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3D3DElectrochemical machining bit.
This is a cheap peace sign earring from the mall, probably made mostly of tin, which I have soldered to a short copper pipe and then used as a bit to carve a (rather blurry) peace sign into a piece of solid steel (shown under iron). The fact that you can set tin head to head against steel and have the tin win is remarkable. It's possible because the machining happens entirely due to electrochemical etching (like electroplating in reverse), not mechanical force. In fact the bit never touches the work: If it does there's a short circuit and the process stops.
The method is called electrochemical machining, and it's described in my July, 2009 Popular Science column.
Source: Theodore Gray
Contributor: Theodore Gray
Acquired: 28 June, 2009
Text Updated: 29 June, 2009
Price: Donated
Size: 0.5"
Purity: >50%