The Ground Forge
In previous articles, I have mentioned the ground forge, and I figured I should cover it in more detail. The original mention is here: http://ironangelforge.blogspot.com/2009/08/blacksmith-basics-forge.html.
The ground forge is really the beginning of blacksmithing as we know it, and is a hold over from the bronze age that preceded it. In many areas of the world, in the deep mists of the past, bronze and iron workers worked side by side, adapting techniques of the older metal into forming the new iron. That transitional stage is a whole other series of posts that we will cover at a later time.
As mentioned in the first post, some parts of the world continue to use ground forges to this day, though most areas developed taller “table” style forges. For the modern backyard blacksmith, historical re-enactment smith or the like, the later table forges are usually a better choice. But when you need a forge and are away from your shop, or are camping and need to make a quick tool, the ground forge is certainly a usable and very simple solution. For those who are interested in bush craft and being able to pack in to the wild very lightly, the knowledge of how to build a ground forge is an invaluable tool.
All you really need is an air source (covered below), a method of getting that air to the underside of the fire, and ground soft enough to dig a hole in. You can use any handy tool to make your hole, but its best to not use your hands, just in case there is a sharp stone or root in the area you are digging. If you find a root, move your hole. If there is a large root in the ground, it could catch fire and that could lead to an issue you don't want. You will also need forge fuel and tools, along with some stock to work.
Once you have found a suitable location that seems reasonably rock free, clear any ground debris such as leaves and sticks back a few feet and make sure there is nothing flammable over head for at least 15 or more feet.
Dig a narrow trench long enough for your air tube and a round hole about 6-8” in diameter. The trench should be a few inches deeper than your forge hole and angle upward out of the hole. The forge hole should be round bottomed, so it will be between 3 and 5 inches deep, with the dirt removed piled up around the outside at a low angle. Lay your air tube in the trench and cover it, at least at the end nearest the fire pit. The dirt covering is there to protect it from heat and keep it from moving. Pack the dirt tightly. Put in fuel, assemble your air system and light it up. You are done!
In case you don't have a set of backpackers bellows (described in an upcoming article) or another portable air source, there are a number of ways you can get air into your forge in a number of ways. The simplest is to blow into the end of the pipe. This will likely make you light headed before you reach a decent heat. You can also make a funnel shape and fan it with something handy to focus more air into the inlet, and this will work pretty well in a pinch. If there is a decent wind, building your ground forge aiming into the wind with a large funnel to catch and focus it may allow you to work in relative ease, the problem is you can not control the amount of heat. This may or may not work at all, depending on wind and location.
If you don't have a portable inlet pipe, you can build one by simply finding something to cover your inlet trench, then sealing it up with dirt. The more fireproof, the better. Bark will work, but it will eventually burn at the forge bowl and the inlet will cave in. Stones may work, but be ware of this; many stones have some water in them, and under heat may split or break, possibly with some force (another reason to make sure you remove them all from your bowl). If you can scrounge up a bit of metal in the field, such as a steel can stomped flat, it will work better than bark or stones. Just be sure to recycle or throw the can away when you are done. And when done, make sure to fill in the hole and trench as well to prevent breaking your ankle in the middle of the night in camp.
If you are in a clay area, you can “glaze” the inside of the bowl with a bit of water to smooth it and help it keep it's shape. If you are using wood or charcoal, the ash will help to harden the bowl somewhat, so if you use the ground forge for a long while it will get nearly concrete like in a clay bed.
In a ground forge, you will find there will be problems with clinker and slag build up at the air inlet, so you may have to tear down and clean your fire more often than in a cast iron pot table forge.
Now that you know how to build a ground forge, you can adapt this technology to make your own charcoal as well. Simply dig a much bigger ground forge, start the fire at the base near the inlet hole, and bury the top with the removed dirt leaving a small hole at the top for smoke to escape through. You don't want an open, flaming fire, just a slow smoldering one. Make sure if you are going to burn charcoal that you have a lot of time open; it will take a while. You can burn dry wood to make charcoal, but wet wood can also be used if you have nothing else at hand. It may not burn as easily or as well, and may even go out, so keep an eye on the smoke coming out the top. You may have to dig it out and relight it a few times with some dry kindling. We may put up a more extensive article on forging with charcoal in the future, and if we do it will have a much more extensive article on making your own charcoal with it.
In an extreme pinch, you can forge with just a wood fire. It will not be as hot as a coal or charcoal fire, and will pop and spit a lot more, so watch out for flying sparks. In a ground forge intended for use with only wood, you may have to dig your pit larger. The easiest way to do this is to dig a long trench with the air inlet coming in at a 90 degree angle. Lay your sections of wood in the trench and push them forward into the fire area as it burns away. You may have to wet it from time to time to keep the fire from spreading up into your fuel reserve. Be careful not to get your main fire area wet, and watch out for bursts of steam from the fire and from the inlet when you water it. Hot steam can blast out several feet, so be careful.
That about covers the ground forge for now. Keep on hammering.
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