For general shaft parts, outside th

For general shaft parts, outside the circle as a benchmark is reasonable, in accordance with the relevant parts of the principle of choosing rough benchmark: when the parts have not processed surface, should choose those processing surface as crude benchmark, when machining on the surface of the parts have many don't, you should choose and machining surface requirements relative position precision relatively tall not processed surface as crude benchmark, learned from the analysis of the parts, gear shaft outside the circle as a benchmark.