Main spindle apparatus of machine tool.

摘要

In a combination of a main spindle (1) and a tool holder (14) of a machine tool, a male screw (11c) is formed on an outer surface of the main spindle at its lower end portion and a plurality of keys (12) are provided on a lower end face of the main spindle. A tool holder is detachably secured to the lower end of the main spindle by means of a clamping nut (13) having a female screw cooperating with the male screw of the main spindle such that said keys are inserted into corresponding key recesses formed in an upper end face of the tool holder. Within the main spindle, there is arranged a driving shaft (2) movably in an axial direction. Within the tool holder, a piston member (21) is arranged movably in the axial direction. To a lower end of the driving shaft (2) is provided a projection (20a) having a circular recess (20b) formed in an outer surface thereof. To an upper end portion of the piston member (21) are secured a plurality of steel balls (26) movably in a radial direction. A lower end of the piston member is formed as an inclined surface (23) which is engaged with a cam surface of a tool fitting plate (24) arranged movably in the radial direction. When the driving shaft is moved downward, the balls are inserted into the circular recess formed in the projection of the driving shaft so that the driving shaft is coupled with the piston member. Therefore, by moving the driving shaft up and down, the piston member is also moved up and down and this movement of the piston member is converted into the radial movement of the tool fitting plate. In this manner, a radial position of a tool can be controlled precisely. By moving the driving shaft upward, the steel balls are removed from the circular recess and thus the piston member is disconnected from the driving shaft, and thus the tool holder may be exchanged automatically.