Spindle attachment device for machine tool

A spindle attachment device attached, for use, to a distal end of a spindle of a machine tool, the machine tool including the spindle rotatably supported about a predetermined axis and a feeding member configured to relatively move the spindle with respect to a workpiece at least in a direction of the axis, the spindle attachment device comprising:

• a hollow casing having an internal space;
• an input shaft rotatably supported inside said casing;
• an output shaft rotatably supported inside said casing;
• a joining member connected to said input shaft, said joining member joining said input shaft to said spindle of said machine tool;
• a transmitting member disposed between said input shaft and said output shaft, said transmitting member increasing a rotation speed of said input shaft for a transmission to said output shaft;
• and
• a tap holder configured to mount a tapping tool on said output shaft;
• wherein the spindle attachment device is configured to increase a rotation speed of said spindle and transmit it to said tapping tool so that a tapping process is performed on the workpiece,
• wherein said tap holder is attached to said output shaft relatively movably with respect to said output shaft along a central axis of said output shaft;
• and
• wherein said spindle attachment device further comprises elastic holding means for holding said tap holder, by an elastic force, at a predetermined position along said central axis of said output shaft.