November 6, 2007

Twelve Sided EB30D

The twelve sided EB30D is a 30 inch (76.2 cm) diameter cooker. Apparently twelve sided cookers were first reported by Tran http://solarcooking.org/plans/DATS.htm and later refined by Paradesi http://www.angelfire.com/80s/shobhapardeshi/twelvesided.html. Both Tran and Paradesi located the pot at the bottom of the cooker where the cooker primarily heats the top and sides of the cooking pot. We believe that our cooker will cook more efficiently because we have located the pot near the mouth of the cooker so that the cooker primarily heats the bottom and sides of the pot. The primary advantage of the 12 sided cooker over the double cone cooker is that it is easier and less time consuming to build. This makes it a good choice for the do it yourselfer.

Figure 1 shows the completed cooker, with a pot on the pot holder.

Figure 1 Twelve Sided EB30D

Cooker Cone

Since we wanted to complete this prototype efficiently, we decided to cut the cooker cone from a piece of double ply cardboard and use aluminum foil for the reflective material. In our next prototype, the cooker cone probably will be built from more durable material. Figure 2a shows the layout for the cooker cone. The cone section can be cut from a single piece of material about 42.4 inches (108.5 cm) by 36,2 Inches (91.9 cm). The tab shown on the lower edge is used to attach the ends together to assemble the cooker cone.. The small blue triangles are cut out. Figure 2b shows an individual cone section. The tabs shown on Figure 2b are folded up and used to attach the inner edges to each other as shown in figure 4.

Figure 2b Single Segment of Cooker Cone.

After cutting out the cone section, aluminum foil was pasted over the complete section. Figure 3 shows the cone section with aluminum foil on it before the foil was trimmed..

Figure 3 Cone Section Covered With Foil

The excess aluminum foil was then trimmed off and some of the excess was folded over the outside rim. After the glue dried, the cone was assembled. The ends were joined and fastened with brass fasteners (Use the ones that normally are used to hold stacks of papers. They are pushed through holes in the cardboard and the ends are spread apart.) Holes were then punched through the tabs and a string was passed through the holes. The string was then tightened to gather the bottom ends of the cone together. Figure 4 shows the rear of the cooker with the tabs and the string through them.

Figure 4 Rear of Cooker

Stand for the Cooker

The U shaped stand that we have developed consists of a base and a Support Structure. One base and two support structures are described here.

Cooker Base

As shown in Figure 5, the base of the cooker consists of two crossed 2 by 4’s (each 2 feet long). Each 2 by 4 is notched half way through at the center. (If you have trouble cutting the notches, one 2 by 4 could be placed on top of the other. You would then need to add extra pieces of 2 by 4 beneath the underside of the upper 2 by 4 to make the bottom level.) A pipe flange is attached to the center of the crossed 2 by 4’s such that the flange mounting screws and glue hold the 2 by 4’s together. Then an 18 inch long piece of one inch iron pipe was screwed into the flange.

Figure 5 Base of Cooker

Cooker Support Frame

Figure 6a shows the cooker support frame. It consists of a 1¼ inch iron pipe that fits over the one inch pipe in the cooker base, a U shaped support, and threaded rods that hold the pot support. We used recycled one inch square steel tubing for the U shaped support, but it could be made from any available material.

Figure 6a Cooker Support Frame

Alternate Support Frame that is Easier to Build

The support Frame shown in Figure 6a performed well, but since it was built from recycled materials it is not easy to reproduce. Therefore, we designed and built a new support frame that can be constructed from parts that should be available at most hardware stores. This support frame is built primarily from PVC pipe that is readily available and easy to work with. The cooker base shown in figure 5 is used with the PVC support frame.

To build the support structure, you will need to buy a 10 foot long piece of 1¼ inch diameter PVC pipe (You only need 5.5 feet but it comes in 10 foot lengths), two PVC elbows and a PVC tee. The PVC pipe and fittings cost us about $6.50. You will need PVC cement to join the PVC parts. We purchased a small can for about $2.

To build the support frame:

Cut four 12” pieces and one 18” piece of 1¼ inch PVC pipe. The PVC can be easily cut with a hacksaw.
Drill a 3/8” diameter hole ¾” from the end of 2 of the 12” PVC pieces for the pot support.
Assemble the PVC parts as in Figure 6b. Join the PVC pieces with the PVC cement. (Caution! The PVC cement sets within a few seconds. Make sure that the parts are aligned properly before putting the joints together with the cement. We recommend first assembling the structure without the PVC cement, and with the 3/8”threaded rod that will eventually become part of the pot support structure in place as shown in Figure 6b. Next, leave the threaded rod in place while taking the structure apart and reassembling it with the PVC cement.)

Figure 6b PVC Support Frame

Pot Support

Figure 6c is a photograph of the finished support frame sitting on the base with the pot support in place, but without the cooker cone. The exact dimensions of the pot support will depend upon the size of the pot you intend to use. When the pot is on the pot support, the center of the pot should be in line with the threaded rods.