Abstract:
A drill configured for drilling ductile materials includes a drill margin with a margin extremity adjacent to a relief surface. The drill includes a drill body and a drill head secured to the drill body via rotational coupling of the drill head on the drill body.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter of the present application relates to drill margins, in particular drill margins of drills and drill heads configured for drilling ductile materials such as low carbon steel and alloy steel. 
       BACKGROUND OF THE INVENTION 
       [0002]    One measurement of drilling quality is the finish provided to workpiece. Providing a high-quality finish on ductile materials, such as low carbon steel or alloy steel, can be particularly challenging, and improved finish is often a desired result. 
         [0003]    U.S. Pat. No. 8,419,322 discloses tool for use in a preformed round hole. More precisely it discloses a cutting insert with a minor edge cutting flank adjoining a minor cutting edge against a direction of rotation, and comprising a support element arranged at a distance from the major cutting edge against a feed direction. The support element has a radius of revolution larger than a pitch circle radius of the cutting insert, during a drilling operation. The support element is mentioned as being able to provide both a supporting function and a smoothing function. 
         [0004]    It is an object of the present application to provide a new and improved drill or drill head. 
       SUMMARY OF THE INVENTION 
       [0005]    The subject matter of the present application is applicable to drills and drill heads configured for creating and/or deepening preformed holes. Notably, drills of the present application are configured for only axially machining (i.e. drilling) and are not configured for machining in a non-axial direction (e.g. shouldering, ramping). More specifically, drills according to the present application are configured only for drilling holes of diameter corresponding to a cutting diameter of the tool. Nonetheless, the term “drill” is inclusive of drills configured to rotate and static drills configured to be static while a work piece is rotated. 
         [0006]    In accordance with a first aspect of the subject matter of the present application, there is provided a drill or drill head having a central axis A C  defining a front-to-rear direction and comprising: a plurality of cutting portions; each cutting portion comprising: a rake surface; a relief surface; a cutting edge formed at an intersection of the rake and relief surfaces and extending rearwardly to a cutting edge extremity defining a cutting diameter of the drill; and a margin extending rearwardly from the relief surface and also extending from the rake surface; wherein each margin comprises a margin extremity adjacent to the relief surface and located outside of the cutting diameter. 
         [0007]    The margin, and more particularly the margin extremity, has been found to provide a burnishing function, and test results received thus far have surprisingly found that longevity of a drill or drill head with such margin extremity is apparently increased over comparative tools. 
         [0008]    It will be understood that a drill or drill head with the above geometry, prior to the present discovery, was expected to shatter upon compression in a hole being drilled. It was theorized and testing has surprisingly confirmed that at least when drilling low carbon steel or alloy steel (believed to be due to the ductility thereof) such geometry is not adversely affected. 
         [0009]    In accordance with another aspect of the subject matter of the present application, there is provided a drill or drill head comprising a cutting portion; the cutting portion comprising a drill margin; the drill margin comprising a margin extremity adjacent to a relief surface and located outside of a cutting diameter. 
         [0010]    It will be understood that the above is a summary, and that any of the aspects above may further comprise any of the features described hereinbelow. Specifically, the following features, either alone or in combination, may be applicable to any of the above aspects:
       A. A drill or drill head can have a central axis A C  defining a front-to-rear direction. A drill or drill head can by rotationally symmetric about the central axis A C . Cutting edge extremities of a drill or drill head can be equally circumferentially spaced about the central axis A C . Margins of a drill or drill head can be equally circumferentially spaced about the central axis A C .   B. A drill or drill head can comprise a plurality of cutting portions.   C. A cutting portion can comprise a rake surface, a relief surface, and a cutting edge formed at an intersection of the rake and relief surfaces.   D. A cutting edge can extend rearwardly to a cutting edge extremity defining a cutting diameter of the drill or drill head. A cutting edge can be configured for drilling ductile materials such as low carbon steel and alloy steel. A cutting edge can have a rake angle θ, at a cutting edge extremity, of twenty to thirty degrees (20°≦θ≦30°).   E. A cutting portion can comprise a margin extending rearwardly from a relief surface and also extending from a rake surface.   F. A margin can comprise a margin extremity adjacent to a relief surface and located outside of the cutting diameter. Stated differently, a margin extremity is located further from a central axis A C  than a cutting edge extremity. Stated differently yet, a margin extremity constitutes a furthermost point from the central axis A C .   G. A margin can extend outside of a cutting diameter beginning from a cutting edge extremity. A margin can extend outside of the cutting diameter beginning from the cutting edge extremity, and continuously increase distance from the cutting diameter until a margin extremity. The continuous increase in distance can be at a decreasing rate (i.e. having a convexly-curved shape in a top view thereof).   H. A cutting portion can comprise a margin edge extending along an intersection of a margin and a rake surface. A margin, at each axial location along the margin edge, can comprise an extremity extending outside of a cutting diameter. A margin, at each axial location along the margin edge, can extend outside of the cutting diameter beginning from the margin edge. A margin, at each axial location along the margin edge, can continuously increase distance from the cutting diameter until an extremity. The continuous increase in distance can be at a decreasing rate (i.e. having a convexly-curved shape in a top view thereof).   I. A margin extremity can extend outside of a cutting diameter by a protrusion distance D P  of at least one micron (D P ≧0.001 mm) For drills with a cutting diameter D C  of eight to nineteen millimeters (8 mm≦D C ≦19 mm), a preferred tested protrusion distance D P  was two to eight microns (0.002 mm≦D P ≦0.008 mm) outside of the cutting diameter D C . For drills with a cutting diameter D C  of twenty to twenty five millimeters (20 mm≦D C ≦25 mm) a preferred tested protrusion distance D P  was three to ten microns (0.003 mm≦D P ≦0.010 mm) outside of the cutting diameter D C . For drills with a cutting diameter D C  of less than eight millimeters, a preferred protrusion distance D P  may be one to six microns (0.001 mm≦D P ≦0.006 mm). For drills with a cutting diameter D C  greater than twenty five millimeters, a preferred protrusion distance D P  may be four to twelve microns (0.004 mm≦D P ≦0.012 mm). A preferred range of protrusion distances D P  would be one to twelve microns (0.001 mm≦D P ≦0.012 mm). A most preferred tested range of protrusion distances D P  is two to ten microns (0.002 mm≦D P ≦0.010 mm). Notwithstanding the above-said, it is also noted that a margin extremity extending outside of a cutting diameter by a protrusion distance D P  of at least two microns (D P ≧0.002 mm) has found to have better performance than at least one micron (D P ≧0.001 mm). A margin, at each axial location, can comprise an extremity extending outside of the cutting diameter by a protrusion distance D P  corresponding to the values above mentioned in connection with the margin extremity.   J. An entire margin can be located outside of the cutting diameter.   K. A margin can extend an axial distance no greater than 0.1 mm from a relief surface, preferably no greater than 0.01 mm from the relief surface.   L. A margin can comprise a margin portion. The margin portion can be the only portion of the margin comprising an extremity located outside of the cutting diameter. The margin portion can extend an axial distance no greater than 0.1 mm from a relief surface, preferably no greater than 0.01 mm from the relief surface.   M. Each cutting portion or margin of a drill or drill head (i.e. all cutting portions or all margins) can have one or more of the features detailed above.   N. A margin width W M  measured from the cutting edge extremity  24  to the flank surface  42  can be between 5% to 10% of the cutting diameter D C  (0.05 D C ≦W M ≦0.10 D C ). With a range of 6%±1% having been successfully tested.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    For a better understanding of the subject matter of the present application, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which: 
           [0026]      FIG. 1A  is a side view of a drill in accordance with an embodiment of the subject matter of the present application; 
           [0027]      FIG. 1B  is a front end view or top view of the drill in  FIG. 1A ; 
           [0028]      FIG. 2A  is a perspective side view of a drill head of the drill in  FIGS. 1A and 1B ; 
           [0029]      FIG. 2B  is a first side view of the drill head in  FIG. 2A ; 
           [0030]      FIG. 2C  is a second side view of the drill head in  FIG. 2A , rotated 90° from the view shown in  FIG. 2B ; 
           [0031]      FIG. 3  is an enlarged view of the encircled portion of the drill head in  FIG. 2C ; 
           [0032]      FIG. 4  is a front end view or top view of the drill head shown in  FIG. 2A ; 
           [0033]      FIG. 5A  is a schematic view of a prior art design, which could be found in a region of a prior art tool corresponding to the region encircled in  FIG. 4 ; 
           [0034]      FIG. 5B  is a schematic view of another prior art design, which could be found in a region of a prior art tool corresponding to the region encircled in  FIG. 4 ; and 
           [0035]      FIG. 5C  is a schematic view of the region encircled in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Reference is made to  FIGS. 1A and 1B , illustrating a drill  10  according to the subject matter of the present application. 
         [0037]    The drill  10  can comprise a drill body  12  and a drill head  14  configured to be mounted to the drill body  12 . 
         [0038]    The drill  10  is for metal cutting operations and the drill head  14  is typically made of extremely hard and wear-resistant material such as cemented carbide, either by form-pressing and then sintering carbide powders in a binder or by powder injection molding methods. 
         [0039]    A central axis A C , about which the drill  10  is configured to rotate in a rotation direction D R , extends through the center of the drill body  12  and drill head  14  and can define a front-to-rear direction D FR . 
         [0040]    Referring now to  FIGS. 2A to 2C , the drill head  14  comprises a plurality of cutting portions  16  located rearward of a chisel  17  of the drill head  14 . 
         [0041]    Each cutting portion  16  comprises a rake surface  18 , a relief surface  20  and a cutting edge  22  formed at an intersection of the rake and relief surfaces  18 ,  20 . 
         [0042]    Referring also to  FIG. 4 , the cutting edge  22  can extend rearwardly from the chisel  17  to a cutting edge extremity  24  which defines a cutting diameter D C . It will be understood from the drawings that use of the words “rearward” or “rearwardly” is not to be construed as strictly parallel with central axis A C  in the front-to-rear direction D FR . 
         [0043]    The rake surface  16  is configured for chips (not shown) from a workpiece (not shown) to flow thereover. 
         [0044]    In  FIG. 2B  a rake angle θ is shown, schematically, at the cutting edge extremity  24 . 
         [0045]    The relief surface  18  can form an internal acute angle β, shown schematically, with the rake surface  16  to provide relief during drilling. 
         [0046]    In this non-limiting example, the cutting edge  22  can comprise two cutting edge portions. For example the cutting edge  22  can comprise a minor cutting edge portion  22 A extending rearwardly from the chisel  17 , and a major cutting edge portion  22 B extending from the minor cutting edge portion  22 A to the cutting edge extremity  24 . The minor cutting edge portion  22 A is also shown to extend radially, whereas the major cutting edge portion  22 B can form an internal obtuse angle α therewith. In any case, the minor cutting edge portions  22 A are preferably one third to one quarter of the length of the major cutting edges  22 B. 
         [0047]    The drill head  14  comprises a plurality of margins  26 . The margins  26  are identical (as are the cutting portions  16 ) and therefore further reference will only be made to one of the margins  26 . 
         [0048]    Regarding rotational symmetry, with specific reference to  FIG. 4 , it is noted that each cutting edge extremity  24  and/or each margin  26  of the drill head are equally circumferentially spaced (S A =S B ) about the central axis A C , for reducing an imbalance of forces when the margins  26  abut an inner surface of a hole (not shown). 
         [0049]    Referring also to  FIGS. 4 and 5C , the margin  26 , at least adjacent to the relief surface  20 , comprises a margin extremity  28  located outside of the cutting diameter D C  which constitutes a furthermost point of the margin  26  from the central axis A C . 
         [0050]    Drawing attention to  FIGS. 5A and 5B , prior art constructions are shown for aiding understanding of the subject matter of the present application. Each prior art drill  10 A,  10 B comprises a cutting diameter D CA , D CB , a cutting edge extremity  24 A,  24 B, a margin  26 A,  26 B and a margin extremity  28 A,  28 B. The prior art drill  10 A in  FIG. 5A  is designed for the margin  26 A thereof to extend along the cutting diameter D CA , and consequently the margin extremity  28 A thereof also coincides with the cutting diameter D CA . The prior art drill  10 B in  FIG. 5B  is designed for the margin  26 B thereof to extend within the cutting diameter D CB , and consequently the margin extremity  28 B thereof is located within the cutting diameter D CB . 
         [0051]    Referring only to  FIG. 5C , the margin  26  can extend outside of the cutting diameter D C  from beginning from a cutting edge extremity  24 . To elaborate, at a point (schematically shown by the reference numeral “ 30 ”) which is adjacent to the cutting extremity  24 , the margin is already outside of the cutting diameter D C . 
         [0052]    The margin  26 , particularly the margin extremity  28 , can extend a protrusion distance D P  of at least one micron (0.001 mm≦D P ) outside of the cutting diameter D C . 
         [0053]    Extensive testing has found that a larger protrusion distance D P  range, at least for specific cutting diameters D C , are preferred. To elaborate, recent testing has found that for drills with a cutting diameter D C  of eight to nineteen millimeters (8 mm≦D C ≦19 mm), a superior performance was found with a protrusion distance D P  of two to eight microns (0.002 mm≦D P ≦0.008 mm) outside of the cutting diameter D C . Similarly, it was found that for drills with a cutting diameter D C  of twenty to twenty five millimeters (20 mm≦D C ≦25 mm) have a superior performance with a protrusion distance D P  of three to ten microns (0.003 mm≦D P ≦0.010 mm) outside of the cutting diameter D C . It will be understood that drills of diameters smaller than eight millimeters and larger than twenty five millimeters can also be manufactured. Even though testing of further diameters has not yet been carried out, according to the principle of extrapolation based on the test results above, it is believed that drills with a cutting diameter D C  of less than eight millimeters may have a preferred protrusion distance D P  of one to six microns (0.001 mm≦D P ≦0.006 mm). Similarly, based on extrapolation, drills with a cutting diameter D C  greater than twenty five millimeters may have a preferred protrusion distance D P  of four to twelve microns (0.004 mm≦D P ≦0.012 mm). Accordingly, a preferred extrapolated range of protrusion distances D P  would be one to twelve microns (0.001 mm≦D P ≦0.012 mm). Nonetheless, it is noted that a maximum upper limit of the protrusion distance D P  at which this concept no longer works has not yet been found. Notwithstanding the above-said, it is also noted that a margin extremity extending outside of a cutting diameter by a protrusion distance D P  of at least two microns (D P ≧0.002 mm) has found to have better performance than at least one micron (D P ≧0.001 mm). In any case, the successfully tested range, and hence most preferred tested range, is a protrusion distance D P  of two to ten microns (0.002 mm≦D P ≦0.010 mm), with even more preferred diameter-specific ranges being those described above. 
         [0054]    The margin  26  can have a convexly-curved shape (i.e. it continuously extends outside of the cutting diameter D C  at a decreasing rate). 
         [0055]    The margin extremity  28  can be located in a margin portion  32  of the margin  26 . 
         [0056]    Referring now to  FIG. 3 , the margin portion  32  extends between an upper limit  33  at an intersection of the relief surface  20  and the margin  26 , to an imaginary lower limit  34  (located at an axial distance D A  of 0.01 mm to 0.1 mm from the relief surface  20 , or more precisely from the upper limit  33 ). It will be understood that due to the receding nature of the margin  26 , as perhaps understood best from  FIGS. 2C and 3 , engagement of the drill head  14  and a hole being drilled (not shown) is only configured to extend to the imaginary lower limit  34 . Stated differently, the margin portion  32  can be the only portion of the margin  26  configured to contact a hole (not shown), however it will be understood that due to tolerances additional portions of the margin  26  may contact the hole. 
         [0057]    Accordingly, it will be understood that while the example shown has a preferred geometry, the entire margin  26  could be constituted entirely by the area shown as the margin portion  32 . In such case, the cutting portion  16  could extend radially inwardly at axial positions lower than the margin portion  32  (not shown). 
         [0058]    In any case, the margin  26  comprises a margin edge  36  extending along an intersection of the margin  26  and the rake surface  18 . The margin  26 , as shown in  FIGS. 2C and 3 , can be formed with a receding geometry. 
         [0059]    At each cross section taken at axial positions which are not adjacent to the relief surface  20  (i.e. axially spaced from the relief surface  20 ; random axial positions are taken at the positions designated as  38  and  40  for exemplary purposes only) the margin  26  has a similar shape to the shape the margin portion  32 , and as shown in  FIGS. 3 and 5C . 
         [0060]    The margin  26  extends from the margin edge  36  to the margin extremity  28 . The margin extremity  28  can be located at an intersection of a flank surface  42  and the margin  26 . 
         [0061]    A margin width W M  measured from the cutting edge extremity  24  to the flank surface  42  can be between 5% to 10% of the cutting diameter D C  (0.05 D C ≦W M ≦0.10 D C ). 
         [0062]    The flank surface  42  can extend inward to the drill head  14 . In any case, as shown in  FIG. 5C , the flank surface  42  extends from a position outside of the cutting diameter D C  to a position within the cutting diameter D C . Stated differently, the flank surface  42  is configured to provide a relief function (i.e. and can be considered a relief surface). 
         [0063]    An outer diameter relief surface  44  can peripherally extend from the flank surface  42 , in a direction away from the cutting edge extremity  24 . The outer diameter relief surface  44  can be entirely located within the cutting diameter D C . 
         [0064]    The description above includes an exemplary embodiment and details, and does not exclude non-exemplified embodiments and details from the claim scope of the present application.