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bigfork

bigfork

Newbie
Original poster
Jan 9, 2013
13
12
Kalispell, MT, 15k w/ 5 craft breweries :)
Hi there ya'll! 

I've posted before about a UDS I built a while ago.  I love it...but now it's time for the RF!  I've been hitting up our local green malls (rural dumpster sites) and sourced a couple of main parts, the CC and FB.  I'd love to shoot the number out there and get an "ok" or a "you're in the ball park" response. I've got a couple of questions to boot.

Here's the skinny:

CC  32x20=10,048 cu in

--it's an nice water tank with slightly domed ends, may be a 3" crown on the dome

FB  19x15=3,357 cu in

--It's a  long propane tank cut down to size, it will have one slightly domed end (factory) and one cut off/flat end

Rec air inlet=10.07 sq in

FB to CC opening=26.86 sq in (I understand the "if round" and "if half moon")

I guess my question is one of order-of-process.  The water tank CC was domed on one end and the same dome was inverted on the other end.  I have cut the inverted end off and I am going to spin it around with a ID OD relationship that works great.  It will looked domed on both ends wit an added seam.   While the end is off, should I get my RF plate installed?   I haven't totally worked out the FB to CC connection and shape (round or half moon).  Do I need to determine this before I install the RF plate in order to maximize CC volume and get the best out of my shelf space?  I was hoping to stuff 3 shelves into the  20" space; the middle being the biggest and close to center of cylinder. 

I recently built a small cabin stove out of a 4gal propane tank.  I found a laser very helpful to "draw" both level and plum lines on the domed end.  There's really no other way to get an exact mitered square box of angle iron to "seat" into a domed end of a tank.   On the coming build, I'm going to use the laser to establish my FB to CC cut lines, my RF plate location, and the location of the shelves in the CC.

I have another question that might be a bit silly.  Do folks ever bridge the FB to CC relationship with a short stack (say 4") of pipe instead of the scribe-like overlapping forms?  One would still have to maintain the proper sq in  from one to the other.  I had thoughts of making the small propane stove (mentioned in the previous paragraph) a FB for a smaller smoker, but didn't want to commit to cutting a half moon out of the back of the dome in the case I want to use it for a garage stove instead.  

Thanks for the help!  I'll get some pics rolling once I'm deeper into the project.

I've really learned an immense amount just sponging around on this site.  The pit calculator is a dandy invention as well!  Kudos to whoever got that going!

thanks again!, bones
 
bigfork said:
 Do folks ever bridge the FB to CC relationship with a short stack (say 4") of pipe instead of the scribe-like overlapping forms? 
Click to expand...
Yes, some do. It is a design feature on DP pits (not a traditional offset), and I have seen offsets fed by cast iron wood stoves via pipe.

Just about anything can be made to work. The direct connection may be more efficient, but it is not the only way. Do it your way and enjoy the ride!
 
 
I have another question that might be a bit silly. Do folks ever bridge the FB to CC relationship with a short stack (say 4") of pipe instead of the scribe-like overlapping forms? One would still have to maintain the proper sq in from one to the other. I had thoughts of making the small propane stove (mentioned in the previous paragraph)
Click to expand...
On a large pit, I do not recommend it due to heat loss making it less efficient, and harder to recover, maintain temps.

But yours is a fairly small build, and your wanting multiple racks. For what your wanting to do, I would recommend something slightly different, maybe something like.....

900x900px-LL-cfb7d0f5_likeso.png
 
Thanks for the advice!

I decided to overlap the FB and CC in the typical elipse scribe relationship instead of the short stack idea previously mentioned.  My CC is retired water pressure tank whose walls are not the thickest.  I think the nestled FB will help with potential heat loss. 

The build is kick'in butt.  I've got the 1/4" back welded onto the FB to close it off with the proper FB to CC hole which is a 5.85" diameter circle cut into the box's back.  The  CC is scribed into the FB to the depth of the 5.85" circle leaving enough room for 3, maybe 4 racks. 

I do have a question on the next step though...

while the pressure tank is opened on one end and before I weld the FB to the CC, it's time to install the RF plate.  My CC is slightly domed so I'm going to have to use a piece of cardboard to get the scribe of the dome from the outside, and then map that to the RF plate.  I'm going to use a tapering wooden shim jig to establish a gentle 1/4" slope from the sides of CC towards the center where a 1" angle iron will functioning as the drain channel.  Am I crazy or do advanced builders add an additional slight slope in the RF plate from one end to the other?  The low end being where the drain is as well as the location where the smoke 'reverses' and returns towards the stack.  The idea of a tapering RF plate with a full length  slope sounds like a bit of a tricky deal.  I suppose if the RF plate had a slight 'dam' on the end where the reverse is, juice or whatever would find it's way towards the drain...if it was sitting perfectly level.  It seems like tipping the RF plate towards the 'reverse' end would constrict smoke flow?  Can I tip it just 1/2" in 33" from one  end to the other without to much flow constriction around the return?  Hmmm

Also, do I ledger the RF plate (with a tight scribe) so it's removable?

Do I just tack it every 8 inches or so with a relatively tight scribe all around, or do I go for tight to the walls and full weld?

I promise to get some pics up. 

This forum is amazing!  I really appreciate all the pointers!  The least I can do is get some pics up.  They speak more than words.

thanks
 
Ive done removable pans that drain to one end.....

900x900px-LL-ff17fc92_waterpan.png


Welded in pans that drain to the center...

900x900px-LL-0e65a7f9_reverseplate.png


And just simple flat plates,

I like the "drain the the center" ones the best and the three I have in progress right now are all to be "drain to center" and non removable.

Now take head...one point that is not talked about much on here is the "hot spot" you get at the beginning of the reverse flow plate, where the heat rises from the firebox and "turns" where it hits the reverse flow plate.    You will need to engineer around this either by air flow or deflector sheild under the reverse flow plate. The thinner the steel, the more this problem is amplified.
 
I wrestled with the geometry of a sloped RF plate (away from the FB) and having to taper the plate for a good fit.  I am planning on trying something a bit different with a sloped center drain.  I'll try to describe it, don't have any pictures or drawings right now. 

I will split my RF plate down the center to gently slope it to a center drain,  I wanted to keep it straight across to keep the air flow unrestricted.   My center drain will be made from 2" square tube or 1 3/4" U channel.   This is material I have on hand so the price it right.  I plan on cutting this channel in a long trianglular shape so it provides the downward slope towoard the drain.  Drain is located opposite side of FB.  This should put most of the welds at about 90 degree and eliminate the need to taper the RF plate. 

I'll get some pictures up once I get some more progress on my build. 

I have read that other guys use their trailer tongue jacks to tweak air flow and get the drains going downhill.

RG
 
trying to match the slope and curvature of a tank for a angled reverse flow plate is a b***h.

Its much easier to keep it level at the top of the plate edges and then divide the plate up to get your slope, or roll the plate like I did in #19.

Here are the two designs I have tried that I like the best, the first drains to the end, the 2nd to the center. Use a piece of foam board to fit the pieces first, then trace them onto the plate your going to cut.

eb96d782_two.png
 
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