The carbide rotary burs with the shape of a cone upside down are kind of very special cutting tools. They have a very important application in model machining. And the function could not be substituted by any kind of other cutter. This paper uses a hyperboloid of one sheet to imitate the cone, uses the straight rural line as the cutting edge, and presents a simple method to machining this kind of cutter with helical cutting edges. Only the tradition machine tool is needed for the generation of this kind of complicated cutting tools.