The key to manual polishing with sandpaper is: when grinding with sandpaper of the current number, make sure to finish the last number. All traces left by sandpaper are worn off! Otherwise, the marks left by the last sandpaper are difficult to complete for the sandpaper under the lower number. The task. Don't be anxious, you must grind more when you start to touch this.

  Another trick is: the grinding direction should be perpendicular to each other, so it is easy to see if the trace of the last sandpaper is worn off. Ratio for example, No. 100 is vertical grinding, then no. 400 is horizontal grinding, and No. 1000 is changed back to vertical grinding. After changing the sandpaper of the next number, the direction of friction is perpendicular to the current one.