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JABOD 55 feedback

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Understandable 8Up, I had to get a friend of mine to help me get up the courage to cut a hole in the roof of my garage lol. One of the best things I've done for the convenience tho. 

You can definately try your setup by adding the vertical stack on the outside and see how it works. 

If you were to keep the current outlet location you could modify the opening slightly to use 45°elbows instead of the 90°s kinda like the quick sketch to the right. It should improve draw. But you might find that adding the external vertical stack and preheating it is sufficient. Try it and see. 


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Ooooh, a punishing response! 

4 hours ago, 8upSmith said:

The stack goes up about 5 feet, makes  a right angle turn and punches out of the wall for about another 3-4 feet.

I  may have missed some of your description but if your stack just punches out the wall horizontally and stops it is not going to draw properly. Only extend the stack horizontally enough to clear the eves and turn it straight up. A good way to make this turn is with a T fitting, the leg coming from the forge hood, the arms oriented vertically, one up the other down. Then run the stack at least 5' IIRC above the highest point of the roof within I THINK 20'(?).

The open end of the T allows cold air to flow down and out of the vertical stack so when you light a fire the warm air doesn't have to push heavier air up and out to get flowing. The other benefit of doing it this way is you don't need to worry about a rain cap as water will flow straight down and out the bottom of the T. Letting the horizontal section slope downwards from the building to the T by maybe a whole inch will prevent any getting in the shop.

Frosty The Lucky.

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Let us start from the drum and work out way up and out of the shop. 

Put the wedges from the hole in the top of the drum on the INSIDE of the chimney. This stabilizes the chimney so it will not slide around and off the drum head. It will self seal to the drum with a little soot and ash given time. The smoke Want to go up and out and does not like changing course. The wedges act as a funnel to direct the smoke into the stack. 3 or so screws will anchor the wedges to the chimney. 

The more wedges you use the better. 4 wedges create a square opening. 6 wedges create a hexagon opening, and 8 create an octagon opening. The more wedges you have, within reason, the closer you get to  circle.  The bends on the wedges should be as close to the interior of the circle of the chimney as practical.

The chimney should be 10-12 inches in diameter so it can move the volume of smoke needed to get it up and out of the building. If you have  inch diameter chimney, try it and see if it works.

From the chimney to the exit opening in the wall should be a straight shot, that is on an angle. A chimney with two 45* bends works better than one 90* bend. When the chimney gets to the exit hole in the wall, use a horizontal run through the wall, it is easier that way. Once outside make a couple of 45* bends to go vertical and clear the eves of the roof and then vertical to a point 4 feet or so above anything height wise within 10 or 12 feet of the chimney. That is the roof, trees, etc.Forget the rain cap for now as you want maximum volatility of the draft. 

Test number one of the system. Scrunch up a couple sheet of newspaper, set them on fire and place them inside the drum forge/hood/chimney to preheat the chimney and get the draft going. Now build a small fire from sticks, kindling, etc to increase the draft and get things moving up and out. Add a wee bit of air and more sticks and kindling to get a nice fire and a bed of coals/embers in the fire pot. Now add your solid fuel to the top of the fire and just enough soft air to get it to burning well. 

Finally go back to the door opening in the drum and close off or block some of the opening at the top of the door to block incoming air. This reduces or restricts incoming air to the bottom part of the door and sucks the smoke up and out. You want to be able to see the fire from where you stand. The rest of the opening is just letting room air into the hood/chimney.  You want it to suck smoke not room air. The door can be reduced with thin tin or sheet metal until you hit the right combination, then run it for a week or so. Adjust as needed.

Let us do some fuzzy math. Forget the formulas for a moment and just use square measurements.  8 inches square is 64 square inches inside. 10 inches square is 100 square inches inside. And 12 inches square is 144 square inches inside. That is 150% increase in area with each additional pipe size. Now measure the area of the door opening and you start to see that a large opening and a small chimney do not work well together.

Put it another way, purchase a soft drink in a cup. Use the lid and straw provided and take a drink. You need a little suction on the straw to get the soda moving and then it is easy to get the drink. Now go to the counter and get a coffee stirrer, the short plastic thing with the little bitty hold made by flattening the center of the stirrer. Try to drink soda through that. LOL  You tell me you can not do it as the hole is too small. Try again and increase the suction and you still do not get much soda.  This is exactly what is going on with your forge and a small chimney.  

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8upSmith, charcoal is good. I like charcoal. :)

How long does your chimney go up once it's outside? You need a good long column of hot gas going up to provide good suction.

Also note that a pair of 45-degree elbows, with a few feet of pipe between them, combined with as short a length of horizontal pipe as possible. Any section of horizontal pipe gives you a volume of air that isn't moving up, increasing drag.

When you go take measurements of your pipe size, take more pictures of your chimney -- all of it, from start to end (outside). That will help us understand why it isn't pulling smoke as much as it could.


2 hours ago, Charles R. Stevens said:

As long as it works, brother I’m happy.

Arthur’s, I like your set up

Thanks Charles! Your various posts on the JABOD forge were a great inspiration. :) 

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Okay, time for an update.

BLUF: After reading through all the posts, following Glenn's math and a healthy dose of whiskey I've learned that my current smokestack is not nearly close to capable of handling the forge. Also, I don't have enough material (or money) to go get more pieces of stack.


Working with the material and equipment I do have, I've mocked up a prototype blower fan exhaust system. It works wonders. Even with the gaping holes in the system (I didn't bolt anything down since it was just an experiment) there wasn't an ounce of smoke accumulating in the workshop. 20190203_140628.thumb.jpg.9677811e508ab01cbd12f6ec9ba4c121.jpg

Solved the old problems, now to deal with the new ones.

I was able to get the steel (very thin bar of mild steel) to a red/bright red heat. It hammered just fine, but I couldn't achieve anything hotter than that.

Conclusion: The exhaust fan is too powerful, and in addition to the intake fan, creates a vortex of moving air that burns the fuel faster than a snowball in the Sahara.

Next modification will be to mount the exhaust fan on the roof. Originally I was going to mount it in the rafters, but I don't have the proper mounting hardware at hand. I'll run a straight pipe from the forge to the ceiling, install a 90 degree turn to connect it the fan and attach a spark catcher to the output pipe. roof.thumb.jpg.c8968e75427ceb33bf49a6ffa33e91cb.jpgAlternatively, there is another idea I've mocked up but don't know how well it would work. Instead of running the exhaust through the fan itself, creating a cut out in the 90 degree bend and blowing across it to create a draft pull.

Along with this, I need to find a better input fan. The shop-vac is simply putting air in too fast.

If I'm understanding it correctly, the air should be max volume/min speed. The shop-vac seems to be quite the opposite of that.

Any thoughts/advice on the new ideas?



Edited by 8upSmith
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18 minutes ago, 8upSmith said:

If I'm understanding it correctly, the air should be max volume/min speed.

The amount of air should be just enough to make the fuel your using just hot enough to heat the metal in the fire. 

Do not get hung up on inline fans, or round chimney pipe.

Any closed material that gets the air flow from point A to point B should work. I have used square and rectangular HVAC ducts, the inside of a hot water heater, the thin skin from the outside of same water heater, and even corrugated roofing rolled up and fastened together.  Nothing wrong with putting two pieces of stove pipe together to make a larger pipe.  I had my eye on some spiral under the road way drain pipe up until they ran a tractor over it, flattened it out, and then folded it in half to get it on the truck to take away. 

If you turn a 90 once outside the wall and go 3 feet above anything within 10 feet of the chimney, it should be good. Save the fan for blowing on the blacksmith during the heat of the summer.


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Thank you all for the copious amounts of advice! This new set up works, without a fan even. I still need to extend the pipe outside the building a few more feet, but adding the larger tank as the initial piece of the pipe seems to have done the trick.

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