Drill a hole to through the large metal can large enough to slide the propane nipple through. Place the hole approximately 3 to 4 inches from the bottom of the can.

Apply a 1-inch thick layer of ganister to the bottom of the metal can. Ganister is a cement-like product made from crushed firebrick and mortar.

Place several firebricks in the center of the can. Tamp them into the ganister to make sure they are seated firmly and level just below the hole for the propane element.

Construct a cylindrical inner form using the sheet metal. The form should have a diameter about 6 to 8 inches smaller than the inner diameter of the metal can. Drill a hole through the sheet metal so it matches up with the hole in the can.

Place the inner form in the can and slide a piece of pipe through both the hole in the can and the inner form.

Lay firebricks vertically between the outer metal can and the inner form. Fill the gaps between the bricks with ganister. Level off the top of the firebrick and ganister mold with a straight edge. Let the mold dry overnight, remove the pipe and the inner sheet metal form and allow to cure for several days.

Set a propane burner in the middle of the furnace and thread the propane nipple through the furnace wall and attach it to the burner.

Connect the nipple to the hose of a propane tank. Open the valve on the propane tank just a little bit and carefully ignite the burner. Use the propane tank valve to adjust the flame.