Introduction: Rocket Grill!
Second Prize in the
Green Living & Technology Challenge
Finalist in the
Play With Your Food Challenge
Want a D.I.Y. way to cook food WITHOUT using fossil fuel L.P. or having to buy charcoal? I know I did. That's why I built a "Rocket Grill"!
This is just one variation of a "rocket stove" - a simple appropriate technology for cleanly burning bio-fuels.
The rocket grill is fired by twigs, wood scraps, wood chips, or nearly anything else you can put in it. It naturally drafts air to maximize combustion. Once the the grill is really going, NO smoke comes out the top, only heat, and the grill really does sound like a rocket!
The grill is designed to not only grill, but also boil, bake, braise, and roast!
Because of the simple design and robust construction, it is nearly maintenance free. Unlike an LP grill, the burner will never burn and rust away to nothingness. (And cost good time and money to replace.) There is no piezo-electric starter or other "modern" technology in the grill, which would be prone to failure.
Despite how it looks, the grill is small and light enough for one grown man to lift into the back of a pickup truck. That way, it can travel with for camping or tailgating. (The lid and side tables are also removable for storage and easy packing.) Because it's covered and enclosed, it also qualifies for use as a "backyard fire-pit" in areas that do not allow open fires.
This project is mostly simple metal work. While it does require welding, it's pretty straight-forward. This was really my first-ever welding project.
So lets' gather together our tools and materials and get started!
Step 1: Tools and Materials
- Angle Grinder
- Grinding disc
- Cut-off disc
- Safety glasses, work gloves, welding gloves, Welding helmet, hearing protection
- Drill and drill bits
- OPTIONAL: Laser Level, Bubble Level
This project is made mostly from scrap metal, but will need several other parts.
Parts for the Grill itself:
- A Base. Something for the grill to stand on. Must be heat-proof. I used a scrap steel farm implement disc.
- Steel Pipe - Diameter of your choice, but will effect cooking size and fuel rate. I used 6.5 inch diameter scrap steel pipe. About 3 feet in length.
- Steel Water Tank. This becomes the "bowl" top of the grill and cooking surface area.
- 4 x pieces of small diameter steel pipe, about 6" in length
- 2 x 90 degree pipe elbows of same diameter
- 2 x pipe flanges of same diameter
- 2 x pieces of flat material that you like to make side countertop surfaces
- Small scraps of steel plate
Parts for the lid of the grill:
- A piece of wood, species of your choice, sized for a lid handle.
- 2 x Carriage bolts (about 5" long) with matching nuts and washers. Stainless steel is ideal, as these will be exposed to both heat and the elements. Plain steel is fine, lower cost alternative.
- 2 x pieces of copper or steel tube or pipe, slightly larger diameter and shorter length than the carriage bolts, to use as spacers.
- The top end of the water tank.
- Steel plate, about 6" side by 12" long. Perferations or slotted is ideal.
- JB Weld
- Large Diameter Pipe
- Water Tank
The large diameter pipe needs to be cut into two sections. Make one about 1 foot, and the other about 20" long. The 20" section will be the "vertical tube", and the 1 ft. section will be the "feeder tube"
That water tank that I chose was 16" in diameter. It was already cut apart from a solar water experiment I worked on. The bottom section of the tank is cut to about 1 foot tall. This becomes the cooking area "bowl" top to the grill. The water tank was also chosen because is is large enough diameter to fit my camping cast iron Dutch Oven, and a stock pot that I use for boiling corn.
Stacked up, the base, vertical tube, and water tank section should come to a comfortable standing height for you. The top of the water tank section is the height that grilling will take place.
To cut the steel, I found that an angle-grinder with a cut-off disc works best. I cuts quickly, without removing to much metal, and makes a nice, straight line. You could also use a reciprocating saw with metal cutting blade, or a plasma-cutter if you have access to one.
To mark a line on a cylindrical object like the pipe or water tank, wrap a straight section of sheet metal around it, and secure with masking or duct tape. Mark this line with a permanent marking pen, then remove the sheet metal.
Cut the pipes and water tank to length, using common-sense safety precautions. (Wear work gloves, eye and hearing protection, etc.)
Cut the top off the water tank, and save to make the lid.
Stack up the base, vertical pipe, and water tank section to get a feel for how your grill will look. If you ware working on a level surface, like a concrete garage floor, you can use a bubble level to make sure your vertical pipe is perfectly straight up and down. (Plumb!)
Step 2: The Special Cut
The most distinct feature of the Rocket Grill is how the feeder pipe and vertical pipe come together.
While the exact angle that they connect at isn't super-important, it should be somewhere between a 90-degree and 45 degree. Having this connection at some angle makes it easier to feed fuel, and not bend over too far. Too steep of an angle will not allow for proper air-flow and can prevent the grill from drafting properly.
Cutting the two pipes to fit together can be geometrically-challenging. An angle-grinder makes straight cuts, but both pipes are rounded. Still, they have to meet together tight enough to get a good weld between them.
What you need to do is imagine how two straight cuts would look projected onto two curved surfaces. One easy way to do this is to use a laser level that has the ability to project a straight line. Several inches up from the end,point the laser at the vertical pipe, at the angle you want the feeder pipe to meet it. Then mark the laser line with your permanent marker. Rotate the laser 90 degrees, and mark the line again.
On the feeder pipe, mark two lines at 90-degrees from each other the same way.
Another way to mark the same cuts is to use sheet metal, which you can wrap around the pipes. It is possible to make a projection of what the cuts should look like, and cut that out of the sheet metal. Then wrap the sheet metal around the pipe and mark it. A friend of mine already had made a sheet metal template, so that's the technique I used.
When you are done, you will have a notch in the vertical pipe, and a "bird's-beak" cut in the feeder pipe.
Fit the two pipes together, and see how close they match up. It's more that likely that you will need to use a grinder to get the parts to fit together well.
Step 3: Welding
Weld together the vertical and feeder pipes.
That's easiest to do with both pipes laying flat and sideways. Weld around one side, then flip it over, and weld the other side.
Next, stand the Y of pipes on top of the base. Make sure it is centered, and that it is plumb and level.
Weld the pipes to the base. (Make sure to always brush down the metal where you will be welding, and where the ground clamp connects.)
The bottom of the water tank needs a hole cut in it, the same diameter as the vertical pipe. Mark that diameter hole on the bottom. One way to do that is just set the other parts right on top of the tank, and trace it.
Then cut the hole in the bottom of the tank. I had a plasma-cutter at a friend's house, so I used that. Otherwise, a cut-off disc, Sawzall, or large diameter hole-saw could work.
Stack the whole grill together upside down and weld the vertical tube to the water tank section. Again, make sure the parts are plumb and level. If there is a "front" to the water tank, make sure it's where you want it to be. On mine, there were two pipe ports that I wanted to be left and right, with the feeder tube on an angle to my right as I faced it.
At this point, the basic grill is done, but we still need the lid and a few other details.
Step 4: Fuel/Air Plate
Another distinct feature of the Rocket Grill is the Fuel/Air plate.
It holds the fuel up and in place, let allows plenty of air to naturally draft into the grill and up through the fuel for a very hot and clean burn.
The plate needs to be able to hold up to high temperatures.
Take some scrap steel plate and cut it to a width just slightly smaller than the diameter of the feeder pipe, and about the same length. This way, the plate sits INSIDE the feeder pipe, and divides it to an upper and lower area.
Fuel goes in ABOVE the plate, and air goes in BELOW the plate.
The plate has holes or slots in it in the far end so that it supports the fuel, but allows plenty of air through. The plate I used was already slotted, but I added a few more for good measure.
You could also use a heavy-duty grate, or weld together re-bar to serve the same purpose.
When you are ready, just slide the plate into the feeder tube. Gravity and friction will hold it in place for you.
Step 5: Building the Lid
When I cut the water tank apart, I also cut off the top, and saved it for use as a lid.
It's already the same diameter as the top of the grill, so it should fit perfect.
It really just needs two modifications, a handle, and a way to let air through.
The length and width of the handle is based on the size of the user's hand, preferably with enough room for an oven mitt.
I found a scrap of Oak firewood, about the right diameter for a handle, and left it long to start with. I could always shorten it later.
Drill two holes in the wood, and push the carriage bolts through.
Use these to mark where they should go through on the lid.
Drill two holes in the lid.
Cut two sections of pipe a little shorter than the length of the carriage bolts. These will be spacers to hold the handle the right distance from the lid. I had some scrap copper pipe around, which is easy to cut and looks very nice.
Slide a washer and then the pipe over the carriage bolts, and then the carriage bolts into the holes in the lid. On the bottom side of the lid, attach washers and nuts, and tighten.
The lid also needs some way for hot air to constantly exit the grill to continue the chimney effect.
You could make a vent, similar to one a Weber brand grill, or even make some sort of chimney right on the lid, but it seemed much easier just to add some small steel tabs. These tabs space the lid away from the grill to allow air flow.
I cut three steel tabs from scrap metal, and welded them evenly around the lid.
On the inside of the grill, I welded in three matching tabs that line up with the ones on the lid. Three tabs makes the lid not wobble.
By simply rotating the lid a little, it can still sit all the way down on the grill (such as when you are done with the grill and want to smother it, or for storage.)
Step 6: Side Tables
What's a grill without some workspace to hold your utensils, your plate of meat, and your favorite beer?
That's why the grill needs side-tables.
The water pressure tank used to make the top of the grill, included pipe connections in the sides. I purchased just a couple short sections of pipe and elbows so that these could support the side tables.
I threaded in a horizontal pipe into each side, then a 90 degree elbow into that, A vertical pipe section then completes an "L" on either side of the grill.
Both side tables have a pipe flange going to a short piece of pipe SMALLER in diameter than the vertical side pipe. That way, the side table pipe sits INSIDE the vertical pipe. This makes it easy to remove the side tables for travel. Drilling a hole through both pipes allows me to slide a small bolt through, preventing the side table from accidentally rotating.
At first, I wasn't sure what I wanted to use for the top surface of the side tables. I dug through my pile of scrap/salvaged/recycled materials and found an assortment of stone, tile, steel, aluminum, and wood.
I simply set different pieces of materials on top of the side-arm pipes to see what looked good. In the end, I decided on a blue/green slate stone for the left side, and a steel deck place for the right side.
For the steel on the right, I just welded the pipe flange to the bottom of it, threaded in the short section of pipe, and slid that into the slightly larger diameter vertical pipe. A horizontally-drilled hole with a bolt slid through it completed that side.
The slate for the left was a little more work. The slate was rough and pointed, but it is a very soft stone. I experimented and found that RUBBING the edges of the stone with a cold chisel allowed me to shape the stone a bit and smooth the rough edges.
To attach the stone to the side pipe, I found some scrap metal about the right size for the bottom of the stone side table. I welded the pipe flange to the bottom of the metal and then glued that to stone with a tube of "JB WELD" adhesive.
Again, the pipe on the side table just slides into the vertical pipe on the side of the grill.
Step 7: Odds and Ends
The water tank section of the grill is painted, and the paint had to be removed before using the grill for cooking.
I thought about what the most "eco-friendly" way to remove all the paint was. I thought about all the nasty chemicals used as paint strippers. In the end, I decided make a very hot test fire to both try out the grill and remove the paint.
The painted easily peeled off.
To hold either the stock pot or Dutch Oven, there still needs to be air space in the bottom of the grill. The easiest answer was just to span the fire tube with two short sections of slotted C-channel. They support the pot, and let plenty of heat and air through. They are not welded in place. I didn't see any reason to, and this way they are removable.
One downside of this grill design is that it gets an extreme hot-spot in the middle of the grill, and is much cooler towards the outside edge. That's a bad thing for cooking burgers and sausages. So in put in a "heat-diffuser" when grilling. It's just a small steel plate that I practiced welding on before welding the grill together. It simply sits directly on the pot bracket and works well to spread out the heat. At some point, I may make a more aesthetically-pleasing heat-spreader, but this one works fine for now.
You may have noticed that there is no ash clean-out on the grill. In truth, I really haven't seen a design for one that I like. I have seen similar steel rocket stoves that use a threaded pipe port, which seems like it would gunk up the threads easy. Also a large diameter pipe port gets expensive quickly, and I was trying to use as many free, inexpensive, and recycled parts as possible. For now, I just flip the whole grill upside down to empty the ash. It makes far less ash then you might think. In the future, I may use the angle grinder to cut an angle out the bottom back side of the grill, and then hinge it, so that there is a flip-up flap to access and empty the ash.
The grate is just a standard round grill grate. It's the medium size. It actually overlaps the top of the grill, which makes it easier to use the entire top. Downside? It's easier to slide a burger right off the top of the grill as well!
Step 8: Fueling and Firing
One of the best things about the Rocket Grill is how it's fueled.
No longer do I have to purchase fossil-fuels to cook my backyard fare!
Because of the amount of air that flows through the grill, almost any bio-fuel burns great in it. This one is really designed for twigs and sticks.
After every wind-storm, all of my neighbor's trees shed their sticks downwind into my yard. Before, I would grumble at the yard-work of picking up all those sticks and moving them back to the brush pile. Now, I instead gather them up looking forward to burgers, corn-on-the-cob, or whatever I am going to cook up next.
To start the grill, I just put a little bit of tinder (usually a bit of newspaper) and a few twigs onto the far end of the Fuel/Air Plate. I light it with a match or cigarette lighter, and then just feed in a few more twigs. After that, a fair amount of sticks, firewood, or other fuel can be loaded on the top side of the fuel plate.
The fire is very simple to light and starts right up.
Even EXTRA LONG fuel can go right in. Just slide it a little farther in every once in a while. The chimney effect makes all the heat goes up the vertical tube. No smoke or fire comes out the feeder tube.
I am right-handed, so I designed the grill so that the feeder tube comes out on an angle to the right. That way, it is easy for me to fuel, but I don't hit my shin on it.
Since pots sit down INSIDE the grill when boiling, the heat transfer of the fire to the pot is very good. The heat hits not just the bottom of the pot, but travels up the sides as well. This means you get a boil going faster, while using less fuel.
I also used my grill in a rain storm a while back. My concern was rain running down the lid and then inside the grill. It wasn't an issue - any rain hitting the lid simply vaporized or sizzled right off!
Step 9: Grill It Up!
So far, I have used the grill for chicken, burgers, brats and sausages, corn on the cob, shish-ka-bobs, and more.
The design also allows me to boil in the stock pot, or bake in the Dutch Oven. (I'm working on baked desserts now too!)
A friend of mine has designed both a giant skillet and a very nice wok for his
Another possible future modification is to create a high-thermal mass pizza oven top for the grill.
Rocket stoves lend themselves well to infinite variation and re-use of existing materials. Combine that with versatility and efficient use of fuel and you have the cookstove of tomorrow, today.
Remember, this isn't rocket science, just good use of appropriate technology!
I hope you find my Rocket Grill to be inspirational. You too can cook net-carbon-zero deliciousness over open flames and take pride in your own design.
If you have built one, please post a photo in the comments section!
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