Abstract:
An end mill type rotary cutting tool and associated cutting inserts that collectively compensate for radial pocket runout, thereby eliminating overlap marks in a machined work piece. The tool has pockets arrayed in helical flutes such that after one insert has abraded the work piece, a subsequent flute makes an overlapping pass. The inserts are so mounted in the cutting tool and have curved corners configured such that no degree of pocket runout due to manufacturing tolerances will cause any portion of the cutting edge of any insert to form an incuse cut in the work piece which penetrates the machined surface by more than the manufacturing tolerance. Thus overlap of inserts eliminate outward projections in the machined work piece and dimensions and configuration of the inserts and their pockets eliminate inward gouges, thereby eliminating visible overlap marks in the work piece.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to machine tools for shaping a work piece, and more particularly to a system including a rotary cutter and associated cooperating cutting inserts. 
   2. Description of the Related Art 
   When machining a work piece utilizing rotary cutters provided with replaceable inserts, it is frequently desirable to impart a final finish in which marks such as discernible ridges due to machining have been eliminated. Such marks may not be objectionable in rough or coarse machining, but are objectionable in fine finishing work. These marks are produced incidentally in machining operations, and result from the relation of cutting edges of the inserts to the work piece. In most cutters such as end mills, tool design emphasizes efficiency and productivity, with little regard for fineness of finish of a machined work piece. 
   Nonetheless, the machine tool industry has appreciated that steps such as eliminating machining steps or operations provides economic benefits. One such area which may be improved is that of eliminating overlap marks. Illustratively, U.S. Pat. No. 5,944,456, issued to Shirley et al. on Aug. 31, 1999, and of common ownership with the present invention, shows an end mill type cutter having staggered, overlapping inserts having radiused corners. Peak shaving of the work piece results in improved finishing characteristics as regards undesirably high peaks or ridges, which would otherwise detract from the finished appearance. 
   However, it is possible for end mill cutters to suffer from leaving lap lines due to carving out valleys or inwardly projecting marks in the work piece, as well as carving out peaks. This may arise due to variations in manufacturing tolerances, which variations may for example cause inserts to display radial runout, or project to unintended degrees from the hypothetical cylindrical envelope or outer surface of a rotary cutter. Radial runout is defined as the variation in the radius between a cylinder or circle and a perfectly uniform or straight cylinder configuration or circle. Runout is apt to gouge out unintended valleys which appear as undesirable conspicuous lap lines. Overlapped, staggered inserts in and of themselves cannot overcome such detractions to otherwise superlative finishes, as staggering can reduce peaks but cannot compensate for overly deep valleys. This situation is depicted in  FIG. 4 , wherein a representative work piece  2  has ideal upper and lower facets  4 , which would result from perfect alignment of cutting inserts (not shown) having flat cutting edges, and one misaligned facet  6 , which could result from an insert (not shown) which is misaligned due to radial runout of its associated pocket. In the situation illustrated, the degree or magnitude of radial runout does not exceed the manufacturing tolerances. 
   It will clearly be seen that an overlap mark  8  exists where the insert which cut facet  6  passed over work piece  2 . This overlap mark  8  is highly conspicuous, and mars what would otherwise be an acceptable finish. There remains a need in the art for a rotary cutter which can control both excessive peaks and also excessive valleys formed in machined surfaces. 
   SUMMARY OF THE INVENTION 
   Briefly, according to this invention, there is provided an advance over known designs by introducing, in a rotary cutting tool bearing inserts, compensation for radial runout resulting in disturbances to the plane of contact established by the rotary cutting tool with a work piece, where radial runout arises from manufacturing tolerances. This is accomplished in the present invention by establishing certain interrelationships between the cutting tool and its associated inserts, and imparting certain configurational characteristics to the inserts. 
   The inserts, which could otherwise be configured as parallelpipeds, are formed with slightly rounded or “radiused” corners. The degree of rounding cooperates with orientation of the insert within an associated pocket formed in the cutting tool such that minor misalignment of the insert from an ideal orientation will not cause overlap marks in the form of gashes or other incuse removal of material in the work piece. The curved profile of the insert, as viewed in plan, bears a relationship to manufacturing tolerances such that an insert, particularly at the corners, never projects from the cutting tool sufficiently to abrade the work piece beyond a predetermined limit, with the consequence that incuse or inwardly projecting lap marks are eliminated. When this arrangement is combined with overlapping of succeeding inserts, both externally and internally projecting lap marks are eliminated. The result, achieved in only one pass by a cutting tool using inserts, is a finish which satisfies final surface finish standards, unmarred by overlap marks. 
   It is, therefore, a feature of the invention to impart a final finish to a machined work piece in a single pass of a rotary cutting tool provided with cutting inserts. 
   In particular, it is a feature of the invention to eliminate both internally and externally projecting lap marks which might otherwise be caused by misalignment of subsequently passing inserts, due to manufacturing tolerances in the cutting tools. 
   It is another feature of the invention to provide improved elements and arrangements thereof by apparatus for the purposes described which is inexpensive, dependable, and fully effective in accomplishing its intended purposes. 
   These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the present invention, as well as the advantages derived therefrom, will become clear from the following detailed description made with reference to the drawings in which: 
       FIG. 1  is a side elevational view of one embodiment of a rotary cutting tool according to the present invention; 
       FIG. 2  is an exaggerated, diagrammatic detail view of two adjacent inserts drawn as though their respective pockets were unrolled from the cylindrical configuration of the tool of  FIG. 1 , and drawn to larger scale than  FIG. 1 ; 
       FIG. 3  is a side elevational, cross sectional view of part of a work piece which has been machined by the tool of  FIG. 1 ; 
       FIG. 4  is a side elevational, cross sectional view of part of a work piece which has been machined by a prior art tool in a manner corresponding to that of  FIG. 3 ; 
       FIG. 5  is a plan view of an alternative embodiment of an insert usable with the rotary cutting tool of  FIG. 1 ; and 
       FIG. 6  is a side elevational view of an insert usable with the rotary cutting tool of  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, wherein like reference characters represent like elements, there is shown in  FIG. 1  a rotary cutting tool  10  with an associated set of cutting inserts  12  shown installed within tool  10 . Tool  10  has a body  14  which is generally radially symmetrical about its rotational axis  16 . Body  14  is preferably cylindrical, and abuts a shank  15 . Body  14  and shank  15  share common rotational axis  16 . Body  14  preferably but not necessarily includes a plurality of flutes  18  each bearing a plurality of pockets  20  therein. Each pocket  20  is configured and dimensioned to receive at least one, but possibly more, of the inserts  12 . Inserts  12  are configured and dimensioned to be received within and secured to the pocket  20 . 
   Pockets  20  are arranged to seat a plurality or series of axially and circumferentially displaced, generally parallel inserts  12 . That is, pockets  20  are arrayed in columns, as seen in the depiction of  FIG. 1 , wherein one pocket  20  is in close proximity to but slightly displaced to the right or left along the circumference of body  14 , of an adjacent pocket  20 . Also, each pocket  20  which is to the left of an adjacent pocket  20  is also higher on body  14  than that pocket  20  to the right. Thus, it may be the that adjacent pockets  20  form a series of axially and circumferentially displaced pockets  20 . The same pockets  20  are parallel so that cutting edges of inserts  12  will be parallel to one another, to assure continuous and even cutting action relative to a work piece. To this end, flutes  18  are helically arranged about the circumferential surface of body  14 , with pockets  20  being disposed within flutes  18 . Within any one flute  18 , pockets  20  are helically arrayed along the length of body  14 , are arranged such that adjacent axially and circumferentially displaced inserts  12  overlap one another slightly along their respective lengths. 
   Overlap is clearly seen in  FIG. 2 , wherein insert  12 A is installed in a pocket  20  of one flute  18 , and insert  12 B (shown in broken lines) is installed in a pocket  20  of a second flute  18 .  FIG. 2  depicts how the silhouettes of inserts  12 A and  12 B would overlap one another when rotary cutting tool  10  is rotated about axis  16 . Also referring to  FIG. 3 , cutting contact generated by insert  12 A made with work piece  100  overlaps cutting contact generated by insert  12 A made with work piece  100 . Cutting contact occurs when rotary cutting tool  10  is both rotated and also brought to bear against work piece  100  by moving tool  10  laterally there against. This results in formation of scalloped cuts or kerfs  102  and  104 . It will be apparent that repeated passes of additional inserts  12  will continue the pattern of scalloped cuts  102 ,  104  formed by inserts  12 A,  12 B according to the number of available inserts  12 . 
   Returning to  FIG. 2 , insert  12 A has a first end  26  and a second opposed end  28 , and at least one cutting edge  30  spanning ends  26  and  28 . A first corner  32  is formed at the juncture of cutting edge  30  and first end  26 , and a second corner  34  formed at the juncture of cutting edge  30  and second end  28 . Each cutting edge  30  has a first tapered section  36  extending from corner  32  part way to corner  34 , and a second tapered section  38  extending from the second corner  34  part way to first corner  32  forming a highpoint  43  therebetween. In the preferred embodiment, taper is imparted by curvature of a single or constant radius. This produces the convex curved configuration shown in  FIG. 2 . However, and as illustrated in  FIG. 5 , it would also be possible to utilize convex curved configuration is that of a variable radius curve. 
   In most cases, tapered sections  36  and  38  are not distinct from one another, designation as different sections being merely for semantic convenience. Similarly, corners  32  and  34  need not be discrete intersections of sides forming points, designation of corners again being a semantic convenience to facilitate explanation of the invention. Although inserts  12  of the embodiment of  FIGS. 1 and 2  are bilaterally symmetrical about center line  40 , they could be asymmetric if desired. Although not shown, in the preferred embodiment, inserts  12  are also symmetrical about their length, having a second cutting edge not seen in the partial detail of  FIG. 2 , so that they are indexable. An indexable insert  12  is substantially a parallelepiped when viewed in side elevation, as seen in  FIG. 6 . 
   Tool  10  is fabricated to a predetermined dimensional tolerance, as is customary in manufacturing. Of critical interest to the present invention, each pocket  12  displays a maximum radial runout dimension (not separately shown). Taper of tapered sections  36  and  38  is of magnitude and configuration which assure that depth of cutting of the work piece performed by either tapered section  36  or  38  will never exceed in magnitude the predetermined dimensional tolerance. Therefore, taper of tapered sections  36  and  38  each establish radial runout compensation for their respective halves or sections of their associated insert  12 . Maximum outward radial displacement of a corner  32  or  34  of an insert  12  from rotational axis  16  is less than the magnitude of the predetermined manufacturing tolerance. Alternatively stated, radial runout compensation dimension  42 , which is defined as the distance between the highpoint  43  and the corner  32  or  34  of an insert  12 , is greater than the magnitude of the predetermined manufacturing tolerance. As shown in  FIG. 2 , the first and second corners  32 ,  34  of each insert  12  lie within a nominal cutting diameter when tool  10  is rotated about the rotational axis  16 . In addition, the highpoint  43  of cutting insert  12   a  and corner  32  of cutting insert  12   b  are substantially circumferentially aligned with each other when tool  10  is rotated about the rotational axis  16 . Similarly, the highpoint  43  of cutting insert  12   b  and corner  34  of cutting insert  12   a  are substantially circumferentially aligned with each other when tool  10  is rotated about the rotation axis  16 . Accordingly, maximum penetration of cutting edge  30  into the work piece is limited to less than the maximum radial runout dimension characteristic of pockets  20  by fabrication thereof when tool  10  is rotated and brought to bear laterally against a work piece. 
     FIG. 2  shows other characteristics of the novel configuration and arrangement of inserts  12 . It will be seen from examining  FIG. 2  that inserts  12 A and  12 B are arranged such that cutting contact made with the work piece by insert  12 A overlaps cutting contact made with the work piece by insert  12 B, which subsequently passes the kerf left by insert  12 A, by more than half of the length of cutting edge  30  of insert  12 A. The degree of overlap exceeds half the length of insert  12 A by the magnitude of arrow pair  19 . This relationship holds true for all inserts  12 . A consequence of this relationship as illustrated in  FIG. 3 , where it is seen that scalloped cuts or kerfs  102  are not as deep as radial runout compensation dimension  42 . Depth of cuts  102  is indicated by arrow set  106 . 
   Again referring to  FIG. 2 , cutting contact with a work piece of insert  12 A intersects cutting contact with the work piece by subsequently passing insert  12 B at the intersection of first tapered section  44  of insert  12 B with second tapered section  38  of insert  12 A. Of course, cutting contact will occur only after rotary cutting tool  10  is rotated and brought to bear laterally against the work piece. In a representative tool  10  having a manufacturing tolerance of 0.002 inch, the magnitude of a deviation dimension indicated by arrow pair  46  would be 0.0002 to 0.0005 inch. In the same tool  10 , the magnitude of radial runout compensation dimension  42  would be, for example, 0.003 inch. 
   The net effect of combining overlap of subsequently passing inserts with tapering as described is that overlapping cutting contact of inserts  12  made with the work piece and taper of inserts  12  combine to eliminate both inwardly projecting lap marks and outwardly projecting lap marks which could otherwise be formed in the course of machining the work piece. As seen in  FIG. 3 , a series of cuts or kerfs (e.g.,  102 ,  104 ) characterize the machined surface of work piece  100 . The entire surface is free from cuts as deep as overlap mark  8 , shown in  FIG. 4 . Thus, an acceptable finish is imparted by rotary cutting tool  10  in a single pass. Subsequent fine finishing operations are eliminated. 
   The invention may be considered as a method of arranging a rotary cutting tool and associated set of cutting inserts to eliminate overlap marks in machined work pieces. This method comprises steps of providing a rotary cutting tool  10  having pockets  20  each disposed to receive at least one insert  12 ; arraying pockets  20  in overlapping fashion such that an insert  12  installed in one pocket  20  generates overlapping cutting contact made with a work piece relative to cutting contact made with the work piece by a subsequently passing insert  12  when rotary cutting tool  10  is rotated and brought to bear laterally against the work piece; limiting a runout tolerance of each pocket  20  to a predetermined magnitude; configuring each insert  12  to have a lateral cutting edge  30  including tapered portions  36 ,  38  such that width of insert  12  is greatest at its center line  40 , and that no part of insert  12  projects radially outwardly from rotary cutting tool  10  when insert  12  is installed in a pocket  20  by a dimension of magnitude greater than that of the runout tolerance of each pocket  20 . The method is then used for end milling by rotating rotary cutting tool  10  and bringing tool  10  to bear laterally against a work piece until each cut made by an insert  12  has been subjected to a subsequent overlapping cut made by another insert  12 . In the preferred embodiment, the invention is best practiced by forming at least two helical flutes  18  in rotary cutting tool  10  and locating pockets  20  along each one of the flutes  18 . In the most preferred embodiment, a further step is practiced, that of locating at least some pockets  20  along any one of the flutes  18 , and preferably for all pockets  20 , such that the end of one pocket  20  overlaps the end of an adjacent pocket  20 . It is also preferred to practice the step of locating at least some subsequently passing pockets  20  which are non-adjacent to one another such that each pocket  20  is overlapped by at least half the length of an insert  12  by a subsequently passing pocket  12 . 
   The rotary cutting tool  10  and its inserts  12  will be understood to include suitable retention elements (not shown) for securing inserts  12  in place within their pockets  20  as well known in the art. These retention elements may include, for example, through holes having shoulders formed in inserts  12  and associated fasteners such as screws for passing through the holes. The retention elements may include clamps, as are known in the art, or any other suitable apparatus for retaining inserts  12  within their associated pockets  20 . 
   It would be possible to provide a cutting tool that has pockets  20  arranged according the present invention, but without flutes.  18  (this embodiment is not shown). For example, each pocket  20  could have its own dedicated chip gully. However, location of pockets  20  within flutes  18  is preferred. It is further preferred to provide two or three flutes  18 . 
   The documents, patents and patent applications referred to herein are hereby incorporated by reference. 
   While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.