Franklin Backyard Smoker Clone

[DoTheEyeThing]

I’ve started work on a fairly close copy of Aaron Franklin’s backyard smoker. I came to appreciate Franklin’s emphasis on clean smoke through good airflow and fire management after my own frustration trying to smoke on a weber kettle and not getting the results I’ve come to know growing up with BBQ in Texas. I would have loved to order one of his pits, but since there’s what seems to be a multi-year wait list I started planning out my own build.

I work a day job as a 3D modeler / artist and love building things, so even though parts of this big project are a bit out of my comfort zone, I think it’ll be really fun and rewarding if I pull it off.

I joined my local makerspace for access to their metal shop and have been sourcing everything for a couple months. Here’s some info on what I’ve picked up so far :

• Drove a few hours from Utah to Wyoming to get some rusty 20” x ¼” pipes in a field for $250 (way cheaper than the $1700+ cost to roll some steel locally! Steel prices are nuts right now). More than enough for my 40” cook chamber and 22” fire box. I cut and had a local shop roll one of the fire box pipes down to 18” ID for the inner fire box sleeve as semi-insulation.

• Had a 20” elliptical head with a 2" straight flange made in Fort Worth, TX - $300 shipped. Cook chamber total length will be 47"

• Got some 5” steel and cast iron casters from casterconnection that look identical to what I see on Franklin’s prototypes - $100

• Four 2’x 2’ x ⅜” surplus steel plates for end caps and hinge plates - $240

• 4.5” smoke stack pipe from scrap for - $8

• 10ft of 2 3/8” pipe for legs. I think about - $90

• A couple ¾” #9 flattened expanded steel grates - $30?

• A Tel-true 4" stem thermometer - $50

I still need a little bit of ¼” plate, some angle iron, some ½” round bar, some square bar etc. Not much left really. Looks like it’ll be just a bit over $1000 in material. I’ve seen Franklin’s costs about $4k after shipping so if I can make mine of remotely comparable quality, I’ll make out pretty good!

Here's a random build clip where I strapped a grinder with a brush wheel to a dowel to get the chunkier rust out of the inside of the pipes. Let the oscillation do most of the work for me.
https://photos.app.goo.gl/Hgtf3WhfBQ458xgc9

I've almost finished a 3D model of the smoker after many hours of grabbing screenshots and matching them to my 3D model as well as using known measurements to measure other parts. Really tedious! I still need to finish up the hinges some and triple check a few things but I think I'm close.

I've got a few questions I'll post soon and I'll keep ya'll up to date on the build!

[DoTheEyeThing]

So after seeing some reviews on this pit, some modifications I'm thinking of doing include :

• Adding an outer flange to the cook door to help prevent smoke leaking

• Adding a hat to the smoke stack to help with shutting down if I ever need to. Undecided how I want to handle the firebox door air intake. I like the holes there as I imagine they could be a decent wind break. I've seen some people add a plate that slides over them.. I might just cut out a thin plate with magnets I can throw over them to shut down

• Thinking I'd like to make the firebox bolt on instead of welded so I can make the 600+lbs more manageable. I'm going to need to move this a few times in the future. The firebox alone weighs about 250lbs

Here's a pic of what I'm thinking for making the firebox bolt on. Basically leave an extra 1"-1.5" flange on the round disc cap at the throat side of the firebox. Add bolts there and several more inside the box around the throat. I think that should work?

[DoTheEyeThing]

I'm also considering the best way to handle door spring once I cut it. I had a lot of spring when I cut open one of my firebox pipes to roll smaller so it's definitely going to happen. I think welding in some cross supports before I cut the door won't interfere with the food too much and seems easier than dealing with a sprung door... Alternatively I could see if a local shop can roll it back down, but when I had my firebox rolled down, the seem was flattened and from what I gather, that might have been a consequence of how rollers work? I don't know enough to be sure. Any thoughts?

[Dirtytires]

Don't fret on the door spring. It can be easily bent back with a bottle jack and a heavy chain. The braces could work but will eat up valuable interior space.

[DoTheEyeThing]

Don't fret on the door spring. It can be easily bent back with a bottle jack and a heavy chain. The braces could work but will eat up valuable interior space.

Thanks Dirtytires I'll try not to I suppose I could even do a small test with extra pipe to see how close I can get it back in shape with a jack and chain.

[Big T]

Welcome aboard! You should check out the recent builds from dacolson and hogaboomer. They built pits like your design with a modified throat baffle similar to what jambo uses and they both said that their pits perform great.

[Pete Mazz]

Welcome

[DoTheEyeThing]

Welcome aboard! You should check out the recent builds from dacolson and hogaboomer. They built pits like your design with a modified throat baffle similar to what jambo uses and they both said that their pits perform great.

Thanks I'll be sure to check those!

[dacolson]

Welcome. Going to be a cool looking rig.

[DoTheEyeThing]

Hey all! I've been making progress - will get more photos soon. I've hit the point where I needed to nail down my plan for making the firebox bolt on and wanted to run it by ya'll.

Right now there's a flange coming up from the firebox with 7x 1/2" Grade 5 bolts through.. and then 7x more 3/8" Grade 5 bolts on the inside.
The plates are 3/8" thick steel and the firebox should weight about 250lbs.

I think the 7 bolts bolts up top should be enough but there's room to add more...do ya'll think 7 is good enough? I'm a noob at how hot heavy metal behaves and want to avoid anything warping / gaps forming / etc.

[hogaboomer]

I'm no engineer, but I would not be at all nervous about 7 half inch bolts holding up 250 pounds.

[DoTheEyeThing]

Yeah I think you're right : )

[Dirtytires]

I would just weld it....but the bolts are fine as far as holding capacity. The shear strength of a standard 0.5 inch bolt is 2345 pounds so you would be fine with just one and still have proper safety margin.

You might consider a gasket if your plates are not flat enough to fully seal.

[dacolson]

Agree on the gasket. Was having the same thought. Could be a thin one just to make sure you have no air leakage in or out.


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[Brewmaster]

This is all sorts of awesome!! Subscribed!

[EverydayDiesel]

Id like to know more about this bi-metal design of franklins which is, from what I understand, what makes that pit preform so well.

[Brewmaster]

Id like to know more about this bi-metal design of franklins which is, from what I understand, what makes that pit perform so well.

I don't think it's solely responsible, but there's some sort of special something going on with it. I can't imagine it bends so much it'd have a huge impact but who knows. The few posting videos haven't mentioned or shown it as far as I've found. I'd like to know more.

[DoTheEyeThing]

Quick update - made a photo album of my progress so far! Not done but getting close! Can't wait! https://photos.app.goo.gl/7wrdAmmb7aEK8ZXk8

Regarding the bimetalic strip, I'm kinda counting on it not being much of a thing. I've only seen the smoker in vids, but I've spent hours inspecting them, taking screenshots, etc.

Some of the things that I suspect help (I'm not an engineer so could be wrong!)
-There's a round bar welded at the top edge of the baffle box that I think helps the smoke flow past it with less turbulence than a sharp edge.
-The elliptical head probably helps the smoke begin to roll into the collector box smoother than a flat plate would.
-Taller stack I think can increase the draw if it's the proper height.
-The drain pipe is always open to the air and at a fairly sharp angle. If air flows in or out of there I think the trajectory might help the air mass in the cook chamber twist a bit due to the angle.

[hogaboomer]

Don't go overthinking this stuff. I doubt he tested all the things you are referencing. Smokers aren't all that complicated.

[EverydayDiesel]

Can I ask why you choose to bolt the cc to the fb?

[DoTheEyeThing]

Can I ask why you choose to bolt the cc to the fb?

Mainly for easier transport. Going to move across the country soon..probably another move not long after that. 600+ pounds seemed a bit intimidating to maneuver at once. Firebox is almost half of that. Maybe it would have been fine but I think it has worked out. Can always weld it later if I wanted.

[Brewmaster]

This build is awesome man, really true to the og and looks like you're well-versed in fab, I love it. I'm a bit of a geek with these things as well so I'll drop my 2 cents worth, I think you're pretty bang-on.

Regarding the bimetallic strip, I'm kinda counting on it not being much of a thing. I've only seen the smoker in vids, but I've spent hours inspecting them, taking screenshots, etc.

-I'm guessing as well, but I think it probably curls downward under there at the food chamber end-cap joint, (when hot) to help eliminate the hard 90 where the top of the baffle plate meets end-cap. If only Wilson will finally spill the beans with some photos, hahaha!

-There's a round bar welded at the top edge of the baffle box that I think helps the smoke flow past it with less turbulence than a sharp edge.

-knowing that air travels in a similar fashion to liquids, 100% that the round bar, or the rolled lip ala Mill Scale baffle, is there to reduce drag and increase overall convection.

-The elliptical head probably helps the smoke begin to roll into the collector box smoother than a flat plate would.

-There's no doubt that helps greatly with convection, eliminating turbulence, and overall wind-speed in the cooker! I mean, if you visualize this as a water pipe the flow would be considerably reduced by a butt-end with a hole in it. I give full kudos to you for going the extra mile $$$ in purchasing that bell-end.

-Taller stack I think can increase the draw if it's the proper height.

-stack effect is real for sure! Longer = greater draw. Also, think a shorter, larger diameter stack, calculated to be the same volume as a smaller diameter stack, won't offer the same draw since the stack effect will be less.

-The drain pipe is always open to the air and at a fairly sharp angle. If air flows in or out of there I think the trajectory might help the air mass in the cook chamber twist a bit due to the angle.

-I believe the drain is a calculated, purpose-built orifice, for more than just grease. I tested the theory by installing the drain down next to the firebox end of an offset and checked it out during a cook with a cig lighter flame; it does indeed inhale air through the open-drain port. I think as the cooler ambient air enters down low that it helps drive the hot air upward thereby increasing convection velocity even more.

Excited to see the final build, keep at 'er!

Quick update - made a photo album of my progress so far! Not done but getting close! Can't wait! https://photos.app.goo.gl/7wrdAmmb7aEK8ZXk8

Regarding the bimetalic strip, I'm kinda counting on it not being much of a thing. I've only seen the smoker in vids, but I've spent hours inspecting them, taking screenshots, etc.

Some of the things that I suspect help (I'm not an engineer so could be wrong!)
-There's a round bar welded at the top edge of the baffle box that I think helps the smoke flow past it with less turbulence than a sharp edge.
-The elliptical head probably helps the smoke begin to roll into the collector box smoother than a flat plate would.
-Taller stack I think can increase the draw if it's the proper height.
-The drain pipe is always open to the air and at a fairly sharp angle. If air flows in or out of there I think the trajectory might help the air mass in the cook chamber twist a bit due to the angle.

[DoTheEyeThing]

Thanks for the detailed response Brewmaster!

I think it's finally done! Might tweak one or two things but we had our first smoke on it over the weekend and it was awesome! Ribs turned out good, though I pulled them a bit earlier than I wanted to as people were getting cold and hungry haha. Someone brought a mackerel - threw it on for an hour and it was delicious. Learned a lot to do different next time. Tending the fire was fun and relaxing. Didn't have any problems keeping the temp up while it was 40*f.

Here's a link to the album
https://photos.app.goo.gl/7wrdAmmb7aEK8ZXk8

[Big T]

Awesome

[Dirtytires]

Nice when it works out as planned....congrats!