Lets do this thing!!

[Stuey1515]

After spending over 12 months amassing the materials and tools to have a crack at making a small off-set, it's now time to do this. My COS is starting to rust away and it's only time before the firebox comes off in my hand when I wheel it out of the shed.

The blue tank pictured below measures 34" long x 22" across. I have stitched together a firebox out off cuts of
1/4" plate and it measures 16" x16" x 20" high, planning around 3" gap beneath the grate for the fire to breath . It ain't pretty but it's what I have to work with.

As you can see I have offered up the tank to the firebox to get a visual on it, but I just can't bring myself to cut the little sucker open. I assume there aren't too many chances when you cut into one of these if you get it wrong. Where to cut through the welds seems important too

I'm looking for some tips on how to cut the doors etc and any other noob errors to keep an eye out for? Open to any and all hints and tips people, if you guys have a moment to educate an enthusiastic wannabe 😁

Thanks in advance for any info, cheers

[RonB]

[FireMan]

We’re awaitin, yes we are! Specten big things outta ya!

[rickgregory]

Henrik and Ahumadora?

[DavidNorcross]

Watching....

[smokin fool]

What was that blue tank used for?
I'd suggest filling it full of water to purge out any remains of pervious contents it held before taking a plasma cutter or torch to it.
Other than that looking forward to your build....

[holehogg]

Very important this ☝. Also suggest opening the tap and letting it rest upside down for a day or 2 then rinse.

[HawkerXP]

Measure once cut twice? No, no, no.

[bardsleyque]

I cut it twice and it's still too short...

[lostclusters]

Stuey1515 What did that tank hold before you acquired It? I would advise that all possible safety precautions be taken before any cutting is done.

[Henrik]

What size is the blue tank? It looks relatively short, so I would strongly advice building a reverse flow smoker.

[Stuey1515]

Henrik as above, "blue tank pictured below measures 34" long x 22" across". Reverse flow is something I had considered, is the tank shape the reason you recommend this, or is this personal preference and experience. Kudos on the pits you manufacture mate, the finish you get is outstanding

[Santamarina]

I think the suggestion for reverse flow comes not from the shape, but the length. 34” isn’t very much room to get a good draw and air circulation, but reverse flow would double the length.

That being said, I’m not sure which way I’d go with this build.

Aaron Franklin has some videos building a tank smoker from start to finish. Might have some good tips for you.

[Henrik]

What Stuey1515, are you saying I should _read_ the post? Lol! Completely missed that one, thanks :-) I recommend RF due to the tank being so short, as Santamarina says. You will get more even temps with RF.

[Donw]

Fill tank with 1 part degreaser (such as Dawn) to 4 parts water. Foamier the better. When draining position drain to lowest point since the gas is heavier than air. At marine engineering school, we were taught to use nitrogen to flush tanks and use meters to determine gas levels, but the instructor also taught us this method for smaller tanks than what we encountered on LNG tankers.

While other members will give good advice I recommend this video series on measuring and fabrication : https://youtu.be/Ks8sM0gnWTU

[Ahumadora]

OK It is a 120 gallon tank. I have only cut up about 180 of those tanks..
Rotate the tank so the weld seam is underneath or on the backside then mark the highest point on the tank and that will be your 12 o'clock position where you take your measurements from. measure down 150mm (6") and that is where the top door cut will be. It is a 762mm diameter tank (30") Run a tape around the circumference, then divide that by 4 and from that number 1/4 of the way around the tank is your 3 o'clock point. From the 3 o'clock measure down a further 50 - 70mm (2") and this will be your lower door cut. For the side cuts, measure in 3/4" from the edge of the tank head welds, as there is a join flange right at the weld.
I use a 9" grinder with cut off discs to cut all my tanks.

[Stuey1515]

Perfect, that is what I was looking for, thanks mate 👍

[jfmorris]

My only comment is that the 16x16 dimension on the firebox seems a little tight, unless you know your wood will always be shorter than 16". Other than that, and seconding the opinion on making it reverse flow due to length, I am just gonna watch this build happen. Sounds like Ahumadora and Henrik have the advice you need.

[jfmorris]

Stuey1515 I said I was done, but I lied. I just checked some measurements, and if you plan to burn wood in that firebox, and not just use this as an offset charcoal smoker, that 16" x 16" footprint is going to be a pain if you buy wood from a firewood vendor. I can buy oak and hickory from a firewood service here, and all of the wood they deliver is 16" long or longer. My offset's firebox is 20" wide, and its a tight fit to get wood in there unless I cut it in half with a chainsaw first. To be honest, my firebox is way too small, and the main flaw on the offset my dad had one of his welders put together to his drawings back in the mid 80's. His firebox design was 20 inches wide, but only 12" deep and 12" tall. Because of this, I mostly burn charcoal and wood chunks. To use only wood I have to split it down small and cut it in half, and keep the fire small and hot, using about half the firebox, otherwise it gets out of hand.

My offset is 24" x 36" for the body - very close to what you are building, and NOT reverse flow. What I found was that I had a 50 degree difference from firebox end to stack end, and there was always a really hot spot right above the opening into the firebox. I solved that a few years ago by making a baffle out of a pan, so that the heat and smoke from the firebox does not come straight up from that opening, but is diverted to the two sides of the opening. It evened out the grate temps to about 10-15 degrees end to end, with only small hot spots at the two corners of the grate, near the firebox.

I guess where this is all going is this. Based on what I've seen over the years in a 24x36 offset, you most definitely want to consider reverse flow, as others have suggested, to even out temperatures as much as for the draw. And... better find out what size wood your firewood comes in, unless you already cut it all yourself, and can control the size. I think in a 16x16 x20 high firebox, you will want wood no longer than 12". If your wood is larger, you might want to think hard on making that firebox a little wider at least in one direction.

Sorry to not use metric in all that, but you had been throwing out inches in your original post, so I stayed with it.

[Stuey1515]

jfmorris I thank you for the detailed reply and I had honestly not considered the very valid point you bring up about the length of the timber I can readily source. I'll do some research, the firebox is only stitched together at this point, so it's not the end of the world if it needs unpicking for mods to the size. I'm definitely going with the RF design after reading the comments made here.

There is no better info than first hand, you mention your offset cook chamber is very similar in size to this one. I was wondering about about the dimensions of your chimney, and any comments/recommendations you may have about it's design and behaviour.

I have no issue with using imperial dimensions. I'm of that certain age where apprentice fitters had to learn both the ancient and modern terms, as Oz went through the change over to metric haha. I still remember the old 41 thou' to the millimetre, 25.4 mm to the inch etc haha

[jfmorris]

jfmorris I thank you for the detailed reply and I had honestly not considered the very valid point you bring up about the length of the timber I can readily source. I'll do some research, the firebox is only stitched together at this point, so it's not the end of the world if it needs unpicking for mods to the size. I'm definitely going with the RF design after reading the comments made here.

There is no better info than first hand, you mention your offset cook chamber is very similar in size to this one. I was wondering about about the dimensions of your chimney, and any comments/recommendations you may have about it's design and behaviour.

I have no issue with using imperial dimensions. I'm of that certain age where apprentice fitters had to learn both the ancient and modern terms, as Oz went through the change over to metric haha. I still remember the old 41 thou' to the millimetre, 25.4 mm to the inch etc haha

My dad built this with an insufficient chimney to provide decent draw, plus its not reverse flow. So its not a good model to go by. I would consult with Ahumadora and Henrik on proper size and height for the stack to have a good draw.

One thing I do like about the smokers my dad built as customer gifts - that is what these were for - was that he included sliding vents in the end opposite the firebox, and a charcoal tray that would slide in through those vents if you removed them. That way it doubles are a large grill. The sliding vent mechanism only worked because he made the ends of the cook chamber flat - not the case for your tank. I suppose the charcoal tray might fit it down in from the top too, with the cooking grate removed. He welded two lengths of steel rod along the lower portion of the barrel to act as a ledge to hold the charcoal tray. So when using as a grill, you had the vent in the firebox, as well as a vent at the opposite end, to control airflow to the charcoal bed. So, if you think you MIGHT want to use the smoker as a grill as well, building a charcoal tray while you are working on this project might be in order.

Another thought, if you can source it, is that if you use expanded metal for your cooking grates, consider using stainless expanded metal. My grates are stainless expanded, and original to the grill, made around 1984-85. Regular expanded metal grates are prone to rust in my experience.