While the glue dries, I thought to review some other design suggestions by gost from the terra preta thread.
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Originally Posted by gost
...building a solar oven for making low temp charcoal. He seemed to feel that the trough of the reflector needed to be about 8 to 10 feet wide in order to achieve the 470 F needed to make the charcoal. It almost seems like he is guessing at this, but I can't tell for sure..... Are you basing your design on an existing concept that has calculated the temps for different latitudes? Is there a simple formula for calculating the parabola?
My thought was to cut two pieces of half inch plywood into the parabolic shape, making the ends of the trough, then simply use a staple gun to attach the mylar posterboard to the edges of the plywood, thus eliminating the need for any ribs. The pipe itself would then go through oversized holes in the plywood, at the height of the focal point, where it would then be kept from touching the wood by the use of 3 adjustment screws.
I had also been planning on using galvanized stovepipe, of the kind used for gas water heaters. Does anybody know if the galvinizing might introduce anything toxic, when heated, that might absorb into the charcoal?
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I am not using an existing design & I simply picked a size suitable to material on hand.
I gave the parabola formula above; it is in every high school algebra book (And they say you'll never need it!
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The idea of using the 'positive' piece of the cut is good. Since I have these as left-overs from my 'negative' form trough, I can use them for another reflector.
I have no idea about metals migrating from the pipe to the charcoal; galvanization is done with zinc & the pipe is steel of some type. You may want to wash the pipe with warm soap & water before use.
While the glue dries I have the struts under construction. By tonight I plan to have the reflective panels glued on. With some cooperative weather I may have temperature measurements from the oven this coming week.
Oooooo! Idea! Popcorn! Oh yeah...
