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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 Holzer Hartstofftechnik 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. 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).
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. |
on a traditional grey grinding wheel is
asking for trouble with shortened tool life and an overheated cutting edge. The newer 'breed' of Aluminium Oxide wheels, often known as 'white wheels' for obvious reasons, have been the favoured solution to this problem for
some years now. These wheels give improved results with HSS tools because their grit is sharper than that of the older-style grey wheels.