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 90° shoulder 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 three main cutting edges which lie along an imaginary equilateral triangle. A material volume V.sub.F of the cutting insert and a void volume V.sub.S of the insert's screw hole 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 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 the 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 circular 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 defines, 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 comprises: first, second and third abutment surfaces which, in said bottom view along the insert axis, extend parallel with sides of an imaginary equilateral triangle; the cutting edge comprises: exactly three main sub-edges, which are the three longest sub-edges of the cutting edge and which, in said top view parallel to the insert axis (A.sub.I), each extend along a side of an imaginary equilateral triangle and define an edge inscribed circle (C.sub.M) having an edge inscribed diameter D.sub.M; wherein: the edge circumscribed diameter D.sub.E fulfills the condition: D.sub.E<6.5 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 and a material volume V.sub.F defined by the amount of material of the cutting insert fulfills the condition: 0.5>V.sub.S/V.sub.F≥0.30; an insert thickness diameter ratio D.sub.S/D.sub.M of the hole diameter D.sub.S and the edge inscribed diameter D.sub.M fulfills the condition: 0.8>D.sub.S/D.sub.M>0.60; an edge length ratio L.sub.M/D.sub.E of a main edge length L.sub.M of a shortest one of the main sub-edges, and the edge circumscribed diameter D.sub.E fulfills the condition: 0.7>L.sub.M/D.sub.E>0.40; and the peripheral surface comprises a lower sub-surface and an upper sub-surface; the lower sub-surface extending upwardly and outwardly from the base bearing surface and comprising the first, second and third side abutment surfaces; the upper sub-surface connecting the lower sub-surface and the rake surface, and the upper sub-surface beginning in the upward direction at a minimum upper sub-surface height H.sub.U above the base bearing surface; and wherein the minimum upper sub-surface height H.sub.U fulfills the condition: 0.50H.sub.I≤H.sub.U≤0.80H.sub.I.

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 circumscribed diameter D.sub.E fulfills the condition: D.sub.E>5 mm.

4. The cutting insert according to claim 1, wherein the cutting edge comprises a wiper sub-edge between each pair of adjacent main sub-edges, each of the wiper sub-edges forming, in said top view parallel to the insert axis (A.sub.I), a right angle with an adjacent one of the main sub-edges.

5. The cutting insert according to claim 4, wherein each wiper sub-edge has an edge length L.sub.W which fulfills the condition: 0.5 mm<L.sub.W<1.5 mm.

6. The cutting insert according to claim 5, wherein the cutting edge comprises exactly three main sub-edges and exactly one wiper sub-edge between each pair of adjacent main sub-edges.

7. The cutting insert according to claim 1, wherein a first relief angle measured at a first point of one of the main sub-edges is larger than a second relief angle measured at a second point of the same main sub-edge, the second point being closer than the first point to a wiper sub-edge which forms a right angle with said main sub-edge.

8. The cutting insert according to claim 7, wherein relief angles gradually decrease along said main sub-edge from a first area adjacent to a first wiper sub-edge which does not form a right angle with said main sub-edge to a second area adjacent to a second wiper sub-edge which does form a right angle with said main sub-edge.

9. 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 the center of the tool holder and defining a forward direction extending from the rear end to the front end, a rearward direction opposite to the forward direction, and an outward direction perpendicular to the rotation axis and directed from the rotation axis to the tool periphery; 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 comprises a pocket formed at the intersection of the front end and the tool periphery; and a cutting insert according to claim 1 mounted in each of the pockets of the tool holder; wherein: one of each insert's main sub-edges is located outside of the tool diameter and defines a cutting tool diameter D.sub.C; and in a side view of the insert mill, said main sub-edge located outside of the tool diameter extends parallel to the rotation axis (AR).

10. The insert mill according to claim 9, wherein: each pocket comprises: a seat abutment surface; a threaded pocket hole opening out to the seat abutment surface; and first and second lateral abutment surfaces which are straight and oriented at an acute angle to each other in a plan view of the seat abutment surface; each first lateral abutment surface extends in an outward and forward direction; each second lateral abutment surface extends in an outward and rearward direction; and the tool diameter D.sub.T fulfills the condition D.sub.T<11 mm.

11. The insert mill according to claim 10, wherein a tool aperture extends through material of the tool holder and opens out at a first end to one of the pockets and opens out to a second end at the other one of the pockets.

12. The insert mill according to claim 10, wherein in said plan view of each seat abutment surface, material of the tool holder extends along the front end, from a portion of the first lateral abutment surface which portion is closest to the tool axis to the tool periphery.

13. The insert mill according to claim 10, wherein in said plan view of each seat abutment surface, a flute wall extending alongside the pocket curves to extend in the forward and downward directions at the front end.

14. The insert mill according to claim 10, wherein, in said plan view of each seat abutment surface, the tool holder is devoid of any abutment surface extending along the tool periphery.

15. The cutting insert according to claim 1, wherein: the cutting edge comprises a wiper sub-edge between each pair of adjacent main sub-edges, each of the wiper sub-edges forming, in said top view parallel to the insert axis (A.sub.I), a right angle with an adjacent one of the main sub-edges; each wiper sub-edge has an edge length L.sub.W which fulfills the condition: 0.5 mm<L.sub.W<1.5 mm; the cutting edge comprises exactly three main sub-edges and exactly one wiper sub-edge between each pair of adjacent main sub-edges; a first relief angle measured at a first point of one of the main sub-edges is larger than a second relief angle measured at a second point of the same main sub-edge, the second point being closer than the first point to a wiper sub-edge which forms a right angle with said main sub-edge; and the relief angles gradually decrease along said main sub-edge from a first area adjacent to a first wiper sub-edge which does not form a right angle with said main sub-edge to a second area adjacent to a second wiper sub-edge which does form a right angle with said main sub-edge.

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 90° shoulder 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 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 which opens out to the base bearing surface 26, 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 radially inward and radially outward directions D.sub.I, D.sub.O. The radially 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 radially 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 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 parallel to the rotation axis A.sub.R and hence 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 and the base bearing surface, 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 FIGS. 2 and 6, the peripheral surface 28 comprises a lower sub-surface 34 and an upper sub-surface 36. The lower sub-surface 34 is unground and extends upwardly and outwardly from the base bearing surface 26, and comprises first, second, and third side abutment surfaces 38A, 38B, 38C (the third side abutment surface 38C only being shown schematically in FIG. 2, as such side is not shown). Hereinafter the identical side abutment surfaces will be identified generally as “side abutment surface(s) 38”).

(41) As shown in FIG. 5C, the side abutment surfaces 38 lie on sides of an imaginary pyramid whose apex is on the insert axis A.sub.I, at a point below the base bearing surface 26. The sides of the base bearing surface 26 itself form sides of an imaginary first equilateral triangle T1.

(42) Referring to FIG. 6, the positive basic shape of the cutting insert 14 means that the lower sub-surface 34 forms a first obtuse internal angle β.sub.1 with the base bearing surface 26. At the left hand side of the insert 14 as shown in FIG. 6, the section is through the peripheral surface 28 at a portion of a wiper sub-edge which forms a second obtuse internal angle β.sub.2 larger than the first obtuse internal angle β.sub.1.

(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 a bulge 40 is acceptably small enough for the side abutment surface 38 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 unground lower sub-surface 34. Even though in FIG. 2, for example, it 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.

(45) The upper sub-surface 36 comprises at least one overhanging portion 44 (exemplified in FIGS. 4A and 4B).

(46) Referring to FIG. 2, the cutting insert 14 can comprise three identical corner edges 46A, 46B, 46C (hereinafter generally referred to as “corner edge(s) 46”), and three identical straight main sub-edges 48A, 48B, 48C (hereinafter generally referred to as “main sub-edge(s) 48”). Preferably, three identical wiper sub-edges 47A, 47B, 47C (hereinafter generally referred to as “wiper sub-edge(s) 47”) extend at right angles between the corner edges 46 and the main sub-edges 48 (i.e. only extending at a right angle in the clockwise direction as shown in a top view, such as that shown in FIG. 3).

(47) Referring to FIG. 5B, there is shown an imaginary edge circumscribed circle C.sub.E having an edge circumscribed diameter D.sub.E. The imaginary edge circumscribed circle C.sub.E is a minimum diameter circle which encircles the entire cutting edge 32 including the main sub-edges 48, the corner edges 46 and the wiper sub-edges 47.

(48) The three main sub-edges 48 extend along a side of a second imaginary equilateral triangle T2, and define an edge inscribed circle C.sub.M having an edge inscribed diameter D.sub.M.

(49) Dimensions of various features are shown as follows: each corner edge 46 can have a radius R (FIG. 5C); each main sub-edge 48 can have a main sub-edge length L.sub.M measured from the transition point of the radius to an intersection with a wiper sub-edge (FIGS. 1B, 5B); each wiper sub-edge 47 can have a wiper edge length L.sub.W measured from the transition point of the radius to an intersection with a main sub-edge (FIG. 5B); and a cutting edge land width W.sub.L is shown in FIG. 4B.

(50) 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 screw hole's upper edge 49 is an intersection of a curved corner 51 and the rake surface 24.

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

(52) Each side abutment surface 38 extends upwardly and outwardly from the base bearing surface 26 at an obtuse internal angle β.sub.1 shown in FIG. 6.

(53) 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 32 is a part of the rake surface).

(54) FIG. 4C shows that at least the portion shown is devoid of an overhanging portion 44, whereas FIGS. 4A and 4B show portions which have an overhanging portion. The at least one overhanging portion 44 has a lowermost point 60 at the minimum upper sub-surface height H.sub.U above the base bearing surface 26.

(55) The upper sub-surface 36 (FIG. 6A) begins, in the upward direction, at a 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.

(56) FIG. 4A shows a first relief angle μ.sub.1. FIG. 4B shows a second relief angle μ.sub.2. The first relief angle μ.sub.1 is larger than the second relief angle μ.sub.2. The larger relief angle, the first relief angle μ.sub.1 is provided for when the area of the main sub-edge is used for a ramping operation and a larger relief is required. However the area of the same main sub-edge shown by FIG. 4B is never used for a ramping operation and can have a preferred smaller relief angle which provides more structural strength. While only two sections have been shown, it will be understood that the change in relief angles can be gradual.

(57) 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 and second lateral abutment surfaces 66A, 66B oriented at an acute angle to each other in a plan view (i.e. the view in FIG. 8C) of the seat abutment surface 62.

(58) As shown in FIG. 7B each first lateral abutment surface 66A extends in an outward and forward direction (D.sub.O, D.sub.F); each second lateral abutment surface 66B extends in an outward and rearward direction (D.sub.O, D.sub.R).

(59) The second lateral abutment surface 66B comprises a recess 67. The use of a recess 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.

(60) 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 66A, 66B.

(61) The first and second lateral surfaces 66A, 66B are preferably typically oriented at the same obtuse internal angle β.sub.3 as the insert's abutment surfaces 38.

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

(63) 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 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. In some embodiments, the first seat distance D.sub.S1 and the second seat distance D.sub.S2 equal each other. Also in some embodiments, the two seat abutment surfaces 62 have 180° rotational symmetry about the tool's rotation axis A.sub.R, in the front view of the tool 12, as seen in FIG. 7C.

(64) Referring to FIG. 1C, a total distance D.sub.S3 is greater than the cutting insert height H.sub.I. It will be understood that the inserts cannot remain with their rake surfaces aligned as there is insufficient 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 inserts' peripheral surfaces adjacent each other.

(65) Referring to FIGS. 9A and 9B, it will be noticed that in such view the cutting inserts actually reach a common radial position. The only reason they do not touch as per the appearance in FIG. 9B is because they have their positive basic shape 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.

(66) Because of the proximity of the inserts 14, reverting to FIGS. 8A to 8C, a tool aperture 70 is provided.

(67) To compensate for the weakening caused by the aperture, material 76 has been added at the front end 13B.

(68) When mounted, the screw 16 secures the cutting insert 14 such that the base bearing surface 26 abuts the seat abutment surface 62, one of the abutment surfaces 38 abuts the first lateral surface 66A, and an adjacent abutment surface 38 abuts the second lateral surface 66B at the two portions thereof. 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.

(69) 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.

(70) The pocket 22, or more precisely, each seat abutment surface 62 extends parallel or approximately parallel to the rotation axis A.sub.R, as best shown in FIG. 7A.

(71) In FIG. 1B, for the insert mill 10 exemplified, one of the straight cutting edges (for example the second straight edge 47A) performs a wiper function and only protrudes a small wiper distance D.sub.W from the tool holder. In this example, the first main sub-edge 48A is the main cutting edge for providing a 90° shoulder milling operation.

(72) Since various techniques have been used to allow a larger insert, and more particularly a larger main sub-edge, a comparatively large cut depth A.sub.P is achievable for a comparatively very small cutting insert.

(73) Finally it is noted that a ramping function can be provided by a small portion of the third sub-edge 48C (FIG. 1B).