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# 20gal build Finially DONE - Page 4

That is interesting. I will look into those pics and see how it works.

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My biggest hang up now is the exhaust.  I was going to go with a 2.5 inch pipe from the local auto store. I was thinking of making it shorter and going with 3in. Does 2.5 inch seem too small or as long as I keep the correct volume does it really matter. I used the chart Dave posted and I am getting with a 3in pipe I will be around 17 to 20 inches with a 2.5 I will be between 20 and 24. I am wondering if I did the math correct because I get a smaller number than Dave listed earlier.  Dave you add on a few inches due to air drag correct?  If so this may be how I get a smaller number.

Edit: I will be around 4 inches down the side of the cooking chamber. I will have side mount smoke stack just as seen in Daves Picture. So I am thinking a 3 inch pipe 20 inches long plus another 4 inches to make up how low it would be mounted down the side. That gives me a 3in 24 inch long exhaust pipe. I do not want to be too long and have it sweat back into the Cooking Chamber.

Edited by regularjoe - 1/18/14 at 7:21am
Quote:
Originally Posted by DaveOmak

Tank = 4620 ci
FB = 1525 ci +++++MINIMUM
FB air inlet 6 Sq in .... additional inlet across from the FB/CC opening about 3 sq in....
FB/CC opening = 20 sq in (24)
Area under the RF plate = 20 sq in (24)
Exh stack vol = 80 cu in. = 2.5" ID x 24" above the CC

Some of the above numbers allow for a correction in friction loss....

FB/CC opening

7" radius semi circle 4" high will give you 24 sq in under the RF plate and FB CC opening... which is good...

That also translates to a RF plate 11.5" wide and it should be welded to the top of the FB and stop short of the weld on the other end of the CC to allow for adequate air/smoke flow around the RF plate....
Cut into the CC at the height of the RF plate when you put it inside to check fitment... I would slide the FB into the CC to just past the weld so the RF plate is in the straight section of the CC....
An easy way to get the FB to fit to the CC is... set the RF plate into the CC.... project a line from the RF plate to the conical end of the tank... cut the end on that line.... slide the FB into the newly cut opening.... scribe the bottom of the CC onto the FB and cut out that part circle... while all this is happening, check the RF plate fitment to the top of the FB... If the FB is too high, no problem.. scribe the RF plate to the FB for height and scribe the CC to the FB for the cut out....
Cut out the part circle on the FB and check all the fits.... install drains etc. and go for it...

The above is what I might do to your tank etc..... after listening to all the folks here and tweaking numbers so the smoker works better...

... click on pic to enlarge ...

I seen Dave rounded up some numbers and said it was due to friction loss. So am I on the right track with my math. Feldons calculator is way different as expected. What is your opinion Dave? Thanks for the help.

You are right, Dave adds to allow for friction loss. His experience trumps the calculator, stay with the 80 cu-in and use either 2.5 or 3, adjust the length accordingly and you will be fine.

Joe, morning..... Volume of the exhaust is not necessarily the definitive criteria.... Height plays a differential pressure role in making the exhaust work properly.... Height is what makes a chimney work in a fireplace.... there is a balance that must be achieved....

Dave

Cooking it out again.

Hit it with a wire brush on a grinder inside and out

Finally nice and shiny. Boy this was a dirty job.

Finally nice and shiny. Boy this was a dirty job. I still want to go over it with some dish soap or something.

Test fit the lower cooking rack.

Got the firebox welded up. We were not able to put the back on because it was cut a half inch out of square. The cutout for the fb/cc was a nice fit too. My metal guy is going to recut it and I hope to hit it again next Saturday.
Hi Regularjoe. I was trying to keep up with all the conversation. I saw one part about you were thinking about clamps to hold the doors shut. I saw and used these on my build. They are destaco p/n 202 toggle clamps in stainless. They have a 200lbs hold down. They are really small and powerful. I found mine on eBay. You can find larger ones at harbor freight if you have one near by. Or order them online. I hope this helps.
Thanks. I actually have four of those ready to go if I need them. It looks like I will be taking this weekend off.

Got the rear on the firebox and welded it on.

Rolled it around on the stand to weld underneath.

Drain install

Got the RF plates installed. I kinda wish I would of made the sides a little bigger so it does overflow in not on even ground.

I need to know how important it is to have the breather straight across the FB/CC opening? Once I put the flange on the door I lost the space that I was going to use to put on a 1in by 4in breather above the door. I have where the flange overlaps marked with a white line. Can it just go on the front of the fire box/ smoker? If it is best above the door I will just add in a piece of steel plate and cut the door down some. I did not finish weld my flange on because I had a feeling I will need to shrink the door down. My breather for the bottom of the firebox will be on the front of the box.

I got the hole cut out and the sides cut for the plenum. I will be using a 3in pipe and will have to try to figure out how long to make it. My plenum box will be 4.5 x 4.5 on the top and the rear is 4.5 x 4 then it will angle down to the box from there. I am guessing to start with a 24in long pipe and go from there.

My neighbor took in a beef and he did not like how much fat was on the beef short ribs so he gave them to me to see if I would like to smoke them. 15lbs. I did some beef ribs before but I don't think they were short ribs. I did some reading on them in the beef section and will try them once I finish the smoker.

Picked up a set of used wheels for the smoker. Two swivel and two are stationary. ,The wheels hold air and are about 6 inches. I think they will go trough my yard pretty good. I will have a handle on the front that can also be hooked up to the tractor. Also brought home 8 pieces of 2x2x24 square tube and 4 30 inches pieces for the frame work.  It may be a little overkill but it was free scrap we had at work.

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