FRETS.COM
Shop Tip #348
© Frank Ford 2006; Photo by FF

Before you even think about mounting a new (or used) grinding wheel, give it the two-screwdriver treatment.  Hold it with one screwdriver and bonk it with the handle of another. You should hear a nice metallic "ring."  If not, get rid of the wheel - it's cracked and likely to explode when it gets up to speed!