I found this interesting page on grinding metals with a grinding machine. Those machines have similar construction to a ball mill and I suppose it wouldn't be too hard to build one.
http://members.shaw....er/grinder.html
A friend of me, made 2 nice metal grinders i compiled it in a pdf file, if there any questions we could open a new topic i think:
Metal grinding machine
Link: http://www.sendspace.com/file/0z7m2v
File: The Metal Grinding Machine.pdf
Size: 1.71 MB