Here's a forge I built about 12 years ago. It is powered by a hair drier. The forge can be built and powered with minimal tools for less than fifty dollars. It can comfortably handle up to a twelve inch blade not counting the tang. The forge is a little slow for the first few heats but once the crucible gets hot it will easily heat up to ¼”X 2”X 12” steel in less than 3 minutes. It burns about 2 pounds of charcoal lump per hour of forging and will easily get hot enough to forge weld. The size of the forge can be scaled up or down to meet your specific needs. I personally use this one to forge large bowie and dagger blades.
The first thing you need is adobe. Adobe is typically a mix of clay, sand, and water. Substitutes and additives can be made. I saw a documentary on adobe missions (local PBS station) where the adobe was made with a “cactus tea” instead of just water. I decided to make my adobe this way to aid in weather resistance; this forge is outside. First gather up about twelve large prickly pear cactus pads and burn off all of the needles over a campfire. Cut them into chunks, place them into a 5 gallon pot, cover and boil for about 3 hours. Mash them into a pulp while still in the pot and boil for another hour, always keeping the water level as high as possible without boiling over. After this is done, strain the liquid through some cheesecloth into a 5 gallon bucket. Discard the pulp (compost pile!), add water until the bucket is full and mix thoroughly. You now have 5 gallons of cactus tea. Pour half into another 5 gallon bucket and set aside.
I found the clay portion of the mix in the bank of a nearby wash. It is a reddish colored clay chock full o’ rocks. I cleaned the clay by putting it in a 5 gallon bucket and adding water to break it up. I reached in and broke up the clay the best I could with my hands, picking out the bigger rocks as I went. I fashioned some wire mesh into a scoop and filtered the clay through it right in the bucket. I kept this up until I was satisfied all the rocks were out. At this point I had a clay slurry about the consistency of pancake mix. If it looks a little thin, add clay or set the bucket in the sun and let it evaporate until it looks right. Now gather a few gallons of fine sand and a couple of gallons of hardwood ashes. Take one of the buckets of cactus tea and add in one gallon of clay slurry, one gallon of sand and one gallon of hardwood ash. Mix thoroughly with a stick or something. Don’t use your bare hands. The ashes in the mix along with the abrasive action of the sand will literally eat the skin off your finger tips. Use gloves when needed.
Build the base of the with four 8”x8”x8” cinder blocks, two on the bottom with the other two broken into “U” shapes and stacked on top. ( see fig.1 ) The sides of the cinder blocks you broke off to form the “U” shapes can be further broke down and used as filler in the bottom two blocks. Mortar the four blocks together with the adobe you just made. Now it’s time to assemble the piping. I used one inch steel pipe fittings purchased from the local hardware store for less than 12 bucks and can be had cheaper from larger suppliers or by scavenging. Here is the material list:

1-1”x8” nipple (threads on both ends)
2-1”x12” nipples
2-tees
1-cap
1-elbow
2-plugs

You will also need PVC adapters to match the diameter of your hair blower or other air source.

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