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First build

post #1 of 72
Thread Starter 

Hello, all

   I am a newbie to the site, and this is my first build. I live in south Florida. My build will be a reverse flow. diameter is 25" by 60" to 72" in length. The metal plate will be turned hopefully sometime this week. First question,  should I leave it at 72" in length or cut it down to 60"? This is a back yard smoker. Normal use is cooking for 5. Guest about 2 to3 times a year will bring that # to 20.

   Second question, firebox size as per the cal. is 24"X24"x24". I am planning a raised stool grate firebox. Do I need to add inches to the height of the firebox for this type? My thoughts are based on the web sit, www.wedlinydomowe.com/smokehouse-plans/smokehouse-firebox , would give me more control.

    Third, How much in inches for a ash pan under all this?  Also the metal on cook chamber is 1/4" and the firebox will be 3/8" steel. I am also thinking about a warmer box on top of the firebox like the lang smokers.

 Looking forward to your advice. Thanks, Brian


Edited by berry1611 - 11/18/12 at 5:34am
post #2 of 72

Raised stool grate is a great idea.......    I like it.....  Are you planning to incorporate the firebox into the smoke chamber like the picture below ??      Dave

 

   smokehouse firebox

 

post #3 of 72
I am in.......

Welcome to SMF....
post #4 of 72
Thread Starter 
The picture that you posted is a gas cylinder. My cylinder camber is being made from steel plate rolled, so I will not have the rounded ends, just flat. I was going to weld firebox butted up to the cylinder chamber. Should I sit the firebox into the chamber somewhat, and if so, how far?
post #5 of 72

Brian, morning.....  After doing all the calculations, I recommend the RF plate be set high enough to have 1 1/2 times the area of the opening of the firebox to cook chamber area under the RF plate....  Set the top of the firebox at that height and have the opening below the RF plate ...  The reason for the larger area under the RF plate is friction loss of heat/air flow..... At the end of the RF plate, where it comes next to the end of the tank/smoke chamber, have that area 1 1/2 time the area of the firebox opening also....  The heat/smoke takes a 180 deg turn and friction loss occurs there also....  This is  a drawing for another smoker build......  Below is a calculator for the circular tank build...

http://www.1728.org/circsect.htm...   The heat deflector is SQWIBS design.... it helps cool the smoker at the firebox end....   

Building the firebox into the smoke chamber helps with heat loss and shortens the smoker length.. generally about 1/4 - 1/3 of the length of the firebox is inserted into the smoke chamber....  It is not necessary...  As far as calculations go for the build, I don't know what calculator you are using...  Below is an excellent calculator that makes for a great smoker.....  

http://www.feldoncentral.com/bbqcalculator.html

 

700700

post #6 of 72
Thread Starter 
Thanks, Dave
That helps, I will leave it at 72" in length. That way by the time I make the opening @ the end for the smoke turn;I will be close to the 60" cooking area I was trying to achieve.
post #7 of 72
Thread Starter 

Good morning and Happy Thanksgiving Dave, I have  further questions. The metal was turned and it came out to have a diameter of 24.75 inches. I used the 25 in the cal. you posted. My thought was it would be better to go with just a hair bigger firebox verses one that was to small. By using a diameter of 25" and making the firebox 23x23x23 inches it came out to be size differential of 103.3%.  In the drawing you posted, it shows the RF plate in blue with a green short section at the end of the RF plate above the firebox; is there a difference in material for that small green area? Then you have two red lines one under the RF plate and then the one slanted into the firebox. In the hand drawing you call it a heat deflector plate and have 2" written. The 2", is that 2" between the deflector plate and the RF plate because the firebox is set into the cooking chamber so that that area would have a equal heat with the other sections of the cooking chamber. If so, how far should it go in and when ending it, is it wielded to the RF plate?

     On my firebox, do I needed to add height to the firebox for the stool style firebox and in the one picture you posted of the stool firebox there is a baffle plate in the firebox, does additional size need to be added to the firebox for this also?    Thanks .

post #8 of 72
Thread Starter 

Hello again Dave, The gray matter between my ears just engaged and I saw that the green colored plate is the firebox, in the cook chamber and the RF plate is starting at that location. Sorry for not engaging the gray matter.

post #9 of 72

Brian, morning.... That drawing is SQWIBS... I'm not sure what the green designates... The heat deflector plate is something that can be added at a later date if needed....  You may want a hotter section for what ever reason later down the road....  To brown chicken skin or something....  If you want to put the plate in later, drilling a few holes and suspending it would be one way to do it.... Length of bolts would set the spacing....  The 2 red plates could be addition #1 and #2 to get the heat adjusted to his preference...  The heat can be checked with a non-contact infrared therm..... 

About the diameter.....  I would not worry about the small difference in size....  You will have a great smoker following the calculator that close...

For the stool firebox, space for ash to accumulate is very important.... as the ash piles up, it will restrict the air to the fire... Space under the grate is basically what ever fits.....  room for wood.... room for ash.... room for access through the door for both....  

Picture yourself putting in wood... cleaning ash....  smoking great food... in the lawn chair having a brewski and enjoying the day...  

Now that is one helluva picture ain't it...   Dave

post #10 of 72
Thread Starter 

700

 

700

 

Thank, Dave

     Here are two pictures of last summer's build. It is a wood fired pizza/bread oven. The pizza cooks in 1 and half minutes. I will post pictures of my smoker build as I go. Thanks again.

post #11 of 72

That pizza oven is in the wrong back yard.....  biggrin.gif ....

post #12 of 72
Thread Starter 

    Dave, good morning, I'm getting ready to cut the steel plate for the firebox. Question that I have is the for the firebox-to-cook chamber opening; the builder calculator is recommending a diameter of 15.74 inches. You recommended that I go 1 1/2 times for this opening. So, I took the recommended firebox to cooker opening area that the build calculator said that is 97.34sq in. and I added 1/2 that comes out to be 146.01sq in. Is this what you meant? The above figures are for a 23x23x23 inch firebox. I am going to make the firebox 5 inches taller for a ash ban to be installed. 28x23x23 inches. The cooker chamber is diameter 25" the length 72". With the changing of the firebox in height for ash collection, do I need to change  chimney size? In the cal. at the recommended chimney volume it states (5% of firebox volume), any thoughts on this?

   I'm trying to get it right the first time. Metal is $$$. Thanks

post #13 of 72
Thread Starter 

Dave, I did a mockup of the cooking chamber end and I came up with a segment of 9", chord of 24" and a arc of 31". This seems to be very large opening and my firebox is only 23" wide. I was hoping to put a second rack in the cook chamber. According to my mockup I will only have about 5 1/2" to 6" from the top rack to the top of the cook chamber, that is with a 6" spacing between the bottom and top rack. Having a second rack in a RF smoker of a 25" diameter cook chamber a pipe dream or am I fiquring something wrong?

post #14 of 72

If your smoker build is just half as nice as that Pizza oven you will have one heck of a smoker...Welcome to SMF !!

post #15 of 72
Thread Starter 

Thank you.

post #16 of 72
Thread Starter 
Here is a photo of my mockup drawling. In photos of other builds on this sight and other photos of the opening from the firebox to cook chamber of similar size RF somokers and even larger ones they all seem to have smaller openings at this area. If I put a baffle plate 2 inches below the RF plate for let's say 18 inches starting over the firebox(1/3 of firebox being placed in the cook chamber) I am running out of room with the mockup that I drew. I guessed I can smoke thin slices of bacon. In this photo the squares are one inch square, the total is 146 sq in. (Help)
post #17 of 72
Quote:
Originally Posted by berry1611 View Post

    Dave, good morning, I'm getting ready to cut the steel plate for the firebox. Question that I have is the for the firebox-to-cook chamber opening; the builder calculator is recommending a diameter of 15.74 inches.

You recommended that I go 1 1/2 times for this opening. So, I took the recommended firebox to cooker opening area that the build calculator said that is 97.34sq in. and I added 1/2 that comes out to be 146.01sq in. Is this what you meant? Use the calculator for the firebox opening.... Use 1.5 X that number for the area under and at the end of the RF plate to overcome friction loss of the air/heat flow... 97 for the firebox/cook chamber opening.... 146 under and at the end of the RF plate....

 

The above figures are for a 23x23x23 inch firebox. I am going to make the firebox 5 inches taller for a ash ban to be installed. 28x23x23 inches.You can change the firebox to h-28"  w-18"  l-24" ... same cu in. volume but added depth for the ash pan.. The calc for the volume of the firebox is good to go.... then no change for the stack is required...

 

The cooker chamber is diameter 25" the length 72". With the changing of the firebox in height for ash collection, do I need to change  chimney size? In the cal. at the recommended chimney volume it states (5% of firebox volume), any thoughts on this?

   I'm trying to get it right the first time. Metal is $$$. Thanks

 

In summary, all the numbers you arrive at using the calculator, are good numbers... No changes from the original crunching are necessary.. The area under and at the end of the RF plate only affect heat and smoke flow...  increasing those areas X1.5 of the firebox/cookchamber insures there will be no restriction of air and heat flow through the smoker... A safety margin for good performance....


Edited by DaveOmak - 12/6/12 at 6:33am
post #18 of 72
Quote:
Originally Posted by berry1611 View Post

Dave, I did a mockup of the cooking chamber end and I came up with a segment of 9", chord of 24" and a arc of 31". This seems to be very large opening and my firebox is only 23" wide. I was hoping to put a second rack in the cook chamber. According to my mockup I will only have about 5 1/2" to 6" from the top rack to the top of the cook chamber, that is with a 6" spacing between the bottom and top rack. Having a second rack in a RF smoker of a 25" diameter cook chamber a pipe dream or am I fiquring something wrong?

In the Arc calculator, use radius of 12.5"....  Segment height (ED) 6.5"....  click calculate.... comes up with a segment area 101 sq. in. .. 

Very close the the 97" needed for the FB/CC opening...  That would be the opening to use....  

Now for the RF plate... 97 X 1.5 = 145 sq in...  Using 12.5" radius and 8.5" segment height.... segment area is 147 sq in...   Perfect for under the RF plate....  You can lower the RF plate if you need the room... 

Then the bottom cook rack 2" above the RF plate leaves 14" clearance for the second rack... 

post #19 of 72

HI Berry

 

I just starting looking at your build and hope you haven't cut it down to 60" yet. What I'm finding is that bigger is always better. The more people that know about your smoker the bigger your party gets. I think I've out grown mine already. Here is the website i used to calculate all my measurements  http://www.handymath.com/calculators.html . Use the complete circular arc calculator and fill in the radius and vol. you need and it will spit out the dimensions for you firebox to chamber opening. I would defiantly butt the fire box against your main chamber it reduces your hot spot and makes connecting your chamber and firebox a lot easier.  I can wait to see pics of your project


Edited by ChinaSmoke - 12/6/12 at 7:49am
post #20 of 72
Sorry I'm late for the party.
Yes the green represents the portion of the firebox inside the smoke chamber (the hot spot)
This is why i tell folks if using a flat side chamber is to mount the FIREBOX TO THE SIDE. DONT CUT IT INTO THE CHAMBER.
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