Tool holder assembly with interference fit key arrangement

A tool holder assembly includes a tool holder with a shank and a key slot having a surface with an angled portion that forms a non-zero angle with respect to a longitudinal axis of the tool holder assembly. A clamping mechanism includes a support block, a ball canister including a key, and a lock rod. An interference fit key arrangement is provided between the tool holder and the clamping mechanism by an abutment surface located along the first side wall of the key. The abutment surface contacts the angular portion of the key slot to cause the key slot to undergo elastic deformation and allow simultaneous contact between the abutment surface and the angular portion of the key slot and the second side wall of the key and the second surface of the key slot, thereby providing for an interference fit key arrangement between the tool holder and the clamping mechanism when the tool holder assembly is placed in the locked position.

BACKGROUND OF THE INVENTION

There are known mechanisms for releasably holding a toolholder shank in a support block bore when the mechanism actuating member is transversely aligned with respect to the longitudinal axis of the toolholder shank and a support block bore. Such mechanisms and articles are used in the cutting and shaping of workpieces where it is not expedient to use the tool support block in connection with a base member having a bore containing an axially aligned power driven means for axially actuating the locking mechanism in the tool support block. Examples of toolholders and support blocks utilizing releasable locking mechanisms having radial activation are shown in U.S. Pat. Nos. 4,573,824; 4,575,293 and 4,135,418 and 4,736,659.

Conventional cutting units and clamping mechanisms in some tool holder assemblies use a key and key slot for radial location of the cutting tool. The tolerances involved allow for various amounts of clearance that can lead to radial inaccuracies that, in turn, can be a problem in certain machining applications. The dimensions and tolerances currently in use are at their practical limit. Tighter tolerances and smaller clearances would require extra machining operations, thereby increasing the cost of the system.

Accordingly, there is a need for an improved mechanism in this field for aligning the toolholder and the clamping unit, thereby reducing or eliminating any variance in the radial location of the cutting tool.

BRIEF SUMMARY OF THE INVENTION

To solve these and other problems associated with conventional toolholder assemblies, a toolholder assembly comprises a tool holder assembly comprises a tool holder including a shank with a key slot forming a first surface and a second, opposing surface, the first surface including an angled portion forming a non-zero angle with respect to a longitudinal axis of the tool holder assembly; and a clamping mechanism for releasably securing the tool holder. The clamping mechanism comprises a support block including a bore extending along the longitudinal axis for receiving the shank of the tool holder; a ball canister received within the bore of the support block, the ball canister including a key formed by a first side wall and a second, opposing side wall; and a lock rod mounted in the support block for reciprocal movement within the tool holder assembly and for urging a locking element radially outwardly to engage the shank of the tool holder when the tool holder assembly is placed in a locked position. An abutment surface located along the first side wall of the key contacts the angular portion of the key slot to cause the key slot to undergo elastic deformation and allow simultaneous contact between the abutment surface and the angular portion of the key slot and the second side wall of the key and the second surface of the key slot, thereby providing for an interference fit key arrangement between the tool holder and the clamping mechanism when the tool holder assembly is placed in the locked position.

In another aspect of the invention, a tool holder assembly comprises a tool holder including a shank with a key slot forming a first surface and a second, opposing surface, the first surface including an angled portion forming a non-zero angle with respect to a longitudinal axis of the tool holder assembly; and a clamping mechanism for releasably securing the tool holder. The clamping mechanism comprises a support block including a bore extending along the longitudinal axis for receiving the shank of the tool holder; a ball canister received within the bore of the support block, the ball canister including a key formed by a first side wall and a second, opposing side wall; a lock rod mounted in the support block for reciprocal movement within the tool holder assembly and for urging a locking element radially outwardly to engage the shank of the tool holder when the tool holder assembly is placed in a locked position; and an interference fit screw at least partially inserted into an aperture formed in the support block. The interference fit screw provides an abutment surface that contacts the angular portion of the key slot to cause the key slot to undergo elastic deformation and allow simultaneous contact between the abutment surface and the angular portion of the key slot and the second side wall of the key and the second surface of the key slot when the tool holder assembly is placed in the locked position.

In yet another aspect of the invention, a tool holder assembly comprises a tool holder including a shank with a key slot forming a first surface and a second, opposing surface, the first surface including an angled portion forming a non-zero angle with respect to a longitudinal axis of the tool holder assembly; and a clamping mechanism for releasably securing the tool holder. The clamping mechanism comprises a support block including a bore extending along the longitudinal axis for receiving the shank of the tool holder; a ball canister received within the bore of the support block, the ball canister including a key formed by a first side wall and a second, opposing side wall; and a lock rod mounted in the support block for reciprocal movement within the tool holder assembly and for urging a locking element radially outwardly to engage the shank of the tool holder when the tool holder assembly is placed in a locked position. The first side of the key provides an abutment surface that contacts the angular portion of the key slot to cause the key slot to undergo elastic deformation and allow simultaneous contact between the abutment surface and the angular portion of the key slot and the second side wall of the key and the second surface of the key slot when the tool holder assembly is placed in the locked position.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIGS. 1-4, a tool holder assembly10is shown according to an embodiment of the invention. In general, the tool holder assembly10includes a tool holder12and a clamping mechanism14for releasably securing the tool holder12in the tool holder assembly10.

Referring now toFIGS. 5 and 6, the tool holder12includes a forward portion20and a tubular shank22. The forward portion20is formed with a tool receiving pocket26adapted to receive a conventional shim21and a cutting insert23. A flange24is formed at the rear of the forward portion20. The shank22extends from the rear face of the flange24. The shank22has a frustoconical shape that tapers inwardly as it extends rearwardly. At the upper end of the shank22, where it joins the forward portion20, the shank22is smaller in diameter than the flange24leaving a rearwardly facing shoulder that extends around the shank22.

Referring back toFIG. 1, the tubular wall of the shank22is perforated at two circumferentially spaced locations by apertures28. The apertures28are spaced approximately 180 degrees apart and extend angularly through the tubular wall of the shank22. The tubular shank22also includes two diametrically opposed key slots30that are disposed at approximately 90 degrees to the apertures28. Each key slot30forms a surface31and an opposing surface33. The function of the key slots30is to cooperatively engage corresponding keys on the clamping mechanism14, and thus to hold the tool holder12against rotation. At least one of the surfaces31and33of the key slots30, for example, the surface33includes an angled portion33athat is formed at a predetermined, non-zero angle35with respect to the longitudinal y-axis (FIG. 9). In one embodiment, the angle35is approximately 8 degrees. However, it will be appreciated that the invention is not limited by the particular angle of the angled portion33aand can be practiced with a desired, non-zero angle depending on design parameters for a specific application.

Referring now toFIGS. 1,7and8, the clamping mechanism14includes a support block32that has a generally rearward facing surface36and side faces38and40. The support block32is adapted to be mounted on a turret head of a machine tool (not shown), with the rearward facing surface36in contact with the turret head. The support block32is secured to the turret head by bolts42that extend through four bolt holes. An axial bore44extends from the rearward facing surface36of the support block32along the longitudinal y-axis. Apertures48,49are formed in the side face38and are adapted to receive a pair of set screws51,53, respectively. In a convention tool holder assembly, the set screws51,53may comprise error-proofing set screws. The support block32includes a forward face43that contacts the flange24of the tool holder12when face contact is achieved in the tool holder assembly10.

In the illustrated embodiment, a tapered bore50is integrally-formed with the support block32. It will be appreciated that the invention is not limited by the sleeve being integrally-formed with the support block, and that the invention can be practiced using a sleeve that is a separate component of the clamping mechanism. The bore50serves two functions. First, the bore50provides a receptacle into which the tool holder12can be inserted. Second, the bore50secures a ball canister60, which is part of the clamping mechanism14, within the axial bore44of the support block32.

Referring now toFIG. 1, the ball canister60is a generally cylindrical structure having a bare flange62. Integrally formed with the ball canister60are two raised keys64that are disposed at approximately 180 degrees with respect to one another. The keys64are disposed within the support block32when the ball canister60is inserted into the aperture44of the support block32. Each of the keys64includes a first side wall66and a second, opposing side wall68. The set screws51,53are received in slots65,67formed in the opposite sidewalls66,68of the keys64. The ball canister60mounts inside the axial bore44. An axial passageway74extends through the ball canister60and aligns with the longitudinal y-axis. Two diametrically opposed apertures76are formed in the walls of the ball canister60.

It will be appreciated that the invention is not limited to the keys64being located on the ball canister60, and that the invention can be practiced with the keys64located on other surfaces of the clamping mechanism14. For example, the keys64may be located on the inside surface of the support block32in a configuration in which the ball canister60is omitted from the tool holder assembly10.

As shown inFIG. 1, the tool holder shank22is secured in the axial bore44between the support block32and the ball canister60by a pair of locking elements78which are loosely retained in the apertures76of the ball canister60. In the embodiment shown, the locking elements78comprise a pair of hardened steel balls. The locking elements78can be urged radially apart to engage the apertures28in the tool holder shank22.

The clamping mechanism14includes a lock rod80that is reciprocally mounted in the axial bore44of the support block32to actuate the locking elements78. The lock rod80includes a front portion82, a central portion83and a rear portion84. As shown inFIG. 4, the front portion82has an end surface86that is in substantial alignment with the forward face43of the support block32when the tool holder10is assembled. A pair of concave surface depressions88is formed in the front portion82of the lock rod80. The concave depressions88are equally spaced from the end surface86and are circumferentially spaced at approximately 180 degrees to each other. The depressions88are dimensioned to receive the locking elements78when the lock rod80is in a release position. The depth of the concave depressions88is set so that the locking elements78can move radially inward sufficiently to disengage from the apertures28in the tool holder shank22, thereby releasing the tool holder12.

The central portion83is larger in diameter than the front portion82and forms a shoulder89that engages a shoulder63in the ball canister60to limit the forward movement of the lock rod80, as shown inFIG. 4. The central portion83is formed with a transverse passage90. The inner walls of the transverse passage90are formed with first and second cam surfaces that cooperate with a cylindrical cam100to forwardly and rearwardly (along the y-axis) displace the lock rod80when the cam100is rotated.

The clamping mechanism14also includes a cam follower102that is disposed around the rear portion84of the lock rod80. When the cam follower102is disposed around the lock rod80, a front portion104of the cam follower102contacts the central portion83of the lock rod80. One or more disk springs106are also disposed around the rear portion84of the lock rod80and abut a rear surface103of the cam follow102so as to provide a desired spring force and bias the lock rod80along the longitudinal y-axis. When the cam100is rotated to place the clamping mechanism14in a locked position, the depressions88of the lock rod80urge the locking elements78radially outwardly into engagement with the apertures28in the shank22of the tool holder12. The engagement of the locking elements78with the apertures28of the tool holder shank22urges the tool holder12rearwardly so that the abutment surface24seats against the front face43of the support block32, as shown inFIG. 4. When the cam100is rotated to place the clamping mechanism14in an unlocked position, the cam100contacts the lock rod80to forwardly displace the lock rod80. As the lock rod80moves forwardly, the locking elements88move radially inwardly into the concave depressions88and the end surface86engages the tool holder12to disengage the tool holder12from the clamping mechanism14.

In the illustrated embodiment, the clamping mechanism14also includes a lock rod end cap110that is partially inserted into the tubular rear portion84of the lock rod80until a shoulder112of the end cap110abuts the rear portion84of the lock rod80. A compression spring114may be inserted into the lock rod end cap110, and a body end cap116is attached to the clamping mechanism14to seal the clamping mechanism14.

It will be appreciated that the invention is not limited by the type of clamping mechanism, and that the invention can be practiced with clamping mechanisms that do not involve the use of a lock rod and ball canister for clamping the tool holder12in place.

When the shank22is inserted into the axial bore44formed between the support block32and the ball canister60, the side walls66,68of the keys64of the ball canister60engage in the key slots30in the tubular shank22. In this manner, the tool holder12is held non-rotatable with respect to the clamping mechanism by cooperative engagement of the keys64with the key slots30. However, one problem with this configuration in certain machining applications is that the tolerances involved allow for various amounts of clearance that can lead to radial inaccuracies of the position of the tool holder. The dimensions and tolerances currently in use are at their practical limit. Tighter tolerances and smaller clearances would require extra machining operations, thereby increasing the overall cost of the system. To address this problem, one aspect of the invention is that an interference fit key arrangement is provided that minimizes or eliminates the radial inaccuracies of the position of the tool holder that is associated with conventional tool holder assemblies.

In a conventional clamping mechanism, the set screws51,53may comprise an error-proofing set screw and a plug set screw with two different diameters. Alternatively, the set screws51,53may comprise a pair of plug set screws that have the same diameter. For example, the error-proofing set screw may a diameter of about 6.000 mm and the plug set screw may both have a diameter of about 3.800 mm to allow the tool holder12to be placed in the clamping mechanism14in either 0 degree or 180 degree orientations.

In one aspect of the invention, the tool holder assembly10includes an interference fit key arrangement between the tool holder12and the ball canister60that comprises an interference fit screw that replaces the error-proofing set screw or one of the plug set screws. For example, the invention can be practiced by replacing the error-proofing set screw51with an interference fit screw55having a relatively larger diameter. In one example, the interference fit screw55having a diameter of about 6.625 mm may replace the conventional error-proofing set screw having a diameter of about 6.000 mm. In another example, the interference fit screw55may having a diameter of about 6.625 mm may replace one of the conventional plug set screws having a diameter of about 3.800 mm. Interference fit screws having other relatively larger diameters are within the scope of the invention. It will be appreciated that the clamping mechanism14using the interference fit screw55of the invention can be retrofit to a conventional clamping mechanism by replacing the interference fit screw55with the appropriate smaller diameter error-proofing set screw or plug set screw, thereby bypassing the interference fit key arrangement of the invention.

The interference fit screw55having the relatively larger diameter includes a front portion55athat is substantially circular cross-sectional in shape that contacts the angular portion33aof the key slot30to cause the key slot30to undergo elastic deformation and allow simultaneous contact between the angled portion66aof first side wall66and the second side wall68of the key64and the surface31and the angled portion33aof the surface33of the key slot30. In other words, the front portion55aof the interference fit screw55is an abutment surface located along the first side wall66of the key64that contacts the angular portion33aof the key slot30. This interaction between the interference fit screw55and the angular portion33aof the key slot30provides for an interference fit key arrangement between the tool holder12and the ball canister60, thereby eliminating any variance in the radial location (in a direction transverse to the longitudinal y-axis) of the tool holder12with respect to the clamping mechanism14.

It will be appreciated that the invention is not limited by the use of the interference fit screw55as the abutment surface, and that the invention can be practiced with other comparable means that causes an abutment surface to engage the angular portion on the tool holder. For example, the invention can be practiced using a pin as an abutment surface, rather than a screw, that can be press fit into the aperture48on the support block32.

In another aspect of the invention is shown inFIGS. 9-11. In this aspect, an angled portion66aof the first side wall66of the key64, rather than the front portion55aof the interference fit screw55, is an abutment surface located along the first side wall66of the key64to provide for an interference fit arrangement between the tool holder12and the clamping mechanism14. Specifically, when the tool holder assembly is placed in a locked position during the clamping cycle, the angular portion33aof the key slot30contacts the angled portion66aof the side wall66of the key64on the canister60to cause the key slot30to undergo elastic deformation and allow simultaneous contact between the angled portion66aof the first side wall66and second side wall68of the key64and the surface31and the angular portion33aof the surface33of the key slot30, thereby providing for an interference fit key arrangement between the tool holder12and the clamping mechanism14.

The documents, patents and patent applications referred to herein are hereby incorporated by reference.