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BBQ Engineer 01-18-2010 03:52 PM

Building the Iron Maiden - Double Walled, Insulated, Reverse Flow
Hi Everyone,

Last summer I built a large trailer mounted smoker that was quite a project for me. I thought I would post the build here so that you can see my adventure too. It is pretty long, so I thought I would post it in sections every few days so if you have any questions about the build I can answer them.

What I wanted was a trailer mounted reverse flow smoker with a side rib rack that was double walled and insulated. The plan was for the horizontal chamber to be 4' in length, and ~26 inches square. I am actually going to cut one corner off, so the side that the doors are on is not sitting vertical, but slanted a bit...sort of like a side view of the old time Ice Machines that sat outside of gas stations and grocery stores...). In my graphic, the red is the fire, and it will traverse the horizontal unit and enter the blue smoking chamber. It will then flow across the meat, and then enter the side rib rack at the bottom (represented by the yellow). It will exit the top through a 4" square chimney.

I had some basic ideas in my head of what I wanted it to look like, but I “Engineered” most of it as I went along and made changes as I needed to. My original idea looked something like this.

I had built some smaller cabinets that were double walled and insulated, so I had a good Idea what I was getting into…

I first problem that I ran into was getting the metal onto the saw horses. I am using 10 Gauge CR steel (.134" thick) and some of the sheets I have are 4' X 10' and weigh 225 lbs. I Had Mrs. Engineer who weighs in at a whopping 130 lbs drippin' wet help me! It was touch and go when we about tipped the sawhorses over, but we got through it. Once I had the sheet on the sawhorse, I decided that a 48" horizontal chamber just isn't going to do it for me, so I decided to go with a 60" horizontal chamber.

I'll start with the tools I am using...Here is my new plasma cutter...It is really nice!

Here is my welder...I used FCAW (flux core) as I weld outside my shop.

Here is a sheet of steel on the sawhorses ready for layout. I actually got the steel for scrap price...don't look like scrap to me!!

Here I am working with my new torch...

Mrs. Engineer was helping me with some photos.

Plasma cutters are really sweet for slicing this stuff up. I am a rookie with my new unit, but I will be a pro in no time.

Plasma Cutter 101 - The Plasma cutter is strictly for cutting metal. Without getting to much into what Mrs. Engineer calls “Nerd Speak”, Plasma is the fourth state of matter (from science class), and occurs when you boost a gas to extremely high temperatures. Plasma cutters utilize this principle by sending a pressurized gas (in this case, regular old compressed air) through a small channel across a negatively charged electrode. When you touch the torch to your workpiece and pull the trigger, a circuit is completed which generates a powerful spark. This heats the air moving through the nozzle until it reaches approximately 30,000° farenheit, moving at 20,000 feet per second. This will make precision cuts in metal, that have the cut quality of using a bandsaw. This is preferred over Oxy Acetylene torches as it is much safer, and the quality of cut cannot be beat. Using the plasma cutter, the surrounding metal gets hot, but the cut happens so quickly that it doesn’t get anywhere near as hot as a regular acetelyne torch. The Oxy Acetylene torch will melt the metal and then blow it away, where the Plasma cutter really just slices through it. I can’t explain it any better than that.

Mig Welder info - My welder is a mig welder, and has a spool of wire inside the unit. When I press the trigger on the gun, this wire acts as the electrode and is fed at a constant rate to the workpiece, melting the workpiece (and wire). The wire is then deposited as well and acts as a filler to fill gaps and voids. I am using flux core wire, which is self shielding because it has a center that, when burned creates a shielding for the welding process. If I didn’t use this, I would have to have some sort of backing gas. Since I weld outside and there is frequently wind here in Kansas, creating the shield at the actual weld is probably better than if I were to use gas to do the same thing.

I got some pieces welded together and am starting to form the horizontal chamber. I started by building a jig out of 2X4’s to form a right angle that I could use to set the pieces on. I have fought and fought with magnets in the past, and I am just not going there. I have also decided that I quickly need to get the bottom side of this thing finished, because it is going to get too heavy to easily move around for me.

Here is the jig I built, and the bottom of the horizontal chamber in place.

Next, I put the back of the horizontal chamber so it sat on the bottom at a right angle. I put some angle iron in the corner and tacked it all together. Then I came back and filled in the rest of the weld so the entire thing was welded. I welded this in sections, as if you just throw heat at it nonstop, the workpiece can warp and twist…therefore I choose to do it in pieces.

Then I cut the front of the inside chamber. Here is a picture of the dross or slag that the plasma cutter leaves on the bottom of a cut. It is nothing compared to an Oxy Acetelyne torch, and pops off if you whack it.

If you touch it with a grinder it leaves a good edge to weld to.

I welded the front inside shell for the horizontal chamber in place.

Here is the inside shell of the horizontal chamber…front, back, and bottom.

I got the side of the horizontal chamber cut out, and it will show what I mean by looking like an old time Ice Chest that sat outside of a gas station or a grocery store.

I don't know if I have shown a decent photo of what a clean cut that a plasma cutter will make. I have never used one before I got mine, so I am in no way a professional with just makes me look like one. Here is a top view of the cut. You can see that it really does slice through, and doesn't heat the metal up hardly at all...the heat affected zone barely extends past the cut! The angle iron is used as a guide so I can keep a straight cut.

Here is the same cut except looking at the cut is really clean. Man, good tools make all the difference!

Messing around with the baffle plate has consumed a lot of time, but I think I am done. I have seen some plates where they use a piece of angle iron in the center and then slope sheets to the center channel. I decided to just slope them to the center in the first place. I will add a drain once I get it welded in place.

I have mounted it 6 inches from the bottom shell, and 6 inches from the side wall. There will be a flat that extends into the firebox. Here is how it will look. I will clean up all the welds before welding it in, because once it is in, I can't get tools in to shine it up. I also have the side of the horizontal chamber welded in place.

I also have started to weld on the frame that will separate the inner and outer wall. It is 1" square tubing, 11 Gauge and .120" wall thickness (far right of pic).

For Insulation, I am going to use a product called "Superwool 607". It is a ceramic fiber blanket that is used in kilns and ovens. It is rated at over 2000° and is way over-kill for what I am doing, but it is easy to work with, has great insulatory properties, and is conveniently packaged. You can check it out here:

WALLE 01-18-2010 04:03 PM

Absolutely a great display of craftsmanship, BBQ E.
If this doesn't deserve poi-nts, then I gotta turn in my hood.. :bounce:

JimmyJoeBob 01-18-2010 04:53 PM

Absolutely beautiful! I wish I had skills like that...I was lookin' for an "atta boy" when I took the garbage out today!:eek: Waiting for the rest!poi-nts

Zeeker 01-18-2010 05:23 PM

Nice, very nice BBQ Eng...:thumb:

bb53chevpro 01-18-2010 07:02 PM

Right on..... Excellent.

Wish I had a plasma cutter. Would make the job 100 times easier.

Richtee 01-18-2010 07:06 PM

I'm thinking yer not gonna get that over to the neighbor's place without a trailer! Heavy DUTY! Fine work, sir!

Uncle-Honky 01-18-2010 07:17 PM

What a killer build! This is going to be thoroughly enjoyable to watch take place. Awesome walk through BBQ Eng. !

Slanted88 01-18-2010 07:31 PM

Sure do like that....just the right size for my use! :thumb:

Capt Dan 01-18-2010 09:02 PM

Lookin really good so far!:thumb:

Whisky Fish 01-19-2010 06:59 PM

Oh man, a plasma cutter! Borrowed one from a buddy for some of my build. I really didn't want to give it back, but he is a good friend, so I had to:lol:
I'll stay tuned for this one. Nice work!


curious aardvark 01-19-2010 07:27 PM

love those little smoking cabinets - any plans for those ?
Thinking a modified version would be ideal for my van.

Plasma is where the outer shells of electrons are stripped from an atom.
Best example are the aurora borealis and the aurora australis - northern and southern lights. Caused by solar winds interacting with the extreme ends of the earth's magnetic field, where the electrons are stripped and the resulting plasma causes the light show.

But a metal cutter is probably a more practical use :bounce:

Slanted88 01-19-2010 07:32 PM


Originally Posted by curious aardvark (Post 87795)
love those little smoking cabinets - any plans for those ?

Been thinkin the same thing....I like that!

Kingudaroad 01-19-2010 07:41 PM

That is an amazing build BBQE!

BBQ Engineer 01-20-2010 10:10 PM


Originally Posted by curious aardvark (Post 87795)
love those little smoking cabinets - any plans for those ?

Hey Aardvark,

I can certainly post some info on the small cabinets that I have built...they are real power houses!

On with the build...Next, I got the baffle plate welded in, and then the top of the horizontal chamber on.

This is looking under the baffle plate

I started on the vertical rib rack and firebox section...Here I am checking it for fit...using my 10 lb micro adjuster to get it positioned properly.

I got the vertical chamber all put together. The smoker is laying on it's back.

I got the two sections welded together, and then turned it right side up to start framing it and putting the insulation and outer shell is freakin’ heavy! At this point in my build, progress stalled when I had an accident while unloading some supplies from the trailer and ended up in the ER to get my leg put back together...18 stitches. The beautiful and talented Mrs. Engineer about came un-glued when I wanted to go down and work on the smoker. In retrospect, Mrs. Engineer was right…I took some time to get healed back up and then hit it again. I am on a timeline, as I had to have this ready for our Neighborhood blowout on the 4th of will see, it is a massive party.

Here it is right side up. I have started framing the doors on the horizontal section, and have put some framing on for the insulation to fit inside.

Here is a pic of where the insulation will fit, between the frame that separates the inside and outside shell.

This next part took a lot of time getting it engineered properly so that the entire front panel is on the same plane. I made sure of this so the doors will fit and seal right. Here is a photo of the doors that I have framed out. They include a piece of channel iron that will accept a rope gasket to seal the doors tight.

Here is a closeup of the door frames, and you can see the channel. I have the trim pieces set in place, as I haven't welded them yet.

Here it is with a small piece of rope gasket in place to demonstrate what I'm going for. The gasket protrudes above the channel so the flat doors (that I have yet to build) will smash against the gasket and create an air tight seal.

Since I am using two outer skins that sandwich insulation, I like to use hardened concrete nails that are 1" and weld them to the inside skin, and then the insulation will punch down on that. This works great on vertical surfaces, as it holds the insulation in place while I mess around and get the outer skin tacked on. It also serves as a method of keeping the skins separated by 1"...not that this is a problem with the heavy gauge that I am using, but what can I say...I'm an over-builder! The main thought behind this on the trailer mounted rig is that this thing is going to be bouncing down the road, and I don't want any settling of the needs to stay in place!

Here are my welds...not to bad for an untrained DIY'er using flux core weld wire!

Here the top is getting ready for some insulation...You can see the nails that I have welded in.

Here is the insulation that I am using. It is Superwool 607, and is rated at over 2000°. They use it in kilns and ovens.

Here is a vertical piece that is the first to get welded shut. Insulation is in, and the outer skin is going on next.

Vertical part of the rib rack is tacked on, and I'm starting to insulate the top of the horizontal chamber.

This is all you need to work with this's pretty cool stuff. About the consistency of a really dense and heavy cotton candy.

Top of the horizontal chamber - insulated and ready for the outer skin.

Fishawn 01-20-2010 10:33 PM

Fantastic Presentation BBQE!..... Got me Jonesing for more! :lol:

rpmorey 01-20-2010 10:48 PM

I thought I was excited about the way mine came out, yours is looking awesome and a half!! I will not be starting over to copy you though. Too much work! poi-nts:drooling:poi-nts

WaysideRanch 01-21-2010 01:03 AM

Killer stuff.

crusty ol salt 01-21-2010 01:11 AM

thats one good lookin build ya got goin on... thats for letting join you via the pics :thumb:

ALX 01-24-2010 12:33 PM

Always love seeing this build Dana....The maiden will serve you well in your comps...Just outstanding sir...

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