The principle of ensuring that the

The principle of ensuring that the machined surface of the workpiece has a certain positional accuracy relative to the unmachined surface: if there is an unmachined surface on the machined part, the unmachined surface should be selected as the rough reference, so as to ensure that the unmachined surface has a relatively accurate relative positional relationship to the machined surface . (2) The principle of reasonable allocation of machining allowances: Considering the uniformity of machining allowances on important surfaces, important surfaces should be selected as rough benchmarks. (3) The principle of easy clamping: In order to stabilize the positioning of the workpiece and the clamping is reliable, the selected rough datum is required to be as smooth and rough as possible, and no forging flashes, forging riser cuts or other defects are allowed, and there are enough support area. (4) The principle that the rough datum shall not be reused: the rough datum is only allowed to be used once in the same size direction.