Double-Sided Cutting Inserts for High Feed Milling

INVENTORS

X. Daniel Fang

Jean-Luc Dufour

David J. Wills

CROSS-REFERNCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application l o claiming priority under 35 U.S.C. § 120 from co-pending U.S. Patent Application Serial No. 12/369,796, filed on Feb. 12, 2009, and entitled "Double-Sided Cutting Inserts for High Feed Milling," the entire disclosure of which is incorporated by reference herein.

BACKGROUND

15 [0002] The present disclosure is directed to a double-sided cutting insert.

The double-sided cutting insert exhibits a combination of favorable cutting edge strength, and unique cutting edge geometry, thus, allowing milling operations at relatively high feed rates and may be useful in face milling, slot milling, plunge milling, and ramping operations.

0 [0003] Cutting inserts, carbide and other types, are well known in the art.

Many indexable cutting inserts are single-handed, either right handed or left handed, due to the geometrical constraints in a rotary machining operation where the cutting tool is rotating against a stationary work piece being ground.

[0004] Recently, there have been increasing demands for reduced cost5 and high productivity in metal machining industries. Two common approaches in the design of indexable carbide cutting inserts, from geometrical point of view, are either to design a double-sided cutting insert, or to design more available cutting edges on a single-sided cutting insert. Double-sided cutting inserts can double the number of available cutting edges, and have cost reduction benefits for both cutting tool end users0 and cutting tool manufacturers. An ideal solution to a productive indexable cutting insert l design can be an indexable cutting insert that has both more available cutting edges and is double-sided. However, the geometric design of a double-sided cutting insert for milling is a more challenging task compared to a traditional single-sided cutting insert, because of the complexity of positioning a double-sided cutting insert in an insert pocket on a cutting tool holder. The difficulty increases as the number of cutting edges increases. Furthermore, the design of a single-handed double-sided cutting insert with more indexable cutting edges for milling operations is even more challenging because the two sides of a single-handed double sided cutting insert may not be a simple mirror image of each other.

[0005] In the case of a single-handed double-sided cutting insert with convex cutting edges and conical peripheral surfaces, design is even more challenging due to the difficulties to secure the cutting inserts having convex peripheral profile as compared to commonly used double-sided cutting inserts in a shape of square, triangle or parallelogram, wherein a lateral peripheral surface is planar or perpendicular to a bottom seat face in an insert pocket of a tool holder. A single-sided cutting insert for high feed face milling is disclosed in United States Patent No. 7,220,083, assigned to the assignee of the present application, and which is hereby incorporated herein by reference, and United States Patent Application Publication No. US 2007/0189864, published August 16, 2007, a continuation patent application of the aforesaid United States Patent No. 7,220,083, which is also assigned to the assignee of the present application, and which is also hereby incorporated herein by reference. This patent and published patent application disclose a single-sided cutting insert having four convex cutting edges, each connected by a nose corner, and each convex cutting edge having a curved cutting edge region and one or more substantially straight cutting edge regions. The curved cutting edge region has a large radius to facilitate high feed face milling operations. However, this insert is single-sided, thus having only four indexable cutting edges.

[0006] Double-sided cutting inserts are disclosed in a number of U.S.

patents. For example, United States Patent Numbers 6,929,429; 7,232,279; 7,241 ,082; 6,921 ,233; 7,306,409; and 6,543,970. The double-sided cutting inserts described above provide more indexable cutting edges, but the cutting edges of these inserts can

9 be less desirable for high feed milling operations than the cutting edges of the single- sided cutting insert described in the aforesaid United States Patent Application

Publication No. US 2007/0189864.

[0007] Therefore, it would be desirable to produce a double-sided cutting 5 insert having eight indexable cutting edges, wherein each cutting edge has features to facilitate high feed milling operations as described in the aforesaid United States Patent Application Publication No. US 2007/0189864.

SUMMARY l o [0008] The present disclosure describes embodiments of a double-sided cutting insert for milling operations, such as, face milling, slot milling, plunge milling, and ramping operations. Various embodiments describe one or more double-sided cutting inserts which may provide six or eight indexable cutting edges, each exhibiting a combination of favorable cutting edge strength and unique cutting edge geometry to

15 facilitate milling operations at relatively high feed rates.

[0009] More particularly, embodiments of a double-sided cutting insert having a plurality of indexable convex cutting edges can generally comprise: a top face and a bottom face separated by a virtual middle plane; at least three convex cutting edges on each of the top and bottom faces, each convex cutting edge having at least a0 curved cutting edge region; at least three nose corners on each of the top and bottom faces, each nose corner connecting two of the convex cutting edges; and at least three peripheral side surfaces extending from each of the top and bottom faces to the virtual middle plane. Each peripheral side surface can comprise a first primary conical peripheral surface extending from a primary curved convex cutting edge region at the5 top face toward a twisted secondary curved convex cutting edge region at the bottom face, and a second primary conical peripheral surface extending from a secondary curved convex cutting edge region at the top face toward a twisted primary curved convex cutting edge region at the bottom face; a first primary planar surface extending from a primary substantially straight cutting edge region at the top face to a virtual0 middle plane, and a second primary planar surface extending from a primary substantially straight cutting edge region at the bottom face toward a virtual middle plane, wherein both the first and second primary planar surfaces are truncated by at least a common lateral seating face which is perpendicular to both the top and bottom faces; and a secondary conical peripheral surface extending from a nose comer toward 5 the virtual middle plane.

[0010] In various embodiments a milling tool system is described. The milling tool system can comprise a cutter body and at least one double-sided cutting insert, such as one or more of the cutting inserts summarized above.

[0011] These and other advantages will be apparent upon consideration of l o the following description of certain embodiments in connection with the following

drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0012] Embodiments of the double-sided cutting insert can be best

15 understood by reference to the following drawing figures, wherein:

[0013] Figure 1 is a perspective view of an embodiment of a double-sided single-handed cutting insert;

[0014] Figures 2(a) - 2(c) illustrate details of the double-sided single- handed cutting insert shown in Figure 1 ;

0 [0015] Figures 3(a) and 3(b) illustrate top and detail views of a nose corner of a the double-sided single-handed cutting insert shown in Figure 1 ;

[0016] Figures 4(a) - 4(c) facilitate an understanding of the mathematical relationship between the single-handed geometry of both sides of the cutting insert shown in Figure 1 ;

5 [0017] Figures 5(a) - 5(c) illustrate another embodiment of a double-sided single-handed cutting insert;

[0018] Figures 6(a) and 6(b) illustrate a further embodiment of a double- sided single-handed cutting insert;

[0019] Figures 7(a) and 7(b) illustrate yet another embodiment of a

0 double-sided single-handed cutting insert; [0020] Figures 8(a) and 8(b) show side and top views of a milling tool holder with double-sided cutting inserts secured thereto;

[0021] Figures 9(a) and 9(b) illustrate an embodiment of a double-sided cutting insert having five sides;

5 [0022] Figures 10(a) and 10(b) illustrate an embodiment of a double-sided cutting insert having three sides; and

[0023] Figures 1 1 (a) and 1 1 (b) illustrate a further embodiment of a double- sided cutting insert having three sides.

[0024] Figures 12(a)-12(c) illustrate an embodiment of a double-sided l o cutting insert having four sets of cutting edges per side.

[0025] Figures 13(a)-12(c) illustrate a further embodiment with reference to Figures 12(a)-12(c) of a double-sided cutting insert having four sets of cutting edges per side.

[0026] Figures 14(a)-(b) further illustrate another embodiment of a double- I 5 sided high feed milling inserts.

DESCRIPTION OF CERTAIN EMBODIMENTS

[0027] It is to be understood that certain descriptions of the present disclosure herein have been simplified to illustrate only those elements and limitations0 that are relevant to a clear understanding of the present disclosure, while eliminating, for purposes of clarity, other elements. Those of ordinary skill in the art, upon

considering the present description of the disclosure, will recognize that other elements and/or limitations may be desirable in order to implement the present disclosure.

However, because such other elements and/or limitations may be readily ascertained by5 one of ordinary skill upon considering the present description, and are not necessary for a complete understanding of the present disclosure, a discussion of such elements and limitations is not provided herein. For example, as discussed herein, embodiments of the cutting inserts of the present disclosure may be produced in the form of face milling inserts and other inserts for materials cutting. The methods by which cutting inserts are0 manufactured are generally understood by those of ordinary skill in the art and, accordingly, are not described in detail herein. In addition, all the geometric shapes should be considered to be modified by the term "substantially" wherein the term "substantially" means that the shape is formed within typical design and manufacturing tolerances for cutting inserts.

[0028] Furthermore, certain embodiments of the double-sided cutting inserts according to the present disclosure are disclosed in the form of face milling cutting inserts. It will be understood, however, that the double-sided cutting inserts may be embodied in forms, and applied to end uses, that are not specifically and expressly described herein. For example, one skilled in the art will appreciate that embodiments of the double-sided cutting inserts may be manufactured as cutting inserts for other methods of removing metal from work pieces.

[0029] Certain embodiments of the present disclosure are directed to double-sided cutting inserts, including double-sided single-handed inserts, which provide an increased number of indexable cutting edges. Moreover, each cutting edge can be configured to provide a combination of advantages exhibited by round-shaped cutting inserts having a very large radius, and square-shaped inserts of conventional size adapted for conventional use in a variety of milling and/or machining applications.

[0030] Referring now to Figures 1 and 2, and particularly the perspective view in Figure 1 , an embodiment of a double-sided cutting insert 10 having a plurality of indexable cutting edges, eight as shown in these figures, which can comprise: a top face 1 1 and a bottom face 12 separated by a virtual middle plane 13; at least three convex cutting edges 21 , 31 on each of the top 1 1 and bottom 12 faces, each convex cutting edge 21 , 31 having at least a curved cutting edge region 22, 32; at least three nose corners 25, 35 on each of the top 1 1 and bottom 12 faces, each nose corner 25, 35 connecting two of the convex cutting edges 21 , 31 ; at least three peripheral side surfaces 19, 20 extending from each of the top 1 1 and bottom 12 faces to the virtual middle plane 13; and at least three lateral seating surfaces 41 , each lateral seating surface 41 being formed on an adjacent pair of peripheral side surfaces 19, 20 of the top 1 1 and bottom 12 faces, such that each lateral seating surface 41 defines a common lateral seating surface for both the top 1 1 and bottom 12 faces. Each peripheral side surface 19, 20 can comprise a primary conical peripheral surface 26, 36 extending from a curved cutting edge region 22, 32 toward the virtual middle plane 13, and a secondary conical peripheral surface 29, 39 extending from a nose corner 25, 35 toward the virtual middle plane 13. In the context of the drawings, and for purposes of this description, the term "face," as used in regard to the "top face 1 1 " and the "bottom 5 face 12," can refer generally to the top "half," or "portion," and the bottom "half," or

"portion," of the double-sided cutting insert 10.

[0031] Moreover, although the double-sided cutting insert is shown being generally rectangular in shape having four "sides," it is to be understood that the double- sided cutting insert 10 could also be triangular shaped, having three sides, or could be l o otherwise shaped, having five or more sides, as will be described hereinafter in

connection with Figures 9-1 1 .

[0032] In certain embodiments, the bottom face 12 is a mirror image of the top face 1 1 about the virtual middle plane 13, such that the top 1 1 and bottom 12 faces are not "single-handed" in the same direction (refer to Figures 6 and 7 described in

15 more detail hereinafter). There can also be chip breaking geometry 45, 46 provided on each of the top 1 1 and bottom 12 faces. In certain other embodiments, even where the top and bottom faces are not twisted relative to each other, the chip breaking geometry can be such that the top and bottom faces are still single-handed in the same direction (refer to Figure 5 which is described in more detail hereinafter).

0 [0033] Furthermore, each convex cutting edge 21 , 31 can be provided with a primary substantially straight cutting edge region 23, 33, provided intermediate the curved cutting edge region 22, 32 and the nose corner 25, 35, and each peripheral side surface 19, 20 can have a primary planar facet 27, 37 extending from the primary substantially straight cutting edge 23, 33 toward the virtual middle plane 13. The

5 primary substantially straight cutting edge 23, 33 (sometimes referred to as a "wiper"), together with the associated primary planar facet 27, 37 functions to improve the surface finish of the machined workpiece. Additionally, each convex cutting edge 21 , 31 can also have a secondary substantially straight cutting edge region 24, 34, provided intermediate the primary substantially straight cutting edge region 23, 33 and the nose0 corner 25, 35, and each peripheral side surface 19, 20 can have a secondary planar facet 28, 38 extending from the secondary substantially straight cutting edge 24, 34 toward the virtual middle plane 13. The secondary substantially straight cutting edge region 24, 34, together with the associated secondary planar facet 28, 38 can provide clearance for the primary substantially straight cutting edge region 23, 33 and

associated primary planar facet 27, 37.

[0034] In embodiments having at least a primary substantially straight cutting edge region 23, 33, each of the top 1 1 and bottom 12 faces can be "twisted", i.e., rotated relative to each other, such that each of the top 1 1 and bottom 12 faces can be single-handed in same direction. In this case, the top 1 1 and bottom 12 faces will not be a mirror image of each other about the virtual middle plane 13.

[0035] Each primary conical peripheral surface 26 associated with the top face 1 1 can extend outwardly and toward the virtual middle plane 13 at a first angle relative thereto, and each primary conical peripheral surface 36 associated with the bottom face 12 can similarly extend outwardly and toward the virtual middle plane 13, at the same first angle, relative to the virtual middle plane 13, as the conical peripheral surface 26 associated with the top face 1 1 .

[0036] As one of ordinary skill in the art understands, the conical peripheral surfaces result from curved features on the faces of the inserts. For example, the curved cutting edge regions result in associated conical peripheral surfaces, i.e., the aforementioned primary conical peripheral surface. Likewise, the nose corners, which also defining curved edges on the top face, also result in conical peripheral surface, i.e., the secondary conical peripheral surfaces. In contrast, where a substantially straight "cutting edge" is provided, such as the primary substantially straight cutting edge regions, the planar peripheral surfaces, or "facets," i.e., the aforementioned primary planar facets, are also created as clearance surfaces for the associated substantially straight cutting edge regions. It is generally understood that "curved" lines, e.g., cutting edges, can consist of a series of small straight line

segments. However, as will be understood by one of ordinary skill in the art, the

"substantially straight cutting edge regions" described herein are separate cutting edge regions, or portions, of the overall convex cutting edge. Thus, the "substantially straight cutting edge regions" are not merely a part or "segment" of the "curved" cutting edge region," but are a separate and distinct portion of the overall convex cutting edge. This is further made clear by the fact that each substantially straight cutting edge region described herein has a planar clearance surface, e.g., planar facet, associated therewith, and not a conical peripheral surface (as are associated with the curved cutting edge regions). The primary and secondary planar facets impart, respectively, a wiper function to the primary substantially straight cutting edge region 23, 33, and provide clearance for the secondary substantially straight cutting edge region 27, 37. The "planar facet" may also be referred to alternatively as a "planar clearance surface."

[0037] Additionally, the curved cutting edge regions and the substantially straight cutting edge regions, as described herein, are "curved" or "substantially straight" as viewed from above, i.e., in "top" views, as depicted in Figures 2(a), 3(a), 4(a), 5(b), 9(b), 10(b) and 1 1 (b).

[0038] Each common lateral seating surface 41 can be formed by truncating portions of adjacent pairs of peripheral side surfaces 19, 20, i.e., adjacent pairs being the peripheral side surfaces 19, 20 of the top 1 1 and bottom 12 faces which are extending toward each other on the same side of the cutting insert 10. In particular, as described above, each peripheral side surface 19, 20 on both the top 1 1 and bottom 12 faces extends toward the virtual middle plane 13, i.e., each peripheral side surface 19 on the top face 1 1 extends towards an "adjacent" peripheral side surface 20 on the bottom face 12, on respective sides of the cutting insert 10. Consequently, the peripheral side surfaces 19 on the top face 1 1 and the peripheral side surfaces 20 on the bottom face 12 will meet, i.e., intersect, each other at the virtual middle plane 13. Each common lateral seating surface 41 can be created, or formed, by truncating, e.g., by grinding flat, the peripheral side surfaces 19, 20 at the intersection of such adjacent ones thereof. As shown in the drawing figures, each of the common lateral seating surfaces 41 can be terminated short of each the curved cutting edge regions 22, 32 on each of the top 1 1 and bottom 12 faces of the cutting insert 10. In other words, the intersecting peripheral side surfaces 19, 20 are ground flat beginning at the virtual middle plane 13 and extending outwards toward the convex cutting edges 21 , 31 on each of the top 1 1 and bottom 12 faces. However, the grinding can be terminated at a certain depth so that the lateral seating surfaces 41 do not extend entirely to the convex cutting edges 21 , 31 . Alternatively, the lateral seating surfaces 41 could be extended entirely to the convex cutting edges 2 , 31 if it were so desired.

[0039] One or more, and typically four, plateaus 16 can be provided, on each of the top 1 1 and bottom 12 faces, although the plateaus are shown only on the 5 top surface 1 1 for purposes of this description. Each plateau 16 can be flat and can define a plane which is generally perpendicular to a central axis 15 of a through-hole 14 which is used to secure the cutting insert 10 in a cutter insert pocket, as described more fully hereinafter in connection with Figures 8 and 9. Each common lateral seating surface 41 can be generally perpendicular to the flat plateaus 16. Each nose corner 25, l o 35 can comprise one or more of a circular arc, a series of circular arcs, and a multi- segment spline curve, and each curved cutting edge region 22, 32 can have a radius which is at least two times the radius of the largest circle that may be inscribed on the top 1 1 or bottom 12 face of the double-sided cutting insert 10. In certain embodiments, each curved cutting edge region 22, 32 can have a radius which is at least four times

15 the radius of the largest circle that may be inscribed on the top 1 1 or bottom 12 face of the double-sided cutting insert 10. Each curved cutting edge region 22, 32 can comprise one or more of a portion of an ellipse, a portion of a parabola, and a multi- segment spline curve.

[0040] The virtual middle plane 13 will generally be located at the half0 thickness of the cutting insert 10. Both the top face 1 1 and the bottom face 12 can

comprise the same face geometry and periphery. As shown in Figure 1 , both faces 1 1 , 12 are single-handed, and are twisted, i.e., rotated, relative to each other. The "twisted" (i.e., rotated) face geometry between the top face 1 1 and the bottom face 12 results because each face of the cutting insert is desired to be single-handed. In many milling5 applications, each of cutting edges is fully engaged in cutting, and in some cases, for example as embodiments shown in Figures 1 -4, there are a number of features associated with both the convex cutting edges and the clearance surfaces for each of the set of cutting edges thereof on each face of the double-sided insert 10.

[0041 ] A through hole 14 with a central axis 15 perpendicular to the virtual0 middle plane 13, and the flat plateaus 16, can be provided for securing the insert in a tool holder. As shown, each face 1 1 , 12 of the double-sided cutting insert 10 can have four sets of convex cutting edges, which can be identical, and each one is connected by a nose corned 25. Using just the top face 1 1 as an example, each of the convex cutting edges 21 comprises a curved cutting edge region 22 having a large radius, a primary substantially straight cutting edge region 23, and a secondary substantially straight 5 cutting edge 24, which is optional. In regard to both of the substantially straight cutting edge regions described above, and as described in connection with other figures hereinafter, the term "straight" means straight as viewed along the central axis 15.

Each of the convex cutting edges 21 can have an associated peripheral side surface 19 which extends towards the virtual middle plane 13 in an outwardly angled direction. The l o peripheral side surfaces 19 can angle outwardly at an angle greater than 90 degrees relative to the virtual middle plane 13, and/or the flat plateau 16 which is generally parallel to the virtual middle plane 13. Each outwardly angled peripheral side surface 9 can be comprised of a primary conical peripheral surface 26 associated with the curved cutting edge region 22, a primary planar facet 27 associated with the primary

15 substantially straight cutting edge region 23, an optional secondary planar facet 28

associated with the optional secondary substantially straight cutting edge region 24, and a secondary conical peripheral surface 29 associated with the nose corner 25.

[0042] Similarly, on the bottom face 12 there can also be four identical convex cutting edges 31 , each one connected by a nose corner 25. Each convex0 cutting edge can comprise a curved cutting edge region 32 having a large radius, a

primary substantially straight cutting edge region 33, and an optional secondary substantially straight cutting edge region 34. Also, just as for the top face 1 1 , each convex cutting edge 31 can be associated with a peripheral side surface 20 which extends towards the virtual middle plane 13 in an outwardly angled direction. Like the5 peripheral side surfaces 19 associated with the top surface 1 1 , the peripheral side

surfaces 20 can angle outwardly at an angle greater than 90 degrees relative to the virtual middle plane 13, and/or the flat plateau 16 which is generally parallel to the virtual middle plane 13. Likewise, each outwardly angled peripheral side surface 19 can be comprised of a primary conical peripheral surface 36 associated with the curved0 cutting edge region 31 , a primary planar facet 37 associated with the primary

substantially straight cutting edge region 33, an optional secondary planar facet 38 associated with the optional secondary substantially straight cutting edge region 34, and a secondary conical peripheral surface 39 associated with the nose corner 35.

[0043] As can be seen in Figures 1 and 2, the peripheral side surfaces 19, 20 associated with the top 1 1 and bottom 12 faces of the insert 10 are not simple mirror 5 images about the virtual middle plane 13. Rather, the peripheral side surfaces 19

associated with top face 1 1 are twisted, i.e., rotated, relative to the peripheral side surfaces 20 associated with the bottom face 12, in order to account for the desired single-handed cutting direction in the milling operations.

[0044] More particularly, the lateral seating surface 41 can be created on l o each of the peripheral side surfaces 19, 20 by truncating, in a direction perpendicular to the virtual middle plane 13, or the flat plateau 16, two adjacent primary conical peripheral surfaces 26, 36 on each of the peripheral side surfaces of the top 1 1 and bottom 12 faces of the insert 10. As shown, the common lateral seating surface 41 is terminated short of each curved cutting edge region 22, 32 on each face 1 1 , 12 of the is cutting insert 10. However, the lateral seating surface could alternatively be extended to the convex cutting edges 21 , 31 if desired.

[0045] As will be described hereinafter, the various geometric features on each face 1 1 , 12 of the insert 10 are arranged in a certain order, from "start" to "finish." For example, referring to the embodiment of the insert 10 shown in Figure 1 , for

0 example, both the top face 1 1 and the bottom face 12 can have an equal number of convex cutting edges 22 connected by nose corners 25. These features can "start" with, e.g., a first/respective nose corner 25 followed by a respective primary

substantially straight cutting edge region 23, and lastly a respective curved cutting edge region 22 having the large radius. Where it is provided, a respective second

5 substantially straight cutting edge region 24 is provided between the first substantially straight cutting edge region 23 and the nose corner 25. Correspondingly, each face 1 1 , 12 of the insert 10 has the aforesaid peripheral side surfaces 19, 20, including conical surfaces and planar facets, associated with the convex cutting edges 2 , 31 , including the curved cutting edge regions 22, 32 and any substantially straight cutting edge0 regions 23, 33 and 24, 34. In view of Figure 1 for example, and just in regard to the top surface 1 1 , the peripheral side surfaces 19 can comprise, in order, the conical clearance surfaces 29 associated with the nose corners 25, followed by the primary planar facet 27 associated with the primary substantially straight cutting edge regions 23, followed by the primary conical clearance faces 26 associated with the curved cutting edge regions 22. Where the second substantially straight cutting edge regions 5 24 are provided, the second planar facets 28 associated therewith can be provided intermediate the conical clearance faces 29 and the first planar facets 27. The peripheral side surfaces 19, 20 associated with each of the top 1 1 and bottom 12 faces can share a single, common lateral seating surface 41.

[0046] The chip groove geometry 45, 46, which can be provided on each l o side of the insert, can vary between each nose corner 25, 35. More particularly, the chip groove geometry 45, 46 can change from one "end" (i.e., close to one nose corner 25, 35) to another "end" (i.e., close to the next nose corner 25, 35). Moreover, different chip groove geometry can also result in the convex cutting edges 21 , 31 having a "wavy" configuration, as observed from a side view, as illustrated in Figures 5 and 7, for

15 example.

[0047] Turning more particularly to Figures 2(a) through 2(c), further details of single-handed double-sided cutting insert 10 are shown, in which Figure 2(a) is a top view, Figure 2(b) is a section view along line C-C which passes through the center of the screw hole 14 and is perpendicular to a common lateral seating surface0 41 , and Figure 2(c) is a side view. As shown, the convex cutting edge 21 can comprise a curved cutting edge region 22, a primary substantially straight cutting edge region 23, an optional secondary substantially straight cutting edge region 24 and a nose corner 25. In Figure 2(a) the insert 10 is illustrated positioned in the same manner as if the insert 10 were held in a tool holder for a machining operation, in which the primary5 substantially straight cutting edge region 23 is positioned perpendicular to a cutting axis on a tool holder (refer to Figures 8 and 9). The primary substantially straight cutting edge region 23 is aligned in this manner, relative to the surface of a work piece being operated upon, in order to improve the surface finish on the work piece. As also illustrated, the maximum depth of cut "DOC" in a milling operation will occur at point 58,0 on the nose corner 25 at the other side of the curved cutting region 22 which is

contacting the work piece. The cutting insert 10 configured as shown in Figures 1 and 2 is designed to only move in a single direction, and is thus referred to as being a single- handed cutting insert.

[0048] Referring to Figure 2(b), an angle A1_top can be defined between the virtual middle plane 13, or a flat plateau 16 on the top face 1 1 of the cutting insert 10, and the primary conical peripheral surface 26. The distance between the curved cutting edge region 22 on the top face 1 1 and the common lateral seating surface 41 can be defined as D_top. As previously described in connection with Figure 1 , each convex cutting edge 21 is associated with an outward-angled peripheral side surface comprising a primary conical peripheral surface 26, a primary planar facet 27, and an optional secondary planar facet 28. Additionally, a secondary conical peripheral surface 29 is associated with a nose corner 25. Each of these peripheral surfaces extend toward, and can terminate approximately at the virtual middle plane 13, which can be at a half thickness of the insert 10.

[0049] Turning to Figure 2(c), an angle A2_top can be defined between the virtual middle plane 13, or the flat plateau 16 on the top face 1 1 , and a surface 52, which can represent any of the above-mentioned surfaces 26, 27, 28 or 29 on the top face 1 1 of the cutting insert 10. Similarly, an angle A1_bot can be defined between the virtual middle plane 13, or a flat plateau 51 on the bottom face 12, and the primary conical peripheral surface 36. The distance between the curved cutting edge region 32 on the bottom face 12 of the cutting insert 10 and the common lateral seating surface 41 can be defined as D_bot. Additionally, an angle A2_bot can be defined between the virtual middle plane 13, or flat plateau 51 , and a surface 53, which can represent, similarly to surface 52, any of the above-mentioned surfaces 36, 37, 38 or 39 on the bottom face 12 of the cutting insert 10.

[0050] Furthermore, an angle A3_com can be defined between a common lateral seating surface 41 and a primary conical peripheral surface 26 or 36, on either the top 1 1 or bottom 12 face of the cutting insert 10. Therefore, having set out the above-described definitions, the following equation (1 ) can be established to

quantitatively describe the relationship between the related surfaces thus being used as a reference in geometry design: A\ _ top > 90"

D _ top - D __bot

A\_ top = A\ _bot

A2 _ top = A2 _bot

Al _^ top = A2 _top

A3 _ com = Al _ top - 90

[0051] One of the important features of the double-sided cutting insert 10 described herein is the common lateral seating surface 41 . The purpose of such a common lateral seating surface is to enable double-sided cutting insert, and particularly a single-handed double-sided cutting insert with convex cutting edges and substantially conical dominated peripheral surfaces, to be properly secured in an insert pocket on a tool holder, while also providing all of the requisite positive cutting geometry in a milling operation. In order to mathematically work out how such a common lateral seating surface is created, it is useful to understand how the two sides of a single-handed and double-sided cutting insert are twisted, i.e., rotated, relative to each other.

[0052] Referring now to Figures 3(a) and 3(b), in which Figure 3(a) is a top view and Figure 3(b) is an enlarged detail view of section "B" in Figure 3(a), a single- handed double-sided cutting insert 55 is illustrated. The outside curve 58 is the external profile at a virtual middle plane at generally the half thickness of the cutting insert 55. The cutting edge regions denoted 61 to 65 in solid lines are on the top face of the cutting insert 55. Cutting edge region 61 corresponds to a curved cutting edge region with a large radius R1_top which is greater than or equal to two times the radius R_ic of the inscribed circle 59 (on either the top or bottom face of cutting insert 55); cutting edge region 62 corresponds to a primary substantially straight cutting edge region (as seen in a top view) with a length of L1_top; cutting edge region 63 corresponds to an optional secondary substantially straight cutting edge region (also as seen in a top view) with a length of L2_top; cutting edge region 64 corresponds to a nose corner with a radius of R2_top; and cutting edge region 65 corresponds to a curved cutting edge region (same as the curved cutting edge region 61 ) which is connected to the other side of the nose corner 64. The cutting edge regions 61 to 63 thus can be understood to comprise one of the illustrated four identical convex cutting edges on the top face of the double-sided cutting insert 55. There is an offset angle A4_top between the primary substantially straight cutting edge region 61 and the optional secondary substantially straight cutting edge region 62. Such an offset angle A4_top can be provided to protect the nose comer 64 from contacting the workpiece surface which is perpendicular to a cutting axis of a tool holder.

[0053] Similarly to the top face of the cutting insert 55, cutting edge regions 71 to 75 in dotted lines are on the bottom face of the cutting insert 55. Cutting edge region 71 corresponds to a curved cutting edge region having a radius R1_bot which is greater than or equal to two times the radius R_ic of the inscribed circle 59; cutting edge region 72 corresponds to a primary substantially straight cutting edge region with a length of L1 _ bot; cutting edge region 73 corresponds to an optional secondary substantially straight cutting edge region with a length of L2_bot; cutting edge region 74 corresponds to a nose corner with a radius of R2_bot; and cutting edge region 75 corresponds to a curved cutting edge region (same as the curved cutting edge region 71 ) which is connected to the other side of the nose corner 74. The cutting edge regions 71 to 73 can thus be understood to comprise one of the illustrated four identical convex cutting edges on the bottom face 12 of the double-sided cutting insert 55. There is also an offset angle A4__bot, as described-above for the top face, provided between the primary substantially straight cutting edge region 71 and the optional secondary substantially straight cutting edge region 72.

[0054] The quantitative relationship among the parameters as above described can be expressed by the following equation (2):

R\ _top = R\ _bot

L\ _ top - L\ _bot

L2_top = L2_bot

R2_top = R2_bot (2)

A4_top = A4_bot

R\ _top≥2 * R _ ic

AA_top < 5 [0055] It is clear from the figures, particularly Figure 3(b), that the top face of the cutting insert 55 is twisted, i.e., rotated, relative to the bottom face of the cutting insert 55. This twist is relative to a virtual nose center line 57 which passes through the center of the inscribed circle 59 and a virtual nose center 70 as if the top and bottom faces were not twisted due to the single-sided effect.

[0056] As the next step to further quantitatively describe a single-handed double-sided cutting insert having convex cutting edges with big radius, a mathematical relationship can be derived between the single-handed geometry from both faces of the cutting insert and the common lateral seating surfaces.

[0057] Turning to Figures 4(a) through 4(c), an embodiment of a single- handed double-sided cutting insert 81 for high feed milling is shown, in which Figure 4(a) is a top view of the cutting insert 81 having an inscribed circle 82 and a screw hole 83 which is coincident with the inscribed circle 82, Figure 4(c) is an enlarged detail view of "D" from Figure 4(a), and Figure 4(b) is a projected side view following the direction along the line PO 84 in Figure 4(c). In Figure 4(c), where some non-relevant lines are removed for easy clarification, the top convex cutting edge 90 in solid lines comprises an optional secondary substantially straight cutting edge region 93 connected to the nose corner 92, a primary substantially straight cutting edge region 94 following the optional secondary substantially straight cutting edge region 93, and a curved edge region 95 connected between the primary substantially straight cutting edge region 94 and the next nose corner. Similarly, on the same portion shown in Figure 4(c), but at the bottom face of the cutting insert 81 , the bottom convex cutting edge 100 in dashed lines comprises an optional secondary substantially straight cutting edge region 103 connected to the nose corner 102, a primary substantially straight cutting edge region 104 following the optional substantially straight cutting edge region 103, and a curved edge region 105 connected between the primary substantially straight cutting edge region 104 and the next nose corner 106.

[0058] As also shown in Figure 4(c), an XOY coordinate system is established with the origin "O" at the center of the inscribed circle 82. The Ύ" axis represents the cutting axis of a milling cutter, and the "X" axis is parallel to the work piece surface being machined. Thus, if the cutting insert 81 is mounted in an insert pocket of a milling cutter, a primary substantially straight cutting edge region 1 1 1 , previously defined as L1_top in Figure 3, will extend in a direction perpendicular to the "Y" axis, i.e., the cutting axis of the milling cutter. Since the four identical convex cutting 5 edges shown on the top face of the cutting insert 81 are indexable about the center of the inscribed circle 82, the perpendicular distance defined by D_ctr_top1 (as seen in Figure 4(c)) from the center "0" to a primary substantially straight cutting edge region 1 1 1 must be equal to the similar perpendicular distance defined by D_ctr_top2 (also as seen in Figure 4(c)) from the center "0" to a primary substantially straight cutting edge i o region 94, which can be mathematically described by the following equation (3):

(D_ctr_top) _j = (D_ctr_top) _i+l , = 1, 2, 3

(3)

(LUop), = (Ll_top) _i+l , / = 1, 2, 3

[0059] In the preceding equation, D_ctr_top is mainly determined by 1 5 design parameters like the radius of a curved cutting edge region R1_top, the radius of the inscribed circle R_ic, and the length of a primary substantially straight cutting edge region L1_top, as well as the number of convex cutting edges, which are four in the embodiments described herein. Similarly a primary substantially straight cutting edge region 104, defined as L1_bot, with a perpendicular distance to the center "0" being0 defined as D_ctr_bot, shown in Figure 4(c), will satisfy a similar mathematical

relationship as below:

(D_ctr_bot)i = (D_ctr_bot) _i+l , / ^' = 1, 2, 3

(4)

(Ll_bot), = (Ll_bot) _i+I , i = l, 2, 3 5 [0060] Further, as already discussed in connection with Figure 3, there is a virtual nose center line 57 passing through the center of an inscribed circle 59 and a virtual nose center 70, as if the top and bottom face were not twisted due to the single- sided effect. There are four such virtual nose center lines, one at each nose corner, as shown in Figure 4(c), for the virtual nose center lines 1 13 and 1 14 which are angled at 90 degrees to each other due to there being four sets of identical convex cutting edges on each side of the cutting insert 81 in the embodiment illustrated. Therefore, the angle A_nose_top on the top face 1 1 , between a primary substantially straight cutting edge region 1 1 1 and a virtual nose center line 1 14, should be equal to the angle A_nose_bot on the bottom face 12, between a primary substantially straight cutting edge region 104 and a virtual nose center line 1 14. In addition, it is clear that D_ctr_top and D_ctr_bot are equal to each other. Thus, the following expression can be derived:

(A_nose_top) _j = (A_nose_bot) _j , = 1, ... , 4

(5)

(D_ctr_top) _j = (D_ctr_bot) _j , = 1, ... , 4

[0061] Once equations (3) through (5) for the single-handed double-sided cutting insert 81 are established, the location and orientation of both a primary substantially straight cutting edge region 94 on the top face 1 1 , and a primary substantially straight cutting edge region 104 on the bottom face 12 can be determined. Next, a line 97 can be introduced by extending a top primary substantially straight cutting edge region 94, and a line 107 can be introduced by extending a bottom primary substantially straight cutting edge region 104. The two lines 97 and 107 intersect at a point "P." A third line 84 can be drawn from point "P" to center point Ό," which is the center of the inscribed circle 82, but which also serves as the rotating point of the four indexable convex cutting edges, on both the top and bottom faces. Then, from the angular relations illustrated in Figure 4(c), using the angle A_nose_top between the lines 97 and 1 13 as reference, the following equation can be obtained to define the line PO in the XOY coordinate system:

Y = tan(A_nose_top - π/4) * X

(6) [0062] Thereafter, the equation for the line 1 16, which is perpendicular to line 84, can be expressed by the following equation (7):

5 X * cos(A_nose_top - T/4) + Y * sin(A_nose_top - ^/4) + PO - D_ cut = 0 (7)

where PO = D _ ctr _ top /cos(A _ nose _top - x/4) and

D _ cut = D _ top * sin( A3 _ com)

ι ο [0063] Thus, line 1 16 can be used to construct a plane that is

perpendicular to a virtual middle plane, or a flat plateau. This plane can be used to truncate the primary conical peripheral surfaces 122 and 123 on the top and bottom faces, to create the common lateral seating surface 121 , as shown in Figure 4(b). Such a lateral seating surface serves as a common seating surface for both the single-sided

15 top face geometry and the singled-sided bottom face geometry, even though both are twisted relative to each other.

[0064] A further embodiment of a single-handed double-sided indexable cutting insert 121 is shown in Figures 5(a) through 5(c), in which Figure 5(a) is a perspective view, 5(b) is an enlarged top view, and 5(c) is a side view. As shown, the0 double-sided cutting insert 121 can have four convex cutting edges 122a to 122d on the top face 23, and four convex cutting edges 124a to 124d on the bottom face 125.

Each of the convex cutting edges on both the top 123 and bottom 125 faces can be identical. Each of the convex cutting edges on the top face 123 can be connected by nose corners 131 , 133, 135, and 138. Although not shown, each of the convex cutting5 edges on the bottom face 125 can also be connected by nose comers. The top face 123 and the bottom face 125 are separated by a virtual middle plane 126, which can be at a half thickness of the cutting insert 121 . In this embodiment of the cutting insert 121 , each of the convex cutting edges 122a to 122d can comprise simply a curved cutting edge region 132, 134, 136, 138 without any of the substantially straight cutting edge regions described in previous embodiments.

[0065] It can be assumed there is a virtual primary straight line 141 which can functions the same as the primary substantially straight cutting edge region 23 in Figure 2(a), or the primary substantially straight cutting edge region 1 1 in Figure 4(c). When the double-sided cutting insert 121 is positioned as shown in Figure 5(b), as it would be positioned in a tool holder for an actual milling operation, similar to that illustrated in Figure 2(a), or Figure 4(c), the virtual primary straight line 141 is thus perpendicular to the "Y" axis (i.e., the cutting axis in a tool holder). Since each convex cutting edge 122a-122d only comprises a curved cutting edge region 132, 134, 136,138, the cutting insert 121 can be double-sided cutting insert without any twist between the top 123 and bottom 125 faces. This is because, first, the convex cutting edges do not comprise any substantially straight cutting edge regions near a nose corner; and second, the nose corner center line 143, which passes through both the center of the nose corner 133 and the center of the inscribed circle 144, is no longer a "virtual" nose center line, like line 1 14 in Figure 4(c). This similarly applies for the nose center line 145 which passes through both the center of the nose corner 131 and the center of the inscribed circle 144. As a result, a line 146, shown in Figure 5(b), can be introduced which is perpendicular to the center line 147 (of a curved cutting edge region 132) that passes through both the center of a curved cutting edge region 132 and the center of the inscribed circle 144. Based on such a line 146, a plane that is perpendicular to a virtual middle plane 126, or flat plateau 150, can be constructed and used to truncate the primary conical peripheral surfaces 151 and 152 on both the top and bottom faces to create the common lateral seating surface 153, as shown in Figures 5(a) and Figure 5(b). The position of the common lateral seating surface 153 is determined by D_cut between the line 146 and the pre-cut external profile 155 which intersects with line 147 at point "P," as shown as phantom lines in Figure 5(b).

[0066] As described previously, an insert designed as described in connection with Figures 1 -4 permits the insert to be operated in only one direction, hence the designation "single-handed." However, for the embodiment shown in Figure 5, for example, although the design of convex cutting edges and clearance surfaces is

2 ! not single-handed, the chip groove geometry on the face of the insert still varies between two nose corners, such that this embodiment is still considered "single- handed." Nevertheless, in this particular embodiment the insert does not have the "twisted" geometry between the top and bottom face as in prior embodiments.

5 [0067] As mentioned previously, the reason why the top side is "twisted" with respect to bottom side, e.g., for the embodiments shown in Figures 1 -4, is that the top side geometry must be arranged in the opposite direction relative to the bottom side geometry so that when the insert is flipped over, to use the bottom side, the cutting edges will be oriented in the same cutting direction as were the cutting edges on the top l o side. Because the peripheral geometry between two nose corners is not symmetric vs. a virtual center plane between the two nose corners, the top and bottom peripheries are not coincident, or completely overlapped. Therefore, because the two curved cutting edge regions with large radius are coincident, the nose corner portions are "twisted" due to the non-symmetry of the entire cutting edge about a center plane between two nose

15 corners.

[0068] Thus, the double-sided cutting insert 121 as shown in Figure 5 is still a single-handed cutting insert because the chip breaker geometry 156 as shown in Figure 5(b) is neither symmetric about a center line 147 nor a center line 145, and furthermore, because a resultant cutting edge like 122a is in a waved form and is not0 symmetric about a center line 157 as seen from a side view like Figure 5(c). This may be regarded as a special case of the single-handed double side cutting insert as described in previous Figures 1 to 4. Thus all the previous equations (1 )-(3) and (6)-(7) can be applied accordingly with some symbolic changes owing to the fact there is no difference between a top face 1 1 periphery and a bottom face 12 periphery, for

5 instance, substituting A_nose for A_nose_top, D_ctr for D_ctr_top, R1 for R1_top, etc.

[0069] Additionally, similarly to the description presented in connection with Figures 1 to 4, the curved cutting edge region 132 can have a radius R1 greater than or equal to two times the radius R_ic of the inscribed circle 144 which is tangent to the external profile 158 at the virtual middle plane 126 of the cutting insert 121 . Each0 convex cutting edge like 122a on the top face 123 forms an outward-angled peripheral surface comprising a primary conical peripheral surface 151 extended downward from a curved cutting edge region 132 towards the virtual middle plane 126 and a secondary conical peripheral surface 159 extended downward from a nose corner 133 towards the virtual middle plane 126. The same method can be applied to create a primary conical peripheral surface and a secondary conical peripheral surface at the bottom face 125. 5 Therefore, the mathematical relationship in this special case can be rewritten into the following group equation (8).

l o [0070] Referring next to the two further embodiments of double-sided cutting inserts shown in Figures 6 and 7, these inserts are not single-handed, but can be considered a "special case" of single-handed designs. In particular, all of the geometric features, e.g., the cutting edges, common lateral seat faces, clearance surfaces, and chip groove geometry, are symmetric relative to a virtual center plane

1 5 between two nose corners. Consequently, these embodiments are "ambidextrous," and can be used in either direction in machining.

[0071] The two embodiments illustrated in Figures 6 and 7 are similar to the embodiment shown in Figure 5, except having symmetrical chip breaker geometry and the resultant symmetrical cutting edges. Thus, both of these embodiments can also0 be considered as two "special cases" of single-handed double-sided cutting inserts.

Moreover, both can be quantitatively described by the above group equation (8). W

[0072] Turning to Figures 6(a) and 6(b), in which Figure 6(a) is a perspective view and Figure 6(b) is a side view, there is shown a double-sided cutting insert 161 . The top face 162 and the bottom face 163 are merely a mirror image of each other about the virtual middle plane 164 at half thickness of the double-sided 5 cutting insert 161. Using only the top face 162 as an example, the cutting insert 161 illustrated can comprise four convex cutting edges 165a to 165d connected by four nose corners 167a-167d. Each convex cutting edge 165a-165d can be identical, and can comprise only a curved cutting edge region 166a to 166d, each of which can have a radius greater than or equal to two times a radius of an inscribed circle. Each nose l o corner 167a-167d can also be identical. The geometrical features of the cutting insert 161 illustrated in Figure 6(a) can be the same as corresponding geometrical features illustrated in Figures 5(a)-5(c), except that both the chip breaker geometry 168 and the convex cutting edges 165a-165d (being straight as seen from a side view) are symmetric about a center line 169, as shown in Figure 6(b), which is created by

15 projecting a view normal to a common lateral seating surface 170.

[0073] Similarly, Figures 7(a) and 7(b), in which Figure 7(a) is a perspective view and Figure 7(b) is a side view, illustrate a further embodiment of a double-sided cutting insert 171 . The top face 172 and the bottom face 173 of this insert 171 are also mirror images of each other about the virtual middle plane 174. Using only0 the top face 172 as an example, the illustrated cutting insert 171 comprises four convex cutting edges 175a-175d, each of which can be identical, and each of which can comprise only a curved cutting edge region 176a-176d having a radius greater than or equal to two times a radius of an inscribed circle. Each convex cutting edge 175a-175d can be connected by nose corners 177a-177d, which can also be identical. The

5 geometrical features of the cutting insert 171 can be the same as the corresponding features illustrated in Figures 5(a)-5(c), except that the both chip breaker geometry 78 and the convex cutting edges 175a-175d (being wavy as seen from a side view) are symmetric about a center line 179, as shown in Figure 7(b) which is created by projecting a view normal to a common lateral seating surface 180.

0 [0074] To make a double-sided insert as described above in connection with Figures 1 through 7, a "blank" insert is first formed in a press machine by a top punch and a bottom punch. The blank insert is formed by placing powdered metal in a mold in the press machine and "pressing" the powder in the mold using the top and bottom punches. The top punch imparts the top face geometry, the bottom punch forms the bottom face geometry, and the mold forms the geometry or the peripheral sides. The blank insert is thus formed as a single piece, and then sintered. The sintered insert is then ground to create the finished insert having the desired final geometry and features, such as the convex cutting edges with curved cutting edge region, one or more substantially straight cutting edge regions and associated planar facets (in certain embodiments), nose radii, common lateral seating surfaces, angled clearances, conical clearances, and the like. The blank insert can have the same general top/bottom side geometry as the finish insert. However, the blank insert can be slightly larger, for example, about 0.2mm per side, extending in radial direction, in order to allow the press formed, sintered insert to be ground to provide the desired final peripheral geometry.

[0075] Figure 8(a) and Figure 8(b) illustrate an embodiment of a milling tool system 200 comprising a tool holder 201 which can hold, for example, five identical single-handed double-sided cutting inserts 202a to 202e. Such a milling tool system can comprise a cutter body and one or more of the previously described double-sided cutting inserts operationally associated with the cutter body for applying the one or more double-sided cutting inserts to a work piece.

[0076] Figure 8a is a side view showing the cutting axis 203 of the tool holder, or cutter body 201 , being perpendicular to a line 205 representing the work piece surface to be operated upon. Figure 8(b) is an top, or end, view showing five cutting inserts 202a-202e held by the cutter body 201 in a circular array around the center "C" of the radial center lines 204. As illustrated, all of the single-handed double- sided cutting inserts 202a-202e can have four identical convex cutting edges connected by four identical nose corners, as described previously. Each convex cutting edge can further comprise a curved cutting edge region, and may have a primary substantially straight cutting edge region. Additionally, a secondary substantially straight cutting edge region may optionally be provided, as previously described in connection with Figures 1 through 4. The primary substantially straight cutting edge regions of all of the cutting inserts 202a-202e are parallel to the assumed work piece surface 205. [0077] Figures 9 and 10 illustrate further embodiments of double-sided cutting inserts with alternative geometric shapes. In particular, all of the previously described embodiments of double-sided cutting inserts are generally square shaped and thus have four peripheral sides surfaces associated with each of the top and bottom 5 faces. However, it will be understood by those of ordinary skill in the art that other

geometric shapes can also be made.

[0078] For example, referring to Figures 9(a) and 9(b), in which Figure 9(a) is a perspective view and Figure 9(b) is a side view, there is shown an embodiment of a generally pentagon shaped double-sided cutting insert 230. Based upon the same i o principles discussed hereinabove in connection with the description of the generally square shaped double-sided cutting inserts having four identical convex cutting edges on each of the top and bottom faces, the generally pentagon shaped cutting insert 230 shown similarly has a top face 231 and a bottom face 232 separated by a virtual middle plane 233. The top face 231 of double-sided cutting insert 230 can have five convex

15 cutting edges, e.g., convex cutting edge 251 , each connected by a nose corner, e.g., nose corner 254, a common lateral seating surface, e.g., common lateral seating surface 248, and five peripheral side surfaces 241 -245, each of which can be indexable about the center 246 of the through screw hole 247, which means this double-sided cutting insert 230 has a total of ten indexable cutting edges. Each of the five convex0 cutting edges can be identical. Using only one peripheral side surface 241 of the top face 231 as a representative example, each convex cutting edge 251 can have at least a curved cutting edge region 252, and may also have a primary substantially straight cutting edge region 253 provided between the curved cutting edge region 252 and the nose corner 254. Each curved cutting edge region 252 can have the aforesaid big5 radius, greater than or equal to two times the largest radius that can be inscribed on the top face 231 . Additionally, each of the peripheral side surfaces 241 -245 associated with the top face 231 can comprises a primary conical peripheral surface 255, extending from the curved cutting edge region 252 toward the virtual middle plane 233, and a secondary conical peripheral surface 257, extending from the nose corner 254 toward0 the virtual middle plane 233. Additionally, where a primary substantially straight cutting edge region 253 is provided, the peripheral side surface 241 can further comprise a primary planar facet 256, extending from the primary substantially straight cutting edge region 253 toward the virtual middle plane 233. Each lateral common seating surface 248 can be formed on an adjacent pair of primary conical peripheral surfaces extending from the top face 231 and the bottom face 232, respectively, in the same, or a similar, 5 manner as described previously in connection with common lateral seating surface on the generally square shaped double-sided cutting inserts. Where the primary substantially straight cutting edge region 253 and associated primary planar facet 256 are included, the double-sided cutting insert 230 will be, as shown, single-handed, in the same direct, for both the top face 231 and the bottom face 232. It is understood that the l o bottom face 232 likewise has the same number and types of features as the top face 231 , including five convex cutting edges connected by nose corners, and in which each convex cutting edge can comprise at least a curved cutting edge region, and may further have a primary substantially straight cutting edge region. The bottom face 232 likewise has four peripheral side surfaces comprising the various conical peripheral

15 surfaces and planar facets described above in connection with the top face 231 , which in the same manner extend from the convex cutting edges on the bottom face 232 towards the virtual middle plane 233.

[0079] Referring now to Figures 10(a) and 10(b), in which Figure 10(a) is a perspective view and Figure 10(b) is a top view, an embodiment of a generally

0 triangular shaped double-sided cutting insert 260 is shown having a top face 261 and a bottom face 262 separated by a virtual middle plane 263. The double-sided cutting insert 260 has a total of three peripheral side surfaces 271 -273 associated with the top face 261 , which are indexable about the center 274 of a through screw hole 277, which means that this double-sided cutting insert 260 has a total of six indexable cutting5 edges. Using just the peripheral side surface 271 of the top face 261 as a

representative example, each convex cutting edge 281 can comprises only a curved cutting edge region 282 which is connected to a nose corner 284. Each of the three convex cutting edges on each of the top 261 and bottom 262 faces can be identical. The curved cutting edge 282 can have a radius greater than or equal to two times the0 largest radius that can be inscribed on the top face 261 . Each peripheral side surface 271 -273 of the top face 261 of the double-sided cutting insert 260 can further comprise a primary conical peripheral surface 285, extending from the curved cutting edge region 282 toward the virtual middle plane 263, and a secondary conical peripheral surface 287 extending from the nose corner 284 toward the virtual middle plane 263.

Furthermore, a common lateral seating surface 278 can be provided adjacent pairs of 5 primary conical peripheral surfaces which each extend towards the virtual middle plane 263 from respective top 261 and bottom 262 faces. It is to be understood that the bottom face 262 can have identical convex cutting edges and associated peripheral side surfaces the same as on the top face 261 . Likewise, the convex cutting edges on the bottom face 262 can have the same curved cutting edge regions, and the peripheral i o side surfaces associated with the bottom face 262 can have the same primary and

secondary conical peripheral surfaces as the top face 261. In this particular

embodiment, the double-sided cutting insert 260 is not single-handed for both the top face 261 and the bottom face 262, and the top 261 and bottom 262 faces are thus not twisted relative to each other.

15 [0080] Further referring to Figures 1 1 (a) and 1 1 (b), in which Figure 1 1 (a) is a perspective view and Figure 1 1 (b) is a top view, another embodiment of a triangular shaped double-sided cutting insert 290 is shown similar to the triangular shaped double- sided insert 260 shown in Figures 10(a) and 10(b). The double-sided cutting insert 290 similarly has a top face 291 and a bottom face 292 separated by a virtual middle plane0 293. The double-sided cutting insert 290 has a three peripheral side surfaces 301 -303 associated with the top face 291 , which are indexable about the center 304 of a through hole 307, which means that each of top face 291 and bottom face 292 together have a total of six indexable cutting edges. Using the peripheral side surface 301 of the top face 291 as a representative example, it can be seen that each peripheral side surface5 301 -303 has a convex cutting edge 31 1 connected to a nose corner 3 4. In this

embodiment, each convex cutting edge 31 1 can comprises both a curved cutting edge region 312 and a primary substantially straight cutting edge region 313, located between the curved cutting edge region 312 and the nose corner 314. The curved cutting edge 312 can, like previously described embodiments of double-sided cutting0 inserts, have the big radius which is greater than or equal to two times the radius of the largest circle that can be inscribed on the top face 291 . Each peripheral side surface 301 -303 associated with the top face 291 can comprises a primary conical peripheral surface 315 extending from the curved cutting edge region 312 toward the virtual middle plane 293, a primary planar facet 316 extending from the primary substantially straight cutting edge region 313 toward the virtual middle plane 293, and a secondary conical 5 peripheral surface 317 extending from a nose corner 314 toward the virtual middle

plane 293. Furthermore, a common lateral seating surface 308 can be provided on adjacent pairs of primary conical peripheral surfaces which each extend towards the virtual middle plane 293 from respective top 301 and bottom 302 faces. Just as described above in connection with the generally triangular shaped double-sided cutting l o insert 260, and the generally pentagon shaped double-sided cutting insert 230, it is to be understood that the bottom face 302 can have identical convex cutting edges and associated peripheral side surfaces which are the same as on the top face 301 .

Likewise, the convex cutting edges on the bottom face 262 can have the same curved cutting edge regions, and the peripheral side surfaces associated with the bottom face

15 302 can have the same primary and secondary conical peripheral surfaces as the top face 301. In this particular embodiment, having the primary substantially straight cutting edge region 3 3, the double-sided cutting insert 290 is single-handed for both the top face 301 and the bottom face 302, such that the top 301 and bottom 302 faces are thus twisted relative to each other.

0 [0081] In various embodiments, a single-sided or double-sided high feed milling insert or inserts may be configured to provide a ramping function, which may be important for mold and/or pocket milling, for example. In more detail, Figures 12(a)-(c) illustrate a non-limiting embodiment of a double-sided high feed milling insert. Figure 12(a) is a three-dimensional view of a double-sided high feed milling insert 400

5 comprising a center hole 403, a top face 401 including a chip breaker 404, and an

identical or nearly identical bottom face 402. The top face 401 of the double-sided high feed milling insert 400 may include four nose corners 405-408. A complete cutting edge may be provided between each pair of adjacent nose corners, providing four cutting edges 41 1 -414 on the top face 402. Since the bottom face 402 may be identical to the0 top face 401 , the bottom face 402 also may include four cutting edges, such as cutting edge 421 , for example. Now referring to Figures 12(b)-(c), wherein Figure 12(b) is a front side view and Figure 12(c) is a top view of high feed milling insert 400, in at least one non-limiting embodiment, each of the four cutting edges 41 1 -414 on the top face 401 may be identical, and the bottom face 402 may be identical to the top face 401 . Accordingly, in at least one non-limiting embodiment, a pair of cutting edges is representative of each pair of cutting edges and is described below. In such

embodiment, the pair of representative cutting edges may be the cutting edge 41 1 (between the nose corners 405 and 408) at the top face 401 and the corresponding cutting edge 421 at the bottom face 402, for example.

[0082] In more detail, as shown in Figures 12(a)-(c), the cutting edge 41 1 at the top face 401 may comprise a secondary convex cutting edge 41 1 a, a primary substantially straight cutting edge 41 1 b, and a primary convex cutting edge 41 1 c. Similarly, the cutting edge 421 at the bottom face 402 may comprise a primary convex cutting edge 421 a, a primary substantially straight cutting edge 421 b, and a secondary convex cutting edge 421 c. The convexity of cutting edges 41 1 a, 41 1 c, 421 a, and 421 c can be appreciated from a top view of the milling insert 400, such as that shown in Figure 12(c), for example. Additionally, a three-dimensional Cartesian or an XYZ coordinate system may help to elucidate certain features of the milling insert 400. For example, as seen in Figure 12(b), an XOZ plane is provided wherein the X axis is aligned in the virtual middle plane 450 of the double-sided high feed milling insert 400, and, as seen in Figure 12(c), an XOY plane is provided wherein the Y axis is collinear with the reference line 461 , which may bisect the angle AJndex. The angle A_index may be equal to approximately 90 degrees as the top face and the bottom face include four identical or nearly identical cutting edges, for example. As shown in Figure 12(b), the primary substantially straight cutting edge 4 1 b may form a portion of a primary planar facet 433 which may be truncated by an angled surface 452 and a lateral face 451 perpendicular to the top face 401 , for example. The position of the primary planar facet 433 near the top face 401 , as represented by one of its boundaries 441 , may be twisted or rotated about point G by an angle A_twist. The angle A_twist may be measured from a reference line 443, which represents the boundary 441 's position if it were not twisted. Correspondingly, the position of the primary planar facet 434 near the bottom face 402 may be twisted or rotated by the same angle A_twist from the dotted line 443 to one of its boundaries 442 which, subsequently, may be co-linear with the boundary 441 as indicated by the reference line 444.

[0083] Now, referring to Figure 12(c), a top view of milling insert 400 is shown. As mentioned above, the cutting edge 41 1 (see also Figures 12(a)-(b)) may comprise cutting edges 41 1 a, 41 1 b, and 41 1 c, at or near the top face 401 (see Figure 12(a)), and the cutting edge 41 1 may be formed between nose corner 408 located at point C and nose corner 405 located at point D. The starting point of the primary substantially straight cutting edge 41 1 b may start at point E and may be connected with reference line 462 that has an angle of A_tw1 with respect to the reference line 461 bisecting the angle A_index. The secondary convex cutting edge 41 1 a may be connected to both the adjacent nose corner 408 and the adjacent primary substantially straight cutting edge 41 1 b. The primary convex cutting edge 41 1 c may be tangent to an inner reference circle, such as inscribed circle 455, for example, and may also be connected to both the adjacent primary substantially straight cutting edge 41 1 b and the adjacent nose corner 405. Mathematically, the three cutting edge regions 41 1 a, 41 1 b, and 41 1 c may be expressed in the following matrix formats, respectively:

X ² + Y ² X Y 1

+ y

= 0 and Z = T/2 0)

2 + y yz

+ y y^

X Y 1

= 0 and Z = T/2 (10)

x4 y ¹

Again, equation (9) represents the secondary convex cutting edge 41 1 a, equation (10) represents the primary substantially straight cutting edge 41 1 b and equation (1 1 ) represents the primary convex cutting edge 41 1 c. In equations (9)-(1 1 ), ( x _t , ),( x ₂ , y ₂ ) and (A- ₃ , ₃ ) are the three points on the secondary convex cutting edge 411a, (A ₃ , y ₃ ) and (x ₄ ,y ₄ ) are the two points on the primary substantially straight cutting edge 411b, and ( x ₄ , y ₄ ),( x ₅ . y ₅ ) and ( .v ₆ , v ₆ ) are the three points on the primary convex cutting edge

411c. Further, in equations (9)-(11), T is the thickness of the double-sided high feed milling insert 400 (see Figure 12(b)). Since all six points ( , , ) to (x ₆ .y ₆ ) are at the top face 401 , where z=T72, a general form of these points may be established as (x _j , y. ,τ/2) and i=1 to 6. Then, a geometric transformation through a rotation of 9=180° about the Y axis (as shown in Figure 12(c)) can be established to transform each point (χ,, y,,T/2) at the top face 401 to the bottom face 402, as given by the following equation (12) and equation (13). cos(#) 0 -sin(0) 0 ^{" "} -1 0 0 0

0 1 0 0 0 1 0 0

R _Y (9= 180°) = (12)

sin(0) 0 cos(6») 0 0 0 -1 0

0 0 0 1 0 0 0 1

(.r',,y,,z',,1) = (A',,y,.,r/2 ,1) = (-x ₍ ,y,,-772 ,1) where i=1...6, (13)

[0084] Once all points at the bottom face 402 (( x . y', . z, > where i=1...6) are obtained, the secondary convex cutting edge region 421c (which may be identical to cutting edge region 411a), the primary substantially straight cutting edge region 421b (which may be identical to cutting edge region 411b), and the primary convex cutting edge region 421a (which may be identical to cutting edge region 411c and also tangent to inner reference circle 455) can be mathematically described, respectively.

[0085] Further, referring to Figure 12(c), since the Y axis may be co-linear with the reference line 461 which bisects the angle AJndex between two adjacent nose corners, such as nose corners 505 and 508, for example, the following relationships may exist between a cutting edge region at the top face 401 and a corresponding cutting edge region at the bottom face 402: L_facet1 = L _facet2;

DJacetl = D_facet2;

A_tw1 = A_tw2;

radius of convex cutting edge region 421 a = radius of convex cutting edge region 41 1 c; and

radius of convex cutting edge region 421 c = radius of convex cutting edge region

41 1 a.

[0086] Now referring to Figure 12(b), a representative peripheral side surface (i.e., one of the four identical or nearly-identical peripheral side surfaces of insert 400), extending from the top face 401 to the bottom face 402, of the double-sided high feed cutting insert 400, may comprises the following regional peripheral side faces:

(i) a first primary conical peripheral surface 432 extending from the primary curved convex cutting edge region 41 1 c at the top face 401 toward the secondary curved convex cutting edge region 421 c at the bottom face 402, which is adjacent to a secondary conical peripheral surface 438 (belonging to another peripheral side surface) extending from the nose corner 405 at the top face 401 toward the nose corner 436 at the bottom face 402;

(ii) a first primary planar surface (or facet) 433 near the top face 401 ,

truncated by an angled surface 452 and a lateral face 451 (perpendicular to the top face 401 ) above the virtual middle plane 450, extending from the primary substantially straight cutting edge region 41 1 b at the top face 401 toward the virtual middle plane 450; and, correspondingly, a second primary planar surface 434 (or facet) near the bottom face 402, truncated by an angled surface 454 and a lateral face 453 (perpendicular to the bottom face 402) below the virtual middle plane 450, extending from the primary substantially straight cutting edge region 421 b at the bottom face 402 toward the virtual middle plane 450; additionally, the two lateral faces 451 and 453 may merge into one common lateral face for seating both the top face 401 and the bottom face 402; (iii) a second primary conical peripheral surface 431 extending from the

secondary curved convex cutting edge region 41 1 a at the top face 401 toward the primary curved convex cutting edge region 421 a at the bottom face 402; and

5 (iv) a secondary conical peripheral surface 439 extending from the nose

corner 408 at the top face 401 toward the nose corner 437 at the bottom face 402.

[0087] As may be seen in a top view of the milling insert 400, such as that provided by Figure 12(c), the first primary conical peripheral surface 432, as

l o mathematically constructed and described above, may form a negative clearance

surface having a variable clearance angle (due to the nature of a conical clearance surface formed by two twisted convex cutting edges) ranging from approximately zero (0) degrees at the nose corner 405 located at point D to a maximal negative value at the primary straight cutting edge 421 b located at point F. Further, the primary curved is convex cutting edge 41 1 c at the top face may extend downward and outward to the twisted secondary curved convex cutting edge 421 c at the bottom face. Similarly, the second primary conical peripheral surface 431 , as mathematically constructed and described above, may form a positive clearance surface having a variable clearance angle (due to the nature of a conical clearance surface formed by two twisted convex0 cutting edges) ranging from 0 at the nose corner 408 located at point C to a maximal positive value at the primary straight cutting edge region 41 b located at point E.

Further, the secondary curved convex cutting edge region 41 1 a at the top face may extend downward and inward to the twisted primary curved convex cutting edge region 421 a at the bottom face.

5 [0088] Accordingly, in at least one non-limiting embodiment, when the cutting edge 41 1 at the top face 401 is presented on a tool holder to be used in a milling operation, the first primary conical peripheral surface 432 with variable negative clearance angles may be used for cutting to any specific depth of cut, while the second primary conical peripheral surface 431 with variable positive clearance angles may be0 used for ramping when there is a need or desire for such a milling operation.

Correspondingly, when the cutting edge 421 at the bottom face 402 is presented on a tool holder to be used in a milling operation, i.e., the bottom face 402 is flipped to become a top face for performing a milling operation, the second primary conical peripheral surface 431 with variable negative clearance angles may be used for cutting to any specific depth of cut while the first primary conical peripheral surface 432 with 5 variable positive clearance angles may be used for ramping when there is a need or desire for such a milling operation.

[0089] Figures 13(a)-(c) further illustrate another exemplary non-limiting embodiment of a double-sided high feed milling insert. Figure 13(a) is a three- dimensional view of a double-sided high feed milling insert 500 comprising a center hole l o 503, a top face 501 including a chip breaker 504, and an identical or nearly identical bottom face 502. In various embodiments, the top and bottom faces 501 and 502 may comprise a flat face or a flat face with a chamfer at the peripheral cutting edges, for example. Three nose corners 505, 506 and 508 may be included on the top face 501 of the double-sided high feed milling insert 500, and a complete cutting edge may be

15 provided between a pair of adjacent nose corners. Thus, in total, there may be three cutting edges 51 1 -513 on the top face 502. Likewise, since the bottom face 502 may be identical or nearly identical to the top face 501 , there may also be three cutting edges on the bottom face 502, such as cutting edge 521 , for example. Now referring to Figures 13(b)-(c), wherein Figure 13(b) is a front-side view and Figure 13(c) is a top0 view of milling insert 500, since cutting edges 51 1 -513 on the top face 501 may be

identical and the bottom face 502 may be identical to the top face 501 , only a pair of representative cutting edges, such as the cutting edge 51 1 (between the nose corners 505 and 508) at the top face 501 and the corresponding cutting edge 521 at the bottom face 502, are described in detail below.

5 [0090] In more detail and as shown in Figures 13(a)-(c), the cutting edge

51 1 at the top face 501 comprises a secondary convex cutting edge region 51 1 a, a primary substantially straight cutting edge region 51 1 b, and a primary convex cutting edge region 51 1 c. Similarly, the cutting edge 521 at the bottom face 502 comprises a primary convex (as seen from a top view) cutting edge region 52 a, a primary

0 substantially straight cutting edge region 521 b, and a secondary convex (as seen from a top view) cutting edge region 521 c. The convexity of cutting edges 51 1 a, 51 1 c, 521 a, and 521 c can be appreciated from a top view of the milling insert 500, such as that shown in Figure 13(c), for example. Additionally, a three-dimensional Cartesian or an XYZ coordinate system may help to elucidate certain features of the milling insert 500. For example, as seen in Figure 13(b), an XOZ plane is provided wherein the X axis is 5 aligned in the virtual middle plane 550 of the double-sided high feed milling insert 500, and, as seen in Figure 13(c), an XOY plane is provided wherein the Y axis is collinear with the reference line 561 , which may bisect the angle A_index. The angle A_index may be equal to approximately 120 degrees as there are three identical or nearly identical cutting edges per each top and bottom face, for example. As shown in Figure l o 13(b), the primary substantially straight cutting edge region 51 1 b may form a primary planar facet 533 which may be truncated by an angled surface 552 and a lateral seating face 551 perpendicular to the top face 501 . Alternatively, in various embodiments, the angled surface 552 may be used as a seating face and the lateral seating face 551 may be at an angle of less than 90 degrees to the top face 501 . For example, in at least one is embodiment, the angle between the lateral seating face 551 and the top face 501 may be between about 45 to about 90 degrees. Additionally, in at least one embodiment, the angle between the lateral seating face 551 and the top face 501 may be slightly less than 90 degrees. In any event, the position of the primary planar facet 533 near the top face 501 , as represented by one of its boundaries 54 , may be twisted or rotated about0 point W by an angle A_twist. The angle A_twist may be measured from a reference line 543, which represents the position of the boundary 541 if it were not twisted.

Correspondingly, the position of the primary planar facet 534 near the bottom face 502 may be twisted or rotated by the same angle A_twist from the dotted line 543 to one of its boundaries 542 which, subsequently, may be co-linear with the boundary 541 , as5 indicated by the reference line 544.

[0091] Now referring to Figure 13(c), a top view of milling insert 500 is shown. As mentioned above, the cutting edge 5 1 (see also Figures 13(a)-(b)) may comprise cutting edges 51 1 a, 51 1 b, and 51 1c, at or near the top face 501 (see Figure 13(a)), and the cutting edge 51 1 may be formed between nose corner 508 located at0 point H and nose corner 505 located at point N. The primary substantially straight

cutting edge region 51 1 b may intersect at point J with reference line 562. Reference line 562 may have an angle of A_tw01 with the reference line 561 bisecting the angle AJndex. The secondary convex cutting edge region 51 1 a may be connected to both the adjacent nose corner 508 and the adjacent primary substantially straight cutting edge region 51 1 b. The primary convex cutting edge region 51 1 c may be tangent to

5 inner reference circle 555, and may also be connected to both the adjacent primary substantially straight cutting edge region 51 1 b and the adjacent nose corner 505.

Mathematically, the three cutting edge regions 51 1 a, 5 1 b, and 5 1 c may also be expressed by the above-discussed equations (9)-(1 1 ), respectively. Similarly, the corresponding points as determined by the above-discussed equations (12)-(13) at the l o bottom face 502 can be obtained to mathematically describe the secondary convex cutting edge region 521 c (which may be identical to cutting edge region 51 1 a), the primary substantially straight cutting edge region 521 b (which may be identical to cutting edge region 51 1 b), and the primary convex cutting edge region 521 a (which may be identical to cutting edge region 51 1 c and also tangent to inner reference circle 555),

15 respectively.

[0092] Further referring to Figure 13(c), since the Y axis may be co-linear with the line 561 which bisects the angle AJndex between two adjacent nose corners, such as nose corners 505 and 508, for example, the following relationships may exist between a cutting edge region at the top face 501 and a corresponding cutting edge0 region at the bottom face 502:

L_facet01 = LJacet02;

DJacetOI = DJacet02;

A_tw01 = A_tw02;

radius of convex cutting edge region 521 a = radius of convex cutting edge region5 51 1 c; and

radius of convex cutting edge region 521 c = radius of convex cutting edge region

51 1 a.

[0093] Now referring to Figure 13(b), a representative peripheral side surface (from one of the three identical or nearly-identical peripheral side surfaces),0 extending from the top face 501 to the bottom face 502, may comprise the following four regional peripheral side faces: a first primary conical peripheral surface 532 extending from the primary curved convex cutting edge region 51 1 c at the top face 501 toward the secondary curved convex cutting edge region 521 c at the bottom face 502, which is adjacent to a secondary conical peripheral surface 538 (belonging to another peripheral side surface) extending from the nose corner 505 at the top face 501 toward the nose corner 536 at the bottom face 502;

a first primary planar surface (or facet) 533 near the top face 501 , truncated by an angled surface 552 and a lateral seating face 551 (perpendicular or forming an angle less or slightly less than 90 degrees to the top face 501 ) above the virtual middle plane 550, extending from the primary substantially straight cutting edge region 51 1 b at the top face 501 toward the virtual middle plane 550; and correspondingly a second primary planar surface (or facet) 534 near the bottom face 502, truncated by an angled surface 554 and a lateral seating face 553 (perpendicular or forming an angle less or slightly less than 90 degrees to the bottom face 502) below the virtual middle plane 550, extending from the primary substantially straight cutting edge region 521 b at the bottom face 502 toward the virtual middle plane 550; additionally, in the case that the lateral face 551 is perpendicular to the top face 501 and the lateral face 553 is perpendicular to the bottom face 502, the two lateral seating faces 551 and 553 may merge into one common lateral face seating for both top face 501 and bottom face 502, and in embodiments where the lateral face 551 forms an angle less or slightly less than 90 degrees to the top face 501 and the lateral face 553 forms an angle less or slightly less than 90 degrees to the bottom face 502, the two lateral seating faces 551 and 553 may intersect at the virtual middle plane 550 and form a folded common lateral face for seating both top face 501 and bottom face 502;

a second primary conical peripheral surface 531 extending from the secondary curved convex cutting edge region 51 1 a at the top face 501 toward the primary curved convex cutting edge region 521 a at the bottom face 502; and

a secondary conical peripheral surface 539 extending from the nose corner 508 at the top face 501 toward the nose corner 537 at the bottom

5 face 502.

[0094] As may be seen in a top view of the milling insert 500, such as that provided by Figure 13(c), the first primary conical peripheral surface 532, as

mathematically constructed and described above, may form a negative clearance surface having a variable clearance angle (due to the nature of a conical clearance l o surface formed by two twisted convex cutting edges) ranging from approximately zero (0) degrees at the nose corner 505 located at point N to a maximal negative value at the primary straight cutting edge region 521 b located at point M. Further, the primary curved convex cutting edge region 51 1 c at the top face may extend downward and outward to the twisted secondary curved convex cutting edge region 521 c at the bottom

15 face. Similarly, the second primary conical peripheral surface 531 , as mathematically constructed and described above, may form a positive clearance surface having a variable clearance angle (due to the nature of a conical clearance surface formed by two twisted convex cutting edges) ranging from zero (0) degrees at the nose corner 508 located at point H to a maximal positive value at the primary straight cutting edge region0 51 1 b located at point J. Further, the secondary curved convex cutting edge region 51 1 a at the top face may be extended downward and inward to the twisted primary curved convex cutting edge region 521 a at the bottom face.

[0095] Accordingly, when the cutting edge 51 1 at the top face 501 is presented on a tool holder to be used in a milling operation, the first primary conical5 peripheral surface 532 with variable negative clearance angles may be used for cutting to any specific depth of cut while the second primary conical peripheral surface 531 with variable positive clearance angles may be used for ramping when there is a need or desire for such a milling operation. Correspondingly, when the cutting edge 521 at the bottom face 502 is presented on a tool holder to be used in a milling operation, the0 second primary conical peripheral surface 531 with variable negative clearance angles may be used for cutting to any specific depth of cut, while the first primary conical peripheral surface 532 with variable positive clearance angles may be used for ramping when there is a need or desire for such a milling operation.

[0096] Figures 14(a)-(b) illustrate another non-limiting embodiment of a double-sided high feed milling insert, which may be generally similar to the milling insert 5 500 illustrated in Figures 13(a)-(c) and described above, except, at least, that the cutting edge 61 1 further comprises an optional secondary substantially straight cutting edge region 621 between the nose corner 608 and the secondary convex cutting edge region 6 1 a. There may be three such secondary substantially straight cutting edge regions 621 , 622 and 623 on the top face 610, dimensionally indicated by the length

l o l__2nd_facet, one on each indexable cutting edge. Since the top face 601 may be

identical or nearly identical to the bottom face 602, there are also three secondary substantially straight cutting edge regions, such as the secondary substantially straight cutting edge region 631 on the bottom face 602, for example. Therefore, as shown in Figure 4(b), each cutting edge, with the cutting edge 61 1 on the top face as a

I 5 representative example, may comprise a primary convex cutting edge region 61 1 c, a primary substantially straight cutting edge region 61 1 b, a secondary convex cutting edge region 61 1 a, and a secondary substantially straight cutting edge region 621 between two adjacent nose corner 605 and 608. The convexity of cutting edges 61 1 a and 61 1 c can be appreciated from a top view of the milling insert 400, such as that

0 shown in Figure 14(b), for example. Each secondary substantially straight cutting edge region may form a secondary planar surface (or facet) by extending downward, for example. Specifically, the secondary substantially straight cutting edge region 621 at the top face 601 may form at least a portion of the secondary planar surface (or facet) 641 and the secondary substantially straight cutting edge region 631 at the bottom face5 602 may form at least a portion of the secondary planar surface (or facet) 646.

[0097] In various embodiments, the addition of the secondary substantially straight cutting edge region 621 to the cutting edge 61 1 may improve the surface finish of a side wall of a workpiece being machined by one or more cutting inserts 600, for example. This may be achieved by constructing a secondary substantially straight

0 cutting edge region 622 at an adjacent cutting edge on the same top face 601 such that the secondary substantially straight cutting edge region 622 is oriented approximately perpendicular to the primary substantially straight cutting edge region 61 1 b of the current cutting edge 61 1 being presented to a tool holder. In such embodiments, the primary substantially straight cutting edge region 61 1 b may be perpendicular to the rotation axis of the tool holder.

[0098] Accordingly, referring to Figure 14(a), any one of the three identical or nearly identical peripheral side surfaces of the cutting insert 600 may extend from the top face 601 to the bottom face 602, and may comprise the following regional peripheral side faces: a first secondary planar surface (or facet) 646 near the bottom face 602, a first primary conical peripheral surface 643, a first primary planar surface (or facet) 644 near the top face 601 , a second primary planar surface (or facet) 645 near the bottom face 602, a second primary conical peripheral surface 642, a second secondary planar surface (or facet) 641 near the top face 601 , and a secondary conical peripheral surface 637.

[0099] Accordingly, certain non-limiting embodiments of the single-handed double-sided cutting inserts for high feed milling are described herein. The single- handed double-sided cutting inserts may be of known sizes and shapes, and may be adapted for conventional use in a variety of drilling applications. It will be understood that the present description may illustrate only those aspects of the embodiments of the disclosure relevant to providing a clear understanding thereof, and that certain aspects would be apparent to those of ordinary skill in the art. Therefore, such aspects as would not be necessary to facilitate a better understanding of the disclosure may not be present in order to simplify the description.

[00100] Furthermore, although only a limited number of embodiments of the disclosure are necessarily described herein, one of ordinary skill in the art will, upon considering the foregoing description, recognize that many modifications and variations of the disclosure may be employed. All such variations and modifications of the disclosure are intended to be covered by the foregoing description and the following claims.