Before buying either, check carefully that the wheel and grinder will work together. I bought an axminster 8" x 40mm wheel which needed bushes to reduce the bore to match different grinder spindles. The wheel plus flanges were so wide that almost no grinder had a spindle long enough to mount it. Axy admitted that they were clearing those wheels because they didn't sell a grinder that would use it and had no idea which grinder would !
Eventually, I matched it up with Records latest 8" made in China grinder which is sold as UNsuitable for CBN wheels, and I just spin the wheel by hand before switching on to take the edge off the startup current surge.
A CBN wheel needs precision bushes and tight tolerances because there's so much weight that a little slop will cause noticeable vibration. Properly centred, they are great.
Like for like, an 8" wheel has 33% more surface area than a 6" so it'll last longer as well as making a less hollow grind.
Oh, and a little googling to find recommended speeds for dry grinding with electroplated CBN wheels gave me this :
"These wheels require speeds of approximately 30 m/s for dry conditions and 60 m/s when run wet."
When considering the use of CBN (cubic boron nitride) grains in an aerospace part grinding process, the first questions that come to mind may be associated with the grinding conditions and machine capabilities. It’s commonly assumed that CBN grinding wheels need very specific operating...
www.aerodefensetech.com
A 200mm dia wheel on a 3000 rpm grinder has a surface speed of 31.4m/S at no load. So just about right.
I'm not convinced by the comment attributed to Mr Irons.
