Kookaburra: I am trying to make a smelter.
Whym: I have bought 20 in total from Auctions, but they are getting a little too prcey, an I figured if I make a smelter it will make work easier.
I think a smelter is purchasable from a tool, mining or hardware vendor. I definitely don't remember making mine. It's good to compare though, as it's often cheaper to buy the finished product than to buy ingots.
If you are into tool crafting, you should learn smelting, it doesn't make sense to buy ingots, you can mine metal and make your own. I recommend also using no-no powder to smelt large amounts of metal, because there is no buff for smelting.
Mining, smelting, and meditating for energy is a prerequisite for tinkering. Tinkering demands ingots for most things- it's only sustainable in the long run for you be able to mine 300 metal rocks and smelt them into ingots for 0 currants.