Pieces of soft metals lodge themselves into all the nooks and crannies of the steel grinding wheel. When they heat up from regular grinding, they expand and force the wheel apart. While the wheel is spinning at high speed, pieces will fly everywhere. Unless, of course, the wheel is desigened for grinding soft metals. Then it's okay.
Here is a blurb from http://en.wikipedia.org/wiki/Grinding_wheel: "Safety is extremely important at all times, especially when grinding wheels are involved. They are a mainstay of the engineering and construction industry and the risks involved with them may tend to be taken for granted. Safety awareness and an understanding of the materials and processes involved is essential. Appropriate safety gear must be worn and all safety procedures must be followed. Always err on the side of caution.
Contact with a spinning grinding wheel will produce a cut. Because of the heat generated in the grinding process, a burn might also be produced. Wood should never be ground on a wheel, as it can clog the wheel's pores and cause the wheel to burst, with fatal results."
Just one of many hits I got on the net. No personal mistake experience, just years of training from my employer.
