Before turning the excircle, top holes can be punched at both ends of the workpiece. Also add a tip to the chuck, so that the turned-out workpiece will not have seams. Alternatively, when drilling the center hole, the excircles at both ends of the workpiece can be turned out and chamfered, and then a cone pit can be turned on the chuck of the lathe. When turning a workpiece, one end abuts against the cone pit of the chuck and the other end abuts against the excircle of the center of the tailstock, so that the surface of the workpiece can be seamless.