Positioning base the choice of gear shaft on the surface of the primary processing purchase, to a large extent planetary gearbox depends on the selection of locating datum structure features and the main shaft of the shaft parts on the surface of the main location accuracy requirement is decided the axis as benchmark may be the ideal not only make sure that benchmark is unified, and make the locating datum and the look datum coincidence outside circle to get crude benchmark additionally, on both sides of a razor-sharp hole for good benchmark concrete also notice the following points: (1) when the choice between machined surface area when the positioning accuracy of high, greatest completed in a clamping surface area processing (2) for rough machining or when two end middle holes (such as spindle cone hole) can’t be used intended for positioning, to enhance the stiffness of the process system during workpiece processing, only cylindrical surface area or cylindrical surface and one end middle hole can be used as positioning reference