1st RF build not sure about measurements

Discussion in 'Reverse Flow' started by dep364, Jun 6, 2013.

  1. dep364

    dep364 Newbie

    I don't think I have the exact measurements down for my RF build. I've got a deal worked out for a 24" by 36" barrel and a 24" by 18" firebox both are suppose to be rolled sheet metal 3/16". I wondering how many inches above the RF plate do I put my first cooking grate. And I'm not sure how tall should I cut the door? I'm wanting to make pull out cooking grates if that makes a difference.

    Thanks in advance for any assistance   
  2. sqwib

    sqwib Smoking Guru OTBS Member

    You can check out my build in my signature "Frankensmoker Build"

    That may help with some of your questions
  3. dep364

    dep364 Newbie

    SQWIB that helped a great deal...Thanks! I'll have to read it again so alil more can soak in. Its the all the geometry that has me confused. Figuring out the 65.14 square inches on the cooking chamber to firebox opening is confusing. Wished I'd listened alil better in school.  

  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    dep, evening.... PM me with the dimensions of the pieces you have collected, a drawing of you idea for the build, and I will crunch the numbers and walk you through the process.....    I use the scanner flatbed to get my pencil drawings on here...  and to PM them as attachments...    Dave
  5. sqwib

    sqwib Smoking Guru OTBS Member

    My main problem with my build is what's quoted below, is this where you're getting confused?

    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

    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.
  6. Dave has you covered Dep.

    remember to post pics.

  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Below is the way I solve the "round to round" connection...  click on pictures to enlarge....   Dave

    Last edited: Jun 7, 2013
  8. Dave

    As always that is some nice work there.

    Do you know anything about wood boiler furnace building?

  9. I'd like to see him overlap the tanks a bit more, on a 24" diameter cooking chamber.  At least another inch. Give him a little more room to dish down the reverse flow plate. Ive been over lapping them about a third, .....now this reduces the room between the grate and reverse flow plate, but they have been breathing and cooking good and it gives me room for the "SQWIB" baffle plate to reduce hot spots at the beginning of the reverse flow plate. 

    As far as the height of the first cooking grate, Ive been installing mine dead center of the chamber to get the most sq inches of surface area...because I like to do ribs. If your more into roasts or birds . you might want to go lower so as to have more room between racks. But even then, if you actually measure a 12 lb bird or 8 lb but, you really don't need as much height as most people think..

    so, let me post a question ....I think its Jambo that has the firebox to cook chamber opening above the lower grate, Ive been contemplating this lately.does anybody have any thoughts on that???.. I'm thinking of doing one as an experiment.  but a little differently than the way he does it.
  10. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    RW, morning.....   With the upper air intake in the FB, does the RF plate get hot enough to need a heat shield ??  That is assuming the upper air inlet is used to  optimize the FB temp / CC temp.....

    And about the Jambo design....    I am seriously considering that design....   A member built one about 6-8 months ago and really like the way it cooks...  The only concern I have is higher, a lot higher temps at the firebox end with no way to reduce that high heat zone... Figure out how to remedy that would you.....  

  11. DaveOmak, I dont know exactly when, but in my early years of pit smoking, I was tought to make the smoke come down onto the meat instead of up through it..  And thats something I have always tried to acheive when building a smoker. I have no science to back it up, but to me it makes a difference.   I dont know Jambo, but looking at the design, I believe he was thinking the same thing. The only problem I see is exactly what you mentioned, higher temps at firebox end, especially when its fully loaded and air flow starts to get restricted.  Im currently tryng to wrap up the three builds I have going on right now, but as Im working on them , my mind keeps making me look at the firebox to cooking chamber opening and coming up with all kinds of crazy ideals.

    I need to throw a mini together and see how it works.

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