In the case of grinding the slender shaft (l/d10), especially in the case of occasionally producing several pieces in a general tool shop, in order to reduce or eliminate the waist drum shape generated during grinding, the grinding of the lumbar drum is generally increased. Number of times and grinding time. In this way, the operator must constantly move the valve of the reversing valve to make the table reciprocate in a short range, so that the grinding wheel can be used to drum the workpiece.