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Mark III JABOD forge


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You may have answered this in the other jbod post and I missed it as I was reading through, but why did you reduce the depth of the firepot down to ~2"? I had thought you wanted the fire depth to be 4-5" at working height to keep out of the oxidizing part of the flame

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That depends on the fuel type, forge design and air flow. That can very from less than 2” to more than 10”. In the case of the double acting bed pump and schedual 40 tuyere that is about an inch above the tuyere for forge temp and about an inch and a 1/2 for welding temp.

Coal and charcoal act diffrently in a forge, and wile a bottom blast with a 2” tuyere requires a shorter fire bed, charcoal requires a taller one. With a side blast using a 3/4-1” I’d tuyer we see just the opposite, the charcoal is much shallower and the coal is higher.  

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On 6/4/2018 at 5:49 PM, Tyler Cech said:

I’m planning on using a large metal bowl I have and setting a brake drum in the center with the pipe coming down for a ash dump and hair dryer,

Probably the worst configuration for a charcoal forge. Did you read this thread?

https://www.iforgeiron.com/topic/57101-inspired-by-mark-iii-jabod/?tab=comments#comment-600968

 

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  • 4 months later...
On 6/5/2018 at 11:15 AM, Charles R. Stevens said:

That depends on the fuel type, forge design and air flow. That can very from less than 2” to more than 10”. In the case of the double acting bed pump and schedual 40 tuyere that is about an inch above the tuyere for forge temp and about an inch and a 1/2 for welding temp.

Coal and charcoal act diffrently in a forge, and wile a bottom blast with a 2” tuyere requires a shorter fire bed, charcoal requires a taller one. With a side blast using a 3/4-1” I’d tuyer we see just the opposite, the charcoal is much shallower and the coal is higher.  

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The tuyere comes in the side of the trench, but instead of a bowl 8" across, instead dig a strate sided trench, 4" wide and 8-12" long. The long sides of the trench slope down to the tuyere making it easy to clean and encouraging fuel to settle down. 

So, let's cover it again, you want at least 3" between the floor of the box and the bottom of the tuyere, and 3-4" above the top of the tuyere to the too of the table. You would have 2" of dirt between the fire and the bottom and an inch under the tuyere Now at this point either use bricks or make mounds of dirt on the long sides of the trench up to about 4" to keep the fuel over the stock from running off. Banking coal works, but with charcol you just end up with all the fuel on fire, and still only get 6" of hot spot . 

I'm getting confused on fire depth for a side blast charcoal.  Right now my fire pot is 4" wide and 8" long.  I have the tuyere about 2" off the floor and about 4" of sides above that.

Would I be better having the tuyere sitting on the bottom of the floor and making the pot shallower? 

Here's a couple of pics of my set up now.

 

20181006_1110400.jpg

20181006_1150150.jpg

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Are you  counting from the floor of the box or the floor fire bowl? I measure from the floor of the box so that would be just an inch or less above the bottom of the fire bowl. That leaves 2” insulation between the fire and the floor.  

As to the shape. A brick sized and shaped fire bowl is fuel efferent for charcoal (8” long 4” wide and 2” deep) with a wall on one or both of the long sides . I find making the back wall 12-16” long works best. The tuyere seems to be happy angled down toward the fire this moves the center out from the wall. 

So look at the forge at the top, you can see the hole in the bricks. The tuyere is right on the bottom. This works fine for charcoal but because of slag it’s not good for charcoal.

So in short your right, your tuyere is to high and the bricks making up the short sides should be layed flat not on edge. 

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Here are a couple of pictures of my jabod that I patterned after the Mark III. It's 5X5 inches square and 3 1/2 deep. The tuyere is 3/4" with the center one inch above the floor. I regularly work railroad spikes and have worked the coupling end of sucker rod to  a one inch hardy hole. Just keep changing the bowl size until you find what works for you. Sorry the pictures aren't so good. I guess my upload failed. I will try again tomorrow.

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I made the modifications to the forge today. Its using way less fuel and is heating up my stock a lot faster. I think I might finally have it set up correctly. 

Thanks for taking the time to post all this info and answer questions Charles!

I actually felt like I was blacksmithing today:D 

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Your welcome. 

Dad taught me about “enlightened self interest” as a kid. Of coars as a kid I came away with “be nice to your neighbor and they will probbably be nice to you” butnas I grew up I relived it was just as important to “help your neighbor” simply because it feels good.

not only do I feel useful, but I get a kick out of watching you new folk learn and grow. Not to mention learning from you as well. 

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  • 3 months later...

I have been reading this website for many months and to see if I enjoy pounding metal I have built one of these forges. Charles your writings have been invaluable in my build. The simplicity of this design is very appealing and I was able to put it together in a few hours including building a mobile stand to roll it around. I have yet to mount the pump but believe I am going to add some additional pipe and mount the pump just under the box at the front. I built mine a bit taller than what I generally see here so the pump will be easily accessible from the front. The box is 22" wide by 32" long. I only have wheels on the back legs so the action of the pump should not move the forge around. For my first attempts I am going to fetch charcoal from my outdoor wood stove and transfer it to the forge. I have a piece of railroad track that I am mounting to use the end (and not the top) as many people have suggested. 

I chose this size of fire pot because of the knowledge that has been shared on this site. I trust that the knowledgeable folks here know better than me what size works most efficiently without wasting charcoal. Most of the sites I have visited have these huge pots that are using a bunch of charcoal and seem to be such a waste since you can only work a few inches of metal at any one time.

Thanks again folks for sharing your knowledge.

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I put some charcoal and air to the forge today. I shoveled some coals from the outdoor woodburner and stuck a 3/8 piece of scrap steel in the coals and within 5 minutes the end 1" was glowing very brightly and was able to be hammered flat with just a couple strikes. I don't have an ASO yet so just laid a sledge on the ground as a striking surface. I heated repeatedly and continued to pound on the steel until I flatted about 4". All told I probably spent 15 minutes with the steel in the forge, so I think it heats pretty nicely. I do see that I may have the fire pot a little wider than necessary, it is 4 1/2" currently and the heat did not radiate to that outside wall away from the blower tube. I made absolutely nothing but a piece of steel with a flat end, still pretty excited about the forge being functional. Next time I will be stacking another brick above the front and going for a little more charcoal to add depth to the sweet spot in the fire. In total I may have burned up about half a lunch bag of charcoal.

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A note on normanclatur. An ASO (as members of the site coined the fraze) is an anvil shaped chunk of cast iron sold as an anvil but wholly unsuited for the perpose. A sledge hammer, on the other hand once mounted in a stump or stand becomes a perfectly servicible anvil (many Iron Age anvils were not but 10# wile hammers were 1 1/2 to 2#) blocks of iron or steel are anvils, horns, heals and hardy holes being recent additions. A trip to a scrap yard for a 4” thick (round, square, plate etc.) drop of steel, even 1018 or A36 make serviceable anvils. 

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It is not about what you make in the forge but that each time you go to the forge you learn something.

Fuel does not make the fire hot, air makes the fire hot. Use only the amount of air to generate the heat you need. You might be surprised just how little  air that is required.

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The rail is 18" in length, so my idea is to mount it by cutting away a large log (stood on end)and set it down into the relief cut into the log. A great deal of what I am doing is being done on the cheap for now, until I decide how much I enjoy the trade/hobby. If I begin to enjoy the craft I will most certainly expand my tooling and anvils. I have poured untold dollars into my woodworking shop, purchasing and restoring machinery from 60 to over 100 years old. I have hopes to use metal working in my woodworking projects. I do not sell items, just make them for our home or for gifts. I guess what I am saying is that I am no stranger to craftsmanship and the time it takes to create items.

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I'm brand new to all this, but this design looked like something I could do. I got it burning today just to try it out. I've got some airflow problems to work out. It threw way too many sparks even with the valve thrown wide open. Still, I'm quite pleased. My makeshift hunk of steel anvil should be here Thursday.

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