May 182011
 

I. TOOLS AND MATERIALS

This section lists all the tools and materials needed to build the

Solar Cooker. The best choice of materials may vary from   place to place. Other kinds of wood or composition board may be cheaper than the materials indicated here in some countries. Any sheet material such as plywood or certain sheet metals, can substitute
for the Masonite.

A. Reflecting Surface

Tools

Fine sandpaper
Paint brush
Safety razor blade or sharp knife
Clean, dry, lint-free cloth
Two (2) spoons
Rubber blade window washer (squeegee) or a smooth
stiff rubber windshield wiper
Rubber roller (double print photograph roller)
Four (4) boards 5 =. x 5 cm. x 135 cm.
Hammer and coping saw (bandsaw if available)
Ruler and pencil

Materials

About 120 cm. x 120 cm. Masonite (0.3 cm. to 0.6 cm. thick)
as free as possible of pits and structure defects,
80% – 95% ethyl alcohol approximately 50 cc/cooker
Epoxy cement (resin, hardener, and solvent 80% – 95%
alcohol) approximately 75 cc. of mixed cement
Clean dry cup
Clean smooth stick (size of pencil)
A roll of aluminized Mylar (.0005″ thickness) 160 cm. wide
Polyurethane paint or if not available use good oil paint

B. Frame

Tools

Paint brush
Ruler and pencil
Protractor
Hammer, hand saw
Screw driver
Drill capable of drilling metal (6 mm. diameter)
Vise

Materials

15 cm. strip of 18 mm. x 3 mm. hot rolled iron
Two (2) 2 cm. x 120 cm. boards (oak for strength but pine
or other woods are sufficient)
Two dozen aluminum nails (or screws) about 5 cm. long
(or other non-rusting material)
10 cm. x 6 mm. bolt with fitting wing nut

C. Utensil Holder

Tools

Ruler and pencil
Drill capable of drilling metal (6 mm. diameter)
Cold chisel or metal cutting hand saw
Vise

Materials

40 cm. strip of 18 mm. x 3 mm hot rolled iron
50 cm. strip of 18 mm. x 3 mm. hot rolled iron
Wood stock 25 mm. x 25 mm. x 80 cm. preferably a hard wood
Two (2) 25 mm. x 6 mm. steel bolts and fitting wing nuts
One (1) 11 cm. x 6 mm. steel bolt with fitting wing nuts
One (1) 3 cm. x 6 mm. steel bolt with fitting nut

II. HOW TO MAKE THE VITA SOLAR COOKER

Note: Be sure you feel you can complete all the steps before
starting construction.

Construction can be divided into nine parts:

1. Applying a sealing finish to the Masonite
2. Making the surface smooth and dust free
3. Applying thin uniform coat of adhesive
4. Applying the aluminized “Mylar”
5. Cutting out the rings
6. Preparing the legs
7. Bending the rings into shape and mounting them on the legs
8. Providing a cooking vessel support
9. Providing an adjustable brace

1. Applying a sealing finish to the Masonite (to keep the Masonite
from absorbing glue and moisture).

A. If the 120 cm. x 120 cm. Masonite is rough to the touch,
sand it smooth with medium sandpaper. If it 1s already
smooth, this step can be omitted.

B. Brush polyurethane paint smoothly on both sides of the Masonite, covering all areas. If polyurethane paint is not available, a coat of epoxy cement may be used in the front side (the side to be used as the reflector),
and varnish or lacquer may be used on the back. Do not use varnish or lacquer on the front.

C. Let the paint dry on a dust-free area.

D. Clean the brush with oil base paint thinner (or alcohol for varnish, or water for epoxy).

2. Making the front surface smooth and dust free.

A. Choose the smoother side of the Masonite as the front  (or the side with epoxy already on it.)

B. Using a safety razor blade, remove major imperfections,   uch as drip marks, from this front side.

C. Rub the surface smooth with steel wool or fine sandpaper,  until it feels very smooth to the touch. If it does not,  apply another coat of sealer to the smooth side, let it  dry and sand it again.

D. From scrap wood cut out four (4) wedges 10 cm. long and  5 cm. high as shown in Fig. 2. These will be used in part 4.

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E. Nail four (4) pieces of scrap wood into a 150 cm. square frame as shown in Fig. 1. This will be used in step 4.

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3. Applying a thin uniform coat of adhesive. See Fig. 2.

Note: Before you prepare the epoxy, complete steps 4A and  4B so that the Mylar will be ready to be glued.

A. Some important notes to remember about epoxy-resin  cements:

The cement hardens in about 20 minutes on the  tools and in a bit longer time when spread  on the Masonite.  Once hardened, it will not dissolve again even   in its own solvent.   Before hardening it may be dissolved in water,   but once water is added it will never harden.
Wash all tools and containers which touch the   cement with water before it hardens if you  want to use them again.  Do not let water come into contact with the cement  being used for the actual cementing.  Do not mix hardener and resin except when actually   preparing to use it.
Do not put a spoon covered with hardener into the   resin can.  Do not put a spoon covered with resin into the  hardener.

B. Mix equal portions of hardener, resin and 80% – 95%  alcohol in a clean dry cup with a clean smooth stick.  Two tablespoons or six teaspoons of each should be    sufficient.

C. Dust the Masonite surface with a clean, dry, lint-free  cloth immediately before applying the prepared cement.   Place the Masonite on a table or a similar large flat   surface, preferably above the ground, to lessen the  amount of dust that will settle on the surface while   you are working.

D. Pour the prepared cement on the center of the Masonite  and spread it evenly over all the surface in a very thin  coat with a stiff squeegee or rubber blade. Use long,   smooth strokes to prevent ridges and press down quite  hard. (See Fig. 2.)

E. Roll the cemented surface with a double-print roller until  the surface appears shiny and uniform from a glancing  angle. Work out ridges and regions of varying thickness   by going back and forth in various directions. Again,   press down quite hard.

F. Clean all the equipment within a half-hour. (You can finish the next step first if you have time.) Don’t   let any water get on the cemented surface of the Masonite and keep the surface away from dust. The cemented surface  will stay workable for at least a half-hour.

4. Applying the aluminized Mylar.

A. Decide which side of the Mylar is aluminized. It is  the underside of the roll (if the Mylar comes in a  roll) or the shinier side or the side from which the   aluminum can be rubbed off with your fingernail and  you can see the scratches you have made, through the
Mylar. The last test is absolutely certain.

B. Using a safety razor blade, cut a 160 cm. x 160 cm.  square section from the Mylar roll.

C. Nail the Mylar to the top of the 135 cm. x 135 cm. square  frame (from step 2E) with the alumunized side down. Use   small nails or carpet tacks or thumb tacks or staples   every foot or so, or nail down four (4) wood strips  along the frame. Stretch the Mylar tightly enough so
that it hangs down a few centimeters in the center. The  Mylar is very strong but it tears very easily so be careful   when you nail it down.

See Fig. 1 for the above two steps. If you have a  Mylar roll, the easiest way to fasten the Mylar is to   drape it vertically down in front of the frame.

D. Place the frame over the glued surface of the Masonite  on the four (4) wedges with the aluminized side down.  Pull the wedges out until the center of the Mylar hangs   a few cm. above the center of the glue-covered Masonite.
(See Fig. 3)

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E. Apply the Mylar to the Masonite with a stiff dry squeegee,  working from the center outward (see Fig. 3A), using

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short, firm strokes. Try to keep the Mylar quite taut  between the glued area and the frame so that the Mylar  does not touch the Masonite until the squeegee strokes  pull it down. If the Mylar rips from the frame and falls   on the Masonite, it will form many ridges and bubbles.
In any case, ridges and bubbles are sure to form and the   Mylar must be lifted and reapplied in the wrinkled regions.

Try the following procedure: spread the Mylar, starting  from the center as far toward the edges as possible, using   the tension suppled by the frame. Gradually lower the   edges, let the force of the strokes rip the Mylar from   the frame. If serious ridges or bubbles appear far from
the edge, free the Mylar from that region either by   lifting the frame or by ripping the Mylar from part of  the frame and pulling it upward and outward by hand. Don’t   worry about the four corners as they will be sawed off   anyway.

Remember that applying the Mylar is the most difficult part of building the solar cooker; it takes some practice  and patience and you are fortunate if the first few   efforts are successful.

F. Trim the overhanging edges of the Mylar with a razor blade.

G. With a needle or the razor blade, puncture all the air  bubbles and press them down; small air bubbles fixed in  this way are hardly noticeable afterward.

H. Clean the surface of any traces of glue with a damp cloth.

I. Allow one day for the glue to dry.

5. Cutting out the rings. (see Fig. 4)

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A. Locate the geometric center of the Masonite by marking  where the two diagonals meet. Be careful not to tear   the Mylar.

B. Cut out the rings with a coping saw or a jigsaw if one  is available, using the holes in the supplied template  as radii. It may be convenient to nail down the center   and rotate the whole sheet, keeping the saw stationary.   This may save the trouble of drawing out the rings.

C. From the inner ring cut out a section with a width at  the outer edge of .5 cm.

D. From the next most inner ring cut out a section with  a width at the outer edge of 2.8 cm.

6. Preparing the legs.

A. Cut Out the two legs, using the template enclosed. (You  may wish to copy the template onto sheet metal.) Use   2 cm. x 12 cm. x 150 cm. pieces of wood. At the center   notch one leg from above and one from below as shown on  the template, so that their edges are flush.
B. Fit the two pieces together at the 2 cm. center slots.   Cut a wooden tie bar about 40 cm. long (with 45[degrees] ends if   you would like) and nail or screw it to the backs of legs   so that the legs form an angle of exactly 90[degrees]. (See Fig. 5)

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7. Bending the rings into place and mounting them onto the  legs. (See Fig. 6)

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A. Place the inner ring (#1) on the frame and squeeze it  closed at one of the cross pieces, nailing both ends to the   same leg. Nail down the ring at the other places where it   crosses the frame as well, using 5 cm. aluminum nails (or   screws).

B. Do the same thing with ring #2; the ring should fit   easily into the slots in the legs.

C. Saw through ring #3 if you haven’t already. Work it  into the slots on the frame and ovelap it somewhere   between two crosspieces. It should overlap 8.8 cm. on the   outer edge and 6 cm. on the inner edge. Clamp it into place.

D. Do the same with the outer ring (#4). It should overlap  19.8 cm. on the outer edge and 14.5 cm. on the inner edge.

E. Place a light source about five meters from the cooker  and point the cooker at this source. Looking at the   cooker from about a meter directly in front, adjust   rings #3 and #4 until the reflection is even all the   way around all four rings. If the rings and legs have    been properly cut, very little adjustment would be    necessary.

F. When you are satisfied, there are two ways to fasten   the outer two rings in place:

1. Close the rings by bolting or riveting   them through the Masonite where they   overlap, at two or three locations not   lying on the same radius. Then nail   them to the frame; or:

2. Cut a wider slat in one of the crosspieces   and overlap the rings on top of this  crosspiece. Nail through the two layers of Masonite. This latter method is less   durable and produces a less satisfactory shape of the outer rings.

G. Clean the rings with a damp cloth and paint or tape the expanded edges of the rings to prevent weathering underneath the Mylar.

8. Providing a cooking vessel support.

Any support will do as long as the pot is placed so that the  pot rests in the bright focal region about one meter from the cooker. A separate tripod is one possibility. Another design is as follows:

A. Drill a 6 mm. hole about 2 cm. from one end of a 50 cm. x 18 mm. x 3 mm. strip of hot-rolled iron. Using a cold chisel, make radial indentations around the hole on one side.

B. Bend the strip into a circle of the desired dimeter  (the right size to hold a cooking vessel), with the  chisel marks on the outside of the ring formed. A   round wooden form will help.

C. Drill a 6 mm. hole in the other end of the strip at the place where they overlap to form the closed ring. Drill   another hole directly opposite this one.

D. Drill a 6 mm. hole 1 cm. from each end of a 40 cm. x 18 mm. x 3 mm. strip of hot-rolled iron. Score around earch hole with the chisel. Place this strip in a vise so that the middle 10 cm. are securely held. Grip the strip about

4 cm. from the vise with a wrench with adjustable jaws;  give a quarter turn so that the end is horizontal. Repeat  this with the other end. (Fig. 7)

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E. Bend the horizcntal ends to form a “U” with the chisel marks on the inside and the ends about as far apart as  the width of the ring formed in step B. (Change the dimensions in step D if necessary.) Drill a 6 mm. hole   in the center of the bottom part of the “U”.

F. Cut a 2. 5 cm.-deep slot diagonally into one end of the support rod (25 mm. x 25 mm. x 80 cm.), a little narrower  than 3 mm. Flatten the edges of the rod and drill a  6 mm. hole across the slot. (Fig. 8)

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G. Secure the metal “U” in the slot with a 3 cm. x 6 mm. stove bolt. Mount the metal ring between the ends of the “U” with  two 25 mm. x 6 mm. stove bolts and fitting wing nuts, with  lock washers between the ring and the “U” if you wish.

H. Cut a short triangular wooden block to fit snugly into position at the vertex of the two legs. Nail it in place.

I. Take the cooker outdoors. Rest the support rod in place in the vertex of the two legs, place a pot in the metal  ring and aim the cooker at the sun. Change the distance   which the support rod projects until the brightest part of  the focal spot is on the bottom of the pot. Mark the position
of the support rod.

J. Chisel off the upper edge of the support rod at its lower end and drill a hole down through it, the vertex of the   legs, and the triangular wooden block. Bolt the rod in  place with an 11 cm. stove bolt with fitting wing nut.
(Fig. 9)

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9. Providing an adjustable brace.

Brace the cooker in a position facing directly into the sun  so that the bright focal spot is on the bottom of the cooking  vessel. It must be adjusted about every twenty minutes as  the sun moves. The angle adjustment can be done with notched  pieces of wood propped against the tie bar. A better system, however, is the leg assembly shown in Fig.

9. This will be more secure. It requires s strip of iron, two 4 cm. bolts, a longer bolt, and two pieces of wood, one about twice as long  as the other. Their exact length will depend on your latitude    and the time of day the cooker is commonly used.

Anchor the legs firmly to keep the cooker from being blown   over by the wind.

Aluminized Mylar and epoxy may have to be imported.  Addreses where they can be obtained in the United States  are:

.0005-inch chrome metalized Mylar, 160 cm. wide, $1.00  U. S. per yard:

Coating Products, Inc. 101 West Forest Avenue   Englewood, New Jersey 07631   U.S.A.

Epoxy: Astro Special 1100, 8 pounds per gallon   at $1.30 U.S. per pound.

Hardener: Astro Special 2950, 8 pounds per gallon   at $1.65 U.S. per pound.

Astro Chemical Company, Inc.
1205 Godfrey Lane
Schenectady, New York 12309
U.S.A.

Figure 10. Using the Cooker

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1. Install the support rod in place in the vertex of the two legs. Aim the cooker at the sun.

2. Adjust the support rod so that the brightest part of the focal spot hits the bottom of a pot placed in the support. Drill a  hole through the support rod, the vertex of the legs and the triangular wooden block. Bolt the rod in place.

3. Brace the cooker so that it faces directly into the sun, with the bright focal spot on the bottom of the cooking vessel. The  shadow of the cooking vessel will be in the center of the cooker.  If the shadow is outside the center, the cooker is not facing   direatly into the sun.

4. Adjust the cooker every 30 minutes as the sun moves.

SOLAR COOKER LEG TEMPLATE

This template is to be used to make a 152-cm (5-toof) template for the legs of the VITA  Solar Cooker. See Paragraph 6A and Fig. 5,

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page 11. The complete template is AB (88.5cm) plus BC (63.5cm). To make the template, cut out the four pieces shown and

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string or a straightedge
to be sure ACB is a
straight line.

SPECIAL NOTE ON THE SOLAR COOKER MANUAL

Although we are sending you the Solar Cooker Manuals, we feel it is important to point out some limitations in its use. These are  partially covered on pages 1 and 2 of the manual and are repeated here for emphasis.

The VITA Solar Cooker is not useful for day by day cooking in most  circumstances. To be useful requires understanding of the following   limitations.

1. The cooker is probably not practical where the  average of the hours of sunlight is under   2000 hours per year.

2. The cooker is not useful for cooking meals in   early morning or late afternoon.

3. The cooker must be frequently shifted in position  during use (once every 10 minutes or so) to take   advantage of the sun’s position.

4. Making a good contact between the Mylar film and   its backing is tricky and requires practice. One   will probably ruin a few cookers in the process of learning how to make this seal. For this  reason it is important to order enough materials   for a few cookers in hopes of getting one good one. After this techniques mastered, there is little material spoilage.

5. It requires the development of some technique to cook with the cooker. This process can be   developed by a trial and error procedure. So   experienced people have compared this learning    process to be about as difficult as learning how to knit.

6. In many areas of the world the cooker cannot compete economically with existing methods of  cooking. For example, one should calculate how long it would take to recover the initial investment in the cooker from the savings on fuel that come about because of its use.

7. To properly introduce the cooker to a local populace requires careful thought and painstaking effort. Those experienced in the process of introduction should be consulted to see how it can best be put to use in the given culture. Aside from local taboos (religious, social
traditional, etc.) there will be the very formidable  barrier of resistance to change. People will be quick  to point out the difference in taste (whether there is  one or not) the longer or shorter cooking times, the   space required to store the heater, the need for being  outside while cooking, etc.

Nevertheless, the cooker does represent a method of putting the free-for-the-asking energy of the sun to work, and if this can be  accomplished economically in your community, it will bring the further  advantages of a more smoke-free atmosphere, less real danger of open
flame, and an opportunity to prove to the local people that a new  method can sometimes prove to be an advantage over old procedures,  thereby reducing that major obstacle to progress, “resistance to    change.”

If you decide to go ahead with the construction and introduction of the cooker with full knowledge of its problems and limitations, and  you think through a plan of introduction, you could well make a real contribution to the people of your community. Do not, however, expect  to quickly build a cooker properly the first time and be adequately cooking with it on your first try. Good luck in your efforts.

 Posted by at 9:59 am