Aluminum casting processing methods include manufacturing, self-processing, cold rolling, hot-rolling, milling and extrusion molding, etc., for example, milling and extrusion molding is common practice. From the perspective of extrusion molding principle, the drilling method can be divided into the profiling method and the fan forming method (also called the forming method). Fan Cheng method is a common method in gear shaft machining, such as gear shaping, gear hobbing, gear grinding, etc. should belong to this method. Fan Cheng method can use a CNC blade to extrude the standard and supervised modified gear tooth profile with the same modification coefficient, the same gear force angle but different number of teeth, and the extrusion molding accuracy is high. When using the Fan Cheng method to extrude the gear shaft , The top of aluminum castings of CNC machine tools sometimes choose too much the roots of the transmission gears of the transmission system, and the precision parts company cuts off a small part of the open gear position of the gear teeth, resulting in undercutting. The undercutting of the gear shaft will reduce the compression resistance, reduce the weight, and reduce the load-bearing capacity. Therefore, the project construction should strive to avoid undercutting.