Experience has shown that the kind of wheel, its periphery speed, the extent of contact between the wheel and the work, and the rate of feed of the wheel over the work are essential factors in successful grinding.

The kind of wheel depends upon three factors, viz., (1) the grinding material of which the wheel is made; (2) the size of grains of this material, and (3) the strength of the cement bond holding the grains together. Wheels are made of emery, one of the many forms of aluminum oxide found in nature; corundum, an artificially made aluminum oxide much purer than emery; and carborundum, a compound of silicon and carbon. Corundum and carborundum are products of the electric furnace. These materials are crushed to powder, and the grains are separated according to their sizes. A wheel is made up by mixing grains of a certain size with a bonding material. Hydraulic cement is much used for bonding high-grade wheels. The wet mixture of cement and grinding material is moulded to shape and burned into a bonded mass in a furnace at high temperature. In operation, the wheel cuts by contact of the sharp hard particles against the material operated on, and as these particles become dull, they gradually crumble away from the bonding material and give place to sharper particles. The softness or hardness of a wheel depends upon the strength of the bonding cement.

Makers of wheels and of grinding machines supply full information of the proper kind, size and speed of wheel for each class of use.

Wheel surfaces are trued by a diamond-pointed tool held against the wheel as it revolves.