Questions about a 120 gallon RF smoker

[BBQJeff]

Other than introducing myself on the "Intro" sub forum, this is my first post regarding the smoker I would like to build. I want to thank everybody in advance for this great site, as I have been reading for days already, and have answered a lot of my previous questions, already, just by reading the wealth of knowledge here.

I have just purchased a 120 gallon propane tank from the local gas provider. The tank has been decommissioned, and they blew a torch hole in the right end bell, and have removed all the plumbing from the 4 ports in the top of the tank.

The tank is 24" diameter, and NOT including the two ellipsed end bells, it is 46" long. I plan on cutting off the right end bell, at least, to make a flat end that transitions to the FB (I'm learning the slang....). I have a million questions, I'm sure, but for now, I'm trying to get my design down so that I can finish purchasing the necessary material needed. The tank is 1/4" thick steel, and I will use 1/4" plate for the FB.

Starting questions:

1. Is there a performance advantage to cutting off the left end bell, too, to make it a flat end, as well? I see them made both ways.

2. If I keep the end bell "as is" in elliptical form, for doing my calculations using the calculator (great tool!) to ascertain volume, do I measure from the cylinder part, which is 46" with the right end bell removed and made flat, or do I add on the length of the left end bell?

3. I want to build a square FB. The door will be on the right end (right end FB, as well). For my tank size, are there optimal FB dimensions that work better than others. I'm a total rookie, and have never used an offset smoker (I have a Weber vertical), so I understand from the calculator that there will be an correct size, volume wise, but not sure what dimensions it should be.

Based on a 48" length and 24" diameter, I need a FB that is 7238.23 square inches. How do I size it correctly, L(?) W(?) & H(?) dimensions that work well. Almost any crazy combination that results in correct math will work, but what is a "good" dimension for a FB of a smoker this size. I plugged in
22" (L) X 20" (W) X 18"(H), and it's 109% of optimal, but I don't know if that is a good working size or not.

OK, I'll stop here, and ask more questions later, rather than writing a book for my first post.

Thanks again for all the future help. I'm really excited about building this, and have THOROUGHLY enjoyed reading over the many builds already posted here.

My name is Jeff, and I have my own YouTube channel, and this build will also be documented there, as well.

[Big T]

That'll be a nice size cooker. 1) I have read a few debates on flat end vs elliptical and some guys believe there's no advantage either way and some believe that the flat end is better because it causes turbulence at the BP gap and they say it's a good thing. I'm not convinced that either is better than the other. 2)There are more calculators at the top of the page that Pete designed, they'll help you figure the exact volume. This is the most important step in designing a pit. If the volume isn't correct then none of the other dimensions will be right and that's the worst mistake that you can make. 3) I like for the FB to be the same width as the CC but that's more my OCD than anything else. You need to think about the size of the fire basket and ash pan and make sure you have enough height for them and what you'll use for fuel. If you cut it yourself it isn't an issue but if you buy it from an individual they normally cut it in the 18''-24'' range (around here) so you need to have room for that. 105%-115% max on the FB so what ever works best in that range.

[Pete Mazz]

2. If I keep the end bell "as is" in elliptical form, for doing my calculations using the calculator (great tool!) to ascertain volume, do I measure from the cylinder part, which is 46" with the right end bell removed and made flat, or do I add on the length of the left end bell?

Use this calc to determine volume if you're going to cut off some of the tank. Put in the overall length and enter the length of any bell end you decide to keep. If you cap off both ends leave them blank or enter zero.

http://planetcalc.com/5185/

[Rodcrafter]

These guys have you headed in the right direction. It's a great thing just knowing them. The only thing I would add is the height of the FB, your size smoker is where the FB can get to be a little bit touchy in my experience. I know BigT likes the width to fit the CC. I like the FB to be tall enough to burn a wood fire without the flame touching the top. I just believe it burns better. You may need to squeeze it in a bit to get that height if you choose to go that way. Play with the calculator for a while until you get it the way you can live with it. It won't cost anything to check it out for a while.


Making memories!

[BBQJeff]

Thanks, guys, for the input. This is going to be a patio smoker, so I will fab a cart for it to roll around on. I know it's going to be heavy. I thought about putting it on a trailer, but I really don't plan on taking this anywhere. We entertain alot, and it's pretty much going to get put on the patio and left there. I'll figure out a cover for it for winter.

Big T, I have the same OCD problem.....I was also thinking that I want the top of the FB to be the exact same width as whatever height I need to mount it to the CC to get the correct FB-CC opening. That will determine at least the width. I'll mess with the two other dimensions to make it function right, so that should take care of that.

I am a professional woodworker by trade, and I have my own sawmill, and also heat my workshop with heat, so I cut all my own firewood here. No problem cutting it down to right size splits. I will be smoking mostly with hickory, maple, and lot of different fruit woods like cherry, apple, etc.....I have a lot of that available to me here, and that should get me going for a while.

Next question.....once I determine the correct mounting height for the FB, should the baffle plate for the RF be at the same height as the top of the firebox?

2. If so, (I saw another build here where a guy used a long plate for the top of the firebox AND the BP), should the BP be angled a little down towards the far end for a drain? I don't want grease just sitting in this smoker, so I was thinking that a little bit of pitch to the drain is a good thing, as long as it doesn't interfere with the smoker's ability to draw correctly. Thoughts?

Once again, I really appreciate the help. And don't worry, I know the rule...................NO PICS< DIDN'T HAPPEN!!!!

I will get some pics of the tank and post them. It's sitting on my trailer, and I need to get it off and clean it before starting to work on it. I bought a 5 lb. box of TSP and some Dawn liquid detergent last night, so I'll be getting after it. My plan is to build the smoker, and afterwards, take it to a soda blaster to clean it up nice before painting the outside and oiling up the inside.

More to come....

[Big T]

I like to mount the BP about an inch above the throat and use a shadow plate for the first 12'' or so and it's mounted at the same height as the throat. It will help absorb the heat right out of the FB and avoid having a hot spot. 2) I mount the BP level from front to back and end to end with a 2'' grease dam and 2'' drain at the BP gap. The majority of the grease and drippings will burn off of the BP while you're cooking and you can scrape the rest of it to the drain.

[temurf]

These folks around here won't steer you wrong.

[BBQJeff]

I like to mount the BP about an inch above the throat and use a shadow plate for the first 12'' or so and it's mounted at the same height as the throat. It will help absorb the heat right out of the FB and avoid having a hot spot. 2) I mount the BP level from front to back and end to end with a 2'' grease dam and 2'' drain at the BP gap. The majority of the grease and drippings will burn off of the BP while you're cooking and you can scrape the rest of it to the drain.

Big T

Thanks for replying. I don't understand what you mean by a "shadow plate." Is there a picture somewhere of this setup? Is this just a short, 12" long "extra" plate (for lack of a better term) welded in just below the BP?

My main reason for choosing a RF smoker is to avoid a hot spot near the FB, so I'm definitely interested in understanding this better.

Thanks.

[Big T]

I'm sure there's a picture somewhere but yes it's just an extra piece of plate that is mounted above the throat with a small air gap to the actual BP. Not everyone uses a shadow plate so it isn't a must have but it certainly helps even out the temps.

[Rodcrafter]

I put one on my last mod to my trailer rig, it does seem to help.

[BBQJeff]

Questions seem to be easier to get noticed 1 or 2 at a time, instead of writing a 3 page essay......I hope you don't mind.

I'm planning on taking a ride to a steel supplier that isn't close, but I have heard tall tales of great prices, so I'm going to make the 90 minute trek. In doing so, I'd like to get everything at once.

1. What is the expanded metal size or name that everybody uses for the grates? I'm planning on just using carbon steel and seasoning them to prevent future rust. I do not have stainless steel welding capabilities (yet) and this is just for personal use.

2. I'm planning on 1 large door for the CC. I'll add a counterweight, only if necessary.

A. Is there a preferred distance in from each end of the CC (left end and right end) to start the door cut?

B. Is using 12:00, aka top dead center, and 3:00 on the CC a good "top and bottom" location for the door, or is there another 'format' that works
better in use? I do plan on making the grates slide out like I've seen here (very nice!) but am not too worried about maximizing an 1" here or
there. At 50" or so for the length of the CC, by 24" in depth, I'm not too worried about running out of rack space.

Thanks again. You guys are great, and my plan is starting to come together. Once I get all the steel here, it's time to start cutting the tank up, and I'm sure I'll have a few questions about that.

[Big T]

It's pretty easy to answer a question or 2 during the day while I'm taking a break from the heat but I don't have time to do a lot of reading and answering so I usually wait until I get home for something like that. 1) 3/4''X9 expanded carbon works fine. 2) I figure out how big the BP gap is going to be and make my first cut at the same spot. I don't have anything above the BP gap so there's no reason for the door to open past the end of the BP, it also helps keep things from getting dropped under the BP. I'm OCD so I make the 2nd cut closest to the FB end the same distance as from the other end. The 2nd cut really only needs to be far enough from the FB that you can put you banding around the edge of the door and the FB doesn't interfere with it. b) I use RC's formula of 1'' past 12:00 to help with water run off and 1'' below 3:00 so that I have a full width rack but you can put the top at 12:00 and the bottom at 3:00 and it'll be fine.

[Squiggle]

In my last build I did a pretty good explanation of the shadow plate, I've put a link below to the thread but crapobucket has just changed it policy on 3rd party hosted pics, so you have to click on the pics to see them to see them all. I'll put a pic below of a couple that should help explain it.

http://www.smokerbuilder.com/forums/vie ... =11&t=5757

This is the shadow plate that extends from the FB



Here you can see the weld marks showing the shadow plate & BP in place.

[Big T]

Thanks Squiggle, I knew I had seen a good explanation recently but I've been racking my brain and couldn't remember who posted it.

[Rodcrafter]

How's that working for you Squiggle? I like mine.


Making memories!

[BBQJeff]

Great pictures, Squiggle! As they say, worth a 1000 words. I get it now.

I found a guy with 100 sheets of expanded metal.....13 gauge 4X8 sheets dirt cheap. That's 3/32" thick.

Is that too thin to make grates from for the smoker? I would also use it for the sides of the firebox, but plan on using heavier rod for the bottom to keep it from warping.

It's cheap, but I don't want to get it if it presents a never ending problem.

Thoughts?

I also found 2 48" X 48" pieces of 3/8" sheet for half price of new! I pick that up next week. It's starting to come together.....

[Squiggle]

I love it when I plan comes together!

How's that working for you Squiggle? I like mine.


Making memories!

Pretty good dude, still getting used to it though.

[Rodcrafter]

It is a lot different than your GF but the Q is really good coming from it. You sure did a good job on it.


Making memories!

[Big T]

You could use 3/32'' for the racks but it'll probably require a few more braces.

[Squiggle]

It is a lot different than your GF but the Q is really good coming from it. You sure did a good job on it.


Making memories!

Thank RC, means a lot coming from you.

[BBQJeff]

Newbie question.....

When you guys weld up the firebox, do you weld just the outside, or do you weld the inside corners, as well?

[Rodcrafter]

I don't weld both, But I do tack both well before just welding away so it doesn't shift due to heat of the welding pass.

[mp4]

My baffle plate is continuous with the top of my fire box. It works, but did warp and tends to burn the drippings near the throat. If I was going to do it again I would design in a shadow plate...for now I'm thinking about placing one above the BP to see if it helps.

[BBQJeff]

I'm going to install a shadow plate at the same extended height as the top of the firebox, with my BP just about 1" above that. I'm still acquiring steel, including picking up two 4'X4' squares of 3/8" plate today.

Thanks for helping me lock down some of the details. I tend to be very.....ok.....extremely OCD on the details of my projects.

Another question.....

What size square tubing do you guys use to make your grates? 1/2", 3/4", 1".....?????

[Squiggle]

I used 25mm angle & then two pieces of 20mm angle welded together(u channel style) to make the runners/slides.