Cook area - plate steel or frame & sheet metal?

quasipickle · Apr 11, 2017

Hi all,

My department at work is designing a smoker for competition and leisure. One of us has smoking experience and none of us have experience building a smoker.

Our current design has the cook area shelled in by 1/4" plate, then a 1 1/4" void for insulation, then 14 gauge metal for the outer shell. Our reasoning was if we have thick metal on the inside, we can weld our shelf brackets directly to it, and it will be strong enough to hold the weight. There is also the thermal mass to consider.

Looking around at other builds though, practically no one does this - it's always a frame and thin metal inside & out. I'm not one to flout conventional wisdom, so can I get some pros/cons of each approach?

Thanks for any and all advice.

Edit: We are doing a horizontal smoker with an offset firebox. The design isn't finished. For scale, the top part is 51" wide.

Smoker - components.png

quasipickle
Apr 11, 2017

noboundaries · Apr 11, 2017

Welcome to SMF quasipickle. Be sure to stop in over at Roll Call and say "hi."

I'm not a builder, but do have a bit of engineering education.

First, let's assume you're building a horizontal smoker with an offset firebox. I like the out-of-the-box thinking. If your insulated shell is a 360° wrap, weight would be an issue. Plus, the extra metal and insulation on the bottom of the smoker would really only help if you set the smoker up as a baffled or reverse flow design due to heat flow out of the firebox.

Now, if you are building a cabinet type smoker with the fire box on the bottom, your design would work nicely and be VERY efficient. The design would also work nicely with an offset firebox and a vertical smoke chamber, just won't be quite as efficient.

Just my .02. Like you, I would really be interested in what the folks say who design/build smokers.

No matter what, have fun!

Ray

quasipickle · Apr 11, 2017

We are doing a horizontal smoker with an offset firebox. I've updated my original post with a picture.

noboundaries · Apr 11, 2017

Ah, I see now. What you have there is actually a cabinet smoker with an offset fire box. You could actually turn that bottom area into a fire box drawer and slide it in and out to start and to add fuel.

Here's what we call an offset horizontal smoker.

offset-smoker-briskets.jpg

noboundaries
Apr 11, 2017

Google Cabinet Smoker in their images section and you'll find lots of pictures along your design, both with offset fireboxes and with pullout drawers on the bottom.

Based upon your plans, you are right on target!

quasipickle · Apr 11, 2017

Fair enough. I skipped the details where we're building this thing in such a way that we can turn it on, leave it for X hours, and come back with our meat properly cooked. We're hooking a computer up to it to regulate temperature & spray sauce, etc.

Regardless, I just wanted to know about the pros & cons of using sheet metal like we currently have planned, vs building a frame & using thinner metal. I do think weight will be an issue. Cost is negligible. I'm wondering about strength though.

chilerelleno · Apr 11, 2017

1/4"? Cut that back to 1/8" on both inner/outer, and you can still more than easily weld the tray brackets to it and have more strength than you could ever need.

Your design shown is a Cabinet or Vertical smoker, which is a good design.
I agree with Noboundaries, if you do as shown, design it with fire box on the bottom with separate access doors and maybe even a slide out fire grate.

Air temp probe and fan controller, check.
Food temp probe and auto shut off when desired temp is met, check.

Just one problem not all cuts are the same, when cooking multiple pieces some may or may not be ready.
10-15' internal temp can mean the difference between fats/collagens rendered fully and probing butter soft, or being slightly under/over done.

Automated BBQ applicator/sprayer?
Oh Boy, glad I won't have to clean thing up, and deal with potential flare ups from drips/overspray.

noboundaries · Apr 11, 2017

Most cabinet smokers are HEAVY, several hundred pounds is not uncommon. So no, weight won't be an issue. Just put it on wheels. I'll let the cabinet builders input whether 14 gauge (just under .08") would be sturdy enough for the outer shell.

quasipickle · Apr 11, 2017

Thanks for the replies. I wasn't sure if 1/8 was strong enough to support the trays, now I know.

We're pretty much sold on having an offset firebox because we want the charcoal and wood to be gravity fed (a la Stumps). If we're doing an 18 hour cook, we want this thing to be able to run for 18 hours with no intervention. Having the box underneath kind of removes the possibility of a gravity fed firebox.

As for weight, our initial plan was to permanently mount this thing on a trailer. But, realizations of the cost soon kicked in so I'm trying to see if there's a way we can just haul it around in the back of a truck. Moving to 1/8 will certainly help.

I'm designing our firebox with 1/2 plate - is that overkill? Would 1/4 or 1/8 be more than enough?

chilerelleno · Apr 11, 2017

The firebox and adjoining wall to the cook chamber is where I'd go 1/4 or maybe 9/32.
With a 51" cook chamber plus firebox/feed system and added automation, you will be better off trailering this build.
It is going to be HEAVY with a full sized gravity feed chute above the firebox and an overall length of 62"+.

Man what a cool contraption this will be... I'm in and look forward to hopefully seeing this a reality.

quasipickle · Apr 11, 2017

Thanks for the tips.

noboundaries · Apr 11, 2017

Sounds like a rocket stove smoker! Cool!

ahumadora · Apr 16, 2017

Quasipickle,

I have built a bunch of these large cabinet style smokers (all reverse flow).

Here's my take.

1./Build the chassis out of larger tube . I would probably use 50x50x2mm (2x2") box and go lighter on the sheetmetal.

2./ Use 1/4" plate for your fire box area, works fine. I just refurbished a smoker I built that has had 5 years of continuous use everyday and is fine.

3./ Rest of smoker use #14 or #16 sheetmetal. (I use #16 for cost). moving the chassis up to 2" allows thicker insulation.

4./ Run an X member on your main door as it can bend with the heat.

5./ Having all flat panels on sheetmetal like in your pic will cause it to bow when hot. Have a sheetmetal shop break an X in the panels. Also welding that big flat sheetmetal panel on will cause it to suck in and look like crap. It only needs a slight X to stop this.

6./ Welding your rack guides directly to the inside sheetmteal will cause them to bow when hot. Either use heavy angle or run an X on the inside sheetmetal facing the ceter away from the guides.

7./ Having the firebox tray slide out the side may look cool in the pics, but you are now limited where you can locate the smoker if it is on wheels and the amount of space it uses has increased greatly.

Heres some pics of some of mine

IMG-20161130-WA0005.jpg

ahumadora
Feb 21, 2017

IMG-20161130-WA0003.jpg

ahumadora
Dec 1, 2016

IMG-20160622-WA0002.jpeg

ahumadora
Jun 22, 2016

c954d200-f766-46ba-a1b1-0e86760adec9.jpg

ahumadora
Jun 13, 2016

9267047c-567a-4c0d-a4ea-9058484d572d.jpg

ahumadora
Jun 15, 2016

See how I ran an X then drilled holes and plug welded the sheetmetal

48bdf040-815c-4c87-9c38-824a73a26471.jpg

ahumadora
Jun 11, 2016

0a9cbe40-5fe9-462c-aa57-ebf09f57bddd.jpg

ahumadora
Jun 7, 2016

sheetmetal with X

IMG-20160124-WA0022.jpg

ahumadora
Jan 24, 2016

IMG-20160123-WA0013.jpeg

ahumadora
Jan 23, 2016

the internal chimneys stop the sheetmetal bowing.

20160122_095638.jpg

ahumadora
Jan 22, 2016

20160122_095944.jpg

ahumadora
Jan 22, 2016

gap between sheetmetal

quasipickle · Apr 19, 2017

Thanks for the advice.

2/ I've designed it out of 1/2" - but I'm glad to hear 1/4" will work.

5/ Great advice for the X. I don't think that would have been an issue with 1/8" metal, but with #16 you're probably right.

7/ The image I uploaded doesn't show the completed design. The reason the firebox is out the side is because we'll have a chute for charcoal and a chute for wood blocks on that side. We want this thing to run for a full cook unattended.

Thanks again.

ahumadora · Apr 20, 2017

Quote" We want this thing to run for a full cook unattended."

Well you can learn to multi task. (Holding a beer while opening the door and checking the meat). Let me know if you need tips on that I am pretty good at it.

quasipickle · Apr 24, 2017

The design has been finalized (or at least the first draft). Please see this thread.

Cook area - plate steel or frame & sheet metal?

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