Cutters

Abstract: For cutting a facing such a countersink or a spot facing a rotary cutter is provided with a body (2) having a central aperture (4) arranged to receive a drill (T) or other guide and at least one cutting insert (10) carried by the body rotates with the drill or guide to cut the facing. The insert has a forward cutting edge (16) which projects radially inwardly to form a step (18) projecting inwards relative to the main body of the insert behind the cutting edge region. The drill (T) has a radially recessed portion, such as the radial relief (R) or the flute of the drill, to accommodate said step of the cutting edge region. Such a cutter can be designed to operate at high metal removal rates and can be used with standard forms of drill and reamer.

Description: This invention relates to cutters for forming, at an open end of a bore or the like, a countersink or spot facing or other such ring-form surface of revolution concentric to the bore. It is particularly concerned with a rotary cutter according to the preamble of claim 1, that can be adjustably assembled with a drill bit or other generally cylindrical leading element producing or fitting the bore, and with a cutting insert according to the preamble of claim 9. This state of the art is shown in WO-A-8 700 100. The use of such cutter attachments mounted upon tools such as twist drills is well known as a means of drilling and countersinking a hole in a single operation. As examples can be mentioned GB 1378869, 1378868, 1304382, 988263, 570099 and 570098. These earlier cutter attachments have disadvantages, however, particularly if they are to be used at the high rates of material removal associated with current cutting technology. They have a tubular body with a central bore in which the associated drill bit can slide for the purpose of axial adjustability, the countersink cutting edges on the body projecting outwardly at the sides of the bore. These cutting edges have a limited operating life before resharpening is required, since they are formed from the same material as the cutter body. Some improvement in this respect is obtained by providing cutter bodies with brazed-on tungsten carbide tips but with all forms of this type of cutter attachment there are high servicing costs because regrinding and resetting is both expensive and time-consuming. In US 4353670 this problem is addressed by providing a special form of drill bit or other carrier for the cutter attachment, a flat recess being formed on the otherwise generally cylindrical carrier and the attachment is arranged to be clamped on the flat recess. A cutting insert of the attachment has its main body disposed partially in the recess or, in the case of a twist drill, in a drill flute that forms an extension of the recess. It is a disadvantage, however, only to be able to use the attachment on a specially adapted carrier. According to one aspect of the present invention, there is provided a rotary cutter for forming a countersink or spot facing or other ring-form surface of revolution concentric to a bore in a workpiece, comprising a cutter body having a central longitudinal aperture for receiving an elongate leading element, such as a drill bit or a cylindrical guide, to locate the cutter radially relative to the bore in the workpiece, the body being provided with means to clamp said element releasably in said central aperture and a cutting insert, having a cutting edge region at the forward end of a main body of the insert for cutting said ring-form surface, received in a recess in said cutter body, said body recess having a radially outwardly facing seating face, that the cutting insert is removably received in said recess with its main body seated against said seating face, and that said forward cutting edge region projects radially inwardly in the form of a stepped extension of said main body passing laterally across a front end of said seating face and into a front-to-rear extending groove in said leading element. According to a further aspect of the invention, there is provided a cutting insert for use in forming a countersink or spot face or other ring-form surface of revolution at the entry to a bore in a workpiece, the insert having a main body of generally plate-like form with a cutting edge region defining a forward cutting edge of the insert and a front face extending from said cutting edge, said cutting edge region having a lateral extension projecting beyond the width of the insert rearwardly thereof to form a step that lies radially innermost in use when the insert is mounted on a rotary carrier for cutting said surface, said front face having a clearance angle which is less in a portion of said front face nearer to said cutting edge than in a portion of said front face further from said cutting edge. The invention will be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side view of a combination of drill and countersink cutter attachment employing the invention, Fig. 2 to 4 illustrate the carrier body of the cutter attachment in Fig. 1 in more detail, being side, end and cross-sectional views respectively, the cutting inserts being shown only in Fig. 3, Figs. 5 to 7 illustrate the cutting insert of the cutter attachment in Fig. 1 in plan and side views and a section on the line A-A in Fig. 5, respectively, Figs. 8 to 10 illustrate alternative combinations of leading elements and cutter attachments according to the invention, and Figs. 11 and 12 illustrate, in partly sectioned side view and in transverse section on the line A-A in Fig. 11 respectively, a further combination of drill and attachment according to the invention. Fig. 1 illustrates a cutter attachment according to the invention mounted on a conventional twist drill T, the attachment comprising a tubular body 2 with a central aperture or bore 4 in which the drill bit T is a free fit. The body 2 can be slid along the drill bit to the required distance from the tip of the bit and be secured in place on the drill bit by a clamping screw 6. In diametrically opposite recesses 8 at the front of the body a pair of plate-like cutting inserts 10 are clamped by screws 12 inserted through central holes 14 (Fig. 5) in the main bodies of the inserts. Each insert has a forward cutting edge 16 lying at an oblique angle to the drill axis and the cutting edge region is given a lateral extension 18 from the main body of the insert to project into the cutting radius of the drill bit itself. The extension 18 is accommodated in a flute of the drill bit or, as shown in Fig. 3, in the relief R behind a side cutting edge of the drill bit. Like the tubular body 2, however, the main body of the insert 10 lies on or outside the cutting radius of the drill bit so that the attachment can be secured with the extension 18 at any position along the drill flutes or reliefs. The recesses in the attachment body locate the inserts with their top faces, and therefore their cutting edges, in a diametrical plane of the drill bit and attachment body. Bounded by the same diametrical plane are a pair of slots 22,24 extending the length of the carrier body, one slot 22 running through the radial thickness of the body and the other slot 24 through only part of that thickness from the outer periphery. The clamping screw 6 bridges the first slot 22 and, when tightened, draws the faces of the slot together so as to clamp the body onto the drill bit passing through its bore. The cutting insert, as can be seen more clearly in Figs. 5 to 7, has its cutting edge 16 at an angle of 45° to the side and rear edges 26,28 of the insert that are held against axial and radial faces 30,32 respectively of a seating in each recess 8 of the attachment body, the insert thus being set to cut a countersink at a corresponding angle. The inner side edge 26 lies at a slightly greater radius than the bore 4, as indicated in Fig. 3, but the lateral extension 18 from the main body of the insert at the cutting edge region projects inwards into the bore radius. The front face at the cutting edge 16 has a clearance angle of 15° when measured in a radial plane of the clamping hole 14 of the insert perpendicular to the cutting edge 16, (ie. the plane of Fig. 7). The lower region of the insert front face also has an angled relief face 36 at 45° (when measured in the same plane) in order to give the insert an adequate clearance at smaller cutting radii. For this purpose, the front face relief is greatest at the radially inner end of the face and its width tapers progressively from that end. The same form of insert and cutter attachment can be employed in the plain-piloted countersinking tool illustrated in Fig. 8, which is generally similar to the attachment of the preceding figures but has a body 2a with a single cutting insert 10. The attachment is shown mounted on a non-cutting pilot spindle 40 having a cylindrical nose 42 and a circumferential relief 44 that accommodates the lateral projection 18 of the insert extending inwardly of the spindle radius in front of the relief. If it is required to form a countersink or the like in conjunction with a reaming operation, the cutter attachment already described can be mounted on the reamer 46, as is illustrated in Fig. 9. In an analogous manner, the lateral projection 18 on the or each insert extends into the flutes or the cutting edge relief of the reamer so that the minimum cutting radius of the insert lies within the cutting radius of the reamer. Fig. 10 illustrates a modified form of cutting insert 10a with a cutting edge 16a and extension 18a at right-angles to the axis of the drill bit T on which it is mounted for a combined drilling and spot-facing operation. The forward end of the cutter attachment body 2b provides insert seatings that conform generally to the right-angled configuration of the inserts, but in other respects the body 2b can be similar to the attachment body already described in more detail above. In the example of Figs. 11 and 12 corresponding parts to those already described are indicated by the same reference numbers. The cutter comprises a countersink attachment with a body 52 having an integral shank 54 at the rear. An aperture or bore 56 extends through the body 52 and the shank 54. A drill bit T is located in the bore 56 to project forwards of the body. Within the shank 54 the bore 56 is given a screw thread 58 which engages a setting screw 60 that has a smaller diameter stem 62 extending forward from the threaded portion of the screw. The stem 62 provides a locating abutment for the rear end of the drill bit T. By driving the screw 60 a greater or lesser distance into the bore thread the location of the drill bit and hence the extent to which it projects from the front of the body is determined. The bit can be locked in the set position by a grub screw 66 threaded into the body 52. This is additional to the clamping screw 6. The same form of cutting inserts 10 are shown as the first-described example and they are mounted in a similar manner. The body 52 also has the two slots 22,24 but these run out in the region of the junction between the body and the shank 54. To allow the body portions on opposite sides of the slot 22 to be contracted together by the clamping screw 6 sufficiently to grip the bit T in the bore, a further slot 68 is formed in a transverse radial plane rearwards of the inserts. A circumferential recess 70 forms chamfers at the edges of the slot 68. It will be seen that the transverse slot 68 leaves the front portion of one half of the body attached to the remainder of the body only by the thickness of material remaining between the slot 24 and the bore 4. It will be apparent that other configurations of cutter attachment and cutting insert can be similarly provided within the scope of the claims. The inserts can be made of a variety of materials, including high-speed steel, tungsten carbide, ceramic, polycrystalline diamond and polycrystalline cubic boron nitride.

Claims: A rotary cutter for forming a countersink or spot facing or other ring-form surface of revolution concentric to a bore in a workpiece, comprising a cutter body (2 or 52) having a central longitudinal aperture (4 or 56) for receiving an elongate leading element (T) to locate the cutter radially relative to the bore in the workpiece, the body being provided with means to clamp said leading element releasably in said central aperture and a cutting insert (10) having a cutting edge region (16) at the forward end of a main body of the insert for cutting said ring-form surface, received in a recess (8) in said body characterised in that said body recess (8) has a radially outwardly facing seating face (30), that the cutting insert (10) is removably received in said recess with its main body seated against said seating face, and that said forward cutting edge region (16) projects radially inwardly in the form of a stepped extension (18) of said main body passing laterally across a front end of said seating face and into a front-to-rear extending groove in said leading element. A cutter according to claim 1, wherein a longitudinal bore extending rearwardly from said central longitudinal aperture (56) holds setting means (62) for determining the position of the leading element axially of the body. A cutter according to claim 2, wherein means (60) are provided for axially displacing said setting means in said bore to adjust the extent to which said leading element protrudes axially from said body. A rotary cutter according to any one of claims 1 to 3, wherein the body (2 or 52) includes at least one axially directed slot (22) for permitting resilient deformation of said body, and means (6) for drawing together opposite faces of said slot to clamp said leading element in said aperture. A rotary cutter according to claim 4 wherein said clamping means are arranged forwards of a coaxial shank portion (54) extending rearwardly on the body. A cutter according to claim 2 or claim 3 together with claim 4 or claim 5, wherein said clamping means are arranged forwardly of the setting means (62). A cutter according to any one of claims 4 to 6, wherein a recess (68) is formed in said body rearwardly of said tightening means, said recess being oriented transversely across said body and opening into said slot, whereby said contraction of said aperture is confined to said body forwards of said recess. A cutter according to any one of the preceding claims, wherein the or each cutting insert has a top face substantially in a plane radial to the rotary axis. A cutting insert for use in forming a countersink or spot face or other ring-form surface of revolution around a bore in a workpiece, the insert having a main body of generally plate-like form with a cutting edge region defining a forward cutting edge (16) of the insert and a front face extending from said cutting edge, characterised in that said cutting edge region has a lateral extension (18) projecting beyond the width of the insert rearwards thereof to form a step that lies radially innermost in use when the insert is mounted on a rotary cutter attachment for cutting said surface, and said front face has a clearance angle which is less in a portion of said front face nearer to said cutting edge than in a portion (36) of said front face further from said cutting edge. An insert according to claim 9 wherein said portion further from the cutting edge has a width that decreases with distance from the inner end of said front face.

Inventors: GREIG ALAN, GREIG, ALAN
Applicants: SANDVIK LTD, SANDVIK LIMITED
Application year: 1990
Main classification: B23B51
IPC codes: B23B51