Some more forge building tips:
1) The burner should enter the chamber from the side at a tangent near the top. It should be angled about 15 degrees forward. It can be horizontal, or even slightly uphill toward the forge. It should not enter straight in the top pointing at the floor. I know you see a lot of those on ebay, but it is terrible knife forge engineering. The burner should make the flames swirl around the chamber walls, not make the floor hot in one place. Multiple burners should be spaced as needed, but should follow the rules for a single burner as far as angles and such. Try and mortar the burner flare into the wool and Satanite as smoothly as possible.
2) A burner flare makes the burner run better and last longer. Stainless is preferred for the flare.
3) The wool can be stiffened with Rigidizer. This makes it easier to apply the refractory coating, as well as stabilizing loose fibers.
4) The wool needs a covering of refractory. Never use it as is, or there will be tiny fibers blown out in the exhaust. Ever heard of mesothelioma?
Most folks use Satanite to coat the wool. Put on a 1/4" layer, let it dry well for a couple days. Try and make the interior as smooth as possible when applying the satanite.
When dry, fire at low for a while, let cool, and fire at medium. Repair any cracks, and when all is good, fire at full heat until the insides are glowing. Shut off and let cool.
5) The refractory will work better with a reflective coating on it. ITC-100 is one common type. Paint on a thin coat, let it dry, and fire it to cure. Sometimes a second coat is a good idea.
6) Avoid anything that resembles an angle or is rough as much as possible. The burner should be smooth inside, have no projections in the path of the fluids ( gas and air), and have smooth curves instead of 90 degree bends. All this isn't always possible, but think of the flow path of the air/gas and try to avoid any turbulence that you can.
7) A mixing chamber in a blown burner is a very good thing. It is merely a place the pipe gets bigger for about 4" and then gets smaller again. This creates a very well mixed gas/air blend to be burned in the chamber. The average manifold pipe is 1.5", so the mixing chamber is usually 3".
8) Front and back ports need to only be big enough to do the interior work ( satanite and ITC-100) and allow the blades you make to go in. The front port is usually about 3X4" and the back about 3X3". The back can be plugged with a fire brick when not needed. The ports should be flush with the chamber floor.
9) The blower motor should be higher than the burner. This is not an absolute, but is good engineering. It prevents any gas from back pooling in the manifold during a power failure and then accidentally igniting by the motor sparks when the power comes back on. The best way to not have to deal with this is to have a master shut-off solenoid valve in the gas line. It should be a NC valve....power goes off - gas stops flowing.
10) While a forge needs to be well built, it can be over built. Unless you need them, whistles and bells aren't much more than trim. One good add-on is a sliding work rest. Weld two pieces of 1/2" ID pipe down the forge body sides. They should be at the position of the forge floor. Make a slide by putting two 24" pieces of round bar in them and setting a piece of 3"X1/4" steel across them. If the steel is roughly at the same height as the forge floor, clamp it on and weld it in place. This will make a 3" shelf at the port when it is pushed all the way in, and a bar/tong support when pulled out. I consider a slide like this the best thing since sliced bread. The pipe pieces can be welded to the legs if that is easier, and the shelf raised as needed. I think that you guys can figure out how to do that.
Safety Note:
Looking into a running forge can seriously damage your eyes. Sun glasses, or glasses made for glass work won't make it safe. Use a pair of glasses made for this job. Even with them, try and avoid starring into the forge for more than a few seconds at a time.
