High School Shop- Reverse Flow Build

[Gijoe985]

Hello all,

I just signed up on here to stay this thread. I'm a high school shop teacher and I teach the big 3, auto, metals, and woods. We've had the idea for some time now to build a large smoker (that could potentially be used for burgers an dogs as well.)

I have a friend who owns a smoking business Cali (we are in Eastern Washington). He has sent me some pictures of his reverse flow offset smoker. His (unlike most I see) is NOT made from a barrel orcylinder, but is bent plate. We have a lot of sheets of metal to work with in a variety of thickness. We even have 1 that is near 1/2".

Al that said, I dont even know what kind of questions I should be asking at this point. We either want to 1) go big or go home or 2) build a smaller guy to get our feet wet first.

I'm not sure if we will build it on a trailer bed or not. It'll depend on how big we decide to go.

We live in an orchard town, so I have an unlimited supply of apple and cherry wood. So, whatever design that would best accommodate that would be best.

Anyway, where do we start?

 

[kruizer]

I would recommend starting small. Take a look at the Oklahoma Joe smokers and maybe pattern on one of the smaller ones.

 

[daveomak]

Follow this build tutorial.... It will get you a great smoker.....

https://www.smokingmeatforums.com/t...eady-to-use-rev5-6-19-15.172425/#post_1264161

 

[Gijoe985]

Very nice, thanks.

 

[radioguy]

Go bigger and put it on a trailer. Experience talking here.

RG

 

[motocrash]

.01 Use Dave's formula.
.02 This sounds like a "municipal smoker" of sorts,I say bigger-trailer mounted.
There's my two cents.

 

[wbf610]

My vote, go big.

I’m not a builder, but does the steel have to bent/rolled? Wouldn't a square box be simpler? Vertical offset?

 

[JckDanls 07]

An octagon one would be one way to go since you have plenty of plate... 1/4"-3/8" for everything ... pending the availability of a brake or a press a few of the corners can be bent instead of every one being welded ...

or as mentioned above... a cabinet smoker would work as well ...

A "themed" smoker would be a good idea as well... If you look at my build (Antique tractor) you will see what I mean.. the link is in my signature line below ...

 

[Gijoe985]

Ok, so, by being such a novice at smokers, the above build calculations are a bit tough to follow.

I have a 120 gallon LP tank. It is about 5'x2'. So from there I am trying to run my numbers. 120x231 is 17720 ci.
That would make my firebox about 9150 ci? For just over 33%. Sound right?

I was planning to build this firebox out of our thick plate. I might even insulate it and add an outer layer.

Anyway, I am going to keep reading and plugging at the above numbers, but extra direction would be great.

 

[daveomak]

5' x 2'
2' = 24"
5' = 60"
24x24x0.7854x60= 27,143.424 cu. in.
27,143 cu. in. x 0.004 = 108 sq. in. openings

Calculate each line and write down the number....
I did take some liberties where cu. in. x ?? = sq. in.
It will work....

 

[Gijoe985]

Am I missing the math for how large the underside passage is supposed to be vs the cooking area?

Anyone have suggestions on door(s) size(s)?

I do need to get more exact measurements of the tank. We just got it today.

 

[Gijoe985]

Ok, I got 29,631ci. So 118si opening. Then the firebox would need to be 9,778ci.

From what I'm understanding, the hole from the FB to the CC is the same size as the cross sectional area of the area under the RF and also the same as the passage where the air comes around to the top portion.

As far as fire boxes are concerned. Is there any advantage to how you build them proportionately? I.e. a perfect cube vs a tall box vs a short and longer box. Etc...

 

[Gijoe985]

Another question (I hope it isn't blasphemy on here), if we wanted to "grill" on our smoker, would it be able to get hot enough/what would we need to do to make it dual purpose?

 

[JWFokker]

Gotta have direct heat to grill, which is the opposite of what smokers are intended to do generally. You can put a top access door on your firebox and a grate to grill on. That's the easiest way to go. Grills and smokers are two different beasts. Tends to be easier to smoke on a grill than grill with a smoker. Most people have a dedicated grill if they need high heat/direct heat.

 

[daveomak]

Sounds like you want a 4 WD and a Honda Accord all in one...
Dual purpose makes for 2 units that don't do anything well.... IMO....

 

[indaswamp]

First question I would ask is how many people do you want to feed? Will you be doing a lot of big cooks? Or a lot of small cooks just for the class? Hard to cook small on a big unit......

If you go big, you can use it for school fund raiser cooks....

 

[Gijoe985]

First question I would ask is how many people do you want to feed? Will you be doing a lot of big cooks? Or a lot of small cooks just for the class? Hard to cook small on a big unit......

If you go big, you can use it for school fund raiser cooks....

Can you describe the difficulties of cooking small on a big unit? Again, I'm learning here. I've only ever smoked on my home grill, bit thought that this would be a fun and appropriate shop project.

I have a friend who smokes as a profession and he told me that (though you won't get direct hear) you could still do some simple burgers and hot dogs on the smoker if you got it hot enough. We do have grills for grilling, so I dont need to make this perfectly multi purpose. I just figured since it was so big, it'd be nice to cook everything in one spot. Hence if we weren't smoking, we could grill. Just an idea. But again, I'm open to redirecting.

The tank we got is .140". So not super thick.

Maybe we will make 2 smokers. A large one and a smaller one. I still have tons of sheets of 1/4" and 3/8" metal that I could use.

 

[indaswamp]

Cooking small on a big unit is different than cooking large. For one, you'd be wasting a lot of fuel. The damper settings will be different...Large cookers are designed to run with a certain amount of meat which acts as a heat sink (think room temperature meat in a 250* smoker). The meat also slows down air flow which is taken into account when the unit is designed. A large cooker will not run optimally mostly empty. You can close off the intake vent to slow the flow down, but now you are choking off the fire. Choke it too much and you sacrifice a clean burn. I'm not saying you CAN'T cook small on a big unit, just that the design parameters won't be met, the vent settings will be different, and fire management will be very different.

 

[indaswamp]

120lb. LP tank is a nice sized unit. I would not call that "large". But I guess size is subjective....

When I think Large cooker, I'm thinking of a 1,000 gallon LP tank, or a pit that can cook 100 Boston Butts at 1 time....

You could cook hamburgers and hot dogs on a 120lb. LP tank fairly easily. Super hot smoke them....275*~350*.

If you want to kick up high temps on it, I would oversize the firebox by 20% to accommodate a slightly larger fire to produce those temps more efficiently.

 

[Gijoe985]

So, maybe a 12,000ci firebox?

Also, does the proportions of the FB matter much? Is taller vs longer any better?

After doing the circle math, my RF should be about 7-7.5" above the bottom of the tank. Chord AB=22" Arc AB =28.375.

Have you guys done math to account for a slight angle of the RF so that a drain can be installed for easy cleaning? I've seen designs with a slight angle leading to a small trough with a tube to drain out. Sounds like a good idea.

Sound good?