A grinding wheel is made up from an abrasive composite material. A cementing matrix bonds the course-particle abrasive aggregate together in the circular shape of a wheel. The centre part of the grinder wheel is made from steel and usually, has a hole in the centre to allow the wheel to be attached to a grinding machine.
Grinding wheels are finely balanced and can be rotated at high speeds. The wheel can be brought into contact with a metal work piece, which is usually also rotating. Part of the surface of the work piece is removed in a highly controlled and precise manner. This is precision grinding. Of all the machine tools that can perform high precision work, milling machines, boring machines and lathes, for example, the grinding machine using high-quality grinding wheels is the one that can perform machining to the very tightest tolerances and greatest precision.
You may think that the thickness of a human hair is a very small measurement, and it is, but it pales into insignificance when compared to the level of precision that it is possible to attain with a grinding wheel. A human hair is, on average, about 0.1 millimetres thick, or one-tenth of a millimetre, which is itself a tiny measurement. However, with precision grinding it is possible to work to tolerances as low as plus or minus 0.001 millimetres. That is one-hundredth of the thickness of the average human hair – a truly minute measurement indeed.
When you use a grinding wheel to achieve a very high-quality precision, you also get a very smooth and shiny finish on the surface of the work piece. This usually mean there is no need to polish the work piece surface, which can be a costly and time-consuming procedure. This, in turn, helps to keep manufacturing costs and times to a minimum.
Precision grinding should not be confused with bench grinding. A bench grinder has a very similar grinding wheel to that of a grinding machine, but it lacks the means to perform precision grinding. A work piece can be hand-held and brought into contact with the rotating grinding wheel, but the main purpose of a bench grinder is to remove excess metal in a controlled, but rough and imprecise manner.
There are different types of grinding wheels. They can differ in both the composite material and shape. In general, the harder the material being grinded, the harder the composite material of the grinding wheel needs to be. The abrasive aggregates that make up a grinding wheel can be composed of aluminium oxide, silicon carbide, ceramic, diamond or cubic boron nitride. Grinding wheels can be shaped as straight, cylindrical, tapered, straight cup, dish cup or saucer wheel.
Grinding wheels are a consumable item. They wear out with use and need to be replaced. Obviously, harder composites will last longer on average than softer composites, and the life of a grinding wheel will also depend on how much it is used. However, the rate of wear can usually be predicted fairly accurately for any given process.