So far I have got the pickup truck tire rim for the base. You have to have two 1/4 to 3/8 inch thick metal plates. Both the top and bottom plate are drilled for 3/4 inch bolts that fit the lug pattern. The plate should fit with in the rim but extend to the side of the rim. Insert 3/4 inch by 2 inch long bolts in the bottom place and then welded in place. Insert the bolt plate in the deep side of the rim. Then fill the deep side of the rim with concrete. You want a heavy base BECAUSE KNOCKING OVER A BURNING FORGE WILL RUIN YOUR WHOLE DAY AND MAY BE YOUR LIFE.
The top plate can now be welded to the 4 inch double extra heavy black iron pipe with 4, three inch right triangle peices for bracing. The 90 degree side of the trianges are welded to the bolt plate and to the pipe. I use 4 pieces.
A third steel plate with drilled bolt holes can now be welded at the top of the double extra heavy black iron pipe with bracing. This is for bolting the forge to the top of the stand.
So now you have a heavy stand for the forge that can be unbolted from both the base and the forge for storage or transport.
Once you have the base finished you can then make a partial steel box. I say partial because all you need is a bottom, back, and two sides plus a small lip on the front and top to cover the thickness of the fire brick bottom and side lining.
The bottom should have holes drilled to fit the plate on the stand. Insert bolts, I use 1/2 inch by 2 inch bolts in the bottom plate and weld in place. This attaches the forge to the stand. Also the thickness of the bolt heads create a plenum chamber for air to be pumped into the bottom of the forge. You might want to weld some more small metal slugs the same thickness as the bolt head to make standoffs for the bottom lining of fire brick. The holes in the bottom lining fire brick allow the high pressure from the plenum chamber to flow evenly into the mass of charcoal burning in the fire box.'
The last part of making the forge is to attach some blowers to the bottom of the rear of the bottom fire box plate. I place these on the side of the fire box about even with the stand. This keeps the size down and aids in the keeping the balance of the mid point of the fire box. I use two Dayton 1TDN3 blowers. These are 115 VAC units that move 29 cubic feet of air per minute. I drilled a bunch of 1/4 holes where the blowers mount to allow the air to move into the plenum chamber.
BE AWARE THAT TWO 29 CFM BLOWERS MOVE A LOT OF AIR AND WILL BURN CHARCOAL LIKE CRAZY. Of course you can reduce the air by only turning on one blower motor.
Now all you have to do is line the fire box sides and bottom with firebrick. The weight of the firebrick and metal lips on the top will keep the side fire brick in place. Use a small masonry drill to drill holes in the bottom fire brick.
Once you get it set up then you have to get an anvil and a set of hammers. I recommend the Nordic hammer set in 1000 gram, 1500 gram and 2000 gram hammers. DON'T GO CHEAP ON AN ANVIL expect to pay $300 to 400 for one. Get one that is heavy as it will stand up the the constant pounding. Also make sure that it has a square hole and a round hole for attaching a strakes, (attachments to anvils that allow for making decorative iron work and drilling holes with a drift)
BY THE WAY YOU MAY THINK YOU WANT A FORGE TO MAKE KNIVES AND SUCH, BUT BELIEVE ME YOU WILL FIND THAT MAKING DECORATIVE IRON FOR FENCES, PORCH RAILINGS, POT HANGERS ETC WILL MAKE YOU A LOT OF FOLDING GREEN STUFF.
I came back to edit this post because you need to understand some small details that make life a whole lot easier. First of all determine the size of fire brick you want to use. Then size the fire box accordingly. DON'T MAKE THE FIRE BOX TOO BIG. Do this for two reasons, one it will be heavy and the stand won't work as well. The second reason is the fire brick locks other fire bick in place and the larger the forge the more unstable the sides and back of the forge become.
My original forge that I bought was made from a tire rim as I discussed above. Over the years I have modified it. I found the original internal size to two feet long and 15 inches wide was really ideal.
The way the firebrick works is you place the bottom fire brick in first. The box should be sized to hold the fire brick securely. Then you place the side fire brick in. They rest on the bottom fire brick and are held in place by the metal lip on the top of the metal box walls. The should also be sized to they fit snugly. The back wall of the forge is then place in and the brick should fit snugly. The back wall of the forge locks the bottom fire brick down at the back and the side walls in place at the back. WITH THE RIGHT SIZE ALL THE FIRE BRICK FIT SNUGLY IN THE FORGE WITH OUT ANY ATTACHING OR MORTAR IN PLACE.
Also once the fire brick get hot from the burning charcoal they tend to even out the heat as the brick holds heat and reflects it back into the work.