SPINDLE FOR MACHINE TOOL

PURPOSE:To increase the stiffness of a bonding part, to prevent the vibration of a tool holder by high speed rotation and the runout of a tool axial line and to obtain a high machining accuracy by forming so that the tapered hole of a main shaft and the main shaft end face are simultaneously closely fitted to a tool holder. CONSTITUTION:A tool holder 8 has a fitting base 9 fitting a tool 7, the flange part 10 having an annular groove 10a for inserting an offtake arm, a taper shaft part 11 and clamp shaft part 12. The pull-in bar 42 to whose tip a collet 43 is fixed is inserted into the hollow hole 41 of a main shaft 13, the collet 4 is spread when pushed out, the tip of the clamp shaft part 12 can be inserted, and when pulled, the tip part is shrinked by the inner wall of the follow hole 41 and the clamp shaft part 12 is interposed. The flange face 10 is closely fitted to an end face 13a simultaneously with the holder 8 being pulled into the tapered hole 14 of the main shaft 13 and the taper shaft 11 being closely fitted to the tapered hole 14 and the bonding stiffness of the tool holder 8 and main shaft 13 is formed higher.