There exist a variety of tool holders for the mechanical clamping of cutting inserts such as rhombic, rhomboidic and triangular indexable inserts with equal angles all around the insert. The material used for such inserts is normally cemented carbide material or ceramic material.

A commonly used locking system for such indexable inserts includes a pin in the holder extending upwardly into the insert-receiving pocket to engage a hole in the insert located in said pocket, and means for forcing said pin to be subjected to a pivoting movement inwardly towards said holder, said forcing means being arranged to actuate the lower portion of said pin, thus urging both the pin and the insert inwards towards an upwardly extending wall formed on said holder rearwardly of said pocket. Such type of tool holder is disclosed in US-Patent 3,314,126. The drawback of such holder, however, is that the forward nose portion of the cutting insert has a tendency of coming apart from the shim plate located underneath said insert which sometimes can lead to insert failure.

In view thereof it is an object of the invention to provide a tool holder such that a forcing means acting on the insert will ensure that said insert is pushed both downwards and inwards. At the same time it is desirable that a front portion of the clamp acting on the insert in best possible way can be protected against wear from the chips obtained during machining from the workpiece. It is also desirable to provide a tool holder that enables using both solid inserts and centrally apertured inserts in such holder. All these desires can be fulfilled by providing said forcing means in the shape of a clamp actuated by a clamping screw which, in a manner known per se, is provided with a first and a second contact surface. The first contact surface is provided on a forward protrusion of said clamp engageable with an upper contact surface of the insert and where the second contact surface is provided on a rear protrusion of said clamp for engagement with a contact surface that is inclined in relation to the axis of said clamp screw. According to

the invention both the upper portion of the clamp screw and the upper portion of a coil spring located between the head and the thread of said screw in a recess of said clamp the central axis of said coil being inclined in relation to the axis of the screw-receiving recess at the same time as said forward protrusion of the clamp is received in a recess of a clamp plate between the insert and the clamp so as to bring said plate into surface abutment with the upper surface of the insert.

The invention will now be described more in detail by reference to the enclosed drawings, which illustrate a preferred embodiment of the invention.

Fig. 1 is a sectional view along the line A-A of a tool holder as shown in Fig. 2 according to one embodiment of the invention.

Fig. 2 is a plan view of a clamp and the insert of the tool holder shown in Fig. 1.

Fig 3 is a longitudinal sectional view of an alternative embodiment of a tool holder of the invention.

Fig 4 is a longitudinal sectional view of the insert of the cutting tool.

Fig. 5 is a longitudinal sectional view along a central line through an alternative embodiment of the invention.

Fig. 6 is a plan view according to Fig. 2 of an insert with a central hole according to Fig. 5.

Fig. 7-9 show a plan view and a perspective view of a clamp plate to be used in this invention.

Fig. 10 is a perspective view and Fig. 13 a plan view of a clamp and an associated clamp plate according to one embodiment of the invention,

and Fig. 12 is a perspective view and 13 a plan view of a clamp and an associated clamp plate according to another embodiment of the invention.

In Figs. 1-2 there is shown a portion of a cutting tool comprising a partially shown tool holder 10 for turning, the forward nose portion of which is provided with a pocket for the receipt of an indexable cutting insert 11 of polygonal shape. This insert has rhombic basic shape and is manufactured from cemented carbide material or ceramic material.

The insert has an upper flat surface 12 and a lower flat surface 13 parallel with said upper surface. The insert has a plurality of side surfaces extending perpendicularly towards said upper and lower surfaces 12,13, two of which are designated 1 la and 1 lb. The insert is arranged to rest in surface abutment with a shim plate 14 having a central hole 15 engaged by a screw 16 that is threadably engaged with the holder 10 the central axis of which extends perpendicularly against the flat surfaces 12,13 of the insert. The insert- receiving site includes a bottom supporting surface 17 and two perpendicularly therefrom-extending support surfaces 18 and 19.

There is a clamp 20 provided for the clamping of the insert into its pocket in the holder 10, said clamp being actuatable by means of a clamp screw 22 that extends entirely through said clamp and threadably engages a bore 21 in the holder 10, the central axis CL, of said screw extending parallel with the central axis of the hole 15 in the insert. The forward end of said clamp is in the shape of a downward-inwards inclined first protrusion 23 intended to engage with a separate clamp plate 24 located between said first clamp 20 and said insert 11, said clamp plate 24 having a central hole 25. More specifically, said first protrusion 23 is arranged, upon tightening said screw 22, to be received in said hole 25 thereby extending a pressure downwardly at pressing points A, and A2 (see Fig. 2) on the surface 55 (Fig. 8) on each side of said hole 25. The central hole 25 is a recessed bore with rotationally symmetrical configuration, including a lower cylindrical or slightly conical wall which expands upwards by increasing its diameter in the direction from the inner cavity to the entrance opening. The forward mantle surface of the protrusion 23 is given a corresponding configuration. The underneath side 24a of said clamp plate 24 is planar ground and has a large surface extension whilst said hole 25 is straight cylindrical.

This ensures spreading the surface pressure over a large surface of the insert, which is essential, especially in case the insert is manufactured from ceramics.

The opposite part of said clamp 20 is in the shape of a second protrusion 28 which has an inclined surface 27 that is preferably convexly shaped and arranged, upon tightening, to come into surface abutment with a correspondingly inclined surface 29a in the holder 10, inclined at same angle to the central axis CL, of said clamp screw 22. At 29b there is designated a lower support surface of the holder 10. The clamp 20 can be tightened by means of the screw that acts against a spring 31 that is partially received in the bore 21 and urges the clamp laterally to an outer position. There is provided a pin 32, acting as stop means, which ensures that the clamp 20 does not rotate upon tightening said screw 22.

The clamp screw 22 has an upper flange-formed head portion 33 integral with an adjacent cylindrical portion 34 with somewhat smaller diameter than said head portion which is integral with a cylindrically shaped waist portion 35 with a smaller diameter than said cylindrical portion 34. The waist portion 35 extends into a lower threaded portion 36 the diameter of which is larger than the diameter of the waist portion 35. Upon tightening, the top surface of the head 33 of the screw becomes essentially flush with the surrounding upper surface or entirely received in a recess 37 of said clamp 20 such that the radial underneath surface of said screw head 33 is located in abutment against a corresponding radially extending surface 38 in the clamp 20 whilst the top surface of said screw head 22 is flush with the top surface of the clamp 20.

In accordance with one aspect of the invention the tool holder is provided with a coil spring 31 around the upper portion of the clamp screw 22, so that the clamp is pressed upwards upon loosening the screw 22. The spring 31 extends axially along the cylindrical waist portion 35 and is partially received in an inclined bore 21 in the clamp 20 and is partially received in a cylindrical recess 39 in the tool holder. More specifically, the central axis CL3 of said bore 21 extends at an acute angle y in relation to the central axis CL, of said screw 22. In accordance with a suitable embodiment the size of the angle y is in the range of 2-15°. As appears from Fig. 1 the upper portion of said coil spring 31 is

received in said inclined bore 21, the arrangement being such that there is a certain play between said cylindrical portion 34 and the hole wall of said inclined bore 21 such that the clamp does not rotate upon tightening the screw 22 whereas the upper portion of said coil spring 31 is brought into surface contact with the hole wall of said inclined bore 21.

The arrangement is such that upon tightening the screw 22 the lower portion 28 of the end surface of said clamp comes into surface abutment with surface 29a and 29b. It is to be understood that once the clamp portion 28 has come into contact with said surface 29b the clamp will be subjected to a certain rotation movement such that the forward clamp portion 23 establishes a downward pressure towards the insert via the press plate 24 to achieve a firm efficient insert clamping. At the same time it is important to ensure that the lower end surface of said clamp portion 23 is arranged with a certain play in relation to the top surface of the insert as is shown in Fig. 1. By having the forward protrusion 23 of the clamp 20 received in recess 25 of said press plate 24 is also ensured that the upper portion of said protrusion 23 does not become subject to wear under the impact of rearwardly directed chips from the metalworking machining process. This effect is furthermore efficient due to the arrangement that the forward portion of said press plate 24 has a raised portion as compared with the rear portion of said press plate.

As mentioned above the upper portion of coil spring 31 is received in the inclined bore 21 of the clamp whereas the lower portion of said coil spring 31 is partially received in a cylindrical counterbore 39 in said holder 10, the central axis of which is the same as the central axis CL). The recess 39 extends to the threaded bore 21, which receives the threaded portion 36 of the clamp screw 22.

The clamp plate 24 of the invention should be made from a material having a larger wear resistance and larger strength than the material of the top clamp 20. The clamp plate 24 should preferably be made of cemented carbide. In a preferred embodiment the thickness of said clamp plate is essentially smaller than the thickness of the cutting insert 11. The forward end surface of said clamp plate 24 is confined by two forwardly converging flat side faces 40 and 41 which are connected by a curved nose portion 42b having a radius of curvature that is essentially larger than the corner radius that is provided at the corner

portion 43 of the cutting insert at which corner said converging side faces 1 la and 1 lob of the insert intersect. The forward side faces 40 and 41 of the clamp plate 24 are inclined downwards against the top face of the insert as appears in Fig. 2 and Fig. 7-8. Preferably said side faces 40 and 41 are inclined at an angle that is smaller than corresponding inclined angle of the nose portion 42 which includes a central curved nose portion 42b and side segments 42a and 42c on both sides thereof. These side segments 42a, 42c should preferably be inclined at a larger angle of 20-45° as compared with corresponding angle valid for the segments 40,41 which lies in the area 5-15°. This accomplishes a more efficient change of the direction of movement of the chip when it approaches the said side segments 42a, 42c.

In Fig. 3 is shown an alternative embodiment of the invention. In this case the protrusion 23 is confined by a lower portion 23b that extends downwards-inwards and an upper portion 23a that extends straight downwards. The entire protrusion 23 has a much larger longitudinal extension than compared with the embodiment in Fig. 1-2. More specifically, the protrusion 23 now extends entirely through the central hole 25 of the clamp plate 24 and additionally also extends downwards so as to engage with a recess 44 of the insert 11. The arrangement is such that the lower end portion of said protrusion comes into engagement with the lower portion of the hole wall of said recess 44. The insert 11 has more specifically been provided with a recess 44 of a rotational symmetric form comprising an inner cavity 45 which is delimited by a cylindrical or slightly conical surface 46 and an external cavity 47 which expands outwards by ever increasing its diameter to the entrance opening in the upper top face of the insert. It is to be understood that such inserts having similar cavities with entrances from both the top surface and the bottom surface of the insert could be used in connection with this invention. Such an insert is also shown in Fig. 4. Such an insert is suitably provided with a solid central portion 48 between two opposite cavities as shown in Fig. 4.

In Fig. 5 is shown an embodiment of the invention wherein the insert 11 has a central through hole 49 with a central axis CL2 that is parallel with the central axis CLs which defines the hole 21 of the holder. In this case the forward protrusion 23 comprises an upper clamp portion 23a that extends straight downwards axially into the insert hole 46

and a lower clamp portion 23b that extends at an inclined angle a downwards-inwards such that the lower clamp portion 23b comes into engagement with the wall of the insert hole 49 at a contact point 26 located a bit downwards in said hole. The forward mantle surface portion of the upper clamp portion 23 and the forward hole wall of said clamp plate 24 is given essentially the same form as in Fig. 1. The inclination angle a ought to have a value in the range 2-15°. As also appears from Fig. 5 there is no surface contact between the lower end portion of the clamp portion 28 and the upper surface of the holder.

When tightening the screw 22 the forward clamp portion 23 will be urged inwards into the insert hole 49. The clamp will thereafter exert a clamping pressure against the clamp plate 24 along the contact zone Al and A2 (also in Fig. 1-2). Upon continued tightening of the screw 22 there will occur a final clamping of the whole system during simultaneous elastic bending of said clamp.

In Fig. 7-9 there is shown some different detailed views of the clamp plate 24. This clamp plate is confined by a forward portion 50 with a wedge-shaped contour towards the forward cutting tip 43 whereas its rear portion is finalized by a convexly curved portion 51. The transition portions between said wedge portion 50 and said rear convex portion consists of two straight portions 52,53 the edges of which extend parallel to each other. As best seen in Fig. 8 the forward upper surface 54 of the clamp plate 24 is raised in relation to the rear upper surface 55. Preferably these surfaces 54 and 55 are planar and mutually parallel. The forward portion of the clamp 20 is intended to rest against said rear surface 55.

Further, the protrusion 23 extends through recess 25 of the clamp plate 24. Further, said rear convexly curved portion 51 is provided with a non-symmetric recess 56 comprising a first portion 56a and a second portion 56b said first portion 56a having smaller radial depth than the radial depth of said second portion 56b.

Further, said first portion 56a is provided with a shoulder 57, the height level of which corresponds to half the thickness of the clamp plate.

In Fig. 10-11 is shown a perspective view and a plan view of a clamp plate 24 in cooperation with a clamp 20. As shown therein said shoulder 57 is intended to receive a clamp finger 58 that extends from said clamp 20. When mounting occurs this finger 58 is first brought to a free position at the area of portion 56b and then said clamp plate 24 is turned anticlockwise to a position wherein said clamp finger 58 is brought into surface contact with the shoulder 57. This clamp finger 58 is suitably of flat shape and somewhat inclined in relation to the flat contact surface 24a of said clamp plate. This turning of said clamp finger occurs by turning a screw 59 that is threadably engaged into the underneath side of said clamp plate, whereby said screw 59 is threadably engaged such that its head becomes recessed at a lower position than the level of the underneath surface 60 of said clamp 20.

In Fig. 12-13 is shown an alternative embodiment of the clamp plate 24. In this case the rear convex portion 51 of the clamp plate is provided with a singular recess 56 confined by a shoulder 57, the height of which preferably is of a value that corresponds to half the thickness of said clamp plate. Also in this case the clamp finger 58 is a flat metal portion of stepped configuration, comprising an upper portion 58a in contact with said shoulder 57 and a lower portion 58b clamped by a screw 59 into recess 61 of said clamp 20. The clamp finger receiving recess 56 comprises two radially extending side surfaces 56a, 56b and an inner surface 56c extending between said radial surfaces 56a, 56b.

In another alternative embodiment this clamp plate 24 could be provided with a number of cooling channels (not shown) on its underneath side aimed to have a number of cooling streams directed towards the cutting tip whilst being supplied from the interior portion of said holder body 10.