Trailer Rectangular Offset Smoker plans

[Mokoro]

Hi guys,

I'm posting from down here in New Zealand, so bare with me here. We work in metric, however I'll translate some of major details to inches.
Unfortunately we don't have the same supply here of propane tanks (down here, we all have piddly little LPG tanks)

Here is an example of the small LPG gas bottles we have here, my current smoker, built from a 45kg LPG bottle








The firebox is just under 1/4 inch (5mm) thick steel, the cook chamber is about half that thickness in steel. As you can see, it does not hold a huge amount of food - so the plan is to build a new, larger smoker.

I've bought two stainless steel mesh food trays, that measure 42" x 21". The design is based around these food racks.

Here are the plans, in millimetres, but in summary the dimensions are:

Food chamber: 45" x 23.5" x 23.5"
Firebox external dimensions: 20.4" x 23.6" x 23.6"
Warming cabinet: yet to be confirmed
Smoke stack: 4" tube, 34" in length



All steel on the new smoker will be 5mm (just under 1/4") thick.
This new smoker will have an insulated firebox, and food warmer. I have purchased a big roll of Kaowool fibre blanket, that is just under 1" thick. The firebox will have a sandwiched layer of this blanket on all sides, except for the door (for simplicity sake, as the firebox door will have the damper on it)
Above the firebox will be a food warmer, again, this will insulation on all sides except for the door. It will be interesting to see how much heat will transfer through from the firebox below.. the heat will need to penetrate:
5mm steel - 25mm kaowool blanket - 5mm steel (total 35mm, or 1.375")

I'm going to have some right angle steel running along the length of the cook chamber to hold tuning plates, and play around a lot once built, to work out how to get the heat as close on each door as possible.

I have in my hands 3x Teltru BQ300 thermometers, one for each food door, and one for the warmer. I've got 1" Lavalock food door gasket, and another firebox gasket material on the way from the States. (along with a Webber iGrill 2 leave-in thermometer)

I have a mixture of Oak, Gum, and Avocado wood, all dry and ready to burn (4 cubic meters, 141 cubic foot, or 5.3 cubic yards, which ever makes more sense to you lol)

Smoker will be mounted on an old used trailer, which will be stripped back, repainted, and modified to take this approx 350kg (770 pound) beast, along with a few storage cabinets for firewood, coal, firetools, etc.

Looking forward to the build, will take pics along the way. Was just wondering if any of you out there had any ideas, input, comments, that might help, before I have the steel all purchased. Again, I would have really preferred to go with a cylinder food chamber, but we just can't get them here in New Zealand! Unless we get sheet steel rolled into a tube, but that is just pushing the budget through the roof.

Cheers guys!

[Rodcrafter]

Welcome to the crew!

I personally really like the square shape it allows you to have many more options


Making memories!

[ajfoxy]

Welcome. Alternative to the round cook chamber is a square cook chamber. Or a combination. Have a look at Squiggles "Wombat" he built recently.

Of course you could always go for the ultimate... "The Mack"... naturally only when the plans are finished...
(caution, dead horse flogging in progress ). Sorry Frank, can't help myself).

[Big T]

Welcome aboard!! That's a nice one that you have built and that you plan to build.

[Pete Mazz]

Welcome

[temurf]

I like the design.
I have Tel Tru therms and have had no issues with them.

I recommend using the pit calculator at the top of the page.
Input the interior dimensions of your cooking chamber and fire box.

[Mokoro]

Ive used the feldon pit calculator.. which gave me the requirements for everything as you mentioned, based on cook chamber volume.

Wow.. that "Mac" smoker is almost identical to my plans! They did list the cook chamber volume, on the first page of the thread. The mack is only slightly larger in cook chamber.
Will be slightly copying that design/build, however mine will be an offset, with tuning plates. After a little thought, I decided I prefer a more direct airflow in my cooker.. even if it means one side is slightly hotter than the other.

And yeah, have heard good things about the Teltru BQ300. i really like the size and ruggedness of it.

The other toy I have on the way, is the webber igrill 2.. cant wait to have a play with that.

Next step is testing out the insulation, to see how it works sandwiched in 1/4 inch steel. Really wondering how much heat will come through, and if I need to have some sort of vent or intake into my warming cabinet..

[Mokoro]

Here is a pic of the insulation I'm using:



It is kaowool, or ceramic fibre blanket, as you can see its just shy of an inch thick and is very flexible. It is rated at 1260°c (2300°f).

Has anyone used this insulation before on their firebox? I'm wondering how hot the top of my square firebox will get after 4 hours burning, with this material sandwiched between two (just shy of) 1/4 inch plate.

[mp4]

I've used that insulation in my syrup arch (which is way hotter than any smoker would get) and have also seen it used in boilers. It is very good stuff.

[Mokoro]

I've used that insulation in my syrup arch (which is way hotter than any smoker would get) and have also seen it used in boilers. It is very good stuff.

Oh cool! Do you find that it all but holds the heat in? I'm just wondering if the outside of my firebox will have any heat at all...

If the insulation works really really well, I will need to build in a heat vent from the firebox to the warming chamber, much like as shown in the Mack

[mp4]

It didn't hold all the heat in, but that would be asking an awful lot from a couple inches of insulation. [emoji2]

[Mokoro]

Nice..

I've changed my mind now.. I'm looking at having my warming drawer down the opposite end from the firebox, having a shutter to allow smoke/heat into the warmer if needed, effectively extending the cook chamber if required, and have a seperate smoke stack on the warmer.

My goal is to have the warmer down really low... between 140°F to 300°F, with a tonne of damper/smoke stack variables to control.

[Mokoro]

Steel arriving today, watch this space..

[ajfoxy]

Now the steel's arrived you have to start the project...

Good luck with the build and don't forget to feed the forum with lots of build pics.

[Big T]

[Mokoro]

The steel: 8x sheets of steel, 95" x 47".
3 of them are just a bit less than 1/4" thick
5 of them are 1/8"

A newer design has been done for the smoker.. it now has 2" of ceramic fibre insulation for the firebox, and 1" for the cook and warmer chamber.
1/4" steel inner, insulation, 1/8" steel outer, throughout.

This thing will be a BEAST, and tolerant of the high and low temps we get down here in New Zealand.

Will take pics as this progresses, but it may be a long project (hopefully not though can't wait to get cooking =D!)

[Big T]

The pictures are deceptive because the steel looks a lot thicker than 1/8'' and 1/4''. I guess it's because there's nothing to use as a reference. It sounds like it'll be a great project, I look forward to watching it progress.

[Dirtytires]

You mentioned you were building around the 2 racks you have...just don't let that restrict your build creativity. Most of us use expanded metal in an angle iron frame so can make it whatever size we need.

Looks like you have your work cut out for you....

[Rodcrafter]

Man that looks like 1/4” and 3/8”


Making memories!

[Dirtytires]

Just show a picture of 3/8 steel and Rodcrafter's ears perk up.

[Mokoro]

Haha. Na the thicker stuff is 5mm, which is ever so slightly thinner than 1/4". Not much to update, but some shapes cut out, taking steel to a workshop today to get some folds, and guillotine cut some of the thinner steel.

[ACC]

Has anyone used this insulation before on their firebox? I'm wondering how hot the top of my square firebox will get after 4 hours burning, with this material sandwiched between two (just shy of) 1/4 inch plate.

Oh cool! Do you find that it all but holds the heat in? I'm just wondering if the outside of my firebox will have any heat at all...

My firebox is somewhat similar to yours. It is 1/4 plate, 2" kaowool, covered by 14 ga. steel. The top of the FB will get warm during a multi-hour cook. I have never experience pain from touching it during the course of cooking. However, it would probably burn me if I pressed my hand hard against it. I place firewood on top of the FB and they get decently warm but not what I call hot. I have not done this, but I suspect that there is enough heat to warm a pot of beans but not enough to cook them. I don't know enough about warming boxes to advise you on whether enough heat would pass through for one.

In the interest of full disclosure, another factor which may effect my results is the fact that the top of my firebox opens up so that I can use it as a grill for steaks, hamburgers or seafood. The seams are all gasketed but surely more heat ecsapes from my FB than a one-piece FB. However, I suspect that after 4 hours run time, you will feel similar heat on your one-piece firebox.

I like your idea of placing a warming cabinet on the other end of the cook chamber. If yours works out ok, I might do that to mine.

Good luck with your build.

[Mokoro]

Build underway...

[Dirtytires]

I see an ash pan cutout and assuming the circle hole is for the air vent?

What are your calculations for sizing as that appears a bit too small.

[Mokoro]

Firebox well on the way