It might be possible to grind coffee fine enough with mortar and pestle. I have used the blade type coffee grinders, which aren't very good for grinding coffee, to make flours from grains. It might be possible to grind coffee fine enough with a blade grinder, but probably not. The process for making chocolate from cocoa beans uses a roller grinder and is called conching. This process is used to make Coffee Thins. Coffee Thins look like chocolate, but they are coffee and (probably) cocoa butter. Small roller mills are used in India to grind spices and they occasionally show up here in the US. I think that these roller mills might also be used to grind pigment for paint. If you can find one, they are pretty pricey. A mortar and pestle and some persistance might be the simplest way to make micro fine coffee. I have wanted to mix coffee and dark chocolate with almonds to make a breakfast bar, but the coffee always seems to be gritty. There are chocolate covered coffee beans made for snacks, but I've never tried the commercial ones and mine did not turn out so well.