My first RF smoker build

Discussion in 'Reverse Flow' started by aussiesmoker84, Feb 22, 2016.

  1. Hi all
    So I'm attempting a smoker build and to say I'm not totally grasping the maths behind it would be an understatement.
    The tank I'm using has an overall length of 33inches and a diameter of 18.5inches, if my math is correct it would be about 33 gallons and that's with allowing less volume because of the end tanks. Is this to small to make a smoker out of?

    I was thinking of starting with the FB/CC half moon opening first so I could work out door placement from there. I've put in a FB dimension in Feldon's bbq calculator and it's given me a half moon opening size of 7.2 inches, now I might sound stupid here haha but do I mark a line from edge to edge that's 7.2inches long? Like this

    Would anyone have an opinion of what FB dimensions I should use?

    Any help would be greatly appreciated
    Thanks in advance
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  3. So I haven't been on here for awhile, had stuff going on. Anyway I'm slowly getting along with my build and need some advice on my firebox intakes. I've marked on the box where I'm thinking of putting the door and intakes but started think having all the intakes under the fire level might not be a great idea. Here's some pics
    Any help or opinion would be greatly appreciated
    Cheers guys
  4. Messing about with different intake positions. Dotted line is the fire tray and the 4 circles are different intake heights I'm thinking.
    Still have some intakes on the other side that are below the fire tray.
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    This set-up has been working for years.....  I'd follow it....

    .. ..
  6. I'm assuming with most of the air intake on the bottom vents?
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  8. Cheers Dave. I should ask before I go welding the FB to the CC, I worked out the my throat cut out height was 2.6 inches. Does that sound about right?
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    4.25" tall cut out....  + probably 1/4" for FB metal thickness..
    Last edited: Apr 6, 2016
  10. Oh wow! I was way off haha
    Last edited: Apr 6, 2016
  11. Like I said not great at maths. How did you work that out? Sorry for all the hassle
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    My mistake...   3.5" tall..... +
    Last edited: Apr 6, 2016
  13. Well 3.5 is better than 4.5 haha. I don't know how I missed by so much. I know it's not on you to work everything out for newbies on their builds but that 3.5 is spot on? Thanks so much I really appreciate it. You've saved me a lot of heartache and anger haha
  14. I went off this when I originally worked everything out months ago
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  16. My apologies, I didn't fully grasp it before but now I understand it(I hope)

    The calculator gave me a FB-CC opening of 23.40

    And this is what I got from the segment calculator

    Then I'm assuming I add 1/4inch on top of that for the thickness of the firebox

    Am I in the ball park?

    Again I'm sorry for being annoying but I do appreciate the help you're giving me

    Last edited: Apr 6, 2016
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    You've got it......  NOW, using Feldon's numbers is NOT the way I would go....   Use my calculations....   Feldon's will cause you an overheated Firebox and poor heat/smoke flows through the smoker....   Have you opened that link and read it ???

    Your CC volume X 0.004 will  be the area between the FB and CC....   area under the RF plate and area at the end of the RF plate...  

    Diam. 18.5 X 33" length....   18.5 x 18.5 X .7854 X 33 = 8870 cu. in. X 0.004 = 35 sq. in. FB/CC opening

    Using the circle calculator, click on radius and segment height box...   put 9" in radius box....  3.5" in segment height box....  

    NOW...   ED is the height of the cut.....   AB is the width of the cut...   ED is how high from the bottom of the CC is where the RF plate goes...   ED is how far from the end of the CC is where the RF p[late ends....

    8870 CC volume X 0.022 = 195 cu. in for the exhaust

    195 / .7854 X 3 x 3 = 27" high stack BUT I would use a 3" exhaust stack 34" tall....

    I'm just trying to help you understand where the numbers come from....   read the tutorial I have put together...  It explains a bunch...  Once you understand why I built a new tutorial and promote it over Feldon's, this krap should make sense....
  18. That's a relief, thanks for that.
    I'll run through those calculations you gave me tomorrow after a good sleep.
    Yep I did open it up and have a read, I think somewhere in that thread or maybe another one you made a post about hoods bending when cutting out. I was cutting out mine and it started bending out so I stopped and welded it back down. Any tips on stopping it doing that?
  19. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

     Any tips on stopping it doing that?

    Not that I know of...  It's from stress during the rolling process...   Maybe, install the FB and exhaust, and build a really hot fire to relieve the stress in the CC tank.....  don't know really......

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