Indexable drilling inserts

Abstract

Drilling tool systems including a drilling body and a drilling inserts are disclosed. The drilling inserts include four indexable cutting edges. The four cutting edges may each comprise a plurality of cutting edge segments. The plurality of cutting edge segments are provided at distinct angles with respect to a reference plane of the drilling insert to provide effective chip breaking and a stronger cutting edge at the drilling insert corners. Furthermore, the side surfaces of the drilling inserts allow the drilling insert to be more stably supported in a pocket of the drilling body. The drilling inserts may be used in a central pocket of a drilling body.

Claims

1. An inboard drilling insert for a drilling tool system having the inboard drilling insert and an outboard drilling insert, the inboard drilling insert comprising: a top surface; a bottom surface having a smaller surface area than the top surface; four side surfaces adjoining the top surface and the bottom surface; and four cutting edges at the intersection of each of the side surfaces and the top surface defining four corner edge portions at intersections between adjacent cutting edges, each of the cutting edges comprising: a first cutting edge segment extending from a first one of the corner edge portions adjacent to a central longitudinal rotational axis of a drilling body when the drilling insert is mounted in the drilling body at a first cutting edge angle with respect to a reference plane passing through the center of adjacent corner edge portions and parallel to an axis of rotation of the drilling insert; a second cutting edge segment located radially away from the central longitudinal rotational axis of the drilling body in relation to the first cutting edge segment at a second cutting edge angle with respect to the reference plane; and a third cutting edge segment extending from the second cutting edge segment at a third cutting edge angle with respect to the reference plane to a second one of the corner edge portions, wherein the third cutting edge segment has a length, L.sub.3, equal to L.sub.C*[(D.sub.CLD.sub.CS)], where L.sub.C is in a range between 0.25 to 0.85, D.sub.CL is a largest cutting diameter that will be used with the inboard drilling insert, and D.sub.CS is a smallest cutting diameter that will be used with the inboard drilling insert, thereby allowing the inboard drilling insert to perform substantially an equal amount of cutting than the outboard drilling insert.

2. The inboard drilling insert of claim 1, wherein the first cutting edge segment, the second cutting edge segment, and the third cutting edge segment are linear.

3. The inboard drilling insert of claim 1, wherein the first cutting edge angle is a positive angle with respect to the reference plane ranging from about 2 to about 30 degrees.

4. The inboard drilling insert of claim 1, wherein the second cutting edge angle is a negative angle with respect to the reference plane ranging from about 0.5 to about 10 degrees.

5. The inboard drilling insert of claim 1, wherein the third cutting edge angle is a negative angle with respect to the reference plane ranging from about 5 to about 75 degrees.

6. The inboard drilling insert of claim 1, wherein the third cutting edge angle is greater than 20 degrees.

7. The inboard drilling insert of claim 1, wherein the first and second cutting edge segments are joined together by a transitional cutting edge segment, the transitional cutting edge segment forming a concave curve with the first cutting edge segment and a convex curve with the second cutting edge segment.

8. The inboard drilling insert of claim 7, wherein the transitional cutting edge segment comprises a linear portion.

9. The inboard drilling insert of claim 8, wherein the linear portion of the transitional cutting edge segment extends outward from the first cutting edge segment at a fourth transitional cutting edge angle with respect to the reference plane, the fourth transitional cutting edge angle is a positive angle ranging from about 5 to about 85 degrees.

10. The inboard drilling insert of claim 7, wherein the convex curve formed between the transitional cutting edge and the second cutting edge segment is located at or between the first one of the corner edge portions and a vertical reference plane bisecting a mounting through hole.

11. The inboard drilling insert of claim 7, wherein the convex curve formed between the transitional cutting edge and the second cutting edge segment defines a leading contact point of the cutting edge.

12. The inboard drilling insert of claim 7, wherein a transition between the second cutting edge segment and the third cutting edge segment defines convex curve, and the convex curve formed between the transitional cutting edge and the second cutting edge segment is at least 0.02 millimeters forward along the central longitudinal rotational axis than the convex curve of the transition between the second cutting edge segment and the third cutting edge segment.

13. The inboard drilling insert of claim 1, wherein a transition between the first cutting edge segment and the second cutting edge segment defines only a convex curve.

14. The inboard drilling insert of claim 1, wherein the first cutting edge segment is closer to an axis of rotation of the drilling insert than the second cutting edge segment and a portion of the third cutting edge segment.

15. The inboard drilling insert of claim 1, wherein when the drilling insert is mounted in the drilling body the reference plane of the drilling insert is provided at an angle of from 0 to 10 degrees with respect to a horizontal reference plane normal to the central longitudinal axis of the drilling body.

16. The inboard drilling insert of claim 1, wherein each side surface comprises a first clearance face extending from the top surface and a second clearance face extending from the first clearance face to the bottom surface, and a height of the second clearance face is greater than or equal to the height of the first clearance face.

17. The inboard drilling insert of claim 16, wherein the height of the first clearance face is less than 50 percent of a total height of the drilling insert.

18. The inboard drilling insert of claim 16, wherein the first clearance face forms an angle ranging from about 1 to about 30 degrees with respect to an axis of rotation of the drilling insert, and the second clearance face forms an angle ranging from about 5 to about 40 degrees with respect to the axis of rotation of the drilling insert.

19. A drilling tool system comprising: a drilling body having a central longitudinal rotational axis, and comprising an interior pocket in a front drilling face, the interior pocket comprising: a rear surface; and a first sidewall portion extending forward from the rear surface; and a central drilling insert capable of being received in the interior pocket of the drilling body and a peripheral cutting insert capable of being received in a peripheral pocket of the drilling body, the central drilling insert comprising: a top surface; a bottom surface having a smaller surface area than the top surface; four side surfaces adjoining the top surface and the bottom surface, the four side surfaces structured and arranged to engage the rear surface and the first sidewall portion of the interior pocket of the drilling body; and four cutting edges at the intersection of each of the side surfaces and the top surface defining four corner edge portions at intersections between adjacent cutting edges, each of the cutting edges comprising: a first cutting edge segment extending from a first one of the corner edge portions adjacent to the central longitudinal rotational axis of the drilling body at a first cutting edge angle with respect to a reference plane passing through the center of adjacent corner edge portions and parallel to an axis of rotation of the drilling insert; a second cutting edge segment located radially away from the central longitudinal rotational axis of the drilling body in relation to the first cutting edge segment at a second cutting edge angle with respect to the reference plane; and a third cutting edge segment extending from the second cutting edge segment at a third cutting edge angle with respect to the reference plane to a second one of the corner edge portions, wherein the third cutting edge segment has a length, L.sub.3, equal to L.sub.C*[(D.sub.CLD.sub.CS)], where L.sub.C is in a range between 0.25 to 0.85, DC.sub.L is a largest cutting diameter that will be used with the central drilling insert, and D.sub.CS is a smallest cutting diameter that will be used with the central drilling insert, thereby allowing the central drilling insert to perform substantially an equal amount of cutting than the peripheral drilling insert.

20. The drilling tool system of claim 19, wherein the first and second cutting edge segments are joined together by a transitional cutting edge segment, the transitional cutting edge segment forming a concave curve with the first cutting edge segment and a convex curve with the second cutting edge segment, and the convex curve formed between the transitional cutting edge and the second cutting edge segment is the most forward point along the central longitudinal rotational axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top isometric view of a drilling insert in accordance with an embodiment of the present invention.

(2) FIG. 2 is a bottom isometric view of the drilling insert of FIG. 1.

(3) FIGS. 3A and 3B are top views of the drilling insert of FIG. 1.

(4) FIG. 4 is a side view of the drilling insert of FIG. 1.

(5) FIG. 5 is an isometric view of a drilling body including a drilling insert in a central pocket of the drilling body and a peripheral insert in a peripheral pocket of the drilling body in accordance with an embodiment of the present invention.

(6) FIGS. 6 and 7 are side views of a drilling body including a drilling insert in a central pocket of the drilling body and a peripheral insert in a peripheral pocket of the drilling body in accordance with an embodiment of the present invention.

(7) FIG. 8 is an isometric view of a drilling body in accordance with an embodiment of the present invention.

(8) FIG. 9 is a side view of a drilling body in accordance with an embodiment of the present invention.

(9) FIG. 10 is a partially schematic side view of a drilling insert in a central pocket of the drilling body and a peripheral insert in a peripheral pocket of the drilling body in accordance with an embodiment of the present invention.

(10) FIG. 11 is a partially schematic side view of a central drilling insert and a peripheral insert in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

(11) FIGS. 1 and 2 illustrate top and bottom isometric views of an indexable central drilling insert 10 in accordance with an embodiment of the present invention. The drilling insert 10 comprises a top surface 12, a bottom surface 14 and a side surface 16 adjoining the top and bottom surfaces 12 and 14. In accordance with an embodiment of the present invention, the body of the drilling insert 10 is structured and arranged so that the side surfaces 16 slope or slant generally inwardly from the top surface 12 to the bottom surface 14 such the bottom surface 14 may have a smaller surface area than the top surface 12 to provide a positive cutting geometry between the drilling insert 10 and a pocket 60 in a drilling body 50, as shown in FIGS. 5-7. The top surface 12 is intersected by the side surface 16 to form a cutting edge 20 on each side of the drilling insert 10.

(12) As shown in FIGS. 1 and 2, the indexable drilling insert 10 comprises a mounting through hole 18 extending from the top surface 12 to the bottom surface 14. A central insert axis 19 of the mounting through hole 18 is perpendicular to the top surface 12 and the bottom surface 14. The central insert axis 19 defines an axis of rotation of the drilling insert 10. The mounting through hole 18 is structured and arranged to receive an insert screw 90.

(13) In accordance with an embodiment of the present invention, each cutting edge 20 may be formed by a plurality of cutting edge segments. As shown in FIGS. 1-4, each cutting edge 20 is formed by a first cutting edge segment 22, a second cutting edge segment 24 and a third cutting edge segment 26. In accordance with an embodiment of the present invention, the drilling insert 10 is mounted in the drilling body 50 having a generally cylindrical body 52 with a central longitudinal rotational axis 54. In certain embodiments, when the drilling insert 10 is mounted in the drilling body 50, the first cutting edge segment 22 is located radially closer to the central longitudinal rotational axis 54 than the second cutting edge segment 24 and the third cutting edge segment 26, and the third cutting edge segment 26 is located radially outward from the central longitudinal rotational axis 54 compared to the first cutting edge segment 22 and the second cutting edge segment 24.

(14) In accordance with an embodiment of the present invention, each cutting edge 20 may be formed by identical cutting edge segments. In accordance with an embodiment of the present invention, the first, second and third cutting edge segments 22, 24 and 26 are substantially linear. In accordance with an embodiment of the present invention, the orientation and length of the plurality of cutting edge segments 22, 24 and 26 provide effective centering and penetration into a work piece at entry, stronger corner edge portions, prevent drifting of a drilling body 50 from its center and more effectively direct the cutting forces, as further described below.

(15) As shown in FIGS. 6, 7, 10 and 11, the width and location of the central drilling insert 10 and the peripheral insert 100 are selected to allow the operational cutting ranges of the inserts to overlap during rotation of the drilling body 50. In accordance with an embodiment of the present invention, the orientation and length of the plurality of cutting edge segments 22, 24 and 26 of the central drilling insert 10 are selected to allow substantially equal cutting to be performed by the central drilling insert 10 and the peripheral insert 100, as further described below.

(16) As shown in FIGS. 1, 3A and 3B, each cutting edge 20 of the drilling insert 10 comprises a transitional cutting edge segment 28 connecting the first cutting edge segment 22 to the second cutting segment 24. In accordance with an embodiment of the present invention, the transitional cutting edge segment 28 forms a concave curve 29A with the first cutting edge segment 22 and a convex curve 29B with second cutting edge segment 24. As shown in FIGS. 2 and 3A, the transitional cutting edge segment 28 may include a linear portion 29C between the concave curve 29A formed with the first cutting edge segment 22 and the convex curve 29B formed with the second cutting edge segment 24. Alternatively, the transitional cutting edge segment 28 may be colinear with the first cutting edge segment 22 and form only a convex curve 29B with second cutting edge segment 24. In accordance with an embodiment of the present invention, the transition between the second cutting edge segment 24 and the third cutting edge segment 26 may form a convex curve 25. In accordance with an embodiment of the present invention, the convex curve 29B formed by the intersection transitional cutting edge segment 28 and the second cutting edge segment 24 may be the first portion of the cutting edge 20 to make contact with a work piece, as further described below.

(17) In accordance with an embodiment of the present invention, the indexable drilling insert 10 comprises four corner edge portions 30 formed between adjacent cutting edges 20. As shown in FIG. 3A, each corner edge portion 30 is formed as rounded segment having a radius R that allows for a connection between adjacent cutting edges 20. For example, the corner edge portion 30 may connect a third cutting edge segment 26 of one cutting edge 20 with a first cutting edge segment 22 of a subsequent cutting edge 20. In certain embodiments, the radius R of the corner edge portions 30 may be determined by the overall height of the insert 10 and the diameter D of an imaginary inscribed circle 38. For example, the radius R of each corner edge portion 30 may typically range from 0.1 to 1.6 millimeters. In a particular embodiment, the radius R of each corner edge portion 30 may be about 0.4 millimeter.

(18) As shown in FIGS. 3A and B, a reference plane 11 passes through the center of adjacent corner edge portions 30 of the drilling insert 10 and a vertical reference plane 17 bisects the mounting through hole 18. As used herein, the term center of a corner edge portion means the radial outermost point of the corner edge portion 30. As shown in FIG. 3A, the reference plane 11 is parallel to the axis of rotation 19 of the drilling insert 10. In the embodiment shown, the reference plane 11 is normal to the vertical reference plane 17. In the embodiment shown, the vertical reference plane 17 may be substantially parallel to the central longitudinal rotational axis 54 of the drilling body 50. In accordance with an embodiment of the present invention, the orientation of the plurality of cutting edge segments of each cutting edge 20 may be described in relation to the reference plane 11. As shown in FIG. 3A, the first cutting edge segment 22 extends away from a first corner edge portion 30 adjacent to the central longitudinal rotational axis 54 at a first cutting edge angle with respect to the reference plane 11, which in the embodiment shown is a positive angle. For example, the first cutting edge angle may be less than about 35 degrees, for example, from 2 to 30 degrees, or from 5 to 20 degrees, or from 7 to 18 degrees. In a particular embodiment, the first cutting edge angle may be about 9 degrees.

(19) As shown in FIG. 3A, the second cutting edge segment 24 extends radially outward in relation to the first cutting edge segment 22 at a second cutting edge angle A with respect to the reference plane 11, which in the embodiment shown is a negative angle rather than the positive first cutting edge angle of the first cutting edge segment 22. The second cutting edge angle A may allow for the convex curve 29B formed by the intersection of the transitional cutting edge segment 28 and the second cutting edge segment 24 to be the first contact point with the work piece and allows for the drilling insert 10 to be rigidly secured within a pocket 60 of the drilling body 50. For example, the second cutting edge angle A may typically range from 0.5 to 10 degrees, or from 1 to 7 degrees, or from 1.5 to 5 degrees. In a particular embodiment, the second cutting edge angle A may be about 2 degrees.

(20) In accordance with an embodiment of the present invention, the second cutting edge angle A allows the convex curve 29B formed by the intersection transitional cutting edge segment 28 and the second cutting edge segment 24 to be forward along the central longitudinal rotational axis 54 compared to the convex curve 25 of the transition between the second cutting edge segment 24 and the third cutting edge segment 26. For example, the convex curve 29B may typically be at least 0.02 millimeter axially forward from the convex curve 25, for example, at least 0.05 millimeter, or at least 0.1 millimeter, or at least 1.25 millimeters axially forward from the convex curve 25. The convex curve 29B may typically range from 0.02 to 3 millimeters axially forward from the convex curve 25, for example, from 0.075 to 2 millimeters axially forward, or from 0.1 to 1.5 millimeters axially forward from the convex curve 25 along the central longitudinal rotational axis 54.

(21) As shown in FIG. 3A, the third cutting edge segment 26 extends from a second cutting edge segment 24 at a third cutting edge angle with respect to the reference plane 11 to a second corner edge portion 30 radially outward from the central longitudinal rotational axis 54. In the embodiment shown, the third cutting edge angle is a negative angle and forms a convex curve 25 between the second and third cutting edge segments 24 and 26. The third cutting edge angle is critical because it allows the active cutting lengths of the central drilling insert 10 and the peripheral drilling insert 100 to be substantially equal over a range of cutting diameters. In addition, the third cutting edge segment 26 is provided at the third cutting edge angle to allow the convex curve 29B formed by the intersection of the transitional cutting edge segment 28 and the second cutting edge segment 24 to be the first contact point with the work piece. For example, the third cutting edge angle may typically range from 5 to 75 degrees, or from 7.5 to 45 degrees, or from 10 to 35 degrees. In a particular embodiment, the third cutting edge angle may be about 22 degrees. In accordance with an embodiment of the present invention, a portion of the third cutting edge segment 26 may be farther from the axis of rotation 19 of the drilling insert 10 compared to the first cutting segment 22.

(22) In accordance with an embodiment of the present invention, the linear portion 29C of the transitional cutting edge segment 28 extends radially outward from the first cutting edge segment 22 at a fourth transitional cutting edge angle with respect to the reference plane 11, which in the embodiment shown is a positive angle. The fourth transitional cutting edge angle allows the transitional cutting edge segment 28 to form the outermost portion of the cutting edge 20 and may provide a first contact point with the work piece. For example, the fourth transitional cutting edge angle may typically range from 5 to 85 degrees, or from 10 to 75 degrees, or from 15 to 50 degrees. In a particular embodiment, the fourth transitional cutting edge angle may be about 38 degrees. In accordance with an embodiment of the present invention, the fourth transitional cutting edge angle is greater than or equal to the first cutting edge angle of the first cutting edge segment 22. In certain embodiments, the fourth transitional cutting edge angle allows the first cutting edge segment 22 to be closer to the reference plane 11 than either the second cutting edge segment 24 and/or at least a portion of the third cutting edge segment 26. For example, the first cutting segment 22 may be closer to the axis of rotation 19 of the drilling insert 10 compared to the second cutting edge segment 24 and a portion of the third cutting edge segment 26.

(23) As shown in FIG. 3B, the first cutting edge segment 22 has a length L.sub.1, the second cutting edge segment 24 has a length L.sub.2 and the third cutting edge segment 26 has a length L.sub.3. The lengths of the plurality of cutting edge segments are selected to provide the desired direction of cutting forces and allow for the rigid clamping of the drilling insert 10 in a pocket. In accordance with an embodiment of the present invention, the length L.sub.1 of the first cutting edge segment 22 may typically range from 10 to 40 percent of the diameter D, or from 20 to 35 percent of the diameter D, or from 25 to 30 percent of the diameter D. The length L.sub.2 of the second cutting edge segment 24 may typically range from 10 to 40 percent of the diameter D, or from 20 to 35 percent of the diameter D, or from 25 to 30 percent of the diameter D. The length L.sub.3 of the third cutting edge segment 24 may typically range from 10 to 40 percent of the diameter D, or from 20 to 35 percent of the diameter D, or from 25 to 30 percent of the diameter D.

(24) In certain embodiments, the first cutting edge segment length L.sub.1 is selected to allow the convex curve 29B formed by the intersection transitional cutting edge segment 28 and the second cutting edge segment 24 to be located at or between the first corner edge portion 30 radially inward from the central longitudinal rotational axis 54 and the vertical reference plane 17. However, as understood by those skilled in the art, the convex curve 29B formed by the intersection of transitional cutting edge segment 28 and the second cutting edge segment 24 may be formed on either side of the vertical reference plane 17. For example, the convex curve 29B may be formed between the vertical reference plane 17 and a second corner edge portion 30. In accordance with an embodiment of the present invention, the first cutting edge segment length L.sub.1 may be greater than either the second cutting edge segment length L.sub.2 or the third cutting edge segment length L.sub.3. In certain embodiments, second cutting edge segment length L.sub.2 is less than the first cutting edge segment length L.sub.1 and is greater than the third cutting edge segment length L.sub.3. In certain embodiments, the third cutting edge segment length L.sub.3 is less than the first cutting edge length L.sub.1 and the second cutting edge segment length L.sub.2. The third cutting edge segment length L.sub.3 is selected to correspond to the overall cutting diameter Dc of the drill body 50 to allow the central drilling insert 10 and the peripheral insert 100 to have substantially equal active cutting edges. In accordance with an embodiment of the present invention, the cutting diameter Dc is provided by a cutting edge 20 of the central drilling insert 10 and a cutting edge 120 of the peripheral insert 100, as shown in FIG. 11.

(25) In accordance with an embodiment of the present invention, the third cutting edge segment 24 length L.sub.3 may be equal to L.sub.C*[(D.sub.CLD.sub.CS)]. In certain embodiments, L.sub.C is a constant ranging from 0.25 to 0.85, D.sub.CL corresponds to the largest cutting diameter that the drilling insert 10 will be used with, and D.sub.CS corresponds to the smallest cutting diameter that the drilling insert 10 will be used with. In accordance with an embodiment of the present invention, L.sub.C is a constant determined based upon the smallest cutting diameter D.sub.CS, the largest cutting diameter D.sub.CL, the third cutting edge angle of the third cutting edge segment 26 and the radius R of the corner edge portion 30. In a particular embodiment, the largest cutting diameter D.sub.CL may be 19 millimeters and the smallest cutting diameter D.sub.CS may be 16.5 millimeters. In accordance with an embodiment of the present invention, the third cutting edge segment 26 length L.sub.3 being a function of L.sub.C*[(D.sub.CLD.sub.CS)] allows the central drilling insert 10 and the peripheral drilling insert 100 to perform a substantially equal amount of cutting.

(26) In accordance with an embodiment of the present invention, the lengths of the cutting edge segments 22, 24 and 26 and the transitional cutting edge segment 28 may be varied depending on the overall size of the drilling insert 10. For example, if the diameter D of an imaginary inscribed circle 38, as shown in FIG. 3B, is increased the lengths of the cutting edge segments 22, 24 and 26 and the transitional cutting edge segment 28 may increase. Alternatively, if the diameter D of the imaginary inscribed circle 38, as shown in FIG. 3B, is decreased the lengths of the cutting edge segments 22, 24 and 26 and the transitional cutting edge segment 28 may decrease.

(27) As shown in FIG. 4, each side surface 16 comprises a first clearance face 40 extending from the top surface 12 and a second clearance face 42 extending from the first clearance face 40 to the bottom surface 14. As shown in FIG. 4, the first clearance face 40 extends toward the bottom surface 14 from the top surface 12 at a first clearance angle .sub.1 with respect to the axis of rotation 19 of the drilling insert 10. For example, the first clearance angle .sub.1 may be at least 1 degree, for example from 1 to 30 degrees, or from 2.5 to 20 degrees, or from 5 to 15 degrees. In a particular embodiment, the first clearance angle .sub.1 may be about 8 degrees. The first clearance angle .sub.1 may prevent rubbing of the first clearance face 40 against machined surfaces by providing clearance between the drilling insert 10 and the machined surface of the work piece. As shown in FIG. 4, the second clearance face 42 extends toward the bottom surface 14 from the first clearance face 40 at a second clearance angle .sub.2 with respect to the axis of rotation 19 of the drilling insert 10. For example, the second clearance angle .sub.2 may be at least 1 degree, for example from 5 to 40 degrees, or from 7.5 to 30 degrees, or from 10 to 20 degrees. In a particular embodiment, the second clearance angle .sub.2 may be about 15 degrees. The second clearance angle .sub.2 allows the drilling insert 10 be easily inserted and removed from the pocket 60 of the drilling body 50. In accordance with an embodiment of the present invention, the first clearance angle .sub.1 and the second clearance angle .sub.2 allow for the top surface 12 to be larger than the bottom surface 14. The first clearance angle .sub.1 and the second clearance angle .sub.2 further provide the first and second clearance faces 40 and 42 at orientations that allow for the drilling insert to be rigidly secured in the pocket 60 of the drilling body 50. In the embodiment shown, the second clearance angle .sub.2 is greater than the first clearance angle .sub.1, however any other suitable arrangement may be used, e.g., the second clearance angle .sub.2 may be less than or equal to the first clearance angle .sub.1.

(28) As shown in FIG. 4, the first clearance face 40 has a height H.sub.1 and the second clearance face 42 has height H.sub.2. In accordance with an embodiment of the present invention, the second clearance face height H.sub.2 may be greater than or equal to the first clearance face height H.sub.1, e.g., up to 75 percent higher. For example, the second clearance face height H.sub.2 may be at least 25 percent, or at least 35 percent, or at least 50 percent greater than the first clearance face height H.sub.1. In certain embodiments, the second clearance face height H.sub.2 is at least 50 percent of a total height of the drilling insert 10, e.g., at least 60 percent of the total height of the drilling insert. The first clearance face height H.sub.1 and the second clearance face height H.sub.2 are selected to allow the drilling insert 10 to be rigidly secured within a pocket 60 of the drilling body 50. The ratio of height H.sub.1 of the first clearance face 40 to the height H.sub.2 of the second clearance face 42 may typically range from 1:1 to 1:10, for example, from 1:1.2 to 1:5 or from 1.5:2 to 1:3. In accordance with an embodiment of the present invention, the first clearance face 40 may provide an abutment surface to be engaged in the pocket 60, and the second clearance face 42 provides a clearance to prevent the drilling insert from contacting the machined surface of the work piece.

(29) The drilling inserts 10 may be made of any suitable material, such as tool steels, cemented carbides, and superhard material, such as cubic boron nitride (CBN), polycrystalline cubic boron nitride (PCBN), polycrystalline diamonds (PCD), tungsten carbide (WC), cermet, ceramic, and the like. The drilling inserts 10 of the present invention may be fabricated by any suitable technique, such as carbide powder pressing, grinding or additive manufacturing to provide the plurality of cutting edge segments.

(30) FIGS. 5-7 illustrate a drilling tool system 5 in accordance with an embodiment of the present invention. The drilling tool system 5 includes a drilling body 50 and an inboard drilling insert 10 and a peripheral or outboard drilling insert 100 installed within the drilling body 50. The drilling body 50 has a generally cylindrical body 52 with a central longitudinal rotational axis 54. In accordance with an embodiment of the present invention, the generally cylindrical body 52 of the drilling body 50 includes a front drilling face 56, a rear mounting end 58 and a plurality of helical flutes 59. The front drilling face 56 comprises an interior pocket 60 structured and arranged to receive a central drilling insert 10 and a peripheral pocket 102 structured and arranged to receive a peripheral drilling insert 100. In the embodiment shown, the generally cylindrical body 52 of drilling body 50 includes two flutes 59, but any other suitable number of flutes may be used. For example, there may be one, three, four, five or more flutes.

(31) As shown in FIGS. 8 and 9, the insert pocket 60 comprises a rear surface 62, a first sidewall portion 64 extending generally perpendicularly forward from the rear surface 62 and a second sidewall portion 66 extending generally perpendicularly forward from the rear surface 62. While a generally square insert pocket 60 is shown in this embodiment, any other suitable shape of insert pocket may be used, e.g., rectangular, triangular or the like. As shown in FIGS. 8 and 9, the rear surface 62 may be configured to engage with a first side surface 16 of the drilling insert 10, the first sidewall portion 64 may be configured to engage a second side surface 16 of the drilling insert 10, and the second sidewall portion 66 may be configured to accommodate a third side surface 16 of the drilling insert 10. As used herein, the terms engage, engages, and engagement and engaging mean that two or more features interact with each other to restrict relative movement between the drilling insert 10 and the insert pocket 60. In certain embodiments, the insert pocket 60 may comprise a bottom seating surface 68 perpendicular to the rear surface 62 and the first and second sidewall portions 64 and 66. The bottom seating surface 68 may be configured to engage the bottom surface 14 of the drilling insert 10. As shown in FIGS. 8 and 9, the bottom seating surface 68 includes a threaded mounting hole 70 that may be configured to receive a mechanical fastener 90 to secure the drilling insert 10 in the insert pocket 60.

(32) As shown in FIGS. 8 and 9, the pocket 60 may include recessed channels 72 in the corners between the rear surface 62 and the first and second sidewall portions 64 and 66. The recessed channels 72 provide a clearance for the insert pocket 60 to receive the drilling insert 10. In certain embodiments, the rear surface 62 and the second sidewall portion 66 may further include cutting edge channels 74 located to receive transitional cutting edge segments 28 of the drilling insert 10. The cutting edge channels 74 are recessed in the rear surface 62 and the second sidewall portion 66 to the prevent the transitional cutting edge segments 28 from contacting the pocket 60. The side surfaces 16 contacting the rear surface 62 and the first sidewall portion 64 may experience the most force during drilling operations. In accordance with an embodiment of the present invention, when the drilling insert 10 is mounted in the insert pocket 60 only the side surface 16 corresponding to the second cutting edge segment 24 may contact the first sidewall portion 64. In accordance with an embodiment of the present invention, any suitable size or shape of insert pocket 60 may be used to engage any shape or size of indexable drilling insert 10.

(33) In the embodiment shown, the rear surface 62 and the second sidewall portion 66 are formed by a plurality of segments. For example, the rear surface 62 comprises a first rear surface segment 80 extending from the recessed channel 72 between the first sidewall portion 64 and the rear surface 62 to a cutting edge recess 74, and a second rear surface segment 82 extending from the cutting edge recess 74 to the recessed channel 72 between the rear surface 62 and the second sidewall portion 66. The second sidewall portion 66 comprises a rearward second sidewall segment 84 extending from the recessed channel 72 between the rear surface 62 and the second sidewall portion 66 to a cutting edge recess 74, and a forward second outer sidewall segment 86 extending from the cutting edge recess 74 to the front drilling face 56. In accordance with an embodiment of the present invention, the second rear surface segment 82 is structured and arranged to engage the side surface 16 corresponding to the first cutting edge segment 22. In certain embodiments, the second sidewall portion 66 does not contact the drilling insert 10. In accordance with an embodiment of the present invention, the first sidewall portion 64 is substantially linear, e.g., the first sidewall portion 64 comprises a single sidewall segment extending from the rear surface 62 to the front drilling face 56. However, any other suitable shape and arrangement of first sidewall portion 64 may be used, e.g., the first sidewall portion 64 may be formed by a plurality of sidewall segments having lengths and angles corresponding to the plurality of cutting edge segments of the drilling insert 10.

(34) As shown in FIGS. 8 and 9, the rear surface 62, the first sidewall portion 64 and the second sidewall portion 66 each include first and second engagement surfaces 76 and 78 structured and arranged to correspond to the first and second clearance surfaces 40 and 42 of the drilling insert 10. In accordance with an embodiment of the present invention, the first engagement surfaces 76 extend perpendicularly from the bottom seating surface 68. In accordance with an embodiment of the present invention, the second engagement surfaces 78 extends from the first engagement surfaces 76 at an angle corresponding to the first clearance angle .sub.1 of the first clearance face 40 of the drilling insert. The first and second engagement surfaces 76 and 78 of the rear surface 62, the first sidewall portion 64 and the second sidewall portion 66 allows for the drilling insert 10 to be more rigidly mounted in the pocket 60. In certain embodiments, the second engagement surface 78 of the first sidewall portion 64 contacts the drilling insert 10.

(35) In accordance with an embodiment of the present invention, the insert pocket 60 and the drilling insert 10 are structured and arranged to allow the convex curve 29B formed between the transitional cutting edge segment 28 and the second cutting edge segment 24 to make first contact with a work piece. In certain embodiments, the second cutting edge segment 24 makes a lead angle with the longitudinal rotational axis 54 of the drill body, e.g., from 1 to 5 degrees. The positioning of the drilling insert 10 in the pocket 60 of the drilling body 50, and the angles and orientation of the cutting edge segments 22, 24 and 28 and transitional cutting edge 28 directs the cutting forces toward the longitudinal rotational axis 54 of the drilling body. Directing the forces toward the rotational axis of the drill balances the cutting forces that the drilling body 50 experiences during the drilling process and thus keeps the drill from drifting away from the center.

(36) The drilling body 50 may be made of any suitable material, such as steel, stainless steel or any other material having sufficient strength. The drilling body 50 of the present invention may be fabricated by any suitable technique, such as machining to provide the insert pockets and flutes.

(37) As shown in FIGS. 10 and 11, the cutting edge 20 of the central drilling insert 10 and the cutting edge 120 of the peripheral insert 100 form a cutting profile 200. FIG. 10 illustrates in phantom the positioning of the peripheral insert 100 compared to the central drilling insert 10 when the drilling body 50 is rotated 180 degrees about its central longitudinal rotational axis 54 in accordance with an embodiment of the present invention. As shown in FIG. 11, the cutting edge 20 of the central drilling insert 10 forms an inner portion 205 of the cutting profile 200 and the cutting edge 120 of the peripheral insert 100 forms an outer portion 210 of the cutting profile 200 relative to the central longitudinal rotational axis 54. The cutting profile 200 formed by the cutting edge 20 of the central drilling insert 10 and the cutting edge 120 of the peripheral insert 100 is symmetrical about the central longitudinal rotational axis 54 of the drilling body 50. The rotation of the cutting profile 200 about the rotational axis forms the cutting diameter Dc of the drilling tool system 5.

(38) In accordance with an embodiment of the present invention, the cutting edge 20 of the central drilling insert 10 may overlap with the cutting edge 120 of the peripheral insert 100. As shown in FIG. 11, an intersection point 220 is formed at the point that the third cutting edge segment 26 overlaps with the cutting edge 120 of the peripheral insert 100. In accordance with an embodiment of the present invention, the intersection point 220 is selected to allow the length of the inner portion 205 of the cutting profile 200 to be substantially equal to the length of the outer portion 210 of the cutting profile 200. However, in accordance with an embodiment of the present invention, the length of the inner portion 205 may be unequal to the length of the outer portion 210. In accordance with an embodiment of the present invention, the portion of the third cutting edge segment 26 that is located between the intersection point 220 and the second corner edge portion 30 may not contact the work piece.

(39) FIGS. 10 and 11 illustrate that the convex curve 29B of the transitional cutting edge segment 28 at the point the transitional cutting edge segment 28 meets the second cutting edge segment 24 forms the most axially forward portion of the cutting profile 200. This allows the convex curve 29B to make first contact the work piece. In accordance with an embodiment of the present invention, a partial length of the inner portion 205 of the cutting profile 200 is more axially forward than the outer portion 210 of the cutting profile 200. In a particular embodiment, the entire length of the second cutting segment 24 of the central drilling insert 10 is more axially forward than the cutting edge 120 of the peripheral insert 100.

(40) As shown in FIG. 11, a horizontal plane 75 is normal to the central longitudinal rotational axis 54 of the drilling body 50. In the embodiment shown, the horizontal plane 75 is parallel to the reference plane 11. Alternatively, the reference plane 11 may be tilted with respect to the horizontal plane 75 at a negative angle. For example, the reference plane 11 may be provided at an angle of from 0 to 10 degrees, or from 0 to 7 degrees, or from 0 to 5 degrees with respect to the horizontal plane 75. In certain embodiments, the first cutting edge segment 22 extends radially outward from the central longitudinal rotational axis 54 at a positive angle toward the horizontal plane 75. In certain embodiments, the second cutting edge segment 24 extends radially outward from the central longitudinal rotational axis 54 at a shallow negative angle away from the horizontal plane 75. In certain embodiments, the third cutting edge segment 26 extends radially outward from the central longitudinal rotational axis 54 at a negative angle away from the horizontal plane 75. In certain embodiments, the transitional cutting edge segment 28 extends radially outward from the central longitudinal rotational axis 54 at a positive angle toward the horizontal plane 75. As shown in FIG. 11, the shallow negative angle of the second cutting edge segment 24 and the positive angle of the transitional cutting edge segment 28 may allow the convex curve 29B to be the closest portion of the cutting profile 200 to the horizontal plane 75. As shown in FIG. 11, the convex curve 29B may be the farthest point of the cutting edge 20 from the reference plane 11.

(41) In accordance with an embodiment of the present invention, the orientation and length of the plurality of cutting edge segments 22, 24 and 26 and the transitional cutting edge segment 28 of the central drilling insert allow for at least a segment of the inner portion 205 of the cutting profile to contact the work piece before the peripheral insert 100, and allow the cutting profile to be formed substantially equally by the cutting edge 20 of the central insert 10 and the cutting edge 120 of the peripheral insert 100.

(42) As used herein, including, containing and like terms are understood in the context of this application to be synonymous with comprising and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, phases or method steps. As used herein, consisting of is understood in the context of this application to exclude the presence of any unspecified element, material, phase or method step. As used herein, consisting essentially of is understood in the context of this application to include the specified elements, materials, phases, or method steps, where applicable, and to also include any unspecified elements, materials, phases, or method steps that do not materially affect the basic or novel characteristics of the invention.

(43) For purposes of the description above, it is to be understood that the invention may assume various alternative variations and step sequences except where expressly specified to the contrary. Moreover, all numbers expressing, for example, quantities of ingredients used in the specification and claims, are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

(44) It should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of 1 to 10 is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

(45) In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of or means and/or unless specifically stated otherwise, even though and/or may be explicitly used in certain instances. In this application, the articles a, an, and the include plural referents unless expressly and unequivocally limited to one referent.

(46) In this application, the use of horizontal, vertical, positive and negative are used as relative terms and it is understood that during use the drilling body and the drilling insert may have different orientations.

(47) Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.