I could almost do an entire different article about the questions and ideas presented here.... I started with 80 and 180 grit CBN wheels. This was in the days before the electroplated CBN wheels were available for woodturners. I picked up some D Way wheels when they first came out, and again, the 80 and 180 wheels. Being some one who is obsessed with experimenting, I now have 80, 180, 320, 600, and 1000 grit wheels. I guess I could get a 60 grit wheel, but if I need that much shaping done, I have a 36 grit belt sander for that.
I don't notice any difference in the scraper burrs between 80 and 180, so, use the 180 because it doesn't grind away the metal as fast. I have tried all the other grits, and don't notice any improvement in the burrs I use for all of my roughing cuts on bowls that I do with a scraper. Perhaps, as the wheels get finer, the burr gets weaker. I once thought that the finer wheels might almost compare to a light burnishing, but that does not appear to be true.
As for the NRS, I think I prefer the 180 grit, kind of the Goldilocks thing, not too coarse, not to fine, just right, but I am still experimenting. For the burr I prefer for shear scraping, best one is the burnished burr. I have my NRSs ground to 25/60 and most of the time I will burnish the grinder burr down, then burnish a cutting burr back up. I like a more blunt angle under the burr as it seems to support the burr better for a longer cutting life. I tried the 40/40 and 45/45 versions similar to skew chisels and didn't like them as much, in part because I couldn't get a good burnished burr on the more acute angles. The burnished burr does last a lot longer than the grinder burrs, and stays sharp longer. I have honed burrs on the NRS moving the card sideways, and it does make for a nice burr, but it just isn't as good as the burnished burr. The grinder burr is gone in seconds. Well, maybe not gone as you can still feel it with your finger, but as Tom said, "if you have to push at all with the NRS, then it is dull". The NRS is excellent for very minor touch ups on pieces, but not for any stock removal.
For shear scraping, I go back and forth, and as much as anything else, it depends as much on the piece of wood maybe more than the actual edge. I go back and forth, some times the burnished edge, some times 180 grit or 600 grit. As I said, some times it is more the piece of wood that determines what will leave the cleanest surface.
For gouges, 90% of the time I will sharpen on the 180 or maybe 320, in part depending more on which grinder is closest. When I got my first 600 grit wheel, I noticed a huge difference when making finish cuts on some punky maple. Far less tear out. So, now, when a piece is being 'difficult' that is my preferred edge for finish cuts. I have tried the 1000 grit, and more experimenting is still needed, but didn't notice that it cut much different than the 600 grit edge. I have tried hand honing with the different grit stones/cards, and that never seems to work as well for me as going to the wheel does. I don't hone the inside of my flutes. Maybe I need to make some MDF wheels for that type of honing.... Oh no, my sharpening station will get a lot bigger......
As for the skew, a tool I don't use that much, but am playing with more, I generally use the 600 grit wheel, and don't go to the 1000 grit wheel. One major discovery for me in trying to figure out this tool, is that even with a 1000 grit wheel, that leaves a burr, even with the lightest touch to the grinding wheel. It would cut fine in one direction, but not in the other, until I went to the stropping wheel on my Tormek. I recently discovered that the different honing and polishing pastes range in grits from about 800 or so for the black stuff from Norton, to 16,000 for some of the other paste formulas, and I am not sure which colored one that is. One friend is a spoon carver, and he had 4 different honing pastes. The scary sharpness that you want for your bench planes and chisels generally ends up finally in that 16,000 grit range.
As for diamond, it is the hardest substance on earth, I believe. The problem with diamond is that heat will cause it to break down. This is why diamond wheels won't work on even the standard 1760 rpm slow speed grinders. They should last almost forever on the Tormek since it turns so slow, and I think this applies even without the water bath. The Tradesman grinder out of Canada does make diamond wheels and their grinder is variable speed. I am pretty sure that it was developed for sharpening the CNC router bits, which means it is very precise, and I think it even costs more than a Baldor grinder.
As for tool steels, all I use any more is M42 HSS, and the V10. I don't notice any difference in edge durability or sharpness between the two of them. I do have a few M2 tools around the shop, but the edge holding difference is huge.
robo hippy
woodturnerswonders.com
(The bit about wheel grit suggestions is just before the conclusion at end of article).
