Cutting discs come in various grades, materials, grain size and spacing, and abrasive types. Most of these characteristics are displayed on their labels to assist you in purchasing the correct wheel for the job.
The actual abrasive type of the cutting disc will depend on the hardness of the material you intend to cut. The different types of abrasives are discussed in a previous article, Choosing an Abrasive. The most common abrasive materials available include Aluminium Oxide (A), Silicon Carbide (C), Diamond (D, MD, SD) and Cubic Boron Nitride (B). The material type is usually displayed on the label in the form of an acronym or a single letter, but some labels may contained detailed abrasive composition specifications.
The type of bond determines how the wheel holds the abrasives. The wheel bond largely affects the wheel speed and the finish it produces. The most common wheel bonds are Vitrified (V), Resinoid (R), Silicate (S), Shellac (E), Rubber (R) and Oxychloride (O).
The wheel grade determines how tightly the bond holds the abrasive. Wheel grade can also affect wheel speeds, feed rates and grinding depth. These are labelled with alphabetic letters - A being the softest and Z being the hardest.
The grain size determines the physical size of the abrasive grains in the wheel. The larger the grain, the faster the cutting and the poorer the finish. Grain sizes are measured in numerals between 8 and 600, 8 being the coarsest and 600 being the finest.
Grain spacing or density is the ratio of the bonded abrasive and air space. The density of the wheel has a large effect on the surface finish. Less dense wheels will cut freely and more widely or deeper with less coolant. Grain spacing is indicated through numerals between 1 and 16, decreasing density with increasing numbers.
A typical grinding or cutting disc label will contain these characteristics in an alphanumeric product specification code as explained in this article. Accompanying these specifications are the maximum rotation speeds in m/s and rpm, the purpose or field of application and the dimensions (diameter, thickness, arbor hole) in mm or inches. Make sure that the label also contains proof that the disc is ISO standards compliant.