2019 February 24    Metal & Shop  


In the first article I built a side-blast forge from a 55-gallon drum.  That was sort of an elevated fire circle.  It worked, but it wasn't that efficient as a blacksmith forge.

In the second article I tried anthracite.  A couple of bricks helped to keep the anthracite heaped up more. 

Now, let's upgrade it to a better design.  Before testing it with anthracite, though, I'm going to fire it up with charcoal and wood.

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In This Article

A Multi-Fuel Forge?

Modding the Drum

The Tuyere

The Platform

Fire It Up

Welding Temperature


Multi-Fuel Forge?

Can the same design work with two or three different fuels?

It depends on the fuels.  Could be that a bituminous forge is not ideal for anthracite, wood, or charcoal.  But then again, it's not far from ideal;  it could be quite usable.

Anthracite and wood both require some fuel depth.  Wood, because the upper zone is slowly turning to charcoal;  anthracite, because the gravel-like pieces would otherwise let too much air at the workpiece, and too much heat would escape the combustion zone. 

Charcoal doesn't require as much fuel depth as wood (because it's already charcoal), but it's easy enough to make a shallower heap of fuel in this forge.  So, the basic design should work for any of these fuels:  wood, charcoal, or anthracite.

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Modding The Drum

Earlier, I found that bricks on edge along two sides can help contain the unruly heap of gravel-like anthracite. 

So I decided to improve on that idea. 

First, I cleared out the unburned fuel and the bricks.  Time to redesign it some.

Next, I made the "side blast" tuyere an actual side blast.  The original had the tuyere and the workpiece in the same access port;  that was unwieldy.  So now, we locate it about 90 degrees from there.  Time to cut some metal.

My favorite tape measure (high mileage).  It helps to have a scratch compass or wing dividers to trace out a 3" circle. 

Also needed:  a couple of cold chisels, a hammer, a power drill with 1/4" black oxide bit, and a die grinder or a half-round file.

Locate a suitable spot about 90 degrees from the center of the original notch.  Mark out a circle 3" in diameter, unless you'll be using a smaller tuyere.  Bottom of the circle should be at the same height as the bottom of the original notch.  A 3" round opening is big enough to fit the common sizes of auto exhaust tubing, even with jogs and slight bends in them.

Closely-spaced holes drilled around the edge of the circle.  A cold chisel can cut through the rest.

To remove the sharp edges, I heated them up and hammered them flat.  A corded or cordless die grinder would have worked better.  Don't forget the eye protection.

So here it is after hammering down the sharp edges:

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The Tuyere

Diameter is larger than ideal, but it's what was available.  (A 3/4" to 1 1/2" tuyere would be better.)  What's important is the amount of O2 available to the combustion reactions.  Adjust the air flow until you get the desired result.  If you want more air velocity into a smaller area, try a reducing adapter.

After making the round cutout in the 55-gallon drum, next I made something to keep fuel chunks from rolling into the tuyere.  (They definitely do, as I found last time.)  So I drilled 9/64" holes and put 3/16" or 1/8" welding rod scraps through. 

I fixed the tuyere at its far end to a post.  Then I built up bricks inside the drum, forming one of the trench walls:

Those empty spaces should have some fill to keep the bricks from falling back when the forge is running.  A mixture of ash and sand works well.  Paver sand works great because it packs easily;  however, play sand should pack alright when mixed with ash. 

If sand is not available, wood ash by itself will suffice.  Dirt works, but this time of year, any dirt that's not snow-covered is going to be frozen mud.  Or, thawed mud. 

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The Platform

The tuyere side of the trench is mostly complete here, except for the backfill.  Now we build the other side, making it more of a table-like surface.  This will hold extra solid fuel. 

Figure on using about five complete bricks for that side, plus two or three half-bricks.  Then, two thin firebricks for the trench wall, and one piece of thin firebrick to take up some of the space along the far side, where a regular brick would be too thick.  If you don't have that, just pack it solid with ash, sand, dirt, or clay.

Now we have the bricks set up on edge.  They create an elevated hearth floor, which acts as a storage platform for solid fuel.  The height makes it easy to push fuel into the trench as needed. 

Fill the gaps with sand-ash mixture:

So there we have a brick hearth with no mortar, easy to re-configure if necessary:

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Fire It Up

First, before coal, I want to make sure it works alright with charcoal and wood.  (And if it doesn't, move bricks around until it does.) 

Small scraps of wood or sawn-up tree branches make a good, cheap fuel for a blacksmith forge.  Very coarse wood chips-- be sure they're untreated-- should also work. 

Notice there's a cutout or pass-through in the side of the barrel now.  This allows working on longer pieces of stock.  (Make the pass-through before you start using the forge.....)  I used a drill and an angle grinder with cutoff wheel, then a file to de-burr the edges.

Here's my sophisticated method for adjusting air flow.  Notice the angle;  probably less than 5% of its output is going into the tuyere.  Charcoal and wood forging require very little extra air, unless you need welding heat.

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Welding Temperature

It takes a while for the heap to turn into charcoal.  The fuel depth here could stand to be a bit more, but it was OK.

With very little air flow, it works great for general hot-forging:

Soon this piece will get borax and go back into the fire:

For welding temperature, angle the hair dryer so more of the output goes into the tuyere.  The air necessary for welding temperatures will also consume the fuel much faster.

So I didn't get a photo of the welded piece, but it did (mostly) weld.  It would have gone better, but by the time I figured out how to get welding temperature, there wasn't much fuel left.

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Future Upgrades

The trench makes for a long fire, which is not always necessary.  I might try putting 1/4 of a firebrick on either side of the air-blast region, making sort of a square firepot. 

Then, the effective depth could be adjusted by stacking more brick pieces.  And of course, adjusting the height of the solid fuel pile.

The brick sides and the hearth design work well, so I think I'll keep those the way they are. 

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This upgrade made a huge difference.  It's a lot easier to work with metal now, and it wastes less fuel. 

So there it is... the base of a 55-gallon drum, a scrap of muffler pipe, some bricks, and some sand and wood ash.  There was no welding required, no bolts, no fancy machining, no special brackets. 

In the next article we'll see how it does with anthracite coal.

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