Positioning base the choice of gear shaft on the surface of the primary processing order, to a sizable extent depends on the selection of locating datum structure features and the primary shaft of the shaft parts upon the surface of the main location accuracy requirement is decided the axis since planetary gearbox benchmark may be the ideal not only ensure that benchmark is unified, and make the locating datum and the design datum coincidence outdoors circle for crude benchmark more commonly, upon both sides of a sharp hole for fine benchmark concrete also take note the following points: (1) when the decision between machined surface area when the positioning accuracy of high, greatest carried out in a clamping surface processing (2) for rough machining or when two end middle holes (such as spindle cone hole) cannot be used pertaining to positioning, to enhance the stiffness of the procedure system during workpiece processing, just cylindrical surface or cylindrical surface and one end middle hole can be used as positioning reference