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Discussion in 'Reverse Flow' started by hurleyq, Mar 9, 2016.

  1. hurleyq

    hurleyq Newbie

    Howdy Folks.  I've been working for a few days with a buddy of mine on a 275Gal oil tank pig cooker/reverse flow smoker combo.  We built the fire box out of an old JobBox that was left at one of our jobsites and other various pieces of scrap metal we have lying around.  We're two days into the build and figure probably at least that many more before it's ready for paint/trailer mounting.

    Here's day one gettin it cut up and figured out

    We built a heat ducting system from the firebox to deliver heat from the FB, through the duct and into an opening in the bottom of the cooker.  Duct is 1/4" plate steel on the sides and 1/8" on the bottom.  We're going to use some 1/8" steel plate to make a heat shield within the cooker that will have some slope to run any grease/whatnot down and out drain on one side of the smoker.

    Here's day two builidng out the duct system and figuring out opening sizes and final mounting.

    I ran the Feldon Calculator to figure the opening size in the FB and am going to use that for the same opening in the bottom of the cooker, and half on each side of the heat shield.  Planning on 2 exhausts in the middle to encourage heat around both sides of the cook surface

    Link to BBQ Pit Calculator

    My intakes are going to large, haven't figure out exactly but plan on providing more than adequate capacity for openings

    Whole thing is going to be mounted rear facing on a 6x6 trailer I picked up on the cheap.

    Looking for first impressions mostly, we're planning on throwing some fire in the box and hitting the various parts with a heat laser to check the heat distribution before welding it all up final.

    Also tossing around the idea of an insert into the cooker for direct heat cooking (some expanded metal on a frame) so I can slip it in if I feel like burning some burgers or the like in it.

    More to come
  2. joe black

    joe black Master of the Pit OTBS Member

    The only thing that is of any concern to me is your fire box. The job boxes that we have at work are not very thick. IMO, a fire box should be at least 1/4" thick. If it's not that thick, you may have a problem with burnout. Some of the builders may want to comment on this.

    Good luck and keep the pics coming, Joe
  3. johnboybaker

    johnboybaker Fire Starter

    Wish you luck looks good so far
  4. hurleyq

    hurleyq Newbie

    Joe- I appreciate the input.  We've been tossing around insulating and plating the firebox, I think the actual fire basket is going to be handling most of the brunt and we've got it framed up with those 4 bars across.  Also, the ash catch on the bottom is 1/8" which sits above the jobbox base.  I guess I'd only be concerned about burnout above the fire basket

    My question is, is the firebox volume in the calculator the entire size of the box, even if the fire is set a foot or two off the bottom of the box?  I assume so, since the fire will have all the volume within the box to build up heat/exchange air.
    Last edited: Mar 10, 2016
  5. hurleyq

    hurleyq Newbie

    Update on Day 3 and Day 4:

    Here's the link to Day 3 of the build:

    We laid out the heat shield and bottom openings in the tank and welded the structure up.  The heat shield will be 1/8" plate welded to the angle supports you see there, which will angle into the a V angle for drippings and whatnot.  The backside will be fully shielded, where as the front will have openings along the frontmost lip and each side.  The total square inch opening in the heat shield is equal to the opening in the bottom of the tank and equal to the opening in the firebox.  Idea is that the heat will come up through the center of the hole, and be drawn to the front and sides by exhaust stacks on the top backside of the cooker

    We plan on putting some gauge flashing under the grate supports to prevent grease from dropping into the duct openings.

    Also finished the firebox duct with a really nice piece of stainless (which will never be seen ever again) that we had lying around.

    Here's Day 4:

    My buddy was smoknig some briskets and pork butts for an event the next day while we were building (they were money).  He's also seen inside the tank getting some welds in the waaaay back.  You can see the heat shield attached to the framing from day 3 and we got the bend out of the top by using many many clamps and a piece of aluminum to bring it to shape and then welded a T shape to hold the form.

    We also cut out the very front where the door is going to go because the tank had a bulge in on either side, so some new 1/8" plate was put in to give a flush surface.

    Trying to find more time to work on the thing, want to get her fired up soon!

    Next steps are sandblasting the tank, fabricating the door and cook surface, then weld cleanup, gasketing/handles for doors, stickpinning high temp insulation to the firebox and covering with plate, marrying the firebox to cooker, figuring out exhaust piping, paint and getting it mounted to the trailer.

    Comments appreciated.  Also, my feldon calculator is calling for some really tall exhaust stacks, I assume I can use multiple stacks to make up the area?  Also, I read that the height of the cooker from the firebox duct to the top counts for exhaust length?

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