500gal lp tank offset smoker project

Discussion in 'Side Fire Box' started by trd22, Feb 14, 2013.

  1.        Currently I am in the process of fabricating my first smoker. I have always dreamed of building my own monstrous smoker but have never had the time to. Luckily for me I'm a student in a welding program and one of the courses is a fabrication class were you have to design and build your own project [​IMG]. For me there was no question in what I was going to build, a smoker out of a 500 gallon LP tank. For those wondering, yes I may have no smoker building knowledge but I have been welding/ fabricating for over 6 years now in plants and structural steel; holding certifications in various processes.

           The first step of making this a reality was to spend countless hours brainstorming and looking threw forums at pictures to generate ideas. The next step was to take these ideas and put them into plans. I used Auto-desk Inventor to help that along by creating a 3-D model of my design. I created just the standard shell so i could use these dimensions to build the trailer frame, firebox, and cut the doors. Once past this stage i would custom fab the grates, vents, handles,etc... and then just add them into my drawling later.

            From my dimensions I calculated that i would need 2- 2"x4"x24' 11 gage wall tubing for the frame and 1- 60"x120"x1/4" mild steel plate to make the firebox. I picked up a 500 gal LP tank from a local scrap yard for a mere 15 cents a pound.

           Once my materials arrived I decided I would start with the trailer frame first to get a base for what was to come. I managed to make all but two cuts on a horizontal band saw. The other two were 160 degree cuts for the tubes that meet at the neck (A frame) which I tacked sheet metal alongside the desired cut path and pushed it threw a vertical band saw. When all of my pieces were cut I set them all out on a layout table clamped them down and squared them all out.

           From here I proceeded to make end caps for the two tubes at the back of the trailer and TIG weld them. Next I proceeded to MIG tack all outside corners of the frame to prevent distortion. Once tacked and measurement checked diagonally (corner to corner) I tacked all inside corners. After tacking inside and outside corners I TIG welded the top side of the frame cross supports and neck; I then flipped the frame and repeated. Finally I MIG welded all inside fillets, outside fillets.

             Before completing this step I called a local trailer parts distributor told them the dimensions of my frame 44" wide and weight load details. They recommended a single 2000lb axle, however knowing my actual weight i decided to go with a tandem axle to even weight. The bad deal with this was on new trailers every wheel has to have brakes in my state. This being said, they recommended 3500lb axles because the smaller brakes of the 2000lb would make it more costly as odd as that is. The day after finishing the frame my kit arrived.

             The kit came with dimensions of how to space the leaf spring hangers and basic instructions; for mine it was 27.5" center to center of hanger. I laid out where i wanted to place each hanger (spaced to specs) and proceeded to weld them to the frame.

           The next step was packing bearing and attaching the brakes/ hubs. Once assembled I then decided to run spring over for more ground clearance to account for the firebox hanging off the back; After tightening up the U bolts I threw the wheels on.

          The day after getting my trailer on wheels I had to postpone finishing it because my 1/4" plate had arrived. This was the best/ easiest part for me due to the fact our school is lucky enough to have a cnc plasma cutting table, which allowed me to transfer my firebox drawings and sit while they were cut for me [​IMG]. After being cut I set my pieces out, started with bottom and worked my way around tacking each piece a minimum of 4 places per outside corner squaring it as I went. Once all tacked I proceeded to flux core (FCAW) all outside corners in the horizontal position flipping the box as I went (with some help from guy on the right).

    Rolling any sharp edges

          After finishing the welding/ flap wheeling on the firebox I redirected my attention towards the trailer. The next step was to cut the support feet for my tank, I decided to cut the factory ones off and make my own for looks and more firebox ground clearance. I cut them at 7 7/16ths", for the tank to be cradled I made a template to cut the needed radius of the tank (37" diameter) in them with a plasma cutter. After cutting the radius's I laid them out 10" from center of trailer to center of foot to match the tank exactly. Once laid out I tacked opposite corners of each foot and MIG welded them to the frame.

    Firebox setting behind for reference size

           I am sorry for not starting this build from day one but as a time reference this the third week of the build, 3 lab periods a week for 3hrs each. Given that there is total of around 27hrs of physical work into this project as of now. I will hopefully be setting the tank on by Monday or Wednesday next week. Feel free to ask questions or give input. I will do my best to keep you all updated, thanks!

    New progress on build..........................

          I was able to get my tank into the lab today.... I set the tank on pipe stands to cut the original feet off

    After cutting the feet off I moved it outside... wheeled the trailer out and proceeded to set the tank on....Once set wheeled it back in flushed the cut up with the back of the trailer frame and rotated the take so the bottom tank weld seam was dead center on the bottom. After lining it up I tacked the tank to the trailer feet.

    Here are the current pictures


    New progress

    After squaring the back cut to the trailer back I three pass flux core welded the tank to the trailer feet.

    After welding the tank to the trailer.... I laid out the cut where the firebox would meet the tank..... I tacked two pieces of filler rod along the line to keep the cut as straight as possible....Then plasma cut the sliver off.

    After making the notch completely square it was time to mate the firebox..... For this step I used a forklift to pick up the firebox and line it up with the tank/ trailer..... Once lined up I flux cored the firebox to the tank/ trailer.

    After welding the firebox on I laid out the cooking chamber door cuts using a pipe tape and a 8ft straight edge... 1.5in from weld, 37.5in wide x 25in circumference tall, 4.25in between doors, 37.5in wide x 25in circumference tall, 1.5in from weld.

    The doors will hopefully be plasma cut this afternoon......


    Todays progress...... plasma cut doors out...... beginning to take form

    Last edited: Mar 4, 2013
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    TRD, morning and welcome to the forum.....   First, you make it look sooooooo easy to build a smoker and trailer... I'm jealous.... So, tell me.... Just how easy is it to have the computers do all the layout, cutting, transferring of dimensions etc....  The project looks great....  Nice job....  

    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
    Last edited: Feb 14, 2013
  3. 05sprcrw

    05sprcrw Smoking Fanatic

    Looking good so far! I would sure love to have one of those modular fixture tables in my home shop.
  4. boykjo

    boykjo Sausage maker Staff Member Moderator Group Lead OTBS Member

    Nice build TRD and welcome to SMF... Were glad to have you aboard...... I woiuld like to make a suggestion. I would want to go with a reverse flow plate and move your stack to the other side. Reverse flow is the way to go for even cooking temps and heat retension through out the cooking chamber...

    Here are some reverse flow  builds




    Just a thought

    Last edited: Feb 14, 2013
  5. I have to agree with Joe on the reverse flow. Take a look and consider it.

    This makes me want to go back to school. Being able to work in that nice shop and play with high dollar tools would be a lot of fun. I would have to learn how to weld on metal that was not covered in paint, rust, and dirt though.

     Keep up the good work and keep us posted on your progress. 
  6. Dave- Thank you! I will start off by saying yes it sounds easy, but there were many hours spent in CAD learning and drawing [​IMG]. However, once the build started it was amazing having exact measurements to follow as blueprints, and equipment to cut the firebox pannels for me. When normally fabricating at home pieces don't always lineup how I want them, the 3-D drawling eliminated all of that and every piece fits like a glove! I would say my skills are above average, but I have to give a lot of credit to the equipment available to me at school that no one would normally have laying around home. 
  7. Thank you! I feel the pain, it sure helps keeping things square while welding and speeds up the layout process.
  8. boykjo- Thank you I appreciate that advice and do understand the more even cooking of a reverse flow, but unfortunately my tank had an existing holes cut in it and I would have to patch it to make reverse flow. Which I really don't wanna mess with and end up cobbling the tank up.  [​IMG]
  9. Thank you, I really was wanting to do the reverse flow but with the existing holes it just makes more sense to build the regular offset.

    Exactly! I was lucky I still had the chance to. I was so used to doing things the old way between plants and structural steel welding it was weird to me being in a lab and having top of the line everything at my disposal, but very very nice!
  10. boykjo

    boykjo Sausage maker Staff Member Moderator Group Lead OTBS Member

    What holes? can you explain..... I can see your fabrication skills are above average but experience will come with age... Just ask us old guys..... yeah I'm talking about you Dave.....LOL
  11. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    My computer, when growing up, was a Dietzgen Slide Rule... Exactly like this one......

  12. I don't have a picture right now.... but either the person who took the tank to the scrap yard or the scrap yard cut two holes in the tank.. one in each end cap just ouside the weld.... and on opossite sides of the tank (one top, one bottom)...... almost as if someone was preping it for a standard offset. I personally just don't feel like messing with making a 1/4" thick patch for it and would rather just build the standard offset.
  13. z
    Last edited: Oct 16, 2013
  14. z
    Last edited: Oct 16, 2013
  15. terrymn

    terrymn Smoke Blower

    That thing is gorgeous, TRD - can't wait to see the finished product, great job!!!
  16. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    TRD, evening.... I'm going to join in on the argument for a reverse flow...  In my signature line are links to calculators, which I'm sure you already have access to.  What is 4 hours more work in that beauty of a smoker you are building...  You will kick yourself for not making it a RF smoker after a few months of use....  Just sayin'....  If you do use the calculator and make a reverse flow, I suggest you take the area of the cook chamber to firebox opening and multiply it by 1.5 for the area under the RF plate... that will help compensate for friction loss... same calc. at the end of the RF plate where the heat/smoke/air flow takes a 180 heading for the exhaust stack....   

    Keep us up to date on the build....  It will be AWESOME...     

    Last edited: Feb 14, 2013
  17. TRD you are doing an excellent job!!! I have built many reverse flow smokers out of propane tanks, patching a hole is not hard at all I always have to patch them where I cut out the fittings. The trailer frame looks just like some of my builds!!!! I always use 2by3 or 2by4 tubing 11gauge and 14 gauge. An offset is fine but I think in the end you will wish you had went reverse flow, but to each his on. Again I commend you on the quality of your work and the pride you are takin. It is the only way to build ANYTHING!!!!!!!!!!!!!!!!!!!!
    Last edited: Feb 14, 2013
  18. Dave- Thank you for that info! I'm starting to come around to the idea...Like you said whats 4 more hrs?..It'd maybe take 2 maximum.. i'll play around with it a little more.... one question I have is my firebox to chamber opening being too high into the tank (almost below dead center) for a RF smoker? Would the baffle run at the height of my chamber opening?

    And another hesitation is that I have seen the offset I based this design off of and it seemed to cook evenly... it is a pretty sharp rig

  19. Thank you! Do you use 1/4" patching your holes? How I look at it is if your going to build something do it right!!!!.....If not then don't bother wasting your time!!!! I take pride in everything I make and know it will last the test of time
  20. TRd I use 3/16 in all actuality most propane tanks are 3/16 i should know I currently have over 100 on hand. Do not flip out and try and make a full penetration weld it is not needed. I usually cut mine a little small and tack a welding rod to it and fit it in, you want some penetration because i would grind near flush then flapper wheel the rest.. Nobody will ever know and it want matter anyway.If you have a big patch whop a little raduis in it with a hammer and vice. Want take much whooping either!!!!

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