Can anyone tell me the best way to clean stove grates made of cast iron?

A stiff metal brush is best. If you do get the grates wet be sure to dry them completely.

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Cleaning stove grates - Google Search

If you have a self-cleaning oven, you can simply leave them in the oven when it is cleaning. They will loose the bright chrome patina, but be clean as a whistle. Been doing it for years

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