Abstract:
The invention relates to a drill bit ( 2 ), having main cutting edges ( 4   a   , 4   b ) which are connected together by a transversal cutting edge ( 6 ). An open surface ( 7 ) which extends into a flute ( 8 ) lies adjacent to each main cutting edge. The drill bit ( 2 ) is ground, in particular, during a continuous three-dimensional grinding process in such a way that the open surface ( 7 ) forms a continuous curved surface which follows a radius of curvature (R) running from the main cutting edge ( 4   a ) in the direction of the flute ( 8 ). The continuous grinding process, in comparison to a conventional two-stage process, produces an improved drill bit geometry which is devoid of ridges ( 16 ). The ridge-free configuration reduces the mechanical stress during drilling to a minimum.

Description:
This application is a Continuation-In-Part application of International Patent Application No. PCT/EP00/11174, filed on Nov. 11, 2000, which claims priority from Federal Republic of Germany Patent Application No. 199 55 172.3, filed on Nov. 16, 1999. International Patent Application No. PCT/EP00/11174 was pending as of the filing date of this application. The United States was an elected state in International Patent Application No. PCT/EP00/11174. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a drill bit and a method for grinding a drill bit having two major cutting edges connected via a chisel edge, adjacent to each of which major cutting edges is a clearance face that transitions into a flute. 
     2. Background Information 
     Such drill bits are used for, among other things, twist drills in which the chips removed by the drill bit are removed via flutes in the drill that run in a spiral pattern. For this purpose, the drill bit and drill are designed in one or two pieces. In the two-piece design, the drill bit is realized in particular in the form of a replaceable insert for a drill base element. 
     The geometric configuration, and especially the grinding of the drill bit, determines to a significant extent the cutting action of the drill and the mechanical load on the drill, especially on the drill bit. The mechanical load during drilling is also determined by, among other things, the configuration of the area around the chisel edge. To reduce the load, the chisel edge is therefore generally pointed during grinding. With pointing, the rake angle is determined in the area of the drill core, which defines the angle between the surface adjoining the chisel edge and the longitudinal axis of the drill. This surface is referred to below as the chisel edge surface. The rake angle in the area of the chisel edge facing away from the major cutting edge is determined, in particular, by where the clearance face associated with the cutting edge transitions into the flute. A positive rake angle is often desired in this area. A positive rake angle means that the chisel edge surface is tilted toward the longitudinal axis of the drill, so that a type of overhang is formed. On the other hand, with a negative rake angle, this surface is tilted away from the axis of the drill. 
     In conventional grinding methods with pointing, the major cutting edges and the chisel edge, as well as the clearance faces adjoining the major cutting edges, are ground in a first process step. The pointing is then carried out in a second working step. For this purpose, it is essential that the grinding wheel used for the grinding be reset. Consequently a ridge, i.e., a discontinuity, is ground into both the clearance face and the chisel edge surface. The ridge in the chisel edge surface is necessarily formed because, under all circumstances, the grinding wheel must be prevented from reaching the chisel edge already ground during pointing. In the area of the chisel edge, this ridge causes stress peaks that lead to increased loading on the drill bit. 
     More recent development trends have attempted to produce drill bits without grinding via a metal injection molding process. 
     OBJECT OF THE INVENTION 
     The object of this invention is to configure a drill bit so that the mechanical loads that occur during drilling are kept low. 
     SUMMARY OF THE INVENTION 
     The invention teaches that this object can be accomplished by a method for grinding a drill bit having two major cutting edges joined via a chisel edge, adjacent to each of which is a clearance face that transitions into a flute, whereby the clearance face is realized in the form of a curved surface without ridges from the major cutting edge toward the flute with a radius of curvature R. 
     A drill tip of this type has the significant advantage that, on account of the curved, ridge-free surface with the radius of curvature R, therefore because the surface has a profile without shoulders, the load on the drill tip during drilling is low. In particular, no stress peaks occur in the area of the chisel edge surfaces of the type that occur on conventionally ground drill tips. 
     Additional preferred embodiments of the drill bit are described in the features of the invention included herein below. 
     The drill bit is preferably a ground drill bit. Alternatively, the geometry described above can also be achieved with a metal injection molding process. 
     In one particularly advantageous embodiment, the drill bit is realized in the form of a replaceable insert for a drill base element. This type of two-part drill, consisting of a drill bit and drill base element, has the major advantage that the drill bit, which is subject to wear, can be easily replaced. The drill base element is generally exposed to much less wear, so that its useful life is several times longer than the useful life of the drill bit. By realizing the drill bit in the form of a replaceable insert, operating costs can therefore be reduced significantly. Moreover, the drill base element can be realized from a more economical and thus generally softer material than the material of which the drill bit is made. 
     The invention further teaches a method for grinding a drill bit that has, among other things, two major cutting edges connected to each other via a chisel edge, adjacent to each of which major cutting edges is a clearance face that transitions into a flute, whereby a grinding wheel used for the grinding and the drill tip are guided toward each other in a continuous grinding process so that the clearance face is realized in the form of a surface that curves from the major cutting edge toward the flute with a radius of curvature. 
     The grinding wheel and drill bit are thereby guided toward each other in a complex three-dimensional grinding process, so that the drill bit is ground in the desired manner without the requirement for two separate grinding processes. On account of the continuous grinding process, no ridges are formed in the area of the clearance face and chisel edge surface of the type that would be unavoidably formed in a two stage grinding process. Therefore, as a result of the three-dimensional guidance of the drill tip and the grinding wheel, the two conventional grinding steps are therefore combined into one grinding step. The advantages of this method are reflected in, among other things, the curvature of the clearance face. On account of the shoulder-less and ridge-less profile of the ground surfaces of the drill tip, the load on the drill tip during drilling is also kept low. 
     One other possible advantage of the above-described drill tip design is that the power needed to rotate the drill during a cutting or drilling operation in some materials can be reduced by as much as approximately 30% over drill tips of the prior art, such as shown in  FIG. 1  of this application. Therefore the energy requirement for operation of a drive or motor mechanism to rotate the drill during drilling is reduced. 
     For the lowest possible load on the drill tip, the method is preferably carried out so that the radius of curvature is between 0.05 and 0.5 times the diameter of the drill. 
     To form the curved surface, the grinding wheel comprises a main grinding surface that is pivoted relative to the drill bit by a pivot angle. This pivoting movement can be executed either by the drill bit, or by the grinding surface, or by both together. The angle referred to as the pivot angle is reduced during this pivoting movement between the surface normals of the main grinding surface and the longitudinal axis of the drill bit. 
     To form an appropriate drill bit geometry, the drill bit is preferably first rotated around its longitudinal axis up to an angle of rotation, and only then does pivoting by the pivot angle occur. Consequently, the clearance face directly adjacent to the major cutting edge, which is called the main clearance face, initially runs obliquely and is then increasingly curved toward the flute. 
     For the most uniform possible realization of the curved surface, as it pivots by the pivot angle α, the drill bit is simultaneously rotated further to a predetermined final angle of rotation. 
     In a particularly advantageous variant, a secondary grinding surface of the grinding wheel and drill bit are pivoted for its pointing in the area of the chisel edge relative to each other by a rake angle. This secondary grinding surface abuts the main grinding surface of the grinding wheel, and the chisel edge surface, i.e., the transition from the chisel edge to the clearance face, is ground with it. The profile of this surface relative to the longitudinal axis of the drill bit then gives the rake angle (the rake angle of the chisel edge). To realize the rake angle, the entire grinding wheel is pivoted relative to the longitudinal axis of the drill bit. 
     The pivoting movements by the pivot angle and by the rake angle are preferably superimposed on each other. The grinding wheel is therefore pivoted by two angles simultaneously. The pivoting movement by the pivot angle then occurs around a pivot axis that runs roughly radially outward from the chisel edge, and the pivot movement by the rake angle occurs around a pivot axis that runs roughly tangential to the chisel edge. As a result of the superimposition of these two pivoting movements, it is guaranteed that, on the one hand, a suitable pointing is achieved and, on the other hand, the ground surfaces transition into each other smoothly and uniformly. In particular, the chisel edge surface makes a smooth transition into the clearance face, i.e. it has no shoulders or ridges. 
     The rake angle is preferably set between a positive rake angle of +5° and a negative rake angle of −5°. The advantage of the method described above is particularly apparent in the realization of a positive rake angle, which can be achieved easily and without problems using the method described above. 
     To realize an appropriate drill bit geometry, the pivot angle is between 30° and 60°, and is in particular approximately 50°. The angle of rotation is preferably between 60% and 90%, and is in particular approximately 80% of the final angle of rotation. This final angle of rotation is typically in a range between 90° and 140°. 
     To correctly grind the chisel edge, in one preferred variant the grinding wheel protrudes above the drill center at the beginning of the grinding process, so that the grinding wheel assumes an above-center grinding position. The drill bit and grinding wheel are then guided into a below-center grinding position, in which the grinding wheel ends before the drill center. The grinding of the clearance face, as well as pointing, can then be done in the below-center grinding position. 
     The advantages and the particular embodiments above with respect to the method can be transferred and applied as appropriate to the drill tip. 
     The above-discussed embodiments of the present invention will be described further hereinbelow. When the word “invention” is used in this specification, the word “invention” includes “inventions”, that is the plural of “invention”. By stating “invention”, the Applicant does not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintains that this application may include more than one patentably and non-obviously distinct invention. The Applicant hereby asserts that the disclosure of this application may include more than one invention, and, in the event that there is more than one invention, that these inventions may be patentable and non-obvious one with respect to the other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail below with reference to the exemplary embodiment illustrated in the accompanying schematic drawings, in which: 
         FIG. 1  depicts a drill bit ground according to a method of the prior art; 
         FIG. 2  depicts a drill bit ground according to a method taught by an embodiment of the invention; 
         FIG. 3  depicts a drill and grinding wheel in an initial position at the beginning of the grinding process, in a perspective view; 
         FIG. 4  depicts the drill and grinding wheel in a center position during the grinding process, also in a perspective view; 
         FIG. 5  depicts the drill and grinding wheel in an end position after the grinding process, also in a perspective view; 
         FIG. 6  is a side view of the drill and grinding wheel; 
         FIG. 7  is a side view of the drill and grinding wheel rotated by 90° in comparison with  FIG. 6 ; 
         FIG. 8  depicts a drill with replaceable drill bit; 
         FIG. 8A  shows the drill with the replaceable drill bit as shown in  FIG. 8 , with additional references; 
         FIG. 9  shows a view of one possible embodiment of a drill insert according to at least one possible embodiment of the present invention, which view is similar to that shown in  FIG. 2  with additional features; 
         FIG. 10  shows a box diagram of at least one possible embodiment of the present invention; 
         FIG. 11  shows another box diagram of at least one possible embodiment of the present invention, similar to that shown in  FIG. 10 ; and 
         FIG. 12  shows yet another box diagram of at least one possible embodiment of the present invention, which embodiment combines the features shown in  FIGS. 10 and 11  . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Equivalent parts in the figures are identified by the same reference numbers. 
     A drill bit  2  of a twist drill  3  that has been ground according to a method of the prior art ( FIG. 1 ) and one that has been ground according to a method taught by an embodiment of the invention ( FIG. 2 ) are contrasted in  FIGS. 1 and 2 . The drill bit  2  has two major cutting edges  4   a ,  4   b , which are joined together via a roughly S-shaped chisel edge  6 . The major cutting edges  4   a ,  4   b  and the chisel edge  6  are depicted in wider lines for purposes of illustration. The cutting edges formed by the major cutting edges  4   a ,  4   b  and chisel edge  6  extend over the entire drill bit  2 . The drill bit  2  is designed to have mirror symmetry. The drill bit  2  is explained below with reference to one of the two mirror-image sides, starting from the major cutting edge  4   a . Adjacent to it is a clearance face  7  that extends to a flute  8 . The flute  8  begins in the drill bit  2  and runs in a spiral pattern in the flute area  9  of the drill  3  adjacent to the drill bit  2 . The clearance face  7  adjacent to the major cutting edge  4  is designed essentially in the form of a conical surface. A surface referred to as the chisel edge surface  10  also extends from the chisel edge  6  to the flute  8 . The chisel edge surface  10  and clearance face  7  transition into each other. The chisel edge surface  10  is ground, in particular, during the pointing of the drill bit  2 . In this case, the angular relationship between this surface  10  and the longitudinal axis  14  of drill bit  2  is set. The corresponding angle is referred to as rake angle δ (cf. especially FIG.  7 ). 
     During a grinding process of the prior art, the grinding wheel is reset in a second process step for pointing and is brought close to the chisel edge surface  10 , especially in the area in which the chisel edge  6  transitions into the second major cutting edge  4   b . To prevent contact between the grinding wheel and the chisel edge  6  and the main cutting edge  4   b  that has already been ground, a certain safety spacing must be maintained relative to these two cutting edges ( 4   b ,  6 ). In the ground drill bit  2 , this separation is apparent in the fact that the chisel edge surface  10  has a sharp bend or ridge  16 . It extends into clearance face  7 . The clearance face is therefore bent at ridge  16  toward flute  8 . Undesirably high mechanical loads during drilling are exerted on this ridge  16 , especially in the area of the chisel edge surface  10 . 
     On account of the continuous three-dimensional grinding process according to the new grinding method, this ridge  16  is avoided in the drill bit  2  as shown in FIG.  2 . Instead, the chisel edge surface  10  makes a smooth transition into the clearance face  7 , and both extend to flute  8  without any sharp bends or ridges. It is also characteristic of the drill bit  2  that is ground according to the new method, in addition to the ridge-free profile, that the clearance face  7  is curved from the major cutting edge  4   a  to the flute  8  and has a radius of curvature R. This radius of curvature R is preferably between 0.05 and 0.5 times the drill diameter D. To illustrate the individual grinding areas, the clearance face  7  is divided into two differently shaded partial areas  7 A and  7 B, partial area  7 A essentially representing the curved portion of the clearance face  7 . The chisel edge surface  10  is also shown shaded as the third grinding area. All three grinding areas ( 10 ,  7 A,  7 B) are ground in a continuous grinding process and make smooth transitions into one another. The outer line  18  of the clearance face  7  running on the periphery of drill bit  2  forms with it in the area of the transition to flute  8  (projected on the longitudinal axis  14 ) a pivot angle α, which is preferably between 30° and 60° (for definition of pivot angle α, also see FIGS.  6  and  7 ). 
     The grinding method taught by an embodiment of the invention is also explained in greater detail below with reference to  FIGS. 3  to  5 , in which the relative position between a grinding wheel  20  and the drill bit  2  is shown in a perspective view and in different grinding positions. The relative movement between drill bit  2  and grinding wheel  20  is decisive for the three-dimensional grinding process described below. For the sake of simplicity, the grinding process is expressed either by movement of the drill bit  2  or by movement of the grinding wheel  20 . It goes without saying that the corresponding movement can also be reasonably carried out by the other part. For greater clarity, only sections of the grinding wheel  20  are shown and are shaded in  FIGS. 3  to  5 . 
     According to the initial position depicted in  FIG. 3 , the longitudinal axis  14  of drill bit  2  is aligned at an angle α′ to a center axis  22  of grinding wheel  20 , which is 90° at the beginning of grinding. The grinding wheel  20  has a ridge with a trapezoidal geometry, viewed in cross section, in which the one outside of the trapezoid is realized in the form of a main grinding surface  24  and the end surface adjacent to this side surface is realized in the form of a secondary grinding surface  26 . The main grinding surface  24  transitions into the secondary grinding surface  26  to form a curve. This curve essentially defines a rounded transition between chisel edge surface  10  and the clearance face  7 . The radial dimension of the main grinding wheel  26  is greater than the drill radius, so that it fully covers the clearance face  7 . This ring-shaped grinding element sits with its trapezoidal base surface on a disk-like support  28  and forms the grinding wheel  20  with it. The grinding wheel  20  is tightened by means of support  28  so that it rotates as necessary. 
     The longitudinal axis  14  is drawn through the tip of drill bit  2 , i.e., the drill center  27 . It can be seen in  FIG. 3  that the main grinding surface  24  protrudes above the drill center  27  in the area of the chisel edge  6 . The grinding wheel  20  is therefore set above-center at the beginning of the grinding process. During the grinding process, the drill  3  is then guided along an x-axis into a below-center position. The above-center initial position is used to grind the chisel edge  6 , which is held approximately perpendicular to the peripheral line  29  of the secondary grinding surface  26  at the beginning of the grinding process. The major cutting edge  4   a  is ground at the beginning of the grinding process. The drill is then rotated around the longitudinal axis  14  by an angle of rotation β, so that the clearance face  7  adjacent to the major cutting edge  4   a  is ground. The major cutting edge  4   a , as well as the clearance face  7 , slope outward from the drill center  27 . The major cutting edge  4   a  and a radial component of the clearance face  7  are therefore sloped at an angle ε to an imaginary cross sectional plane  34  of drill bit  2  (cf. also FIG.  6 ). In the vertical alignment of the longitudinal axis  14  to the center axis  22  this angle ε is determined by the trapezoidal angle ε between the main grinding surface  24  and the line perpendicular to the base surface of the trapezoid. 
     In addition to the rotational movement around the angle of rotation β and the initial displacement along the x-axis, the drill bit is advanced in the direction of the longitudinal axis  14  toward the grinding wheel  20 , so that the clearance face  7 , and indeed its tangential component, runs at an angle λ obliquely to the imaginary cross sectional plane  34  of drill  3 . The outside line  18  therefore curves obliquely in the direction toward flute  8 , starting from major cutting edge  4   a  (cf. FIG.  6 ). 
     In the center position as shown in  FIG. 4 , the drill bit  2  is situated relative to the grinding wheel  20  in a below-center grinding position, i.e., the chisel edge  6  lies next to the secondary grinding surface  26 . Its peripheral line  29  now runs roughly tangentially to the chisel edge  6 . The grinding process up to the depicted center position essentially corresponds to a conventional grinding process of the prior art. The new process is characterized by the fact that, starting from the center position, the drill bit  2  is pivoted relative to main grinding surface  24  on the one hand, and relative to secondary grinding surface  26  on the other hand. Pivoting relative to main grinding surface  24  occurs by pivot angle α around a main axis  30 , and pivoting relative to secondary grinding surface  26  occurs by rake angle δ around a secondary axis  32 , as can be gathered from  FIGS. 6 and 7 . By pivoting by pivot angle α, the angle α′ between the longitudinal axis  14  and center axis  22  connected to pivot angle α is reduced. This can be gathered from  FIG. 5 , from which it is apparent that the drill  3  is now aligned at all acute angle α′ relative to center axis  22 , after having been originally aligned perpendicular to center axis  22  at the beginning of the grinding process. 
       FIGS. 6 and 7  illustrate more clearly the pivoting movement that is carried out between the drill  3  and the grinding wheel  20  in the transition from the center position to the end position. The grinding wheel  20  is shown in a schematic side view, again only in sections and by a broken line for the sake of clarity.  FIG. 6  shows a side view, in which the direction of viewing is essentially perpendicular to the chisel edge  6 , and  FIG. 7  shows a side view in which the direction of viewing is approximately in the longitudinal direction of the chisel edge  6 . 
     It can be gathered from  FIG. 6  that the major cutting edge  4   a  runs at angle e to an imaginary cross sectional plane  34  of drill bit  2 . It can also be gathered that the peripheral line  18  of clearance face  7  runs initially obliquely at angle λ in the direction toward flute  8 , beginning from the major cutting edge  4   a , and then has a curvature with a radius of curvature R. To form this curve, the grinding wheel  20  is pivoted with its main grinding surface  24  around the main axis  30  by pivot angle α. This angle is defined as the angle between the longitudinal axis  14  and the tangential component of the main grinding surface  24 . 
     The grinding wheel  20  is preferably pivoted simultaneously around secondary axis  32  by the rake angle δ to form a rake angle in the area of chisel edge  6 . A positive rake angle δ of up to +5° is preferably set for chisel edge surface  10 . The chisel edge surface  10  is ground by means of the secondary grinding surface  26 , so that it forms a type of overhang, as can be gathered from FIG.  7 . The rake angle δ establishes the angle between the secondary grinding surface  26  and the longitudinal axis  14 . Because of the fixed angular relationship between the two grinding surfaces  24 ,  26 , the rake angle δ is determined by the alignment of the radial component of the main cutting surface  24  to the longitudinal axis  14 . 
     To summarize, the preferred grinding process can be broken down into the following steps: 
     1. Beginning of the grinding process in an above-center grinding position at an angle of rotation β, in which the longitudinal axis  14  is aligned perpendicular to the center axis  22  (starting position, FIG.  3 ). 
     2. Movement of the drill  3  into a below-center grinding position along the x-axis. At the same time, there is an advance in the direction of the longitudinal axis  14 , as well as a rotational movement around this axis up to an angle of rotation β of approximately 80% of the final rotation angle γ. There can simultaneously be a translation movement of the drill along a y-axis which runs perpendicular to the x-axis. The x-axis and the center axis  22  are parallel. (Center position, FIG.  4 ). Three movement components are therefore superimposed in the transition from the initial position to the center position. 
     3. Further rotation of the drill  3  to an end angle γ, so that the drill  3  executes a roughly 120° rotation, beginning from the starting position. At the same time, there is a further advance in the direction of the longitudinal axis  14 , as well as movement along the x-axis, and pivoting by pivot angle α, as well as by rake angle δ. A total of five movement components are therefore superimposed in the final working step until the end position is reached. 
     Pivoting by the rake angle δ as described in No. 3 above is optional here. The formation of a rake angle δ is determined by the application for which the drill  3  is intended. The method makes it possible to easily and very flexibly adjust the rake angle δ easily and very flexibly. The decisive advantage of the method is seen in the fact that the grinding process is conducted in a continuous method, and a second setting of the grinding wheel with the necessary ridge-like transitions in the area of clearance face  7  and chisel edge surface  10  connected with this can be eliminated. 
     The drill  3  is preferably designed in two parts as shown in  FIG. 8 and , for this purpose, has a drill base element  36 , having a recess  38  on its end, into which the correspondingly designed drill bit  2  can be inserted, and specifically so that it can be replaced as necessary. The drill bit  2  is secured in drill base element  36 , for example, by a clamping force exerted by two arms  40 . As an alternative, or in addition, the drill bit  2  can be fixed in the base element  36  by a locking device (not shown). The flute  8  running in the drill base element  36  extends into the drill bit  2 . This configuration, with a replaceable drill bit  2 , makes it possible to keep the operating costs for the drilling tools low, because the component that is exposed to the highest mechanical loads is realized in the form of a replaceable part. 
       FIG. 8A  shows the drill with the insert as shown in  FIG. 8 , with additional references. Specifically, the edges  101  and  107  of the flute portion of the drill bit insert are indicated. 
       FIG. 9  shows a view of one possible embodiment of a drill insert according to at least one possible embodiment of the present invention. The drill insert has similar features as the drill tip shown in FIG.  2 .  FIG. 9  shows an additional partial area of  FIG. 7 , designated as area  7 C. Areas  7 A and  7 C are both relatively flat surfaces. A rounded transition section  103  between areas  7 A and  7 C is illustrated. The rounded section  103  extends up to the chisel edge  6 . Another rounded transition section  105  between areas  7 B and  7 C is also illustrated. This rounded section  105  also extends up to the chisel edge. In the embodiment shown in  FIG. 9 , area  7 B has a slightly curved surface that curves upward to the major cutting edge  4 A. The radius of curvature R 2  is substantially smaller than the radius of curvature R 1  shown in FIG.  2 .  FIG. 9  also shows the flute edges  101  and  107  shown in FIG.  8 A. 
       FIG. 10  shows a box diagram of at least one possible embodiment of the present invention. The drill bit  2  and the grinding wheel  20  are represented. In this particular embodiment, the drill bit  2  is mounted in or connected to a numerical control device  201  which controls the three-dimensional movement of the drill bit  2  during the grinding process. The numerical control device  201  moves the drill bit  2  into and out of engagement with the grinding wheel  20  in order to grind the different surfaces and curves, such as areas  7 A and  7 B and curve  103 , to achieve the desired shape of the drill bit  2 . A computer  203  is utilized to program and control the numerical control device  201  to execute a particular series of movements to properly grind the drill bit  2 . The grinding wheel  20  is mounted in a stationary manner in this particular embodiment. 
       FIG. 11  shows another box diagram of at least one possible embodiment of the present invention, similar to that shown in FIG.  10 . However, in this embodiment, the grinding wheel  20  is mounted in or connected to a numerical control device  205  which controls the three-dimensional movement of the grinding wheel  20  during the grinding process. The numerical control device  205  moves the grinding wheel into and out of engagement with the drill bit  2  in order to grind the different surfaces and curves, such as areas  7 A and  7 B and curve  103 , to achieve the desired shape of the drill bit  2 . The computer  203  is utilized to program and control the numerical control device  205  to execute a particular series of movements to properly grind the drill bit  2 . The drill bit  2  is mounted in a stationary manner in this particular embodiment. 
       FIG. 12  shows yet another box diagram of at least one possible embodiment of the present invention, which embodiment combines the features shown in  FIGS. 10 and 11 . In this embodiment, both the drill bit  2  and the grinding wheel  20  are each mounted in or connected to their respective numerical control devices  201 ,  205 , which control the three-dimensional movement of the drill bit and the grinding wheel  20  during the grinding process. The numerical control devices  201 ,  205  move the drill bit and the grinding wheel into and out of engagement with each other in order to grind the different surfaces and curves, such as areas  7 A and  7 B and curve  103 , to achieve the desired shape of the drill bit  2 . The computer  203  is utilized to program and control the numerical control devices  201 ,  205  to execute a particular series of movements to properly grind the drill bit  2 . 
     One feature of the invention resides broadly in a drill bit  2 , having two major cutting edges  4   a ,  4   b  joined together via a chisel edge  6 , adjacent to each of which is a clearance face  7  that transitions into a flute  8 , characterized by the fact that the clearance face  7  is realized in the form of a surface with a radius of curvature R that is curved without ridges from the major cutting edge  4   a ,  4   b  toward the flute  8 . 
     Another feature of the invention resides broadly in a drill bit  2 , characterized by the fact that the radius of curvature R is between 0.05 and 0.5 times the drill diameter D. 
     Yet another feature of the invention resides broadly in a drill bit  2 , characterized by the fact that the clearance face  7  forms a pivot angle α at the transition to flute  8  with longitudinal axis  14  that is between approximately 30° and 60°, and is in particular approximately 50°. 
     Still another feature of the invention resides broadly in drill bit  2  characterized by the fact that a pointing having a rake angle δ that is between +5° and −5°, is made in the vicinity of the chisel edge  6 . 
     A further feature of the invention resides broadly in the drill bit  2 , characterized by the fact that it is realized in the form of a replaceable insert for a drill base element  36 . 
     Another feature of the invention resides broadly in a method for grinding of a drill bit  2  that has two major cutting edges  4   a ,  4   b  connected via a chisel ridge  6 , adjacent to each of which is a clearance face  7  that transitions into a flute  8 , characterized by the fact that a grinding wheel  20  and the drill bit  2  are brought together in a continuous grinding process, that the clearance face  7  is realized in the form of a surface that has a radius of curvature R curved from the major cutting edge  4   a ,  4   b  in the direction toward flute  8 . 
     Yet another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the radius of curvature R is between 0.05 and 0.5 times the drill diameter D. 
     Still another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that a main grinding surface  24  of grinding wheel  20  and the drill bit  2  are pivoted to form the curved surface relative to each other around a pivot angle α. 
     A further feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the drill bit  2  is initially rotated around its longitudinal axis  14  to an angle of rotation β, and pivoting around pivot angle α then occurs. 
     Another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that during the pivoting of drill bit  2  around its longitudinal axis  14 , it is further rotated up to a final angle of rotation γ. 
     Yet another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that a secondary grinding surface  26  of the grinding wheel  20  and the drill bit  2  are pivoted relative to each other around a rake angle δ for pointing of the drill bit  2  in the area of the chisel edge  6 . 
     Another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the pivoting movements by the pivot angle α and by the rake angle δ are superimposed. 
     Yet another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the rake angle δ is between +5° and −5°. 
     Still another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the pivot angle α is between 30° and 60°, and in particular is approximately 50°. 
     A further feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that the angle of rotation β is between 60% and 90%, and in particular approximately 80% of the final angle of rotation γ. 
     Another feature of the invention resides broadly in a method for grinding of a drill bit  2 , characterized by the fact that at the beginning of the grinding process, the grinding wheel  20  protrudes above the drill center  27 , so that an above-center grinding position is present, and that the drill bit  2  and grinding wheel  20  are then guided into a below-center grinding position, in which the grinding wheel ends in front of the drill center. 
     The components disclosed in the various publications, disclosed or incorporated by reference herein, may be used in the embodiments of the present invention, as well as equivalents thereof. 
     The appended drawings in their entirety, including all dimensions, proportions and/or shapes in at least one embodiment of the invention, are accurate and are hereby included by reference into this specification. 
     All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if more than one embodiment is described herein. 
     All of the patents, patent applications and publications recited herein, and in the Declaration attached hereto, are hereby incorporated by reference as if set forth in their entirety herein. 
     All of the patents, patent applications or patent publications, which were cited in the German Office Action dated Aug. 29, 2000, and the International Search Report dated Mar. 22, 2001, and/or cited elsewhere are hereby incorporated by reference as if set forth in their entirety herein as follows: DE 21 54 924 B2; DE-AS 15 02 529; DE 28 51 183 C2; U.S. Pat. No. 5,273,380; EP 0 333 651; and EP 0 127 322. 
     The corresponding foreign and international patent publication applications, namely, Federal Republic of Germany Patent Application No. 199 55 172.3, filed on Nov. 16, 1999, having inventors Bernhard BORSCHERT and Dieter MUEHLFRIEDEL, and DE-OS 199 55 172.3 and DE-PS 199 55 172.3, and International Application No. PCT/EP00/11174, filed on Nov. 11, 2000, having WIPO Publication No. WO01/36134 and inventors Bernhard BORSCHERT and Dieter MUEHLFRIEDEL, as well as their published equivalents, and other equivalents or corresponding applications, if any, in corresponding cases in the Federal Republic of Germany and elsewhere, and the references and documents cited in any of the documents cited herein, such as the patents, patent applications and publications, are hereby incorporated by reference as if set forth in their entirety herein. 
     All of the references and documents, cited in any of the documents cited herein, are hereby incorporated by reference as if set forth in their entirety herein. All of the documents cited herein, referred to in the immediately preceding sentence, include all of the patents, patent applications and publications cited anywhere in the present application. 
     The details in the patents, patent applications and publications may be considered to be incorporable, at applicant&#39;s option, into the claims during prosecution as further limitations in the claims to patentably distinguish any amended claims from any applied prior art. 
     Some examples of drills and/or drill bits that may possibly be utilized or adapted for use in at least one possible embodiment of the present invention may be found in the following U.S. Pat. No. 6,220,117 B1, issued to Butcher on Apr. 24, 2001; U.S. Pat. No. 5,740,872, issued to Smith on Apr. 21, 1998; U.S. Pat. No. 5,725,313, issued to Singh et al. on Mar. 10, 1998; U.S. Pat. No. 5,421,425, issued to Griffin on Jun. 6, 1995; U.S. Pat. No. 4,506,432, issued to Smith on Mar. 26, 1985; U.S. Pat. No. 4,169,637, issued to Voitas on Oct. 2, 1979; U.S. Pat. No. 4,087,137, issued to Voitas on May 2, 1978; U.S. Pat. No. 6,220,117 B1, issued to Butcher on Apr. 24, 2001; U.S. Pat. No. 4,971,485, issued to Nomura et al. on Nov. 20, 1990; U.S. Pat. No. 6,135,218, issued to Deane et al. on Oct. 24, 2000; U.S. Pat. No. 6,029,544, issued to Katayama on Feb. 29, 2000; U.S. Pat. No. 5,979,571, issued to Scott et al. on Nov. 9, 1999; U.S. Pat. No. 5,836,409, issued to Vail, III on Nov. 17, 1998; U.S. Pat. No. 4,241,483, issued to Voitas on Dec. 30, 1980; U.S. Pat. No. 4,200,159, issued to Peschel et al. on Apr. 29, 1980; U.S. Pat. No. 4,169,637, issued to Voitas on Oct. 2, 1979; U.S. Pat. No. 5,882,152, issued to Janitzki on Mar. 16, 1999; U.S. Pat. No. 4,211,294, issued to Multakh on Jul. 8, 1980; U.S. Pat. No. 6,241,036 B1, issued to Lovato et al. on Jun. 5, 2001; U.S. Pat. No. 5,743,346, issued to Flood et al. on Apr. 28, 1998; U.S. Pat. No. 5,154,550, issued to Isobe et al. on Oct. 13, 1992; and U.S. Pat. No. 4,720,371, issued to Shirley on Jan. 19, 1988. 
     Some examples of milling cutters that may possibly be utilized or adapted for use in at least one possible embodiment of the present invention may be found in the following U.S. Pat. No. 6,231,281 B1, issued to Nishikawa on May 15, 2001; U.S. Pat. No. 6,220,795 B1, issued to Matthews on Apr. 24, 2001; U.S. Pat. No. 6,217,262 B1, issued to Wright on Apr. 17, 2001; U.S. Pat. No. 6,176,648 B1, issued to Mizutani on Jan. 23, 2001; U.S. Pat. No. 6,158,927, issued to Cole et al. on Dec. 12, 2000; U.S. Pat. No. 6,146,059, issued to Rohr on Nov. 14, 2000; U.S. Pat. No. 6,109,838, issued to Rivière on Aug. 29, 2000; U.S. Pat. No. 6,042,308, issued to Schmitt on Mar. 28, 2000; U.S. Pat. No. 5,967,706, issued to Hughes, Jr. on Oct. 19, 1999; U.S. Pat. No. 5,957,628, issued to Bentjens et al. on Sep. 28, 1999; U.S. Pat. No. 5,934,842, issued to Gupta on Aug. 10, 1999; U.S. Pat. No. 5,919,008, issued to Shimomura on Jul. 6, 1999; U.S. Pat. No. 5,899,642, issued to Berglöw et al. on May 4, 1999; U.S. Pat. No. 5,868,529, issued to Rothballer et al. on Feb. 9, 1999; U.S. Pat. No. 5,848,858, issued to Jager et al. on Dec. 15, 1998; U.S. Pat. No. 5,820,308, issued to Hoefler on Oct. 13, 1998; U.S. Pat. No. 5,762,452, issued to Mina on Jun. 9, 1998; U.S. Pat. No. 5,672,031, issued to Oles on Sep. 30, 1997; U.S. Pat. No. 5,542,795, issued to Mitchell on Aug. 6, 1996; U.S. Pat. No. 5,542,794, issued to Smith et al. on Aug. 6, 1996; U.S. Pat. No. 5,529,439, issued to Werner et al. on Jun. 25, 1996; U.S. Pat. No. 4,990,035, issued to Scheuch et al. on Feb. 5, 1991; U.S. Pat. No. 4,938,638, issued to Hessman et al. on Jul. 3, 1990; U.S. Pat. No. 4,930,949, issued to Giessler on Jun. 5, 1990; U.S. Pat. No. 4,848,978, issued to Keritsis on Jul. 18, 1989; U.S. Pat. No. 4,799,838, issued to Kubo et al. on Jan. 24, 1989; U.S. Pat. No. 4,789,273, issued to Wiacek et al. on Dec. 6, 1988; U.S. Pat. No. 4,729,697, issued to Lacey on Mar. 8, 1988; U.S. Pat. No. 4,728,228, issued to Okunishi et al. on Mar. 1, 1988; U.S. Pat. No. 4,627,771, issued to Kieninger on Dec. 9, 1986; U.S. Pat. No. 4,623,284, issued to Greiff on Nov. 18, 1986; U.S. Pat. No. 4,533,282, issued to Lindlar et al. on Aug. 6, 1985; U.S. Pat. No. 4,519,731, issued to Jester et al. on May 28, 1985; U.S. Pat. No. 4,493,594, issued to Okada on Jan. 15, 1985; U.S. Pat. No. 4,461,602, issued to Zettl on Jul. 24, 1984; U.S. Pat. No. 4,359,299, issued to Sagarian on Nov. 16, 1982; U.S. Pat. No. 4,204,787, issued to McCray et al. on May 27, 1980; U.S. Pat. No. 4,097,174, issued to Heinlein on Jun. 27, 1978; U.S. Pat. No. 4,093,392, issued to Hopkins on Jun. 6, 1978; U.S. Pat. No. 4,061,076, issued to Robertson on Dec. 6, 1977; U.S. Pat. No. 4,050,129, issued to Jester et al. on Sep. 27, 1977; and U.S. Pat. No. 4,050,128, issued to Lange on Sep. 27, 1977. 
     Some examples of grinding devices or grinding methods for use in grinding drills which may possibly be used in at least one possible embodiment of the present invention may possibly be found in the following U.S. Pat. No. 6,071,047 entitled “Method and apparatus for feeding coolant liquid and separating and recovering it in cutting machine and grinding machine”; U.S. Pat. No. 5,735,732 entitled “Precision drill sharpener and grinding wheel assembly therefor”; U.S. Pat. No. 5,649,853 entitled “Drill bit grinding machine”; U.S. Pat. No. 5,311,703 entitled “Multiple purpose tool grinding device”; U.S. Pat. No. 5,263,286 entitled “Drill and drill grinding method and apparatus”; U.S. Pat. No. 5,231,802 entitled “Drill and drill grinding method and apparatus”; U.S. Pat. No. 5,210,977 entitled “Drill grinding device”; U.S. Pat. No. 5,181,811 entitled “Drill and drill grinding method and apparatus”; U.S. Pat. No. 5,179,809 entitled “Drill grinding machine”; U.S. Pat. No. 5,125,186 entitled “Drill grinding machine”; U.S. Pat. No. 5,090,159 entitled “Multi-purpose grinder”; U.S. Pat. No. 4,858,389 entitled “Apparatus for grinding twist drills”; U.S. Pat. No. 4,680,896 entitled “Tool unloading mechanism for automatic tool grinding machine”; U.S. Pat. No. 4,642,942 entitled “Method and apparatus for grinding the tip of a twist drill”; U.S. Pat. No. 4,608,643 entitled “Automatic tool grinding machine with computerized control”; U.S. Pat. No. 4,590,711 entitled “Semi-automatic grinding machine”; U.S. Pat. No. 4,574,529 entitled “Apparatus for grinding twist drills”; U.S. Pat. No. 4,574,528 entitled “Apparatus for grinding twist drills”; U.S. Pat. No. 4,468,891 entitled “Machine for point grinding drills”; U.S. Pat. No. 4,365,444 entitled “Drill point grinding machine”; U.S. Pat. No. 4,148,161 entitled “Loading unit for an automatic bur grinding machine”; U.S. Pat. No. 4,142,332 entitled “Drill grinding fixture”; U.S. Pat. No. 4,106,242 entitled “Workhead for an automatic bur grinding machine”; U.S. Pat. No. 4,078,457 entitled “Method of grinding concave raking surfaces of blade of circular saw”; U.S. Pat. No. 4,052,821 entitled “Automatic bur grinding machine”; U.S. Pat. No. 4,023,552 entitled “Method of dressing the grinding wheel in a sharpener for twist drills”; U.S. Pat. No. 4,016,680 entitled “Sharpener for twist drills including grinding wheel dressing means”; and U.S. Pat. No. 3,952,616 entitled “Adjustable grinding apparatus”. 
     Some examples of numerical control systems or devices which may possibly be used or adapted for use in at least one possible embodiment of the present invention may possibly be found in the following U.S. Pat. No. 6,384,560 entitled “Abnormality detection apparatus for tool and numerical control apparatus provided with same”; U.S. Pat. No. 6,344,724 entitled “Numerical control apparatus for NC machine tool”; U.S. Pat. No. 6,256,546 entitled “System and method for numerical control processing of an in-processing part”; U.S. Pat. No. 6,232,736 entitled “Numerical control machine tool positioning system”; U.S. Pat. No. 6,107,768 entitled “Numerical control apparatus for a machine tool”; U.S. Pat. No. 6,101,444 entitled “Numerical control unit for wellbore drilling”; U.S. Pat. No. 6,036,347 entitled “Numerical control information generator for controlling machine tool processes which require tool exchanges”; U.S. Pat. No. 5,944,079 entitled “Numerical control router enclosed by a housing”; U.S. Pat. No. 5,815,400 entitled “Machining method using numerical control apparatus”; U.S. Pat. No. 5,608,641 entitled “Method and apparatus for simplifying the task of retrieving and accessing a segment of a numerical control (NC) program”; U.S. Pat. No. 5,603,149 entitled “Table replacement apparatus in a numerical control router”; U.S. Pat. No. 5,532,932 entitled “Numerical control unit”; U.S. Pat. No. 5,493,502 entitled “Numerical control unit for controlling a machine tool to machine a workpiece at an instructed feed rate along linear and rotational axes”; U.S. Pat. No. 5,493,193 entitled “Numerical control apparatus and numerical control method”; U.S. Pat. No. 5,486,746 entitled “Positioning rule stopper apparatus in a numerical control router”; U.S. Pat. No. 5,465,215 entitled “Numerical control method and apparatus”; U.S. Pat. No. 5,323,821 entitled “Suction table apparatus of a numerical control router”; U.S. Pat. No. 5,310,397 entitled “Computerized numerical control automatic complex lathe”; U.S. Pat. No. 5,270,915 entitled “Apparatus for generating numerical control information based on shaped data for each machining step”; U.S. Pat. No. 5,255,201 entitled “Numerical control information generating apparatus”; U.S. Pat. No. 5,255,200 entitled “Numerical control information generating system”; U.S. Pat. No. 5,245,544 entitled “Method for determining inner diameter machining method in numerical control information generating function”; U.S. Pat. No. 4,978,901 entitled “Machining data forming system for numerical control device”; U.S. Pat. No. 4,972,322 entitled “Method for preparing numerical control data for a machine tool”; U.S. Pat. No. 4,914,364 entitled “Numerical control apparatus”; U.S. Pat. No. 4,902,950 entitled “Numerical control method with response delay compensating function”; U.S. Pat. No. 4,862,380 entitled “Numerical control unit”; U.S. Pat. No. 4,831,906 entitled “Numerical control machine”; U.S. Pat. No. 4,794,311 entitled “Numerical control system”; U.S. Pat. No. 4,788,481 entitled “Numerical control apparatus”; U.S. Pat. No. 4,751,652 entitled “Numerical control drilling restart control system”; U.S. Pat. No. 4,719,579 entitled “Numerical control method”; U.S. Pat. No. 4,706,373 entitled “Numerical-control machining center for structural sections”; U.S. Pat. No. 4,667,294 entitled “Numerical control apparatus”; U.S. Pat. No. 4,636,938 entitled “Method and apparatus for producing numerical control programs”; U.S. Pat. No. 4,624,607 entitled “Computed numerical control drilling machine”; U.S. Pat. No. 4,617,635 entitled “Numerical control machining system”; U.S. Pat. No. 4,606,001 entitled “Customized canned cycles for computer numerical control system”; U.S. Pat. No. 4,604,705 entitled “Numerical control machining method and system therefor”; U.S. Pat. No. 4,591,771 entitled “Numerical control system”; U.S. Pat. No. 4,588,339 entitled “Tool holder for a cutting machine provided with numerical control”; U.S. Pat. No. 4,549,270 entitled “Method of controlling selection of tools in a quadriaxial numerical control lathe”; U.S. Pat. No. 4,547,854 entitled “Method of controlling lineup of tools in numerical control machine tool”; U.S. Pat. No. 4,484,286 entitled “Numerical control system”; U.S. Pat. No. 4,255,991 entitled “Method and apparatus for electromechanically retrofitting a conventional automatic screw machine to accept numerical control”; U.S. Pat. No. 4,199,814 entitled “Computer numerical control machine tool”; and U.S. Pat. No. 4,149,235 entitled “Computer numerical control system for machine tool”. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 AT LEAST PARTIAL LIST OF REFERENCE NUMBERS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  2 
                 Drill bit 
               
               
                   
                  4a, 4b 
                 Major cutting edges 
               
               
                   
                  6 
                 Chisel edge 
               
               
                   
                  7 
                 Clearance face 
               
               
                   
                  8 
                 Flute 
               
               
                   
                 10 
                 Surface 
               
               
                   
                  9 
                 Flute area 
               
               
                   
                 14 
                 Longitudinal axis 
               
               
                   
                 16 
                 Edge 
               
               
                   
                 18 
                 Outside line 
               
               
                   
                 20 
                 Grinding wheel 
               
               
                   
                 22 
                 Center axis 
               
               
                   
                 24 
                 Main grinding surface 
               
               
                   
                 26 
                 Secondary grinding surface 
               
               
                   
                 27 
                 Drill center 
               
               
                   
                 28 
                 Support 
               
               
                   
                 29 
                 Peripheral line 
               
               
                   
                 30 
                 Main axis 
               
               
                   
                 32 
                 Secondary axis 
               
               
                   
                 34 
                 Cross sectional plane 
               
               
                   
                 36 
                 Base element 
               
               
                   
                 38 
                 Recess