Instructables
A pie tin, a sheet of aluminum foil, and a little glue to make a spherical reflector. I call it a Reflexor.

I first made one of these around 1980 and I am unable to recall the circumstance of my inspiration. It's quite easy to make and the results can be quite good depending on the care you put into it and the materials used.

This demo uses household aluminum foil which has the drawback of being unpolished resulting in some difusion of the sunlight.

I once made one with the blank side of an aluminized mylar balloon and it proved to be a very good reflctor. I remember that I was able to reflect a near perfect inverted image from the window onto the wall beside the window.

Caution is advised! Focused sunlight is VERY intense, and this is so lighweight, you can flash yourself while handling.
 
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Step 1: Puncture the pie tin.

I had originally made this many years ago with a home baking cake tin, but what I had on hand, and sufficient for this demonstration, was a Marie Callender's pie tin. Adding a small hole with a straight pin was not difficult. I hammered it in with a spoon.

Step 2: Lay the foil out.

If you want to be perfectionist, you can stretch the foil out a bit with tape to make it slightly taut.
For this demonstration, I just wanted to get it done quick for photos.
I did take care to tear the foil carefully to avoid wrinkles.

Step 3: The adhesive.

I used E6000 for this, but later found that it didn't cure well between the tin and the foil.
It worked well enough, but I recommend epoxy, or some other adhesive that doesn't require evaporative curing.
Put it all the way around. If you use a 5 minute epoxy, you want to get it all on in a couple of minutes.
Alternatively, you could put invert the tin on the foil first, then epoxy the seam.
piaferre4 years ago
this is GREAT!
renuka4 years ago
this info needs to be more helpfull its lame lame lame
godofal4 years ago
how about using this with a regular 12 volt solar panel?
would that couse any damage to the panel?
Sam Grove (author)  godofal4 years ago
If you mount it so the focal point does not fall on the solar panel, why not?
You'd want the concentrated sunlight to cover the entire solar panel.
Kiteman7 years ago
Nice. I wonder if it would work with tougher plastic film, sprayed silver? That would last longer before you accidentally crush it.
Sam Grove (author)  Kiteman7 years ago
Aluminized mylar works very well. I discussed this in one of the steps. I have some very wide aluminized mylar out in my garage which I want to install on a snow disc. I wanted to get this published before I attended the Maker Fair in San Mateo county today
http://www.Mirrorsheeting.com has mirrored vinyl and mylar up to 52" wide for a reasonable price.
I'm thinking emergency blanket and a childs wading pool.
Sam Grove (author)  regularbasscase7 years ago
You're thinking of the aluminized mylar sheet that can be used as survival gear. Yes, as long as it is free of pinholes or cracks. The child's wading pool is another matter. You will be able to evacuate some air, but it may be susceptable to buckling if you try to take too much out. Snow discs are much sturdier.
Snow disks! Perfect! Now I wonder who carries them in Miami?
I think unless it is a very sturdy wading pool it would collapse or at least distort unless you reinforced it before removing the air. Perhaps you could stack two or three of the pools together to make them stiffer.
macrumpton5 years ago
Very cool! A couple of thoughts: if you were to heat the pan/reflector after you punched the hole, and then clogged the hole before the pan cooled the air cooling/contacting inside should create enough vacuum to create the parabola. No pump necessary! if you made a larger hole so you could pour some plaster inside before you suck the air out, then when the plaster cured it would keep the shape of the parabola without the vacuum. To make a larger one you could stack a couple of bike wheel rims with the spokes removed. You would have to plug the spoke holes. A shopvac might do the air removal/
ehudwill6 years ago
I tried making a reflector out of an old satellite dish. I lined it with aluminum tape, but it doesn't reflect the light to a single point but in a line. Do you think the pie tin would work with aluminum tape?
toogood7 years ago
would the bottom of a coke can work if it polised?
Sam Grove (author)  toogood7 years ago
Maybe, the solar flux area is rather limited though. The key point with the pie tin is you get a decent area and really light weight making it easy to handle or mount.
cool i'll try it
meddler7 years ago
Hey Sam, i have made a few solar ovens (the panel reflector type) and i bought an emergency survival blanket and cut up the material then glued it to cardboard. It worked great, i wonder if it would work here? It does rip fairly easy though.
Sam Grove (author)  meddler7 years ago
Aluminum foil is very vulnerable. I used the regular thin stuff for this demo. Good thing, I bet getting a decent curvature on the heavy duty foil would have collapsed this cheap pie tin. I think mylar film might be more durable, as it is more flexible.
lemonie7 years ago
This looks good, but I don't see the wood busting into flames. Do you know why your previous build worked better? L
Sam Grove (author)  lemonie7 years ago
It was an early sun, I was holding the reflexor (my name for it) in one hand and camera in the other. I wasn't using a 2 x 4 then either, I did detect a whiff of smoke, though. Tthe pie tin is pretty flimsy and probably distorted a bit and the texture of the foil disperses the focal point. Also, I was tilting the tin a fair amount so the board wouldn't block too much sun. I just wanted to get the picture.
Under the circumstances you described, a whiff of smoke is pretty good going. I've had fun with a Fresnel lens, but I like the look of this much more. L
HOMEPIE647 years ago
dude i love this
Sam Grove (author)  HOMEPIE647 years ago
Thanks. This demo was so easy to make, I did a rebuild this morning which took about 20 minutes.