What is CBN? The acronym "CBN"
stands for Cubic Boron Nitride: a ceramic grain almost equalling diamond in hardness but which can be used for sharpening High Speed Steel (the material of which most turning tools are now made). The suitability of CBN for grinding HSS is important because, despite attempts to use it, diamond is not a suitable abrasive grain to use when grinding tools on a high speed dry wheel as it affects the steel at relatively low temperatures - well within the range of temperature achieved when grinding, even briefly.

These outstanding wheels, which have an almost indefinite life if treated with respect, are used in place of a normal granular wheel on a 6" or 8" high speed grinder. Thanks to the nature of the bonding between the CBN grains and the supporting steel hub, the wheels can be used dry, without coolant. Very little pressure need be applied to sharpen the tool, the weight of the tool alone being enough in many case. The grind created is very fine - akin to a 100 grit, or finer, finish - and material removal is fast. Unlike normal grinding wheels, there are virtually no sparks produced and the wheel and the tool remain very much cooler than is the case with conventional wheels, making it almost impossible to burn or blue the tools unless the user is very heavy handed or careless.

The wheels are supplied with a 32 mm (1.1/4") bore and can be bushed to suit most popular shaft sizes using standard grinding wheel bushes. Wheels are available to suit both standard, narrow wheel, grinders and those with the extended width wheels. In addition to the edge of the wheel, a distance of approximately 15 mm of one side face is also coated with CBN grains (see illustration) - excepting on the coarse grit wheels which have no side coating.

Finally, we also offer aluminium grinding wheel mounting bushes to suit the most common sizes of grinder spindles. Compared to the "normal" plastic bushes these solid turned bushes offer far superior wheel alignment and support and fit very closely within the wheel bore, permitting no radial movement. The bushes incorprate a substantial flange, giving good support to the wheel as well as serving to ensure that the wheel is mounted square to the grinder spindle. These aluminium bushes should be considered as essential where heavier wheels, such as the CBN wheels, are in use.

The wheels are offered in a choice of grit grades and the guidance for selection is as follows:

Extra-Fine: The smoothest grind available, finer even than a whetstone so suitable for finish grinding of bench tools. Tools can be burnished directly after this grind.
Standard: The General Purpose grit for most sharpening, eg. of turning tools. (By any other standards this would be considered a fine wheel!)
Coarse: Use only for re-shaping tools. Fast material removal. Coarsest finish - though still finer than many standard grinding wheels will produce!