Ancient blacksmiths devised the first forges which were just clay-lined pits in the ground. The blast (or air supply) was provided by the lungs of several apprentices, or later with crude bellows (those included at the end of the article were devised in the Dark Ages). This arrangement works: I’ve used a wood fire in this type of forge to heat half-inch stock to a bright red heat. Of course, you’ll want to build your forge higher than ground level. Building a forge from masonry is a time-consuming and low-tech option, but if you’re using salvaged bricks or field rocks, it’s also an economical choice. It’s going to require a lot of room, but it’ll be around almost forever, so take the time to do it right. A masonry forge needs a foundation no less than 24″ square, preferably concrete and extending below the frost line. If you’re using a mixer, consider building your forge completely out of concrete. Figure 2 illustrates a typical example; use your judgment when placing forms and re-bar. If you’d rather use bricks or rock for the sides (instead of piecing concrete forms together), use the drawing as a guide.

The bed of the forge is built to a comfortable height (usually waist-high for the intended smith). It slopes—like a hopper—so fuel has a tendency to self-feed into the fire. At the bottom of the hopper is the grate (Figure 3), which is an outlet for the air supply, the blast. When the blast is fed through burning fuel, forging heat is produced above the grate. When your forge is built, plan on replacing the grate; it “burns” away quickly. Figure 3 shows a simple air pipe (called a tuyere) and grate combination; it’s just a piece of scrap 2″ or 3″ pipe. Embedded loosely in the forge, it can be easily replaced. A more sophisticated system uses a separate grate and tuyere; the added difficulty of building it pays off with a longer work life and easier grate replacement.

You will require a chimney if you’ve decided to build this forge indoors, but masonry is a poor choice in earthquake country. It’s also an expensive option. Sheet metal duct work is just fine. I’m not going to recommend that you install a chimney without a permit, but I do recommend at least consulting the Uniform Building Code. Appropriate chapters were written to keep people from accidentally incinerating their buildings. Look into it.

Tags: Rock, Solid
Filed under: Education, Information, Material, Nature