Frank Groffie's miscellany

Go to content

Main menu

Construction

Outdoorsy stuff > DIY wax-powered backpack stove

The primary stove unit starts as just a tin can from your pantry or recycle bin. You'll then make a trip to the electronics store for a few small purchases (total $9) for the air blower, and a trip to to hardware store for aluminum sheet metal and other miscellany. That's the easy part. Then you're up against some tricky measurements and assembly operations.

Why anyone would want to make this stove I’m not sure. Consider it a challenge. All things considered, it rates only about equal to your average stove, though it is more powerful than stoves using alcohol or Esbit
® tabs. It does perform well. It's certainly unique and quirky, perhaps cool, even.

Perhaps a Boy Scout troop wanting to work on their Metalwork and Plumbing merit badges and needing stoves for their 50-miler wilderness trek would enjoy the learning opportunities to be gained from the stove's construction and its low cost and good performance in cold and wind.

General tools and materials
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Here’s a partial list of tools and materials you’ll need, some ordinary and some special: handheld sheet-metal shears, some sheet steel and sheet aluminum, a small Bernzomatic® torch, MAPP® gas, bronze brazing rod, a drill and ⅛-inch bit, a stepped drill bit for making large holes in sheet metal (Unibit® by Irwin®), soldering iron, solder, hot-glue gun, pop riveter, rivets, wire, aluminum-foil tape, hammer, file, pliers, and vise.

All pop rivets mentioned are of the ⅛-inch (diam.), short variety. Rivets for the primary stove unit should be steel. Rivets for the supercharger should be aluminum.

A cross section, somewhat schematic and not scaled, is shown below.



Primary stove unit
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

The stove body consists of a tin can formerly holding about 15 ounces of tomatoes or what-not, give or take an ounce. Regardless of the contents, these cans are all of a standard size: 4½ inches tall by 3 inches across. Drill a ¾-inch hole almost midway up one side for the stoke port. Drill another ¾-inch hole near the bottom for the air tubing. When drilling the hole for the air tubing, measure for, and take care to leave intact, the can’s bottom flange, which serves a strengthening function.

The air tubing, while shown as one piece in the diagram, actually consists of three pieces: a ¾-inch 90° elbow with two female ends that each receive a short piece of common ¾-inch copper tubing. Solder the two pieces of normal tubing into both ends of the elbow.

The tubing cap is another standard ¾-inch-diam. copper plumbing piece. Give it three slots sawed horizontally using a circular saw fitted with a metal-cutting blade. While sawing, leave three small support “posts” in between the cuts to support the top of the cap. Just hand tighten the cap onto the air tubing, no soldering necessary.

For the stoke port, prepare a piece of ¾-inch copper tubing by cutting at the angle shown in the diagram. To make the port cap, start with another standard ¾-inch-diam. copper plumbing piece. Saw off excess so it’s only about ⅜ inch long. Attach this to a nearby stove leg using a thin chain and rivet so you don’t lose it.

Ready your equipment for cheap home welding: bronze brazing rod, brazing flux, and a torch powered by MAPP
® gas. Braze the air tubing and stoke port to the stove body. It is essential to create a wax-tight fit all around when brazing the air tubing to the body to prevent future wax leaks. Place soapy water in the can to check for leaks.

Make four stove/pot supports from steel rod (12 gauge) cut from an old oven rack. Toward the end of the process, you'll attach these supports near the top of the stove body with four small rectangular brackets made of sheet metal. These brackets are shown in the photos but not in the diagrams. Bend each bracket around some rod material placed lengthwise to make a slot pocket for the support. Make a small dent in each bracket so as to engage a notch in the support strut (next step). File a notch in each support strut, aligned with the bracket dent, so that the stove/pot support can turn 90º between sticking straight out for stove operation and snug against the stove body for packing. The dent-and-notch combination keeps the supports from sliding up or down within the brackets, thereby keeping the stove level on the ground and pots properly supported on the stove. Drill four corner holes in each bracket for rivets. Find suitable 12, 3, 6, and 9 o’clock bracket positions on the stove body that won’t interfere with the air tubing or stoke port. Mark for bracket holes on the stove body, taking care to leave about a ½-inch gap between the top of the stove body and tops of the supports, for flame discharge. Drill holes in the stove body for the brackets. Attach each bracket to the stove body using four steel pop rivets placed in the corners. Use a steel washer on each rivet, inside the stove body, to counteract the thinness of the can material. Finally, crimp a length of wire around the bottoms of the supports to hold them against the stove body.

The wick can be cut from a strip of thick corrugated cardboard 1⅜ inches wide by about 16 inches long. Bend it back and forth in multiple places to create a flower shape when viewed from above, as shown here. (The cardboard should last through many uses; at the end of its life, I will probably switch in a strip of woven fiberglass exhaust wrap, sold in automobile parts shops.) It doesn't need to be perfect and should not fit tightly. Insert it down into the bottom of the stove around the air tube. Do this after the brazing, or else the wick will completely burn up during the brazing.

The flame focuser is made from a circular piece of thin sheet steel. The disk starts at 3½ inches diameter. Cut per the diagram at right. Compress the sheet slightly and overlap and rivet the “ends” so as to form a cone-like shape to fit the stove body. Shape it so it will fit inside the stove tightly while resting on the rivets for the leg brackets. A kidney-shaped hole at the top should result. Carefully press and/or hammer down the upper edges slightly so the kidney-shaped hole has a level, horizontal top. File down the high points of the edges of the hole in order to make the hole truly level.

Before connecting the flame focuser permanently to the stove, charge the wick with wax. Melt some wax in another separate clean, dry tin can. Cover the stove’s tubing cap, especially its air slots, with some aluminum foil. Carefully, slowly, pour the wax onto the wick so as to saturate the wick. This initiation step is important, because we don't want to burn the wick "dry," without fuel, or else it would just burn up. Pour in (a lot) more wax so that ¼ to ½ inch of wick is exposed.

Do not pour in more wax than this. More is not better. Too high a wax level leaves too little of the wick exposed, which causes poor stove performance.

Now insert the flame focuser so it rests on the rivets for the legs, or about ½ inch down from the top of the stove. Install one rivet in the stove body directly above the flame focuser to hold it in place. Don't insert more rivets, because you may want to remove the focuser to switch in a new wick someday.

Cut the flame control plate from a piece of sheet steel slightly larger than the kidney-shaped hole in the top of the flame focuser.

Braze a control rod (I used 12-gauge wire) to the top of the plate. Make a loop in one end of the control rod so as to wrap around one of the pot support struts. The control rod should extend through a horizontal slot cut out in the stove body. Make arrangements so the control plate will completely cover the hole in the focuser in one position and expose the hole in the alternate position.

Wrap insulation in a strip 1½ inches wide around the base of the stove; shown in the diagram but not in the photos. This is a cold-weather improvement that I added after experiencing very slow starting at around 30 ºF. The insulation consists of fiberglass house insulation about ½ inch thick wrapped with aluminum foil adhesive tape.


Supercharger
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

The supercharger shell consists of a complex bottom piece and a lid. The bottom piece begins as a “net” cut from sheet aluminum. Fold in the rear tabs, and fold up the side faces and rear face. Drill a hole in the rear face for the switch. The lid begins similarly, and its side flanges are folded down. Don't attach the lid yet. Save this step for way later.

A battery holder in the 9-volt size costs about $1 at Fry’s Electronics (a big-box retailer in the western U.S.; elsewhere undoubtedly you'll have an equivalent). Note the tiny predrilled mounting holes in its backing plate. Select two of these holes at diagonal corners, and enlarge them to receive rivets.

The fan is a slick little unit fully contained in a black plastic housing. It is rated at 12 volts and is made for cooling electronics. It measures 40 cm on each side by 20 cm deep. Such a fan retails for about $6 at Fry’s. Don’t be dismayed by the low cost, plastic construction, and seemingly low air output. It will serve well and not melt during use, thanks to the shielding given by the supercharger housing and the way it is distanced from the stove heat. And its gentle air output will be plenty, as you’ll observe when you use the stove. Clip away its yellow wire. Plug the fan’s four tiny tubes at its corners with dabs of hot-melt glue, to minimize fan backflow and maximize efficiency.

The switch is a miniature toggle switch that retails for about $2 at Fry’s. It will include a threaded shaft and properly threaded nuts, handy for attaching to the supercharger.

Wiring is shown schematically in the diagram. Shorten the fan's red and black wires so that the lid can comfortably hinge all the way up but the supercharger isn't crammed with more wire than necessary. Connect and solder the wiring between the three electrical components while they’re still outside the supercharger. Solder the red (positive) wire from the fan to the positive (+) terminal on the battery holder. Solder the black (negative) wire from the fan to the switch and then, with another piece of black wire from the switch, to the negative (-) terminal on the battery holder. Coat all soldered connections with hot-melt glue to lend these connections some strength and to prevent corrosion and shorting.

Rivet the battery holder to the lid of the supercharger, with the holder’s electrical terminals facing rearward on the lid. You need only use two aluminum rivets, heads facing outward, on diagonal corners of the holder. Clip off excess from the rivet tails (inside) and file down most of the remainder so they won’t interfere with battery placement.

When both the electrical assembly (plus connected lid) and the supercharger housing are ready, only then place the electrical assembly inside the supercharger. Attach the switch using its provided nut. Rivet the fan at two or three corners where the rivets won’t interfere with the fan blades. Connect the lid to the supercharger bottom using two rivets at their rear corners. The result is a pivoting lid that allows battery access.

Make the shroud out of one or more pieces of thin sheet aluminum. My preference is to make the shroud out of a one-piece net of aluminum, as in the diagram at right (not to scale). First drill a ¾-inch-diam. hole in your uncut metal to eventually accept the air tube of the main stove body. Only then (to prevent tearing up your work during drilling) make your cuts and folds around the hole. Attach the shroud to the supercharger using aluminum foil tape (my method, see photos) or aluminum rivets.


Disclaimer
Execute this DIY project and use any resulting product solely at your own risk.

Disclaimer

This web page and the information therein have received no input, authorization, or endorsement from,
and the author has never had affiliation with, any mentioned individual, manufacturer, or retailer.

Back to content | Back to main menu