Solar parabolic cooker with the mechanical mathematician!
14 Steps
I now think that "compound" parabolic dishes have numerous advantages. (A compound parabolic solar cooker can also be made with the mathematician and I can add instructions later.)
Use hardiplank, cardboard, plaster concrete or cob to make any size or shape parabolic reflector with this device! Solar cookers can be made from waste cardboard boxes covered with kitchen foil. Mostly people use math to figure out the parabola or use a template. Lots of mcguyver types are not into math and waste cardboard comes in all shapes and sizes with cuts all over the place so templates are not always suitable..
This method of making a solar cooker is suitable for a one off or assembly line and will work with ANY cardboard Box. Please try one and spread the word about this way of making parabolic cookers.
I cook in dark glass containers and use an oven bag to reduce thermal heat loss.
Currently, I use My cob solar cooker to steralize soil. At 5 pm when i come home, my soil is still at about 60 C (after cooling down for about 3 hours!) And suitable for growing seedlings.
I feel that this method of making solar cookers will prove very adaptable, very affordable and find use all across the world.
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Step 1: Introducing the mechanical mathematician!

Parabola's are hard to make unless you have some fairly fancy math skills.
But there is another way! The mechanical mathematician!
This little genius solves the parabola for all points on the curve! Using some string to help him. The string is attached at the focus of the parabola and goes through a point on the parabola (on a piece of metal for hanging curtains) and ends up tied at the pipe joiner.
There are many ways to make the mechanical mathematician, and the other one was used to make a cob solar cooker. Which works good.
It was made from old metal chairs and junk!
Rob Cook says: Feb 8, 2011. 6:20 AM
In this post i came to know more about Solar parabolic cooker which i was searching since long. so thanks for the excellent description and detailing diagram for solar cooker

http://www.thehomeappliances.net/solar-cooker-review-of-smart-sun-solar-cooker.html
gaiatechnician (author) says: Feb 8, 2011. 6:12 PM
Honestly, it is not that good.
I have continued my "research" and things are now much better.
The clam shaped solar cookers are still a work in progress but are probably a whole lot better than this.
frikkie says: Dec 20, 2010. 10:01 PM
one also covers the satelite dish with foil.At my previous job we played around with that.almost melted the plastic rubbish bin.Haha
frikkie says: Dec 20, 2010. 9:59 PM
nice!
One that does not want to construct the dish can always use an old satelite dish used to watch cable tv as you guys would call it.
You can also build a mechanical device which you can control with a sunseeker circuit.Which is nice if you want the dish to be in the sun the whole day cooking or heating something up.
gitm says: Mar 9, 2008. 2:26 PM
Also, if you measure the length of string used to draw the parabola you'll have the focal length. You can even choose a length of string in order to choose your focal length accurate to about 1/2 cm. or better.
gaiatechnician (author) says: Mar 28, 2008. 6:42 PM
I don't think that is exactly correct. But certainly, you can get the focal length you want by measurement at the central post. The length of string you need will be twice the focal length +the height to where it is attached on the saddle.
http://groups.google.ca/group/Sustain-the-development/web/the-mechanical-mathematician has some new info about making a mathematician and mould at the same time.
(It is part of the accumulating barbecue project).
I used a hinge and post and rested the arm on the frame for the mould to make a stronger construction with a much more steady mathematician. This should mean a more accurate dish (or part dish)
I no longer make dishes. I make sections of dishes and there are a number of reasons to do this.
gitm says: Apr 3, 2008. 9:50 PM
The string is intended to draw an arc for creating the curved surface. Once the focal length, and therefore the arclength, have been chosen and drawn, a piece of string half the length of the secant line of the arc can be used to draw the circumference. I'm not sure what is meant by "central post" and "saddle". Perhaps we're thinking of two different things.
gaiatechnician (author) says: Apr 4, 2008. 8:19 AM
I think we are thinking of 2 different things. I think secant generally refers to circles. The device above draws the surface of a parabolic dish, not a circle. The "saddle" is in blue in the diagram above and it slides back and forth. There is a picture of my latest mathematician at
http://www.appropedia.org/Image:Cobmould.JPG and in that case, the saddle is made of wood, and it is on a wooden "arm" that is hinged to the central post. In that case, I am not trying to make a total dish, just a mould for a piece of a dish.
(This might start to make sense if you look at the "tracking solar barbecue, the wave of the future" video which might be in the related column on your right.)
Attamet says: Dec 2, 2009. 10:01 PM
I don't understand why this makes parabola's
to me it looks like it just makes circles, because the string keeps a constant radius, which makes a circle, while a parabola has to have a constantly changing radius.
could you please explain why this works?
gaiatechnician (author) says: Dec 3, 2009. 9:40 AM
The drawing is not clear enough but it  has image notes to explain it.
The string is attached at the focal point and at the saddle.
It is not attached at the slider bar.
String passes through an "eye" in the slider bar.
As you move the saddle nearer or further from the central Post, string passes through the eye so it is not a constant radius.
It traces a parabolic dish.

Attamet says: Dec 3, 2009. 10:02 AM
thanks now i see what you mean
AnarchistAsian says: Sep 16, 2008. 11:02 AM
cool! i'm listed as a collaborator! ... but what do you need? was it a mistake?
gaiatechnician (author) says: Dec 15, 2007. 7:47 PM
higgrobot says: Sep 3, 2007. 9:26 AM
Another non math way to derive a parabolic curve is to get a length of dowel and just stretch a length of string from end to end. Just use the resulting curve as a profile, works ok.

Other non math solar cooker designs that may interest you
Harf
http://www.thefocsle.net/solar/howtobuild.html

Parvati
http://www.angelfire.com/80s/shobhapardeshi/ParvatiCooker.html

This may come in handy if you decide to make one of them, just print it out and stick it to something
http://www.lucasinjection.com/Degree_wheel_100.jpg
gaiatechnician (author) says: Sep 5, 2007. 9:35 PM
I took a look at the harf link. I think that link is useful to parabola makers too. Your parabola does not need to be close to the focus. You can make the parabola a bit to one side of the focus if you wish! The advantage? Imagine aiming at a 9 inch round fish bowl. A bunch of the light from a 9 inch square directly under will miss it. But if your light is reflected at an angle, your square can be bigger and nearly all the light will hit the fish bowl. So less bends are needed.
gaiatechnician (author) says: Sep 3, 2007. 11:07 AM
Although it is a little harder initially to make the mechanical mathematician, the cardboard is more efficiently used by this method. More surface area is available to collect sunlight.
Also, the mechanical mathematician is adaptable. If a larger piece of cardboard comes along, or a larger cooking vessel is available, You can reset the focus or the size of the segments to use that too. I have a video on utube about using the mechanical mathematician to make a parabolic oven with cob.
These videos are pretty long though! Not for everybody's taste!