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New r/f build

calebcooper

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Hey guys I have a 200lb (50) gallon propane tank I'm making a smoker out of. My firebox will be 20"x24" 1/4" thick. I plan on making the firebox with a lid on top also so it can be used for a charcoal grill when not smoking. I used the formulas and came up with 11550 si cc which gives me 46.2 for Fb/cc opening. Playing with the numbers I came up with 3" ed and 14.283 ad. The question I have is this, is the green area your finding for the half football the only thing you cut out or will you take that and flip it to the top like a mirror image so the cut out will be round? I'm kind of confused on this part. Also wanted input on firebox size. I know it's a little on the big side for what I have but I wanted the extra room for ash pan and wood basket plus enough space to grill on. I don't plan on stuffing it full of wood so I don't think it'll be a problem. What do you guys think?
 

daveomak

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Use half the football for a "square" FB.... For a round FB, figure out the green using 1/2 the calculated area, then flip it to make a "round" green area....

What is the dia. and Length of the CC.....
 

daveomak

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CC about 13,300 cu. in. volume....
you need about 53 sq. in. under the RF plate, and FB/CC opening

About 300 cubic inches for the exhaust stack......
I would use a 4" dia. stack 35" above the CC....
2020-11-13 (2).png


This circle calculator lets us know the RF plate should be ~17.5" wide and 4" clearance from the bottom of the CC..
Set the RF plate inside the CC and mark it... Mark the top of the plate... Then cut out the end of the CC cutting past the weld joint... Slide the FB into the opening and tack everything in... TACK... so if you have to change something it's easy... You can weld the FB in from the inside.... Tack the RF plate last...
 
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daveomak

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If you put a hydraulic jack on the RF plate and put a mild "bow" in it, the fat will run down the middle and out the drain you will put in it... Drain to the outside of the CC... into a bucket...
 

calebcooper

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If doing a round Fb would I measure up 8" from bottom and draw the arc for the football or stay at 4" and do it? This is the part I'm a little confused on. I may be overthinking it but I want this part to the t so it operates correctly.
 

daveomak

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If doing a round Fb would I measure up 8" from bottom and draw the arc for the football or stay at 4" and do it? This is the part I'm a little confused on. I may be overthinking it but I want this part to the t so it operates correctly.
If doing a round FB, looking at the circle calculator, solve for 1/2 the segment area... Then flip the 1/2 football over to complete the top half of the football... 1/2 + 1/2 = a perfect segment area....
The problem with a round FB... The cut out area is much taller for a round FB... It can interfere with RF plate height and smoker room ...
 

calebcooper

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If doing a round FB, looking at the circle calculator, solve for 1/2 the segment area... Then flip the 1/2 football over to complete the top half of the football... 1/2 + 1/2 = a perfect segment area....
The problem with a round FB... The cut out area is much taller for a round FB... It can interfere with RF plate height and smoker room ...
I understand where your coming from. I think it will be beneficial for me the way I have it laid out though . I planned on using 4" stack like you mentioned but wanted to ask if you think I should just go from the top of cc or run it down between the two grates. Also I have 2 4" pin wheels for intakes do you think these are big enough or should I go a little bigger?
 

daveomak

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Personally, I prefer functional air inlets to the pinwheel......


FB air flow diagram 2.jpg



Smoker Exh and Intakes 2.jpg
 

daveomak

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I understand where your coming from. I think it will be beneficial for me the way I have it laid out though . I planned on using 4" stack like you mentioned but wanted to ask if you think I should just go from the top of cc or run it down between the two grates. Also I have 2 4" pin wheels for intakes do you think these are big enough or should I go a little bigger?
If you want a very nice engineered exhaust stack that flow exhaust gasses about the best there is, take a little time and install this design... Use the 4" exhaust... Cut the stack off flush, with the inside of the CC...

3 EXH.jpg
1 EXH..jpg
2 EXH..jpg
4 EXH.jpg
 

calebcooper

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He did a good job on the stack. I think I'll do mine the same way. One more question regarding Fb I cut my opening in the cc last night and got my fit up right. Question is do I go to the inside of cc and scribe Fb to cope the top out or leave it square on the end?
 

daveomak

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If you slid the FB into the CC, and you cut out the CC opening PAST the weld seam, the RF plate will be easier to fit up, not having to scribe around the weld seam and make allowance for the curvature of the end of the tank..
Then measure the inside of the CC for the RF plate width... and weld the RF plate to the top edge of the FB...
If you have the CC sitting on the ground, make it level... Then take level measurements on the inside of the CC that match to where you will weld up the RF plate to the FB, so the RF plate sits level OR, allow to about a 1/2" drop so grease will flow to your drain...
For the drain, cut a hole the same as a 1" pipe coupling in the RF plate... so it will slide in the hole.... Cut a hole in the bottom of the CC so a 1" pipe nipple will slide in... Match it up with the hole in the RF plate... Once the RF plate is tack welded in, slip the pipe nipple into the hole in the CC and slip the coupling up into the hole in the RF plate... Tack it in flush.... us a ball valve or gate valve or pipe cap on the pipe nipple... DO NOT TIGHTEN THE CAP, if that's your choice... finger loose is fine...
 

daveomak

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Picture of the FB end so we can see the upper and lower air inlets....
 

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