Your question is complicated by a lack of good information. This is not intentional, however, using CBN wheels or diamond wheels with a Tormek is an after thought. The CBN market is primarily woodturners using eight inch high speed dry grinders. The Tormek market uses primarily the traditional Tormek grinding wheels.
When I started researching CBN wheels several years ago, I corresponded with Dave Sweitzer of D-Way and Ken Rizza of Woodturnerswonders. I trust both of them, however, both of them inadvertently gave me inaccurate information regarding using their CBN wheels wet with the Tormek. I attribute this misinformation to well meant high speed dry grinding backgrounds.
Both brands of CBN wheels work well wet with a Tormek, The keys to successful use are using an antioxidant solution and not leaving the wheel in water. Diamond wheels have the same anti oxidant and dry storage requirements. When used this way, I have had good success with both CBN and diamond wheels. Ignoring these two usage requirements was what caused Woodturnerswonders to void the warranty if used wet. The problem is not the wheels; the problem is carelessness.
We have been brainwashed with the "need" to have perfectly flat, polished backs on our bench planes and chisels. Once you learn David Charlesworth's ruler trick, you will never again waste time flattening the entire back of a plane iron. Only a millimeter or two is needed. This is easily achieved with a bench stone. For fine work, a chisel back should be flat and the part near the edge highly polished. Rougher work is not nearly so critical. How many chisels do we really need for hand cutting dovetails. Chisels are marketed in sets. How many of those dozen chisels do we really need. If we buy top quality, factory flat chisels, and only a very few sizes, we will have no need for side grinding with either CBN or diamond. In my opinion, side grinding is a marketing strategy designed primarily to sell more expensive wheels.
My work with CBN and diamond wheels has been almost entirely with searching for a coarse wheel for the Tormek. The SG is frustratingly slow for heavy grinding. The problem is the grit size, not the grit material. Norton 3X grinding wheels in 46 or 80 grit make formidable grinding wheels for the Tormek. Tormek has never been able to get past its one wheel made more versatile with a stone grader philosophy. In my opinion, a proper coarse grit wheel, either Norton, CBN or diamond, eliminates the need for a dusty dry grinder conversion.
I am withholding my thoughts on the SB blackstone until I have a chance to use an 80 grit diamond dressing plate with it. (Wootz' recent post) This may solve the glazing problem which has caused me to sideline my SB.
I now feel confident that the historic lack of a coarse grinding stone has been solved with any of the three options, I will start thinking about finer stones for day to day sharpening. My gut feeling is that the SG, if kept properly trued and dressed, is quite adequate for most users, including me. Anyone who is actually doing high volume knife sharpening might think a diamond or CBN wheel in the four to six hundred grit range is essential. As long as that "need" is only a future possibility, I would stay with the SG and develop your skills. I would follow the forum closely for diamond plate options to the stone grader.
I think we are still in early days with both diamond and CBN. Chances are that future developments will cause your next wheel not to be your "forever" wheel. For anyone looking to buy a second wheel in diamond or CBN, I would look for a simple, straight wheel in a fairly coarse grit, the 360 grit in diamond or the 180 or 80 grit in CBN. For those of us with a T4, the DWC-200 is a real joy to use (360 grit diamond wheel marketed for the T2, but quite usable with the T4).
Between diamond and CBN, I don't feel there is a bad choice. Both work well.
Ken
