Abstract:
The present invention relates to a spot and chamfer drill insert which can be utilized to create accurately located spots for subsequent drilling operations while simultaneously providing a chamfer for the finished hole. The present invention utilizes web thin clearance surfaces that are formed at web thin clearance angles, wherein the web thin clearance angles are oriented with respect to a projected plane normal to a plane through the web thin cutting edge and parallel to the longitudinal axis of the insert, wherein the projected plane is tangent to the web thin cutting edge.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to a drill having a specialized drill insert for boring holes into metals. More specifically the invention relates to an improved spot and chamfer drill insert which can be utilized to create accurately located spots for subsequent drilling operations while simultaneously providing a chamfer for the finished hole.  
         BACKGROUND OF THE INVENTION  
         [0002]    In typical drilling operations, especially with deep-drilled holes, the hole is first accurately located by using a spot drill. A spot drill improves the positional accuracy of subsequent drilling operations. After the spot drilling operation is complete, a standard drill is used to drill the hole to the desired depth. A third drill is then typically used to put a chamfer on the edge of the drilled hole. Accordingly, the drilled hole requires at least three drill tools, more if the hole must be trued with a boring cutter and/or reamed to size with a reamer. This takes significant time for at least three operations, requires at least three separate tools, and utilizes at least three tool holder positions on the machine.  
           [0003]    One attempt to overcome these problems has involved the development of a combination spot and chamfer drill insert. While this insert was able to reduce the number of operations, the spot point of the insert was constructed with clearance surfaces that were formed at a clearance angle from a projected plane normal to the thickness of the insert. These inserts had excessive clearance at the point which increased the length of the chisel edge resulting in unstable cutting requiring increased thrust and generating more heat at the cut. Therefore, there remains a need in the art for a drill tool insert which can reduce the number of drilling operations to complete a finished drilled hole by combining at least two of operations identified above and having an optimized spot point.  
         SUMMARY OF THE INVENTION  
         [0004]    An object of the present invention is to provide a drill insert with an improved point geometry that can provide an accurate spot cut and, if desired, a finish hole chamfer in one operation. These and other advantages are provided by a drill insert comprising a drill insert body having at least a first end opposite a second end and a first face side opposite a second face side; wherein the first end of the drill insert body is a generally planar surface and the second end has at least two main cutting edges formed thereon at a first inclusive angle, a web formed between the two main cutting edges, and a web thinning notch formed on either side of the web, forming web thinning cutting edges at a second inclusive angle and separated from each other by a chisel; wherein the chisel is formed by the intersection of at least a primary web thin clearance surface behind each web thinning cutting edge; wherein the primary web thin clearance surface is formed at a primary web thin clearance angle with respect to a projected plane normal to a plane through the web thin cutting edge and parallel to the longitudinal axis of the insert, wherein the projected plane is tangent to the web thin cutting edge.  
           [0005]    These and other advantages are also provided by a drilling tool assembly comprising: (1) a holder having first and second ends and a rotational axis, wherein the second end is adapted to be fixedly attached in a drilling machine, and the first end comprises a holder slot having a bottom seating surface over at least a portion of the holder slot, the holder slot also including a locating boss extending from the bottom seating surface; (2) a drill insert comprising a drill insert body having at least a first end opposite a second end and a first face side opposite a second face side, wherein the first end of the drill insert body is a generally planar surface and the second end has at least two main cutting edges formed thereon at a first inclusive angle, a web formed between the two main cutting edges, and a web thinning notch formed on either side of the web forming web thinning cutting edges at a second inclusive angle and separated from each other by a chisel, wherein the chisel is formed by the intersection of at least a primary web thin clearance surface behind each web thinning cutting edge, wherein the primary web thin clearance surface is formed at a primary web thin clearance angle with respect to a projected plane normal to a plane through the web thin cutting edge and parallel to the longitudinal axis of the insert, wherein the projected plane is tangent to the web thin cutting edge; and (3) wherein the first side of the insert is adapted to have at least a portion thereof positioned in the holder slot in seating engagement with the bottom seating surface and including a locating slot formed in the bottom side which cooperates with the locating boss of the bottom seating surface to allow the insert to be seated against the bottom seating surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention and developments thereof are described in more detail in the following by way of embodiments with reference to the drawings, in which:  
         [0007]    [0007]FIG. 1 is an exploded assembly view of the drill tool assembly according to a preferred embodiment;  
         [0008]    [0008]FIG. 2 is a partial perspective view of the holder associated with the assembly;  
         [0009]    [0009]FIG. 3 is a top plan detail view of the point of the insert of the present invention;  
         [0010]    FIGS.  4 A- 4 D are a variety of different views of an insert according to a first embodiment of the present invention;  
         [0011]    FIGS.  5 A- 5 D are a variety of different views of an insert according to a second embodiment of the present invention having chipbreakers;  
         [0012]    FIGS.  6 A- 6 B are a face side elevational view and a cross-sectional view of the insert, respectively, with the cross-section taken perpendicular to the insert face and through a portion of a main cutting edge; and  
         [0013]    FIGS.  7 A- 7 C are a rotated perspective view, a corresponding cross-sectional view of the insert taken at an angle generally perpendicular to the web thin cutting edge and through a portion of a web thin cutting edge, and a detail cross-sectional view of the web thin cutting edge clearance surfaces. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Turning now to a preferred embodiment of the invention, FIG. 1 illustrates a drill tool assembly  10  generally indicated. Drill tool assembly  10  comprises a holder  12 , which has a body  14  and head portion  16  associated therewith. In the preferred embodiment, holder  12  has, in general, a cylindrical shape with a first end  20  and second end  22 . As also shown in FIG. 2, the first end  20  of holder  12  has a clamping or holder slot  30 , which may extend across the entire diameter of the head portion  16  or, at least, over a center portion thereof at the general location of the rotational axis  18  of holder  12 . The holder slot  30  has a bottom wall  32  positioned in substantially perpendicular orientation relative to the rotational axis  18  of the holder  12 . In the preferred embodiment, the assembly  10  may further include a locating boss or dowel pin  24 , which is positioned precisely with respect to the axis  18  and extends from the bottom wall  32  of the holder slot  30 . The pin  24  may be positioned within a hole  26  extending downwardly from the bottom wall  32  of slot  30  along the axis  18  of the holder body in a press fit relationship to position pin  24  as best shown in FIG. 1. Alternatively, the locating boss, which, in the preferred embodiment, comprises pin  24 , may be configured in another manner to achieve the corresponding functionality of pin  24 , such as an integral member extending from bottom wall  32 . Within the holder slot  30 , a drill insert  35  is precisely positioned with respect to the holder  12  to perform the desired drilling function in conjunction therewith. As will be hereinafter described in more detail, the insert  35  has a point geometry comprising a plurality of cutting surfaces, which are precisely positioned with respect to the axis  18  of the holder  12  to minimize errors in a resulting drilling operation using assembly  10 .  
         [0015]    More particularly, the preferred embodiment of holder  12  is shown in FIG. 2, and may be configured to include at its first end  20  a pair of clamping arms  34 , which extend about holder slot  30 . The clamping arms  34  preferably include apertures  36 , which accommodate screws  38  (see FIG. 1) to secure the drill insert  35  in its position within the holder slot  30 . In the preferred configuration, the holes  36  are threaded to engage screws  38 , and mate with screw holes formed in the drill insert  35  in a predetermined manner to precisely locate the drill insert in a predetermined location within holder slot  30 , as will be described in more detail. Each of the clamp arms  34  may also include a lubrication vent  28 , which allows the application and flow of lubrication adjacent the cutting surfaces of the drill insert to facilitate the drilling operation. The clamp arms  34  may also include angled or curved surfaces, which facilitate chip removal via chip evacuating grooves  37  on each side of the holder  12 . The seating surface  32  is also shown to be designed as a planar surface, which corresponds to the planar bottom portion of the preferred drill insert  35 , although another configuration of bottom surface  32  may be employed and is contemplated herein.  
         [0016]    Turning to FIGS.  4 A- 4 D, a first embodiment of the drill insert  35  is shown. The drill insert  35  may form a spade drill blade, comprising an insert body having opposing face sides  75 , a leading end  73  and a base end  77 . Insert  35  also comprises apertures  70  which allow the insert  35  to be secured to the holder  12  by screws  38 . Base end  77  is a generally planar surface having a recess  65  formed therein to mate with pin  24  of the holder  12 . The insert body also has opposing side edges  60  being generally parallel with the rotational axis  18  of the holder  12  once the insert  35  is positioned and secured with holder  12 . When secured with holder  12 , drill insert  35  will also have a rotational axis, which desirably is coaxial with axis  18  of holder  12 . The drill insert  35  will also have a width  61 , which, upon being rotated with holder  12 , forms an outside diameter of the assembled tool. The drill insert  35  further includes main cutting edges  64  on leading end  73  formed at a V-shaped first inclusive angle Φ, with cutting edges  64  on each side of the axial center  62 , also known as the dead center. The first inclusive angle Φ is shown at about 90 degrees which produces a conical cut in the work piece. Although not shown, the present invention may also include main cutting edges  64  having any included angle Φ which produces a desired conical cut such as, but not limited to, common chamfer/countersink included angles of 60 and 82 degrees. The main cutting edges  64  may include a plurality of cutting components, which cooperate together to provide the desired cutting surface  64  for the material and/or drilling application. In general, the insert  35  is designed to cut when rotationally driven in conjunction with holder  12  in a predetermined direction, and is not reversible, although such drilling blade configurations are known to those skilled in the art and could be used in conjunction with the present invention if desired.  
         [0017]    Referring now to FIG. 6A which is a cross-sectional view perpendicular to the face surfaces  75  of insert  35  through a portion of the cutting edge  64  as shown in the face side elevational view of FIG. 6B. Insert  35  further comprises a primary clearance surface  84  behind each cutting edge  64  which is formed at a primary clearance angle α such that only the cutting edges  64  are in contact with the material to be cut. A secondary clearance surface  86  may also be formed adjacent the primary clearance surface  84  at a secondary clearance angle β to provide additional clearance behind the cutting edges  64 . The primary and secondary clearance angles, α, β, are oriented from a plane projected normal to a face surface  75  of the insert and tangent to the respective main cutting edge  64 . The interface between the primary and secondary clearance surfaces is referred to as the clearance cut  89 . The clearance cut  89  is typically either parallel or transverse to the cutting edges  64 . The clearance surfaces  84 ,  86  prevent additional friction during the cutting operation and provide additional room for facilitating the removal of chips cut from the material.  
         [0018]    Insert  35  also includes a web thinning notch  66  as best shown in FIG. 3. Notch  66  is located on either side of the chisel  68  which is formed across the insert web and extends through axial center  62 . The web thinning notch  66  forms web thinning cutting edges  67  which provide the transition from the main cutting edges  64  to the chisel  68 . The web thinning cutting edges  67  may be formed at a second included angle θ, shown as an obtuse angle, but not limited thereto. The second included angle θ is larger than the first included angle Φ. The larger web thin included angle θ aides in strengthening the point of the insert  35 . The notch  66  forms a type of flute on either side of insert  35 , which reduces the web and length of chisel  68 . This reduces the thrust needed when drilling by reducing the length of the chisel  68 . It is also contemplated that the notch  66  may be of the V-notch type disclosed in the co-owned pending U.S. patent application Ser. No. 09/975,221, entitled DRILL INSERT GEOMETRY HAVING V-NOTCHED WEB, herein incorporated by reference.  
         [0019]    Many prior art drill inserts have a flat chisel. With a flat chisel there is a tendency for the drill to walk around the chisel during drilling operations resulting in runout and wander of the drilled hole. Another negative feature of drill inserts and twist drills, in general, is that the flat chisel must act as a cutting edge. The chisel typically has a neutral or negative rake angle, which does not cut efficiently but rather deforms the metal. This flat chisel and the neutral or negative rake angle result in high thrust forces being required and excessive heat being developed at the point. In the present invention, the chisel  68  is typically formed as a multi-faceted chisel point  68  forming a single point at the dead center  62 . The point  62  of the multi-faceted chisel  68  point is not as apt to wander as a flat chisel and provides increased stability, which in turn helps produce very round and very accurately positioned spot cuts.  
         [0020]    In typical prior art inserts having a multi-faceted chisel point, the facet surfaces are formed by the intersections of a primary and a secondary clearance surface on both sides of the insert, meeting at the chisel. As described with respect to the present invention, the primary and secondary clearance surfaces are formed at clearance angles which are conventionally measured from a plane projected perpendicular from the face sides  75  of the insert  35  and tangent to the respective main cutting edges  64 . However, in the present invention, the primary and secondary clearance surfaces  84 ,  86 , do not extend to chisel  68 . The multi-faceted chisel  68  is formed from web thin primary clearance surfaces  82  and web thin secondary clearance surfaces  83  formed behind web thin cutting edges  67 .  
         [0021]    While the prior art spot and chamfer drill also had web thin clearance surfaces, those surfaces were oriented from a projected plane normal to the face of the insert. This meant that the prior art web thin clearance surface was the resultant angle of the clearance angle and point included angle. Accordingly, the prior art spot and chamfer tool provided a less stable point with too high of a clearance behind the web thin cutting edges resulting in an increased chisel length.  
         [0022]    Referring now to FIGS.  7 A- 7 C, FIG. 7B is a cross-sectional view of insert  35  taken perpendicular to the web thin cutting edge  67  as shown in the perspective view of FIG. 7A. FIG. 7C provides a detail view of the top portion of the cross-section of FIG. 7B. In the present invention, the web thin primary and secondary clearance surfaces  82 ,  83  are formed at primary and secondary web thin clearance angles y,  6 , respectively, which are orientated from a projected plane normal to a plane through cutting edge  67  which is parallel to the longitudinal axis  18  of the tool, wherein the projected plane is tangent to the web thin cutting edge  67 . Basing the web thin clearance surfaces  82 ,  83  off of the web thin cutting edge allows the clearance to be optimized along the entire length of the web thin cutting edges  67 . As best shown in FIG. 3, web thin clearance surfaces  82 ,  83  are radially outwardly bounded by at least one of the primary clearance surface  84  and secondary clearance surface  86  and are each also bounded by chisel  68  and by web thin cutting edges  67 . The web thin clearance surfaces  82 ,  83  are also bounded from each other by a central intersection line  91 , bisecting the chisel  68  at the dead center  62  and extending radially outward to at least one of the primary clearance surface  84  and secondary clearance surface  86 . The central intersection line  91  may be either parallel or transverse to the cutting surfaces  67 , however the central intersection line  91  is offset from any clearance cut  89  such that the two are transverse to each other. The orientation of web thin clearance surfaces  82  and  83  to web thin cutting edge  67  (formed at an included angle θ which is larger than the included angle Φ of cutting edges  64 ), enable less material to be removed from the web resulting in a stronger drill point. The web thin clearance surfaces  82 ,  83  provide a reduced clearance angle at the web cutting edge  67 , which provides increased stability which helps produce a very accurate spot cut. Web thin clearance surface  82  and  83  reduce the length of chisel  68 , forming it generally perpendicular to the main cutting edges  64  of the insert  35 , although the present invention is not limited to such a configuration. The multi-faceted chisel  68  of the present invention allows the insert  35  to penetrate into the workpiece in a more aggressive fashion, which results in higher feed rates and increased stability while, at the same time, creating less heat generated at the tip of the insert  35 .  
         [0023]    In the point geometry configuration of the present invention as shown in FIG. 3, the chisel  68  may be generally perpendicular to the main cutting edge  64  that precedes it, next to the cutting edge of the notch  66 . This configuration provides an easy exit path for the material plowed up ahead of each side of the chisel edge  68 , which can flow down the clearances surfaces  83 , adjacent the associated cutting edge  67  and into the adjacent web-thinning notch  66 .  
         [0024]    Another embodiment of the present invention is shown in FIGS.  5 A- 5 D. A drill insert  35 ′ is shown which is similar to drill insert  35  except for the addition of chipbreakers  88  to the main cutting edges  64  of the drill insert. The chipbreakers  88  aid in the formation and removal of chips during the drilling process.  
         [0025]    It is contemplated that the drill insert is made of high speed steel. However, the drill insert may also be comprised of a sintered metallic hard material such as carbide, cermet, ceramic, monocrystalline and polycrystalline diamond, or boron nitride.  
         [0026]    Although the present invention has been described above in detail, the same is by way of illustration and example only and is not to be taken as a limitation on the present invention. It is contemplated that changes could be made to the embodiments shown without going beyond the scope of the invention. For example, a flat chisel formed by only primary web thin clearance surfaces in accordance with the present invention could be substituted for a multi-faceted chisel. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.