An adjustable parabolic trough will help you fine tune your shapes to heat the way you wish. Start with a plastic FOR RENT sign (PVC SHEET). Take that to a sign shop and ask if they will cover it in chrome mirror sign vinyl decal material. A sign supplier can provide you with various thicknesses of PVC sheet. Sure you can use poster board. It won't last.
Hardware stores have large sheets too; for use in a bathroom, we'll use the smooth back. Now you have a lightweight and flexible mirror. This material is the same kind of material you see on all kinds of advertising signs. It comes in chrome, gold, chrome with a color tint, and more. They have fake gold and real gold.
The material can not take excessive heat. It will melt. So if your whole oven gets hot then don't use it. If you are using thermal cookware it should work. It is ideal for any situation where the reflector itself will never be too hot. When the material is on steel or wood, embers have little effect. If an ember lands on the material while not backed or thinly backed with plastic, it will melt. But for many applications it is ideal and comparitively inexpensive. And it's very easy to use. Line the inside of nearly and cavity, aim it at the sun, cover with glass and get cooking.
You don't need finely machined anything. To conduct experiments with it you can try bending it and realizing the results. You'll be able to focus sunlight away at various height for various reasons. This parabolic trough will produce a very powerful beam of light extending as long as you want to go with it. Start for instance by clamping or glueing the center of the mirror to something like a piece of plywood. The middle is fixed now and the sides can be bent and aimed exactly where you like, near, or far to infinity. When you have the sweet spot focal point where you want it you can fix it in position permanently.
The other day it occurred to me that I could use a sheet magnet which is flexible and usually used for magnetic signs, and make a sheet mirror that will stick to parabolically shaped sheet metal. They would be easy to remove and wash. You could stick the walls of your cooker on a metal wall to dry at night.
On the next eliptical or round parabolic dish cooker I can apply a kit of magnet mirror triangles to the dish. The dish is made of steel so the satellite tv company can keep their cost down. Steel is even cheaper than plastic. For us it could be fantastic. With so much steel around we have a wide array of shapes we could stick magnet mirror vinyl too, then cook all day and remove the magnets to clean them as needed.
Magnet mirrors could be used to extend the width of your project a bit beyond the edge of the metal, or to make external mirrors for your oven. I can make a kit for someone if needed. Say goodbye to aluminum foil and expensive mirrors.
Here's another experiment for someone to try: See if mirror window tint can make good enough reflections to be used for cooking somehow. Perhaps it could be applied on plastic sheets, or metal sheets, maybe white ones.
What happens if mirror tint is applied to a solar oven's window so as to try to keep light bouncing around in the box? Could mirror tint be used to make flexible mirrors?
What about using mylar, lexan, or plexiglas mirror? Cooking mirrors don't always need to withstand heat themselves. The food may be hot enough to burn you and the mirrors stay cool.
Build your own Kramer junction or Nevada one power plant. I will try to tell you how. Solar electricity does not have to cost so much. You'll need: Any suitable bendable sheet material in covered with chrome mirror vinyl. You may need a pump for very hot oil, thermosyphoning may be enough to circulate the oil. You'll need a big tank of water for collecting steam, a small steam turbine directly connected to a suitable generator. Add that to the production of hydrogen by electrolosis and you'll have power to get you through the night, and run your car. I envision the same steam generator running on hydrogen quietly during the night hours. Now you don't need a battery bank or some bogus fuel cell contraption designed to keep you dependant on big business. Near morning, the oil could also be easily pre-heated by the hydrogen in anticipation of the sun. We need someone to prove this concept for the good of all mankind. The hot oil pump could be a power steering pump. The top of a mower looks much like a steam turbine. Old cars have generators. I'm just speculating, if you blow yourself up doing this don't blame me. Producing hydrogen by electrolosis uses very little power to create great amounts of power.
Will thermosiphoning circulate hot oil? Will it circulate it through a heat exchanger system steam turbine electricity generator? It works for solar water heaters? If so does the liquid's thermosiphoning speed increase with increased heat? How much? Is there a peak or max or ideal?
A parabolic trough does not have to aim straight at the sun to be effective. The focal point can be eccentric. This will allow you to aim at something without casting shadows on the trough. The trough does not have to be directly under the thing you are heating.
The synthetic oil used at Kramer Junction and Nevada one is probably the same as in your car's engine. Add soot and you have an oil which collects solar heat, I suspect.
The trough could also be covered in glass to retain more heat. More kept heat means more efficiency.