Tool holder and machining method

A tool holder for use in a machine tool which is provided with a spindle in which the tool holder is installed, and a rotation angle position of the spindle is controllable, the tool holder comprising:

• an outside portion which is connected and affixed to a housing of the spindle,
• a first member having a shank which is gripped and rotated by the spindle at a first rotation speed,
• a second member rotatably supported inside the first member, wherein rotational power is transmitted from the first member, via a speed change mechanism, to the second member so that the second member rotates at a second rotation speed different from the first rotation speed, wherein the second member defines a threading,
• a conversion mechanism including a body part defining a first rack extending a predetermined length along a rotational axis of the spindle, and a threading which engages the threading of the second member, and a pivot part defining a first pinion which engages with the first rack and a second pinion, wherein the body part of the conversion mechanism is moved along the rotational axis of the spindle by the rotation of the second member through the engagement between the threading of the body part and the threading of the second member, and the pivot part is rotated by the movement of the body part of the conversion mechanism along the rotational axis of the spindle through the engagement between the first rack of the body part and the first pinion of the pivot part,
• a slider which is moved in a first direction intersecting the rotational axis of the spindle by power from the second member, wherein the slider defines a second rack which engages with the second pinion of the pivot part, the slider is moved in the first direction by the rotation of the pivot part through the engagement between the second pinion of the pivot part and the second rack of the slider, and
• a cutting edge which is moved in the first direction by the slider between an origin position and a maximum diameter position and which is rotated by the first member,
• wherein the second member comprises a clutch mechanism that is configured to prevent transmission of power from the second member to the conversion mechanism by intercepting rotation from the second member prior to transmission to the conversion mechanism,
• wherein the clutch mechanism comprises a driven component that defines the threading of the second member which engages with the threading of the body part of the conversion mechanism, and the transmission of power is intercepted as a result of rotational torque on the driven component exceeding a predetermined value.