Cutting tool

Abstract: The present invention relates to a cutting tool, especially the cutting tool having a head segment releasably attached to a shank segment. According to one aspect of this invention there is provided a cutting tool comprising: (i) a head segment (2) rotatable around an axis thereof and a forward end portion having at least one cutting-insert (3) receiving seat and a rearward end portion; (ii) a shank segment (1) rotatable around an axis thereof having a forward end portion adapted to be coaxially joined with the rearward end of the head segment and a rearward end portion adapted to be fixedly secured to a machine spindle; (iii) an engaging hole (25) coaxially formed on one of the above segments, which is provided with at least two internal threads (22) communicating between the hole and the external surroundings through a peripheral surface of the segment; (iv) an engaging projection (20) coaxially formed on other one of the segments and engagingly fitted into the hole; and (v) clamp screws (23) respectively threaded through each internal thread, in which bottom ends of the clamp screws are contacted with a surface (24) of the engaging projection (20).

Description: The present invention relates to a cutting tool comprising a head segment and a shank segment. Related Art FIGS. 10 and 11 show a conventional cutting tool which has a generally cylindrical cutting tool body 10 having a shank segment 11 and a head segment 12. The shank segment 11 is adapted to be fixedly secured to a machine spindle (not shown) so that the cutting tool body 10 can be rotated about an axis passing therethrough. The shank segment 11 is made of a high-rigid material such as a cemented carbide alloy which can be used for preventing deflection or chatter vibration of the body 10. The head segment 12 has a generally hemispherical forward end and a rearward end and is made of an easy-processing material such as a steel. In general, at least one insert receiving recess is formed in the forward end of the head segment 12, in which a cutting insert 3 is fixed by a clamp screw 4, while the rearward end of the head segment 12 is joined with the shank segment 11 at a joint portion 13 by means of brazing. However, the conventional cutting tool described above has some problems: (i) it is difficult to detach the head segment from the shank segment because they are joined each other by the braze as mentioned above, so that the head segment can hardly be exchanged for another one when the head segment is damaged or when a different type of the head segment is required; (ii) it is also difficult to bring the end face of the head segment in contact with the end face of the shaft segment with a required accuracy, so that the head segment and/or shank segments requires at least one positioning marker or positioning mechanisms. FIG. 12 shows another type of a conventional cutting tool which is fabricated for solving the above problem (i). As shown in the figure, an external thread 17 is coaxially provided with the shank segment 14, while an internal thread (not shown) is coaxially formed on the head segment 15. Consequently, these segments 14 and 15 are joined by threads so that the head segment can be easily replaced with another one. In this case, however, the internal and external threads have their own tolerances so that it is difficult to adjust the relative position between the head 15 and the shank 14 in a circumferential direction. For example, it is difficult to adjust the relative circumferential position between a cutting insert 3 and a chamfered corner 16 of the shank 14 when the head 15 and the shank 14 are tightened with the external thread 17. Accordingly, the above described joining means cannot be used for the work rotating cutting method but can be used for the tool-rotating cutting method. Furthermore, it is difficult to fabricate the external thread in a unitary construction with the shank when the shank is made of a cemented carbide alloy. In addition, in the case that an external thread segment is manufactured from an easy-processing material such as steel and joined with the shank segment by means of brazing, additional processing steps or the like would be required, resulting in a complicated fabricating process of the cutting tool. EP-A-0 366 047 discloses a threading tool comprising a head segment rotatable around an axis thereof having a forward end portion having a radially projecting cutting edge adapted to be driven into the work being cut for grooving or threading purposes. The threading tool comprises an intermediate section which is formed of a steel material and which is positioned between a rearward section and the forward cutting section. The rearward section is a cemented tungsten carbide body having a longitudinally extending flat section on the outer periphery for engaging a holding mechanism. The forwardly projecting cutting section is preferably made of cemented carbide or hardened steel. The rearward end of the cutting section is connected to an intermediate section by means of a threaded bore which extends in an axial direction entirely through the intermediate section. The forward portion of the threaded bore is adapted to receive a threaded fastener in the form of a bolt having a head. The threaded shank of the fastener extends through the bore of the cutting section and threadingly engages the threaded bore permitting the cutting section to be securely fastened to the intermediate section. The rearward portion of the threaded bore is adapted to receive the threaded end of a draw bar to securely fasten the intermediate section to the rearward section. The intermediate section is preferably made of steel material. US 4 877 360 discloses a locking mechanism in which two segments are connected by a clamp bolt which passes through a drive shaft and is threaded into an adapter. The adapter is tightly inserted into the drive shaft to be aligned coaxially. It is the object of the present invention to provide a cutting tool comprising a head segment and a shank segment wherein the adjustment of the relative position between the head and the shank is improved and wherein the cutting tool can easy be manufactured. This object is solved by the features of claim 1. Advantageous embodiments are characterized by the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the present invention will be apparent from the following description, reference being made to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown. In the drawings: FIG. 1 is a front partial sectional view of a cutting tool in accordance with the first aspect of the present invention; FIG. 2 is an end view of the cutting tool of FIG. 1 as seen in the direction indicated by the arrows II-II in FIG. 1; FIG. 3 is another end view of the cutting tool of FIG. 1 as seen in the direction indicated by the arrows III-III in FIG. 1; FIG. 4 is a front view of a part of the cutting tool of FIG. 1; FIG. 5 is a cross-sectional view of a part of junction between a head segment and a shaft segment of the cutting tool of FIG. 1 as seen in the radial direction thereof; FIG. 6 is a cross-sectional view of a part of junction between a head segment and a shaft segment of the cutting tool of FIG. 1 as seen in the axial direction thereof; FIG. 7 is a front view of a part of a cutting tool in accordance with the second aspect of the present invention; FIG. 8 is a cross-sectional view of the cutting tool of FIG. 7 as seen in the axial direction thereof; FIG. 9 is an end view of the cutting tool of FIG. 7; FIG. 10 is a front elevation of a conventional cutting tool; FIG. 11 is an end view of the cutting tool of FIG. 25; and FIG. 12 is a front elevation of another conventional cutting tool. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Various embodiments of the present invention will be described hereinafter with reference to the accompanying drawings in which the same reference characters are used to designate like parts or elements in several views. [Example 1] FIGS.1 to 6 depict a ball end mill in accordance with the present invention comprising a shank segment 1 and a head segment 2. The shank segment 1 has two end portion: a forward end portion coaxially provided with an engaging projection 20 adapted to be joined with the head segment 2; and a rearward end portion which is adapted to be fixedly secured to a machine spindle (not shown). In this example, the shank segment 1 also comprises a through hole 25 which is coaxially formed in the shank 1 and the engaging projection 20, and thus the through hole 25 is opened at the rearward end face of the shank segment 1 and a forward end face of the engaging projection 20 so that a clamp bolt 27 is inserted from an opening at the rearward end of the shank segment 1 and is penetrated through the engaging projection 20. As shown in FIG. 1, the through hole 25 comprises three parts: a tapered opening portion 25a at a side of the rearward end of the shank segment 1, which is responsible for a step of inserting the clamp bolt 27 into the through hole 25; a bolt-head receiving portion 25b, which is responsible for holding a head 28 of the clamp bolt 27; and a reduced diameter portion 25c which is formed such that its inner diameter is slightly larger than the outer diameter of a threaded portion of the clamp bolt 27. In addition, the shank segment 1 and the engaging projection 20 are fabricated in a unitary construction by using a material of cemented carbide alloy. Furthermore, a peripheral surface of the engaging projection 20 is chamfered so as to form two flat portions 24. As shown in FIG. 5, these two flat portions 24 are opposed to each other so as to be symmetrical with respect to an axis of the engaging projection 20. The head 2 segment, which is made of a steel, comprises a hemispherical forward end portion and a reward end portion. The forward end is adapted to receive a cutting insert 3 thereon, while a rearward end portion having an engaging hole 21 which is coaxially formed therein so as to be joined with the shank segment 1. The head segment 2 also comprises two internal threads 22 and two clamp screws 23. That is, the internal threads 22 communicate between the engaging hole 21 and the external surroundings through a peripheral surface of the head segment 2, through which the clamp screws 23 are respectively threaded. These internal threads 22 are opposed to each other so as to be symmetrical with respect to an axis of the head segment 2. In a bottom face of the hole 21, the internal thread 26 is coaxially formed. This internal thread 26 has a diameter smaller than that of the hole 21 and is responsible for receiving the clamp bolt 27 penetrated through the shank segment 1. Referring to Fig. 5, the clamp screws 23 are respectively threaded into each internal thread 22, in which bottom ends of the clamp screws 23 are respectively contacted with the flat portions 24 of the engaging projection 20. Referring to FIG. 6, there is a gap between a peripheral surface of the engaging projection 20 and a side wall of the hole 21. In a radial direction of the tool, the gap size as indicated by a reference character A1 in the figure is in the range of approximately from 0.01 to 0.04 mm. In this example, the shank segment 1 and the head segment 2 are joined with each other by following steps: (i) thrusting the clamp screws 23 loosely into each internal thread 22 of the head segment 2 in such a manner that a bottom portion of the clamp screw 23 is not penetrated from the internal tread 22; (ii) inserting the engaging projection 20 of the shank segment 1 into the engaging hole 21 of the head segment 2; (iii) inserting the clamp bolt 27 into the through hole 25 of the shank segment 1 and temporary tighten with the head segment 2; (iv) radially positioning the engaging projection 20 in the engaging hole 21 by means of the clamp screws 23, for example tightening one clamp screw and loosening other screw to change the relative position of the head segment 2 and the shank segment 1; and (iv) tightly threading the clamp bolt 27 into the internal thread 26 of the head segment 2 to obtain a cutting tool. In the obtained cutting tool, the trajectory of the cutting edge is a circle as indicated by alternating long and short dash line C in FIG. 5. This circle has a diameter of D which can be varied in the range of A2 (= A1) by means of changing the relative radial position of the above segments 1 and 2 which can be determined by tightening or loosing of the clamp screws 23. Accordingly, it is preferable that the clamp screws 23 and the clamp bolt 27 are alternately tightened to same extent in several times for positioning the cutting edge with a high accuracy. In this example, the cutting insert 3 has a threaded bore into which a clamp screw 4 is threaded so as to fixedly secured to an insert-receiving recess of the head segment 2. An axis of the clamp screw 23 is parallel to top and bottom surfaces of the cutting insert 3 so that an effect of the cutting resistance against the cutting insert 3 can be reduced. [Example 2] FIGS. 7 to 9 depict a cutting tool in accordance with the present invention which differs from the first example in that an axis of the clamp screw 23 is perpendicular to top and bottom surfaces of the cutting insert 3 for positioning the cutting edge with a high accuracy. The Examples 1 and 2 can be modified as follows. The number of the clamp screws for positioning the head and shank segments is not restricted to the number thereof as described above. For example, more than two clamp screws can be used for the positioning. As described above, a cutting tool according to the present invention can be fabricated without using the brazing method or the like for joining the head and shank segments, which can be easily attached and detached from the head segment.

Claims: A cutting tool comprising: a head segment (2) rotatable around an axis thereof having a forward end portion having at least one cutting-insert receiving seat and a rearward end portion; a shank segment (1) rotatable around an axis thereof having a forward end portion adapted to be coaxially joined with said rearward end of the head segment (2) and a rearward end portion adapted to be fixedly secured to a machine spindle; an engaging hole (21) coaxially formed on said head segment (2), which is provided with at least two internal threads (22) communicating between said hole and the external surroundings through a peripheral surface of said head segment, said internal threads being formed so as to coaxially coincide with each other; an engaging projection (20) made of a cemented carbide alloy and coaxially formed on said shank segments (1) in a unitary construction and engagingly fitted into said hole (21); clamp screws (23) respectively threaded through each internal thread (22) in which bottom ends of said clamp screws are contacted with a surface (24) of said engaging projection (20); said engaging projection further including flat portions (24) on an outer peripheral surface thereof for respectively receiving said bottom ends of the clamp screws; a through hole (25) being coaxially formed in said shank segment (1) and said engaging projection (20); an internal thread (26) being coaxially formed on a bottom face of said engaging hole (21); a clamp bolt (27) coaxially passing through said shank segment (1) and said engaging projection (20) and engagingly fitted into said internal thread (26); said cutting tool having a gap between the peripheral surface of said engaging projection (20) and a side wall of said hole (21) in a radial direction of said cutting tool. Cutting tool according to claim 1, characterized in that said shank segment further comprises at least one chamfered portion on a peripheral surface thereof. Cutting tool according to claim 1, characterized in that said gap (A1) is in the range of from 0.01 to 0.04 mm.

Inventors: NAKAYAMA MASAAKI C O TSUKUBA-S, OKAWA MASAYUKI C O TSUKUBA-SEI, SAITO JUNICHI C O TSUKUBA-SEIS, NAKAYAMA, MASAAKI, C/O TSUKUBA-SEISAKUSHO, OKAWA, MASAYUKI, C/O TSUKUBA-SEISAKUSHO, SAITO, JUNICHI, C/O TSUKUBA-SEISAKUSHO
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1992
Main classification: B23B29
IPC codes: B23B31, B23B29