This is my second attempt at a solar oven. My first was made from cardboard and worked okay. The first I built to make sure I understood the science. This one is an improved version.

Step 1: Tools/Materials

You can get by with fewer tools. These are the ones I used.

Tools
Table Saw
Miter Saw
Jig Saw
Drill
Drill bits
Square
Ruler
Corner Clamps
Staple Gun
Clamps
Sandpaper

Materials
Plywood
Boards
Screws
Insulation (in my case I used an emergency blanket)
High Heat Grill spray paint
Aluminum foil
Duct tape
Mirrors
Mirror holders
Pane of glass
Zip Ties
Small clip
Staples

Step 2: Make the Inner Box

The plywood I used was from an old stage. It was 1/2 an inch thick. Make sure you know what pans/dishes you will be using in the oven so you can make it to the correct size. I wanted my inner box to fit a 9 inch pan with plenty of room to reach in and take it out. I made the inner box 13"x13"x6". Accounting for the 1/2" thickness of the wood, made the inside of the box 12"x12x6". Plenty of room for my pans. I used a table saw to cut the plywood, and sanded the wood after cutting it.

Here are the measurements for the panels that made up the box.
2 panels 12"x6"
2 panels 13"x6"
1 panel 13"x13"

After that screwed the panels together using corner clamps. If you do not have any corner clamps do your best to make sure the box is square. You don't want any leaks that might let heat out. Then I sprayed the interior of the box with high heat black spray paint.

Step 3: Make the Outer Box

The outer box needs to have some space to allow for your insulation. I made the outer box 16"x16"x10". This allowed for about an inch of insulation. I made this one in the same way I did the other.

Here are the measurements for the panels that made up the box.
2 panels 16"x10"
2 panels 15"x10"
1 panel 16"x16"

Step 4: Insulation

I learned in my research that most of the heat lost from a solar oven is through the glass. In hindsight I might have been able to make the oven without the outer box. I did not perform any experiments with just the inner box. That would be a project for another time. For the insulation I decided to use an emergency blanket. It said it reflected 90% of body heat. I figured it would work well for what I needed. Also do not use Styrofoam. It can melt and release chemicals into your food.

Step 5: Combine the Two Boxes

Now put the two boxes together. I made a spacer so that the smaller box would be flush with the top of the larger box. At first I thought I might fill the box with stones since they hold heat well, but decided it would be too heavy. Besides most of the heat is lost out the top through the glass.

The spacer I made was 3.5 inches high. Once you have the boxes flush use some wood to seal the two pieces together.

Then I made a slot for the glass to slide in. I took the plywood I was using and cut a slot in it wide enough for the glass to easily slide into. The slot was an inch deep and about a quarter of an inch wide. I used the glass from a cheap picture frame to cover the opening. I lined the outside of the glass with duct tape to keep it from cutting me when I use it.

Step 6: Make the Reflector

I got the measurements for the reflector from this instructable on solar ovens. The widest size of the trapezoid is 2.25 x cook chamber width and the height is 1.25 x cook chamber width. I used my jigsaw to cut the reflector pieces. I made one and used it as a guide for making the others.

I drilled holes at the top and bottom corners of each reflector. Then I wrapped the reflectors in aluminum foil shiny side out. I used duct tape to secure the foil. Then I attached mirror holders to the reflectors. I used twist ties to attach the reflectors to each others. I also added a small piece of wood to the back of each reflector to help stabilize it.

Step 7: Test

Test your oven. See how it is working and make see if there are any improvements you can make. You can see my testing data here. In the third test I added the glass from a scanner to the top of the oven. It did not completely cover it, but it did increase the temperature. Clouds were an issue that could not be helped, but I found if I checked it every half an hour to make sure it was angled toward the sun it did better.

From my testing I concluded that making the glass as thick as possible , and keeping the oven pointed toward the sun will help keep the temperature high in the oven.

We like to cook granola bars in ours. Post what you have cooked in your own solar oven in the comments below.