One of my recent battery builds required some unusual terminals, which I figured I'd make, but I didn't have any copper stock of suitable size... I already had some experience melting things, so it turned out to be a piece of cake... some pictures below. Besides the obvious caveat with machining equipment being expensive, the actual copper element is pretty affordable - electric furnace can be purchased on Ebay for less than $200. I went the lazy route of making a very rough piece of stock with the intention to machine it, but it's possible to cast much nicer bus bars that are ready to use after minimum clean up. Source material for melting was scrap wiring, so definitely decent grade of copper in terms of conductivity.