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I have been using a negative rake scraper with good results with a burr straight off a 180# CBN wheel. Yesterday I was getting some tearout with it on the inside of an ash bowl, although another ash bowl cleaned up nicely. I honed off the burr with a 1200# diamond card and turned a fresh burr with a carbide burnisher- problem solved. I turned the burr down and back up a couple of times before I was done. Many thanks to John K. Jordan and Robo Hipppy for schooling me on this technique.
I had similar results today with a hickory bowl. Mainly from Robo Hippy's info I made a carbide burnishing tool last week and today was the first time I used it to turn up a burr on a NR scraper vs. just using the burr off the 180 CBN wheel.
I can't say for sure it was entirely the different burr that made the difference as I was also concentrating on taking very light passes with the scraper. In any case, I did successfully get a much better surface inside my bowl before sanding.
Who says you can't teach an old dog new tricks?
The burr off the grinder is generally way too big as well as being ragged and not very strong. A burnished burr will almost always work better, and can readily be adjusted (by altering the pressure you use to draw it) for a heavier cut vs a fine finishing cut. It's also faster to refresh than returning to the grinder. What's not to like? It's a little bit harder on a NRS since you have a smaller bevel to rest your diamond hone on than with a regular flat top scraper, but gets easier with practice.
I prefer the burnished burr. I don't have much luck with it on the skew chisel type NRSs though, I can hear the edge fracturing as I draw the burr, even with very light pressure. My skews are sharpened at about 25 degrees, and if you have a NRS that is sharpened at 40 or so, it may work better. It takes surprisingly little pressure to turn a burr, and you don't want to really crank on your burnisher as you raise the burr. You can turn a huge burr that way, which may not cut as well as a smaller burr.
As for the grinder burrs, again, how you sharpen them can make a big difference. Very light pressure, and you get a smaller burr. Really heavy pressure, and you get a bigger burr. Then, there are those who prefer an upside/down sharpening to raise the burr. This is supposed to make a sharper burr. I haven't really played around with that much though.
robo hippy