Blakes (Newby) Offset smoker build

[daveomak]

Jambo design works very well and make a great smoker... I'm a fan of the Jambo smoker....
From what I've noticed, they use a larger diameter exhaust stack than SFB or Reverse flow smoker...
They really need draw to suck the heat downward, through the meat grate... That concept goes against physics....

 

[daveomak]

Smokin-Aces Jambo design.....

First Big Smoker Build. Advice welcomed!

Hey guys, I am starting my first "big" smoker project, and of course big is relative. I have built two 55 gallon double barrel smokers in the past (one this May and one a few weeks ago), but I decided to step into the big leagues and make a trailer smoker. The smoker I am making is a tank...

www.smokingmeatforums.com

 

[Blizzo]

thanks dave, I have had a good read of that and looks like he has had great success with an out of the usual design, I love to see that stuff work / payoff.

I have attached a concept of my design here. the FB-CC is a copy of the jambo design, with the bottom of the inlet level with the grate but a deflector angling it up more. On the Jambo backyard pit he has the bottom of the stack level with the top of the grate, I've opted for a half under half over design to help pull the smoke down. Can you see any issue here?

Ive decided against constraining myself to the 3" outlet already on the tank, and will remove it to construct a wide mount manifold with a 4" ID stack to cry get a good amount of draw here. Any guess on stack height to make this design work?

The other question id like answered relates to insulated firebox's, especially on smaller smokers such as my design. Does it really make a noticeable difference? is it worth the extra fab work, as it is quite a bit more work. Decent wood is pretty scarce where i am (mostly pine and cypress) so efficiency would be handy, and I also have young kids so the idea of not "peel your skin off hot steel" kind of appeals.

Also, in terms of "some liberties dave, how much liberty should i add for such a small smoker, 10% increase, 20% increase? im mostly concerned about CC/FB opening and FB air inlet.

Inside length of CC = 39.25"
Inside Dia of CC =15.25"
Inside Radius of CC = 7.625"
Internal volume of CC =716.466 Cubic Inches
Internal volume of CC = 31.067 US Gallons
Desired FB/CC Opening = 28.7 Square inches
For a 13.75" dia circle (leaves an edge for a grease dam) , to achieve 28.7 si height from bottom of circle = 3.42"
Minimum FB Volume = 2,368.23 Square inches
Air inlet = 7.18 Square inches (20% above grate, 80% below)
Desired Stack volume above CC = 157.9 Square inches
For 3" ID Stack, stack height above CC = 23"


As always, guidance and advice is well appreciated! cheers

 

[daveomak]

You need the stack to end ~35" above the CC... I would go with a 4" stack and a plenum to attach it to..... NO 90 deg. elbows... They Kill the air flow...

It is critical the smoker be air tight so the only air in is FB air control...

 

[Blizzo]

You need the stack to end ~35" above the CC... I would go with a 4" stack and a plenum to attach it to..... NO 90 deg. elbows... They Kill the air flow...

It is critical the smoker be air tight so the only air in is FB air control...

View attachment 475450

Thanks Dave, are you able to answer my other questions in regards to firebox insulation, overall design and the liberties to the numbers for a small smoker.
Also, do you think i'm barking up the wrong tree, for a smoker of my size, should I only be considering reverse flow?

 

[daveomak]

That smoker should run great with the Jambo Design....
The stack should take care of the size of the smoker....
You want to insulate the FB with a welding blanket ?? or build an outer skin and stuff Rock Wool in the space....

 

[Blizzo]

I was thinking of the second skin of slightly thinner gauge steel with a ceramic type wool. But if it doesn’t make a dramatic difference to the use of the smoker I probably wouldn’t bother, and could then run a cowboy type grill on the top of the firebox

 

[daveomak]

That would work... either one..
If insulated, it should be stored where it can't get wet... Wet insulation forever would be bad...

 

[BBQBakas]

Hey team. Blakehere from what is most likely a long way away from all of you, New Zealand (i'm struggling converting all your imperial measurements in my head!)

Ive been wanting to try low n slow bbq for a while and was about to buy an OK Joe, but they are super expensive here in NZ and thought shit im pretty good and welding and fab work ill just make one.

So I called past an engineer mates yard and picked up this -
View attachment 473966

Its appx 41" long and 16" in diameter. The wall thickness is bloody thick, around 10mm so i guess that makes it about 3/8"

View attachment 473967
One I pop that middle piece out of this end outlet it will give me just over a 3" hole which should work alright for the smoke stack, my calcs using 0.2% of the CC puts it at around 23-24 inches long for the stack.

Bonus is it comes with some cool patina which seems to be trendy these days, dumb thing is its pretty oily inside, so ill have to burn the shit out our that.
View attachment 473968

I've got some cool cast iron vintage wagon wheels on the way, and will grab some steel for legs next week.

I just need some help with design now, unless i can find some suitable pipe ill probs go for a square firebox as i can draw it up and have it laser cut which makes life easy. what size would everyone reccomend? ive looked at the calculators (feldon) but most people seem to say to steer clear from it these days. Id like to incorporate a cowboy grill with the firebox for reverse searing steak and what not. Im not too sure on the firebox size, inlet size and size of the gap from the firebox to the CC. Any help with all this would be greatly appreciated!
Cheers

Welcome! Once you get your smoker built, you have some of the world's best wine to go with your BBQ. I've had some Pinot Noir and Syrah from NZ that is out of this world.

On a side note, my understanding about good airflow is you want your smoke stack attached right in the center of the end rather than above center. It helps with a more even air draw.

Post pics when you're done!

 

[Dudeck’s Distributing]

great thread read for me as I am currently puroosing the build threads for tips/tricks for my next build. Ive learned alot in a short amount of tim eon this site! Made 2 double drums this year and looking to build a traditional offset next but I want to build it once not 3 times hahah

thanks for asking all the questions Blizzo

 

[Blizzo]

So i had a crack at starting this. I got some 16" 3/8th thick steel pipe so cut that 18" long for the firebox. sunk a few cutting discs into that!


After doing all my calcs i then got cracked into cutting the opening of the CC, soon realised why this thing was so frekin heavy, its 9/16" thick!! eventually got that all cut and ground out to fit the firebox perfectly, poor grinder got a workout.


Then it was onto the legs, braced them up and cut them out trying to get all square, close enough that a blind man would be happy anyway. then got the castors on the stack end while im still waiting for my wagon wheels to turn up for the FB end. will make sire eveything levels out when i put those on, hopefully my garage floor is flat or it will wind up wonky.


Next up is cutting the most of the door out except for a few tabs while i wait for my hinges to be lasercut! at least it looks a bit more like a smoker now

 

[Blizzo]

You guys reckon this is about right for my door cutout? Top is based on just being able to see the back of the rack from standing without bending down. Do you think it’s wide enough or shall I go out another 3/4” on either side?

 

[daveomak]

 

[Blizzo]

Air inlet and door design time! any direction here would be helpful.
I'm thinking 6x 1x2" inlets at the bottom in line with the middle of the grate (12.4 sq inch), so plenty of airflow under the fire (the fire will be set back a bit from the door) these will be non adjustable. I then have a total of 3 square inchs on inlet up the top, these will be adjustable with a slider plate.

am i on the money here? i figured making the bottom ones adjustable would be difficult and not necessarily needed, am i wrong?

 

[daveomak]

The bottom air inlets should be below the wood grate and they MUST be adjustable... Their function is to control the amount of air to the fire to control the temperature....
The upper inlets are to move heat from the FB to the CC without adding air to the fire...

These numbers are what you calculated.....
Air inlet = 7.18 Square inches (20% above grate, 80% below)
So, 2 sq. in. above and 6 sq. in. below.. both adjustable.....

 

[Blizzo]

The bottom air inlets should be below the wood grate and they MUST be adjustable... Their function is to control the amount of air to the fire to control the temperature....
The upper inlets are to move heat from the FB to the CC without adding air to the fire...

These numbers are what you calculated.....
Air inlet = 7.18 Square inches (20% above grate, 80% below)
So, 2 sq. in. above and 6 sq. in. below.. both adjustable.....

ok I’ll have a play around with the design. Might be better to have the inlet on the actual firebox not on the door.

I have changed my FB-CC opening to around 32sq inch now would that have any change?

why is it that designs such as Aaron franklins backyard and workhorse pits smokers don’t have the inlet below the grate? I see Aaron’s ones are sort of at grate level.
Cheers

 

[daveomak]

It's my understanding, Franklin adjusts the air flow in his smokers by opening the door...
That's pretty much having no control over the process,...

The lower opening is like using a thermostat... The upper inlet is like having a duct system and a fan to circulate the heat and smoke....

If you install the inlets as described and calculated and don't particularly care for complete control and reduced fuel consumption, you can always leave them closed and use the door for control....

These numbers are what you calculated.....
Air inlet = 7.18 Square inches (20% above grate, 80% below)
So, 2 sq. in. above and 6 sq. in. below.. both adjustable.....

1" X 2" = 2 sq. in.
2" X 3" = 6 sq. in.

 

[Dave Davis]

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

I am building a smoker and was looking at your calculator. I am wondering why the stack is 36". I guessed it works best in most cases. So I think my design would qualify as a reverse flow and the calculations may work out. The stack however I don't see the advantage to having it taller other than posibly a better draft. It will be on my lid so I wanted to keep it short. Like 10"-12" or shorter. The egg shaped smokers have little to no stack and seem to control the smoke flow with vents. For appearance sake a 6" vent would look best. The top of the smoker will be around 55" off the ground. Am I overthinking this?

 

[daveomak]

Do what looks best.... Then, live with the results...