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Offset build question for veteran builders.

 
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heavymand
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Joined: 30 May 2009
Posts: 41

PostPosted: Sun Mar 19 17 10:50 am    Post subject: Offset build question for veteran builders. Reply with quote

Ok. I built a 15" x 15" x 20" firebox from 1/4" plate. That part is done, no going back. I have a 80 gallon compressor tank for the cook chamber that is 20" in diameter and 60" long. I used the pit builder calculator after I built the firebox that is 25% too small and then googled how to measure my half moon cut out on my tank. I came to a pretty difficult calculator, that I'm sure a lot of you have seen posted on another forum, and got my dimensions. The pit calculator says that I need a 36sq. in. (approx) firebox to cook chamber. So I put that number in the other calculator and it tells me how tall (3.4") and wide (9.75") to make my cut out. So long story long, I have this 5' long 20" diameter tank with what looks like a very small firebox to cook chamber opening. My tank was built in the 50's i believe and has double walled end caps. I measured my cut from the outside of the tank initially so the double wall will cut down my opening by 3/16" to a 1/4". I'm building a traditional offset not a reverse flow. I see a lot of pits that the firebox extends almost to the center of the tank. I have a good feeling that I'm thinking way too hard on this but I only want to build it once if you get my drift. I just need to know if my firebox to cook chamber opening is too small. Thanks fellas.
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k.a.m.
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Joined: 12 Dec 2007
Posts: 26012
Location: Southeast Texas.

PostPosted: Sun Mar 19 17 12:17 pm    Post subject: Reply with quote

I would use a half moon 10" wide by 5" tall. This will allow you a 1" to 1.5" grease bridge
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Maniac
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Joined: 02 Oct 2010
Posts: 2432
Location: Pa

PostPosted: Sun Mar 19 17 12:30 pm    Post subject: Reply with quote

heavymand I think you are a little small on your numbers. that only comes out to 33.15 if it were me I would make it a little bigger because you are already short on the fire box, better flow not less flow just makes more sense to me. my chamber is a 20 " but a reverse flow but the opening is close to the same, if you look at the first page on my build you will see how I layed out mine...I was round to round. I went a little bigger and she runs great. JM2C
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heavymand
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Joined: 30 May 2009
Posts: 41

PostPosted: Sun Mar 19 17 11:42 pm    Post subject: Reply with quote

So pretty much because my firebox is already small I need to increase my opening to allow for enough air flow. I bet this thing is gonna eat more fuel than I'd like but maybe not too bad. K.A.M. you mention a grease bridge. I've been thinking on just how I should build a grease bridge but I can't settle on anything. I'm sure I'm way overthinking it. Thanks for the help guys.
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k.a.m.
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Joined: 12 Dec 2007
Posts: 26012
Location: Southeast Texas.

PostPosted: Sun Mar 19 17 11:49 pm    Post subject: Reply with quote

heavymand wrote:
K.A.M. you mention a grease bridge. I've been thinking on just how I should build a grease bridge but I can't settle on anything. I'm sure I'm way overthinking it. Thanks for the help guys.

Lay out the half moon to where it touches the bottom of the cooking chamber. Come up 1.5" draw a horizontal line and now that is your bottom cut. Basically the half moon has a flat bottom above the bottom of the chamber.
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heavymand
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Joined: 30 May 2009
Posts: 41

PostPosted: Sun Mar 19 17 11:56 pm    Post subject: Reply with quote

So basically, I don't need to "build" a grease bridge, I just don't cut the entire half moon out on my firebox and use it as a grease bridge. I'm picking up what your putting down. Ya see? This is why I joined this site. That's a great tip. Thanks K.A.M.
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