Make a Rocket Stove

I had some steel pipe I wanted to use. I decided to make a rocket stove.

Materials

1. Steel pipe -- 4 1/8 Inches in diameter (internal diameter), about 21 inches in length
2. 3/8 inch concrete rebar
3. 1/2 inch concrete rebar
4. 3/16 inch flat steel
5. 1 1/2 inch angle iron

Tools

1. Speed square
2. Level with laser
3. Metal cutting bandsaw
4. Hacksaw
5. Angle head grinder with grinding disc and with cutting disc
6. Arc welder
7. Spring clamps
8. Vise

I need precise cuts to miter the pipe so I get a good fit up for welding. A flexible magnetic rule seemed like it should work, but a slight "S" curve developed as the flexible rule went around the pipe and fit up was poor. Grinding for a better fit became necessary. I want to use the beam from a laser level to project a straight cut line and mark it on masking tape.

I clamped a right angle steel corner to the edge of a table top. I used a spring clamp to hold the level so the laser lens pointed downward toward the floor. (Ignore the blue portable air tank in the photo.) Note the yellow laser level pointing downward. The steel corner is not visible, but one of the clamps is. Note the laser beam falling on the pipe below on the floor. By moving the pipe slightly and checking with a speed square the laser beam can be made to indicate a desired angle. See the next step for additional detail.

I needed to make two cuts on the pipe to make two joints. The first step is to cut the pipe at a 22.5 degree angle for a 45 degree elbow.

See the first photo. I had a piece of pipe 21 inches long. I measured about 5 1/2 inches from the end. (See the second photo. [This photo was taken after the project was completed, but illustrates the process.]) I used the beam from my laser level and a speed square to mark approximately 22.5 degrees. I placed masking tape on the pipe and used a pen to mark the location of the laser beam on the masking tape.

Measure approximately 1 inch to locate the second cut at 45 degrees (See the third photo.) for a 90 degree elbow. As before, use the laser beam to mark for a 45 degree cut. See the fourth photo.

Cut along the line on the masking tape for each of the two joints. The first photo shows cutting for the 90 degree elbow on the 45 degree line. The 45 degree elbow (22.5 degree cut) has already been cut and welded in this photo. Having that done already did keep the pipe from rolling a few degrees while cutting.

The throat on my power bandsaw is too small to complete the cut. I finished it by hand with the deep throat hacksaw I described in another Instructable. See the second photo. The fit up for welding was quite good. See the third photo. One piece from each cut will be rotated 180 degrees to make a 90 degree corner from a 45 degree cut or a 45 degree corner from a 22.5 degree cut.

Any welding process would work as long as there is enough power to penetrate material thickness. I used a 230 volt stick welder with 1/8 inch 6011 electrodes for this project. I have much more experience with 6013 electrodes, but wanted to practice using 6011 electrodes. When using 6011 electrodes reduce the welding amperage to about halfway between the setting for 3/32 inch 6013 electrodes and 1/8 inch 6013 electrodes. I need to be very careful not to stick the 6011 electrodes when striking an arc, but a little practice helps. Often I can simply bring the end of the electrode near to the steel and an arc usually jumps to the steel. I find also I need to hold a longer arc to avoid sticking the electrode. That also helps to see better while welding. I like the results I get with 6011 electrodes. They dig through rust and paint quite well, and they have good penetration. Leaving a gap in the joint about the width of the welding rod helps, too. When welding I made short runs and moved around the joint to keep heating even. Many will do a cover pass afterward with 7018 electrodes to make the joint prettier.

The first photo shows the stove with nearly completed legs. Legs keep the stove elevated so it does not come into contact with something that could catch fire. They also add stability so the stove does not tip over with your food.

See the second photo. I cut a piece of 1/2 inch concrete rebar 4 to 5 inches long and welded it at an angle that looked about right.

See the third photo. I welded a second leg at the back while holding it so it looked right. I put a wood block under the front of the stove and used a small level to check for needed adjustments to the legs. Some adjustment is possible with a big hammer or by grinding the end of a leg too long. Too much use of a hammer may cause a tack weld to break.

After making the vertical part of the stove plumb left to right, I welded a front leg in place and adjusted for plumb front to back. Adjusting the legs so the vertical tube is plumb consumed more time than most other parts of the project.

I made foot pads from steel 3/16 inch in thickness, placed them under the tips of the legs and welded them in place. Foot pads will keep the stove from sinking into soft soil.

Rocket stoves need air, yet their fuels are thin and could compact together to choke off air. I added a piece of 1 1/2 inch angle iron for an air passageway. I think I will move it from the bottom of the fuel opening to its top. A trial run with charcoal briquets found fine ash closed the air passage. Photos of commercial rocket stoves show about 1/4th of the opening dedicated to an air passage. In use I found I did not pack twigs so tightly in the intake that I choked of the air supply. Plenty of air was getting in to make a hot fire. A dedicated air inlet may not be necessary.

See the first and second photos. I wanted to support a pan or pot with six equally spaced supports. I placed masking tape around the top and marked the front center position. Six equal angles measured with a protractor might seem the only way. I prefer to multiply the outside diameter by pi and divide by six. Then I used a rule to follow the circumference and mark off segments. My calculations were very close and I adjusted only a little.

I ran out of 1/2 inch concrete rebar and switched to 3/8 inch rebar. The first photo shows one piece almost three inches long ready to weld to a riser piece just under one inch for an "L" shaped piece that will be welded to the rim of the vertical tube.

See the second photo. I clamped a piece of wood to the side of the rocket stove and rested the "L" on it to hold it in position for welding. Position three "L"s equidistant around the circumference of the stove chimney and weld them in place. Adjust the "L"s so they are on the same flat plane.

See the third photo. Clamp a piece of wood across two of the "L" supports welded to the chimney. The piece of wood needs to be three or more inches wide.

See the fourth photo. Measure between the top of the chimney and the bottom of the piece of wood. Subtract the thickness of the concrete rebar. Cut a piece of rebar to fit the difference. Weld to make an "L."

See the fifth photo. Clamp the "L" to the bottom of the wood piece. Weld to the chimney. This process keeps the pan supports on the same plane, or nearly so. Repeat this for the other two "L" supports needed. Adjust the "L" supports by bending so they all touch the bottom of a pan as equally as possible, but the fit should be pretty good already. Hopefully, when finished the six support arms are at an equal height and a pan sits on them in contact with all of the arms, and the bottom of the pan is level. Adjustments may be necessary.

"L"-shaped pan supports keep the area under the pan open so hot gases can flow freely. An "X"-shaped support would be easier to make, but also divides the hot gases into sections. It is a judgment call by the maker.

A handle for carrying the rocket stove is handy. It should be set off from the chimney tube not to be too hot to maneuver. I used a piece of black pipe long enough to extend beyond the width of my hand. I used a couple of pieces of concrete rebar as standoffs.

The handle will be located near the bottom of the rocket stove so the stove feels balanced when carried. Pick up the stove and find a place with your hand where the weight of the stove naturally balances. These stoves are a bit heavy. When the stove is picked up by the handle ash spills out the angled lower end of the stove. Be sure all coals are out or the coals are falling on a safe place.

I welded the standoffs to the black iron pipe. I used a spring clamp to position the handle until I could get a tack weld. Then I finished welding the handle standoffs to the chimney tube.

Grind rough edges smooth to prevent cuts and scratches.

Some rocket stoves have clean out doors and trays. I envision simply picking the stove up by its handle and letting ash fall out of the opening. Rocket stoves do make quite a bit of ash when in use.

Lighting the fuel in the stove can be challenging. It may seem like cheating, but using a handheld torch is quick and effective. The flame may rise out of the lower end of the stove. Once the twigs are burning well the flame will soon reverse itself and hot gases will go up the chimney instead. It happens automatically. The fire will need nearly constant stoking with new twigs for the maximum heat. In retrospect, a larger iron pipe would have been good, but I had this scrap piece four inches in internal diameter and wanted to use it.

I tried using charcoal in this stove. It was not very satisfactory. Results might have been better if I had let the coals become fully ignited outside the stove rather than trying to light them while in the bottom of the stove. I did once cook two hamburger patties in a cast iron pan on an identical rocket stove I made about a year ago. I used short scraps of wood for fuel and it worked quite well, even though I used a bare minimum of wood. Serious cooking on a rocket stove requires quite a pile of smaller wood sticks. The process works better with food in a pot or pan rather than using an open rack.