Method for forming grooves on workpiece and for dressing a grindstone used in the groove formation

A method for dressing a grindstone used in a grinding apparatus by means of a rotary dresser having a dress groove, comprising:

• a first positioning process for relatively moving the grindstone in a first direction along the axis of the rotary dresser from a position in which the grindstone faces an inner surface of the dress groove, detecting a first contact position reached the moment the grindstone touches one side edge of the dress groove, and stopping the movement;
• a second positioning process for relatively moving the grindstone in a second direction along the axis, detecting a second contact position reached the moment the grindstone touches the other side edge of the dress groove, and stopping the movement, the second positioning process directly following the first positioning process;
• a third positioning process for moving the grindstone to an intermediate position between the first and second contact positions;
• and
• a dressing process for moving the grindstone toward the inner surface of the dress groove in a direction perpendicular to the axis, thereby bringing a distal end portion of the grindstone into contact with the inner surface of the dress groove, the dressing process directly following the third positioning process.