Patent Publication Number: US-RE28896-E

Title: Cutting tool assembly

Description:
This invention relates to an improved cutting tool assembly. 
     The machining of certain types of work pieces with a profile that requires compound surfaces be turned; e.g., the crankpins of a vehicle engine crankshaft, presents several considerations including tool life, accuracy, the time required and the cost of the equipment. With the crankpin as an example, to achieve accuracy with the acceptable tool life, a two step machining operation is required; i.e., a rough machining step followed by a finish machining step. Therefore both additional equipment and time are needed to meet present mass production requirements. One of the reasons for this two step operation is the lack of an acceptable cutting tool. Single cutter blades with several different cutting edges have not been acceptable because if one cutting edge is damaged, the entire cutting blade has to be replaced or an expensive regrinding process is required. 
     With the foregoing in mind, a new and different cutting tool assembly is contemplated that enables compound surfaces to be formed accurately on a work piece by a single step operation. 
     Further contemplated is a cutting tool assembly that is durable, easily serviced and that can accurately and efficiently form plural surfaces on a workpiece with a plurality of cutter blades. 
     Also contemplated is a cutting tool assembly that utilizes a plurality of cutter blades uniquely mounted so as to provide desired cutting angles and also the proper overlap to accurately turn compound diameter and shoulder surfaces on a work piece. 
     Other objects include the provision of a cutting tool assembly that in a novel way maintains a plurality of cutter blades in place on a cutter body so as to achieve enhanced tool life, accuracy and operational efficiency and that can be used by present mass production equipment to machine plural surface profiles. 
    
    
     The foregoing and other objects and advantages of the invention will become apparent from the following description and from the accompanying drawings, in which: 
     FIG. 1 is a side elevational view of a cutting tool assembly incorporating the principles of the invention; 
     FIG. 2 is a top elevational view, looking in the direction of arrows 2--2 in FIG. 1, of the cutting tool assembly shown positioned for machining a vehicle crankshaft; 
     FIG. 3 is a front elevational view of the cutting tool assembly looking in the direction of arrows 3--3 in FIG. 1; and 
     FIG. 4 is a fragmentary enlarged view with parts removed of a portion of the cutting tool assembly as viewed in FIG. 2. 
    
    
     Referring first to FIG. 1, the numeral 10 denotes generally a cutting tool assembly that is adapted for positioning relative to a rotatable workpiece, such as a crankshaft 12. The cutting tool assembly 10 is adjustably mounted upon a block 14, which in a well known way can move the cutting tool assembly 10 into and out of the cutting relationship with the crankshaft 12. 
     For example, the block 14 may be a part of a conventional feed mechanism (not shown) for some kind of a production line transfer machine or a lathe. For purposes of demonstration and without limitation, the crankshaft 12 is in the form of a forging and has, as seen in FIG. 2, a crankpin portion 16 which when unmachined, has the shape shown by the dashed line at 17. When machined by the cutting tool assembly 10, the crankpin portion 16 will have the depicted profile including a crankpin surface 18 and a shoulder clearance surface 20, each being machined to a different dimension and in one step as will become apparent. 
     The cutting tool assembly 10 has a cutter body 22 with a bottom V-shaped mounting surface 24, which is seated on the block 14, and a top surface 26. The body 22 also has at its cutting end 28 a cutter blade mounting provision in the form of a pair of substantially V-shaped slots 30. 
     Each of the V-shaped slots 30 has a seating surface 32, which is inclined forwardly at an angle 33, as viewed in FIG. 1, and outwardly at an angle 34, as seen in FIG. 3. Each V-shaped slot 30 also has extending transversely from the seating surface 32 as depicted in FIG. 4, an inside locating surface 35, an outside locating surface 36, and a rear surface 38. In this embodiment each of these surfaces are either perpendicular to the seating surface 32 or tapered towards the seating surface to facilitate cutter blade retention. 
     Positioned in each of the slots 30 is a rectangular shaped side cutter blade 40 formed of a suitably hard machining metal, such as tungsten carbide, and preferably made to extremely close tolerances. With each blade 40 substantially identical in shape and dimension, they can be discarded when damaged and replaced with a new blade. Each of the cutter blades 40 has opposite parallel sides 42 and 44 and rounded cutting edges 46. These edges 46 can have other than the depicted rounded contour. The side cutter blades 40 when in place in the slots 30 engage the outside locating surface 36 and the rear surface 38, which has a contour at 48 that conforms to the rounded cutting edges 46, but can have other shapes. When in the operative position, the side cutting blades 40 each extend beyond the side of the cutter body 22, as viewed in FIGS. 2 and 4. 
     Also for mounting purposes, a cutter blade support provision is included in each slot 30 in the form of a cutter blade support member 50 that has the depicted triangular configuration. When the support members 50 are in position each engages the parallel side 44 of the associated side cutter blade 40 and also the inside locating surface 34 of the slot 30. Thus, the support members 50 function somewhat as a wedge for maintaining the side cutter blades 40 in their operative positions. The cutter blade support members 50 each have a through center opening 52 for purposes to be explained. 
     A locking provision is provided for maintaining each of the cutter blade support members 50 in place. This provision includes, as illustrated in FIG. 3, a dowel pin 56 or the like that is received in a blind hole 58 in the cutter body 22 and extends from the hole 58 upwardly and into the center opening 52 in the associated cutter blade support member 50. The dowel pin 56 has a relatively loose fit in the hole 58 but a relatively good sliding fit in the support member opening 52. To complete the locking provision, set screws 60 are threadedly carried by the cutter body 22 at point near the lower end of each of the dowel pins 56 and when tightened force the dowel pin 56 rearwardly and, accordingly, each of the cutter blade support members 50 so as to form a wedged relationship with the slots 30 and the side cutter blades 40. 
     Positioned on each of the cutter blade supporting members 50 is an indexable front cutter blade 62 of a relatively thin triangular shape. The front cutter blades 62 are of the throw-away type being also formed of hard cutting material, such as tungsten carbide, and manufactured to extremely close tolerances. The front cutter blades 62 have a center opening 64 and relatively straight cutting edges 66 and end cutting edges 68 on all sides. When in the depicted FIG. 3 operative position each of the front cutter blades 62 engages the side 44 of the side cutter blade 40 and the inside locating surface .[.34.]. .Iadd.35 .Iaddend.of the slot 30 has the proper radial alignment with the crankshaft 12. 
     If preferred the cutter blade support members 50 can be the same as the front cutter blades 62 and thus, would provide an auxiliary cutter blade in event replacement of one of the front blades 62 was required because of damage. It is also possible to use a damaged front cutter blade 62 in place of the support member 50. 
     For holding the front cutter blades 62 in the operative position within the slots 30, clamp elements 72 are provided. Each of these clamp elements 72, as best observed in FIG. 1, has a cutter blade engaging surface 74 with a depending pin 76 (FIG. 3), and rear inclined surface 78 and an intermediate relieved portion 80. The depending pin 76 of each clamp element 72 fits within the center opening 64 in a respective one of the front cutter blades 62, whereas the rear inclined surface 78 engages one of a pair of inclined or tapered surfaces 82 on the cutter body 22. Each of the cutter body inclined surfaces 82 is formed with a compound angle that has the same angle of inclination outwardly as the seating surface angle 34 (see FIG. 3) and an angle of forward inclination, as shown at 84 in FIG. 1. The angle 84 has a total angular extent equal to the sum of a predetermined angular amount and the forward inclination of the seating surface angle 33. Each of the clamp element inclined surfaces 78 has a complimentary inclination so as to have a substantial area thereof in engagement with the inclined surface 82 on the cutter body 22. Also, the clamp element cutter blade engaging surfaces 74 have a relatively large area thereof in engagement with the face of the respective one of the front cutter blades 62 to facilitate maintenance of the blades 62 in the operative position. The FIG. 1 clamping position for each clamp element 72 is maintained by a suitable holding screw 86 which extends through an elongated opening 88 (FIG. 2) in the clamp element 72 and threadedly engages the cutter body 22. The holding screw 86 is threaded into the cutter body 22 at an angle with the same outward inclination as the seating surfaces 32 have in FIG. 3 at the angle 34. 
     Referring again to FIG. 1, the angle 84 of the inclined surface 82 is selected so that when the holding screw 86 is tightened, the resolutions of forces will be such that the cutter blade 62 is forced rearwardly and in the plane of the seating surface 32, thus facilitating the wedging relationship for holding both the front cutter blade 62 and the side cutter blade 40 in their operative positions. If the angle 84 of this inclined surface 82 is too steep; for example, perpendicular to the top surface 26 of the cutter body 22, the clamp element 72, when forced into the clamping position by the tightening of the holding screw 86 would tend to raise the cutter blade 62 from its viewed position in FIG. 1. Contrariwise, if the angle 84 of the inclined surface 82 is not steep enough, there will not be an adequate force imposed upon the cutter blade 62 to maintain it in its operative position. By way of example and without limitation, it has been determined that if the inclination of the seating surface angle 33 is 5°, then the angle at 84 should be 30° plus the 5° or 35°. 
     Completing the assembly is a holder 90 which is slidably positioned on the top surface 26 of the cutter body 22. The holder 90 has extending the length thereof a depending center portion 92 (FIG. 3), which engages a complimentary slot 94 in the top surface 26 of the cutter body 22 so as to provide sliding adjusting movement only in the direction towards and away from the workpiece. This sliding adjusting movement can be made by a differential screw 95, which threadedly engages both the holder 90 and a bracket 96 suitably attached to the cutter body 22. The holder 90 is releasably maintained on the cutter body 22 by one or more screws 97, which threadedly engage the cutter body 22. The holder 90 and the cutter body 22 are both releasably fixed on the block 14 by a pair of elongated screws 98 that threadedly engage the block 14. 
     As viewed in FIG. 2, the holder 90 has a narrow front portion 100 that extends between the two clamp elements 72. This narrow portion 100 has an upper inclined surface 102 and at the end thereof a cutter blade receiving slot 104 which can also be triangular shaped. This slot 104 has a seating surface 106 (FIG. 1) on which is mounted a triangular shaped middle cutter blade 108 including a center opening 110. The blade 108 can be of the indexable throw-away type and thus similar to the front cutter blades 62 and is appropriately inclined by the seating surface 106 so that the proper cutting angles are provided and also so as to be in the required approximate radial alignment with the center of the crankpin portion 16. 
     For holding the middle cutter blade 108 in the operative position, a clamp element 112 is employed that is similar structurally and functionally to the clamp elements 72. This clamp element 112 has a cutter blade engaging surface 114 provided with a depending pin 116 and a rear inclined surface 118. When in the FIG. 1 clamping position, the depending pin 116 engages the center opening 110 in the middle cutter blade 108, the surface 114 is flush against the face of the blade 108, and the rear inclined surface 118 engages a top portion 120 of the holder 90. As with the clamp elements 72, the angular relationship is such as to provide the proper restraining forces for urging the middle cutter blade 108 rearwardly in the plane of its seating surface 106. A suitable screw 122 holds the clamp element 112 in the depicted position. 
     As viewed in FIGS. 1 and 2, the alignment of the front cutter blades 62 and the middle cutter blades 108 respectively on the cutter body 22 and the holder 90 takes into consideration the different plane location of the middle cutter blade 108 and is such that an uninterrupted diametrical cut is made on the crankpin surface 18. Also, the blade sizes are selected to provide the FIG. 2 illustrated crankpin profile. As the cutting tool assembly 10 is fed into the crankpin portion 16, it will be noted that the side cutter blades 40 and the front cutter blades 62 have substantially more metal to remove than the middle cutter blade 108. This the described cutting tool assembly 10 can accompllish accurately in one step and without sacrificing durability. Also, it will be noted that the end cutting edges 68 of the front cutter blades 62 provide the crankpin surface 18 with the proper size fillet at 124 and that the side cutter blades 40 provide the shoulder clearance surfaces 20, which terminate in a larger diameter at a fillet 126. This surface 20 and fillet 126 provide somewhat of a boss for facilitating the installation and positioning of the vehicle crank in the crankpin portion 16. 
     The single machining step is done with indexable throw-away cutter blades that can be replaced in a minimum amount of time without concern about realignment. Furthermore, when the support members 50 are the same as the cutter blades 62 they can serve as auxiliary blades and be used to replace one of the damaged front cutter blades 62. The resolution of the forces with respect to the clamp elements 72 and the clamp element 112 provide optimum holding forces that maintain the wedge like relationship so that the cutting blades 62 and 40 cannot shift or move so as to be damaged or damage the crankshaft 12 during the machining operation.