80 Gallon RF Smoker Build(First homemade build!)

Discussion in 'Reverse Flow' started by mjg2688, May 10, 2016.

  1. Welcome!  I have been smoking and cooking meats for at least the past 10 years, I know it's really not that long but considering I am only 27 it's been a good portion of my life.  I have always used grills and cheap store bought smokers(think Brinkman stand up) but have ALWAYS envied some of the home brewed smokers I've come across in the past.  Problem was up until about two years ago I knew NOTHING about fabrication/welding outside of what I practiced in high school.  Fast forward to the present and I feel comfortable with my abilities to accomplish this task, not only that but the opportunity just sort of fell into my lap in just the past few days.  Due to the unforeseen demise(aw shucks)of an 80 gallon air compressor I have acquired said tank for this project. Best part was it's FREE! 

    With that said pictures of the tank are below, including the original plate from the manufacturer.  Appears to be in decent shape considering it was manufactured in 1959!  Although I was told it has a hole I haven't found any obvious ones yet, however did find a spot which has been patched in the past. I will get better pics once I actually get it into the shop and start working on it.  And on that note being able to work on this project in the shop I work at is for sure going to come in handy!  I have already been talking to the engineer about getting the program to cut the parts of the smoker with our production plasma cutter, although unsure yet if I will have to pay for those materials of if we may have the material "laying around."  On top of all that we also have a sandblasting booth which will definitely come in handy!

    Onto what I've worked out so far.  I got some rough OD dimensions(approx 63.25" in circumference, 20" diameter, and 66" length)  of the tank and put them into Feldon's Calculator, but I'm curious if I should use the 80 gallon capacity for my calculations or the physical dimensions of the tank?  I tried both and there is about a 2,000 cubic in. difference in CC size.  Worked out the numbers using the 80 gallon capacity and CC comes out to 18,480 cubic in.  Recommended FB size is 6,160 cubic in. the FB I worked out at H-28" W-12" L-20" comes out a little larger at 6,720 cubic in.  Intake openings are recommended to be 20.16 cubic in. I worked it out to four openings at 3.675"x1.375".  Plan to use a 5" diameter chimney which comes to 17.12 in. to achieve a recommenced 336 cubic in.  Where I get lost is the FB to CC opening numbers, I mean I understand what they mean but how do I figure out 53.76 sq in. on the tank itself?  Any input on this would be appreciated.  My next question is about the RF plate itself.  I understand striking it so that the fat collects in the center and eventually flows to a drain, but which to which end? The obvious direction would be towards the FB so aid in the smoke flow into the CC but wont things tend to drain into the FB?  Also how much of a drop from end to end over 66" will be needed to flow efficiently?  Also I am building the FB out of .25" plate will I need to install an insulating layer around the FB?  I live in the Northwest, Vancouver, WA to be exact and temperatures can get cold but not often much below freezing.

    Again any and all input will be appreciated as I am going into this project totally blind, but I am looking forward to it quite a bit!  I look forward to meeting people within the community and gaining some knowledge along the way.  

  2. Bump for assistance
  3. Hey Mjg,

    Sorry I'm quite new myself but can I recommend you simplify your post into some clear dot points.

    That way people can easily quote your questions and answer them 1 by 1. Also it has been pointed out through real world application that Feldon's calculator has some flaws for building a reverse flow smoker.

    I would suggest you use the link on top of the reverse flow thread for Dave Omaks calcs. http://www.smokingmeatforums.com/a/reverse-flow-smoker-how-to-calculate-build-tutorial 

    They have input from a great deal of people and seem to be optimised for a well functioning smoker.

    Last edited: May 12, 2016
  4. Yes after digging a little more I've found out feldons calculator has a few flaws, thank you for the suggestion. Will go through this afternoon and organize things a little better.

    On the bright side I got the outside of the tank sandblasted yesterday so now I can begin the repair work. Guessing it'll be next week before I make any of my cuts, which will give me the weekend to research and get a solid game plan.
  5. Ok so I have FINALLY reworked all my numbers using Dave's calculations.

    The tank is 66" in length, 20" OD so with 3/16'' wall 19.625" ID.

    CC - 19.959.22 cubic inches or 86.40 gal(Oversized for expansion I assume as it's labled an 80 gal tank)

    FB/CC Opening - 79.84 sq inches

    Area under the RF plate - 79.84 sq inches

    Area at the end of the RF plate - 79.84 sq inches 

    Minimum FB size - 6,586.54 sq inches

    Air inlet to FB - 20 sq inches(4" across from FB/CC opening, and 16" at fuel height)

    Exhaust Stack Volume - 439.10 sq inches

    Exhaust Stack height/diameter - 35"x4x4=439.82 sq inches

    And the numbers from the circle calculator(screenshot below)


    RF plate width-18.19

    Works out to 80.62 sq inches(a little over the 79.84 needed)

    Can someone double check my numbers please and thank you!  :)

    Last edited: May 18, 2016
  6. sqwib

    sqwib Smoking Guru OTBS Member

  7. sqwib

    sqwib Smoking Guru OTBS Member

    If I could do it over again I would probably do figure #2, ask around and get input on this before you cut, figure # 3 is how I reduced the hot spot.



    Post from my site

    Update 9/01/10.

    I was a bit unhappy with my last cook, I was getting an average of 70 degree difference from left to right, sometimes peaking to a 90 degree difference, this was unacceptable. I did not realize the difference was so great until my cook last weekend.
    I tried Fire management and that had no effect.

    The top of the firebox was getting hammered with heat and 6" of the firebox is inside the cooking chamber.
    There is definitely a lot of convection going on.

    Here is how I fixed the problem.

    The Green represents the top of the firebox that is inside the cooking chamber, the Blue represents the reverse flow plate and the Red represents the baffle plates installed to reduce the heat from hammering the top of the firebox, causing excessive radiant heat.

    FIG #3

  8. sqwib

    sqwib Smoking Guru OTBS Member

    Tweaking my fire skills helped even more
  9. sqwib

    sqwib Smoking Guru OTBS Member

    I also Highly suggest a log lighter and heavy duty fire grate.. I'll use this to start the splits and sometimes cook during foiled stages.

    And finally got around to making the fire grate.


    Had to test out the NEW fire grate this weekend so fired it up, starting with the preheat burner.

  10. sqwib

    sqwib Smoking Guru OTBS Member

    20" diameter was the hardest part for me determining where to put the reverse flow plate and the grates, if you plan it in such a way that you can install grill cooking grates, you will be happy.

    I also found this extremely helpful.

    Here is where I started double guessing myself, I put the fire box in place and cut some wood to get an idea of what size thermal plate will be needed and checking height to make sure there is enough clearance from the thermal plates to the cooking grid and at the same time making sure there is enough opening from the firebox to the smoke chamber.

    The firebox is right at 5.25" from the top of the firebox to the bottom of the smoke chamber I want it exactly where it is.
    The top of the firebox and the thermal plate to the bottom of the cooking grid will be 6" and from the top of the cooking grid to the top of the smoker chamber lid will be a little over 8".

    My concern is, "will it be enough of an opening to the smoke chamber from the firebox?"
    The pit calculator has no way to accept odd shapes, but the Firebox to smoke chamber inlet will be exactly 1/4 of the tank diameter
    The board in the picture is a tad lower than the cooking grates will actually be, the cooking grate will be 6" from bottom of the grate to top of thermal plate.
    Hopefully this formula is correct

    20" DIAMETER TANK 10" X 10" X 3.1358024 divided
    by 4 = 78.395, actually that does not apply to sectioning the tank in this matter, but thanks to a fellow builder and his CAD program he came up with my numbers actually being, 61.418, so I am good to go.
    Below is an explanation of this from JIRodriguez at SMF.

    Quote: Figured out where the difference was coming from the formula 3.14xRxR gives you the area of a wedge shaped opening exactly 1/4 of a 20" dia. pipe (like a pizza cut top to bottom & side to side).

    But the shape profile is different when you split the pipe with parallel lines every 5". The two areas closest to the center point have a larger area than the two areas on the outside. So you end up with the two middle sections measuring 95.661 in. sq., and the two outside sections measuring 61.418 in. sq.

    The racks slide so nicely 

    Received my Porcelain coated Cast Iron cooking grates Monday and did a dry fit.

    [​IMG]These were a bit pricier at Partstore.com and I found them cheaper at ThePartsBiz.com but they never have any thing in stock and they always bill you before they check stock. I even emailed them to check for availability and they said yes these are in stock, this is the second attempt in ordering from these guys I would stay away from them if you can.

    I was a bit worried they would be too tight but they are perfect. They will be mounted 6 inches above the thermal plate. I leveled everything and cut some wood to hold the angle iron in place the angle will be tack welded in case I need to make adjustments down the road.



  11. I intend to split up my air intake openings in my FB to combat the possibility of a hot spot in my fb/cc. Need a total of 20 sq inches of air intake. Plan to put a 1"x4" slot in the top of the FB across from the opening into the CC to draw the heat in more efficiently, and the remaining 16"(probably 4-1"x4" openings) split up on the bottom right at the level of my fire grate.
    Last edited: May 19, 2016
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Can't see the drawing....

    1)Is the height of my FB cutout too big?  Did you use the circle calculator to figure it out ??

    2)How far into the CC (lengthwise) should I cutout?  Cut into the CC past the weld for the dome....

    3)My understanding is the opening at the end of the RF plate should be the same as my FB cutout, is this correct if not what should it be?  The same or larger...

    4)Is a 1.25" incline for my RF plate going to be enough for the grease to flow to my drain?  That drop will cut the air flow and restrict it...

    5)Measurements on the door on the CC and cooking grates are just rough guesses, any input would be appreciated.  

    6)Will my 20"x 20"x 18" FB be adequate?  Is it 1/3 or more of the CC volume.....Also, [Chord AB] corresponds to the width of the RF plate... NOTE... for ease in fitment, the FB should be at least as wide as the RF plate..

    7)I am using .25'' plate for the FB do I need to worry about and insulating layer on the FB?   No...
    Last edited: May 19, 2016
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  14. [ATTACHMENT=2819]SmokerDrawing.jpg (509k. jpg file)[/ATTACHMENT]
    Last edited: May 19, 2016
  15. Just tried posting my drawing again not sure why it didn't show up for you.
    Last edited: May 19, 2016
  16. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    How so when the incline will be from the FB to the end of the RF plate leading into the CC, wont that increase airflow?  So you are sloping the RF plate toward the FB ??    That won't be a problem as long as you have a "dam" between the FB and CC on the end of the RF plate...

    Chord AB came out to 18.19" which seemed a bit wide to me, FB is going to be 20'' wide so will extend about an inch beyond the RF plate. That makes for easy fit up....

     Cut into the CC past the weld for the dome....     There is a double plate at the weld seam...  get past it for ease in fit up for the RF plate...

    So there is not exact measurement to go by?   There are no exact measurements...   An inch or 2 won't make a difference...
  17. sqwib

    sqwib Smoking Guru OTBS Member

    MY 2 cents and not necessarily the consensus...  I would not pitch it towards the firebox, mine pitches towards the other end and the drain is located there. Your Drain is too close to firebox.

    Remember if you pitch the RF plate you will need to account for that on the cut (wont be a perfect rectangle) or you can work the pitch in with a bend, I did both.

    My RF plate pitches near an inch and has a slight bend in the middle and a lip at the end so grease cant flow off the plate. I hear lots of guys mention nose down and nose up to control the heat, but to be honest mine runs fine perfectly level with the pitch that is built in the RF plate.

  18. Awesome thanks for the help guys! Took some better measurements this morning and going to refine my drawing over the weekend and start cutting it apart next week. Engineer here at work is making a true drawing to go by. Hopefully have that at the end of the day.
  19. Apologies to anyone that was following this build, things have been crazy lately to say the least but I am BACK!  

    Cut the lid and opening for my firebox yesterday and got the inside sandblasted.  Surprisingly it cleaned up well and I only had two small holes to weld up.  There are some thin areas but nothing that concerns me terribly.  I'm waiting on gas for the plasma cutter so won't have the plates for my firebox until next week probably.  Did manage to get a "seal" on my door using 1"×1/8" flat bar and got that welded out.  To my amazement it really didn't warp all that badly.  Plan to add a high temperature gasket later on down the road.  

    Today I am going to focus on a hinge to reattach my door, a handle, and my smoker stack/damper.  If I have time this afternoon I will also work on some kind of stand for this thing, as of now I have no idea what I'm going to do.

    Look forward to getting this build done and sharing my progress along the way.


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