Octagon SFB - 1st Smoker build - First Fab project

Discussion in 'Side Fire Box' started by jjsul, Sep 16, 2017.

  1. jjsul

    jjsul Newbie

    Hey fine folks,

    Thank you for having me over here at SMF. I'm so glad I found you guys when I did! I bought a welder this spring so I could build stuff for my truck, but my brother-in-law helps us out with the house so much I want to make him a little something. 

    He has a couple friends with smokers and loves to grill, so I figured I could dive into my first big fabrication project and make him something in return. 
    This design is based off of a popular mechanics article (http://www.popularmechanics.com/home/food-drink/how-to/a778/3372796/) and from this fine gentleman, Allen. (https://www.youtube.com/user/underthehood1000) Just like to give credit where its due :thumb1:  

    I was going to build it like the pop mechanics article suggested, but I couldn't find anyone that would / could roll the 10 gauge. Then I saw Allen's videos on making octagon shaped smokers and I figured I'd give that a shot. Again, first big fab project for me, so I'm learning as I go, and the going is slow! 

    All that being said I'm hoping for some advice. I started on this project with less of an understanding of how precise a design could be. Right now I have a smoke chamber with a door and shelf, a firebox that needs one more door, and the stand all welded together. 

    I'm hoping you guys can help a newbie out. I feel a bit in over my head. I've done a fair bit of reading to get an understanding of how to move forward, but I'm still feeling confused and a bit lost! Any help would be greatly appreciated. :77:  

    Here are my questions so far.

    We're going for about 1/3 size firebox to smoke chamber, right?

    Smoke chamber - 5279.885 in3
    firebox - 1912.057 in3

    That makes the firebox 36% of the smoke chamber. Does this seem appropriate?

    Is my throat gigantic at the moment?
    The throat is essentially 80 in2. I think it is supposed to be way smaller, more like 15 in2 according to the smoker builder bbq pit size calculator. I have a piece of plate that I could weld back in and create a smaller throat. Just want to get my calculations and sizing right before I go any further.

    Does the height of the throat opening matter?
    I think I placed the firebox a little high on the smoke chamber. I'm assuming the throat should be at the top of the FB and bottom of the SC? Right now I think the top of the FB is about 8" from the bottom of the SC. When / If I redo the throat, should I have it lower? If I do drop the throat down, that would place it lower than the top of the FB. Is that okay?

    Does grate and smokestack placement matter? 
    Where do I place the rack relative to the throat and smoke stack? I see some smokestacks high up on the SC, and some are lower. 

    ​What materials can I use for the smokestack?
    I read somewhere that I shouldn't use dryer vent material that I could find at Home Depot or Lowes. I'd love to just buy the last few parts and finish this bad boy off. Would 6" be too big for this size smoker? 3" or 4"?

    Do I need baffles and dampers inside the SC or FB?
    I hadn't considered either of these when designing the smoker. Are they necessary? Should I spend the time to plug them in somehow? 

    I think thats about all for the moment. I need to re-read about prepping the inside of the FB and SC and how to season them, but I should be able to handle that on my own. I may come back for some help on the intake size, but this should keep me busy for a little bit.
    Last edited: Sep 16, 2017
  2. ahumadora

    ahumadora Smoking Fanatic

    1./ 36% size for firebox is perfect

    2./ you have welded in all in, so it is a bit late to change without alot of work.     Is it going to be reverse flow or standard?     Just add a  large deflector plate angling down and you are good.

    3./ See above

    4./ Are you running just 1 rack?    Place it at the bottom of the door cutout. 

      Much easier to run a 4" square tube for chimney and use a grinder with cutoff wheel to cut the hole than messing with a round tube.

    Mount it so the chimney draws from below the centerline of the smoker, close to grate height.

    5. Use 4x4" #14  for stack.   probably will be in the 50-60cm above the top of cooker final height  range.

    6./ See # 2  
    jjsul likes this.
  3. jjsul

    jjsul Newbie

    Thank you for the advice!!

    This will be a standard smoker. Not a reverse flow.

    The defector plate would just be a piece of plate to direct the heat downward? A baffle plate would run most of the length of the cook chamber and allow heat to rise through increasingly sized holes. Do I have this right?

    I think one rack will fill up the cook chamber pretty well. So I’ll stick w that unless you all push for a second rack.

    I will either fab up a chimney from the 10 gauge or go out for some 14 if I can find it locally.

    Thanks again. I’ll keep this post updated as I make progress. Might be a little slow over the next couple weeks, we have two wedding coming up. Stay tuned!
  4. ahumadora

    ahumadora Smoking Fanatic

    Yes you are correct on the damper .     Tuning plates would be easier to fab out of 6" flat bar than messing around drilling holes in a deflector plates.

    Also it would be easier to remove for cleaning
  5. jjsul

    jjsul Newbie

    Ok so I got the side door cut and hung and tacked in the trim for the side and top door on the fire box.



    I cut out a piece for the deflector plate. How’s this look?



    The deflector plate sits at the top of the throat and finished about 5” from the bottom of the cook chamber.

    Do I need to calculate the size of the tuning plates? I have about 19” from the edge of the deflector plate to the other side of the cook chamber.
  6. jjsul

    jjsul Newbie

    Cut out and tacked the smoke stack together. Should put me about 20" higher than the top of the smoker in the end.

    I haven't cut the exhaust yet, so I'm just holding it to get a quick photo, hopefully you get the idea.

    Kind of learning as I go, hope it turns out well for my BIL!!


  7. jjsul

    jjsul Newbie

    Do you all think the deflector plate is good as it is? Should I have it drop a bit lower?

    Right now it’s about 5” from the bottom of the cook chamber.
  8. ahumadora

    ahumadora Smoking Fanatic

    Fine where it is. Now the time I just saved you from having to move it, you can use to have a beer :)
    jjsul likes this.
  9. jjsul

    jjsul Newbie

    Haha! Yes, thank you!

    I didn’t even tack it in place.

    Got the smokestack burned in and starting making the frame for the cooking grate this afternoon.


    Edit: I promise you all, it looks almost as crooked in real life as it does in that pic:D
    Last edited: Oct 13, 2017
  10. jjsul

    jjsul Newbie

    I leveled out the front shelf, added expanded steel for the shelf, fabbed up a cooking grate w angle and expanded steel, and fabbed up some spring handles.

    Closing in on it

  11. jjsul

    jjsul Newbie

    Well it’s pretty much all buttoned up. Only thing left is to replace the thermometer. The stem broke off as I was tightening the wing nut!





    Now we just need to fire it up, season, and smoke!
    phathead69 likes this.
  12. phathead69

    phathead69 Smoke Blower

    Newbie here but looks good
    jjsul likes this.

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