When the plane polishing machine is polishing, the grinding surface of the sample and the polishing disc should be absolutely parallel and lightly pressed on the polishing disc evenly. Pay attention to prevent the sample from flying out and new grinding marks due to too much pressure. At the same time, the sample should be rotated and moved back and forth along the radius of the turntable to avoid local wear of the polishing fabric too fast. During the polishing process, polishing liquid or other polishing aids should be continuously added to keep the polishing fabric in a certain humidity. If the humidity is too high, the wear scar effect of polishing will be weakened, and the hard phase in the sample will be embossed, and the non-metallic inclusions in the steel and the graphite phase in the cast iron will cause a "tail" phenomenon; if the humidity is too small, the friction heat will cause the sample to be When the temperature rises, the lubricating effect decreases, the grinding surface loses its luster, and even black spots appear. The light alloy will scratch the surface, and the phenomenon of yellowing will appear.