IN SELECTION OF THE GRADE OF WHEELS TOLLOWING FACTORS ARE GENERALLY CONSIDERED:

     1.Hard wheels should be selected for grinding soft materials; while soft wheels for hard materials; but when very soft and tough materials are to be ground, soft wheels should also be selected as the working surface of the wheel is easily loaded with chips.
　　In grinding workpieces of less heat conduction, less hard wheels are also used so as to prevent them from burning.

　　2.When the contact area between a wheet and a workpiece is large in the course of grinaing. less hard wheel should be selected. For form grinding, in order to ensure the geometric size and precision of the workpiece, wheels of properly higher hardness may be selected. In order to avoid burning and annealing, wheels of too high hardness should not be used for sharpening cutters.

　　3.In the course of grinding. it higher speed of the wheel is used ,lower hardness of it should be selected; if high speed of the workpiece is used, proper higher hardness of the wheel should be selected. Wheels used in dry grinding should be of 1 to 2 degrees softer than those used in wet grinding.