COMPLEX-GEOMETRY, ROTARY INERTIA AND GYROSCOPIC MOMENT EFFECTS ON DRILL VIBRATIONS

Increasing demand for better quality products and higher production ra tes requires a more complete undersanding of drill dynamics. A transve rse vibration model for drill bits is presented which includes the eff ects of gyroscopic moments and rotary inertia. The model is used to de monstrate the significance of these effects, and of complex drill geom etries, on the natural frequencies of drill bit transverse vibration. Advances in bearing technology are likely to increase spindle speeds t o more than 60 krpm; a speed at which gyroscopic moments and rotary in ertia were found to have significant effect. The most significant para meter associated with complex drill geometries was found to be the num ber 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 geo metry parameters (material properties, web taper, coolant holes) were not found to be as significant. (C) 1995 Academic Press Limited