Turn a flat sheet of anything flexible into a parabolic reflector.
Step 1: Prove it to yourself
Download this template and print it on cardstock, add something shiny cut it out and tape the edges together, don't cut all the way to the center. The template is Deltacad 6 format
Step 2: Now what?
Wel, you're done, you can print that template out any size and go to town, the plywood dish at the beginning was made that way. However if you like, in the next step i'll give you the math.
Step 3: So here's the math
Sort of, for the educated its based on the difference between the arclength integral and x, you can take it from there, for those not fond of thinking read the attached file.
Step 4: Now to build one
You could just cut one out with a jigsaw like the one at the beginning, but for better accuracy I printed out a section and made a router template
Step 5: Next I acquired the materials
I want to say I acquired all these signs LEGALLY, with permission, from the dumpster of a polling place, and I'd really like to see more instructables based on this resource, i know i'm sickened that signs are printed on a material designed to last a million years and are up an average of 2 days.
Nothing like dumpster diving in the rain
Once again these were collected legally.
Step 6: Now cut them out
quick work with a router, lots of plastic curls eveywhere, once they're cut out apply shiney aluminum tape from the hardware store.
Step 7: Now find a cool spot to work
And tape the peices together, or use cable ties, it came out a little peaked so I added a ridgid disk in the center to flatten the curve, I should have done that first.
Step 8: Finally flip it over and tada a parabolic reflector, now to turn it into a solar oven
eventually I hope to turn it into a tracking solar oven with drill head motors. a word on the coroplast plastic in these signs, to glue it u can flash it with a blow torch and use super glue, and hot glue works well to glue it together, the "rigid disk is just two pieces with the corrugations orthogonal glued with hot glue. Sorry no pix in operation, it's dark out.