First ~160 gallon build starting in Finland

[rikun]

Hi all,

After almost a year of hunting suitable tank, I found this:



It's around 160 gallons and measures about 6' long, diameter is 24.5". Everything is 3/16" steel.

I'm planning to make it into a standard reverse flow design with two slidable racks and eventually mount it on a trailer. It has to weight under 1350 pounds or otherwise I can't legally tow it without brakes. The firebox is going to be almost square and made out of 2/5" (10mm) steel.

I've run the numbers through the calculator and here are the results: Link to BBQ Pit Calculator

I also used the circle calculator and came up with these measurements (there may be slight differences, since I played with the FB size a bit after I calculated these):

Half-moon segment height 6.85" (height of the half-moon opening from FB to CC?)
Area under reverse flow plate 9.2" (height to mount my RF plate from the bottom of tank?)
Chord AB: 24.559" (The width of the reverse flow plate at a height of 9.2" from the bottom of CC tank?)

Also, what is the optimal area of my RF to CC opening? I've seen various opinions about this, some say it should be my FB to CC opening +10%, some say it should be AT MOST the same as my FB to CC opening.

Also, how do I calculate the area since the end of the tank is elliptical? Do I use the same half-moon math? I guess not, since the radius of the elliptical endcap is way different than the radius of my tank.

How does the math look? Do you think it would work if I mounted my RF plate a little lower? Or would I be better of lowering my lowest cooking rack closer to my RF plate than 4"? I've done a rough sketch and looks like with two racks it's going to get a little bit tight on a 24.5" diameter tank...

Would you do a two doors or one on a tank this long? I'm fearing that one door might compromise the tank rigidity and maybe not hold on it's own without support on the middle...?

I have very limited experience in metal fabrication, I might take a class and do the work myself, or I'll get someone else to do it for me. Nevertheless I'd like to know as much as I can in the planning stages, so bear with me sinceI have some very stupid questions about actual handywork:

How do you measure and mark your tanks for cut-outs? Do you level the tank on jack stands / whatever and then use a spirit level to mark straight lines?

Do I need to use square bar in my firebox to support it when using 2/5" steel? Would it still be easier to construct if I used it...?

There is a large hole on my tank, how would you patch that up? Would I need to have a plate of 3/16" rolled to match the curvature, or could I just tack weld a piece of sheet metal from the other side and use some force / heat to shape it?

Notching the firebox inside the tank, is it done for stronger construction? Should I extend my RF plate on top of the firebox notched into my tank all the way to the end of the CC? How much would you notch your firebox into your chamber? What width should I make my firebox for easy notching, the same width as my tank's diameter?

Should I make my RF plate slope towards grease valve, or would it be better to adjust my trailer?

How far do you make your counterweights for the door "hang out" to the other size? Do you think a 45 degree angle would work for attaching them to my door(s)?

The chimney length in the calculator is apparently the length outside the CC, right? I got a free 6" pipe with my tank, but it's only around 1/10". Do you think it would last or am I just shooting myself in the leg trying to save in the wrong place...?

Thanks, this is probably the first build of its kind in Finland, so I'd like to do it right

[Big T]

I'll try to answer a few of your questions for you. Your counter weight will be determined by the size of your door and the angle you want it to open, so you'll have to figure that out when you get to that point. I would think that you'd want two doors on a rig this size but I'm not sure what you plan on cooking on it. I would install the baffle plate level and tilt my trailer. Try not to recess the FB into the CC anymore than you have to, this will help avoid a hot spot on that end. The BP is normally an extension of the top of your FB, some guys raise the BP an inch higher than the FB. The BP opening on my pit is the same as the throat from the CC to the FB, some are built to be adjustable and then tuned to your liking. There are a lot of pits on here that are similar to what you're wanting to build so I would suggest looking through here and getting some ideas. Once you come up with a rough sketch of what you're going to do just put a picture on here and the guys will help out when ever you need it. This is just my opinion and I'm sure others will come along and help you out better than what I can.

[Puff]

Rikun,

Hi and welcome. My own personal thoughts are that you have found the right place. You'll probably have all of your answers within a few days. I believe that your chimney stack thickness is fine. I am using similar 6" tubing but thanks to the encouragement of Gizmo, a founder here,I am using an elbow that allows the stack to be removed for transport. And guess what....if it totally disintegrates in a few years, it's a simple straight piece that is easily just cut and slipped on..and the measurement is the vertical portion only. So that's one point.

From what I have come to understand, Big T is correct... you are better off keeping the baffle plate level and adjusting your trailer tongue up or down for the angle.

Your firebox will be best made from 1/4" or better so your 2/5" is great. I did not use any support frame in my FB just edge to edge welding contact and it is coming out great. It is heavy however. As for your trailer weight, I am using a 3500# spring but my 275 tank and trailer only seem to weigh in around 950 lbs so far. It's not finished yet but would have never thought the weight would add up this high. It was the guidance I got right here that brought me to the bigger capacity and I am SO happy it worked out this way. I don't see your creating something with an additional 500 lbs, although possible. The folks here know what the plan should be and give the greatest advice so ask away

[Pete Mazz]

Chord AB: 24.559" (The width of the reverse flow plate at a height of 9.2" from the bottom of CC tank?)

This doesn't seem to add up as the diameter of the tank is 24.5".

[Gizmo]

First things first.
Hello and Welcome to the site - we're glad you brought your project here and I'm sure you will find the right advice to 'get 'er done'! … always nice to hear from across the pond.

I'm right-handed so I like the FB on the left end of the tank as you approach the CC door since there is always a table sitting at 90 degrees to the tank at the other end for holding meat, tools, etc. - make that decision now.

Pick a top-dead-centre on the tank (maybe opposite the hole you're patching to put it at the bottom?) then roll the tank on the ground against a piece of angle iron to act as a straightedge and mark the tank lengthwise at that point. (A sharpie works well)

Using a dressmaker's tape measure, determine the circumference and measure from this line 1/4 of the way around for your door height. I agree that 2 doors would certainly be easier to manage for nearly all cooks except whole hog. If it's 2 then leave a center post about 4 inches (10cm?) when you draw the doors on. Using this gauge steel I wouldn't worry about vertical support much if you go with a single door though.

2 ways to control the hot spot and you need to make that decision right now…..

1) cut into the tank end to allow your FB to mount INTO the tank volume and leave the top on the FB all the way to the throat opening and put the BP an inch above that. The top of the FB that's inside the CC will act as a 'shadow plate' forcing the radiant heat in the FB roof to re-radiate to the BP. ….. slightly warmer - yes ….. a true hot spot - not likely.

2) cut the end off the tank just inside the end bell seam. Cut a new flat end plate with the throat opening already removed (see Earl's build thread). Butt the FB throat opening against that opening. You just moved your hot spot outside the CC where it won't be a tribble at all (Star Trek reference) This method is obviously more expensive since you have to buy new end plate steel.

Either way - hang onto the drop offs because you can cut a piece from them to patch that hole you mentioned.

Stack opening is another early decision….

If you go the first method it's easier to just go out the top of the tank at the end so it will move your door opening back some from the FB end to allow room for the stack exit hole.

If you go the new end plate method then build a simple elbow (see Earl's build thread) and come out the new end plate. Advantages to this method are that your door can be larger (longer) and drippings from inside the stack (typically high creosote content) fall into this elbow and can't fall onto what you're cooking.

Talk to your helper and get his take on fabricating these methods - you'll find a good compromise and be moving forward in no time.

If you get frustrated repeat after me; "It's a HOBBY"…. remember that there are stiff penalties for not posting pics and having fun …. just sayin'

[Rodcrafter]

Sounds like these guys have you headed in a good direction. Have fun!

[bluecatfish]

You have come to a good place for advice. It is good to look at several of the builds here and then use the designs that will work for you in your build.

[Smokeone]

The guys are on a roll, some great advice there!

[rikun]

Thanks for all the great advice, especially that tip for marking the door, never would've thought of that myself

My tank is actually 25.6" in diameter, probably a typo on my part previously. I checked the reverse flow plate by drawing it in Sketchup, the width seems to put it at the correct height. Here's a rough idea what I'm thinking.



As you can see, there's just barely space for a second rack.

What do you think about the rack spacing? I'm going to be mostly cooking pork necks (similar to butts but smaller), brisket packers and brisket flats. If I need to cook something taller, I'll just use the bottom rack and remove the upper one.

I'm going to cut into the tank and notch the FB. I may have a CNC controlled plasma at my disposal, so I'm thinking I'll cut the FB plates with it and make all the openings at the same time (half-moon, intakes, etc). And of course all the other parts I can

The hole I need to patch up is pretty huge, I would say it's at least 12-15" in diameter.

Just though of something, since I need to buy and modify an existing trailer, it's probably made out of galvanized steel. Could I burn off the galvanization from a few spots from the frame in well ventilated area wearing a half-mask respirator and then weld my smoker frame to these bare spots...?

The reason I need to buy an existing trailer is that it's very difficult to make a trailer road-legal here in Finland, it's much easier to buy one that already has all the required paperwork done and is approved for traffic.

[Big T]

Your sketch is almost identical to my 25'' smoker so I would say it will work just fine. I have used a grinder to remove the galvanized coating on a lot of boat trailers and weld mild steel beams in place so I don't think you'll have any problems with that.

[Gizmo]

I just had an idea … I KNOW - scary right?

What if you made 2 smaller cookers out of this 1 tank and sold one of them? Would that pay for the other one? Would it be a large enough cooker for your plans? Should I go back and sit down in the corner?

jm2cw

[rikun]

Good idea,

But not nearly big enough ;)

Is there any disadvantage to cutting my CC door bigger than 1/4 of the circumference? I'm thinking I want my first rack exactly at the center, so I'd either need to make my door bigger or make it further down than 3 o'clock position.

That would leave me around 3" to reverse flow plate, so that's probably ok.

Also, I just had an idea for the racks. I was going to buy a sheet of flat expanded, but it's a bit expensive here.

How 'bout if I use the CNC plasma to cut a lot of holes into 1/8" steel? I probably could even cut diamond pattern, if there's any advantage over round holes...

[SmokinFF]

Don't see why that wouldn't work.

[Gizmo]

A lot of guys have gone an inch past noon and 3 o'clock just for rain run-off on top and to allow the bottom grate to be exactly at 3 o'clock.

If you're gonna use a CNC plasma to cut your grate out of sheet-metal at least cut out your initials or flame shapes instead of just diamonds …. just sayin'

[Big T]

[rikun]

Yeah that's true, I'm just concerned how a "wild" cut-out would affect cooking. Or am I fine just by cutting out something almost uniform with around 50% open area...? I guess it's not so important in indirect...

I marked my doors today, used existing welding seams on tank to measure straight lines, I think they are straight enough.

Also decided to go with two doors, fantasized a while about doing only one door, but realised it would be really impractical.

Am I fine with 102% firebox size if I want my smoker to run at 350 F sometimes...?

[rikun]

Still haven't made a single cut, I know I'm overanalyzing a bit, but...

What are the advantages of mounting my firebox lower and extending the baffle plate all the way to the end over the FB versus mounting my firebox higher and welding the baffle plate to my firebox?

I already decided to mount my firebox higher and weld my baffle plate to it, but then started thinking (too much) once again

And also, in what order should I proceed with the build? I'm thinking I should first patch the huge hole even before cutting doors, so that the heat from patching the hole won't warp anything...? Or could I cut the doors out first? Can't find a "hand-held" regular plasma anywhere, so I'll have to cut them out with angle grinder

[Rodcrafter]

I would say either way, as long as you don't cut the doors in the patched spot.

[Big T]

I have seen some guys have an extreme hot spot when they tucked their FB too far into their CC. If I was going to tuck the FB into the CC I would do it a little lower and run my BP over the top of the FB and leave at least an inch of clearance between the FB and BP, maybe a little more if it didn't interfere with my throat. JM2CW.

[Gizmo]

Listen to BigT - he speaketh good advice…

[rikun]

Damn, that's gonna make it a lot harder to weld in... I'm thinking the BP is going to have a drain in the middle and both plates sloped a little bit towards the drain.

Do you think I would get a hotspot if I tucked my FB just to the edge of my CC so that no food would be on top of the FB part?

That's how I've been planning to do it, tuck the FB to the outmost weld seam and stop my racks about and inch before the inner weld seam.

[Big T]

That should be fine, I have seen a lot of cookers with the FB tucked. I would tuck it as little as possible and let it ride.

[rikun]

Thanks,

I'm going to cut the doors next week (getting to use plasma then). What's the minimum you would leave between the doors? I have now around 3.15" drawn.

What's the best way to cut the vertical door cuts with plasma? Just freehanding or bending some flat bar for guide? I though of making a circular guide out of plywood that slips on the tank, but that's a lot of work for a guide... The guide would need to be at least 0.5" thick from the tank due to the plasma torch design. It's a PT-31XL torch.

Going to get some steel for the build, what's your opinion on food grates, angle vs square tubing? The lower grates are roughly 30" x 25". I've seen both, but the main difference seems to be that with angle you have two options how to mount the expanded. I remember reading that the grates are easier to clean if the expanded is attached so that the angle is other way around, just can't remember which way. The most common design seems to be that the welding is hidden under the angle, which I think looks best.

One culprit is that I can't find 1" angle thicker than 1/8" here. Would that sag with 30" wide racks? Middle support?

Sorry, nothing to show for yet, it's freezing here (0 F) and I don't have a warm shop.

[Gizmo]

rikum did you decide to go with the tucked-in FB or a flat end plate?

You might have some wasted height there that you could use for cooking but it depends on which method you are attaching the FB.

[rikun]

Tucked in. I don't think I have any wasted height, ran the numbers quite a bit.