20" Pipe RF Smoker

Discussion in 'Reverse Flow' started by geothermal, Jul 17, 2014.

  1. geothermal

    geothermal Smoke Blower

    Another great idea Dave! Thank You! Got the hinges welded on and "blind welded" the bottom flange, which worked great. Drilled 3/8" holes 4" apart and welded from the inside. After cutting out the rest of the door, it would only lift up about 1/4 of the way before binding. The pipe had expanded almost 1/4" over the 41" opening, so the two middle hinges were higher and binding on that 5/8" rod. So I pounded out the rod and I'm going to make the holes in the two middle hinges more oval. Then use short 5/8" bolts and washers on all 4 hinges instead of the rod.That will allow the two inside hinges to open without binding and the washers will cover the enlarged holes. The two outside hinges will remain snug to keep the door corners tight agains the CC, which for the most part are still lined up all around despite the expansion.
    Last edited: Jul 28, 2014
  2. geothermal

    geothermal Smoke Blower

    This might be a dumb question, but do you score the top or bottom of the RF plate, or just cut it all the way through? I'm guessing the top if you score it halfway through, but then you have to grind down the welds. If you socred it on the bottom, you wouldn't have to grind them down and you would have nice smooth valleys on the top to the drain. I got the door finished yesterday. I was able to correct the binding and still use the 5/8" rod by grinding out the 2 middle hinges a little. Blind welding the flanges worked great and will have a nice clean look. .

    Last edited: Jul 28, 2014
  3. geothermal

    geothermal Smoke Blower

    Question on the chimney size and length. For an RF smoker, I know your supposed to size the FB to 100%  of the CC on Feldons's calculator in order to get the opening between the FB and CC, then multiply that number by 1.5. So if I make my FB larger than 100% should I use the re-calculated size for the chimney to adjust for the larger FB, or use the size that was originally calculated when it was 100%?

    I plan on fabing up a plenum similar to Dave's scetch located near the center of the CC between the RF plate and top of CC.


    20" dia X 18" FB = 100%

    Pipe dia = 5" X 14.41" long

    20" dia X 24" = 133.4%

    Re-Calculated Pipe dia = 5" X 19.21" long.
    Last edited: Jul 28, 2014
  4. lendecatural

    lendecatural Smoking Fanatic

    Use the numbers that come out of a 100% firebox. Additionally, look at the note under the chimney size.. The note indicates that 14.41 may be too short so you should consider 4" to get it closer to the 30-40" window for length.

    "Enter the diameter of your chimney pipe to find out how long it should be.
      • A chimney that is too short may produce insufficient draft (drawing of air). A chimney that is too long may cause the air to cool before it exits, reducing effective draft and worse, dripping of exhaust materials onto food!
      • Many horizontal smokers have an exhaust between 30-40 inches in length, but there is no hard and fast formula."
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Len has a very good point..... The stack height is necessary for good draft "SUCK" to keep things moving.....
  6. geothermal

    geothermal Smoke Blower

    Thanks again Len and Dave. Well I cheated a little yesterday and had this tank manufacturer cross bend the RF plate. Best $20 I ever spent and saved me hours of work. The plate came out perfect with about a 1/4" - 3/8" drain to the center and nice and clean looking. Started welding on the round end cap last night. Once that's done I'll weld in the plate. Then on to the FB. Making more progress than I thought.
  7. geothermal

    geothermal Smoke Blower

    Finished welding and grinding the end cap tonight. RF plate is next.

  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    You gonna have to trim the edges of the RF plate to make it square ???? Let us know how that cross brake worked...

    I would think the edges would have a "very slight" bow to them, and they wouldn't be straight enough to fit the tank walls... I could be wrong... been wrong before.... will be again.... and probably soon too....
  9. geothermal

    geothermal Smoke Blower

    Hi Dave,

      I kind of wondered about that myself, but since the brake was from corner to corner both ways, all edges remained straight and square. I set it in the CC afterwards and leveled it up to cut the drain holes and it fit nice and tight against the sides of the pipe.
  10. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Well that's good news......
  11. geothermal

    geothermal Smoke Blower

    Got the RF Plate and drain welded today. Although I don't think it's necessary, I will weld on a 1" high piece on the end of the plate in case I want to fill the plate with water at times. It has a gentle 1/4" slope from the end and sides to the center drain. On to the FB!!!

    Last edited: Jul 30, 2014
  12. type

    type Newbie

    Looks good, How thick is your plate? I used 16 gauge so I didnt dare to weld from the fear of extreme warpage.
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Typically RF plates are 1/4".... for thermal mass and no warping...
  14. geothermal

    geothermal Smoke Blower

    Got the plenum fabed up and welded on to the plate that connects the CC to the FB. Plate is partially welded on. I ran out of welding rods.

  15. geothermal

    geothermal Smoke Blower

    Yes, mine is 1/4".
  16. geothermal

    geothermal Smoke Blower

     Got a start on the FB. I'm just wondering if it's too big/long before I go further. It's 20" wide 24" long and will be 22" high once I weld on the half pipe. I think it's more a question of proportion to the CC than anything. I will be using the other piece of the half pipe for the bottom. I've got questions on how to do the door also, but will wait until I get all sides of the FB welded up.

    Any thoughts or concerns on the big firebox? I'm thinking it might look better if I cut off 2, 3 or 4 inches.

    Back side.

    Top of FB to RF plate.

    Had to quit early due to Thunder Storms moving in.

    Last edited: Aug 2, 2014
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Oversize FB's seem to work very well..... 1/3 of the CC and larger.... More space under the wood grate for ash to collect.... More wood controlled at a lower temp for long duration cooks... More of a uniform heat for consistent temps... BUT, aesthetics is important also....

    Personally, I would lean toward a perfect smoker, that cooks better than whatever is my second choice....

    For the doors, do you have something similar planned for what is pictured below...... Dave

    ......click on pics to enlarge.....

    Last edited: Aug 2, 2014
  18. geothermal

    geothermal Smoke Blower

    Thanks again Dave,

      Yes, although my FB will be rounded at the bottom, I do plan on having the vents where you have them in this drawing. My concern is how to design the door to close and seal. I was thinking

    of wrapping the perimeter of the entire 1/4" end plate with 3/4" angle and installing a gasket in the corners of it. But I thought the back perimeter of the FB could warp without having a flange welded to it. Without a drawing, it's kind of hard to describe. So I guess I'll leave the 24" long firebox. Like you said, building the perfect smoker is the priority over aesthetics. I picked up a couple of 32" dia antique steel wagon wheels today that will mount to the FB, so that will help hide the oversized FB a little. I'll post some pictures once I have the remaining sides of the FB welded.
    Last edited: Aug 2, 2014
  19. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    .........:2thumbs: ....... :popcorn
  20. geothermal

    geothermal Smoke Blower

    While the build is going, the smoking must go on. Trying Jeff's Rub Recipe on these Butts.


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