New forum member and new smoker build. A few questions?

Custom manufactured BBQ Pits, Do-it-Yourself projects, parts and ideas.

Moderator: TBBQF Deputies

Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

New forum member and new smoker build. A few questions?

Postby Ken226 » Thu Jun 06, 2019 2:31 pm

So, ive been smoking meats for a couple decades, but always on small smokers.

I have no kids or family to entertain, so i only really cook for me and the wife. I've been using a 30" Masterbuilt electric smoker for about 5 years and am happy with the results.

Recently a coworker decided to start a BBQ business, and since he knew that i have an engineering background and the tools/equipment to do fabrication work, he enlisted me to build a large smoker. He paid for all of the materials and i donated the labor/cad and design work.

When i got to about the 95% point in the smoker build, he had a change of heart due to frustration with his job, and decided to unload a buch of stuff and move.

I offerred to give him back his monetary investment and keep the smoker. So, now i own a rather large smoker, with which i'll use to occasionally smoke a brisket or rack o ribs for myself and the wife.

I built the whole thing from scratch, including the trailer.

The trailer was built with 2"x4"x3/16 rectangle tube and the smoker itself was built from 1/4" steel plate. The steel was all brand new from a local steel supplier, so very $$$$.

Ive test fired it empty a couple times, and ut seems to run OK. Its my first time building a smoker this big, so im a little concerned about the temperature variation in the cook chamber.

How much is normal?

The cook chamber is 108" long , 36" deep and 36"tall. An upside down pentagon in section shape.

The firebox is 36" x 30" x 26"

Pics to follow:
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Thu Jun 06, 2019 3:31 pm

First test tow! It towed nice and strait.

Image

Before paint pics:

The warming cabinet and fire box.
Image

Imagekey bank branch near me

Imagesuntrust atm near me

Imagemybpstation com station finder

Image

Image

Image

Image

Image

Imagefallout 3 44 magnum

Image
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Thu Jun 06, 2019 3:37 pm

User avatar
OldUsedParts
Deputy
Posts: 14185
Joined: Sun May 15, 2011 7:09 pm
Location: Montgomery, Texas
Contact:

Re: New forum member and new smoker build. A few questions?

Postby OldUsedParts » Thu Jun 06, 2019 4:23 pm

Very Creative Design and Craftmanship :tup: :salut: :cheers:
"Good BBQ Comes From Experience, and Experience, Well, That Comes From Bad BBQ "
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Thu Jun 06, 2019 5:04 pm

Ive smoked 1 rack of ribs on it so far for me and the wife. :)

It uses a (appx 4"x4"'18") stick of wood per half hour to maintain temp. My concern is the temp variation in the cook chamber.

I've built a couple small stick burners before, but never actually ran one. Im not sure yet if i just need to learn to run the machine, or if i need design changes.

I have the left and right side gauges mounted 6" above the lower grate, and the center gauge 3" above the upper grate.


The temp variation isn't very linear.
For example, with the chimney wide open, if i adjust the air intakes to get the lower left to 240, the lower right gauge runs 255 and the top center runs 320.
(So, basically, that setting gets me 15° difference left/right and about 75° difference upper/lower.


But, with the chimney still wide open, if i adjust the air intakes to get the lower left to 225, the lower right gauge runs 235 and the top center runs 275.
(So, basically, this setting gets me 10° difference left/right and about 45° difference upper/lower.


The closest i can get to an even temp with the chimney wide open, is with all my intakes closed except the lower firebox door intake, which i leave halfway open. A fairly small fire, which gives me 200° on both the left and right gauges, and 210 on the top gauge. But this 200-210 range is to low.
User avatar
Rambo
Deputy
Posts: 3540
Joined: Mon Apr 02, 2012 10:39 pm
Location: Lufkin, TEXAS
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Rambo » Thu Jun 06, 2019 5:37 pm

Wow :cheers: I can't wait for KAM to see this
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Thu Jun 06, 2019 6:10 pm

My hypothesis on the upper/lower temp variance is as follows:
The hot smoke exits the reverse flow chamber and floats up to the top of the cook chamber, filling the cook chamber from the top down. This keeps the hottest smoke at the top of the cook chamber. The hot smoke rising to the top displaces the cooler smoke, pushing it lower.
Since the chimney only extends 3.75" into the cook chamber, the hotter smoke is flowing into the chimney and creating draft, allowing the cooler smoke to stay low in the cook chamber, thus creating my vertical temp variance.

Does that sound reasonable?


Currently, since the chimney extends 3.75" into the cook chamber and the upper grate is only 4" below the bottom of the chimney, i cant simply extend the chimney deeper into the cook chamber.

Im wondering, if i fabricate big upside down L shaped manifold, to allow the chimney to draw smoke from about the lower grate level, the chemney would then be drawing the coolest, (thus oldest), smoke from the cook chamber, as fresh, hot smoke from the reverse flow chamber fills the cook chamber, from the top down?

Sound reasonable? Is it standard practice to have the chimney draw hot smoke from the top, or cooler smoke from lower, in the cook chamber.

Thats the theory. But, at this point in the project im going to start comparing theory/science to the experience of those who have done it.




Oh, i forgot to mention earlier. I'm rather proud of the door/counterweight design. The door weighs 186lbs according to CAD (including welds), and the counterweight is another 160ish.

I got the linkage and arm geometry dead nuts. I can open the door with 2 fingers. It takes about 10 lbs of force to lift it, or pull it down. In the center of its range of motion (60° from open/closed, 120° total range) it balances perfectly.
User avatar
k.a.m.
Outlaw
Posts: 2486
Joined: Mon Jun 25, 2012 6:38 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby k.a.m. » Fri Jun 07, 2019 8:50 am

First off let me say your work is very nice I love what I am seeing. I have some questions before I can try to see what may cause larger than normal variations in the chamber.
Does the firebox top have openings into your warmer that stay open all the time?
What is the size of the firebox to cook chamber opening?
Is the opening opposite the firebox for your return air the same or larger than your firebox opening?
How close is the reverse flow plate to your lower grate?
What is the diameter and length of your exhaust?
How big of a coal base were you running?
Lastly what temp variations up down, left and right were you experiencing?
Note: Empty cookers will run differently than loaded ones. Much like a stream with no boulders it will flow effortlessly but add boulders and the water flow is disrupted and changes in the stream.
Always remember slow and steady wins the race.



My Hybrid cooker.
Competition trailer #2.
amusick10
Pilgrim
Posts: 21
Joined: Fri Aug 28, 2015 6:29 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby amusick10 » Fri Jun 07, 2019 9:01 am

And that’s why you can’t turn engineers loose on a project!! Lol!!

That thing is a beast and an awesome design, not the norm and I like it.

KAM has way more knowledge on this but I agree with where he is heading, fill her up and see what happens. I also think the stack needs to be a little lower if you can work around the racks. Having them L around the rack with play with the flow a little so it may take some playongwith.


Sent from my iPhone using Tapatalk
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Fri Jun 07, 2019 10:31 am

KAM,

I know this is alot to read, sorry for the long winded answers, but thers no way to explain everything in fewer words.

Ill try to answer all your questions, but i may miss some, as its a little tough to type answers on my phone while scrolling up and down to reread and refresh my memory.

1. No, the top of the firebox absorbs heat from the fire, and heats the air inside the sealed chamber just above the firebox. That heated air rises, and drafts fresh cool air in, through those small holes visible around the perimeter of said chamber. The fresh air drafted in through those holes, is heated by the top of the firebox. The heated air rises into the warming cabinet through and adjustable slider, on the bottom of the warming cabinet. The top of the warming cabinet has a sliding gate to control airflow into the warming box chimney.

2. This will be a long explanation, to illustrate how i came up with the shape/size. The firebox to cook chamber opening is a somewhat enlongated triangular shape. Like an upside down triangle, with the bottom point cut off. The area of the triangle is (9×26×.5)+(4×9)=153"^2. 153 square inches.
This is about 3/4 the size recommended by the Feldons calculator, but was done on purpose. I calculated the heat soak rate of the 1/4" reverse flow plate, the draft pressure of the chimney, and the air(smoke) flow volume and velocity through the reverse flow plate, then adjusted the area/volume of the chimney and area of the firebox/cook chamber opening, so that the smoke flows through the reverse flow chamber fast enough to heat the entire plate evenly. I wanted to avoid having the reverse flow plate be too hot on the firebox end. Ive confirmed that it works with a laser thermometer. The firebox end of the reverse flow plate stays about 10° hotter than the opposite end.
As it is, the chimney draft creates a draft pressure of (negative of course) .000435 lb per square inch, which draws smoke through the reverse flow chamber at a velocity of v=4005×square root of the delta in pressure, 83.5 feet per minute, which gives a volume/time of 84.72 cubic feet of smoke through the reverse flow chamber per minute.
So, ive confirmed that the draft pressure is moving smoke through the reverse flow chamber in a sufficient volume/velocity to evenly heat the reverse flow plate.

3. The openinig from the reverse flow chamber into the cook chamber (opposite end to the firebox) is the same shape as the firebox/reverse flow opening, but scaled up larger. It is (36×12×.5)+(4×12)=264"!^2 or 264 square inches.

4. The reverse flow plate is 7.5" below the top face of the lower grate. I originally wanted 4" but the guy i was building it for (before he backed out), wanted at least 7.5.

5. The exhaust is 8x8x1/4 steel square tube, so its internal area is 7.5"^2 or 56.25 square inches. It is 24" long. With an ambient outside temp of 65°f and a internal smoke temp of 250°f it creates a draft that reduces the cook chamber pressure .000435 psi below ambient outside pressure. This was designed such, to move smoke through the reverse flow chamber at about 83ft per minute and move about 84 cubic feer per minute of smoke through the reverse flow chamber. The goal was an even temp across the reverse flow plate.

6. Coal base was half a bag of kingsford briquettes. About 1.5 square ft x a couple inches deep.

7. The temp variation changed with respect to the intake setting, in a not so linear.

For example, with the chimney wide open, if i adjust the air intakes to get the lower left to 240, the lower right gauge runs 255 and the top center runs 320.
(So, basically, that setting gets me 15° difference left/right and about 75° difference upper/lower.


But, with the chimney still wide open, if i adjust the air intakes to get the lower left to 225, the lower right gauge runs 235 and the top center runs 275.
(So, basically, this setting gets me 10° difference left/right and about 45° difference upper/lower.


The closest i can get to an even temp with the chimney wide open, is with all my intakes closed except the lower firebox door intake, which i leave halfway open. A fairly small fire, which gives me 200° on both the left and right gauges, and 210 on the top gauge. But this 200-210 range is to low.



My 2 test runs were completely empty, chimney set wide open, and smoker clean and unseasoned. Its got about 10hrs of burn time on it so far. 2 different days, about 5 hours per day burning Alder and Maple.

Amusick10:

I totally get what your saying, the heatsink effect of a smoker full of meat would likely completely change the characteristics.
The problem is, its just me and the wife. No family and very few friends. Im a temp transplant to the Pacific Northwest. This thing will hold 24 or so briskets on the bottom rack, and half that on the top.
Me, the wife and our German Shepherd would probably take 2 years to eat that much meat. I didnt intend to end up with this smoker, the guy i was building it for changed his mind, and i thought it would make a cool addition to my back yard. I've never even used one of these before :)
User avatar
Rambo
Deputy
Posts: 3540
Joined: Mon Apr 02, 2012 10:39 pm
Location: Lufkin, TEXAS
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Rambo » Fri Jun 07, 2019 12:20 pm

Sounds like you need to sell this before it gets dirty; JMHO
Ken226
Pilgrim
Posts: 20
Joined: Thu Jun 06, 2019 2:00 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Ken226 » Fri Jun 07, 2019 1:09 pm

Rambo wrote:Sounds like you need to sell this before it gets dirty; JMHO



I likely will.

After im certain that it works well enough or make any needed changes, ill probably get the trailer titled and list it on craigslist.

One change i want to make already, is to add an adjustable gate between the cook chamber and warming cabinet. So the warming cabinet can also be used to smoke meat.
Jamboro23
Pilgrim
Posts: 8
Joined: Thu Jun 06, 2019 4:54 am
Contact:

Re: New forum member and new smoker build. A few questions?

Postby Jamboro23 » Sat Jun 08, 2019 6:15 am

Rambo wrote:Sounds like you need to sell this before it gets dirty; JMHO


Who are the lucky customers?
User avatar
spacetrucker
Outlaw
Posts: 2281
Joined: Sun Jun 02, 2013 4:36 pm
Location: Round Rock Texas
Contact:

Re: New forum member and new smoker build. A few questions?

Postby spacetrucker » Sat Jun 08, 2019 10:13 am

great looking build, I am interested to see what and where K.A.M. goes with this, he is very knowledgeable on this subject.
I would really like to have similar but, have learned a few things in my years...
first it is easier to cook for free than try to make money in the restaurant business...
Second, I like you, only have a couple to cook for; occasionally I bother the neighbors with food, and rarer than that the kids.... :D
Don't count every day, Make every day Count
Good Cue to ya..
User avatar
k.a.m.
Outlaw
Posts: 2486
Joined: Mon Jun 25, 2012 6:38 pm
Contact:

Re: New forum member and new smoker build. A few questions?

Postby k.a.m. » Sun Jun 09, 2019 8:58 am

Ken226 wrote:KAM,

I know this is alot to read, sorry for the long winded answers, but thers no way to explain everything in fewer words.

Ill try to answer all your questions, but i may miss some, as its a little tough to type answers on my phone while scrolling up and down to reread and refresh my memory.

1. No, the top of the firebox absorbs heat from the fire, and heats the air inside the sealed chamber just above the firebox. That heated air rises, and drafts fresh cool air in, through those small holes visible around the perimeter of said chamber. The fresh air drafted in through those holes, is heated by the top of the firebox. The heated air rises into the warming cabinet through and adjustable slider, on the bottom of the warming cabinet. The top of the warming cabinet has a sliding gate to control airflow into the warming box chimney.

2. This will be a long explanation, to illustrate how i came up with the shape/size. The firebox to cook chamber opening is a somewhat enlongated triangular shape. Like an upside down triangle, with the bottom point cut off. The area of the triangle is (9×26×.5)+(4×9)=153"^2. 153 square inches.
This is about 3/4 the size recommended by the Feldons calculator, but was done on purpose. I calculated the heat soak rate of the 1/4" reverse flow plate, the draft pressure of the chimney, and the air(smoke) flow volume and velocity through the reverse flow plate, then adjusted the area/volume of the chimney and area of the firebox/cook chamber opening, so that the smoke flows through the reverse flow chamber fast enough to heat the entire plate evenly. I wanted to avoid having the reverse flow plate be too hot on the firebox end. Ive confirmed that it works with a laser thermometer. The firebox end of the reverse flow plate stays about 10° hotter than the opposite end.
As it is, the chimney draft creates a draft pressure of (negative of course) .000435 lb per square inch, which draws smoke through the reverse flow chamber at a velocity of v=4005×square root of the delta in pressure, 83.5 feet per minute, which gives a volume/time of 84.72 cubic feet of smoke through the reverse flow chamber per minute.
So, ive confirmed that the draft pressure is moving smoke through the reverse flow chamber in a sufficient volume/velocity to evenly heat the reverse flow plate.

3. The openinig from the reverse flow chamber into the cook chamber (opposite end to the firebox) is the same shape as the firebox/reverse flow opening, but scaled up larger. It is (36×12×.5)+(4×12)=264"!^2 or 264 square inches.

4. The reverse flow plate is 7.5" below the top face of the lower grate. I originally wanted 4" but the guy i was building it for (before he backed out), wanted at least 7.5.

5. The exhaust is 8x8x1/4 steel square tube, so its internal area is 7.5"^2 or 56.25 square inches. It is 24" long. With an ambient outside temp of 65°f and a internal smoke temp of 250°f it creates a draft that reduces the cook chamber pressure .000435 psi below ambient outside pressure. This was designed such, to move smoke through the reverse flow chamber at about 83ft per minute and move about 84 cubic feer per minute of smoke through the reverse flow chamber. The goal was an even temp across the reverse flow plate.

6. Coal base was half a bag of kingsford briquettes. About 1.5 square ft x a couple inches deep.

7. The temp variation changed with respect to the intake setting, in a not so linear.

For example, with the chimney wide open, if i adjust the air intakes to get the lower left to 240, the lower right gauge runs 255 and the top center runs 320.
(So, basically, that setting gets me 15° difference left/right and about 75° difference upper/lower.


But, with the chimney still wide open, if i adjust the air intakes to get the lower left to 225, the lower right gauge runs 235 and the top center runs 275.
(So, basically, this setting gets me 10° difference left/right and about 45° difference upper/lower.


The closest i can get to an even temp with the chimney wide open, is with all my intakes closed except the lower firebox door intake, which i leave halfway open. A fairly small fire, which gives me 200° on both the left and right gauges, and 210 on the top gauge. But this 200-210 range is to low.



My 2 test runs were completely empty, chimney set wide open, and smoker clean and unseasoned. Its got about 10hrs of burn time on it so far. 2 different days, about 5 hours per day burning Alder and Maple.

Amusick10:

I totally get what your saying, the heatsink effect of a smoker full of meat would likely completely change the characteristics.
The problem is, its just me and the wife. No family and very few friends. Im a temp transplant to the Pacific Northwest. This thing will hold 24 or so briskets on the bottom rack, and half that on the top.
Me, the wife and our German Shepherd would probably take 2 years to eat that much meat. I didnt intend to end up with this smoker, the guy i was building it for changed his mind, and i thought it would make a cool addition to my back yard. I've never even used one of these before :)

I appreciate your passion for numbers but sometimes we can overthink a problem by no means am I knocking your build with what I am about type it is just some information to get to the end.

I need to give you a bit of history on Feldons calculator. It was deigned by a professor of thermodynamics that just so happened like to cook and build cookers the original was actually on an excel spread sheet which I still use today. Morgan Feldon created the online version because not everyone had access to excel back in the day lol.

The calculator is based on a 1/3 rule for building a cooker that will perform and draft properly, when it is altered it no longer performs as it should. In your case I believe by decreasing the firebox opening you have created more of a blast furnace under the plate pushing the air with such velocity that your heat smoke is the one doing the cooking with little help from the plate.

Reverse flow cookers rely on radiant heat for a good portion of their efficiency, the lower plate and air moving quickly is part of your issues. Your first thoughts on having the plate at 4" was dead on in my opinion.
The cooker is built and I would not change a thing so now we get to the fun part mapping out the grate temps. I rarely if ever rely on door therms to map out a cooker I prefer four digital therms placed on the upper and lower grates this way I know what is happening there. Once I have these numbers then I can use the door therms as references to what the grates are actually doing.

You do not need meat for mapping I use aluminum pans with about an inch of water in them to change the dynamics of the heat/smoke flow. You have a lot of options for intake use be careful in windy situations as you can create a cross draft if you are using intakes opposite each other. I would start with the lower door intakes wide open as well as the exhaust and let the cooker run until the temps more or less stabilize this could take an hour or more heating up all the steel. Your coal base was probably about right for this size cooker just remember to keep the coal base active and fed so you are not relying on flames and burning wood as your heat source.

Learning when to add a split is all part of fire management with offsets and in my opinion the hardest to master. Once I have these temps mapped depending on what I am running at I would go to the side intake that is away from the wind and open it up then give the cooker an hour of running and map these temps.
These are the steps I would take in mapping out this cooker but please remember in the world of reverse flow cookers or any cooker for that matter getting upper and lower temps within 20° is about as close you may ever get and I can live with that because I use the different areas for certain meats.
You may want to add a Vee to your basket to contain your coal base I started adding these to mine and it helped greatly on the larger baskets.
005.JPG

If you would like to call and talk my number is 409-673-3884
Always remember slow and steady wins the race.



My Hybrid cooker.
Competition trailer #2.

Return to “Custom Built Pits, Build Your Own Pit & Pit Modifications”

Who is online

Users browsing this forum: No registered users and 2 guests