Propane gas forges can be very dangerous when mishandled, and can result in very disastrous consequences.
Both Nathan Creel and BLADESIGN disclaims any responsibility or liability for any damages of any kind incurred from the use of the information published herein.

present  gas forge tutorial is based on a real forge that Nathan Creel built for me after finishing my Dha as a natural sequence of our correspondence.
All the pictures and credits are due to Nathan Creel who once more accepted the invitation to produce a tutorial for all who may find it to benefit.
I would therefore wish to publicly thank Nathan for adding his contribution to others who have taught how to build forges.
Antonio Conceição Júnior aka Antonio Cejunior

Making a forge is a project most smiths undertake for a few reasons. First, building a forge is much cheaper than buying one, though finding one to buy that suits the needs of a particular smith can be difficult. Suitable forges are often not available commercially. Thus, secondly, a smith can build a forge based on his or her particular needs. Lastly, if a forge is ever in need of repair, fixing it should not be a problem because the user built it and is familiar with its construction and use.

After assessing one’s needs, a design must be decided. Several resources are available for designs. See the links portion for information on designs and materials. Finding materials and a design are the most time consuming part of building a forge. The first forge one builds will often not have all the necessary features; but with use, modifications can be devised as well as plans for a future forge. I hope that I will be inspiring to those who want to build a forge by sharing my own experiences.

After a design has been chosen, a suitable shell must be acquired. Many materials can be used for a shell such as freon cans, sheet metal rolled and welded, or even a compressed air tank as shown here. Also pictured here is a high heat spray paint in flat black made particularly for barbecue grills. These products can be easily found at hardware stores and other miscellaneous stores.

WARNING: Care should be taken when cutting and welding any tank that has formerly held a gas. Freon tanks have an oil residue that is highly toxic when burned. I use abrasive blades to cut metal as often as possible, but round holes often must be cut with a cutting torch.

Shown here is the shell of the forge cut to length. Depending on the length needed it may or may not need to be shortened or lengthened. Here I’m building a 14” forge with a 9.5” diameter. Once the length is known, the number of burners must also be decided as well as the spacing between them, which may be determined by the type of burner used and the method of plumbing the gas. Thus, I construct burners first to determine the distance between them.
Note: a hole can be drilled in an unpressurized tank. Once the hole is drilled, it can be filled with water and cut with an appropriate tool. The water will expel any remaining gas from the tank. This procedure is especially needed when using tanks that have held flammable gas because sparks or a torch would ignite remnants in the tank.

I use atmospheric type burners, and this is a variation called a side arm burner. It can be seen on Mr. Larry Zoeller’s website. It is very easy and quick to build and adjust. A parts list for one burner will include:

1 1/8” x 4” schedule 80 (very important that it is sched. 80) black pipe nipple
1 Tweco 14T mig welding tip with 0.035” hole (Other sizes may be used, but this seems to work the best.)
1 ½” to 1/8” reducing bushing
1 1 ¼” to ½” reducing bushing
1 1 ¼” x ¾” x 1 ¼” Ward standard black reducing tee (Ward brand in this size is the best, other reducing tees are considerably lower in performance.)
1 ¾” x 8” black pipe with one side threaded
1 burner nozzle (Stainless steel burner nozzles can be purchased from Zoeller Forge. Nozzles can be made, but getting the flare just right is difficult. See Mr. Reil’s sight for the correct flare dimensions.)
1 choke assembly (Gas oxygen mix must be adjusted for smooth operation at several pressures.)
2 8-32 screws
1 1 ½” x 3” black pipe without threads
3 ¼”-20 x 1” bolts.

Some of these parts may be difficult to find. Mig tips can be found at welding supplies. Hardware stores and plumbing supplies should have the rest. Zoeller forge has some as well.

The 1/8” pipe nipples are tapped with ¼”-22 threads. These threads are the same threads of the Tweco 14T mig welding tip. Other tips may be used as long as the threads are the same.
Some people recommend soldering the tip in place; but if the joint is not leaking gas, I don’t feel it is necessary. Plus, tips can be changed in the future to increase or decrease the size of the orifice.
I use thread sealant on all joints that come in contact with gas. It prevents leaks and lubricates for a tighter fit and easy future disassembly. Teflon tape is not appropriate for gas pressure holding joints; use paste. All joints on the actual burner body are not sealed, because

they do not hold pressure and tend to get hot when the forge is cooling down.

The ½” to 1/8” reducer (left) must be drilled out to accommodate the 1/8” pipe. A 27/64” drill bit is recommended by some, but I use a 7/16” drill bit with a set screw. The ½” to 1/8” reducer will give a better center point to drill for the gas jet, but a 1 ¼” black pipe plug is a cheaper alternative. If 1 ¼” to 3/8” reducers are available, a 3/8” to 1/8” reducer can be used in place of the ½” to 1/8”. I used a set screw on the reducer tapped to 8-32 threads.

For the choke assembly, a simple plate of steel available through Zoeller Forge works very well. I drilled it to slide around an 8-32 screw and tapped the reducing tee to 8-32 threads. A spring washer will keep the plate in place, but tightening the screw when needed also works.

Next, I plumb the gas jets to see how far apart the burners are. I attempted to keep them as close to 5” apart as possible. With this plumbing, they are 5 3/8” apart on center.
The picture is not entirely accurate. One more reducing bushing is on the right but not shown, and the close nipple on the bottom was not used. This plumbing will be determined by parts available, distance between burners, and gas supply. Brass or black pipe is appropriate. Black pipe is generally cheaper, but brass may be more accessible. As I mentioned before, use paste thread sealant.
Parts I used include:

2 ¼” to 1/8” reducing bushings
2 ¼” street ells
2 ¼” gas valves
2 ¼” close nipples
1 ¼” tee.

For the gas supply, the parts include:

1 1/4" X 1/4" FPT 3-35 lb Fisher Regulator with handwheel and gauge port
1 0 - 30 PSI Gauge bottom connect with 1/4" mpt
1 8 foot long High Pressure LP hose with 1/4" mpt fittings on both ends.
1 1/4" MPT x full flow Hard Nose POL 7/8 hex.

Here are all the parts together. I’ve painted the burners so they will match the forge body. Valves are in accessible positions, and excess thread sealant is wiped away.

Next, I construct the burner seats. I tap three holes 1” from one side and equidistance around the circumference. The holes are ¼”-20 thread and hold the ¼”-20 x 1” bolts. This burner seat will be welded to the forge body.

Here is the forge body with holes cut and re-welded. A cutting torch is used to cut the holes for the burner seats and the actual forging area. The burner seats must be placed in a position to get a nice vortex when burning. The body is painted, and the insulation and burners are installed.

WARNING: Ceramic wool insulation can be inhaled and may cause cancer. Always use a respirator when handling.
Once the burners are installed, a stabilization leg may be needed. Several designs for legs on the forge body can be made. Having little time, I devised something simple and quick. Leveling screws on the bottom and a cross legs work with the existing legs of the air tank. The leg design below added better stability, so I scrapped the leg in the picture to the right.

The ceramic wool insulation must be covered with some type of refractory to prevent fibers from entering the air and being inhaled by the user.

ITC-100 is a refractory that refracts 95% of the heat and, thus, increases the efficiency of the forge.

The ITC-100 is mixed with water 1:1 and spread with a wet brush. Spray the surface to be coated with water and maintain a moist surface before application.

The ITC-100 can be cured by firing the forge for 30 minutes. When placing the jets in the burner bodies, I like to pull them in and out to find the optimal placing while the forge is burning and tighten the set screws when I’ve found it. One must be very careful while doing this. Once the jets are in place, the choke should be adjusted until the burners are burning smoothly. With low pressure, the choke must be mostly closed. The higher the pressure, the more air it can use. The more closed the choke is, the more reducing is the flame because it has less oxygen. The more open the choke, the flame is more oxidizing.

Here you can see the vortex slightly. It is more noticeable in the dark.

Here is a picture of the forge and burner assembly while it is burning at 5 psi. Notice that the flames cannot be seen exiting the forge though it is burning. It will be visible in darkness, but not in the daytime.

The entire setup.
Here is the forge heating a piece of metal. The plywood on the left is to block the wind. Forging in the open has many drawbacks like wind, rain, and daylight; but it is very convenient space-wise.
Often a fan may be positioned on one side of the mouth of the forge to direct the heat away from the used. Long handled tongs are also helpful especially when working at higher pressure levels.
The ITC-100 may have to be re-coated in 6 months depending on how often the forge is used. The size of the propane tank used will also depend on the amount the forge is used in one period of time. Smaller tanks are more likely to freeze up from the liquid propane movement. The paint may have to be touched up over time, as well. However, it is only aesthetic, while the ITC-100 will save gas.
That’s the forge in a nutshell. Always practice safety first. Below are some links for resources on forges. Have fun.
Nathan Creel