Grinding wheels and polishing wheels can complement each other, in a way. Once a work piece has been ground down to the correct dimensions, it can be polished to a high finish; the two are really part of a single process. Of course, grinding wheels can be used on their own, and the same goes for polishing wheels.
Grinding wheels are made from an abrasive composite material. The course-particle abrasive aggregate that makes up the wheel is bonded tightly together with a cementing matrix into the circular shape of a wheel. The grinding wheel is rotated around its centre, which is an inserted metal part with a hole in it. This allows the grinding wheel to be attached to a grinding machine where it can be rotated at high speed to become a highly efficient machine tool.
Polishing wheels are similar to grinding wheels in their general make up, but instead of a course-particle abrasive aggregate, the wheel is made from a compressed soft material, such as cotton, for example. As a polishing wheel does not require any kind of precision engineering, unlike a grinding wheel on a precision grinding machine, its centre part can be made from stitched leather, plastic or shellac. These centres can be fitted tightly on to a tapered spindle.
Polishing wheels, also known as buffing wheels, are available in various diameters. The size to use will depend on the work piece requiring polishing. They can be as small as 25 millimetres in diameter, up to 15 centimetres in diameter or more. There are many different styles and types of polishing wheels, but they all are available as either combed or uncombed. The main difference between the two is that the uncombed type needs to be broken in. They are rougher with a harder surface than a combed wheel.
Grinding machines are used for high precision work. They can produce work to extreme tolerances of plus or minus 0.001 millimetres, if required. This is a measurement of about one-hundredth of the thickness of the average human hair, which is a very tiny measurement indeed! Grinding machines should not be confused with a bench grinder. Technically, this is a grinding machine, but it is not used for extreme accuracy. A bench grinder usually has two grinding wheels, one rough and one smooth, and the work piece is usually hand-held, resting on a solid guide and fed in to the revolving wheel to perform rough grinding. Bench grinders are often used to sharpen cutting tools for lathes or drilling machines.
Grinding wheels are available in various different types. Silicon carbide wheels are useful for light grinding and cleaning of non-ferrous metals. Wire wheels and brushes are used mostly cleaning and smoothing out rough surfaces, and are useful for non-ferrous metals. Aluminium oxide and ceramic wheels are useful for light grinding, and the hardest of grinding wheels are those made from industrial diamond and cubic boron nitride. There are also a number of useful grinding accessories available.