The choice of pneumatic valve processing locating datum

in the processing of used as the benchmark according to the locating datum for the positioning. Locating datum choice: when choosing crude benchmark should be paid attention to make machining surface to surface has a certain position accuracy, and makes the processing surface has reasonable machining allowance. Benchmark crude can only be used once. When choosing a fine benchmark, in order to avoid the benchmark misalignment error, should choose the design basis for the locating datum for the machining surface ( Benchmark superposition principle. When the parts on several position accuracy requirement of high surface, and the surface is not be processed in an installation, in order to ensure the precision requirement, in the process of all installation should use the same benchmark (Ann Benchmark unified principle. In addition, the choice of positioning base should be easy to work piece clamping and machining, and the fixture structure is simple.