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starting my reverse flow

post #1 of 35
Thread Starter 

Been a while since I've posted, but been lurking quite a bit. I've been gathering parts,






so I'm in the planning and cutting stages of my reverse flow build.  Starting with a small trailer I snagged to $50, a tank I snagged for free $$ and a firebox that will be a recycled woodstove that I also scored for $50.  I have a total of $100 in this thing so far so I think I'm ahead of the game at this point, although it has taken a bit of time waiting on parts to magically appear cheap,  Best I can tell before cutting, the CC is 1/4" wall and the FB is definately 1/4".  Plan something along the lines of M7's Chain hinges.  Scored some large chain from work for free.  Best I can tell I'm missing the reverse flow plate and cooking grates.  Have my feelers out for wedge grating from the local coal mines for grates.. love the stuff.  Anyway this is what I'm starting with, what do ya'll think. I know so far that I need to rethink the vent openings in the FB door.  As you can see, the original openings are basic woodstove screw type,  And I need both below and above the fire openings. So I need ideas or pics of what ya'll did there.  New door?  Using the calculators here I came up with the following dimensions. What do ya'll think




CC volume - 105.75 gal

FB volume - 61 gal      so my firebox is larger than the recomended

Vents - 4@2.25 under  and 1@ .5 over


stack =8"d x 10.7 L


And using the circle calculator


Radias  12"

Chord AB - 22.5

Segment ED - 7.8


Any feedback before I start cutting from ya'll is greatly appreciated.  

post #2 of 35
Hey amcjeeper,
Congrats on the cheap scores. The three main pieces for 100 bucks is sweet. Is that a jet ski trailer? Hard to tell in the pics but it looks like it has 4 bolt hubs. That suggests to me that it has a 1000 - 1200 lb axle. My cousin built an RF with the same size CC as yours and he added a warming box, he built his on a jet ski trailer. The weight adds up fast so he put in heavier springs. After a few years of towing he said the axle is actually bending/twisting on one side and he's planning on putting a heavier trailer under it. The total weight of his cooker/trailer is 1700lbs. I helped my son build a slightly smaller version with a warming box, on casters and it weighs 1200. Both cookers are 1/4 CC, 1/4 RF plate, 1/4 WB & 1/4 FB. I'm no expert at building pits and I'm not saying your plan won't work. But make sure to total all your weight beforehand including the RF plate, cooking racks, chimney and warming box if you are planning one. Of course the amount of towing you are planning makes a difference too. Good luck with the build, looking forward to seeing more pics.
post #3 of 35
The oversized firebox will be fine... don't worry about it....

cc vol = 24,429 x .004 = 98 sq. in FB/CC opening and area under the RF plate etc...

24429 x .001 = 24 sq. in. FB total air inlet... ~20" lower and 4" upper

circ. calc. 6.5" ED = 99 sq. in. segment area and chord AB = 21.33 inches in length....

Exhaust stack..... 24,429 x 0.022 = 537 cu. in.. / [ .7854 x 4.5 x 4.5 ] = 34" stack above the CC..
post #4 of 35
Thread Starter 

Thanks for the replies folks.  

Wango - Don't plan to pull the smoker much.  8 to 10 miles would be the farthest, if any.  Mostly just to move it around at my house.  The trailer is actually a bit larger than a jetski trailer.  I'll look on the axle and see if I can find a load rating.



  or anyone else who can answer.  Is the area under the reverse flow plate and at the end for the 180  a 2 dimensional measurement.  As in is the measurement of the entire area under the plate for the entire length or just a cross section.  My brain tells me that area is 2d and should be the cross section.  Total length would be volume and be 3d.  Am I correct there?

post #5 of 35
Yu are correct.... 2D for the openings.... I know it seems weird to calculate volume then magically end up with 2D measurements.... but that's the magic of smoking foods....
post #6 of 35
Thread Starter 

Got some time away from work and did some wire wheel cleaning on the tank I'm using for a CC.  After searching the info on the tag it looks like I have a pressure booster tank for an industrial boiler system.  Should work just fine.  My question is in the placement of the door.  This tank has multiple bungs for various valves and regulators and what not.  I'm wanting to reuse an existing bung as a drain for the bottom which leaves me two sides as options for the door for the CC.  Would it be better to cut near the seam on the tank.  Or stay 180 away and try to fill in the large bung openings on the other side.  I'm afraid that the door will spring if I cut close to an old weld.  Dont have much experience here.



post #7 of 35
I would put the seam on the opposite side from the door.... the seam "may" be under stress and cause warping..
post #8 of 35
Thread Starter 

Thats what I was leaning towards.  Thanks Dave.

post #9 of 35
Thread Starter 

Had beautiful weather today, so I took the opportunity to get some work done on the smoker build.  And I even got my 12 yr old off the playstation long enough to try out some garage time with dad.  Turned him on to the welder.




Thats the bottom platform that was on the tank - repurposed as feet to raise the tank up a bit.  Even got the CC opening cut.  And I was nervous as all get out.  Didn't want to screw up my tank.  Was pretty happy with the results.  And yes the opening looks pretty deep but its actually just 7".  I went 1/2" past the weld seam.



Hope to get the FB opening cut tomorrow and maybe mount the FB to CC so I can cut the door out.  Felt like all I did today was measure and remeasure. 

post #10 of 35

Looks good so far.
I tell you what, there were days on my build that all I did was measure and contemplate, but it was time well spent.

post #11 of 35
Thread Starter 

Got some more work done on the smoker and found more that I need to re-adjust. Nothing more cutting and welding cant fix.  Just adjusting heighth of the CC on the trailer so I can get the FB mounted.  Got some hinges mocked up modeled after M7's chain hinges. Thanks M7 for the design idea.




Here are my questions for the experienced guys on here.  When setting up door geometry,  does the pivot of the hinge go directly over the door gap, or is it offset one way or the other. And is there a calculation for that or just fudge it.  I know I need it angled as shown to account for heat draw but is there anything else I'm missing.


Also what width of strap material do you guys use as door gap cover.  Is this welded directly to the door or is there a spacer to allow for gasket material underneath.  Thanks in advance for any help.  I wouldn't have gotten this far without this forum.

post #12 of 35

Most people put the hinge axis above the door gap, but only because it has to go somewhere and that spot is as good as any.

You can put the hinge axis in other locations, just do the math and make sure everything clears when you open it.


Strap material is usually 1.5" to 2" wide. Most people weld directly to the door with no spacer. If gasket is needed you can mold a silicone gasket to fill the gaps.

If you want to add a 1/8" thick fiber gasket, you can space the hinges for it instead of gapping the strapping.

post #13 of 35

The hinge pin must be outside the door seal so the seal doesn't interfere when the door opens....




post #14 of 35
Thread Starter 

Thanks guys.

post #15 of 35

It can depend on how you are going to hinge the door.... heres a hinge centered with the gap. There is a flat bar welded to the inside of the tank to stop the smoke from going out through the crack



post #16 of 35
Thread Starter 

Got some more done today.  Adjusted the height of the legs and was able to get the FB welded to the CC.




Question for the highly experienced folks here.  Is there any pros or cons to having one CC door or two.  I'm thinking about two 24" doors seperated by a 3" divider.  The divider will be bolted down but will also be hinged just in case I want to throw on a hole hog sometime.So I could always tie the doors together with the divider and have one 51" door if my heart desires.


post #17 of 35
Thread Starter 

So I decided to go with two 24" doors instead of 1 long one.  Just thought it looked better and had a wider range of functions that way.  I can always tie the doors together and make one big one later if I feel frisky.  Pretty happy with the turnout.  Time to really burn this CC out and start on the reverse flow components.


post #18 of 35
Thread Starter 

And on a side note.  If anyone happens to mix things like welders, power tools, and beer.  You may find yourself admiring the little glowing ball of orange loveliness on the end of your welding gun after burning a bead. Or you may simply forget that its there.  DO NOT under any circumstances touch said orange glowy thing to bare skin either accidental or otherwise.  It makes you say bad words and the neighbors look at you funny.

post #19 of 35
Originally Posted by amcjeeper View Post

... It makes you say bad words and the neighbors look at you funny.

True Dat.

post #20 of 35

Nice work. How did you come up with the 7" to inset the fire box to the cc? i'm just in the process of my build and i see as lot of fb inserted into the cook chamber, is there any benefit to this? Or does it matter if Fb is on the outside? Im sure The Guru will have some input.........Dave? 

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