Here's a few photos of my first natural gas forge, it's interior is 7 1/2"ø x 22". You can see the forced air manifold to the right with the blower below it. There's a sliding type air gate in the neck between the blower and the manifold. The inner chamber is cast refractory. I made my own mix using "Parker High Temp. Cement" and volcanic perlite. The cement is rated for use up to 3000ºF. I bought it from "McMaster-Carr Supply". The perlite is the very same kind you can find at any garden center. I mixed the two 50/50 and cast it between two cardboard concrete form tubes. These are available from any good mason or builders supply house. The outer diameter is 12"ø and the inner is 7 1/2"ø.

After these set for one week I lit a slow fire inside them and heat cured the cylinder. Once the chamber was hard, I built the housing by rolling a plate 6" larger than the chamber itself. The chamber sits in flat bar rings welded to the inside surface of each of the end plates (see photo of the interior). The space between the chamber and the steel housing is filled with packed, dry sand. I was hoping to allow the chamber room to expand without strain and also insulate the forge. Keeping the heat in, is not only more comfortable for the smith, but makes for more efficient fuel use.

Setting the chamber in a bed of sand has worked out very well thus far. Even after a day of moderate forge work, the housing remains cool enough to touch. When I have fuel consumption information I'll be sure to update this page. Thus far there has been no stress cracking of the refractory. I attribute this to the manner in which the refractory chamber is supported by the sand without restricting it's expansion upon firing.

I had to use forced air to stabilize the burner flames. I experimented with Venturi type burners but since the natural gas was regulated at 1/3 psi they never developed the force needed to overcome the backpressure created when the forge doors were both closed. Forced air also greatly increased the amount of heat I got from the same amount of gas. If you've got propane available, you probably don't need forced air ( see alternate gas forge designs at Ron Reil's forge design site ).

However, there are certain advantages to forced air you should consider. Besides heating the chamber rapidly by creating greater heat, the forced air cools the burners and piping while the forge is lit and allows the forge to cool down quicker and safer at shut down time by closing the gas valves and allowing the blower to continue to run. Many other designers make a big point of tangental nozzle positions and "swirling" fire patterns. These are completely superfluous to a forced air system, since the power of the blast creates even heat throughout the interior regardless of whether a burner is blocked by iron being heated inside or an arrangement of bricks disturb the flame.

After a preliminary test firing, I allowed the forge to cool and applied a 1/2" thick layer of pure Parker High Temperature cement to the interior. So far I've had excellent results from this forge.