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How to Make a Forge From an Old Propane Tank for Blacksmithing

Blacksmithing is both a hobby and a useful skill. I initially planned to forge knives, but smaller projects are easier when first learning.

Propane Tank Forge With Punch About to Quench

Propane Tank Forge With Punch About to Quench

Your First Forge From an Old Propane Tank

This was the second propane forge that I made, and the current one that I use. I learned a lot from building this forge, and I hope that you will learn much using these instructions to build your own homemade propane tank forge.

I recommend using an empty and old tank. If you have a choice, choose a tank with the older-style valve, which looks like a five-pointed star or cowboy spurs. Most refill and exchange stations will charge more to exchange these older tanks. A newer overfill protection device (OPD) valve will be triangular, and it should be able to be exchanged or refilled normally.

Step 1: Remove Propane Valve on Tank

Attach your propane tank to a telephone or power line pole using tie-down straps. The straps should be made to be tight, keeping any movement to a minimum.

Using a monkey wrench, or even a 1.5″ diameter metal pipe, unscrew the propane valve from the tank. The 1.5″ pipe should fit over the propane orifice that would normally be attached to a grill. Unscrewing the valve will be difficult, as propane tanks are built to last, so a larger wrench or pipe will help give you more leverage.

I initially attempted this by attaching the tank to a desirable tree. I found that this damaged the bark on the tree, and it was ultimately unsuccessful.

Using tie-down straps, attach your propane tank to a power line pole.

Using tie-down straps, attach your propane tank to a power line pole.

Step 2: Fill the Tank With Water

All propane tanks, even "empty" ones, should be purged with water once the valve is removed. This displaces any residual propane, which is obviously flammable. The escaping propane will smell pretty bad for a while and will attract flies. I used a hose to fill my donor tank with water. The escaping propane may cause the water to splash around a bit while it is filling.

Note: Despite the picture showing the guard removed, I recommend removing the valve first, then filling it with water to displace the propane. Only once the propane is removed and dissipated, should you use the angle grinder on the tank. One way to see if the propane has dissipated is that the flies will have flown away.

Fill the tank with water.

Fill the tank with water.

Bracket removed with angle grinder; valve removed with plumber's monkey wrench

Bracket removed with angle grinder; valve removed with plumber's monkey wrench

Step 3: Remove Valve Guard and Metal Ring

Now that the tank has been purged and water emptied, cut off the valve guard on top and the metal ring on the bottom of the tank. I used an angle grinder to do this. Cutting the welds was very easy and quick.

As mentioned above, ensure all propane has been expelled from the tank before you use an angle grinder, or any other sort of cutting device, on the propane tank.

My tank with valve and guard, and ring removed

My tank with valve and guard, and ring removed

Step 4: Remove Paint and Rust

I used a flap disk for my angle grinder and carefully removed all the paint and rust from the forge. I also cleaned up the weld that was used when the tank was first made.

You can use an angle grinder with a flap disk like I did, block sand, power sander, or any other way to remove the paint and rust. The existing paint is most likely not good for high-temperature applications, plus the forge will look much better with a fresh coat of black paint on a smooth surface.


Step 5: Trace Your Planned Cuts

Choosing the size of your opening is an important part of designing your forge. The smaller the opening, the better your forge will be at retaining heat. However, too small of an opening can make retrieving pieces difficult, and make you unable to have more "irons in the fire."

The opening I made in this build ended up being much too large for my needs. In my next build, I will make a much smaller opening.

Consider adding an opening to the rear end of the forge, so that you can heat middle sections of metal by feeding through the other side. This opening can be much smaller than the forward-facing opening, maybe 3″ x 3″, or whatever you think is the largest stock you will use in this relatively small forge. Again, the one I made in this build is too large for my needs. My next forge build will have much smaller openings.

I used a paint stick as a guide for drawing these guidelines by drilling holes in it. Ensure that your forge will not move, so that these lines are misaligned. You will drill holes that will enable you to draw a horizontal line of the dimensions you require. I would recommend about 1" above and below the center. Repeat this on the other side, though with a smaller opening. Draw vertical lines to complete the outline in which to cut. While the large arched opening I did in this build looks nice, it lets out significantly more heat than desirable.


Step 6: Cut Out Your Traces

Using a metal cutting blade, cut out the traces you made earlier. Generally, cobalt or high-speed steel will be needed. Wood-cutting blades will not cut through metal well, if at all, and likely be ruined after being used for this project.

I did not have a metal cutting hole saw, but I would recommend using one for the propane burner entry point. I used a cobalt jigsaw blade to cut out the front and back openings. Use an angle grinder with a grinding attachment to clean up the edges of these cuts.

Offsetting your burner entry point to one side will improve efficiency, but still, attempt to have it face directly downwards. You want the heat to roll down the sides of your forge towards the center, as opposed to straight down the center.

Cutting into your forge this way can be a little tricky, so if you are unsure if you can do this, straight-down burners function just fine. Many commercially built small forges are not offset in this way.


Step 7: Line Your Forge With Ceramic Fiber Blanket

Please Note: If you are going to make legs and burner holders with nuts and bolts, you should do this now, before the ceramic fire blanket is placed inside.

Properly insulating your forge will help it retain heat. The more insulation that is used, the less heat you will have to use to reach forging, and possibly welding temperatures. While I was able to forge using one inch of insulation in my first forge, two inches is somewhat of a sweet spot.

Ceramic fiber blanket comes in different temperature ratings. Both types will work, but the higher temperature (2600 Fahrenheit) blanket is somewhat superior. I recommend getting three or four (or equivalent) 1" x 12" x 24", as this is just about the right size to line your forge with reduced need to trim, and working with a 1″ blanket is easier to work with than 2″.

Step 8: Cut Holes in Ceramic Fiber Blanket

In this build, the front opening did not require lining, but the rear side did. I placed the rear-opening side of the forge on the ceramic blanket and traced it out using a permanent marker. I then cut the tracing out using a razor blade.

If you place this piece inside the forge, you can then trace the rear opening onto the ceramic blanket. Cut this tracing out with the razor blade. Consider putting a second layer of insulation on the rear of the forge if you purchased enough ceramic blanket. If necessary, repeat this process for the front of the forge.

If you are able to weld, it may be easier to cut the front of the forge off with an angle grinder and then weld back on (or perhaps put a hinge and clasp on it to fit larger pieces of metal) for the next step. Once the front and back are in place, line the outer shell with two inches of fiber blanket. Folding the blanket will make it easier to fit it through the openings. Push it so that it is flush with the outer shell of the tank.

Add enough layers of fiber blanket to achieve two inches of total insulation. Use a keyhole saw or hacksaw blade to cut through the blanket where your propane burner will go.


Step 9: Seal Your Ceramic Fiber Blanket

While not required, a rigidizer can be used to seal the ceramic fibers in the blanket. However, you can simply coat your ceramic blanket in refractory cement or a reflective coating ("kiln wash") like matrikote, plistix 900, or ITC-100. I have used Meeco's red devil refractory cement on all my forges, but kast-o-lite is also highly recommended. The lining of your forge will get damaged when used and should be examined for damage from time to time. Open areas should be repaired with refractory or kiln wash.

Sealing can be done with a gloved hand, especially for hard-to-reach areas, but a straight edge can make things easier and neater. A large paint stirring stick was very helpful and is available at most hardware stores. Multiple smaller coats of sealant that are allowed to dry are more effective than thick/larger coats.

When sealing the burner hole, give it a slight outwards taper as it opens into the interior forge area. This will act as a crude burner flare, but also give room for a proper burner flare once you have one. If you already have your burner flare, you can use it to mold the opening for a custom fit. If you already own the flare, plan to have it sit up within the insulation, not flush with the interior lining of your forge. This will protect it, making it last longer.


Step 10: Add Legs and Burner Holder (and Paint)

Legs can be of many different sizes and designs. For this build, I purchased a 48x1/2x1/8 stock and cut about two 24″ sections. Using my paint can forge, I heated and bent both pieces of metal at 4″ and bent them to about 75 degrees, and welded them in place.

For the burner holder, I used a piece of galvanized steel exhaust connector available at a car parts store. It is very important to strip the galvanized coating off of anything that goes close enough, or into your forge, that it may get hot. If you do not remove the zinc coating, it will create a toxic gas that can kill you once heated. Removing the zinc coating can be done by soaking the piece in vinegar overnight. Then empty the vinegar and zinc residue out and place the piece in new vinegar. This should only take one overnight soak but repeat it again to ensure safety.

Using a properly sized drill bit and matching threading tap, drill three or four holes equidistant from each other into your burner holder. Using the tap, create threads in each of these holes. Purchase bolts or screws to fit these holes. It will then need to be welded in place onto your forge.

Finally, to prevent rust from forming, give all exposed metal a nice coat of high-temperature spray paint. Grill paint should be available at any hardware store.

The only thing left to add is a propane torch, which can be purchased online or built using plumbing parts, also available at any hardware store. Options are also available on eBay, Etsy, etc.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Devin Gustus