"End Mills for Graphite" rake wear (crater wear). At higher cutting speed, cutting large thickness of the plastic case of metal processing, heat resistance and abrasion resistance when the CNC tool slightly less, chip rake face often grind a crater. The rake face crater generated corresponding to the place, its highest cutting temperature, and therefore also the maximum wear, thereby forming a recess (crater). Between the crater and the cutting edge of a small edge. In the wear process, gradually expanding the width of the crater. When extended to make the crater edge becomes very narrow, greatly weakened the strength of the cutting edge, can easily lead to chipping. Crater wear KT represents the amount of its depth.