A New Method for Reliable Rotary Tool Shank Use at Speeds above the Critical Speed Range

Dynamic tool characteristics affect both the design and the use of rotary tools applied to high-speed cutting. At present, spindle-driven tools commonly operate at speed values below their critical bending speed. Currently, this is the only way to guarantee reliable tool operation. Consequently, the low natural frequency – in particular for tools with a high length-to-diameter ratio – often results in spindle speeds that utilise neither the cutting materials’ nor the machine tools’ potential. The paper elucidates a method to design tool shanks and tools to be run above the critical speed, as well as its implementation. The reliable and safe operation of these special tool shanks is based on the physical effects of self-centering and self-balancing, which come into play above the critical speed.