Machine tool

A machine tool, the machine tool comprising:

• a tool holder configured to include at least two machining inserts;
• and
• a ram spindle configured to fasten the tool holder in a state of clamping the tool holder and to rotate the tool holder in order to change locations of the machining inserts;
• wherein the ram spindle comprises:
• a housing;
• a center part rotatably accommodated inside the housing;
• a first outer part disposed outside the center part, and configured to be co-rotated with the center part;
• a second outer part disposed between the housing and the first outer part and fastened to the housing;
• and
• an actuator unit accommodated inside the housing, and configured to selectively move the center part and the first outer part upward and downward;
• wherein outer ribs protruding at equal intervals are formed on an outer circumferential surface of the first outer part, and protruding inner ribs spaced apart at predetermined intervals are formed on an inner circumferential surface of a cavity of the tool holder at equal intervals;
• wherein a respective protrusion is formed on each of the outer ribs, and wherein a corresponding respective depression is provided on the tool holder adjacent to each of the inner ribs, each of the depressions being configured to be seated over a respective one of the protrusions.