After the grinding wheel of grinding machine is used for a period of time, the sand grains on the circumferential surface of the grinding wheel will gradually become dull, and the grinding force of the grinding wheel will increase, so that some sand grains will be broken along a certain crystal plane, exposing a sharp cutting edge to continue cutting, which is the self-sharpening of the grinding wheel. But it can't be completely sharpened, and the grinding force drops obviously after working for a period of time. At this time, it is necessary to dress the grinding wheel and restore its grinding performance. In addition to the sinking of sand particles, the gap between sand particles is blocked by debris or sand particles, so the grinding wheel has lost its grinding ability and must be dressed. In addition, the uneven shedding of sand particles also requires dressing the grinding wheel. Dressing the grinding wheel is dressing the grinding wheel with a diamond pen. Generally, the diamond pen is installed on the base, and the base is sucked on the electro-magnetic disk, so that the diamond pen stops directly below the grinding wheel, and the grinding wheel is moved laterally to dress the surface of the grinding wheel.