My hearth has been in a constant state of flux. Flowing from fire-pot to fire pot as my whims or work requires. When I first started working on my latest forge I decided to try as many types of fire pots as I could. having never used a real forge I wasn’t positive the advantages of one style over another. You’re first forge can be as simple as you’d like see my first forge it was awkward and ill designed, but it worked!. A quick youtube search for a simple forge and you’ll find a ton of great idea’s to get started hitting hot metal. Once the bug bites you’ll probably find a brake drum or hole in the ground just doesn’t cut it for all you want to do.
Charcoal is a great fuel. I love it, I’d use it all the time if I had time to make it in vast quantities efficiently. But it doesn’t contain its self very well. Coal on the other hand when it gets hot sticks and clumps together on the outside with the aid of a little water. It’s often referred to as self insulating, but I haven’t observed that. I’ve found it’s radiating. The outside of the coking coal may provide nominal heat retention, but it’s the inside that is coked and glowing that radiates heat. This means that a fire can burn hot with just a shell of slightly coked coal around an air inlet, or tuyere. If there are no coke fines, small bits of coke, burning inside this shell your fire is burning hollow. That means atmosphere is allowed inside your hearth and your work will scale rapidly because it’s inside of an oxidizing flame.
An ideal fire is one where just enough atmosphere, or oxygen, is introduced to feed the fire up to the desired temperature.
This is especially important when making tools, knives or anything else where carbon content is valuable. To get the sort of fire I like to work in is a laborious task that is more time-consuming than difficult. It involves getting a nice sized fire going with newspaper, wood shaving and kindling. Adding coke fines about the size of dimes. Hitting the blower lightly and waiting until I have a decent start to a fire. Wood and paper do create a lot of ash which isn’t a problem for me as the ash tends to gather in the small cracks here and there and doesn’t need to be removed till the next day.
Once the fire is going well enough I toss on some more coke, and then surround the whole fire top bottom and sides with coal to coke up. At this point I tend to turn the blower to full throttle just until the coal catches light and then I cut the air off, open the ash dump and sprinkle the coal with water. I simply walk away at this point and do something else for a little while. 5-15 minutes later sometimes more or less I have a very well coked fire that has started to draw air on its own from the ash dump below the tuyere. Sprinkling a bit of water to contain the fire while waiting for a drafting fire is important to keep the fire from spreading outside of the fire-pot. I can often get a deep orange above the curie temperature without any forced air. I believe a big reason for this is the large diameter of the air pipe between the open ash dump and fire-pot. To me this is the best way to create a tool making fire, and is the way I make most of my fires. (for a pictorial on building and managing a coal fire click here)
I’ve tried more than a few fire-pot configurations and have found hard fire bricks, really insulate a fire and trap the heat, soaking up the heat and radiating it back inwards. After a forging session, when the fire is scattered, the bricks turned inside-out they have a bright glow. Because I was using a raised fire-pot above the level of my table, I’d often have a huge mound of coal. It’s easier to rake around a level fire pot. Keeping coal on top and at the end of a fire wasn’t a problem. But coking coal from the sides is difficult. This types of hearth required a lot of attention not to tear down a well made fire by sliding bricks around or worse removing all that glowing coke from the pot when inserting or removing irons. This leads to a lot of down time as you fill the fire-pot with more coke (you’re not making as much coke on the sides) and either let it naturally build back up, or introduce a lot of air to get things rolling again.
I needed a better way to do things. I had an idea of what I liked. Also I knew what I didn’t like. I really like the forge at the Dixie clasic fairgrounds. This “real forge” made things were very clear. So the other day I fabricated and installed a new fire-pot. Along the sides I installed a slurry of wood ash and coke dust/ash. This was mostly because the fire-pot is a bit larger than necessary and it can be reshaped to fit my needs. I’m not certain which is more detrimental to a fire pots lifespan. Direct Heat or rust formed from rain mixing with the ash.
I’ve had a really good time using it the past couple days and while I still have a lot of work to do on my forge; I feel this has been a step in the right direction. I use a bit more fuel because I’m able to keep coal all around the fire easily. While I haven’t worked any great lengths of stock with it yet, I’ve had a much easier time working without destroying my fire. Thats what my trench forge is for anyway.