Building a Coal Forge, Part 1- The Fire Pot

by Albin Drzewianowski

There are a lot of options for heating up steel with coal. The very earliest coal forges were shallow pits in the ground, built on hillsides where the prevailing winds could be funneled into the pit to stoke the fire. The Asian blacksmithing experience was to have the forge at ground level and in many countries it still is. The European experience started at ground level, for example the Vikings, but soon moved up to bench height.

Various books, such as Weyger's "The Complete Modem Blacksmith ", and Tucker's "Practical Projects for the Blacksmith" have examples of home made forges. ABANA just recently published a long pamphlet, written by Stephen McGehee?, on building coal forges (see book review elsewhere in this newsletter). Randy McDaniel? has the plans for welding up a coal firepot in the back of his book, "The Blacksmith Primer".

So, there is information out there to help you get started. Basically, you need 3 things for a coal forge: you need some way to contain the fire; you need a controllable source of air to stoke the fire up to forging temperatures (covered in the next newsletter); and you need a chimney system to remove the smoke generated (probably covered next newsletter or the one after that).

One of the simplest methods for containing the fire would be to take the original fire pit and raise it to bench level. Make a box out of 2x6's or 2/8's about 18 inches square and about 12 inches deep. Add 4 legs so that top of box is about 30 inches off the ground. To introduce air to the fire, you could put a 2" hole in the bottom of the box to allow for the tuyere (French word for the plumbing we use to bring air into the fire) or you could put a hole in one side of the box at the bottom and introduce a 1 !/2 or 2 inch pipe horizontally across the bottom of the forge then drill a series of 3/8" holes in the part of the pipe that points up. This pipe type tuyere especially lends it self to making long narrow fires, such as knife makers would use. Next you get clay. Here in Carroll County, you could just go in your back yard, dig down below the top soil and you will have all the clay you want. Sift the clay to remove all rocks. Moisten the clay to the consistency of play-dough and fill the box with the clay leaving a bowl or trough shaped depression for where the fire will go. Ram the clay into place with a wooded mallet. All wood portions should have about 3 to 4 inches of clay between wood and the fire. If you do not have access to "back yard" clay, hook up with a local potter or pottery supplier and get some clay. You could also use refractory cement instead of the clay. With both the clay or cement you could mix in vermiculite which would make the forge lighter, especially if you have to move it around. An alternative to the wood box, cold be a large metal washtub. Again, line with clay, set up with legs or use on the ground.

The air openings of your tuyere should be just barely exposed in the bottom of the pit or trough. Let the clay dry slowly. For your first fire just build a small fire from newspaper and kindling. Let it burn out. Build a second bigger fire of kindling or this time BBQ briquettes. Finally you can build a coal fire. The idea here is to drive the moisture out of the clay (or cement) slowly so that it does not crack. If the clay cracks, that is not a big deal. One of the advantages of this type of forge using clay, is that you can fairly easily reshape your firepot simply by re-arranging the clay. With the pipe type tuyere you can control the length of the fire by plugging or unplugging the holes drilled in the pipe.

Another do-it-yourself coal forge would be to take a used truck brake drum, turned horizontally, it looks like a big bowl. Get one from a Vz or 3/4 ton pickup truck. Brake drums from bigger tucks, like a semi, would be too large, unless you need "really" big fires. Add legs to the brake drum, or set it in a metal tabletop. Where the axle would pass through the brake drum affix a piece of pipe and a grate so that you can blow air into the fire.

My very first firepot was a small circular BBQ pan, about 15" across and 3"-4" deep. I replaced the spindly metal tubing legs with black pipe and I drilled out a hole in the bottom to introduce a 2" pipe flange for the tuyere. If I had kept it painted with high temp paint I could still be using it. The bottom rusted out and the 2" pipe tuyere fell out.

For a really nice permanent forge, get a real cast iron coal firepot from Centaur Forge or one of the other blacksmith suppliers. The standard firepot from Centaur Forge will run you about $150. Or you could weld up a fire pot from 1A" plate, like the one in the back of Randy McDaniel?' s book. Either of these should last you a lifetime of hobby smithing. Make a metal table and set the firepot into the metal table top. Or you can go all out and set the cast iron in a masonry forge, like the one we use in the Historic forge at the Farm Museum.

This system will work for coal, commercial coke and charcoal. If you know that you are always going to use charcoal, then you would want to introduce the airblast from side rather than from the bottom.

OK, so there are some do-it-yourself options.

-- RebStaup - 25 Jan 2008