This Instructable will show you how to build the ultimate backyard barbecue pit. This trailer mounted smoker was built using an old 250 gallon propane tank and is the perfect size large parties, catering, competitions, or whole-hog barbecue. However, the design principles and manufacturing process could be easily applied to any size pit. My goal was to make a simple, traditional offset smoker that was very fuel efficient and maximized airflow in order to maintain a clean burning fire. The design of this smoker was largely inspired by the smokers used at Franklin Barbecue in Austin, TX considered by many to be the best barbecue in the country. While this is a large project, it can easily be completed in a backyard or garage a few basic tools.

Step 1: Design

This first major design choice you must make when building a smoker is what you're going to make the cooking chamber out of. For this build I used an old 250 gallon propane tank because they're made of thick 1/4" steel and relatively easy to find but any other kind of steel tank or pipe will work just fine.

For the firebox I used 1/4" plate steel but also included 1.5" of ceramic insulation to help retain heat and improve fuel efficiency. I would recommend using at least 3/16" steel for the firebox as anything lighter will loose heat quickly causing you to burn more fuel and will warp and burn out over time. The insulation is not necessary but definitely improves the performance of the smoker.

A good rule of thumb for sizing your firebox is to make it roughly 1/3 of the volume of your cook chamber in order to provide enough heat for you cooker. This calculator is a wonderful resource to use when thinking through your design and deciding on the different dimensions.

For this smoker I used a much larger and taller smokestack than is traditionally recommended in order to maximize airflow through the cooker and ensure a clean burning fire. When a smokestack is too short it doesn't create enough draft causing incomplete combustion in your firebox which leads to thick smoke and bitter tasting meat. I'd recommend a smokestack that is 6" - 10" in diameter. You'll also notice that the smokestack draws from the side of the cook chamber rather than the top like many other cookers. This is to ensure that the hot air and smoke flows directly across the grates where the meat is instead of pooling in the top of the cook chamber.

Step 2: Tools and Materials

Tools

MIG Welder
Angle Grinder
Cut off wheels (lots of them!)
Abrasive wheels
Clamps

Optional Tools

Oxy-Acetylene Torch
Metal Cutting Chop Saw
Metal Cutting Circular Saw
Jig Saw
Welder's Magnets

Materials

250 Gallon Propane Tank (cook chamber)
1/4" Steel Plate (firebox)
Square Tubing (firebox and cooking grates)
Ceramic Insulation (firebox)
Expanded Metal (cooking grates)
Angle Iron (cooking grate brackets)
Round Stock (hinges and handles)
Tubing (hinges and handles)
Flat Bar Stock (door seals)
Large pipe (smokestack)
Thermometer

Step 3: Cutting the Doors

IMPORTANT: Cutting into a propane tank can be very dangerous if not done safely so I'd recommend having a professional clean and cut the tank for your if you're not comfortable doing so. A good method for cutting into a propane tank safely is to fill the entire tank with water and dish soap in order to remove any residual propane and safely cut into the tank.

The first step is to mark out where your doors are going to be. I like to measure a quarter of the way around the tank for the bottom of the door and then have the top of the door a few inches from the top of the tank. Use a level and soft tape to ensure your lines are straight. If you're building a smoker for cooking lots of whole hogs you may consider having just one door instead of two. However, when you only have one door you have a greater risk of distortion when you cut out the door. All the internal stresses in the steel are released when the door is cut from the rest of the tank and the doors can flatten or distort heavily making fitting them much trickier. This is why I recommend two doors instead of one. It is also a good idea to weld your hinges onto the door before you finish cutting it out so the door remains in alignment.

There are many different types of hinges you can buy but you can just as easily make your own using some tubing and round stock. If you're making your own hinges you can cut some tubing and round stock to length using an angle grinder and a cut off wheel or a metal cutting chop saw if you have one. First, tack weld the tube just above where you will cut out your door.

Next, make the hinges that will slide into the tube by bending some round stock in a vice. I was able to easily bend the round stock in a vice using a piece of tube to increase the the bending force but you could also use a torch to heat the material and make the bending easier. I used a simple jig to create a relief bend in the hinges to leave room for the door seal at the top of the door.

Now that you've got your hinges ready you can start to cut out the doors but be sure not to cut out the whole door until you've got your hinges fully welded on. Cut along the lines you marked with an angle grinder and a cut off wheel. If the tank still full of water this part can get quite messy!

Once you've got the doors mostly cut out you're ready to weld on your hinges. Simply slide the L shaped round bar pieces into the tube and weld them onto the door. Once your done welding the hinges you can finish cutting out the doors.

Step 4: Door Handles

You can make door handles in much the same way you made the hinges. I bent two more pieces of round stock and fit a tube in between them in order to make handles. These types of handles are nice because the tube rotates on the round bars as you lift the door which makes opening the doors much easier. However, anything you weld onto the door that you can grab will suffice as a handle.

Step 5: Door Seals

While not entirely necessary, adding trim along the doors helps to keep smoke and heat from leaking out the cracks while you're cooking. I used 1" x 1/8" flat stock for these door seals and progressively clamped and welded down the door to match the curvature. Use a flexible tape measure to calculate the length of the curves or just leave the piece long and trim it once it's welded in place.

Step 6: Smokestack

Now that you've got your doors finished it's time to start on the smokestack. The easiest way to attack a smokestack is to cut a hole in the top of the cook chamber and weld a pipe to it. However, as I mentioned before, you will get much better results by moving your smokestack to be in-line with your cooking grates at the middle of the cook chamber. For the smokestack I'd recommend finding a large steel pipe (5" - 10" in diameter) and leaving it long as you can always cut it down to length once you know how your cooker performs. It is much harder to make a stack taller than it is to shorten one.

First, mark on the tank where you want the opening for the smokestack to be. I marked a centerline and went a few inches above and below it to get a big enough opening. You also want the opening to be wide enough so that it collects air from the whole width of the smoker and not just the center. Once you've got your opening marked you can cut it out with the angle grinder.

Next you'll want to cut a notch into your pipe that is the same height as your opening. Then you'll cut out pieces to form the rest of the smoke collection. For these pieces you can use 1/8" sheet or match whatever wall thickness your pipe is. You can use a piece of cardboard as a template to get the shape to match the curvature of the cook chamber and the pipe. I cut these pieces out with a jig saw but you could also use a cut off wheel on the grinder if you don't have a jig saw.

Once you've got all your pieces cut out you're ready to weld them onto the tank, starting with the bottom plate, the pipe, then the side pieces and top. Make sure your bottom plate is welded in well enough to support the weight of the tall smokestack.

Step 7: Cooking Grates

The next step is to make the cooking grates. There are many different methods for creating a cooking surface but I like to keep it simple with with two removable cooking grates located in-line with the bottom of the doors. If you want to increase your cooking surface you could easily add more shelves above the bottom ones. The easiest way to build a cooking surface would be to weld a piece of expanded metal directly to some supports in the tank but making your grates removable makes cleaning much easier and you'll thank yourself later.

For these cooking grates I used expanded steel (#9 thickness and ¾" opening size), ¾" x ⅛" angle iron, and ¾" square tubing.

First you'll want to weld in some angle iron into the cook chamber to support the grates. Make sure these supports are parallel to each other and perpendicular to the door so your grates will fit properly.

The next step is to measure size of your grates and and cut out your expanded metal and square tubing for the frame. Make a rectangular frame with the square tubing to support the expanded metal then weld it all together. Make sure to jump around with your welds on the expanded metal so you give the metal time to cool and don't cause any warping in the grate.

Once you've got your expanded metal welded on you're ready to install the grates. There is a small gap between the two doors which I later welded a small piece of expanded directly to the angle iron in order to increase my cooking area.

Step 8: Building the Firebox

Now that you've got the main chamber complete it's time to build the firebox. You want your firebox to be roughly ⅓ of the volume of your main cook chamber and should preferably be made of ¼" steel. If you use thinner steel you will loose a lot of heat out of the firebox causing you to burn more fuel and risk warping over time. I also chose to insulate my firebox with a layer of ceramic insulation of the top and sides to help with heat retention and fuel efficiency.

Finding a large piece of steel pipe or a smaller fuel tank is the easiest way to build a firebox but I chose to fabricate my own box so I could insulate it and get the exact size I wanted. For this firebox I used ¼" thick steel plate for the interior box and 14 gauge steel for the exterior skin covering the insulation.

The first step is to cut all the sides of your box. You can have a steel supplier do this for you to make it easier but you could also cut it yourself using a metal cutting circular saw or a cutting torch. Once you've got all the sides ready you can tack weld all the sides together and then run welds along every edge. Be sure not to but the edges completely together so that you have a gap you can fill in with your welds in order to achieve a stronger joint.

Once you've got the box all welded up you can cut out the opening for the door and the connection to the cook chamber. I built the door for the firebox using the same method as I did for the cook chamber doors.

If you're going to insulate the firebox the next step is to weld some square tubing along the sides your going to insulate. I used 1 ½" thick ceramic insulation which I ordered online and 1 ½" square tubing to capture the insulation. After you've got the tubing tacked in and insulation in place you can complete the firebox by covering the insulated sides with some thinner steel. I used 14 gauge sheet to save weight and cost. However, do not cover the top of the firebox yet as you'll need the ¼" plate exposed for welding onto the cook chamber.

Step 9: Attaching the Firebox

Now that the firebox is finished you're ready to attach it to the cook chamber. This is one of the tricker parts of the build because of the weird geometry involved between the two shapes but shouldn't be too difficult if you approach it incrementally.

The first step is to cut an opening in the cook chamber. I marked a line half way down the tank at the same width as the firebox. I place the firebox here so that the hot air and smoke enters the cook chamber right at the grate level and travels straight across the tank to the stack opening. From that line you want to cut straight down and around the tank to create a half moon shaped opening. I used a cutting torch but you could also use a cut off wheel for this step. You'll likely have to do some grinding to get the right fit.

Once you got a good fit you can weld the firebox on along the edges around the tank. After welding the top edge you can put in the insulation and weld on the cover sheet to complete the firebox.

Step 10: Seasoning

Now that you've got the smoker mostly completed you need to do a burnout and season your cooker. The first step is to fill the cook chamber and the firebox with a bunch of charcoal or wood and get it as hot as you can. This step is necessary for burning off any debris or chemicals that have been left from the tank or the manufacturing process.

Let it burn for a few hours and thoroughly clean out any debris. Now you want to season the cooker in order to get it ready for cooking. Get some vegetable oil in a spray bottle or on a clean rag and coat the entire interior of the cooker. Now you'll want to get a nice hot fire going in the firebox and let it cook for several hours. Once it has cooled you'll want to wipe it down and repeat this process. Now your cooker should be clean and ready for cooking!

Step 11: Building a Trailer

Now that you've got a finished smoker you'll need to get some wheels on it. I would recommend looking for an old utility trailer to mount it on but I decided to build my own trailer because I couldn't find one that quite suited my needs.

Building a trailer is pretty straightforward and there are several tutorials already online so I won't go into too much detail here but may post another tutorial for building a trailer in the future. If you want to build your own trailer you can buy trailer kits online that include the axle, wheels, springs, hitch, and lights so all you've got to do is weld up a frame. For the frame I used 2" x 3" tubing because it is very sturdy and easy to weld but you could also use angle iron or C channel. The biggest challenge with building a trailer is getting everything square and straight so that the trailer tracks straight when driving with it.

Step 12: Mounting It to the Trailer

Now that you've either purchased or built a trailer you're ready to mount the smoker on to the trailer. The biggest trick here is maneuvering the smoker around in order to get it onto the trailer. For this entire project I used a chain hoist which I got from Harbor Freight for around $50.

You'll want to block up the smoker until you find a height that feels good. I like to have the grates roughly at waist level for the most comfortable use. Once you've determined the height you can weld some supports onto the trailer to accept the smoker. I used the same rectangular tubing to support the bottom of the tank and angled pieces to support the sides. Finally I notched out the back of the trailer and welded the firebox sides directly to the trailer. You don't have to worry about cutting into the trailer as welding the smoker onto the frame will make up for any structure lost from cutting into the frame.

Step 13: Finishing Touches

Now that the smoker is complete and its got some wheels you're all ready to cook but there are some final finishing touches that you may want to add on to the smoker.

First, you'll likely want to add some thermometers to the cook chamber so you can maintain a consistent temperature. You'll want to mount these at grate level so get an accurate reading of the temperature where the meat will be. I'd recommend buying Tel-Tru thermometers or another high quality brand. They can be expensive but are very accurate and consistent. Cheap thermometers are an easy way to screw up some great bbq.

You can also paint your smoker to protect it from rust but you definitely don't need to. If you are going to paint it you'll need to get some high temperature paint so that it won't start peeling away from all the heat. You can get this paint at most hardware stores in rattle cans. You could also take your smoker to an auto shop to get a more professional finish if you'd like.

You may also want to add a grease drain somewhere in the bottom of the cook chamber with a valve so you can make clean up easier. This is as easy as welding on a piece of pipe with a valve onto the bottom of the tank.

Another useful addition is adding a grate to the firebox to help air flow around the fire or adding a layer of firebrick to help with insulation.

You could also add a damper on the the smoke stack or create an airflow valve on the firebox to control the temperature. I don't think these are really necessary as I can easily control the temperature by opening and closing the firebox door and controlling the size of the fire but many people like having these features to fine-tune their temperatures.

Step 14: Cooking Time!

Congrats! Now the hard work is done and you're ready to enjoy the fruits of your labor. It always takes some time to get used to a new smoker and how it cooks but the more you use it the better you'll get and the better your results will be. Remember, cook low and slow, be patient, keep a clean burning fire and you'll wowing your friends and family with some amazing barbecue as well as your beautiful craftsmanship.