Cubic boron nitride (CBN) replacment wheels for bench grinders.
Although we in the woodworking "industry" have done much to improve the performance of our sharpening systems over the years, especially in regard to the grinding wheels which we use (remember when folk tried to sharpen HSS on grey wheels!!), there has been little in the way of change in the fundamentals of the abrasive grinding materials we use. A recent introduction into the market by Diamet & The ToolPost changes that, calling upon expertise which has been in the domain of engineering manufacturing but which remained unattainably pricey for non-industrial use until now. That development is the use of CBN grinding wheels.
What is CBN? The acronym "CBN" (a trade mark of General Electric Corp.) 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. 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 though we strongly recommend the use of the precision aluminium bushes and flanges listed below for an accurate installation. Click for advice on bush size selection. 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 incorporate 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 guidance for selection follows. Note that the grain sizes of diamond, CBN and other similar abrasives are not measured in the same way as standard oxide grits. We have therefore tried to give an indication of the ground surface as well as stating the true grain size:-