wrote in message
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On Wed, 26 Dec 2007 02:05:42 GMT, "Harold and Susan Vordos"
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Why is one white and one grey? The Al2O3 white one is meant for HSS
and apparently does a better job on that, so what is the grey one
meant to do?

Sorry----I failed to address your question about the gray wheel.

I think you'll find it is bonded harder than the white one, so it is
intended for grinding soft materials, such as mild steel, or even high
carbon steels in the annealed condition. The rule of thumb is hard wheels
for soft materials, and soft wheels for hard materials. It's all about how
long it takes for the wheel to shed dull bits to re-sharpen itself.

Hardness, in grinding wheels, is not related to the media, it's related to
how the wheel is bonded. A J wheel is softer than an M wheel.

Harold