Positioning base the choice of gear shaft upon the surface of the primary processing purchase, to a huge extent depends on the selection of locating datum structure features and the main shaft of the shaft parts on the surface of the primary location accuracy necessity is decided the axis since benchmark may be the ideal not only ensure that benchmark is unified, and make the locating datum and the look datum coincidence outdoors circle meant for crude benchmark more commonly, upon both sides of a razor-sharp hole for good benchmark concrete also take note the following factors: (1) when the decision between machined surface area when the positioning accuracy of high, best completed in a clamping surface area processing (2) for tough machining or when two end center holes (such as spindle cone hole) can’t be used designed for positioning, to improve the stiffness of the process system during workpiece processing, only planetary gearbox cylindrical surface area or cylindrical surface and one end center hole can be used as positioning reference