Rock grinder.
https://s3-us-west-1.amazonaws.com/h...ck_grinder.gif
Previously:
https://www.homemadetools.net/forum/...3037#post97899
https://www.homemadetools.net/forum/...2114#post75761
https://www.homemadetools.net/forum/...2360#post76209
https://www.homemadetools.net/forum/...1250#post74040