*** 5/31/09 *** I will be making a new, revised charcoal foundry instructable as soon as I get some spare money. This setup is adequate, but there's always room for improvement.
Step 1: Materials and Tools
-One normal sized coffee can (6")
-One hair dryer with a cool mode and preferably two speeds
-One 1.5" x 10" galvanized/black iron pipe nipple
-One soup can
Required to operate furnace...
-Long tongs or pliers to grip crucible
-Steel spoon w/ holes in it
-Heavy leather work gloves
Step 2: Making the Furnace Shell
Step 3: Making the Forced Air Blower Assembly
Next, use a little piece of tape to make sure the cool button will be held down constantly.
Step 4: The Crucible
Step 5: Using the Furnace
1. In the area between the outer shell (coffee can) and the crucible (soup can) put in your charcoal.
2. Drench it in a generous amount of lighter fluid.
3. Light it.
4. Wait for the lighter fluid to completely burn out before you turn on your blower.
5. The furnace is now ready to use.
A little info on metalcasting:
Aluminum cans tend to oxidize and burn rather than melt because they are so thin. If possible, find another source of aluminum such as lawn chair tubing, roof flashing, etc. If, like me, you use soda cans, crush them flat first to reduce surface area and they'll melt fine but with a lot of slag.
Soda cans per pound of aluminum they'll give you:
12 cans = 1/3 lb.
24 cans = 2/3 lb.
36 cans = 1 lb.
-Those are not exact numbers, but rather close.
http://www.backyardmetalcasting.com It's the best website I've seen for metal casting, building furnaces, etc.
1. When the furnace is ready and the crucible is glowing red hot, put in your aluminum.
2. Wait for it to fully melt and get very hot so it will all pour it and not remain in your crucible.
3. I pour my aluminum into mini-muffin tins to make ingots, which can be later re-melted.
-The furnace gets VERY, VERY hot during operation. ALWAYS use the leather work gloves.
-Before melting aluminum, let the can heat red hot to make sure it has an oxide coating. If your soup can does not, the aluminum could eat through the can. Getting an oxide coating is as simple as getting the whole thing to red heat. It will take on a dull blue gray color when ready.
-Make sure there is NO water in your source of aluminum. This could result in molten aluminum explosions.
-Use common sense.
-Liquid aluminum is hot enough to burn through many things.
-Keep your hair dryer away from the furnace during operation. I do not fully insert the iron pipe nipple into the furnace because it blows too much air (yes, on the low setting) and it gets too hot. Just aim your blower at the hole you made and it will get very hot. Trust me.
-However, if you choose, you can fully insert your blower into the furnace if you desire that much heat or your crucible requires it. It won't kill your hair dryer as long as you have a 10-inch or more length of iron pipe nipple between the furnace and hair dryer.
-I used a galvanized iron pipe nipple because that's all Home Depot had in stock. I HIGHLY advise against it. When galvanized things reach a certain temperature, they give off extremely toxic fumes which can give you Metal Fume Fever. Use black iron if possible. If you use galvanized, you have 2 options. Don't stick the pipe directly in the furnace, or heat the whole thing up and burn off the coating. If you choose the latter, stay away from it while it's burning off.
I was thinking this could be used as a mini-forge too. Just don't use a crucible, keep the forced air, and you could heat metal with it. While I don't think it will get it hot enough to actually forge something, I know for a fact it can be used to anneal and harden steel. I make small knives out of shaped and sharpened files with the teeth ground off, and it would work for those. I'll post here in this paragraph if I ever do that.
-Thanks for looking! Watch for more Instructables over time.