Abstract
Increasing demand for better quality products and higher production rates requires a more complete understanding of drill dynamics. A transverse vibration model for drill bits is presented which includes the effects of gyroscopic moments and rotary inertia. The model is used to demonstrate the significance of these effects, and of complex drill geometries, on the natural frequencies of drill bit transverse vibration. Advances in bearing technology are likely to increase spindle speeds to more than 60 krpm; a speed at which gyroscopic moments and rotary inertia were found to have significant effect. The most significant parameter associated with complex drill geometries was found to be the number of flutes. Using a comparable three or four fluted drill versus a two fluted drill can increase the stiffness and, thus, the fundamental frequency of the drill bit by as much as 54%. Other complex drill geometry parameters (material properties, web taper, coolant holes) were not found to be as significant.
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