Positioning base the planetary gearbox decision of gear shaft on the surface of the primary processing order, to a huge extent depends on the selection of locating datum structure characteristics and the primary shaft of the shaft parts upon the surface of the primary location accuracy requirement is decided the axis as benchmark is the ideal not only ensure that benchmark is unified, and make the locating datum and the look datum coincidence outside circle pertaining to crude benchmark more commonly, upon both sides of a sharp hole for fine benchmark concrete also note the following points: (1) when the decision between machined surface when the positioning accuracy of high, best carried out in a clamping surface processing (2) for tough machining or when two end center holes (such as spindle cone hole) cannot be used meant for positioning, to improve the stiffness of the process system during workpiece processing, just cylindrical surface or cylindrical surface area and one end center hole can be used as positioning reference