Both the inner ring inner bore machining of the bearing and the inner raceway machining of the outer ring can be machined by the inner circular mill through a plunge or oscillating type. The grinding process is divided into coarse grinding, semi-finishing, fine grinding and non-sparking grinding because of the different application parameters. Inner ring machining is called inner hole grinding. The outer ring machining is called the outer ring inner race grinding. Since the inner race of the outer ring is in direct contact with the rolling elements, the machining accuracy is usually higher than that of the inner ring.