Freon Tank Forge (2)

Disclaimer/Printing Acknowledgment


I had been blacksmithing for about 10 years off and on and had only used coal. In early 1999 I got involved with the North Texas Blacksmith's Assn. (NTBA) and discovered that there were hundreds of other things and ways to express myself in metal and a propane forge was one of them. This is my interpretation of the Freon tank forge. I am not a gas and fluid mechanics engineer or a thermodynamics engineer, but this project was easy enough after reading over Ron Reil's and David Wilson's designs and pouring over the photos and drawings. There were dozens of other web sites and I saw about 5 or 6 propane forges in NTBA members' shops. Talking to others and seeing the real machines was what made all the difference for me. Maybe the best advice was from James Ryan ... don't run the forge without insulation in it ... good advice, it would hardly heat bailing wire without insulation ... after the Dura-blanket was in place, things went from toasty to bright orange heat. I have heated a 2" bar in this forge ... it was workable ... rolled around ... something of an experience after being used to the constant scorching of a coal and coke fire.

It took me over a year to have the time and amass the materials and experiment to get this done. And it took needing a forge, NOW to finish a project to get this forge working. As others have pointed out, this is not a step by step or a detailed plan, but my way of showing what I have done.

I already have seen that this is too small for some things, but it was a great inexpensive project to get me working at home. My lovely young bride wouldn't let me start a coal fire in the yard, and that is the end of that. This forge makes some noise and the hammering is sorta noisy, but as long as I sell a few things here and there and make her yet another plant hanger, bird feeder stand, shepards hook etc., she is much more accommodating now.

I have since changes the leg design, burner design and working on a door …. More to come.

My First Freon Tank Forge

... Front Left
Before Legs ... in progress ...
You can see a corner
of a split fire brick
as a hard floor
in the forge.

Insulate it before
You try it!!!!!


(I meant my first big forge, after my 3# coffee can with a 32 oz. soup can insert with 1” Dura-blanket) and 3/4” burner, BBQ grill regulator and a small electric blower.)

From the photo, note that the use of a grill size (20#) propane bottle. It will not stand up to a full day of work, but for an hour here and there it has been performing well. It is also easier to move and work around in my garage than a 100# bottle. I was able to buy a 100# bottle at a Pawn Shop for only $20. The valve leaked and when I went to my standard industrial gas supplier for a re-fill, they swapped out the tank for one that was almost new. I am not complaining. I hope you all have as good a luck. I started small, and am working on building up. For me this has been a hobby. As I progress I will buy bigger and better toys, I mean tools.

Thanks, te


The North Texas Blacksmiths Assoc. held a Freon Tank Propane Forge workshop in Plano at Dancing Hammer's, on Friday April 12, 2002. There were 14 forges completed and a lot of design improvements made. Below are some pictures and text about those improvements and some since then. For example the burn design completely changed. Most of all we proved that a bunch of amateurs can make forges and enjoy blacksmithing. I will try to write a short piece about how to run the workshop, but here I will concentrate on building the forge and adding pieces missing in the previous pages.

Note that the entire forge is screwed together. This was done for ease of assembly (less welding) and to allow the Freon tank to be changed later with ease ... just remove the screws. Also welding the parts to the thin Freon tank require a lot more expertise and smaller wire or rod than I possess. Also being able the unscrew things makes it easy to change and experiment. Further making the burner fit into the top flanged burner bushing allows the forge to be made shorter for easier transporting or storage.

SCALE: The "standard" combination square in these pictures is 1" wide and 12" long.


General Construction Steps



Propane Plumbing

Burner Bushing/Mount

Freon Tank Sub Sections

Cut the front opening

Remove the Paint

Wire Brush, degrease and paint

Make Legs, adjust, paint and attach to tank

Alternative method for Legs

Cut top and rear openings

Cut/Install Insulation

Install the Burner Bushing

Test Forge

Add/Dry Refractory Cement

How well does it work




Try to paint all the parts. Wire brush to remove rust, paint and scale and use a degreaser if you are inclined. I use MEK (methyl-ethyl-ketone). Work in a well ventilated area with no open flames and wear protective gloves, goggles etc. Use Bar-B-Que paint, the stuff I buy claims to be good up to 1200 degrees F. I like at least two coats of paint. Use wire to hold the parts and hang them to dry. Put a long rod in the ground and hang the tank (newly cut open “front” down and paint the tank. Paint will smooth out the un-uniform look of things, prevent rust and make the forge look great. DO NOT use a primer … unless you have one for high temperatures.


Some paint around the openings will burn off, but not too much … it is, after all, a forge with propane burning at near 5900 degree F.




  Complete Burner


This is a modification of the Mongo burner that Ron Reil and his followers are making. This varies from my previous burners by removing the “bell” (2” pipe section and 1” washer or a reducing coupling), 1/8” pipe and 0.040” orifice and makes a holder for a Tweco #14 MIG tip.


Use the MIG tips for the Miller welders, as they have 1/4”-28 threads and a 1/8” NPT brass pipe cap can be easily threaded to accept the Tweco tip. The Tweco T14 for 0.045 wire works best for me.  The T is a Tapered tip, but the straight walled tips work fine in the forges that I have build. I used what I had. The taper probably does allow more air flow in some small burners, but I do not see the advantage. Certainly experts or engineers would have a different opinion.


A 9/16” 3/8” drive socket accepts the 1/8” pipe cap with Tweco “nozzle” and keeps it aligned. Heat the socket to “red” to anneal it and then drill and tap for a set screw … I use 1/4”-20 screws. Choose sockets with a large hole through them … large enough for the MIG tip to pass through. Otherwise drill the socket to accept the MIG tip (an extra step).


Make a “tripod” using 1/4” rod to support the 9/16” socket centered about 2.5” over the “top” of the 1” pipe burner tube.


Use a 3/8” x 1.25” fender washer and cut 1/4" wide gaps in the edge at 120 degree separation deep enough to allow the baffle to slide inside of the “tripod”. Weld the baffle on the underside of the 9/16” socket. This will block most of the air entering the burner to work with the choke described later.


Cut a 4”-5” piece of 1.25” pipe and drill and tap a 1/4“-20 hole near one end for a thumb screw. Slip this over the burner tube to cover the “tripod” to make a choke to control the air intake. Weld a small piece of stock (a 1/4" nut works great) low one the burner tube as a stop to allow the choke to clear the opening but not to fall off of the burner tube.


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 - Choke

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 - Choke Washer

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 - Burner Close-Up

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 - Choke Open

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 - Tweco Tip & Ell removed

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 - 9/16" Socket Close-Up


Propane Plumbing


Combine the parts as seen in the photos /drawings. Add an elbow, hose barbs, hose and clamps/ferrules and attach ball cut-off valve. Then connect a hose from the valve to the propane regulator. Test all joints under pressure using a rich soap and water solution. Look for soap bubble and tighten or otherwise fix the leaks. Choose a propane regulator with at least an outlet gauge and with a range from 0-40 psi or so. The lower the high range, the better you can read the low settings. Gauges over 100 psi work but the graduation for low settings are hard to duplicate and are not as accurate. This is especially important if you change pressures a lot. Reading on other web pages or books would be best as I can’t possible cover much in this web page.


Burner Bushing/Mount


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 - Burner Bushing

The bushing is a 4” section of 1 1/4” black pipe welded in an opening in a 4” square of ~1/8” sheet with 4 7/32” holes drilled in the corners to accept #10 self tapping screws.


Cut the 4” square, drill the holes in the corners and cut a hole large enough to accept the 1 1/4” pipe. Clearances to be filled by welding so don’t get it too big.


Hot or cold , bend the square to the outside radius of the tank you are using. Bend the square on the diamond – across opposite corners. I like the shape and it is easier to bend. You can heat the part in a forge or use a torch and press it against the side of the tank for a perfect fit. Note that perfect is relative since there is a weld bead in the center of the tank where you will be mounting this flange. You can leave it and have some space under the flange, or take care and grind this weld down and make a better fit. This is all in how you do your work.


Weld the pipe into the flange and ensure that the pipe is plumb in all respects.


The bushing is a 4” section of 1 1/4” black pipe welded in an opening in a 4” square of ~1/8” sheet with 4 7/32” holes drilled in the corners to accept #10 self tapping screws.


Cut the 4” square, drill the holes in the corners and cut a hole large enough to accept the 1 1/4” pipe. Clearances to be filled by welding so don’t get it too big.


Hot or cold , bend the square to the outside radius of the tank you are using. Bend the square on the diamond – across opposite corners. I like the shape and it is easier to bend. You can heat the part in a forge or use a torch and press it against the side of the tank for a perfect fit. Note that perfect is relative since there is a weld bead in the center of the tank where you will be mounting this flange. You can leave it and have some space under the flange, or take care and grind this weld down and make a better fit. This is all in how you do your work.


Weld the pipe into the flange and ensure that the pipe is plumb in all respects.


Freon Tank Sub Sections


Cut the Front Opening


Ensure that the “knockout:” has been knocked out and there is NO PRESSSURE IN THE TANK. Place the tank on secure surface with the handles up. Mark a circle about 1.5” from the edge of the tank. This will cover the end of the tank some to protect the Dura-blanket and you will not use as much refractory cement. This also gives the largest opening. You can always make it smaller. After the insulation and cement are in making the opening larger gets harder. I use a cut-off wheel (1/16” or 3/23”) in 4.5” angle grinder. Hold the wheel perpendicular to the tank and cut away trying to keep the “circle” going. The edges will be sharp take care not to get cut. Use a wire wheel in a grinder to “dull” down these edges and remove any burrs etc. In the future am considering making a 1/4” round hoop to weld around this opening to dress it up and make it safer.


Remove the Paint


I burn the epoxy paint from the outside of the tank. You can use a sandblaster, sander, or a wire wheel to remove the paint. The paint hangs on well and burning seems to work best/easiest for my tools etc. Use protective clothing, goggles, dust mask, well ventilated area etc.


On burning, put the forge on two fire brick. I use a flame holder on the front of my forge burner in the put in the front of the tanks so the flame heats a section of the tank. When the paint is “scorched” and dusty on one section, I turn the tank to a new section, moving the burn as needed until all the paint is subdued and can be removed using a wire wheel.


Wire Brush, Degrease and Paint


See the painting section earlier in this document.


Make Legs, Adjust, Paint and Attach to Tank

The layout for the legs: These legs were 15" of 1/8" or 3/16" x 1" flat bar. Drill two 7/32" holes on each side of center 2" from the center ... e.g. 4" apart centered on the bar. Mark the bars 4" from each end and bend these 4" sections in the same direction at a right angle. Next heat the center section and holding it by both legs (using tongs) bend it to the shape using the top of the forge for a form. Hold it in place until it cools to a black heat to avoid it deforming. Attach to the extreme front and back on the bottom of the Freon tank, using #12 self tapping screws, or use your favorite attachment method. Pay (Interpret "favorite" as use the screws, bolts of whatever you have available.) Pay attention to the top and ensure that the burner is vertical ... it looks better and avoids the flame from hitting off center in use.

Not shown is a 3/8" bolt in the shortest leg used as a leveler ... actually it doesn't matter if the forge is level, but adding a bolt in the shortest leg allows the legs to be adjusted so they all touch the "table", no matter what surface the forge is on. In the picture at the top right, note the rail road spike used to "level" the forge. This leg will someday have a 3/8" bolt mounted in it. I will bend that leg out level and drill and tap it. It is of no consequence how high this bend is ... only that it is high enough to allow the forge to be "leveled". One design I saw researching for this forge used leveling bolts in all four legs. This seemed to be overkill and extraneous. For my work, one if more then sufficient.

Warning: So the forge is not off balance and might tip over, move the legs as far forward and back as possible!


More pictures to come.


You might think about bending about 1” of the shortest leg out horizontal and drill and tap for a 3/8” bolt to use and an adjustable foot to make sure all four legs touch so the forge won’t wobble. We ran out of time at the workshop to do that minor mod. It is worth the time.



Alternative method for Legs

Use only 3 legs. The same front legs as above and one straight down the middle to the back. This eliminates wobble and even the adjustable leg. These legs in the photo are 1/2" square tubing. The front legs are made similar to those in the previous section. The back single leg is cut to fit from the front legs to the back of the forge and the legs portion is started about 2.5 inches from the end of the work. The first ones that I made, I cut long and made some measurements after welding the legs together to make the “platform” level. The front legs and back leg for a “T” with the back leg welded to the center of the front leg.



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 - Legs

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 - Legs

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 - Bottom View of Legs




Cut Top and Rear Openings


As with cutting the front opening I use a cutoff wheel in an angle grinder for the top and rear openings. Make and be careful not to injure yourself. Wear safety clothing etc.


Only mark and cut the opening after the legs are in place as this will effect where the actual TOP is. Cutting earlier things may get catawampus.


In the view at the top right, the "back" opening is cut out of the Freon tank, but not the Dura-blanket. I decided to leave it in to see how things worked. The large "front" opening was sufficient to allow the forge to operate well without the extra exhaust out the 2" x 4" "back" opening. Or cut an opening large enough for a fire brick to fit easily. Cut a piece of fire brick to fit the rear … about a 3” section works, to close off this opening if needed/desired.

Note that the atmospheric burner will not work correctly if it is closed off too much. Remember that the propane air mixture expands over 7 times when burned. This expanding gas has to leave to forge without causing any back pressure against the burner. The hot gasses exiting the forge also contribute to the suction in the burner tube, "drawing" the fuel air mixture into the forge.

With the burner in the mounting bushing, center and plumb burner. Hold the bushing in place and remove the burner. Using a drill with a nut driver, drive the four #10 x 3/4” self tapping screws via the four holes in the flange. You can use a center punch and pre-drill it you like … I have used a 1/16” drill with good success.


Cut/Install Insulation


Measure the front width of the tank. For a small Freon tank it is about 9” and the larger tank is about 11”. Cut a square of Dura-blanket to that measurement. Cut the corners off to form an octagon with even sides. Fold this in half and put it in the tank and press it against the back.


Next cut a piece of Dura-blanket 12” wide and long enough to fit all the way around the inside of the forge … about 32” for the small tank and about 35”-37” for the large tank. Verify this by holding the blanket in a circle and hold it next to the front of the tank.


Roll the blanket into a tight roll and place it in the forge. Stating at the bottom, press the blanket against the tank, forcing it over any screws and slowly unroll it while forcing it outwards to fit the inside of the tank. When you reach the bottom again, force any excess to fit against the other side of the blanket leaving no holes. If you have any holes, use the scraps from cutting the blanket and push pieces into the holes/gaps.


The blanket will hold itself in place, not fasteners, glues etc. are required.


Install the Burner Bushing


Use a pencil or screwdriver and push it through the Dura-blanket at the hole cut for the burner. Move the screwdriver around toe widen the opening until it just fits the burner bushing. This should give a squeeze fit for the bushing. Slip the bushing into place and secure 4 #10 self tapping screws.


Test Forge


Important: Test the forge before you add the refractory cement.


Wear protective goggles, leather gloves etc. Clear the area of combustible material and have a fire extinguisher on hand. Be safe. Insert the burner into the burner bushing and hand tighten the thumb bolt. Ensure that the cut-off valve is OFF. Turn on the propane and adjust the regulator to about 10 psi. Ensure that the choke is closed completely. Hold a small piece of paper in tongs and light it on fire. While standing clear of the front and back opening and not leaning over the forge, hold the lit paper in the forge and turn on the cut-off valve. The propane/air mixture should ignite and yellow flames should be exiting the front of the forge. Withdraw the tongs and then slowly open the choke. The yellow flame should abate and turn to blue and then disappear on the outside of the forge. You will here a “jet engine” sound as the air is increased. The blue “cone” coming form the burner mouth should not touch the bottom of the forge. If the cone is touching the bottom of the forge, SLOWLY and CAREFULLY hold the burner tube and loosen the thumb screw and slowly raise the burner until the cone is about 1”-2” long. Or adjust or the best heat in the forge for your needs/use. You can increase/decrease the pressure and experiment with the choke settings for the best burn.

After you find a good setting, turn off the cut-off valve and allow things to cool. Mark the burner tube at the top of the burner bushing. Tack weld a small nut of other piece of steel at this location to form a stop, similar to the choke stop. You could also use a hose clamp and you could adjust things later if needed.


Check for burned paint on the outside of the forge. This may indicate a hole in the installation. Locate the holes and press small pieces of insulation into the holes (the corners that you cut off the piece used in the back of the forge). Wire brush and re-paint the burned spots. Start the forge again and inspect for burned paint. Repeat until all the holes have been “patched”.


Add/Dry Refractory Cement


Trim the Dura-blanket about ˝” back from the front and back openings. Apply Derby 3000 ( or your preference of high temperature refractory cement) in these areas. Add enough to cover and protect the insulation and smooth the openings to your liking. Use a nice radius to blend with the interior of the forge.


Apply a 1/4” – 3/8” thick layer of Derby 3000 to the inside of the forge, protecting the Dura-blanket. The Derby eliminates the need for a split fire brick in the bottom of the forge.


Derby 3000 is a pre-mixed refractory cement rated up to 3000° F. It is sold in 50# buckets for about $24US. It is spread by hand, I find that easier as this stuff sticks to gloves and trowel and is hard to manipulate. If you add water to make it less gooey, that will add to drying time ….


I have heard good results from Krycon 3200 XR. This is dry refractory cement with some aggregate similar to Portland cement. Krycon is sold in about #50 bags for a price that is comparable to Derby 3000. Mix the powder with small amounts of  water to a thick, peanut buttery consistency.


Both Derby and Krycon should be dried slowly as there is water tied up in crystals that will take time to remove. It takes a long while to dry. Put a light bulb in the forge for about a week then add a low flame and work up … if you dry it too fast (e.g. too much heat too soon) the cement will break up when the water turns to steam and escapes violently. After the light bulb heating/drying I have used another gas forge to heat the new forge slowly bringing the temperature up. I have had the best success with my gas grill, however. I turn the forge with the front end down on the grill and set the grill to the lowest setting. Leave it for about an hour and then increase the temp in about 1/8 – 1/4 increments until satisfied that it is dry. Don’t  patch cracking and unless it is severe. As long as the Dura-blanket is protected this cement is doing its job.


The instruction for drying Krycon  are complex, but here is a thumbnail sketch: Dry for 1 hour per inch of refractory in 50 degree F steps up to working temperature.


Spread the cement to about 3/8” and start on the back. If you stop in the middle, leave the edges rough to bind to the next section when you start again. Take care when you wash your hands while spreading this stuff, too much additional water will make for a mess and again make for longer drying time.


Leave crosswise ridges on the bottom of the forge to allow stock to rest on these points. This will allow hot gasses to surround the work for even heating. If you use a split fire brick in the bottom as with designs that do not use refractory cement, add some broken up fire brick to raise the work to allow hot gases to flow around the work to heat evenly.




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Get it hot and hit it hard!

Repeat as needed!

Here is the forge in use. There are two split fire bricks standing on end on a full fire brick in front of the over sized opening of the forge. I chose to cut the opening as large as possible leaving just enough end of the Freon tank to cover/protect the end of the Dura-blanket. The fire brick acts as a baffle to keep some of the heat in and reduce the blast of the escaping hot gasses from impinging on the blacksmith. The Addition of the refractory cement will protect the Dura-blanket and if you add a split door, you can cut the front even wider.

The large opening makes it much easier to put the Dura-blanket in the forge. This is especially true for those of us with large hands.

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How well does it work

It works great ... it gets to a bright orange heat ... about 2000 degrees F. It is not quick, but I can live with it. The opening might be too clam as you cannot get wide pieces in the front, even though it is larger inside. For example I had to re-think how I do a fork ... the second prong is traditionally bent to the side at 90 degrees, but that is too wide for the forge. I had to bend it double, back along side of the handle. It turns out that I like this orientation even better than the right angle method. I have since adopted that as my standard. It is much easier to work the tine out front, without the unwieldy second tine stuck out in the way. I can see it being easier to get into a coal fire and to withdraw also, without the "rake" of a second tine sticking out ... "like a sore thumb".

For a note of performance several of these forge have welded and I know that they will melt the 2800 degree F fire brick together. “How ‘bout them apples.”

This burner design doesn't support a flame in open air, but it works great in the forge. My guess is that the forge is too closed up and has enough back pressure to slow the gas down so it will burn in the forge. This might be a draw back and I will find out what happens when I open up the front more, and make an opening in the back of the forge. The back opening will make the forge much more useful. I have only operated it for about 4 hours, and have already found that it is much too short ... for some items. I have however, stacked it full with 4 complete brands and there was room to spare, just none to move too much around.

Regulator vs. Fine Control Valve - First - Safety, you should always have a ball valve or some other quick shut off. You do not want a valve that requires 5-6 turns to shut off. Other automatic shut offs for flame outs and electrical failures (for blower forges) and check valves are a must. Safety should be first. As for a regulator you can know what pressure you are working at ... you can also duplicate that pressure for future testing or specific tasks. With a fine control valve, like a needle valve, you can count turns for a particular setting, but there is know way to judge flow or fuel consumption, as you might do with a pressure. As far as a regulator goes, however, a needle valve and a gauge near the jet tube would give you a more accurate account for what is going on and eliminate errors due to hose pressure drop. Some designs put the gauge on jet tube opposite the gas inlet. It is apparent that you need some method to adjust the inlet pressure and thus the flow.

More pressure = more fuel/air flowing, should = hotter forge.

I say should equal, because the perfect neutral flame gets colder with an addition of more fuel. Lots of other factors affect the temperature in the forge. The fuel efficiency drop and forge temperature drops due the turbulence created at the high speeds when the fuel pressure is increased. It is all a balancing act.

Some philosophy

The forge does not really have a "front" of "back", unless you do not cut a hole in the "back" for passing long pieces through for heats in the middle. I am also convinced that the "front" might be the "back" depending on which end you feed parts into the most, or at the time. If you are heating long thin sections that are not being bent, the 3" x 5" opening might be sufficient for the work (thus being the "front") and let the blast of heat out the larger exhaust opening in the "back". If you are only heat treating or making knives that fit in the forge, an opening in the "other end" is not necessary. Also, note the Dura-blanket hasn't been cut out of the smaller opening in some of the pictures. This allows the buyer to cut it out if they want … that is at least in forges where I do not put in the Derby 3000, as was the case before I put Derby 3000 in the forges. I cut a fire brick about 3:” long to fill this small opening, just incase, but have never done so in my application.



I bring these items to most NTBA Meetings see link on main page for schedule. I might consider selling Dura-blanket via USPS … e-mail me. $20 post paid per Freon Tank Forge. The other stuff is quite heavy and shipping is prohibitive. Some fireplace shops sell refractory cement in 5#-15# tubs. This is more economical than the 50# tubs or sacks that commercial suppliers carry. Ceramics shop might carry a similar product.


Dura-blanket, Derby 3000, Krycon 3200 XR

            Thorpe Products Co.

            2200 Regency Dr

            Irving, TX 75062

972-785-9900                          FAX 972-785-9910


Fire Brick

            Boral Bricks Inc.

            1400 N. Broadway St.

            Carrollton, TX 75006

            972-245-1542             FAX 972-242-8172


Last Updated: 2004.09.13 - - © 2000-2007
Comments to: Tom Essary -
Member - North Texas Blacksmiths Assoc. and ABANA