first rf build with a question

Discussion in 'Reverse Flow' started by bigsmoken, Sep 12, 2013.

  1. So I have a question on my own build and I'm sure you pit gurus can answer my question. I pluged my tank dimentions into the pit calculator and it told me that the hole between the cc and fb should be 14 inches at the top of the half moon. My question is this...The propane tank I have to use is kinda short and squat. between the two welds that put the endcaps on it is 27 inches. its 8ft around. with the cooking chamber being that squat is the hole from the fb to the cc going to be sufficient or should it be bigger? I did start another thread but I'm sure I did it on the wrong forum. Any help at all would be appreciated. I want to get my dimentions down before I start the cutting
     
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    bigsmoken, morning and welcome to the forum....  So your smoker is about 30" in diameter and 27" between the welds...  That 's about 22000 cu. in or so guessing at the end caps...  FB should be about  7,100 cu. in. or so....  FB to CC opening should be about 57 sq. in....  Air inlet to the FB should be about 21 sq. in....   Chimney volume should be about 360 cu. in...  FB should be 16x25x18 or so...  Stack should be about 4" ID x 30" above the CC.....  

    FB to CC opening of 57 sq. in.  using 15" as the radius, draw an arc...  measure up from the edge of the arc and measuring up 4" would be the minimum and 5" would be perfect..... Draw a line from the 5" mark to each edge of the arc you drew....    That are is the circumference of you CC and measuring up 5" is the "segment height" of that partial circle you just drew...   That is what I would make the opening under the RF plate....  Looks like a 5" tall "Smile" that is 20 1/4" wide...  Hope that gets it for you.....

    Please take a moment and stop into " /Roll Call/   " and introduce yourself and get a proper welcome from our members.... Also, if you would note your location in your profile, it will help in the future when answering questions about smokin'...   elevation, humidity etc....    

    We're glad you stopped in and joined our group...    Enjoy the long smokey ride....     Dave
     
  3. Thank you so much for that....The only other question I have is should the size at the end of the rf plate be the same as the opening between the cc and fb or should it be a bit smaller.
     
  4. My theory is that by having the end opening smaller than the firebox opening will give you somewhat higher but more even temps

    So it depends on how you like to cook,  if you like the 225 to 250 range, I'd think about making the firebox opening as close to possible as the pit calculator and either go the same size or slightly larger at the end of the plate.  This will be bottle necking your heat at the firebox end so plan on using some kind of doubler or deflector plate to keep from getting a hot spot on that end of the reverse flow plate.

    Me , I tend to say more around 275 to 325 with 300 being ideal. So Ive choked down my last build at the end of the reverse flow plate,...so far the heat has been really even, smoke has bee super clean,  and it seams to have cut down on wood usage, but the temps are running kind of high so I'm waiting for the weather to cool off some before I mess with it any more. Its so hot here now that the temp guage shows 165 with out and fire just sitting in the sun. Its been a really hot summer.
     
  5. So I do like to cook a little on the lower side. So I was planning on making the fb as part of the RP but it does make sense to make a deflector plate. I'll put that into the design thank you. How far out do you think the deflector plate has to be or would doubling up on the firebox by putting the RP on top of it and then doubling up on the metal a little bit out from the FB. how far would I have to go out? And I just cut the place for the FB out and I do have photos but havent put them into the computer yet so I'll post them once I get a chance. Thanks again for all the help.
     
  6. You dont have to go really far, and putting a 2nd plate on the top of the firebox with a small air gap is the way I prefer to go,... just imagine how the air will flow from the firebox into the cooking chamber....then imagine where it will hit the reverse flow plate and have to change direction in order to flow horizontally under the plate....That will be the exact area you want the deflector plate to protect...

    also, by locating your vents properly in the firebox can help you keep a smoother (straighter) flow of air through the firebox and under the reverse flow plate
     
  7. Just remember, anywhere the air flow has to make a turn will create a hot spot, dont try to eliminate , but rather take advantage of those hot spots and redirect them,
     
  8. with the whole redirect theme do you think that fins on the underside of the rf plate would help that or would that be just unneeded overkill
     
  9. Ive though about and had quite a few discussions about fins under the reverse flow plate.  My thoughts right now are that fins ( if done correctly)  would absorb more heat from the area under the reverse flow plate and transfer it up through the plate. The increased mass would help hold in the heat., and they could possible help the cooker to be more efficient.

    But I have not had to use them. Choking down the opening at the end of the reverse flow plate and installing the deflector plate at the firebox opening has already accomplished that, and on my most recent, it may have done it too well ( I'm still playing with it and its been way to hot here to do any serious testing anyway) .

    I would think about fins on a really large build, or to correct issues on an odd ball shaped build, but honestly don't feel its necessary on most of the build sizes I see on here.

    And remember, adding mass with metal under the reverse flow plate reduces air volume, so even though the the fins will absorb more heat, the air will be forced to move faster through that portion of the cooker (unless you raise the plate to add more volume to that area) which in turn could cause other issues.
     
  10. Yeah I was thinking the same thing well even without it I've gotten all the info I need to make an awesome smoker.
     
  11. alaska

    alaska Meat Mopper

    Hello from Alaska..... I saw you are also building a RF and so am I. Cannon City Hmmmm.... Same stomping grounds, I went to college in Pueblo. Jerome
     
  12. the funny thing is that I would love to live in Alaska. I assume you smoke a lot of game meat up there? I smoked some bear roasts not to long ago and they came out amazing....although I've never seen a meat so eager to take on as much smoke as the bear did.
     
  13. alaska

    alaska Meat Mopper

    The only smoking I have done is for our salmon that we send out to family. We have always used a 3X5 wooden box but have always wanted to do more then I found this site so now I'm stuck.... Picking up some diamond plate now that I will use for my box...
     
  14. diamond plate....dang fancy dancy. I'd love to use some of that. put some bling on the new grill already dubbed "Big Mac". lol Its just a bit on the expensive side. Hell metal in general is on the expensive side. I want to use this grill for some competitions so I'm giving myself about a year to do it. I know its a long time but its mostly a money thing and if you have the time you aint got the money and when you have the money you aint got the time. How much would you charge to send me some smoked salmon? I've always wanted to go catch one send it to myself and smoke it here.
     

  15. yeah I hamed it up for the camera....gotta make it good for the scrapbook


    after the cut still with water in it. I had to fill it while it was standing then push it over


    tank after cut...as you can see its pretty squat
     
  16. sholmes

    sholmes Smoke Blower

    I am getting ready to cut my cc door and do not have a plazma.  How thick was your tank and how did it cut with the sawzall?  My tank is also pretty short and fat.  I think it should make for some nice deep racks.

    Looks good so far!
     
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    An angle grinder with the "thin" cut off blade works well...     get a several cut off blades to make sure you can complete the job.....
     
  18. dave is right on the money...I used the sawzall to cut at first because to be honest I was a bit nervous about the sparks.. it was a diablo blade short and made for metal demo. 3 bucks at home depo...after I was convinced it wasent gonna blow up on me I switched to the thin metal cutters. It took me about three of them to finish the job but it cut easier and the sawzall blade actually dulled and didnt want to cut anymore after a quarter of the job, I just ended up using it on the corners though just to give me better cuts without making a cross cut. but i'll def be using the wheels for the door and leaving the corners intact untill I can get the inch metal around the door and the hinges on first.
     
  19. smokenado

    smokenado Smoke Blower

    Looks like some thick steel can't wait to see the finished smoker!
     
  20. its about 1/4 inch thick and for the moment its on hold the rain here has been crazy.
     

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