I did this at TechShop Menlo Park! http://www.techshop.com
Casting is a ton of fiery hot fun! Once you try this you will never stop. It is dangerous though so properly assembling your equipment is essential in an effort to keep your face and other body parts. This is what you'll need to do:
Step 1: Furnace
Check out your furnace, make sure to clear out any debris and set a refractory brick in the middle of the inside. The brick will serve as a shelf you will place your crucible onto.
Step 2: Propane
Get a full tank of propane as running out of gas in the middle of your process is really sad. Place the propane tank as far away as possible from the furnace to prevent the heat from getting to the tank. You can imagine the tragedy that would cause so make sure to remember it! Then screw in the gas line to the propane tank. This end of the hose will have a regulator on it. The other end of the line screws into the opening located right next to the venturi air vent lid.
Step 3: Gas Flow
Open the propane tank with the valve on top. Open the regulator and keep in on high. You will need a substantial amount of fire in order to keep it going once the air is introduced. Open the line valve with handle located close to the furnace end of the line.
Step 4: Ignite!
With your gas line open and the venturi air vent lid closed light the fire! You can use a match and throw it in the furnace, I like to use a map gas torch as it allows a little more space between me and the ignition of a large fire. The fire should be big and come up to about chest height.
Step 5: Introduction of Air
With the air vent lid closed plug in the motor. You will hear the motor running but it will not affect the fire until you open the air vent lid. When opening the vent lid do it gently, and just a little bit at a time until you hear a big Hwooosh sound resembling a jet engine. This is the sound you're looking for: it means the fire is circulating inside your furnace ensuring even heating of the crucible.
Step 6: Melting Metal
Aluminum has a low melting point so it is fast and easy to melt. Use aluminum scraps of whatever kind you can get your hands on. Smaller pieces arranged with some space around them are much faster melting then a big hunk of it. When closing the furnace lid use a metal pole and do it from the sides ( it takes two people). Be careful when looking at your melting metal through the peephole on top of the furnace lid. Your eyelashes and eyebrows are the first to go.
You are now ready to use your imagination and creativity and pour molten aluminum into the molds of your choice. See investment casting instructable for assistance in this portion of your project.