Metal Spinning?

I feel that one of the primary missions of anyone with a blog is to answer questions. So it is time, once again, for me to answer a question that you did not even know you wanted to ask. Ready? So your question is:

"How do they form nearly perfect spheres (and hemispheres) out of aluminum or other metals? Shouldn't that be pretty difficult?"

The answer is metal spinning. It doesn't sound amazing, but it looks amazing when you watch metal spinning on video. That's when you realize it's totally awesome.

(Video is from Century Metal Spinning of Besenville, IL)

YouTube has an example from a metal spinning company that is making a vase:


I feel like that NBC public service program, The More You Know. Except they deal with smoking, violence prevention, HIV/AIDS, and other public health / public policy priorities, while I deal with machining metal. Actually, perhaps I should post more about machining metal to tight tolerances - it's an important subject that just does not receive much attention in our society. Children in our country really have no idea how hard it is to hold a .002" profile tolerance. Hell, given the general state of knowledge about engineering in this country, almost no one has any idea why tolerance analysis is important. No one discusses advanced manufacturing or design, I mean, did you know such a thing as water-jet machining existed?