New Guy and this will be my 1st Reverse Flow Smoker Build

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Been a while since I posted an update. Seems like as soon as I save a little money for my steel some thing else in my house breaks.

In the mean time I've been looking at other builds and making plans for my own. I've seen 250's with single doors to the CC but mostly double doors. I think I would like the ability to cook a whole hog if the need should arise, so would need a single door. But, at the same time if I'm cooking smaller cooks or a number of pieces I'd like to be able to open 1 door at the time to conserve heat in the CC. I've also seen double doors that open into one big opening, but you can't open the doors separately. Seems one or the other has to be opened for the 2nd door to open. kind of like one door seals on the other door. Then there's the gull wing smokers. Don't think I want doors on both sides. That would only make my build more difficult, I thought about hinging the center section between the 2 doors and figuring out a way to temporarily tie the individual cooking grates together for a whole hog. I'm open to ideas and It looks like I have plenty of time to plan my design. 
 
Hmmmm......

Tricky.

I would be tempted to do sliding doors such that either side can slide open sideways, but have them mounted on hinged rails so that both together can open vertically as one big door in conventional fashion.
 
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That tank is 250 gallons.... 30 x 30 x 0.7854 x 82" (length adjusted for round ends) / 231 (cubic inches in one gallon) = ~ 250 gallons... Dave
Well, I bit the bullet and ordered the 1/4 plate for my builds. Notice I said "builds", as in 2. i picked up another 250 tank just like the 1st one. Using Dave's numbers above (except I used 29.50 x 29.50 x 82") here are my calculations. My plate should be here early this week but before I start cutting I want some of you guy's to check my numbers. If you have any questions about how I got them or any corrections PLEASE let me know. I'll be cutting for 2, so if I make a mistake it will be double.

Here they are, 
Calculations for a standard design, reverse flow smoker..

Gallons X 231 = volume in cubic inches.... Sometimes the tag, in gallons, reflects a 20% air space for expansion....

Volume of the Cook Chamber.... Use the Inside Diameter of the tank... 29.50

Diameter X Diameter X 0.7854 X Length = Volume in cubic inches 56046.54

Volume in cubic inches X 0.004 = FB/CC opening in square inches 224.19

Volume in cubic inches X 0.004 = Area under the RF plate in square inches 224.19

Volume in cubic inches X 0.004 = Area required at the end of the RF plate in square inches 224.19

Volume in cubic inches X 0.33 = minimum volume of the Fire Box 18495.36 Plan for FB to be

27L X 30W X 27T. That should leave room under the grate for ash and coals.
The above areas are necessary for great air/heat/smoke flow.... using less may cause an overheated FB.... Narrow / Long CC may require an increase in those numbers due to increased surface area friction to volume... Wide/Fat Short CC may use smaller numbers due to reduced surface area friction to volume...

Volume in cubic inches X 0.001 = FB air inlets in square inches... 56.05 4-5@ 2X3 ea.side, 2@ 2X3 in door

Recommended upper and lower air inlets... Upper air inlet directly across from the FB/CC opening to facilitate moving heat from the FB to the CC, and insuring good air flow through the CC.. The lower air inlet should be situated at or below the fuel grate.... The two air inlets can share the designated square inches of opening....

Volume in cubic inches X 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV) 952.79

Exhaust Calculation..

ESV in cubic inches_____________________________ ... = Stack Length in inches (36" +/-) 6"ID = 33.70
0.7854 X Stack Diameter X Stack Diameter

Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
this is for round stacks only..


This circle calculator is really cool... It does it all.... Just fill in the necessary blanks...
......click on this link......
http://www.1728.org/circsect.htm

For calculating the FB/CC opening.... You are calculating for the GREEN area... that will be the cut-out area in the FB that mates to the CC....

The green area is a segment. It is called a "Segment Area"... That area is the same as the FB/CC opening....



When you open the "Circle Calculator" link, Click on the "bullet" to the left of Radius & Segment Height ED....

Circle Calculator

Click on the 2 variables you know

......Radius and Central Angle...........................Radius & Chord AB
[X] Radius & Segment Height ED.....................Radius & Apothem OE
......................................................Radius & Arc AB
......Chord AB & Segment Height ED................Chord AB & Apothem OE
......Segment Height ED & Apothem OE...........Chord AB & Arc AB

You should have opened the circle calculator and a bunch of boxes will appear below..
and a box called [CALCULATE]..

Enter the radius in the box so marked.... If you tank is 24" OD, and has a 3/8" thick steel wall, the ID of the tank 23.25".... the radius is 11.625"..... these numbers need to be accurate if you want stuff to fit... ALSO, take into account the thickness of the FB steel when cutting out the tank... 14.75 R

Enter a guess for the Segment Height ED... I'd start with 6.0 10.72

Click on [CALCULATE]....

The other boxes will fill with numbers....

The [Segment Area] box is what you area going to compare with the FB/CC opening in square inches...

If the FB/CC opening number is smaller, change the number in the Segment Height ED box to 5.... continue changing that number until the [Segment Area] matches the FB/CC number.....224.36

Now look at the colored circles above.... Segment height ED is how tall the green area is and corresponds to the area to be cut out.....10.72

Also, [Chord AB] corresponds to the width of the RF plate... NOTE... for ease in fitment, the FB should be at least as wide as the RF plate..28.38
 
Way to go Fred, you have it covered. Keep us posted on the progress. 
icon14.gif
 
Can't wait , this is going to be a nice one

Gary
 
 
Been a while since I posted an update. Seems like as soon as I save a little money for my steel some thing else in my house breaks.

In the mean time I've been looking at other builds and making plans for my own. I've seen 250's with single doors to the CC but mostly double doors. I think I would like the ability to cook a whole hog if the need should arise, so would need a single door. But, at the same time if I'm cooking smaller cooks or a number of pieces I'd like to be able to open 1 door at the time to conserve heat in the CC. I've also seen double doors that open into one big opening, but you can't open the doors separately. Seems one or the other has to be opened for the 2nd door to open. kind of like one door seals on the other door. Then there's the gull wing smokers. Don't think I want doors on both sides. That would only make my build more difficult, I thought about hinging the center section between the 2 doors and figuring out a way to temporarily tie the individual cooking grates together for a whole hog. I'm open to ideas and It looks like I have plenty of time to plan my design. 
My brother and I just finished our 250 gallon last week and cooked a whole hog this past weekend. We have a two door setup. and it worked really well. we just put a flange on the right door that overlaps onto the left door. used 5/8"x1/8" high temp gasket around and between both doors and it sealed nicely without even using door latches. we're gonna still add some latches to seal up the very limited amount of leaking we had. here's a picture of it in action Saturday. Hopefully you can see what I'm talking about with the doors.

 
Glad I looked at the calculator. I noticed it got revised right after I posted my numbers. Therefore my

Volume in cubic inches X 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV) 952.79

has changed to

Volume in cubic inches X 0.022 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV) 1233.02

which means my stack that was

ESV in cubic inches_____________________________ ... = Stack Length in inches (36" +/-) 6"ID = 33.70

0.7854 X Stack Diameter X Stack Diameter

and has now changed to

ESV in cubic inches_____________________________ ... = Stack Length in inches (36" +/-) 6"ID = 43.61

0.7854 X Stack Diameter X Stack Diameter

almost 10" taller. I already have my 6" ID pipe so there's no turning back on the ID size. Luckily I had it cut at 48".

Now I'm wandering about the "Stack Length in inches (36" +/-)". I'm not gonna be close to 36". What do you guys think?

Dave, Is there a way, instead of just editing the thread in the future, that you can make a comment on the last page of the thread so it automatically goes to the top the list? I was not aware that the calculator had change until today's post by Brad.
 
The newest change was made because of some data that showed better "across the food rack" improved temps... I would go with the new numbers if it's convenient... the old numbers worked very well....
As far a updates, I try to remember to change the "heading" to reflect the current date...

FWIW.... be glad you aren't using the old feldon calculator.... what folks have done here to help improve a smoker is AMAZING.... smokers have come a long way on this forum because of it's members... hopefully we all will continue to improve on this "smoking meats" journey....
 
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Thanks Dave. I questioned the Feldon's shortly after joining here. So do you think I'm OK with a 43.61 stack?
 
Fred, morning.... Pick a number and use it.... Do you have any pics of that smoker yet.... let's see how it's coming....
 
No pics yet. Haven't had time to get anything done other than cut my firebox material. Been looking at several builds and trying to decide how I want to do my doors. Don't want to cut the tanks until I'm sure.
 
 
Quick question for y'all. I started cutting my tank this weekend and wanted to know where to make the Vertical cut, before the weld seam (dome side) or after the seam (cylinder side)?
I would cut it just after the weld seam.  I wouldn't want that weld seam to show.  If you leave it in you will in effect have two weld lines side by side which to me would look odd.  Functionally I don't think it makes a difference other than setting your firebox into your smoke chamber an inch farther. Just my opinion.
 
I would cut it about 2-3" past the weld seam.... "Usually" there is a backing plate inside on the weld seam... which makes fitting a PITA.... A double layer of steel makes for problems... Trying to fit the RF plate around the seam is a PITA also..... Fit the RF plate on the straight portion of the tank..... always think 2-5 steps ahead... makes the build easier......

I have seen tanks that the weld seam is built like this.....

 
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Got the end for the firebox cut. Now on to the door cutouts and I have a couple questions. Look at my drawing and tell me where you think my door cutouts should be top and bottom. Note that if I cut the bottom at 3:00 my lower grate will be over 4" from my RF plate. I could go lower I suppose. Let me know your thoughts.
 
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