 ′ of the center cutting edge  25 ,  25 ′ and to the face  11 ,  11 ′ of the major cutting edge  3 ,  3 ′. The major cutting edges  3 ,  3 ′ have adjoining them center cutting edges  25 ,  25 ′. The first flanks  15   a ,  15 ′ a  are angled opposite to the faces  11 ,  27  so that the major cutting edges  3 ,  3 ′ and center cutting edges  25 ,  25 ′ run at a constant apex angle α outward in the direction of a circumferential surface  17  of the drill  1 . 
         [0068]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.