Abstract
In a die machining, the unbalance of a spindle system consisting of a spindle and a tool holder decreases the machining accuracy and the holding function of the machine tool. A new method has proposed to adjust the unbalance of the spindle system and an unbalance adjustment system has been developed which able to easily adjust the unbalance of the spindle system of a high speed machining center. The outline of the system has been given. The performance test results show that the new system is effective certainly to decrease the unbalance of the spindle system.