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I Forge Iron

My Japanese style forge project

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Hi everyone,

I have been busy for a while designing a new forge to smith blades in and most importantly: harden them. The old one doesn't work well and stands in the way. This one has served me for many years, I poured it from fireproof concrete, it is reinforced and I made it when I was about 16 years old. It was about four years back and I made it with the little knowledge I had at the time, but was determined to build a Japanese style forge. It gave me a lot of understanding and experience, so it's time for improvement.

Foto's of everything can be found here: Foto's of my whole project

Now that there is room in my backyard, a very nice 2x2meter concrete plateau, I want to build a new and better forge there. Since the old one is still good, I will use it as a base. With firebrick and cement I will build up the old one to the design I made. On top of the forge I will build a cover to prevent hot sparks and smoke to get everywhere, my neighbours are good friends, so I don't want to smoke em out, and I don't want the trees and hedge to catch fire either.

When the forge is full of hot charcoal, and I blow a lot of air through it, it only gets hot on the bottom near the tuyère (airpipe). It won't get me enough heat efficiently on top of the fire to effectively heat blades.
My idea behind the new design is that the tuyère blows air in from the side in the bottom of the forge. Because of the upside-down-roof-shape of the centre of the forge, all the air and heat from the charcoal will be pushed upwards. This was the mayor design flaw in the old forge. Because of the flat bottom with the tuyère on bottom level all the air, and with it the heat, could escape on all the sides. No matter how much air was blown in, it was simply blown away to the back and front and couldn't send all the heat upwards towards the blade that is in the fire.

Let me know what you think,


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I would suggest looking at the diagram of the forge in the book, "The Craft of the Japanese Sword, by Kapp & Yoshihara, page 59. I have photos of sawmaker, Yataiki, at work in two separate forges. He is right handed, and his box bellows is parallel with the wall to his left. The forge is to the right of the bellows about 20 inches{?} with a firewall of concrete in between the two. There is a hood. The bed of the forge is dug below grade maybe 6" and filled with charcoal powder up to grade. The fire of larger charcoal pieces is built on top of this. Your idea of a side blast is typically Japanese, the tuyere of about a 2" diameter and about 2" above the forge bed.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

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Interesting that you mention "The Craft of the Japanese Sword" I have it and it has been a very good read. would you be able to post the pictures of the saw maker you have? I have a map with photo's of Japanese hearths saved to study, my design is very much inspired on these kind of forges and I am always looking for more to learn from.

Thanks, Louis

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Here are some links to how I built my Japanese style forge as well as a box bellows.

Please note the section where I explained how I modified it later to be more efficient. It still needs some work and will rebuild it again. What Frank said about the charcoal powder bed is key. Also the 2" pipe needs to point slightly down.



I have been inactive for several years but am starting again in a new location.

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Hi Danocon, good to have you on the forum.

I have seen your website with the forge long ago, it was very interesting and educational to see how you went through the whole process of building your forge.

When I look at your design, the pipe is about 2inches above the base of the forge and tilted down. Thinking of my old forge, I believe this would get me the exact same problem I had in the first place: that the fireball would be on the bottom of the forge. All the air would be blown towards the bottom and with it all the heat. I want the air and heat to be blown up trough the piled up charcoal and against my blade.
With solid fuel forges you don't stick your blade on the bottom of your forge, you lay in on top, with a little charcoal to cover it. Then the air will be pumped in from the bottom, traveling upwards trough the charcoal blowing the heat up against the blade.
I am trying to make my design as efficient as possible and be able to get it to hardening and forge-welding temperatures. Seeing your pictures it looks like you put the steel almost on the bottom, right in front the airpipe. I did this too with my old design, but it would not give me enough heat.

Does the heat travel upwards or do you put the steel right in front of the tuyère? You said you wanted to change your forge in the future; What would you change about the design then? And why is the charcoal powder bed so essential?


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Hi Louis,

If everything is working correctly the fire can be very big. The idea is that the air is blown in a slightly downward direction and away from the steel so that you do not oxidize it.

The design looks very simple but there are lot of dynamics involved.

1) width of the firebox
2) Height of pipe above floor
3) Angle of pipe
4) Material on floor

When I was working with the Japanese smiths for the short time that I had I didn't think to take exact measurements. Hey, it was a trench in the ground with a pipe what else do I need to know? Oh well.

Other factors I have found that affect how this works

I never could get hardwood charcoal to work well in this system. I burns into small pieces and a lot of ash. There is no place for it to go. Pine just burns away-Really fast though.

Processing the charcoal:

Cut the charcoal into about 2x2 squares for general forging. Sift out everything smaller and ALL the fines and dust.

For heat-treating use 1x1 squares and again sift out anything smaller and all the fines and dust.

Small pieces, fines and dust are what restricts the air flow.

After I made this tutorial I did some more experimenting and then shut everything down to start a new job AND build my house myself. House is now far enough along and I will start again in my new location.

Will keep you informed.


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Hi Dan,

When I was working with the Japanese smiths for the short time that I had I didn't think to take exact measurements. Hey, it was a trench in the ground with a pipe what else do I need to know? Oh well.

That's a petty, but I can understand it, I was thinking exactly like that when I was just starting. "forge, ah well, it's just a hole in the ground with two mounds on the side and air blasted trough it, what can be so difficult?"
But the four points you mention make a big difference. I have a friend that studies architectural engineering (if that's the proper English word), I was hoping that I could borrow some knowledge from him, but they are just starting in airflows and things like that.
An inch more or less can make a big difference for how the forge performs. I have been trying to get some information about airflows, heat dispensation, conduction etc. but It's a very hard nut to crack.

About the charcoal, the process is called Sumi-wari in Japanese and like you said it is a very important step in the forging and hardening process. This link I have saved gave me some good info about that: Sword making process

I am starting to have doubts about my new design, I am worried that I might get a small fireball on the base of the forge and that it doesn't have enough room to spread it's heat upwards without risking over-heating (and burning away) the charcoal on the bottom.
I made some changes that would get me closer to the original Japanese style design that I had put aside.
This would make a good fireball on the bottom of the forge with plenty of room for the heat to dispensate. I have included the picture. The squares are like the first drawings: one square is (in real life) 2x2 inches, so the scale is 1:10. The pencil stripes in the second drawing is how I expect the air to flow. post-13738-049853000 1273261743_thumb.jp
Let me know what you think.

I have a lot of respect for you building your own house, I don't know anyone that would go at it like that.
Good luck with your new house and forge!! let us know how it's coming along.

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