Refractory metal cutting tools exhibit an unusually high probability of edge chipping and gross fracture when suddenly unloaded after cutting a strong material at high speeds and feeds. After identifying three possible mechanisms of brittle fracture when a cutting tool exits a cut, that associated with so-called “foot” formation is discussed in detail. This involves a sudden shift from steady state chip formation by concentrated shear to gross fracture of the workpiece as the end of the cut is approached. The other possible mechanisms are discussed in a companion paper to follow.