Abstract:
A quick-change tool holder includes locating means for repeatably locating a cutting unit at a predetermined angular position with respect to a support member. The support member includes an axial bore for receiving a tubular shank on the cutting unit. The tubular shank of the cutting unit includes a keyway having a first locating surface along one side thereof. The clamping mechanism includes a key having a second locating surface along one side thereof. Upon actuation, the clamping mechanism imposes a torque force on the cutting unit to rotate the first locating surface on the cutting unit into abutting relationship with the second locating surface on the key to repeatably locate the cutting unit at a predetermined angular location. The torque force imposed on the cutting unit by the clamping mechanism therefore overcomes any inaccuracies in center-height adjustment attributable to the tolerance between the key and its corresponding keyway.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to quick-change tooling for metal-working operations, such as boring and turning, and more particularly to a method and apparatus for adjusting the center-height of the cutting tool. 
     A quick-change tool holder typically includes two separate components--a tool support member and a cutting head. The tool support member is installed on the machine and the cutting head clamps to the support member. The tool support member will normally receive many different types of cutting heads which can be interchanged with one another relatively quickly. Thus, quick-change tooling greatly reduces set-up time when switching from one machine operation to another. 
     The drawback with quick-change tooling, however, is that it is more difficult to maintain proper center-height adjustment of the cutting tool. Quick-change tooling requires a greater number of parts than conventional fixed tooling. Even when the parts are manufactured according to close tolerances, the cumulative effect of such tolerances can have a significant effect on center-height adjustment. Improper center-height adjustment may result in increased cutting forces in the tool which could significantly affect tool life. Other problems associated with improper center-height adjustment include excessive chatter during machining operations, rough surface finish on the workpiece, and unacceptable variations in the size of the finished workpiece. 
     In our co-pending application filed contemporaneously with this application, a mechanism is disclosed for adjusting the center-height of the cutting tool in a quick-change tool holder assembly. Briefly, the clamping mechanism includes a key which engages a corresponding keyway in the shank of the cutting unit to angularly locate the cutting unit. The clamping mechanism is mounted in the axial bore of the support member and means are provided for rotating the clamping mechanism. Since the center-height of the cutting tool is dependent on the angular location of the cutting unit, rotation of the clamping mechanism provides a convenient method for adjusting center-height of the cutting tool. 
     The above-described system is more than adequate in all but the most demanding applications. However, the adjustment mechanism does not assure exact, center-height repeatability. By necessity, there must be some clearance between the key on the clamping mechanism and the keyway on the cutting unit. Each time the cutting unit is clamped to the support member, a different side of the key could possibly engage with the adjacent side of the keyway. Further, it is possible that the clamping mechanism itself could locate the cutting unit such that the key does not engage either side of the keyway. As a result, exact location of the cutting head cannot be assured. 
     Accordingly, there is a need for a center-height adjustment mechanism in which exact angular location of the cutting unit can be obtained to assure center-height repeatability. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The present invention is a quick-change tool holder having means for adjusting the center-height of the cutting tool. The tool holder includes a support member which is adapted to be mounted on a lathe turret or mounting block, a cutting head formed with a seat for receiving the cutting tool, and a clamping mechanism for clamping the cutting head to the support member. 
     The clamping mechanism utilizes a pair of locking balls which are driven into engagement with apertures formed in a tubular shank on the cutting head. The locking balls are driven into engagement with the tubular shank by an actuating member. The locking balls and the actuating member are contained within a ball canister which is disposed in the axial bore of the support member. The ball canister includes a key which cooperates with a keyway on the tubular shank to angularly locate the cutting head. 
     Center-height adjustment is achieved by rotating the ball canister about a longitudinal axis. Various methods may be used for rotating the ball canister. The disclosed embodiment utilizes a ball and screw arrangement. More particularly, the ball canister is formed with a pair of detents or recesses. The detents are engaged by force transmitting balls, each of which is activated by a cup-point adjusting screw. The axis of the adjusting screws are offset with respect to the axis of the canister and provide counter-balancing torque on the canister. The canister can be rotated in either direction to adjust the center-height of the tool by loosening one screw and tightening the opposite screw. 
     To assure repeatability of the center-height adjustment, the key on the canister is shifted slightly off-center with respect to its corresponding keyway in the tubular shank of the cutting unit. The off-center key causes the cutting unit to slightly misalign when it is inserted into the axial bore of the support member. Thus, when the locking balls engage the tubular shank, they impose a torque force on the cutting unit which effects functional engagement of one side of the key with the adjacent side of the keyway. Using the off-center key assures that the same side of the key will always engage sides of the keyway. 
     Based on the forgoing, it is apparent that the primary objective of the present invention is to provide a quick-change tool holder having means for adjusting the center-height of the cutting tool. 
     Another object of the present invention is to provide a quick-change tool holder wherein the effect of tolerances on center-height adjustment are largely eliminated. 
     Still another object of the present invention is to provide a center-height adjustment mechanism for a quick-change tool which guarantees repeatability of the center-height adjustment. 
     Yet another object of the present invention is to provide a center-height adjustment mechanism which has sufficient load carrying capacity that is can maintain its position during machining operations. 
     Still another object of the present invention is to provide a quick-change tool holder having a center-height adjustment mechanism which is relatively simple in construction and which can be produced economically. 
     Another object of the present invention is to provide a quick-change tool holder with a center-height adjustment mechanism which will be relatively easy to use and which can be adjusted relatively quickly. 
     Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of one embodiment of the tool holder assembly of the present invention. 
     FIG. 2 is a partial section view of the tool support member taken along a medial plane of the support member. 
     FIG. 3 is cross-section view of the tool support member taken through line III--III of FIG. 2. 
     FIG. 4 is a front elevation view of the tool holder assembly with a portion shown in section. 
     FIG. 5 is a cross-section view of the tool support member taken through line V--V of FIG. 4. 
     FIG. 6 is a partial top plan view of the ball canister with a portion shown in section to illustrate the recess. 
     FIG. 7 is a section view of the ball taken through line VII--VII of FIG. 6. 
     FIG. 8A is a cross-section view through the tubular shank of the cutting unit. 
     FIG. 8B is a cross-section view through the support member and the ball canister. 
     FIG. 9A is a cross-section view through the support member with the cutting unit inserted and the locking balls in a disengaged position. 
     FIG. 9B is a cross-section view through the support member with the cutting unit inserted and the locking balls in an engaged position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and particularly to FIG. 1, the tool holder assembly of the present invention is shown therein and indicated generally by the numeral 10. The tool holder assembly includes a tool support member indicated generally at 12, a cutting head 14 adapted to receive and hold the cutting tool, and a clamping mechanism 16 for clamping the cutting head 14 to the support member 12. 
     The support member 12 includes a generally cylindrical shank 18 which is received in an axial bore formed in the turret or mounting block (not shown) of the machine. The shank has one or more flats 18a formed in the surface thereof which are engaged by set screws (not shown) to secure the support member 12 in the turret or mounting block. A flange 20 is formed adjacent the forward end of the support member 12. The flange 20 includes a rearwardly facing surface 22 which seats against the face of the turret or mounting block. A flat surface 24 is formed on one side of the flange 20. An axial bore 28 is formed in the forward end of the support member 12 and is surrounded by a forwardly facing seating surface 26. The axial bore 28 has a slightly frusto-conical configuration and is adapted to receive the cutting head 14 as will be hereinafter described. 
     Referring now to the cutting head 14, it includes a forward portion 30 and a rearwardly extending, tubular shank 32. A rearwardly facing abutment surface 34 is formed at the junction between the tubular shank 32 and the forward portion 30. The forward portion 30 is formed with a tool receiving pocket 36 adapted to receive a conventional cutting insert 38 and shim 40. The cutting insert 38 includes two converging cutting edges which meet to form a rounded cutting tip. The top of the cutting insert 38 is engaged by a clamping member 42 to secure the insert 38 and shim 40 in the tool receiving pocket 36. The clamping member 42 is secured to the forward portion by a clamp screw 44 which threads into a corresponding hole (not shown) in the top of the forward portion 30. 
     The tubular shank 32 is integrally formed with the forward portion 30 and is preferably machined from a single piece of steel. The shank 32 has a frusto-conical shape which matches the axial bore 28 of the support member 12. Two diametrically opposed apertures 46 perforate the tubular shank 32. The tubular shank 32 also includes two diametrically opposed key slots 48 which are disposed along a radial axis that is perpendicular to the axis of the apertures 46. 
     When mounting the cutting head 14 to the support member 12, the tubular shank 32 is received in the axial bore 28. The clamping mechanism 16 is disposed in the axial bore 28 for securing the cutting head 14 on the support member 12. 
     As seen in FIGS. 2 and 3, the clamping mechanism 16 includes a ball canister 50 which is secured in the axial bore 28 of the support member 12 by a double-ended screw 52. A first end of the double-ended screw 52 threads into a corresponding screw hole 54 in the bottom of the axial bore 28. The second end of the screw 52 threads into a corresponding screw hole 56 in the base 58 of the canister 50. 
     The ball canister 50 includes an upper portion 60 having a key 82 formed on its exterior which is sized to fit into one of the key slots 48 on the tubular shank 32 of the cutting unit 14. Two transverse passages 62 and 64 are formed in the canister 50 which extend perpendicularly to the longitudinal axis of the tool holder. A bump-off pin 66 is loosely mounted in a longitudinal passage 68 in the top of the ball canister 50. The bump-off pin 66 includes a shoulder 70 which is engaged by two small screws 72 to retain the bump-off pin 66 in the longitudinal passage 68. 
     An actuating member 74 is disposed in the first longitudinal passage 62 of the ball canister 50. The actuating member 74 includes a head portion 76 and a shank portion 78. The shank portion 78 is externally threaded. An actuating screw 80 provides means for reciprocally moving the actuating member 74. The actuating screw 80 includes an internally threaded bore 84 which engage the threads on the shank portion 78 of the actuating member 74. The actuating screw 80 also includes external threads 86 which are opposite to the threads in the threaded bore 84. The external threads 86 engage a threaded opening 88 in the support member 12. On the end of the actuating screw 80 which is accessible from the exterior of the support member 12, there is a hexagonal depression 90 which is adapted to be engaged by an Allen wrench. 
     The head portion 76 of the actuating member 74 includes a pair of ball driving ramps 92 on opposite sides thereof. The ball driving ramps 92 are adapted to engage locking balls 94 which are loosely received in the transverse passage 64. The ball driving ramps 92 decline inwardly as they extend away from the shank portion 78 until they join concave-spherical depressions 96. The actuating member 74 also includes an inclined surface 98 adapted to engage a corresponding surface 100 on the bottom of the bump-off pin 66. 
     It will be readily apparent from the foregoing description that when the actuating screw 80 is turned in a first direction, the actuating member 74 will be moved to roll the locking balls 94 out of spherical depressions 96 and on to the ball driving ramps 92. The locking balls 94 are thus driven outwardly as best shown in FIGS. 3 and 4. When the actuating screw 80 is rotated in a second direction, the actuating member 74 is moved in a second direction to allow the locking balls 94 to roll back into the spherical depressions 96. At the same time, the inclined surface 98 on the actuating member 74 engages the corresponding inclined surface 100 on the bump-off pin 66 to push it upward. The bump-off pin 66, in turn, pushes upwardly against the cutting head 14 to separate the cutting head 14 from the support member 12. 
     In use, the cutting head 14 is mounted on the support member 12 by inserting the tubular shank 32 of the cutting head 14 into the axial bore 28 of the support member 12. After inserting the cutting head 14 into the support member 12, the actuating screw 80 is rotated in a first direction, normally clock-wise, to clamp the cutting head 14 to the support member 12. As already described, the rotation of the actuating screw 80 causes the actuating members 74 to urge the locking balls 94 radially outward into engagement with the apertures 46 in the tubular shank 32. As shown best in FIG. 4, the walls of the aperture 46 are slightly inclined so that the engagement of the locking balls 94 with the apertures 46 exerts a rearward force on the cutting head 14 and seats the abutment surface 34 against the seating surface 26 on the support member 12. Once the cutting head 14 is mounted on the support member 12, the angular location of the cutting head 14 is determined by the engagement of the key 82 on the ball canister 50 with the corresponding key slot 48 in the tubular shank 32 of the cutting head 14. Ideally, the key and key slot 48 should always locate the cutting head 14 so that proper center-height adjustment is obtained. In actual practice, however, proper center-height adjustment cannot be assured due to the number of components and the tolerances to which they are made. The present invention attempts to eliminate, to a large extent, the effect of these tolerances on center-height adjustment by providing means for adjusting the center-height of the cutting tool. 
     Referring now to FIGS. 4-7, the center-height adjustment means comprises a pair of cup-point adjusting screws 102 which exert counter-balancing torque on the ball canister 50. The adjusting screws 102 are threadably engaged in adjusting-screw holes 104 in the flange 20 of the support member 12. Each adjusting screw 102 engages a spherical force-transmitting element 106 which in turn engages a recess 108 in the base 58 of the ball canister 50. The recess 108 includes a seating portion 110 in which the force transmitting element 106 makes contact, and a clearance portion 112. The seating portion 110 is formed with a ball nose end mill whose diameter is roughly equal to the diameter of the force transmitting element 106. The clearance portion 112 is formed with a ball nose end mill having a slightly larger diameter. 
     As best shown in FIG. 6, the seating portion 110 of the recess 108 includes a flat portion 110a which is formed by moving the end mill laterally in a horizontal plane. The seating portion 110 remains generally circular in the view shown in FIG. 7. This configuration permits the force transmitting element 106 to make line contact with the seating portion 110 throughout the range of adjustment of the canister 50. The force transmitting element 106 also makes line contact with the cup point adjustment screw 102. The line contact is important in giving the adjustment mechanism sufficient torque-carrying capacity to resist movement during machining operations. 
     To adjust the center-height of the cutting tool, a first adjusting screw 102 is loosened and the second adjusting screw 102 is tightened to rotate the ball canister 50. When the desired position is attained, the first adjusting screw 102 is then retightened to lock the ball canister 50 in the adjusted position. The rotation of the ball canister 50 realigns the key 82, which in turn, causes the angular position of the cutting unit 14 to be changed. The center-height of the cutting tool is determined by the angular location of the cutting unit 14. 
     In certain applications, it is important that the center-height of the cutting tool be repeatable. That is, it is desirable for the precise angular location of the cutting unit, which determines the center-height of the cutting tool, be achieved each time the cutting unit is secured to the support member. With some modification, the adjustment mechanism described above can be designed to assure repeatability of the center-height of the cutting tool. 
     The locking mechanism of the present invention tends to be self-centering. When the cutting unit is off-center, the clamping mechanism imposes a torque force on the cutting unit which rotates the cutting unit to be a centered position. The self-centering nature of the clamping mechanism can be used to assure precise angular location of the cutting unit. 
     Referring now to FIG. 8A, which is a cross-section through the tubular shank 32 of the cutting head 14, it is seen that the ball receiving apertures 46 are disposed along a first radial axis r 1  and that the keyway 48 is disposed along a second radial axis r 2 . The radial axes r 1  and r 2  are perpendicular to one another. In FIG. 8B, the same radial axes r 1  and r 2  are superimposed on a cross-section of the support member 12. The transverse passage 64 in the ball canister 50 lies along the same radial axis r 1  as the ball receiving apertures 46 in the tubular shank 32 of the cutting head 14. The key 82 on the ball canister 50, however, is slightly offset by distance &#34;a&#34; from the radial axis r 2 , which is the center line CL of the keyway 48. 
     When the cutting unit 14 is inserted into the axial bore 28 of the support member 12, the offset key 82 will cause the cutting unit 14 to be rotated off-center such that the apertures 46 do not align exactly with the locking balls 94 as seen in FIG. 9A. 
     As the locking balls 94 expand radially outward, the balls 94 engage the misaligned apertures 46 in such a manner as to apply a torque force to the cutting head 14 as shown by the arrow in FIG. 9B. The resulting torque imposed on the cutting head 14 will rotate the cutting head 14 back towards a centered position and force one side of the key 82, called the locating side, into engagement with a corresponding side of the keyway 48. Because the key 82 is shifted off-center, the same side of the key 82 will always make contact with the keyway 48 to assure center-height repeatability. When proper adjustment of center-height is made, the present invention effectively eliminates the effect of tolerances on center-height adjustment. 
     Based on the foregoing, it is apparent that the center-height adjustment mechanism provides an easy and convenient method for adjusting the center-height of the cutting tool. By adjusting the center-height, the forces on the cutting tool can be reduced, chatter can be eliminated, and a better surface finish on the workpiece can be obtained. Moreover, the present invention assures center-height repeatability making it suitable for the most demanding applications. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.