Our CuBoroN high performance CBN grinding wheels are heavy items and need to be mounted on a substantial bush. The plastic inserts used on standard grit grinding wheels are not sufficiently robust for this purpose.
These bushes, which comprise a flanged bush and a loose flange, are manufactured for us specifically for use with our CBN wheels. The bush is inserted in the wheel with the fixed flange to the inside - next to the motor housing - whilst the loose flange is used on the outside of the wheel, next to the retaining nut.
It is vital that these bushes are fitted dead square into the bore of the CBN wheel. If you can't slide the bush into the bore easily under hand pressure (and they are usually tighter than that) then either use a press or you can use your lathe headstock with a faceplate mounted and the tailstock quill to push the bush home. Just make sure head- and tail-stock are aligned before doing this and ensure that you support the centre of the wheel both sides so that you don't put pressure on the parts of the wheel which are plated with CBN.
Tip 1: Before sliding the bush onto the spindle we suggest taking emery paper (or you could use your woodturners AlOx cloth) or a fine file to carefully 'dress' the end of the grinder shaft such that you create a very fine 'lead', or chamfer, no more than 1 mm long. In our experience, most grinders have a burr on the end of the shaft which inhibits the bush sliding smoothly onto the shaft.
Tip 2: It appears that the folk who manufacture grinders, especially if they are based in China, believe us to be too stupid to be told the true decimal diameter of the grinder shaft. Hence they frequently describe, in manuals, labels and on product packaging, that a 1/2 inch diameter shaft is 13mm - which it is not, it is 12.7mm. To those of us who require a precision fit they are far from being the same thing. If your grinder professes to be one of these odd-ball sizes, we suggest that you carefully measure your grinder spindle
Producers of grinding wheels and special tooling using CBN abrasives to give youir tools the finish they deserve in the shortest time possible.
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 introduction into the market by Diamet & The ToolPost a few years ago changed 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. CBN grinding wheel for sharpening of woodturning tools.
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 significantly cooler than is the case with conventional wheels.