J. Ford Brett

Bit whirl; A new theory of PDC bit failure

This paper presents the results of a study showing that the most harmful polycrystalline-diamond-compact (PDC) bit vibrations can be attributed to a phenomenon called bit whirl. During whirl, the instantaneous center of rotation moves around the face of the bit, and the bit whirls backward around the hole. Cutters on a whirling bit can move sideways, backward, and much faster than those on a true rotating bit. The impact loads associated with this motion cause PDC cutters to chip, which, in turn, accelerates wear. Laboratory and field results show the detrimental effects of whirl on PDC bit rate of penetration (ROP) and life.