Make the grinding stone contacted with the workpiece surface
that the actual grinding process occurs.
The grains penetrate into the workpiece, and grind it with chips
by reciprocating and rotating the grinding stone or the workpiece.
While building up chips, the bond wears moderately.
Dull grains in use fall off, and sharp new grains are produced.
This process is called self-sharpening.
The grinding stone grinds the workpiece properly.