Thanks for checking out this Instructable.
First I need to give credit where credit is due. I might add this cooker design is by no means my invention and is not a new theory.
Professor Steven E Jones of BYU I think originally designed and tested the model. Follow the link to his page and read how he did it.
I decided to post my version and my results here as, just one more way to work with this existing design.
Okay let's get started!
First off hunt for a cardboard box anywhere from aprox 30" tall with bottom and top unassembled.
You will be looking for aprox a 2:1 ratio in size. I.E. 60" wide by 30" tall, twice as wide as tall if that helps.
I happened to have some black duct tape on hand so that ended up being what I used. It has no significant purpose other than it was available.
I also had one piece of vertical blind that had broken off at the top, so I decided to recycle it by using it as support members along fold lines. This is not really needed but I like a good durable unit when I finish a project. ( I PLAN ON USING IT)!
Next I taped all the box corner/fold seams both front and back. This gives a nice surface to work with. Let me make a note here****
USE THE 2:1 ratio for size. If you box is other than that cut it to fit aproximately . It doesen't have to be perfect. An inch or two longer would be better than shorter of course.
I used a box that was too long and you will see later where I just folded one side back and used it for added strength. You can do this if you wish but trust me depending on the thickness of your cardboard you could be having to work to hard to keep the shape you want in the finished product.
You will notice is taped the support pieces to the cardboard box. DO NOT TAPE THEM OVER A BOX JOINT **** if you do folding up and storing it later on will be very hard to do. I taped them on next to the folds and often over lapped the tape with the tape at the joint itself.
Step 1: Time for Shaping and Gluing
As you can see in the first picture the box when too long stretches out quite aways.
Next I cut the 7" radius out of the center of one panel (sorry no picture) but you can see it on the link in the first step or in the photo where I am attaching mylar around it.
After cutting the radius I folded the box to create the aprox 60 Degree angle of folds. Picture the center at 90 degrees to the long side in the top center of the radial cut. then fold 30 degree bends to the right and left respectively to get your funnel shape. 30 + 30 is 60.
Another way to say it is you have folds that look like sunbeams coming from the cut out does that help?
After getting my folds right and of course my plastic blind sections to bend :) then I applied gorrilla glue to all the fold lines and a few other areas along edges etc. I then spread out the mylar on the floor and with the assistance of my partner we turned the cardboard over and laid it in the middle of the mylar sheet. we then piled on the books to help the glue fully connect with both the mylar and cardboard.
You may not need this step... but then it was time to go get some dinner :) After an hour or so I came home and removed books and finished wrapping and taping the mylar to the back side. (notice I didn't say glue) with the tape if you need some flex room you can lift and retape etc.
as you fold over the mylar on the back you will also have to make a way for the mylar at the cut out to be secure. I used clear packing tape on the front around the cut out to make sure it was stable and would not ripe unexpectedly.
Step 2: The Funnel Is Complete Except for Testing
When you have finished the funnel you are pretty much ready to go. You will notice from the picture that I used clips to hold the funnel together. I am currently trying to figure out just how I want to fasten it on a semi permanent basis.
In other videos I have seen screws used etc.
For the cooking Jar you will need to locate a wide mouth canning jar (CLEAN). I bought cheap FLAT black spray paint. The bargain Betty in me likes CHEAP so I went for the $1.18 can at Home Depot.
I have found that some of the more expensive High temp paint also can come with a bit of a semi gloss finish. BE CAREFUL this is NOT what you want to use. Under no circumstances do you want to use a paint with any hint of gloss. The flat black needs to absorb the suns rays not reflect them back off the Jar.
You will notice the picture of the cooker in one of my balcony lawn chairs. You will also see the clip that holds it in place. This lawn chair or and old one I have may become the final cooking stand when I am done testing it out.
Now for the Acid... I mean oatmeal test!
Please picture in your mind the following conditions:
80+ F September 10th 2012 Denver Colorado.
70% clouds in the sky. I starting at 3:30 pm concluding 4:50pm it was pretty late and unfavorable conditions for this test.
There was 1:20 minutes total cook time
Instant oatmeal packet + 1/2 cup tap water 50+F out of the tap.
I placed the black cooking jar in a 1 gallon ziploc bag just for the test. I have seen HDPE cooking bags used (like you roast a turkey in.)
The Cooker jars external temp was 120.1F as I took it out of the ziploc bag, and the internal temp was 112F when opened after cooking. The final temperature was 102F by the time it was in the bowl with a spoon.
The oatmeal nicely cooked tasted great. Under normal sun conditions I would bet you could cook one serving in 40-50 minutes time.
I suppose it would have been much hotter if there was no clouds and the time was 12-1pm.
If you have questions or comments feel free to ask or add them. Peace and happy eating, Bryan