The hardness of the grinding wheel refers to the hardness of the abrasive grains on the surface of the grinding wheel falling under the action of the abrasive force. The hardness of the grinding wheel is soft, which means that the abrasive grains of the grinding wheel are easy to fall off, and the hardness of the grinding wheel is hard, which indicates that the abrasive grains are difficult to fall off. Grinding wheel hardness and abrasive hardness are two different concepts. The same type of abrasive can be made into grinding wheels of different hardness, which is mainly determined by the yield and quantity of the bonding agent and the grinding wheel manufacturing process. The significant difference between grinding and cutting is that the grinding wheel is “self-sharpening”. Choosing the hardness of the wheel is actually choosing the self-sharpening of the wheel. I hope that the sharp particles of grinding will not fall off too soon, and will not break or fall off. . The general principle for selecting the hardness of the grinding wheel is to use a hard grinding wheel to prevent the abrasive from falling off prematurely when processing soft metal. When processing hard metals, in order to timely remove blunt abrasive particles to expose new abrasive grains with sharp edges (ie, self-sharpening), a soft grinding wheel is used. The former is because when polishing soft materials, the working abrasive grains in the wheel wear very slowly and do not need to be separated too soon; the latter is because when grinding hard materials, the grinding wheel’s working abrasive grains wear faster and must be faster. Update. In the case of fine grinding, to ensure the accuracy and roughness of the grinding, a slightly harder grinding wheel should be used. When the workpiece material has poor thermal conductivity and is prone to burning and cracking (such as hard alloy polishing), the selected grinding wheel should be softer.