US3137917A

US3137917A - Tool bits

Info

Publication number: US3137917A
Application number: US31577A
Authority: US
Inventors: Joseph F Dowd
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-05-25
Filing date: 1960-05-25
Publication date: 1964-06-23
Anticipated expiration: 1981-06-23

Description

June 23, 1964 J, ow 3,137,917

TOOL BITS Filed May 25, 1960 3 Sheets-Sheet l IIII f WW INVENTOR Joseph F Dowd BY M ATTORNEY J. F. DOWD June 23, 1964 TOOL BITS Filed May 25, 1960 5 Sheets5heet 2 I F76. ll

INVENTOR Joseph F Baum ATTORNEY June 23, 1964 J. F. DOWD 3,137,917

TOOL BITS Filed May 25, 1960 3 Sheets-Sheet 3 I f s 33 s f v IINV'ENTOR. Joseph E Don/c2 "WMw United States Patent 3,137,917 TOOL BITS Joseph F. Bowl, 323 N. Main St, Orange, Mass. Filed May 25, 196i), Ser. No. 31,577 7 Claims. (Cl. 2995) This invention relates to improvements in cutting tools, and particularly to improved cutting tool bits such, for example, as are used in lathes, shapers, planers, and boring mills.

This application is a continuation-in-part of application Serial No. 684,439, filed September 17, 1957, now abandoned, by the same applicant.

It has been known that tool bits for use in various types of cutting equipment can more efficiently and more economically produce a certain amount of work when such bits are made as readily replaceable units for mounting in supporting holders. Various types of holders have been devised and a variety of shapes of bits have been found to be useful for forming the various cuts required in working different types of metals and for making various types of cuts. These replaceable tool bits often are formed as button or throwaway insert bits, which are made with two closely spaced opposite substantially parallel plane faces with a side surface extending between these faces which may or may not be at right angles thereto.

In order to use such a readily replaceable tool bit, it is essential that it be rigidly supported and that its cutting edge project further toward the surface which is being cut than any other part of the tool, else the other parts of the tool would rub against the workpiece and be damaged or would damage the workpiece itself during the cutting operation. It has, therefore, been found necessary either to make the sides of the bit extend at an acute angle to the parallel face with which it forms a cutting edge, known as a positive rake bit, or to tilt the bit at an angle to the work so that the side surface of the bit at right angles to the plane parallel faces extends away from the surface of the work which is being cut. With a bit of this latter type, in which the sides are perpendicular to the two parallel faces, it is, therefore, necessary that the parallel faces be tilted and extend at a corresponding angle to a plane through the cutting edge and normal to the workpiece surface at the cut. Such an arrangement of the tool bit is known in the trade as having a negative rake. This negative rake is measured in terms of degrees which the parallel plane faces of the bit make with reference to the plane through the cutting edge of the bit normal to the workpiece surface at the cut. This negative rake also is the angle which the side surface of the bit makes with a plane through the cutting edge of the bit parallel to the workpiece surface at the cut.

Tool bits with a negative rake may be used to make both right-hand and left-hand cuts, and can be used with tools capable of cutting a flat surface, as well as tools capable of cutting fillets or other types of arcuate surfaces. Throw-away bits having a negative rake provide a very sturdy construction in that there is a solid metal supporting backing extending from the cutting edge of the tool through the tool to the tool holder surface. These bits do, however, have the disadvantage of a relatively blunt cutting edge, and, therefore, cannot generally be operated as efficiently at the same high speeds as tools having sharper cutting edges; that is, cutting edges which are formed between surfaces extending at an acute angle to each other. Negative rake bits also are not generally practical for cutting or turning the softer metals, suchas aluminum, copper, brass, and the like, at efficient speeds and depth of cuts.

3,137,917. Patented June 23, 1964 Cutting tool bits having cutting edges formed by surfaces extending at right angles to each other and adapted to be arranged in a holder at a negative rake have another big advantage over conventional positive rake bits in that a cutting edge may be formed on each edge of the opposite parallel plane surfaces of the bit. Thus, if a bit he triangular in shape, it may have six cutting. edges; if it be quadrangular in shape, it will have eight cutting edges; and for any other number of sides to a bit the cutting edges will be equal to twice the number of sides, to the point where a disc shape bit will have an almost infinite number of cutting edges.

In the cutting art, it has been found desirable to make certain cuts in some materials with a sharper edge than can be provided by bits having the cutting edge formed by two surfaces extending at right angles to each other and also to make the cuts with a tool having a leading or front surface which enters the material at an acute angle. Cutting tool bits having these characteristics also have been formed similar to the button or throwaway insert bits used as negative rake tools and have required the provision of tool holders having supporting surfaces which will provide for mounting the closely spaced parallel plane faces of the bits so that these faces form an acute angle with reference to a plane through the cutting edge normal to the surface of the material at the cut. Holders and bits of this type are known in the trade as having a positive rake. This positive rake is defined as the angle formed by the plane of the parallel face of the bit on one side of the cutting edge with a plane along the cutting edge normal to the surface of the material at the cut. This positive rake angle is also the angle of the side surface of the bit with the surface of the material at the cut.

Since bits having a positive rake have an acute angle between the side of the bit and one of the two parallel faces of the bit, the angle which the side of the bit makes with the other of the two parallel faces of the bit necessarily is an obtuse angle. This obtuse angle between the second parallel face and the side of the bit makes an extremely blunt edge along the intersection of the side and the second parallel face of the bit, and, therefore, is not usable as a cutting edge. A conventional positive rake bit has, therefore, a cutting edge or edges only along the intersection of the side of the bit with the parallel face of the bit forming an acute angle therewith. Consequently, a positive rake bit with three sides conventionally has only three cutting edges, a positive rake bit with four sides has only four cutting edges, and a positive rake bit always has only the same number of cutting edges as it has sides, and, therefore, has only half the number of cutting edges which a similar sided negative rake bit possesses. Thus, although a positive rake bit provides a sharper cutting edge and, therefore, enables its use at a higher cutting speed than a negative rake bit and makes possible the removal of more stock in a given time; that is, it may take a deeper cut, it is subject to the disadvantage of having only half the number of cutting edges of a negative rake bit with the same number of sides. Furthermore, both positive and negative rake bits are subjected to the disadvantage of requiring a different tool holder for each different angle of positive or negative rake which it is desired to use. Conventional positive rake inserts have a standardized 5-degree rake and noprovision is conventionally made to provide any other effective positive rake, which may be desirable for certain material or cuts. In present day practice, it also has been found desirable to provide chip curlers or breakers for association with the cutting tool bits, so as to break up the material which is cut away and to minimize the formation of undesirably long curls of cut-away material.

The present invention is directed to an improved cutting tool bit which possesses the advantages of the sharper edge and the acute angle of the leading surface as it enters the material, as is obtainable with a positive rake bit, and the advantage of having twice as many cutting edges as the number of sides of the bit, as in negative rake bits. In addition to this, it possesses the advantage of providing a chip curler or breaker as part of the bit itself and, therefore, does away with the need for an additional chip curler or breaker as is required with present conventional throwaway type tool bit combinations. These desirable features of an improved bit made in accordance with this invention are obtained by making the bit with the desired number of sides extending perpendicular to the two parallel plane faces thereof and providing a relatively narrow shallow groove in each of the parallel faces along each cutting edge, presenting an outwardly tapered surface terminating in a sharp cutting edge at a predetermined acute angle at the intersection of the outer groove surface with the side surface and face of the bit. This forms a sharp cutting edged bit which may be mounted in a negative rake holder to provide the desired positive rake.

Another inherent advantage of this formation of a tool bit is that the positive rake of each bit can be very accurately predetermined by simply choosing a bit having a predetermined acute angle at the cutting edge which will give the desired positive rake in the particular negative rake holder in which it is to be mounted. This results in a very substantial economy in machine tools required in a shop, as a single negative rake holder adapted to receive a bit of a specified shape can be used in combination with bits embodying the present invention to make cuts at any desired positive rake of the cutting tool. Since a negative rake holder is utilized in combination with the present invention, there will be no interference between the holder and the workpiece irrespective of the positive rake provided by the cutting bit. In addition, right-hand or left-hand cutting bits may be formed by merely extending the groove respectively from the left or right-hand side of the bit adjacent to the side forming the cutting edge in question. Since the sides of bits made in accordance with this invention are perpendicular to the two parallel faces of the bits, the grooves forming the positive rake are cut in both of the parallel plane faces of a bit, so that the bits provide twice the number of cutting edges as the number of sides of each bit, in the same manner as in negative rake bits. Furthermore, the grooves are of substantially uniform width throughout their effective length and the concave inner surface of each groove acts as a chip curler and breaker, with the inner side thereof serving to direct the chip in the desired direction. This makes the use of a separation chip breaker unnecessary. In addition, where a workpiece is of a metal requiring a special chip breaker of greater width or spacing from the cutting edge or of sharper curvature, these can readily be provided by simply forming the groove of the required width or the inner surface of the groove on the desired radius.

Generally, bits made in accordance with this invention may conveniently be formed of high speed tool steel, but other suitable materials such as carbides, cast alloys, and ceramics may also be used. Certain of these materials may be very brittle and may tend to chip if the positive rake is high or the cutting speed and the metal are such that the bit tends to heat up. Chipping of the cutting edge can usually be minimized by leaving a very slight land along the cutting edges.

An object of this invention is to provide an improved cutting tool bit.

Another object of this invention is to provide an improved positive rake cutting tool bit having twice as many cutting edges as the number of sides of the bit.

A further object of this invention is to provide an improved cutting tool bit of the throwaway type having an acute angle between the surfaces forming each cutting edge and having twice the number of cutting edges as sides of the bit.

Still another object of this invention is to provide an improved throwaway type tool bit having an acute angle between the surfaces forming each cutting edge and a chip curling and breaking surface formed in the bit and associated with each cutting edge.

Further objects and advantages of this invention will become apparent from the follower description, referring to the accompanying drawings, and the features of the novelty which characterizes this invention will be pointed out with particularity in the claims appended to and forming a part of this specification.

In the drawings:

FIG. 1 is a perspective view of a conventional cutting tool holder provided with a bit made in accordance with this invention;

FIG. 2 is a sectional view of a bit and tool holder, taken along the line 22 of FIG. 1, and illustrating this section in cutting relation to a workpiece;

FIG. 3 is an enlarged sectional view taken at right angles to the cutting edge of a segment of a bit incorporating this invention;

FIG. 4 is a perspective view illustrating a triangular bit incorporating an embodiment of this invention adapted to be used as a right-hand cutting tool;

FIG. 5 is a perspective view of a triangular bit, similar to that shown in FIG. 4, but provided with grooves extending from the edges opposite to those of FIG. 4, whereby it is adapted to be used as a left-hand cutting tool;

FIG. 6 is a perspective view of a square right-hand type bit incorporating an embodiment of this invention;

FIG. 7 is a perspective view of a diamond shaped righthand bit embodying this invention;

FIG. 8 is a perspective view of a rectangular lefthand bit embodying this invention;

FIG. 9 is a perspective view of a hexagonal righthand bit embodying this invention;

FIG. 10 is a perspective view of a circular or cylindrical bit embodying this invention;

FIG. 11 is a sectional view taken along line 1111 of FIG. 10;

FIG. 12 is a perspective view of a conventional type cutting tool holder provided with a circular bit embodying this invention, such as that shown in FIG. 10;

FIG. 13 is a perspective view of another type of conventional cutting tool holder provided with a left-hand quadrangular bit made in accordance with this invention;

FIG. 14 is a perspective view illustrating a triangular bit similar to the bit in FIG. 5 and incorporating a modified groove made in accordance with another embodiment of the present invention;

FIG. 15 is a perspective view of a square bit similar to that shown in FIG. 6 and provided with a modified form of groove made in accordance with this invention;

FIG. 16 is a cylindrical or disc type of bit similar to the bit shown in FIG. 10 and provided with a different form of groove made in accordance with the present invention;

FIG. 17 is an enlarged sectional view taken at right angles to the cutting edge of a segment of a bit such as that shown in FIGS. 14, 15, and 16;

FIG. 18 is a sectional view taken along line 1818 of FIG. 15;

FIG. 19 is a perspective view of a triangular bit similar to that of FIGS. 5 and 14 and provided with grooves made in accordance with another embodiment of the present invention;

FIG. 20 is a perspective view of a square bit similar to those shown in FIGS. 6 and 15 and provided with grooves made in accordance with a further embodiment of this invention;

FIG. 21 is an enlarged sectional view taken along line 2121 of FIG. 20; and

FIG. 22 is an enlarged sectional view taken at right angles to the cutting edge of a segment of a bit provided with grooves similar to those shown in FIGS. 19, 20, and 21.

Referring to the drawings, a cutting bit 1, embodying this invention, is shown in FIGS. 1 and 2 secured in position on a conventional cutting tool holder of the righthand type which is adapted to be used with a conventional lathe for turning a workpiece. An improved bit, of this type, is formed with two substantially parallel plane faces 2 and 3 which are spaced relatively closely together so as to form a relatively thin button type bit, with sides 4 extending at right angles to the two plane faces of the bit. In order to provide a relatively sharp cutting edge to the bit, a shallow groove 5 is formed in each of the plane faces of the bit along the intersection of the side surface of the bit with its two plane faces. The desired design of the cutting angle or degree of sharpness of the cutting edge 0 may be obtained by forming the surface of the groove 5 adjacent to the side 4 of the bit at a suitable angle. This is more clearly illustrated in FIG. 3, which is an enlarged view of a section of such a bit.

Bits of this type are adapted to be mounted in negative rake tool holders, as shown in FIGS. 1, 2, 12, and 13, which provide for supporting the parallel plane faces 2 and 3 of the bit tilted at an angle n to a plane through the cutting edge 0 of the bit normal to the surface of a workpiece 6 at the cut, indicated by the line 0h, in FIGS. 2 and 3. As is more readily seen from FIG. 3, the side surface 4 of such a bit also forms the same angle n with a plane (indicated by the line 0--c) through the cutting edge 0 parallel to the surface of the workpiece 6 at the cut. This angle n is normally referred to as the negative rake of the tool holder.

A conventional negative rake tool holder suitable for use with throwaway bits of this improved type is shown in FIGS. 1 and 2 and comprises a shank 7 and a cutting tool holder head 8, which is adapted to receive the but ton or throwaway insert bit 1 in a suitable aperture 9. For purposes of illustration, a quadrangular bit, of the type shown in FIGS. 6, 7, and 8, is shown mounted in the aperture 9 on a supporting shim or anvil 10, with the outer side 10' of the anvil and the outer side 4 of the bit arranged substantially in alignment with the angularly extending side face 8 of the head of the tool holder. As is more clearly seen in FIG. 2, the face 8' and the

sides

4 and 10 of the bit and anvil form an angle with the adjacent surface 6' of the cut forming a shoulder on a workpiece 6, so that there is a working clearance between the surface 6' and the adjacent surfaces of the tool holder, shim, and bit. This is conventional structure in negative rake tool holders and assures against interference of the cutting tool surfaces with the surfaces of a workpiece.

The ease of cutting material depends upon two structural features of the cutting tool, the sharpness of the cutting edge and the angle made by the leading or front surface of the bit adjacent to the cutting edge with a plane normal to the surface of the workpiece at the cut. The sharpness of the cutting edge varies directly with the acuteness of the angle between the side surface 4 of a bit and the surface of the groove 5 along the cutting edge 0, indicated by the line 0t. This latter surface may be a plane forming an angle at with the adjacent leading. plane face 2 of the bit or may be cured as part of an are extending partly from the cutting edge 0 to the chip breaker inner surface or as a continuous arc from the edge 0 to the face at 5'. When the face of the groove 5 is arcuate, the acute angle which determines the positive rake is measured by a tangent to the curved surface of the groove at the edge 0, as is also indicated by the line 0t in FIG. 3. The angle x is equal to the sum of the negative rake angle 11 and an angle p. This latter angle is the angle which is formed by the previously mentioned plane indicated at 0t and a plane through the cutting edge normal to the surface of the workpiece at the cut, indicated by the line 0h. The angle h0 --t is designated as p and is the positive rake of the cutting tool.

Various types of metals and various types of cuts in particular metals require different speeds at which a out can be made to a predetermined depth in order to obtain a desired finish without unduly wearing or damaging the cutting tool. The efiicient speed of operation and the depth of cut to obtain a desired finish also depend upon the sharpness of the cutting edge and the positive rake of a tool. Withbits embodying this invention, a single negative rake tool holder can be used to provide any desired positive rake by merely inserting a bit having the proper angle x to provide the desired positive rake angle p, which is the difierence between the angle x and the negative rake of the tool holder.

A bit incorporating the present invention may be supported in any suitable conventional negative rake tool holder which is adapted to receive the particular size bit to make the desired cut. In a tool holder as shown in FIG. 1, the bit 1, supported on the anvil 10, may require the use of a second shim or clamping plate 11 arranged above the bit 1 and secured in assembled relationship by a suitable clamping or locking screw 12. The shim 11 will normally take the place of the conventional chip curler or breaker and is preferably arranged with the outer edge thereof adjacent to the inner edge 5' of the groove 5 where this groove intersects the plane face 2 of the bit. The concave inner surface of the groove 5 serves to direct a chip 13, which is cut from a workpiece, so that it tends to curl and break into relatively small pieces and minimizes the formation of undesirably long curls of material. This provides the bit with a chip curling and breaking surface inwardly spaced from and closely adjacent to the cutting edge and makes it unnecessary to provide a separate chip curler or breaker, although the adjacent edge of the shim 11 may serve the auxiliary purpose of aiding in curling and breaking chips cut away from the workpiece.

Bits of this type preferably are formed with the shallow grooves 5 extending from one side of the bit adjacent to the cutting edge 0 towards the other adjacent side of the bit at the other end of the cutting edge with the groove 5 stopping short of this other side, so that it does not intersect the groove formed along the cutting edge of this other side. In addition, this type of throwaway bit is adapted to be formed with the grooves 5 in both of the parallel plane faces of the bit so as to provide twice the number of cutting edges as the number of sides to the bit;

As is more clearly shown in. FIGS. 4 and 5, these bits may be formed as right-hand and left-hand. cutting tools for use respectively in right-hand and left-hand tool holders by extending the grooves 5 respectively from the left and right-hand sides of the bit. The. configuration of these bits can also be varied in order to provide the desired types of cuts and may take a variety of forms. FIGS. 4-10 show triangular, quadrangular, hexagonal, and circular bits as illustrative of some of the various shapes in which these improved bits can. be made. Some of these bits are shown as right-handed and some as lefthanded.

In FIG. 13, a conventidonal left-handed tool holder, of a different type from that in FIG. 1,. is shown having a shank 14 and a tool holder head. 15 with a bit anvilreceiving seat 16. In this construction, an anvil. shim 17 and a. clamping shim 18 are arranged respectively on the under and'upper sides of a left-handed bit which is secured in position by a clamping plate 19 and a suitable clamping screw 20.

In some instances a fillet or arcuate cut may be desired,

and a round or disc shaped bit 21, such as that shown in FIGS. 10, 11, and 12, may be mounted on any conventional negative rake tool-holder adapted to receive such a bit. A circular or disc bit of this type is made with a pair of closely spaced parallel plane faces 22 and 22, perpendicular to the cylindrical side 23, similar to other throwaway bits embodying this invention, and is formed with a relatively shallow groove 24 in each of the two faces along the edges adjacent to the cylindrical side of the bit. The tapered outer edge surface of the groove 24 intersects the side of the bit and forms an acute angle therewith, providing a relatively sharp cutting edge 25 around the circumference of both of the plane faces 22 and 22'. Such a circular bit provides an almost infinite number of cutting edges along both of its faces and may be used in either a right-hand or a left-hand type negative rake tool holder. In FIG. 12, such a bit 21 is shown supported on an anvil 26 on a seat 27 on the head 28 of a right-hand negative rake tool holder 29. In this construction, the bit 21 is secured in position by a suitable clamping bar 30, which is fastened to the tool holder head 28 by a suitable locking or clamping screw 31.

In FIGS. 14, 15, and 16, throwaway bits embodying this invention are illustrated in which the grooves which provide the positive rake to the cutting edges of the bits comprise plane tapered outer surfaces. The plane of these surfaces extends in each instance at a predetermined acute angle to the face of the bit inwardly sufliciently far to allow the material cut from the workpiece to be led away, and the grove terminates in an outwardly curved surface which assists in directing and curling material cut from a workpiece upwardly out of the groove and curling it back toward the workpiece. The sectional views shown in FIGS. 17 and 18 illustrate more fully the contours of the grooves in these bits.

Each groove is formed relatively narrow and shallow and of substantially uniform width, parallel to an edge of the bit. As has been explained with reference to the embodiments shown in FIGS. 2, 3, 12, and 13, these bits are adapted to be mounted and secured in position in pockets of any suitable negative rake tool holder. The negative rake of any given tool holder is designed into the bit supporting structure and remains constant. This negative rake of a tool holder tilts a bit which is mounted therein, so that its faces and sides extend ata predetermined angle with reference respectively to a plane normal to the surface of the workpiece which is being cut and to this workpiece surface. As shown in FIG. 17, the surface of the workpiece which is being cut is represented by the line c' and a plane normal to this workpiece surface is represented by the line 0lz. The angle between the workpiece surface o--c and the side 32 of the bit is indicated as n and is the negative rake angle of the negative rake tool holder. This same angle n is formed between the upper face 33 of the bit and the plane normal to the work surface 0'c', represented in FIG. 17 by the line 0'-h'. Thus, the angle formed between 0'h and the face 33 is the same angle 11' which is the negative rake of the holder in which the bit is mounted.

It has been found that for certain uses and for certain materials of which the insert bit may be formed it is desirable that the tapered surface s of each shallow groove along the cutting edges of a bit preferably should be a plane surface, as is more clearly shown by 0' in FIG. 17. This assures a maximum of force and heat transmitting material to back up the cutting edge of the bit. Such a construction not only provides a stronger cutting edge to the bit than is provided by a bit having an arcuate tapered surface along the cutting edge, but also serves to remove the heat more efiectively from the cutting edge, thereby to minimize burning or otherwise damaging the cutting edge due to excessive heating thereof.

The inner surface of each shallow groove preferably is formed as a curved tapered surface which extends from the outwardly tapered surface s to the face 33 of the bit.

This curved surface is represented in FIG. 17 by the line fa. The radius and the center of curvature of this inner surface preferably should be such that a tangent to the curved surface at the point a where it intersects the face 33 is an obtuse angle. Furthermore, this obtuse angle should be great enough so that material cut from the workpiece, in passing along the groove, will not become jammed against the chip curling surface fa but will be directed upwardly out of the groove and curled back towards the workpiece. In certain instances it may be found desirable to utilize grooves having a chip curling and breaking surface which has a very large obtuse angle at the point where the chip breaking surface intersects the upper bit face 33. In such instances the groove may be made slightly wider than usual, and the radius of curvature of the chip curling and breaking surface can be longer than for the usual groove. Such a surface is indicated by the dotted curve fb in FIG. 17.

This embodiment of the present invention can be utilized with any configuration of throwaway insert bits as is shown by the triangular bit in FIG. 14, the square bit in FIG. 15, and the disc or cylindrical bit shown in FIG. 16. Any other configuration of bit which might be desired for special cuts can equally well be made with the desired positive rake along a groove having a plane surface s extending to the cutting edge of the bit. The positive rake of such bits is determined in the same manner as has been explained with reference to FIG. 3 and, in FIG. 17, is the difference between the angle x, subtended between the upper face 33 of the bit and the tapered surface s of the groove, and the negative rake n of the tool holder in which the bit is mounted, and equals the angle p. Any desired positive rake for a bit can, therefore, readily be obtained by simply inserting a throwaway bit in a given negative tool holder wherein the angle x between the plane groove surface s and the face 33 of the bit minus the negative rake n of the tool holder equals the desired positive rake. Thus, the most effective cutting edge for any given rate of operation and any given workpiece material can be obtained simply by utilizing a throwaway bit having the proper positive rake.

FIGS. 19, 20, 21, and 22 illustrate a further modification of the present invention, wherein throwaway insert tool bits are formed as modified conventional negative rake bits having two closely spaced opposite substantially parallel plane faces 35 with sides 36 extending between the faces substantially perpendicular thereto presenting cutting edges at the intersection of both parallel faces with the sides of the bit. As in the other embodiments of this invention, a shallow relatively narrow groove is formed along each cutting edge which presents an outwardly tapered surface at a predetermined acute angle to the respective face and side of the bit. These grooves, as in the other embodiments, are of substantially uniform width throughout the length thereof and preferably do not intersect; that is, the groove along one cutting edge terminates short of the adjacent groove which starts in the side along which the first groove extends. This is clearly shown in FIGS. 19 and 20.

For certain applications it is desirable to use bits formed of very hard or brittle material, such as tungsten carbide or ceramics. Bits made of these materials may tend to chip or break along the cutting edges if the rate or depth of cut is high, such that the advantages of a sharp positive rake cutting edge may be lost because the depth of cut must be less than could be obtained by the use of a negative rake bit or the rate of cut must be reduced to prevent overheating and chipping or breaking of the cutting edge. It has been found that these disadvantages generally may be overcome by providing a more substantial backing to the cutting edge.

The embodiments of the invention illustrated in FIGS. 19-22 disclose positive rake bits made in accordance with the present invention wherein the material along the cutting edge is substantially greater than that in bits formed in accordance with the embodiments illustrated in FIGS. 1-18. FIG. 22 is an enlarged sectional View through a segment of a bit showing details of a cutting edge formed in accordance with the modifications of the present invention illustrated in FIGS. 19-21.

In accordance with this embodiment, the throwaway bits are formed with two parallel closely spaced faces 35, as in the other embodiments, with sides 36 extending substantially perpendicular .to the two faces. The cutting edges are formed along the intersection of the two faces with the perpendicular sides. A shallow relatively narrow groove 34 is formed along each edge and presents an outwardly tapered surface at a predetermined acute angle to the respective face 35 in which the groove extends. This tapered surface of the groove 34 may be arcuate, FIG. 21, or may be formed along the tangent to the arc of the groove at the point of intersection of the groove with the face 35 or it may be formed as a plane surface extending at the predetermined desired acute angle, FIGS. 19 and 22, as in the embodiments illustrated in FIGS. 14-18.

According to this embodiment, the tapered outwardly extending surface intersects the face 35, in which the groove is formed, slightly inwardly of the cutting edge. This is more clearly shown in FIG. 22, which shows the tapered surface intersecting the face 35 at a point q spaced a distance I from the cutting edge This leaves a very narrow land which extends in the plane of the face 35 along the cutting edge. In accordance with the present invention, this land must not be of such a width as to make the cutting edge so blunt that the bit is essentially a negative rake bit rather than a positive rake bit. The preferred width for such a land is between 0.003 inch and 0.005 inch. Such a land is not sowide as to affect the positive rake characteristics of a bit and yet is sufficiently large to provide a substantial backing to the cuting edge for more efficiently removing heat from the cutting edge and reducing the unit area stress, thereby minimizing chipping and breaking of the cutting edges of a bit. Further considerations which generally affect the determination whether a land should or should not be used include the nature of the material of the workpiece and the rate of cut or feed of the machine in order efficiently to machine the material without undue wear of the tool to obtain the desired finish of the cut.

As a very general rule, relatively soft materials, such as aluminum, magnesium, copper, rubber, and the like, are preferably machined with bits having sharp edges without lands, even if the bits be made of realtively brittle materials, such as carbides or ceramics. Harder materials, such as stainless steel, may best be machined with bits having a land along the cutting edge, especially if the bit is formed of a brittle material. Such lands must be only wide enough to provide the desired additional strength to the cutting edge without adversely affecting the effect of the positive rake of the edge. Also, the land must not be so wide that the chip simply rides over the groove forming the positive rake without even contacting the chip curling and breaking part of the groove. Where a land is desirable, it has been found that about one-third of the feed generally is basically satisfactory; e.g., for a machine having a feed of 0.012 inch per revolution, a land of 0.004 inch would be basically acceptable, care always being exercised not to lose the positive rake characteristics, as previously explained. For high feed machines, the ratio of land to feed might be reduced somewhat in order to retain the positive rake of the cutting edge. It has been found that a land having a width l of not more than 0.010 inch will still give a bit the characteristics of a positive rake when formed with a groove as shown in FIG. 22.

The grooves 34 are formed of substantially uniform width and, as shown in FIG. 22, may be formed with an outwardly tapered surface q-f along a plane which extends at an angle x" to the face 35, so as to provide a positive rake 2", equal to the difference between the angle x" and the negative rake n" of the tool holder in which the bit is mounted. As in the constructions shown in FIGS. 1418, the inner surfaces of the grooves 34 are tapered preferably in a curve f-d which intersects the face 35 at an obtuse angle, for the reasons previously explained with reference to FIG. 17. The width of the grooves 35 and the curvature of the inner surface f-d which forms the chip curling and breaking portion of the groove also can be varied as has been explained with reference to FIG. 17.

Furthermore, if desired, the outwardly extending tapered surface of the groove may be formed along the tangent of the curvature of the groove where it intersects the face 35 at the point q, as shown by the dotted line qf'-d. The positive rake p of a bit provided with this latter type of groove would be equal to the angle x minus the negative rake n" of the tool holder in which the bit is mounted.

The same effective positive rake p can be obtained by forming the outwardly extending surface of the groove as a plane surface, represented in FIG. 22 by the line q-f", and providing such a groove with an outwardly curved chip curling and breaking surface f"-e. This latter type groove provides a relatively sharper edge to the bit with the same positive rake, but also has the disadvantage that there is less backing-up material to the cutting edge and, therefore, there is less material available for transmitting and dissipating heat generated at the cutting edge and for transmitting the forces developed along the cutting edge. This type of groove, however, may be found more efficient for cutting certain materials, such as soft metals, than one formed as a tangent to a curved or arcuate groove.

In all throwaway bits embodying this invention the side surface of the bit is perpendicular to the two parallel plane faces of the bit, so that the bit is an invertible tool, and the provision of a groove adjacent to the intersection of each plane face of the bit with the side of the bit provides a bit having twice the number of cutting edges as the sides of the bit. In addition, such bits may be formed to have any desired configuration to provide various types of cuts and can be used in connection with any conventional negative rake tool holder appropriate to the shape of the bit. This results in a definite saving to any machine shop, as the desired positive rake for any particular cut may be obtained by simply inserting a bit having the proper angularity in the groove surface forming the cutting edge to give the desired positive rake for the cut in question. According to this invention, bits can very readily be made having top positive rake of the desired angularity, as from 5 degrees to 30 degrees.

While particular embodiments of this invention have been illustrtaed and described, modifications thereof will occur to those skilled in the art. It is to be understood, therefore, that this invention is not to be limited to the particular arrangements disclosed and that the appended claims are intended to cover all modifications thereof within the spirit and scope of this invention.

What is claimed is:

1. A throwaway insert tool bit for use with a holder, said bit being formed with two closely spaced opposite substantially parallel plane faces and a side surface at right angles to the planes of said faces presenting a cutting edge on each face, a relatively narrow groove of uniform width in each face along each cutting edge parallel thereto having an outwardly tapered surface terminating in an effective positive rake sharp cutting edge at a predetermined substantially constant acute angle along substantially the length of the cutting edge at the intersection of the plane of the respective one of said faces with said side surface and in an inwardly curved surface extending to said one of said faces adapted to form a chip curling and breaking surface inwardly spaced from and closely adjacent to said respective cutting edge, said two opposite parallel faces each having a relatively large plane central portion providing a tool holder support and clamp engaging surface inside said relatively narrow grooves.

2. A throwaway insert tool bit for use with a holder, said bit being formed with two closely spaced opposite substantially parallel plane faces and a side surface at right angles to the planes of said faces, an arcuate relatively narrow groove of uniform width in each face along each edge adjacent to said side surface parallel thereto having an outwardly extending surface terminating in an effective positive rake cutting edge on a tangent to said arcuate groove at a predetermined substantially constant acute angle along substantially the length of the cutting edge at the intersection of the plane of the respective one of said faces with said side surface and in an inwardly curved surface extending to said one of said faces adapted to form a chip curling and breaking surface closely adjacent to said respective cutting edge, said two opposite parallel faces each having a relatively large plane central portion providing a tool holder support and clamp engaging surface inside said relatively narrow grooves.

3. A replaceable button tool bit as set forth in claim 2 wherein said bit is formed with a land along each cutting edge in the plane of each face of not more than 0.010 inch.

4. A throwaway insert tool bit for use with a holder, said bit being formed with two opposite parallel plane faces and a plurality of sides extending between said faces at right angles thereto presenting polygonal faces and multiple straight cutting edges on each face equal to the number of said sides, said faces forming force transmitting tool holding surfaces extending into close proximity to said cutting edges, a relatively narrow shallow groove in each face along each straight cutting edge parallel thereto and successively starting from the same respective end and extending in the same respective direction along each edge and stopping short of the adjacent groove which starts in the side along which the respective groove extends, each of said grooves having an outwardly tapered plane surface terminating in a sharp cutting edge at a predetermined substantially constant acute angle along substantially the length of the cutting edge at the intersection of the plane of the respective one of said faces with one of said sides and an inwardly curved surface extending to said one of said faces and forming a chip curling and breaking surface, said two opposite parallel faces each having a relatively large plane central portion providing a tool holder support and clamp engaging surface inside said relatively narrow grooves.

5. A throwaway insert tool bit for use with a holder, said bit being formed with two closely spaced opposite substantially parallel plane faces and a plurality of sides extending between said faces perpendicular thereto presenting polygonal faces and multiple straight cutting edges on each face equal to the number of said sides, a relatively narrow shallow groove in each face along each straight cutting edge having an outwardly tapered plane surface terminating at a predetermined substantially constant acute angle along substantially the length of the cutting edge to the respective one of said faces and intersecting said respective face slightly inwardly of the cutting edge forming a land of not more than 0.010 inch along each cutting edge in the plane of said face and having an inwardly curved and tapered surface extending to said one of said faces adapted to form a chip curling and breaking surface spaced inwardly from said cutting edge, said two opposite parallel faces each having a relatively large plane central portion providing a tool holder support and clamp engaging surface inside said relatively narrow grooves.

6. A tool bit as set forth in claim 5 wherein said land is betweeg 0.003 inch and 0.005 inch wide.

7. A throwaway insert tool bit for use with a holder, said throwaway insert bit being formed with two opposite substantially parallel plane faces and a cylindrical side surface substantially at right angles to the planes of said faces presenting a continuous cutting edge on each face, a relatively narrow groove of uniform width in each face along each cutting edge parallel thereto having an outwardly tapered surface terminating in an effective positive rake cutting edge at a predetermined substantially constant acute angle along substantially the length of the cutting edge at the intersection of the plane of the respective one of said faces with said side surface and an inwardly sharply curved surface extending to said one of said faces adapted to form a chip curling and breaking surface closely adjacent to said respective cutting edge, said two opposite parallel faces each having a relatively large plane central portion providing a tool holder support and clamp engaging surface inside said relatively narrow groove.

References Cited in the file of this patent UNITED STATES PATENTS 1,756,516 Klopstock Apr. 29, 1930 2,233,724 Bannister Mar. 4, 1941 2,641,048 Vreeland June 9, 1953 2,697,866 Greenleaf Dec. 28, 1954 2,854,735 Dukes Oct. 7, 1958 2,870,523 Richard Jan. 27, 1959 2,897,580 Huber Aug. 4, 1959 3,060,554 Kirchner Oct. 30, 1962 FOREIGN PATENTS 315,005 Germany Oct. 20, 1919 470,207 Germany Jan. 7, 1929 894,494 Germany Oct. 26, 1953 896,896 Germany Nov. 16, 1953 1,099,534 France Mar. 23, 1955 1,185,161 France Feb. 9, 1959 OTHER REFERENCES Article-Negative Strength Land from Steel Magazine, December 11, 1945, p. 134.

Article-Soviets Claim New Cutting-Tool Geometry Eliminates Vibration, from American Machinist Maga- Zine, March 12, 1956, pp. 190-194.

ArticlefiSintax Ceramic Cutting Tool Tips, from Sept. 14, 1956 issue of Machinery, vol. 89, page 632.

Disclaimer 3,137,917.J0seph F. Dowd, Orange, Mass. TOOL BITS. Patent dated June 23, 1964. Disclaimer filed Nov. 17, 1970, by the inventor.

Hereby enters this disclaimer to

claims

1, 2, 4, and 7 of said patent.

[Oyficial Gazette Mamh 2, 1971.]