The Construction of My Freon Tank Miniforge

Read an e-mail I received about this forge on 12/23/00

Contact me by phone: (208) 462-4028
Note: Due to spam problems I no longer post my e-mail address.

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The Shepherd's Hook Forge it's Not ... But it Could Be


I provide the following information as a service to the blacksmithing community. Although the designs I employ in building my burners and forges are safe and reliable in the way that I use them, the same may not be the case for you. You assume all risk in using this information, or any other information on this page. Other designs that I have posted here have been submitted by other smiths, and I have no experience with most of them. Use care and good sense in using any of these designs. Get help from a knowledgeable smith if you are new to this work. Don't take chances because these tools can cause injury, blindness, or even death, if used improperly. Also, be sure you are in a well ventilated space (see the Nighthawk CO & explosive gas detector paragraph), or better yet, work outside. Additionally, never operate a forge that is connected directly to a propane tank that is near a forge, or indoors. An emergency pressure valve release could instantly place you in the middle of a fireball. Follow all local codes regarding indoor use of propane, and I believe indoor use of a propane tank violates code everywhere in North America, and most of Europe. A new concern has arisen with the introduction of the "Mongo Burner Series." Please read carefully all the information in the separate "Safety Warnings and Considerations" information which heads the "Mongo Burner Series" section. Thank you.

An additional item that should be of interest to you is obtaining an explosive gas/CO detector for your working space. Mark Manley, of "Manley Metal Works," Silverton, Oregon, provided a short piece of very important information in the Winter 2000 issue of "Hot Iron News" that I feel needs to be passed on to a wider audience. There is a very reasonably priced digital read-out combination explosive gas and CO detector available in local hardware, building supply, and other stores. I was concerned about having a CO monitor in my shop, even though I have a very good induced draft hood in my shop. The detector is made by "Kidde Safety" and is called the "Nighthawk." I will not go into the specs for the instrument here, it is available on the Internet if you look up "Kidde Safety," but will say that it is a very finely designed and built instrument. It runs on 110VAC, and has a 12VDC back-up. It plugs directly into an outlet, or the transformer plug detaches for remote mounting, up to 6' from the plug. You can easily check your CO level with a quick glance at the digital read-out, and if it detects either propane or natural gas will instantly sound an audible alarm, and the word "Gas" will display on the digital display. If it detects a 50 PPM threshold level of CO, it will also sound a different audible alarm. Also, you will know its operating because the blinking decimal point in the digital read-out indicates its operating and sampling the air in your shop.

I bought one of these instruments for my shop, and was so impressed with it that I went down and bought a second one for my home, which has natural gas heat, gas hot water, and a natural gas fireplace insert. I priced CO detectors on the McMaster-Carr web site, and they alone were $170, where this combination instrument is only $59 at my local Home Depot. Considering how deadly CO can be, this instrument is very inexpensive, well worth the investment, and it may well save your life. After Mark installed his "Nighthawk," he discovered that he had been exposing himself to CO levels from 30-160 PPM for a long time while running his forge! Thanks for the tip Mark.

Note: There has been a recall of Kidde Safety "Nighthawk" gas and CO detectors. This does not affect any detectors sold after the date that I posted the above information, however you may check your unit by going to  

A Word About Obtaining My Help

I am no longer able to offer my support to help solve problems you may have with your burners or forge. I have reached the point that something has to give. Two to three hours a night answering questions has brought my metal working each evening of the week to a stand still. I will continue to update my blacksmithing pages, and will now also have the time to clean out all the outdated and conflicting information in my pages, however, I will no longer be able to troubleshoot your system. I still want to receive your e-mails if they do not pertain to forge or burner problems. If you build your burner to the design specs and information shown and discussed on my pages, including in the Troubleshooting Document and FAQ, your burner should work well. If it doesn't, then its not built correctly, and you will need to make some adjustments after looking through the available information. The best thing to look at when fine tuning your burner are the various flame images I have posted. If yours looks like these images, you have it right. Here are a few helpful links.

Note: If you e-mail me, please be sure your e-mail in "txt" (text) format, not html. I am now averaging two to three virused e-mails each time I download my e-mail, so I have to be very careful. If your e-mail is not in "txt" format I will most likely delete your e-mail without opening it in order to protect from possible virus infection. It's certainly sad that we have idiots in our society that feel they must cause such problems.


Forge & Burner Troubleshooting Document

Some Often Asked Questions

EZ-Burner Construction

Rich To Lean Flame Image

1) T-Rex Flame Image - Ideal Neutral Flame

2) Side-arm Burner Flame Using Temporary Cast Iron Test Nozzle - Slightly Reducing Flame

3) Another Flame Image - Oxidizing Flame

The bottom three flame images give you views of burner flames adjusted to 1) neutral, 2) slightly reducing, and 3) strongly oxidizing. The burners have nothing to do with it, just the choke settings. All of these images could have been done with the T-Rex, or Side-arm burners. At your high end gas pressure, if you have achieved a flame similar to the oxidizing flame shown in the bottom image, #3, you will then have full control over the burner flame across the full pressure range. This will allow you to achieve oxidizing, neutral, or reducing, flames as needed by simply adjusting the choke. You will then have a properly functioning burner.

About This Page

This page is a rough step by step record of the construction of my Freon tank "Mini-Forge," the smallest of my four forges. There are many forges out there that have been constructed from Freon tanks, but this one is a little bit different from most of them. I will provide a simple description, along with images, but this is not designed to be a step by step set of construction plans. Also, I get most of my refractory supplies locally from an excellent pottery supply shop. I have no additional resources other than those listed on my main Forge and Burner Design Page, in the subsection titled "Sources For Refractory Materials," so please don't ask for anything additional, as I just don't have anything for you. You will have to explore for materials sources on your own if my listed sources don't have what you want. Thank you.

Note: I have intentionally produced this page using a small font size to make printing of the page for use as an instruction sheet more convenient. If you find it difficult to read this small font, your bowser has font size selections which can enlarge it for you.

The Freon Tank Mini-forge

Dimensions: The finished dimensions of the Freon Tank Mini-forge, as measured from cut end to cut end of Freon tank are 11-1/2", and 9-1/2" in width. The interior chamber dimensions can only be roughly given because of its horseshoe shape, flat floor, and rough Kaowool interior surface. It is roughly 4" in diameter and 9-1/4" long. This calculates out to approximately 116 cubic inches of chamber volume, or 0.4 of the total 300 cubic inch volume a "Reil or EZ Burner" can heat to forge welding temperature if the chamber is ITC-100 coated. If a Nanomongo burner were to be used in this forge it would be a searingly hot forge indeed, for sure requiring UV eye and skin protection against UV flash burn.

Burner Mounting: The Nanomongo burner, or T-Rex, produce such intense vacuum and gas stream pressure that they can be mounted horizontally along the base mounting structure of the forge, and a supply pipe run up to a short nozzle mounted in the forge shell.  This would make the forge much neater in appearance, without the long burner tube sticking up and out to the side. The burner would act like a carburetor to supply the gas mix to the supply line or manifold. Because the gas in the supply line is an air and propane mixture, flashback will occur while shutting down the system when the gas stream velocity drops below the burn velocity. This should not be a problem other than creating a "pop" when the gas supply valve is closed. The greater the volume of the supply plumbing, the greater will be the flash back effect. If you opt to use this method, be sure to use supply line and manifold line diameters of sufficient size to prevent excessive back-pressure on the supply burner.

This little forge is the smallest of my four forges, two coal, and two propane. I sold my commercial natural gas forge a few years ago, or it would be my 5th forge. It is not designed to be my everyday forge, but to be an easily portable forge that I can use for demos, remote heating requirements, or just when I need to take a quick heat on a small piece of iron. I would not suggest you build one this small for a first or primary forge. It is too limited in what it can hold for regular forging, although it would be a very fine bladesmithing forge if you didn't wish to make long blades, say 10" or less. It could handle a longer blade if needed by having the end stick out the back of the forge. It would serve very well for making small hand tools, like chisels and gouges, if you are a woodworker. In fact it would be superb for such use.

An Update: I recently had to do some upsetting on the ends of two 1" square pieces of 1085 steel bar. They were to be used for the posts on two ball topped stake tools, one of 4", and the other 5" diameter. The weather was questionable, so I elected to use this little forge instead of my big one. It took about 4 hours to complete each post by the time I had formed the cup and perfected the shape of each one to my satisfaction. The diameter of the upset portion when finished was almost 2". The little forge did an outstanding job of heating the heavy steel, even though the opening was quite small for easy handling of the metal. This forge can handle much larger sections than I would have thought.

Some Background Information

You can often obtain empty Freon tanks from your local recycling yard. There are about 50 of them sitting in mine at the time of this writing. If that doesn't produce results, check with some of your local heating and AC shops. They have them and generally burn holes in the top or side before disposing of them. If you explain what you want it for they may be happy to give you one. They tend to be wary of guys who want them for air receiver tanks, since that is an illegal use and can get them in trouble, the reason they burn holes in them prior to disposal.

Scribe circles on the ends to allow you to cut the ends out, grind to final shape, and end up with a good circular hole on both ends that is well centered. You will be limited in how small you can cut the top end out because of the blow-off plug. Cut it out as small as you can however, as the curved in ends provide great structural strength, and will also secure the Kaowool in the forge in a superior manner. And besides, it just looks good.

I used my portable "EZ- Burner" for this forge, and decided for portability and easy storage I didn't wish to tie up a burner permanently as part of the forge. This idea has proved to be an excellent one, requiring only insertion of the burner nozzle up to the nozzle collar, and gently tightening three thumb screws...takes all of 10 seconds to do. Also, when I am finished with the forge I can quickly loosen the screws and pull the burner out so that it doesn't act like a chimney, venting the extremely hot chamber gasses through the burner and heating it excessively. The burner is cool to the touch at the moment of shut down, but will quickly get very hot from the exhaust gasses.

The materials used in constructing the forge are; two layers of 1" thick Kaowool chamber insulation, 1" thick Kaowool board for the end panels, and a 4" wide piece of a high alumina 1" thick kiln shelf for the floor. Note: The 1" Kaowool will expand while handling it to around 2", so will seem like its far more than 1" thick. The floor slab sits on compressed Kaowool, as well as four 1" kiln shelf posts that sit on the bolt protrusions that hold the forge support leg structure on. I fabricated the burner mounting from a large "B" grade construction washer for the flange, and a piece of pipe brazed into the center hole of the washer for the mounting tube to hold the burner.  The pipe is a very close fit to the outer diameter of the burner nozzle. I drilled and tapped three 1/4"- 20 thumb screw holes in the tube as shown in the images. Be sure you form the washer to match the forge shell radius before you braze in the pipe section. The washer will require annealing before you can cold work it, or you can just work it hot if you prefer. I worked it cold to prevent scaling. It needs to closely fit the radius of the outer surface of the forge shell. You will also have to grind off a little of the weld rib that circles the tank where the washer will contact the shell to allow a close fit. Attach the collar to the forge shell with two or three 1/4" counter sunk machine bolts. You can get whatever kind of adjustable feet and carrying handle you prefer. My handle is solid brass, which does get too hot to handle while the forge is in operation. You may prefer a different design.

The forge is painted with high temperature stove paint, as is the forge support leg structure. I cold bent the support structure from shear drops that I had in my rack. You may use whatever looks good and is available in your stock rack. The last step in the construction process was to coat all interior surfaces with ITC-100. Any gas forge will operate at higher temperatures, heat the steel quicker, and experience significant fuel savings, with the use of this Zircon ceramic IR reflecting refractory coating. It will protect the Kaowool from erosion and prevent dangerous ceramic fibers from coming out in the exhaust of the forge. It is worth the cost and effort to coat your forge chamber with this excellent material.

What Burner to Use

There are a wide variety of burners to chose from on my Forge and Burner Design Page that will do a good job with this forge. The standard work-horse burners have been the "Reil and EZ-Burners," but now there is a new choice that you should consider. As you can see from the e-mail I have at the top of the page, the standard burners will do everything you may ever need, but the new "Minimongo Burner" is an alternative that has a much higher output, but it is also larger in diameter, 1-1/4" burner tube, and is really too much burner for this little forge. A better choice might be the Micromongo, which is a 3/4" bore, just like the "Reil Burner." I should add one thing. I have information about the Reil and EZ Burners posted on two different pages. One source is located on my Forge Page, and the other on my Forge and Burner Design Page. These links will take you directly to the specific "Reil/EZ" burner information. Please read both pages if you want all the necessary information. You may also want to have a look at the new Side-Arm burner design, which is in the Mongo section on my Design page. It has now been perfected, and its an excellent burner.

I need to update this section to include the "Shorty Burner," which was designed specifically for this forge by Mike Porter in Seattle, and is being commercially produced by Rex Price in Georgia. I have information about the burner on my Forge Design page, which is linked in the previous sentence, but you can go directly to Rex's web site if you wish. This is the perfect burner for this forge, and really turns it into a beautiful tool. 

A Few Words About Burner Injection Angle

Many smiths prefer to have their burners aimed at a tangent to the interior chamber surface. This creates a vortex action as the gasses circle around the interior of the chamber. They achieve a more uniform heating within the chamber by doing this. You will notice that I prefer a more direct injection angle, directed at the center right of the forge floor. This creates a hot spot about 4" in diameter, however the remainder of the forge chamber attains an intense bright yellow heat as well. I prefer to have the hot spot available for use in forge welding, and differential heating of steel. This brings up the temperature of my iron more quickly, and allows me to heat only the desired section of a piece of steel more quickly than would be possible otherwise, and without constant cooling in water of the part I don't wish to heat. I would not want to say that my way is superior, it isn't. It is just the way I prefer to have my forge operate, and what I am used to using. You will have to decide this issue for yourself, and build your own forge accordingly. On my big 4 burner forge, my burner mounts are designed to allow the burners enough angular mobility that they can be adjusted for either situation as desired, although certainly not to a full tangential angle, but the effect is very much the same. I did not do that with this forge because it was never intended to be my primary "work-horse" forge. You may choose to do otherwise however, because the Mini-Forge is truly an outstanding little forge.

Forge Doors

There is a desire in some people to add sliding or swinging doors to their forges. Before you do this, consider the following. This is a naturally aspirated Venturi burner gas forge, and to work properly it can't have any back pressure working against the burner. If you attempt to close the doors while the burner is running you will eliminate the intake air from being drawn into the burner, but not the propane flow. This will result in raw gas filling the chamber and being forced out of the spaces around the doors and burner, where it will burn. When you open the door the large volume of unburned gas may explode. Doors work well on electric furnaces, kilns, and some other kinds of forges, but not on gas forges that do not have an additional exhaust opening provided . Please leave off the doors. It will be cleaner, neater, easier to build, and much safer to use.

The Picture Gallery

Image #1

This image shows the finished and painted, inside and out, freon tank shell. I have completed the bending and welding together of the forge support structure, and the adjustable feet are in place temporarily. It is still unpainted. To the right of the leg structure are the four 1" kiln shelf supports which hold the floor slab in place. Note the holes in the posts that allow them to be placed over the bolts that hold on the leg structure. I also filled each one with "Tenax" refractory to stabilize them from movement during the placement of the Kaowool. The ends of the Freon tank are in the picture to show what they looked like after cutting them out with the torch. I used a 4" angle grinder to true up the holes. You can do as well with a file if no grinder is available. Be very careful while cutting the ends out with your torch because the green paint on the tank creates a highly toxic smoke when it burns.  Also, the burning of any residual Freon will create deadly phosgene gas. Wear a carbon cartridge respirator, or it may lay you low with just one breath! Be very careful.

Image #2

Here the forge shell is temporarily in place on the legs. You can see the bolts over which the four kiln shelf posts, shown in front, will be placed. The bolts are not level horizontally, but due to the width of the posts this presents no problem in leveling the floor slab. The handle is in place, and the burner penetration hole is finished. Notice that the legs on the left side are longer than the ones on the right. This was done to support the additional weight of the burner which is mounted on, and projects to, the left side. This arrangement provides a very stable forge while in use.

Image #3

This shows the forge shell with kiln shelf posts in place prior to filling with Tenax refractory. After filling them with Tenax they can be adjusted in their location a small amount to obtain the best fit for the floor slab and then allowed to cure. Any kind of mastic refractory will work as well, or perhaps even better, than Tenax.

Image #4

This image clearly shows how the slab supports are not level, but the width of the support posts allow the floor slab to be levelled perfectly. I was able to adjust the set of supports on the right to be further to the right when I filled each hole with Tenax. The leg structure has now been painted.  You may certainly modify the leg design in any manor that suits you. The burner support collar is done and in place but still unpainted. I used a fine paste refractory to seat it to the shell as I bolted it in place. Be sure the refractory is completely dry prior to firing up the forge. I didn't, and it bubbled out moisture, ruining my paint in that area. The area around the burner mounting had to be cleaned and later repainted.

Image #5

It is starting to look like a forge. The two layers of Kaowool are in place, and the floor slab is seated on the kiln shelf posts. Despite the image, the forge floor is level. The burner mount has been painted, and you can also see the square socket I have brazed on to the burner mounting flange. (Please see the alternative socket I have a link to under image #9) It will be used later for the support arm that will hold the front Kaowool board wall in place, but will allow easy removal for changing floor protection plates used for forge welding, or for maintainence of the interior. The square socket was forged from a piece of 5/8" ID pipe. If you are careful you can end up with a square tube that looks as though it was machined, and not forged, after you have ground the surface and filed the scale from the interior. You can just see the corner of the rear Kaowool board wall which has been installed and is held in place by the squeezing action of the Kaowool....a friction fit. I cut it about 1/4" wider and higher than the interior surface dimensions of the Kaowool......see below. It fits very much like the ends of a wooden keg, and is very solid. Use a smooth thin knife blade, such as a butter knife, to act like a shoe-horn to work the piece into place. You can depress the Kaowool by reaching in from the other end too, and that is of great help in getting the piece into place. Once its all coated with ITC-100, and has been fired for a period of time, the Kaowool will take a "set" and the end wall will be very secure, even if bumped accidentally with the end of a long piece of iron.

Image #6

This image shows the Kaowool back wall in place in the back of the forge. The opening is primarily an exhaust port, but will allow longer pieces of steel to protrude through when necessary.

Image #7

Well, its almost done. I have used a small horseshoe for the mounting bracket to support the front Kaowool board closure. The Kaowool board has been taper cut to fit into the opening of the forge like a cork in a bottle, and is held on to the horseshoe by four stainless wood screws. It is difficult to see the detail of the support arm arrangement, but the horseshoe is supported by a forged piece of 3/8" square section which sockets into a forged square socket that has a thumbscrew lock. There is more to it than I have described, and I will attempt to clarify it with the image below. It is fully adjustable, and will release the front Kaowool closure for instant removal with just a twist of the thumb screw. The forge still has to have its new ironwork painted, the ITC-100 interior coating applied, and it will then be complete and ready for service.

Image #8

This  image shows the support bracket, and its attachment to the burner support collar, along with the "EZ-Burner" locked into position. The burner collar has a precision forged square socket, made from a 5/8" diameter steel pipe, and attached to the bracket collar with brazing. It is already painted black in this image. It was forged to exactly engage the 3/8" square rod that is socketed into it. The  3/8"rod is bent 90 degrees, and the other end is brazed into the back end of a second, and longer, precision forged square section tube that has a thumb screw on its end to the right. The rest of the bracket mechanism is clearly shown in the image. The attachment to the horseshoe is a weldment, as I was concerned that it might get hot enough in that location to melt a brazed connection. When making the precision forged sockets I forged them slightly undersized, about two thousandths, and then filed and polished the surfaces of the 3/8" rod, and interior of the socket, to perfectly engage without play. Doing it this way resulted in a connection that has no scale in it and is perfectly smooth. Most casual observers would think it was machined instead of forged. Probably the most difficult part of the entire bracket was getting the position of the horseshoe into exact alignment in all three axes. I found that to try to get it exact prior to welding was impossible. I simply welded it, prepositioned as closely as possible, and then tweaked the alignment in the post vise while cold.

Note: To forge a square cross-section out of a round pipe, do not use a square mandrel, but simply work it hot on alternate sides, much as you would to draw out a long square taper on a bar. It will automatically form into a perfect square shape inside and out. It is very surprising the first time you do one of these forgings how perfectly it will come out if your hammer work is carefully done. If you have started with the correct size pipe it will end up almost perfect, with flat interior faces, square interior and exterior corners, and a uniform thickness all around. If the pipe you started with is too large, the extra metal will cause the interior surfaces to bulge inward, and "cold shuts" will form in the four interior corners, greatly weakening the forging. Throw it out and try again with a smaller pipe. Be very careful when quenching pipe. Scalding steam and boiling water often come shooting out the top of the pipe, and can hit you squarely in the face or burn your arm. Always keep it aimed well away from you! Pipe is very dangerous to quench. You would be well advised to just allow it to cool in the air if you are not experienced in this kind of work.

Image #9

Alternative Burner Mounting Bracket Design - Image 9a

Todd's Forge as Completed *

*This alternative burner mounting flange is one that I installed on a forge I build for another smith. It has several modifications that make it more functional, and actually easier to build, because you will not have to forge a pipe into a square tube. I used a 3/8" diameter pipe that I ground flat on one side for brazing to a flat that I filed in the mounting bracket flange to match. I used a short length of 3/8" hot rolled rod bent into a 90 degree elbow to socket into the 1" length of pipe mounted on the flange. On the other end of the 90 degree, 3/8" rod, I brazed on another straight length of 3/8" pipe in which I drilled and tapped a 1/4"- 20 hole to accept the locking thumb screw. Making it this way will allow full motion up and down, as well as rotational, so that the front Kaowool board door panel, which is secured with this fitting, will fit more easily and precisely. Finding 3/8" black iron pipe is not an easy matter, so I finally bought a couple of feet of 3/8" galvanized pipe and burned off the zinc coating in the forge....don't breath the smoke! I was quite pleased with the tolerances of the pipe, and hot rolled rod. Once the weld rib was removed from the interior of the pipe the fit was quite tight and secure. I would strongly recommend this method over my original burner mounting bracket method pictured above, although successfully forging a perfect square section out of round pipe will make your day.  :-)

The rather poor image above shows the curing of the forge, its first firing with everything in place. The Kaowool board closures are blackened from their initial burn off of contaminants, but show the nice clean white color slowly replacing the black discoloration. I ran the forge at a low pressure for about 15 minutes to drive off most of the water from the ITC-100 application the previous day. Once the steam quit coming off, I cranked it up to an intense heat, 40 psi, for about 30 minutes to see what would happen. It worked very well, so it is all done now except for some minor repainting where the burner mounting paint job was damaged during its initial firing a week earlier. The horseshoe was quickly blued by the heat, so may actually scale during extended use, although I will probably never run it at the intense heat it is experiencing in this image. The gas pressure was about 40 psi, and normally it would never be run greater than about 8 psi, more likely 4-5 psi. Well, that is the end of the project. Now I will enjoy using this beautiful new tool. Thank you for following along in its construction.  :-)


A Comment After Using the Forge for a Month

I have now been running this forge for extended periods, as much as 8 hours at a time, for over a month. The horseshoe, which I painted with a high temperature black paint, shows no signs of distress. The whole forge seems very stable, with no heat damage to the paint job visible anywhere. It appears that the shell and metal fittings will hold up well during extended periods of use far into the future. The only negative comment I would make, is that the opening in the front is quite small for using some of my larger tongs. I have to be very careful when placing or withdrawing my irons so as not to damage the Kaowool board, or the ITC-100 coating on it. Otherwise, it is a joy to use, and quickly cools off enough to put away. I want to stress however that this forge was not intended to be a primary workhorse forge, but to be used only for that occasional quick heat that comes along when you really don't wish to heat up your much bigger main forge. An exception to this might be if you want to forge blades.

Thank You For the Visit

Thank you for visiting this page. I hope you find it of help in your own forge construction. Remember, I can no longer provide help or support in the construction of my burners or forges. If you want to contact me for another reason you may do so from the link at the bottom of this page. Thank you.

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Page By: Ron Reil

Updated: 3 Mar 06

Golden Age Forge