What is the best diameter for steel ball bearings? Would three 1" ones crush faster than twenty 1/4" ones? I'm grinding consumables so I can't use lead.

Well, one could take a sledgehammer or take fine grit sandpaper and see how long each take to grind up something. The time it takes to grind something and how fine you want it are usually mutually exclusive.

Are ball mills good for anything besides chemistry lab stuff? Food? Anything?

I have all those paint motors that'd be perfect for making ball mills, but I don't know what I'd grind in it. I just have an urge to build one. I could sell them on ebay maybe? I got 9 motors and a lot of time, and a lathe, so I could probably make a sturdy mill out of wood. Would wood work ok?

depends what your grinding. of course, more balls = more surface area = faster grinding. however, more balls = smaller balls = less mass = inability to grind harder substances.

What is the problem with using lead balls on food. You could try ceramic or aluminum. Plutonium is a good option too.

I think you'd have better luck with a bunch of 1/4" spheres. Steel is safe for most anything except black powder, if you ever care to make some.

Nerdlock, plutonium is one of the most poisonous elements. Even a few micrograms can kill you. I suggest not using it.

lol troll'd

you could use whatever you want, probably something that wont transfer to your food. would brass balls work?

btw if youre grinding "consumables" im assuming its cannabis. in which you should use a mortar and pestle. though a M&P would actually suit all your kitchen grinding needs. i even use them to make confectioners(icing) sugar