Single-sided three-way indexable milling insert having high void volume to material volume ratio and insert mill therefor

Abstract

A single-sided three-way indexable milling insert for feed milling operations, includes a positive basic shape, a rake surface, a peripheral surface including side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has a cutting edge including exactly three main cutting sub-edges and three secondary cutting sub-edges. A material volume V.sub.F of the cutting insert and a void volume V.sub.S of the insert fulfill the condition V.sub.S/V.sub.F≥0.30.

Claims

1. A single-sided three-way indexable cutting insert having a positive basic shape and comprising: a material volume V.sub.F defined by the amount of material of the cutting insert; a rake surface; a base bearing surface located opposite the rake surface; an insert axis (A.sub.I) extending perpendicular to the base bearing surface and through a center of the insert, the insert axis defining: an upward direction from the base bearing surface towards the rake surface, a downward direction opposite to the upward direction, and an outward direction perpendicular to the upward and downward directions and extending away from the insert axis; a cutting insert height (H.sub.I) measurable parallel to the insert axis, from the base bearing surface to a highest point of the rake surface; a peripheral surface connecting the rake surface and base bearing surface; a cutting edge formed along an intersection of the peripheral surface and the rake surface, the cutting edge defining, in a top view parallel to the insert axis (A.sub.I), an imaginary edge circumscribed circle (C.sub.E) having an edge circumscribed diameter D.sub.E; and a screw hole opening out to the rake and base bearing surfaces, the screw hole comprising: a screw hole bottom at an intersection with the base bearing surface; a screw hole top at an intersection with the rake surface; a void volume V.sub.s defined as the volume of a void extending from the screw hole bottom to the screw hole top; and a hole circle (C.sub.S) defined, in said top view parallel to the insert axis (A.sub.I), at an intersection of the rake surface and the screw hole, the hole circle (C.sub.S) having a hole diameter D.sub.S; the base bearing surface defining, in a bottom view parallel to the insert axis (A.sub.I), an imaginary base circumscribed circle (C.sub.B) having a base diameter D.sub.B; the peripheral surface including an upper sub-surface adjacent the rake surface, the upper sub-surface comprising an overhanging portion; the peripheral surface further including a lower sub-surface between the upper sub-surface and the base bearing surface, the lower sub-surface comprising six side abutment surfaces including first, second, third, fourth, fifth and sixth side abutment surfaces; the cutting edge, in said top view parallel to the insert axis (A.sub.I), defining an edge inscribed circle (C.sub.M) having an edge inscribed diameter D.sub.M, the cutting edge comprising: exactly three main sub-edges and exactly three secondary sub-edges, the main sub-edges alternating with the secondary sub-edges with a corner sub-edge at each intersection between the main and secondary sub-edges; each main sub-edge having a main sub-edge length L.sub.M which includes one-half the lengths of the corner sub-edges adjacent thereto, and each secondary sub-edge having a secondary sub-edge length L.sub.S which includes one-half the lengths of the corner sub-edges adjacent thereto; wherein: the lower sub-surface comprises a chamfer located between the base bearing surface and a remainder of the lower sub-surface, the remainder being located between the chamfer and the upper sub-surface; the remainder of the lower sub-surface is parallel to the insert axis (A.sub.I); said six side abutment surfaces are formed on said remainder of the lower sub-surface, said six side abutment surfaces also being parallel to the insert axis (A.sub.I); the edge circumscribed diameter D.sub.E fulfills the condition: D.sub.E<6 mm; the base circumscribed diameter D.sub.B is smaller than the edge circumscribed diameter D.sub.E; a volume ratio V.sub.S/V.sub.F of the void volume V.sub.S to the material volume V.sub.F fulfills the condition: 0.5>V.sub.S/V.sub.F≥0.30; an insert thickness diameter ratio of the hole diameter D.sub.S to the edge inscribed diameter D.sub.M fulfills the condition: 0.80>D.sub.S/D.sub.M>0.60; and an edge length ratio of the main sub-edge length L.sub.M to the secondary sub-edge length L.sub.S fulfills the condition: L.sub.M/L.sub.S>0.80.

2. The cutting insert according to claim 1, wherein the volume ratio fulfills the condition: V.sub.S/V.sub.F>0.35.

3. The cutting insert according to claim 1, wherein the edge length ratio fulfills the condition: L.sub.M/L.sub.S>1.0.

4. The cutting insert according to claim 1, wherein an effective ramp edge length L.sub.R is a length of the secondary sub-edge measured adjacent a relieved peripheral surface portion and fulfills the condition: 0.4L.sub.S>L.sub.R>0.8L.sub.S.

5. The cutting insert according to claim 1, wherein, in said top view parallel to the insert axis (A.sub.I), all internal angles formed between the main and secondary sub-edges are obtuse.

6. The cutting insert according to claim 1, wherein the edge circumscribed diameter D.sub.E fulfills the condition: 6 mm>D.sub.E>4 mm.

7. The cutting insert according to claim 1, wherein the base bearing surface is the only ground surface of the cutting insert.

8. The cutting insert according to claim 1, wherein the six side abutment surfaces are perpendicular to the base bearing surface.

9. The cutting insert according to claim 1, wherein a relief recess is formed under a portion of each secondary sub-edge.

10. The cutting insert according to claim 9, wherein in said bottom view parallel to the insert axis (A.sub.I), a largest spacing between any of the six side abutment surfaces and an adjacent cutting edge portion is located adjacent to one of the three main sub-edges.

11. The cutting insert according to claim 10, wherein in said bottom view parallel to the insert axis (A.sub.I), a smallest spacing between any of the six side abutment surfaces and an adjacent cutting edge portion is located adjacent to one of the secondary sub-edges.

12. An insert mill comprising: a tool holder comprising: a rear end; a front end; a tool periphery extending from the rear end to the front end; a rotation axis extending through a center of the tool holder, the rotation axis defining a forward direction extending from the rear end to the front end, a rearward direction opposite to the forward direction, an outward direction perpendicular to the rotation axis and directed from the rotation axis to the tool periphery, and an inward direction opposite to the outward direction; a shank portion extending forward of the rear end; and a cutting portion extending forward of the shank portion to the front end, the cutting portion having a tool diameter D.sub.T at the front end and exactly two circumferentially spaced flutes extending rearwardly from an intersection of the front end and the tool periphery; each of the flutes comprising a pocket formed at the intersection of the front end and the tool periphery; and a cutting insert according to claim 1 mounted in one of the pockets of the tool holder; wherein: exactly one of the insert's main sub-edges extends forward of the tool holder; exactly one of the insert's secondary sub-edges extends forward of the tool holder; and exactly one of the insert's secondary sub-edges extends outward of the tool periphery.

13. The insert mill according to claim 12, wherein: each of the pockets comprises: a seat abutment surface; a threaded pocket hole opening out to the seat abutment surface; and first, second and third lateral abutment surfaces which are transverse to the seat abutment surface; each first lateral abutment surface is located adjacent to the tool periphery and extends in the outward and forward directions; each second lateral abutment surface is closer to the rotation axis than the first lateral abutment surface and is separated from the first lateral abutment surface by a first relief recess, each second lateral abutment surface extending in the inward and forward directions; each third lateral abutment surface is closer to the rotation axis and more forwardly located than the second lateral abutment surface, and is separated from the second lateral abutment surface by a second relief recess, each third lateral abutment surface extending in the inward and forward directions; and the tool diameter D.sub.T fulfilling the condition D.sub.T<11 mm.

14. The insert mill according to claim 13, wherein the second and third lateral abutment surfaces, in a plan view of the seat abutment surface, are not parallel to each other.

15. The insert mill according to claim 13, wherein a support web extends between the two pockets to a forwardmost point of the support web, which forwardmost point is recessed from the front end of the tool holder.

16. The insert mill according to claim 15, wherein the support web has an elongated shape.

17. The insert mill according to claim 15, wherein the support web has a forwardmost surface and: (a) a central portion of the forwardmost surface is planar; or (b) in a side view of the tool holder, the forwardmost surface is concavely shaped, or (c) both.

18. The insert mill according to claim 15, wherein the third lateral abutment surface is at least partially formed on the support web.

19. The cutting insert according to claim 1, wherein the entire cutting edge lies on a plane.

20. The cutting insert according to claim 1, wherein: the overhanging portion has a lowermost point at a minimum upper sub-surface height H.sub.U above the base bearing surface, the minimum upper sub-surface height H.sub.U being measurable parallel to the insert axis; and the minimum upper sub-surface height H.sub.U fulfills the condition: 0.35H.sub.I≤H.sub.U≤0.85H.sub.I.

21. The cutting insert according to claim 1, wherein: in at least one cross-section of each main sub-edge, the peripheral surface adjacent to the rake surface, is perpendicular to the rake surface; and in at least one cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface forms an acute relief angle (ε) with the rake surface.

22. The cutting insert according to claim 21, wherein: in at least one other cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface is perpendicular to the rake surface.

23. The cutting insert according to claim 1, wherein: in at least a first cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface, is perpendicular to the rake surface; and in at least a second cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface, forms an acute relief angle (ε) with the rake surface.

24. The cutting insert according to claim 20, wherein: the minimum upper sub-surface height H.sub.U fulfills the condition: 0.4H.sub.I≤H.sub.U≤0.6H.sub.I.

25. A single-sided three-way indexable cutting insert having a positive basic shape and comprising: a material volume V.sub.F defined by the amount of material of the cutting insert; a rake surface; a base bearing surface located opposite the rake surface; an insert axis (A.sub.I) extending perpendicular to the base bearing surface and through a center of the insert, the insert axis defining: an upward direction from the base bearing surface towards the rake surface, a downward direction opposite to the upward direction, and an outward direction perpendicular to the upward and downward directions and extending away from the insert axis; a cutting insert height (H.sub.I) measurable parallel to the insert axis, from the base bearing surface to a highest point of the rake surface; a peripheral surface connecting the rake surface and base bearing surface; a cutting edge formed along an intersection of the peripheral surface and the rake surface, the cutting edge defining, in a top view parallel to the insert axis (A.sub.I), an imaginary edge circumscribed circle (C.sub.E) having an edge circumscribed diameter D.sub.E; and a screw hole opening out to the rake and base bearing surfaces, the screw hole comprising: a screw hole bottom at an intersection with the base bearing surface; a screw hole top at an intersection with the rake surface; a void volume V.sub.s defined as the volume of a void extending from the screw hole bottom to the screw hole top; and a hole circle (C.sub.S) defined, in said top view parallel to the insert axis (A.sub.I), at an intersection of the rake surface and the screw hole, the hole circle (C.sub.S) having a hole diameter D.sub.S; the base bearing surface defining, in a bottom view parallel to the insert axis (A.sub.I), an imaginary base circumscribed circle (C.sub.B) having a base diameter D.sub.B; the peripheral surface including an upper sub-surface adjacent the rake surface, the upper sub-surface comprising an overhanging portion; the peripheral surface further including a lower sub-surface between the upper sub-surface and the base bearing surface, the lower sub-surface comprising six side abutment surfaces including first, second, third, fourth, fifth and sixth side abutment surfaces; the cutting edge, in said top view parallel to the insert axis (A.sub.I), defining an edge inscribed circle (C.sub.M) having an edge inscribed diameter D.sub.M; wherein: the lower sub-surface comprises a chamfer located between the base bearing surface and a remainder of the lower sub-surface, the remainder being located between the chamfer and the upper sub-surface; the remainder of the lower sub-surface is parallel to the insert axis (A.sub.I); said six side abutment surfaces are formed on said remainder of the lower sub-surface and are also parallel to the insert axis (A.sub.I); the edge circumscribed diameter D.sub.E fulfills the condition: D.sub.E<6 mm; the base circumscribed diameter D.sub.B is smaller than the edge circumscribed diameter D.sub.E; a volume ratio V.sub.S/V.sub.F of the void volume V.sub.S to the material volume V.sub.F fulfills the condition: 0.5>V.sub.S/V.sub.F≥0.30; the overhanging portion has a lowermost point at a minimum upper sub-surface height HU above the base bearing surface, the minimum upper sub-surface height HU being measurable parallel to the insert axis; and the minimum upper sub-surface height HU fulfills the condition: 0.35HI≤HU≤0.85HI.

26. The cutting insert according to claim 25, wherein: the minimum upper sub-surface height H.sub.U fulfills the condition: 0.4H.sub.I≤H.sub.U≤0.6H.sub.I.

27. A single-sided three-way indexable cutting insert having a positive basic shape and comprising: a material volume V.sub.F defined by the amount of material of the cutting insert; a rake surface; a base bearing surface located opposite the rake surface; an insert axis (A.sub.I) extending perpendicular to the base bearing surface and through a center of the insert, the insert axis defining: an upward direction from the base bearing surface towards the rake surface, a downward direction opposite to the upward direction, and an outward direction perpendicular to the upward and downward directions and extending away from the insert axis; a cutting insert height (H.sub.I) measurable parallel to the insert axis, from the base bearing surface to a highest point of the rake surface; a peripheral surface connecting the rake surface and base bearing surface; a cutting edge formed along an intersection of the peripheral surface and the rake surface, the cutting edge defining, in a top view parallel to the insert axis (A.sub.I), an imaginary edge circumscribed circle (C.sub.E) having an edge circumscribed diameter D.sub.E; and a screw hole opening out to the rake and base bearing surfaces, the screw hole comprising: a screw hole bottom at an intersection with the base bearing surface; a screw hole top at an intersection with the rake surface; a void volume V.sub.s defined as the volume of a void extending from the screw hole bottom to the screw hole top; and a hole circle (C.sub.S) defined, in said top view parallel to the insert axis (A.sub.I), at an intersection of the rake surface and the screw hole, the hole circle (C.sub.S) having a hole diameter D.sub.S; the base bearing surface defining, in a bottom view parallel to the insert axis (A.sub.I), an imaginary base circumscribed circle (C.sub.B) having a base diameter D.sub.B; the peripheral surface including an upper sub-surface adjacent the rake surface, the upper sub-surface comprising an overhanging portion; the peripheral surface further including a lower sub-surface between the upper sub-surface and the base bearing surface, the lower sub-surface comprising six side abutment surfaces including first, second, third, fourth, fifth and sixth side abutment surfaces; the cutting edge, in said top view parallel to the insert axis (A.sub.I), defining an edge inscribed circle (C.sub.M) having an edge inscribed diameter D.sub.M, the cutting edge comprising: exactly three main sub-edges and exactly three secondary sub-edges, the main sub-edges alternating with the secondary sub-edges with a corner sub-edge at each intersection between the main and secondary sub-edges; wherein: the edge circumscribed diameter D.sub.E fulfills the condition: D.sub.E<6 mm; the base circumscribed diameter D.sub.B is smaller than the edge circumscribed diameter D.sub.E; a volume ratio V.sub.S/V.sub.F of the void volume V.sub.S to the material volume V.sub.F fulfills the condition: 0.5>V.sub.S/V.sub.F≥0.30; in at least one cross-section of each main sub-edge, the peripheral surface adjacent to the rake surface is perpendicular to the rake surface; and in at least one cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface forms an acute relief angle (ε) with the rake surface.

28. The cutting insert according to claim 27, wherein: in at least one other cross-section of each secondary sub-edge, the peripheral surface adjacent to the rake surface is perpendicular to the rake surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the subject matter of the present invention, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings derived from a scale model, in which:

(2) FIG. 1A is a side view of an insert mill comprising a tool holder and inserts according to the subject matter of the present invention, rotated to show a side view of one of the inserts;

(3) FIG. 1B is a side view of the insert mill in FIG. 1A, rotated to show a front view of one of the inserts;

(4) FIG. 1C is a front end view of the insert mill in FIG. 1B;

(5) FIG. 2 is a perspective view of one of the inserts shown in FIG. 1A;

(6) FIG. 3 is a top view of the insert in FIG. 2;

(7) FIG. 4A is a cross-section view taken along line IVA in FIG. 3;

(8) FIG. 4B is a cross-section view taken along line IVB in FIG. 3;

(9) FIG. 4C is a cross-section view taken along line IVC in FIG. 3;

(10) FIG. 5A is a side view of the insert in FIG. 2;

(11) FIG. 5B is a top view of the insert in FIG. 5A;

(12) FIG. 5C is a bottom view of the insert in FIG. 5A;

(13) FIG. 6 is a cross-section view taken along line VI-VI in FIG. 5B;

(14) FIG. 7A is a side view of a tool holder of the insert mill shown in FIG. 1A, rotated to show a side view of one of the pockets;

(15) FIG. 7B is a side view of the tool holder in FIG. 7A, rotated to show a front view of one of the pockets;

(16) FIG. 7C is a front end view of the tool holder in FIG. 7A;

(17) FIG. 7D is a perspective view of a portion of the tool holder in FIG. 7A;

(18) FIG. 8A is a perspective view of a pocket of the tool holder in FIG. 7A;

(19) FIG. 8B is a side view of the pocket in FIG. 8A;

(20) FIG. 8C is a top (i.e. axial) view of the pocket in FIG. 8A, and also constitutes a plan view of the seat abutment surface of the pocket;

(21) FIG. 9A is a view of the inserts shown in FIG. 1C, without the tool holder and screws being shown, and schematically showing the tool circumscribing cutting diameter circle;

(22) FIG. 9B is a side view of the inserts shown in FIG. 9A, also corresponding to the orientation of the inserts as shown in FIG. 1B; and

(23) FIG. 9C is a side view of the inserts shown in FIG. 9B, and the screws for mounting same to the tool holder, rotated to correspond to the orientation of the inserts as shown in FIG. 1A.

DETAILED DESCRIPTION

(24) FIGS. 1A to 1C illustrates an insert mill 10 configured for feed milling operations.

(25) The insert mill 10 comprises a tool holder 12, cutting inserts 14 and screws 16 for securing the cutting inserts 14 to the tool holder 12.

(26) The insert mill 10 is configured for rotating about a rotation axis A.sub.R which extends longitudinally through the center thereof.

(27) The rotation axis A.sub.R defines opposite axially forward and rearward directions D.sub.F, D.sub.R, and opposite rotational cutting and non-cutting directions D.sub.K, D.sub.N.

(28) The tool holder 12 comprises a rear end 13A, a front end 13B and a tool periphery 13C extending therebetween.

(29) The tool holder 12 further comprises a shank portion 18 and a cutting portion 20 extending forward therefrom.

(30) The cutting portion 20 comprises exactly two flutes 21. Each flute 21 comprises a pocket 22 (see FIG. 8A) formed at the intersection of the front end 13B and the tool periphery 13C.

(31) The cutting inserts 14, screws 16 and pockets 22, in the examples given, are identical therefore features described with respect to one should be considered to apply to all.

(32) The cutting insert 14 will now be described with reference to FIGS. 2-6.

(33) The cutting insert 14 is a single-sided three-way indexable cutting insert having a positive basic shape. It comprises a rake surface 24, a base bearing surface 26, a peripheral surface 28, a screw hole 30, and a cutting edge 32.

(34) An insert axis A.sub.I (FIG. 6) extends perpendicular to the base bearing surface 26 and through the center of the insert 14. The insert axis A.sub.I is provided to assist defining directions and features of the cutting insert 14. Generally speaking, while it is most preferred that a screw hole of the present invention is located in the center of an insert and is perpendicular to a base bearing surface, resulting in an insert axis of the insert also extending through the center the screw hole, it will be understood that it is possible a screw hole can be slanted or not perfectly central to a cutting insert, resulting in a screw hole axis (not shown) which is not coaxial with the insert axis A.sub.I (whereas in the present preferred example they are coaxial). Nonetheless, given that the present invention seeks to minimize material usage to the greatest extent possible, certainly for the purposes of structural strength the exemplified central and perpendicular screw hole is preferred. Therefore in the given example the insert axis A.sub.I also extends through the center of the screw hole 30.

(35) Referring to FIG. 6, the screw hole 30 can comprise a screw hole bottom 31 and a screw hole top 33.

(36) In FIG. 5B, a hole circle C.sub.S is shown defining a hole diameter D.sub.S.

(37) The insert axis A.sub.I defines opposite upward and downward directions D.sub.U, D.sub.D, and, as exemplified in FIG. 5C, opposite inward and outward directions D.sub.I, D.sub.O. The outward direction D.sub.O is not meant to define one specific direction but rather all possible 360° outward directions from the insert axis A.sub.I, four such directions being exemplified. This is also true, in the opposite direction, for the inward direction D.sub.I, even though only one example is shown. This is also true for the inward and outward directions D.sub.I, D.sub.O shown regarding the insert mill 10 in FIG. 1C.

(38) As shown, for example in FIGS. 4A to 4C and 6, the rake surface 24 can preferably slope inwardly and downwardly from the cutting edge 32 to form an acute internal angle α for chip forming purposes. The acute internal angle α formed between the rake surface 24 and the peripheral surface 28 is also referred to as a positive rake angle. Such positive angle compensates for the orientation of the seat abutment surfaces, which in this non-limiting but preferred example, extend slanted to the rotation axis A.sub.R and do not provide a positive cutting angle themselves.

(39) The base bearing surface 26 is generally planar as shown, but it will be understood that this definition does not preclude the possible inclusion of a small rounded transition edge between the peripheral surface 28 and the base bearing surface 26, as shown for example in FIG. 7 of EP 3050655. In the shown embodiment, a chamfer 27 (FIGS. 5A and 5C) is provided. For the purposes of the specification and claims, the base bearing surface 26 is considered to be the lowest surface, i.e. not including any chamfered or rounded area. Thus, in FIG. 5C, the base bearing surface 26 defines, in a view parallel to the insert axis A.sub.I, an imaginary base circumscribed circle C.sub.B having a base diameter D.sub.B.

(40) Referring to FIG. 5C, the positive basic shape of the cutting insert 14 means that the base bearing surface 26 has a smaller base diameter D.sub.B than a circumscribing diameter D.sub.E of the cutting edges 32 (FIG. 5B).

(41) Referring to FIGS. 2, 5C and 6, the peripheral surface 28 comprises a lower sub-surface 34 and an upper sub-surface 36. The lowermost portion of the lower sub-surface 34 comprises a chamfer 27. The chamfer 27 connects the base bearing surface 26 to a remainder of the lower sub-surface 34 which extends parallel to the insert axis A.sub.I, the remainder being located between the chamfer 27 and the upper sub-surface 36. The lower sub-surface 34 is unground and extends upwardly from the base bearing surface 26, and comprises first, second, third, fourth, fifth and sixth side abutment surfaces 38A, 38B, 38C, 38D, 38E, 38F, which are located on the aforementioned remainder and thus also are parallel to the insert axis A.sub.I. (Hereinafter the identical side abutment surfaces will be identified generally as “side abutment surface(s) 38”). Radius portions 39 (FIG. 2) extend between the side abutment surfaces 38 but have no abutment function in the example shown.

(42) It will be noted that the insert's abutment surfaces 38 serve as bearing surfaces which form an internal right angle β1 with the base bearing surface 26, as best seen in FIG. 6.

(43) Each of the side abutment surfaces 38 is generally planar. To elaborate, an exaggerated schematic convex bulge 40 is shown in FIG. 3. The bulge 40 typically results from a sintering process. Since the inserts of the present invention are small, distortion resulting in such bulge 40 is acceptably small enough for them not to require grinding. Generally speaking, such convexity or concavity (not shown; which can be considered an inward “bulge” for the purposes of the specification) is measured as a maximum distance from a plane connecting adjacent corners of an insert to such bulge.

(44) Thus, the insert is stated to have an unground lower sub-surface. Even though in FIG. 2, for example, the unground lower sub-surface appears to have a discontinuity line 42, this is merely a result of this particular drawing showing a curvature line. An actual product which has not been ground does not have a discernable line, and smoothly transitions from the generally planar portion to the radius portion 39.

(45) The upper sub-surface 36 comprises an overhanging portion 44 extending in this example around the entire insert 14 (exemplified in FIGS. 4A to 4C).

(46) Referring to FIG. 2, the cutting insert 14 can comprise six corner edges 46A, 46B, 46C, 46D, 46E, 46F (hereinafter generally referred to as “corner edge(s) 46”), and three identical main sub-edges 48A, 48B, 48C (hereinafter generally referred to as “main sub-edge(s) 48”), and three identical secondary sub-edges 47A, 47B, 47C (hereinafter generally referred to as “secondary sub-edge(s) 47”).

(47) Referring to FIG. 5B, in connection with the cutting edge 32, there is shown an imaginary edge circumscribed circle C.sub.E having an edge circumscribed diameter D.sub.E, and an imaginary edge inscribed circle C.sub.M having an edge inscribed diameter D.sub.M. The edge circumscribed circle C.sub.E is the smallest diameter circle which encloses all portions of the circumferentially extending cutting edge 32, while the edge inscribed circle C.sub.M is the largest diameter circle that fits entirely within the circumferentially extending cutting edge. 32

(48) Dimensions of various features are shown as follows: each corner sub-edge 46 can have a radius R (FIG. 5C); and each main sub-edge 48 can have a main sub-edge length L.sub.M measured from the center of the bordering corner sub-edges 46, the main sub-edge length L.sub.M being the actual dimension usable during a feed operation. Furthermore, each secondary sub-edge 47 (measured from the center of the bordering corner sub-edges 46) can have a secondary edge length L.sub.S; each ramping portion 43 of a secondary sub-edge 47, i.e. the portion thereof having a relieved peripheral surface portion thereunder, i.e. a relief recess 53 thereunder, can have an effective ramp edge length L.sub.R; and a cutting edge land width W.sub.L is shown in FIG. 4B.

(49) Referring to FIG. 6, a void volume V.sub.S of the cutting insert 14 is defined by the boundaries of the screw hole 30. Specifically, a screw hole height H.sub.S is defined from the base bearing surface 26 to an upper edge 49 of the screw hole 30 (also designated in FIG. 4). Stated differently, the void volume V.sub.S is calculated as the volume of the void extending from a bottom of the screw hole 30, defined at a lower plane P.sub.L perpendicular to the insert axis A.sub.I, to a top of the screw hole 30, defined at an upper plane P.sub.T a perpendicular to the intersection of the screw hole 30 and the rake surface 24, i.e. at the height of the upper edge 49. More precisely, the upper edge 49 is an intersection of a curved corner 51 and the rake surface 24.

(50) The material volume V.sub.F is the volume of the actual material of which the cutting insert 14 is made.

(51) Each side abutment surface 38 extends, preferably, upwardly from the base bearing surface 26 at a right angle 131 shown in FIG. 6.

(52) A cutting insert height H.sub.I extends from the base bearing surface 26 to a highest point of the rake surface 24 (noting the cutting edge is a part of the rake surface 24).

(53) The overhanging portion 44 has a lowermost point 60 (FIG. 6) at the minimum upper sub-surface height H.sub.U above the base bearing surface 26.

(54) The upper sub-surface 36 (FIG. 6A) begins, in the upward direction, at the minimum upper sub-surface height H.sub.U above the base bearing surface 26, the minimum upper sub-surface height H.sub.U being measurable parallel to the insert axis A.sub.I.

(55) As seen in FIG. 2, the secondary sub-edge 47A has a first edge portion 54 adjacent to one corner sub-edge 46B and a second edge portion 56 which extends from the first edge portion 54 in the direction of the adjacent corner sub-edge 46A. Referring to FIGS. 2, 4A and 4B, a relief recess 53 is formed under the second edge portion 56 of each secondary sub-edge 47. The relief recess 53 is as short as possible in a direction along (underneath) the secondary sub-edge 47 to provide the desired ramping function capability without weakening adjacent portions of the cutting edge. For example, under the first portion 54 of the secondary sub-edge 47A, there is no relief at the overhanging portion 44, as shown in FIGS. 2 and 4A. This results in a vertically extending, planar non-relieved surface 55 which extends below and along the first edge portion 54. In contrast, below the second edge portion 56 of the secondary sub-edge 47A, the overhanging portion 44 is inwardly sloped in the direction of the base bearing surface 26, thereby forming the relief recess 53 below and along the second edge portion 56, as shown in FIGS. 2 and 4B. Stated differently, the relief recess 53 could be described as having a step shape in the direction along the secondary sub-edge 47.

(56) The step shape allows the remainder of the cutting edge to be strong. Alternatively, a gradually relieved shape in the direction along the second sub-edge 47 could be used.

(57) FIG. 4B shows a relief angle E. Notably, the other surfaces adjacent to the rake surface 24 in section views 4A and 4C are perpendicular thereto, thus providing preferred stronger cutting edge support.

(58) Referring to FIG. 5C, a largest spacing 57 of an abutment surface from an adjacent cutting edge portion is shown adjacent to a main sub-edge 48. A smallest spacing 59 is shown adjacent to a secondary sub-edge 47. More particularly adjacent to a relief recess 53.

(59) Referring now to FIGS. 7A to 8C, the pocket 22 comprises a seat abutment surface 62, a threaded pocket hole 64 opening out to the seat abutment surface 62 and defining a minimal pocket hole inscribed circle I.sub.P and an associated minimal pocket hole diameter D.sub.P, first, second and third lateral abutment surfaces 66A, 66B, 66C (referred to collectively as “lateral abutment surfaces 66”) perpendicular to the seat abutment surface 62 are shown.

(60) Between the lateral abutment surfaces 66 are first and second lateral recesses 67A, 67B (referred to collectively as “lateral recesses 67”). The use of lateral recesses 67 helps define contact points of the insert 14 and the pocket 22. Notably the contact points are shown with hatch lines in FIG. 8A.

(61) The pocket hole 64 can similarly be comparatively large in cross section compared with the distance to the lateral abutment surfaces. This can be seen from the pocket hole diameter D.sub.P and the distances from the pocket hole 64 to the lateral abutment surfaces 66.

(62) The first, second and third lateral abutment surfaces 66A, 66B, 66C are preferably oriented at the same orthogonal internal angle 131 as the insert's abutment surfaces 38.

(63) A screw axis A.sub.S can preferably be offset from a center of the seat abutment surface 62, i.e. slightly more proximate to where the lateral abutment surfaces 66 are closest to each other (i.e. the area generally designated 68) so that a screw holding the cutting insert to the pocket 22 will bias the cutting insert towards the lateral surfaces.

(64) As shown in FIG. 7A, the pocket is preferably slanted in the forward direction D.sub.F and cutting direction D.sub.C with respect to the rotation axis A.sub.R, as shown by a pocket slant angle μ. The pocket slant angle μ can preferably fulfill the condition 2°≤μ≤9°, and more preferably 5°≤μ≤8°.

(65) Referring to FIG. 7C, a first imaginary extension line L.sub.1 extending from a front edge 72 of one of the seat abutment surfaces 62 can be parallel with a second imaginary extension line L.sub.2 extending from a front edge 74 of the other seat abutment surface 62. A central tool plane P.sub.C contains the rotation axis A.sub.R, and is located between, and parallel to, the first and second extension lines L.sub.1, L.sub.2 such that each seat abutment surface 62 faces the central tool plane P.sub.C. A first seat distance D.sub.S1 is defined from the first extension line L.sub.1 to the central tool plane P.sub.C. A second seat distance D.sub.S2 is defined from the second extension line L.sub.2 to the central tool plane P.sub.C. A total distance D.sub.S3 which is a sum of the first seat distance D.sub.S1 and the second seat distance D.sub.S2.

(66) The total distance D.sub.S3 can be alternatively defined relative to the insert. Referring to FIG. 1C, a total distance D.sub.S3 is greater than the cutting insert height H.sub.1 (only shown in FIG. 6 since in FIG. 1C the inserts are slanted). It will be understood that there is limited space given the dimensions. It will also be understood that if the inserts are positioned with their peripheral surfaces distant from each other instead of the present arrangement (i.e. if the insert on the right side of FIG. 7C would be moved towards the bottom of the page and the insert on the left side towards the top) then the tool holder structural strength for the pocket 22 will be weakened (as there is less material supporting the insert). Conversely, if the inserts 14 are moved in the opposite direction, there might be insufficient chip evacuation space in the flutes. Accordingly, the most preferred arrangement is with the peripheral surfaces adjacent each other.

(67) Referring to FIGS. 9A and 9B, the latter showing the relative positions of the seated cutting inserts as in a front end view of the tool, the cutting inserts only have a small gap therebetween. To alleviate this they are provided positive basic shapes and their positioning as shown in FIG. 9A (i.e. the cutting edges are not adjacent and each insert's peripheral surface is adjacent a portion of the other insert's peripheral portion). Using such features is one way to mount relatively large inserts (relative to the tool holder diameter) in a relatively small circumscribing cutting diameter circle C.sub.C. The ratio for these features is described above.

(68) Referring to FIGS. 7A and 7D, because of the proximity of the inserts 14, a limited length support web 70 is provided.

(69) The support web 70 extends to a forwardmost point 71A (in the center thereof, also coinciding with the rotation axis A.sub.R) which is recessed rearwardly from the front end 13B of the tool holder 12. It will be noted that the circle shape 71B shown merely indicates a planar surface. As shown in FIG. 7A, a forwardmost surface 71C is concavely shaped.

(70) When mounted, the screw 16 secures the cutting insert 14 such that the base bearing surface 26 abuts the seat abutment surface 62 and three of the insert's abutment surfaces 38 abut the pocket's three lateral abutment surfaces 66. It will be understood that the cutting insert 14 can be repositioned three times in the pocket 22 and that the exact designation of which specific abutment surfaces contact at any given time is not important.

(71) It is noted, for example from FIG. 1A, that the upper sub-surface 36 does not contact the tool holder 12 and therefore inserts with slightly different cutting edges can be mounted to the same tool holder 12.

(72) In FIG. 1B, for feed operations the main cutting sub-edge 48 contacts a workpiece (not shown). The cut depth A.sub.P is relatively small compared to other types of milling operations.

(73) Of note is that in this non-limiting example, the main cutting sub-edge 48 is spaced far away from the rotation axis A.sub.R (exemplified by the distance F). This is typically disadvantageous but allows the very small diameter insert mill an acceptable cutting width A.sub.E.

(74) For ramping operations, only the ramping portion 43 contacts the workpiece (the remainder of the secondary sub-edge 47 is not used).