Abstract:
A cutting tool insert having a specialized spur point geometry at the center of the insert. The insert comprises a spur point cutting portion and a blade cutting portion wherein the spur point provides stability by providing a spot and allowing a flexible workpiece to partially spring back when the spur breaks through. The spur point insert facilitates the cutting of relatively thinner workpieces and workpieces requiring the tool to have a longer reach to the hole, while minimizing the burr resulting from the drilling operation.

Description:
TECHNICAL FIELD  
         [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/391,797 filed Jun. 27, 2002, hereby incorporated by reference. The present invention relates generally to a cutting insert to be placed into a tool holder for boring holes into metals. More specifically, the invention relates to a cutting tool insert having a specialized spur point geometry at the center of the insert which facilitates the cutting of workpieces, for example, relatively thinner workpieces and workpieces that are at a distance from the cutting machine.  
         BACKGROUND OF THE INVENTION  
         [0002]    Drilling systems are frequently used to provide cylindrical holes in metallic workpieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.  
           [0003]    However, one particular application which provides problems for prior art cutting tools involves drilling holes through the web portion of structural steel I beams, for example. The flanges of the I-beam require the tool to reach a significant distance to the web of the I-beam. The reach distance can cause a severe instability problem for the tool when attempting to cut a hole through the web. As a result, the tool may wobble or “walk” resulting in an oversize hole, run-out, bellmouthing, and/or an off location hole. Another problem is that the web in these applications are typically relatively thin. During the drilling process, the drill pressure pushes against the thin wall of material allowing it to deflect. As the tool breaks through the material, the material snaps back to its original position, resulting in an irregular shaped hole. Still another problem presented by this and similar applications is that a large burr is produced on the backside of the material. As the tool breaks through the material, the built up drilling pressure causes the tool to lunge through the drilled hole which results in the creation of a burr on the backside of the material. This typically requires an added de-burring process to the machining operation in order to remove the burr. In applications such as with structural steel it is critical that not only the hole be round, but that there is no burr to interfere between the register surfaces of beams and connector plates which must lay flat when they are being connected. A burr can result in an improper connection length and also decrease the strength of the connection by preventing a proper preload of the fastener used to connect the beams.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a spur point insert for a drilling tool which has increased stability and reduces tool lunge on break through. These and other advantages of the present invention are provided by a drill insert comprising a drill insert body having at least a first side and a second side, wherein the first side of the drill body comprises a generally planar surface, wherein the second side comprises a first cutting portion formed on a first insert diameter and a second cutting portion formed on a second insert diameter, wherein the first cutting portion comprises at least two cutting edges forming a primary included angle and wherein the cutting edges of the first cutting portion extend from opposite ends of a chisel point to the first insert diameter, wherein the second cutting portion comprises at least two cutting edges forming a secondary angle, wherein the cutting edges of the second cutting portion extend from the first insert diameter to the second insert diameter.  
           [0005]    These and other advantages of the present invention are also provided by a drilling tool assembly comprising 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; and a drill insert body having at least a first side and a second side, wherein the first side of the drill body comprises a generally planar surface, wherein the second side comprises a first cutting portion formed on a first insert diameter and a second cutting portion formed on a second insert diameter, wherein the first cutting portion comprises at least two cutting edges forming a primary included angle and wherein the cutting edges of the first cutting portion extend from opposite ends of a chisel point to the first insert diameter, wherein the second cutting portion comprises at least two cutting edges forming a secondary angle, wherein the cutting edges of the second cutting portion extend from the first insert diameter to the second insert diameter and wherein the first side 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 first side of the drill insert body 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]    FIGS.  3 A- 3 D are a variety of different views of an insert according to a first embodiment of the present invention having a 180 degree secondary included angle; and  
         [0010]    FIGS.  4 A- 4 D are a variety of different views of an insert according to a second embodiment of the present invention having a secondary included angle less than 180 degrees. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    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 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 . 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 spur 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 .  
         [0012]    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.  
         [0013]    Turning to FIGS.  3 A- 3 D, a first embodiment of the spur point drill insert  35  is shown. The spur point drill insert  35  is a spade-type drill blade, with side edges  60  including margins  63  of the blade 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  71 , which, upon being rotated with holder  12 , forms an outside diameter  71  of the assembled tool. The drill insert  35  comprises a first spur cutting potion  64  having a minor diameter or spur diameter  61  and a second blade cutting portion  74  having a major diameter or blade diameter equivalent to the insert width  71 .  
         [0014]    The spur cutting portion  64  includes cutting edges  66  on its upper surface in the form of a V-shape having a first or primary included angle θ. Cutting edges  66  are formed on parallel planes on opposite sides of the drill insert  35  and extend generally radially inward and terminate on opposite ends of a chisel  90  formed across the web  92  of the insert  35 . The cutting edges  66  extend along parallel planes generally radially outward to the spur diameter  61 . For most applications, the best performance is achieved when the spur diameter  61  is generally half to one fourth the size of the blade diameter  71 . However, it is contemplated that other ratios may also be used and the spur diameter  61  is not intended to be limited to any particular ratio with respect to the blade diameter  71 .  
         [0015]    The second blade cutting portion  74  includes cutting edges  76  on its upper surface. Cutting edges  76  may either be perpendicular to the rotational axis and having a 180 degree angle as shown in FIGS.  3 A- 3 D or in the form of a V-shape having a second or secondary included angle Φ as shown in FIGS.  4 A- 4 D. Cutting edges  76  are formed on parallel planes on opposite sides of the drill insert  35  and extend generally radially outward from the spur diameter  61  to the blade diameter  71 .  
         [0016]    The cutting edges  66 ,  76  may include a plurality of cutting components, which cooperate together to provide the desired cutting surface  66  for the material and/or drilling application. These cutting components may include, but are not limited to, chip breakers, corner clip, corner radius, edge treatments, etc.  
         [0017]    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. The drill insert  35  further preferably includes apertures  70 , which cooperate with the apertures  36  in clamp arms  34  to secure insert  35  within holder slot  30  and seated against seating surface  32 . Additionally, each of the apertures  36  and  70  are preferably formed with countersunk portions formed as a bearing surface adapted to be engaged by a corresponding tapered or like surface on the screws or other fastening mechanism  38 . The enlarged clamping head of the screws  38  may be of any convenient shape, such as conical, ball-shaped, or in another form to correspond with the similar surfaces in the tool holder  12  and insert  35 . In a typical fashion, by offsetting the axes of the apertures  36  and  70 , upon securing insert  35  within slot  30  by means of screws  38 , the planar bottom portion  59  of insert  35  will be forced downwardly against the seating surface  32 . Insert  35  may include a locating slot  65 , which allows positioning of the locating pin  24  therein. This connection is further described in co-owned U.S. Pat. No. 5,957,635, which is herein incorporated by reference.  
         [0018]    In operation, the spur cutting portion  64 , or spur, aggressively engages the material to be cut and helps center the tool during the initial cut. As the spur  64  is formed at a minor diameter  61  or spur diameter that is smaller than the major diameter  71  or width of the cutting tool  10 , there is less deflection of the workpiece when the spur  64  is engaged. When the spur  64  breaks through the opposite side of the workpiece, a significant portion of the built up drill pressure is released. In addition, the margins  63  of the drill insert  35  are typically fully engaged with the material hole diameter at the time when the spur  64  breaks through the opposite side of the workpiece which provides additional stability to the cutting operation. Therefore the stability of the cutting tool  10  is retained and the secondary or blade cutting edges  76  are in effect milling the remaining workpiece material in the hole. The reduction of built up drill pressure also results in a significant reduction of lunge upon completion of drilling the hole, resulting in a minimization of the creation of unacceptable burrs.  
         [0019]    Turning to FIGS.  4 A- 4 D, a second embodiment of the spur point drill insert  35 ′ is shown. Drill insert  35 ′ is similar to drill insert  35  except that drill insert  35 ′ comprises a second blade cutting portion  74 ′ having a secondary included angle Φ which is less than 180 degrees and the spur diameter  61 ′ is about a fourth the size of the blade diameter  71 .  
         [0020]    It is contemplated that the drill insert  35 ,  35 ′ is made of a sintered metallic hard material such as carbide, cermet, ceramic, monocrystalline and polycrystalline diamond, or boron nitride. However, the drill insert may also be comprised of high speed steel.  
         [0021]    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. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.