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I Forge Iron

A Question About Bellows ...

Sam Falzone

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Greetings all.
I'm in the process of planning out a bellows project for my travel forge rig. However I've hit upon a possible snag/question that i hope someone here can help with.

First the details ...
-my protable rig is a charcoal forge
-the fire pot itself is around 12" x 12" x 3" deep (fire brick).

-- The bellows will be a double-lung (over/under) model
-- I want the bellows to provide enough air delivery to get the forge to welding temperatures.

My question is, "Is there a formula to figure out the minimum or maximum size the lungs need to be?" Or does it not matter?

Thanks all.


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Not directly you just have to pump a smaller set more vigorously which sort of defeats the purpose of the double lunged set.

I built mine from a commercial set we borrowed from a museum but the true factor on size was how many pieces could we get from 2 4x8 sheets of plywood so we designed it to get all 3 solid pieces and 2 horseshoe pieces from the 2 sheets.

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Based on the tire inner tube bellows linked from the post 21, and measuring a couple tires (I couldn't locate an inner tube to measure), I estimated 16x16 inch boards, and 12-16 inch of throw for each chamber, for a volume of about 1.7 to 2.3 cubic feet per chamber.

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hi another thing to consider is the out let pipe size my bellows have a 3/4" outlet that i closed down to less than 1/2" as i found it blew bits of charcoal over anybody watching demos, this seems to work well for anything from 1/4" upto 1" reaching fire welding temp very quickly using charcoal http://a1.sphotos.ak.fbcdn.net/hphotos-ak-prn1/562112_148572791936739_2065722429_n.jpg

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Forgot to mention that back in the '60's there was a style of kitchen tables (at least here in the USA) that used tapered tubular steel legs. I scrounge those at the scrapyard and illegal dump sites as they make a nice bellows nose and you can cut them at the size you want for the tip. (starting small and trimming back until you are happy uses fewer of them than starting large and using another one for each try...)

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