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Small patio reverse flow smoker design and build.

triax

Newbie
8
2
Joined Oct 18, 2019
Designing a reverse flow smoke from two gas canisters all going to plan based around the guide provided by dave on this forum. I have been trawling through threads but can't find an answer to what must be a common occurance.

Given I have two round cylinders for the FB and CC I'm wondering how the area under the RF plate is kept the same as the area between the FB and CC.

Does the area under the RF plate need to be the same as the CC/FB area? If so how is this normally accomplished since with a flat RF plate the area will be larger?

Thanks in advance.

Numbers below as starting point.


Cooking chamber volume 5661 cubic inches.

minmum Firebox volume (can be larger)
0.33 1868.13
Firebox to cooking chamber opening
0.004 22.644
Cross section of chamber under reverse flow plate
0.004 22.644
Area required at the end of the reverse flow plate
0.004 22.644
Exhaust stack volume above cooking chamber
0.022 124.542
Firebox inlet above and gelow grate total
0.001 5.661
 

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daveomak

SMF Hall of Fame Pitmaster
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Joined Nov 12, 2010
Good point.... Well, those 2 areas don't need to be the same, as you surmised..
The "football" opening is the area of concern... That allows for the smoker to breathe properly... The RF plate must be above that opening and any "extra" volume, is what it is... Doesn't hurt the operation of the smoke... Steals a bit of space from the cooking zone is all...
 

kmmamm

Meat Mopper
183
65
Joined Apr 30, 2016
Keep in mind you will need the same volume as the fb-cc opening on the opposite end of the plate where it rises into the main cc. Given the rf plate will need some degree of fall to drain grease and excess moisture, the rf plate will be mounted higher over the fb-cc opening and taper to a point such that the that opposite end is flush with the top of your fb-cc opening. As Dave indicated, archiving proper pitch and clearance on the rf can really eat into your available cc volume consequently effecting rack placement. Also be sure to account for the area between the end of the rf plate and the cc tank.
I have found the easiest way to insure your plate is the proper height is to trace the actual fb-cc opening onto A cardboard template and then use the template to cut out a couple plywood jigs. I use one jig to set the far side height of the rf plate and the other to check end clearance. I then cut a cardboard mock-up the rf plate and use it to check for clearance between rf and lower rack, determine drain location, etc. When everything is set, I will use the mock-up as a tracing template for rough cut of the actual rf. Granted, there are a bunch of different ways to do the same thing, but that is what works best for me.
 
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triax

Newbie
8
2
Joined Oct 18, 2019
Hi, Basic layout complete.
Based on the numbers in one of the attachments or embeded images.
The only driving factors are the propane tanks which make up the cooking chamber and firebox.

I've plumed for 25% increase in numbers.
Firebox Approx 20% larger than it needs to be and a length so I can fit logs in a foot long minus the bark.

All suggestions welcome.
Next stage tweeking design and then sourcing box sections and wheels etc.

reverse flow smoker.200.png

Smoker section cad.png

Numbers used.jpg
 

daveomak

SMF Hall of Fame Pitmaster
OTBS Member
SMF Premier Member
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Joined Nov 12, 2010
Looks like you've done your homework to get a great smoker built... Now comes the fun part...
 

triax

Newbie
8
2
Joined Oct 18, 2019
Hi, finally started building after lockdown lifted in the UK. Advice please. How to remove rust from inside of cooking chamber? Also do I need to season underside of reverse plate prior to welding in? How do I prevent rust long term. Thanks.

Since the post above. I’ve been reading the forums and looks like people generally advice against using any rust inhibitors. My only concern is I’m welding in my reverse flow plate. I thinking my only option is to season really well with oil on my gas BBQ and go from there?
Ed.
 

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kmmamm

Meat Mopper
183
65
Joined Apr 30, 2016
Glad you got started. Removing rust from the inside of the tank can be done several ways. If there is a lot of heavy scale rust present, a pneumatic needle scaler will knock it off quickly. If it is light rust, 35 or 60 grit flap pads on a sidearm grinder will work.
Alternatively, (provided the fire box isn’t welded on yet), you could set up a shallow acid bath and chemically remove all of the rust. Acid can be as “gentle“ as common vinegar or aggressive as muratic. If you go with acid, be sure it is done in a well ventilated area and provisions are made to fully neutralize the residual acid before disposal.
Don’t worry about the underside of the ref plate. Simply knock the loose surface rust off before welding it into place, no paint or seasoning ever necessary on the underside.
 

triax

Newbie
8
2
Joined Oct 18, 2019
Hi, As is in the photo. Slow job hr here and there. Good call on the acid i'll see what I have. all comments welcome.
 

radioguy

Smoking Fanatic
763
143
Joined Jan 12, 2013
Knock off all the loose rust with a wire wheel or flapper on your grinder. Doesn't have to be shiny bright. Don't worry about underside of RF plate. Weld it in, clean up the welds, wire brush or flapper. Clean the tank soap and water, dry it and season with food grade oil. Use PAM or spray canola, burn and recoat a few times. That oil will build up and protect the inside much like a cast iron skillet.
Good luck, have fun,

RG
 

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