Working with aluminum can be a rewarding hobby. Most people can't say that they create works of art out of metal. The process of melting aluminum is fairly simple, you just put the metal into a crucible and heat it. The difficulty can lie in maintaining an even temperature in order to properly melt the aluminum. A furnace helps to solve this problem, distributing the heat evenly.
Mix a small batch of fire cement with water according the the mixing ratios provided on the cement bag.
Pour 1 inch of fire cement into the first coffee can and allow it to dry.
Cut the plastic tube a few inches taller than the coffee can with a hacksaw.
Seal the open bottom of the large plastic tube with duct tape.
Paint the sides and bottom of the plastic tube with petroleum jelly.
Set the plastic tube in the center of the coffee can, on top of the fire cement base.
Mix another batch of fire cement and pour it into the coffee can, around the plastic tube. Make sure the tube stays in the center. The cement should fill the coffee can all the way to the top.
Allow the cement to dry, then pull out the plastic tube. If you used enough petroleum jelly it should pull free easily.
Drill a 1-inch hole in the side of the furnace body, 2 inches up from the bottom.
Set an iron crucible to hold the aluminum in the center of the furnace.
Cut the bottom inch off of the second coffee can with a hacksaw. This will form the furnace lid.
Drill holes in the sides of the can and bolt on two handles, one on either side.
Fill the lid with fire cement and allow it to dry.
Drill a 2-inch hole through the center of the lid with a masonry bit. This will serve both as a chimney to allow heat and exhaust to escape, as well as an access hole to drop pieces of aluminum into the crucible without removing the lid (which would allow all of the heat to escape).
Place the lid on the furnace.
Light a blowtorch and direct the flame into the hole on the side of the furnace to heat it.
Aluminum melts at 1,220 degrees F. For metals with a higher melting point, you must construct a furnace with thicker walls.
Only operate this furnace away from flammable materials, with a fire extinguisher nearby. Use heavy pads or gloves when grabbing the lid handles of a hot furnace.