Grain flatten

• 

  Make the grinding stone contacted with the workpiece surface
  that the actual grinding process occurs.

• 

  While reciprocating and rotating the grinding stone or the workpiece
  the bond wears less, so self-sharpening does not occur.

• 

  The cutting edge of grains wear down in use and become dull,
  so the grains do not penetrate into the workpiece.

• 

  This process that self-sharpening does not occur,
  so the grains become dull and they do not grind is called
  Grain flatten.