PURPOSE: To prolong the life of a medium and maintain abrasive force by forming projected/recessed sections in a grain form on the flat surface of the medium.

CONSTITUTION: The dimension of projected/recessed sections in a grain form formed, for example, on the upper surface of a medium depends on the amount of removal from a work. For example, when the work is made of plastics, it is desirable that height is roughly 0.1 to 0.5mm, and width is roughly 2 to 3mm. Furthermore, the shape of the tip end section of the projected/recessed sections usually includes an angular section, it shall be, however, tapered or curved depending on the amount of removal from the work. And a medium 2 made of resin or ceramics is recommended, which is lighter than metal and excellent in wear resistance.