As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine such as a milling or boring machine to securely interface a cutting tool to the machine during the cutting of a work piece. A rotary cutting machine typically includes a motor-rotated spindle to which a tool holder is attached, the tool holder being configured to accommodate a shank portion of a cutting tool which is ultimately used to cut a work piece. The attachment of the tool holder to the spindle is generally accomplished by providing a cavity in the spindle into which an upper end or shank portion of the tool holder is secured, as with an externally threaded bolt which is advanced through a portion of the spindle and is threadably received into an internally threaded bore extending axially within the shank portion of the tool holder. In most prior art tool holders, a central aperture is also formed in a lower end or mounting portion of the tool holder for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine via the tool holder. Subsequent to the insertion of the shank portion of the cutting tool into the central aperture of the tool holder, the shank portion of the tool holder is drawn or pulled tightly into the spindle by the tightening of the above-described bolt so as to rigidly maintain the cutting tool within the tool holder.
Though interfacing the cutting tool to the cutting machine, prior art tool holders typically possess certain deficiencies which detract from their overall utility. More particularly, while slower rotational speeds generally permit the cutting machine to perform adequately, high speed cutting, which is preferred, can cause substantial difficulty in producing a satisfactory work as a result of the development of vibratory forces that occur between the spindle and the tool holder. Specifically, at higher rotational cutting speeds, the cutting tool often begins to chatter or vibrate such that adequate tool control cannot be maintained and damage to the work piece, along with potential injury to the operator, can realistically occur. More particularly, the transfer of the harmonic resonance into the tool holder may give rise to slight movements thereof relative to the spindle, and in extreme cases may result in the tool holder loosening within the spindle. As will be recognized, the resonance of the tool holder relative to the spindle results in the cut in the work piece being substantially out of tolerance.
A further deficiency with prior art tool holders is that the manner in which the shank portion of the cutting tool is secured within the central aperture of the tool holder often results in the non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is unacceptable in modem, high tolerance machining applications such as those performed on a vertical milling machine wherein minor variations in the concentricity of the cutting tool within the tool holder often cause catastrophic failure in the cutting operation.
The present invention addresses these and other deficiencies of the prior art tool holders by providing a tool holder which includes a dampening member for eliminating the harmonic resonance which typically occurs during the use of cutting tools in high speed milling applications. In the tool holder constructed in accordance with the present invention, the non-concentric mounting of the shank portion of the cutting tool within the tool holder is also substantially eliminated by the heat shrinking of the shank portion of the cutting tool within the tool holder. These, as well as other features and advantages attendant to the present invention will be discussed in more detail below.