河南读者崔海伦来信说 ,拖拉机盘式制动器的压盘是最关键的零件 ,而压盘上 3个螺旋球窝又是关键的加工部位 ,它们加工精度要求高、尺寸不易控制。请介绍在普通机床上加工这种零件上球窝的方法。　　压盘零件如图 1所示。选择在Ｘ6 2Ｗ型万能卧式铣床上利用万能分度头加工 3个球 Cui Hailun, a reader in Henan, wrote that the pressure plate of a tractor disc brake is the most critical part. The three screw bosses on the pressure plate are the key processing parts. They require high machining precision and are not easy to control in size. Please introduce the method of machining such parts on the ball socket on a common machine tool. Pressure plate parts shown in Figure 1. Choose to use the universal indexing head to machine 3 balls on the X6 2W universal horizontal milling machine