I have been using a bottom blast fire pot that I inherited for seven or eight months. I am using charcoal and looking at the jabod types. When I saw the Mark III I knew that was it. Four hours at the forge and and only one coal bucket of charcoal, where I had been going through a bucket an hour. Thanks Charles and everyone else for posting pictures and ideas.

What made such a difference to your charcoal "consumption"? The reduced air supply?

There are those on the forum who can probably explain the particulars. I would say the air supply is part of it, size of the fire bowl, and somehow the angle of air delivery. Sorry I can't be more descriptive.

Nice looking forge Laynne. 

Not being a pyrochemist or physicist I can only make some educated guesses and share my observations. 

We have known for a wile that bottom blast forges required a deeper coal bed than side blast forges when burning charcoal. Part of the problem is probbably the volume of air, but perhaps also the fact that one one pushes the air in sideways it takes a fraction of a second longer to turn and move up threw the fuel (being an ex mechanic and used to thinking about the fixed amount of time the flame front moves across a piston vs the amount of time it has to do so at higher RPMs) 

in the case of the Mark III JABOD forge the fire bowl is only about 2” deep (1” above the tuyere) 4” across and 6-8” long. You pile a cuple of inches of fuel on top of the hearth as well (my experiments show coal likes more air and a slightly deeper fire in the side blast configuration) using a dubble acting bed pump and only bringing the fire up to forging temp also helps me conserve fuel. The stock heats slower but more thoraly and when the stock isn’t in the fire you burn less fuel. To weld bring the stock to forging temp then pump more vigorously to reach welding temp. 

Now the Mark III is build to burn charcoal, using a bed pump and be portable. But being a pile of bricks and cat litter it is also easy to reconfigure to use your air supply and materials on hand. The JABOD forge was from its inception an inexpensive test bed and demonstration in low buck blacksmithing. The Mark III is a portable demo forge that uses what I learned from the first two. 

Very interesting, thanks both.

Thanks Das.

I am going to adapt my hand cranked blower to it and see if I like it better. I am not planning on being mobile for some time. Still learning.

Charles thanks for the insight.

Keep getting back to us with what you learn, that way not only do you learn, I learn and any one coming along in the future can learn from your experience. 

I also find it much easier to work multiple irons in a charcoal forge. whilst you'e got one at the anvil the others are soaking in the residual heat with no danger of burning, once you return it to the forge and add air, the next piece is soon up to temp and ready to forge and the first piece sits soaking, working this way gets more work for less fuel and in less time.

Although this doesn't work so well with anthracite, which needs a constant blast to keep from going out entirely.

Yesterday I spent four hours at the forge with the blower connected. For my purpose it is the way to go. Six minutes from lighting the paper to glowing horse shoe. I was turning at about 12 rpm or once every five seconds. Heart of the fire was consistent. I also reduced the bowl size. It was originally 6x9 now 4x6. 

As much as I like the jabod I had one thing that was giving me a problem. The heart of the fire was right against the brick I was banking the charcoal to. I went deeper bowl, tue pipe low, one inch up, hard wood charcoal, pine charcoal, mixed the two with no change. This afternoon I removed the rock from under the tue pipe and angled it down to the floor of the bowl. This moved the heart of the fire out about two inches which is the center of the bowl. It is a one inch drop over maybe a foot. Maybe this will help if anyone else is interested.

Laynne

The fire sitting right at the base of the tuyere is coming for side blasts.  I like your simple fix.  Another fix is higher pressure air but then you are buying blowers.  

 I had the same issue with the fire wanting to stay right along the back. I just pushed my pipe in a bit past the brick and covered it with my clay mix tapered up to the top of the back wall.  I get a nice bed of burning coke with the heart in the center now with either my hand crank or my little electric inflator

Historical evidence suggests (and manuals from about one hundred years ago) tuyeres angled down

Rehder mentions an angle of 14 deg above horizontal in a smelting furnace in "The Mastery and uses of fire in Antiquity" Changing the angle changed how well the bloomery worked.

On 5/31/2018 at 1:31 PM, JHCC said:

Although this doesn't work so well with anthracite, which needs a constant blast to keep from going out entirely.

I had the same trouble with store bought coke.  It was shocking how fast the fire would go out without air blast.  

Latest experiment. I took a one inch I'd pipe and flattened the delivery end to about a 3/4 inch oval opening. After several days of use I am pleased with it. I didn't try this with the 3/4 pipe so I can't say if the oval shape makes a difference or if it is just a matter of volume. Maybe I will switch back and see.

Laynne