Procedure: Drive nail into middle of 28-inch to 30-inch-long 2-by-8, 1/4-inch in from one edge. Then — using the nail as a pivot — swing and slide a framing square so that its corner moves precisely along the 2-by-8's opposite edge. Stop the square frequently as you move it along and, with a pencil, draw a series of overlapping lines along the square's other leg as shown. These overlapping lines will describe a perfect (for this solar hot dog cooker) parabolic curve.
MOTHER EARTH NEWS STAFF
Here's just the thing to add a little extra fun and excitement to all those outdoor excursions, picnics, and cookouts that your family will be enjoying during the coming months. It's a solar hot dog cooker built of wood, a few pieces of hardware, and either reflective mylar or something called Flex-Sheet-Mirror. The whole shebang can be put together for less than $30 ... much less if you're good at scrounging. (Note: Click on the Image Gallery link above for more illustrations and details about building this solar hot dog cooker.)
Materials to Build a Solar Hot Dog Cooker
2 each: 2-by-8-by-28-inch to 30-inch lumber
1 each: 1/8-by-26-by-32-inch paneling
2 each: 3/4-by-1-by-20-inch pine
1 each: 1/8-inch or 3/16-inch diameter stainless steel welding rod
4 each: 3 large, 1 small wooden beads to fit rod
1 each: 1/4-by-2-inch wooden dowel
2 each: 1/4-by-3-inch carriage bolts with nuts and flat washers
1 each: glue and paint as needed
2 each: 18-by-24-inch Flex-Sheet-Mirror*
*Flex-Sheet-Mirror costs about $3.50 a square foot in 1978. You'll need six square feet, or $21 worth. Or you can do the same job for less money by substituting two sheets of 12-by-36-inch 2-mil reflective mylar. The mylar was priced at $3.75 a sheet in 1978. The mylar will do the job ... it just won't last as long as the mirrors.
Building the Solar Hot Dog Cooker
MOTHER EARTH NEWS' Travis Brock whipped up the broiler you see here as a Christmas gift for a friend. "The principle of the cooker's operation is very simple," says Travis. "When aimed at the sun, the unit catches all the solar radiation which strikes its curved face and focuses it into a concentrated line of heat that falls on the broiler's skewer."
Travis further points out that the only real trick to making the hot dog or shish kebab cooker work properly lies in designing the collector's curved back so that it, in fact, does focus the sun's rays into one narrow and intense band of heat. "But that's not as difficult as you may think," Brock explains. "You can either calculate the curve mathematically with a formula, or — and this is even easier yet — you can lay the parabolic out in a jiffy with a nail and a framing square as shown in the accompanying sketch."
Use a band saw, saber saw, or coping saw, and either a rasp or sandpaper to cut your curve out and smooth it down once you have it drawn. Then use what's left of the first 2-by-8 as a pattern to mark and cut a second. These two curved pieces of wood will be your cooker's sides.
Cut a 1/4-inch square notch (centered right on your parabolic curve's pivot point) out of each of the sides. Your broiler's skewer will fit into these notches when the cooker is finished.
Then cut a bigger notch (1 1/4-inch deep and 1 1/2-inch long) into one of the sides as shown. Drill a 1/4-inch hole 1-inch deep into the floor of this indentation taking care to make the hole as perfectly perpendicular to the face of the piece of wood as possible. Finally, put a little glue on one end of a 1/4-by-2-inch wooden dowel and push or tap this "aiming" peg as far into the hole as It will go.
You're now ready to glue and nail the 1/8-by-26-by-32-inch piece of paneling to the curved faces of the two wooden sides. Trim the paneling as necessary to make everything fit together the way it should.
When the back is in place, glue the Flex-Sheet-Mirror (or reflective mylar) to the inside of the paneling. If you use the flex mirrors, you'll have to cut a strip of one edge of the sheeting and refit it as necessary to fill the entire trough with the reflective facing.
Make legs for your little sun scoop by drilling the necessary holes and bolting the two 3/4-by-1-by-20-inch pieces of pine to the cooker's sides. The skewer is finished off by gluing one small and three larger wooden beads onto a length of 1/8-inch stainless steel welding rod (or use a heavier rod if you prefer). File four flat spots on the small bead once the glue is dry. Then, when the squared bead is placed in the skewerholding notch, you'll be able to turn your broiling goodies a quarter-turn at a time as they cook.
Add a coat of non-toxic paint to all the sun scoop's wooden parts and you're ready to "start cookin'." Spear three or four wieners or a string of shish kebab fixings on the stainless steel rod, set the skewer into its notches, and point your broiler at the sun. It'll be aimed precisely at Ole Sol when the little round peg in the big square notch casts no shadow at all. Reaim the cooker as necessary as time goes on and the sun moves across the sky.
On a good day, hot dogs will be steaming tender and juicy all the way through in only four to five minutes ... a shish kebab will take a little longer. And don't worry about the juice that drips onto the mirrors ... it'll wipe off when you're finished. Or you can save all those delicious drippings (and make your broiler cook better on marginal days to boot) by painting some aluminum foil flat black on one side and wrapping it — juice-tight — around the franks or shish kebab (painted side out, of course).