Get Medieval: How to Build a Metal Forge | Popular Science
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Get Medieval: How to Build a Metal Forge

Make a propane-powered forge in your garage and get your hammer and anvil ready

Propane Forge

The forge, assembled.

Vin Marshall

Forging steel is significant for several reasons. It's one of the oldest metal-forming operations in existence. Blacksmiths throughout history have (and continue to) forge steel to create things ranging from practical to beautiful and everywhere in between. Industrial processes often involve forging not only for the efficiency with which it forms metal, but also for the way in which it strengthens the part by aligning the grains in the steel along the lines of its shape. Did you know that you could be doing this same time-tested technique at home? Here is how I built my own propane forge.

At my old shop, I had a talented blacksmith as a neighbor (check out his work: www.andyuprightmetalworks.com) who got me interested enough to take a stab at forging on my own. I did some interwebs research and came upon a few Web sites on which people documented their own forge builds. Almost all of them used a burner design called the "Reil Burner," which has the distinct DIY advantage of being constructed almost entirely from plumbing parts. If you have access to a drill press or a drill and a very steady hand, you can build this burner.

After finding out how easy this was to do, I was hooked on the idea of forging at home. I needed three things to start. A hammer, an anvil and a forge. One of the things that I find most fascinating about blacksmiths is that they traditionally build all the rest of their tooling starting with those three simple items, and in so doing, learn their trade. The hammer and the anvil are easy to obtain. Lets look at how to construct a simple propane forge.

Propane Forge

The forge, assembled.

Vin Marshall

We need two things for our forge: A box to hold heat and a burner to make heat.

Lets look at the burner first. There is an awful lot of forge related and other information on Ron Reil's page, including the details of just how and why his propane burner works so well. If you want to cut to the chase, as I'm going to do here, then start with this set of plans for the Reil Burner. I also recommend reading at least some of the supporting documentation on the site, such as this page about the EZ-Burner.

Propane Forge

The forge, assembled.

Vin Marshall

I made my burner very slightly differently than the Reil burner. Using an idea I stole years ago from someone else's forge page (I cannot remember exactly where or I would cite it), I used a MIG welding tip as the propane gas jet instead of a #60 drill hole. In theory, that would have allowed me to adjust the fuel / air mixture by changing welding tips, though I never did. I'm fairly certain that either method will work equally well. I also mounted my 1/8" gas tube through the pipe reducer rather than on the face of it. Again, I don't think this makes any difference in the function of my burner. It just seemed like a cleaner way to assemble the burner.

To build this burner, you will need to acquire the following:

  • 8" long, 3/4" black pipe nipple
  • 1 1/2" to 3/4" pipe reducer
  • 3" long, 1/8" pipe nipple (I used brass here because I ended up sourcing parts at Home Depot and that was what they had. Either brass or steel will work fine.)
  • 1/8" pipe cap (of the same material as the 1/8" nipple)
  • 1/8" to 1/4" NPT bushing (same material as above)
  • 1/4" ball valve
  • An 0.040" or 0.045" MIG welding tip (if you decide to use this as the gas jet)
  • 3" of 1" I.D. pipe
  • 5 3/4" long #4 set screws.
  • If you are mounting the 1/8" nipple used to the face of the pipe reducer, you will only need 3 of the above set screws. You will also need two small U-brackets suitable for holding the 1/8" pipe nipple and 4 machine screws of a suitable size to use with those brackets.

The pipe reducer must be modified slightly to accept the 1/8" pipe nipple that will carry the gas flow. If you choose to follow the construction of my burner, drill two 7/16" holes in the sides of the reducer such that the pipe nipple can pass through the center of the large end. This is the arrangement pictured. You will also need to drill and tap two holes for set screws in the back of the reducer. These set screws retain the pipe nipple.

Alternately, pipe hold-down clamps can be used to attach the 1/8" pipe nipple. This will require four holes to be drilled and tapped so that the clamps can be bolted to the back of the reducer.

Propane Forge

The forge, assembled.

Vin Marshall

The 1/8" pipe nipple itself must also be modified. This pipe provides the gas flow to the burner and contains the gas metering jet. In the simplest implementation of this design, a #60 wire size hole in the pipe nipple is sufficient (really small drills are given numerical sizes called wire sizes. You will probably have to order this drill if you do not already have one, unless you have a great local hardware store). I decided to make my life a bit more complicated - probably needlessly so - and drilled and tapped this pipe nipple to accept a MIG-welding-gun tip.

After the pipe reducer and the 1/8" pipe nipple have been prepared, the rest of the burner basically bolts together.

Propane Forge

The forge, assembled.

Vin Marshall

The 8" long 3/4" pipe nipple threads into the 3/4" side of the pipe reducer. The 1/8" pipe nipple is inserted through the holes or under the clamps on the other end of the pipe reducer. If you are taking the welding-tip-as-gas-jet approach, install the welding tip now. Using teflon tape or pipe dope, assemble the pipe cap onto one of the protruding ends of the 1/8" pipe nipple and the plumbing necessary to connect to the propane line from your regulator on the other. In my case, that plumbing consisted of a brass 1/8" NPT to 1/4" NPT bushing and a 1/4" NPT ball valve. From there, a 1/4" propane hose connects to a regulator mounted on the propane tank.

Propane Forge

The forge, assembled.

Vin Marshall

The last bit of fabrication in the burner is the cone. This requires some forging. You can either improvise with an oxy-acetylene torch and a rosebud tip, use someone else's forge, or wait until yours is set up to make this last piece. When you do make it, following the Reil burner plans, flare one end to be about 1/8" larger all around. After the cone has cooled, you'll need a way to attach it to the business end of the burner. Drilling and tapping for three set screws 120 degrees apart worked well for me. Ron Reil's EZ-Burner page gives instructions for positioning this cone on the burner to give a properly tuned flame.

At this point, you have a working basic burner. There are many refinements that could be made (the idle circuit some people use would be a great improvement), but you have at least enough of a burner to begin forging. So now let's build the box.

Propane Forge

The forge, assembled.

Vin Marshall

When shopping for a propane regulator and fittings, make sure to get a tank connection that looks like the one attached to the regulator in the picture. The new-style connection, pictured sitting next to the regulator, has a safety feature built in that shuts down the propane flow if it thinks you have a massive gas leak. This is good for BBQ grills, but unfortunately for us, this burner behaves a lot like a massive gas leak. The older style connection won't trouble you with that "safety" feature.

Propane Forge

The forge, assembled.

Vin Marshall

The forge itself is basically a box made of refractory material and the steel needed to contain and support it. In my forge, I used refractory brick purchased from a friend with a ceramics supply and kiln repair business. If there is no such business near you, you can order a variety of refractory material.

Propane Forge

The forge, assembled.

Vin Marshall

As you can see in the pictures, I built a very simple and small forge. I wasn't sure how much forging I actually planned to do, and I didn't want to go overboard. This size was adequate for everything I did, even though a larger forge would have been convenient at times. Were I to do it again, I would build a forge that was longer, with two burners to keep it uniformly heated, and wider as well. This forge's width was dictated by the length of my brick. A wider design would call for either different refractory material, or an arch-like arrangement of the bricks to span the distance. Also, while I left the back of my forge open to accommodate longer work pieces, I would close all but a window in the back of a larger forge. I would probably also build a door for the front. This forge loses a lot of heat through the front and back. I address this partly by piling extra refractory bricks in front of and behind the forge when I am working.

Propane Forge

The forge, assembled.

Vin Marshall

Refractory brick is easy to work with in that it is very easy to cut and drill. It's hard to work with in that it is brittle. Buy a bit more material than your forge design will actually require on the assumption that you will destroy some of it.

To construct the forge, come up with a design that works for your expected needs. Plan the layout of the refractory material you have chosen. Then design an outer support of steel that will keep that refractory material in place once assembled. On the inside, your layout of refractory material must support itself. As you can see in my design, I went with a very simple arrangement of the bricks that is held in by a minimal frame of angle. Your design will depend on the size and shape you've chosen for your forge.

Propane Forge

The forge, assembled.

Vin Marshall

Finally, you need to combine your burner or burners with the forge you've built. Choose a central location for the burners and determine how they will attach to the frame of the forge. In my design, a piece of flat bar bent into a U shape clamps the 3/4" black pipe of the burner to the forge frame. (There are U clamps available for black pipe like this 3/4" pipe, but I didn't have one on hand when I was building the forge.)

Propane Forge

The forge, assembled.

Vin Marshall

A hole needs to be cut where the end of the burner passes through the refractory material. The fire brick is so soft that I was able to easily use a hole saw by hand to make this hole.

Propane Forge

The forge, assembled.

Vin Marshall

Once everything is assembled, you're ready to fire up the forge and begin forging. If you find that it captures your attention, you can learn more about the art in many places. One good place to start is Anvil Fire and another is ABANA.

We'd like to see your forge and things that you've forged. Add the pictures to the PopSci Pool on Flickr.

A Note About Safety:

Please pay attention to safety. The forge is HOT. The metal coming out of the forge will be HOT. Keep in mind that, while we've shown you have to build a forge here, no information has been provided as to how to forge. You must do your research and learn these techniques before you jump in. Keep in mind that this forge burns propane and produces waste gasses including Carbon Monoxide. Only use the forge outside or in a very well ventilated indoor space. Use your common sense and always wear eye protection.

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