500 gal offset build

Horizontal smokers with a side firebox and tuning plates.
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Militant83
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500 gal offset build

Post by Militant83 » September 5th, 2019, 8:37 pm

Well here is the beginning of my 500 gal standard offset build. The guy offered to cut the doors for me and I knew I should have passed on the offer. It looks like he made them about 6" too tall. But Oh well we can weld that back up and fix it pretty easily. The top of the may also be a little low on the tank but oh well we will deal with that. Tomorrow I will begin cutting out the areas where the valves where and patching them up if I have time. This may be a rather slow build as I will work on it as time and money allow so bare with me and I will update as much as possible.

Now correct me if I'm wrong but the bottom of the doors should be at the center point of the tank?

When looking for pipe for a stack all I can find around here is sch 40 steel pipe and it is stupid expensive. The guy I bought the tank off of had one built with a square stack which from what I have seen is cheaper than the round pipe. Will a square stack work just as well?

If I'm using the pitcalc correctly it looks like I should need the following dimensions for the rest of the build

Square firebox- 34x34x34 39304 in³ ( slightly bigger than recommended but not much)
Square Stack- 8 X 8 X 30.71 1965.44 in³ (this seems awfully short to be coming out of the side of the cooker at grate level)
Firebox air intake 3x10 120 in²

If I was to use a round stack it calls for this- 8 X 39.12
Says I should have a throat size of 314.43 in² but I didn't see a section to put calculations in to figure out size.

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Last edited by Militant83 on September 6th, 2019, 11:39 am, edited 3 times in total.



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Re: 500 gal offset build

Post by Big T » September 5th, 2019, 9:22 pm

If you're going to have slide out racks then the bottom door cut needs to be 1'' below center. That allows the rack to be at the widest part of the tank and gives you maximum rack size. The stack can be round or square, just be sure to use the stack calculator on the smokerbuilder calculator section because a square stack is a little different in size vs round.


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Re: 500 gal offset build

Post by Militant83 » September 5th, 2019, 9:37 pm

Big T,

I plan to have a full bottom rack that is doesn't slide but possibly some upper sliding racks. I added my calculations to the original post as long as I used it correctly I believe they are correct.



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Re: 500 gal offset build

Post by Militant83 » September 6th, 2019, 9:31 am

https://bbqsmokersupply.com/hinges/othe ... steel.html

Has anyone used the above hinges in a build? I was wanting to make my own "Franklin" style hinges however, I don't feel like trying to find someone with a torch that I can use and definitely don't want to spend $300+ on a set of torches to make one set of hinges.



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Re: 500 gal offset build

Post by Dirtytires » September 6th, 2019, 7:00 pm

Just something to consider.....that bottom rack can get pretty deep and especially on a pit that big. I can see a whole lot of benefit to a sliding bottom rack. Not a necessity but definitely easier to put in now vs later.



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Re: 500 gal offset build

Post by Big T » September 6th, 2019, 7:37 pm

:yth: I haven't used those hinges but I built some that were similar on my last pit and they worked fine. I recently started using the bullet hinges and I really like them.


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Re: 500 gal offset build

Post by Militant83 » September 6th, 2019, 8:17 pm

Now when it comes to the stack I know it recommends 30" which seems way to small to me. How big is too big when you start getting poor performance out of the stack? The one on the cooker the guy had that I got the tank off of was about 5' tall that is a pretty big stretch from 30" and it is almost an identical cooker to the one i'm building.



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Re: 500 gal offset build

Post by Wicky » September 6th, 2019, 8:32 pm

Cut the feet and lifting point off the tank. Then rotate the tank. Your door will be closer than you think.



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Re: 500 gal offset build

Post by Militant83 » September 6th, 2019, 9:48 pm

What size are the doors supposed to be ideally? He said those are cut to be 1/4 of the circumference of the tank. He said that is what they typically should be.

Wicky,

That would make it extremely difficult to maneuver at this point.



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Re: 500 gal offset build

Post by Big T » September 6th, 2019, 10:25 pm

I normally make the top cut 1'' past top dead center and the bottom cut 1'' below 3 o clock. That keeps water from being able to run through the top cut and allows the bottom rack to be at the widest part of the tank. The stack is based off of volume so the larger the diameter the shorter the stack. You could use a smaller diameter and that would make it longer. I like for the stack to be tall enough to keep the smoke out of my eyes but not so tall that it won't fit in a standard garage door. You could make the larger diameter stack a little taller than recommended if you put a damper on it so it can be closed off a little if need be.


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Re: 500 gal offset build

Post by Militant83 » September 7th, 2019, 2:41 pm

I can see where the recommended size would be a good measurement if it was coming off the top of the tank like most do because you have the chamber space above the bottom grate as well that functions as part of the stack. But since I plan to come out the side in the middle would it be too much to add half the depth of the tank to my measurement? for example my stack on top of the tank is 30" above the top of the tank and it was 20" from top of the tank to the center point I would make the stack coming out of the side 50" should end up being at the same height as on top in the end.



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Re: 500 gal offset build

Post by Big T » September 7th, 2019, 3:20 pm

That will probably be fine but I would put a damper on the top of the stack just to be safe. The stack/draft controls how fast that the heat is drawn out of the FB and across the cooking grate so building it according to the calculator is basically like have a governor on an engine that controls max speed. If you have a damper you could choke it down a little if you need to. If air is moving too rapidly through the CC it can cause some real headaches with trying to manage your temps as well as the flavor from the wood. I've seen several pits that guys have built without using a pit calculator and they had different problems for various reasons. A lot of guys try to build Jambo clones without understanding the thermal dynamics that are involved and they never work right until they make a few modifications.


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Re: 500 gal offset build

Post by Militant83 » September 7th, 2019, 8:04 pm

Big T, Thanks for the info and yes a damper was in the plan..Decided to just weld up where the doors were cut wrong inside and out then grind down and cut new doors on the other side according to one of Franks 500 gal plans. I should have done the doors myself in the first place but ya live and learn I guess. I do think I will go for the slide out racks as well per the recommendation.

I was listening to the BBQ Culture in the cruiser today and heard Frank talking about baffles in a standard offset. Something like plates with varying size holes in them and the holes increase in size the farther away they get from the FB. What are your guy's thoughts on those, originally I was just going to make it true Texas style offset with no baffles/tuning plates or whatever you want to call them. How many do you put in? Do they stretch the whole length of the cooking chamber?



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Re: 500 gal offset build

Post by Pete Mazz » September 8th, 2019, 4:20 am

They're called tuning plates . No need for holes, just make them 8 or 10" wide and start at the FB end with small gaps, gradually getting wider . the idea is to get even temps but you can also adjust for different zones .


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Re: 500 gal offset build

Post by Dirtytires » September 9th, 2019, 11:01 pm

You probably have seen them with holes tho and they do the same thing. The separate plates like Pete described are easier because you can move them to adjust the heat and fine tune your pit. The holes you mentioned are drilled in a solid plate which makes adjusting it more difficult. It works great for a commercial pit where they already did the tuning and can punch them out.



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Re: 500 gal offset build

Post by Militant83 » September 14th, 2019, 9:57 am

Dirtytires,

So if you are going to put in baffle plates across the pit why not go reverse flow at that point? Even though I started this thread in the standard offset category, while still being in the early stages of the build I have not completely ruled out changing the pit design to reverse flow.



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Re: 500 gal offset build

Post by Big T » September 14th, 2019, 11:27 am

Not to butt in but a RF and an offset with TP are two different animals. The RF will be pretty even in temperature from from side to side and a minimal difference from top to bottom rack. The TP's can be adjusted to have a huge temperature difference from side to side and will have an increase from bottom to top as well. Once you build the RF, you pretty much have what you have as far as temp zones go but the TP's can be adjusted at any time so you can tune for whatever you're cooking. A lot of guys will run the end closest to the FB at a higher temp to cook chicken and a lower temp for the ribs at the other end, that's not something that you can do with a RF although you could cook a little hotter on the upper racks. I built a RF with a WC and added dampers between the FB/WC and CC/WC so I can cook at a low temp in the main chamber and a high temp in the WC during the same cook. I guess you would really need to decide what will work best before proceeding because they definitely both have their pros and cons.


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Re: 500 gal offset build

Post by Militant83 » September 14th, 2019, 11:52 am

Big T, That makes since I can see the benefits in being able to create heat zones. I guess I wasn't really thinking of it in that way. I was thinking in terms of redirecting your air flow to keep from getting hot spots near the cook chamber and create a more even cooking environment. But having the ability to cook chicken at a slightly higher temp to get crispier skin could be beneficial. Definitely have some thinking to do while the project is at a brief stand still.



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