Accurate wear modeling has always been desired, but has also been difficult and elusive. Most useful wear models have relied on experimental calibration because the physical wear mechanisms are not fully understood. This is particularly true in machining, where contact stresses and temperatures can be extremely high. In machining, the two wear modes most frequently discussed are crater wear and flank wear. Flank wear receives much more attention because it is easier to measure and the mechanism of material loss is thought to be better understood for most machining situations. This work focuses on flank wear for the same reasons. In hard turning, tool life is relatively short and both crater wear and flank wear influence the cutting process substantially. Understanding the progression of flank wear at various cutting conditions is beneficial in itself, but the ability to predict this progression will be extremely valuable. This work addresses both. Experimental flank wear progression is shown for uncoated and ceramic-coated polycrystalline cubic boron nitride (PCBN) tools at a range of cutting conditions. These data are used to calibrate a proposed mechanical wear model that predicts the progression of flank wear and tool failure points based on the cutting speed, feed, and cutting depth. The model was validated by additional experiments, which show good agreement with the predictions.