Chip wrote:

: The harder the material that you want to grind, the more friable you
: want your wheel to be. When a grain becomes dull, you want it to break
: off and expose a new sharp surface. If this does not happen the wheel
: will glaze over and will not grind anymore. Thus white aluminum oxide
: will be suitable for harder material while brown aluminum oxide will be
: okay for softer material such as mild steel. Silicon carbide will be
: suitalbe for non-ferrous material such as aluminum.



You bring up aluminum. There is a post at Lee Valley's website, stressing
that you should never grind steel and aluminum on the same wheel.
It apparently can create thermite, and the result can be an exploding
wheel.

-- Andy Barss