Introduction: Pie Tin Solar Reflector

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.

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I had originally made this many years ago with a home baking cake tin, but what I had on hand, and sufficient for this demonstration, was a Marie Callender's pie tin.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.

Step 4: Invert the Tin.

Just place the tin on the foil. If you use the alternative suggestion from the last step, add epoxy now.

Step 5: Press and Cure.

Weight the tin against the foil while the adhesive cures for a good, smooth seal.

Step 6: Trim the Foil.

It looks much better this way, and the excess foil won't get in the way.

Step 7: Prepare the Valve/seal.

The first time I did this, i used black plastic electricians tape and use my mouth to suck air out and close the seal.
Place a piece of tape over the pin hole so the hole is not sealed shut, because next...

Step 8: Vacuum Pump

This is a wine bottle sealer which uses a silicon rubber cork replacement and a hand vacuum pump to pull air out of the wine bottle that you didn't finish drinking.

Step 9: Evacuate and Seal.

The cork is placed in the pump then placed over the tape, being careful not to seal the tape, and pull a few strokes on the pump to remove some air from the tin. The MC pie tine I used actually began to collapse a bit. When done pumping, slide the cork to the side to seal the tape around the hole.

Step 10: Take a Look.

You should see a distinct curvature in the foil. Notice the grain on the foil.
If you can get polished foil, you'll get much better results.
I once used the plain side of an aluminized mylar balloon, it worked beautifully and could actually cast images from the outside onto a wall by a window. Mylar leaks air more than aluminum.

Step 11: Check the Focus.

Be Careful. The focal area is intensely bright and hot.
I did this several years back and obtained such a tight focus that a piece of wood I held in the focal point burst into flame in about 15 seconds.

That's it.

I have a snow disc hanging out in the garage.
When I get the time.

Comments

author
morsed2 made it!(author)2016-04-27

I want to say its a great instructable. But everyone else has already said it. How about it's better that great?

One quick question, do you know if the concave form is a parabola?

I have added it to my fav's and collections and may try to make it in a couple of days.

Thanks for taking the time to document this instructable.

Steve

author
Sam+Grove made it!(author)2016-04-27

It's a spherical section as the pressure difference is equal over the surface.

author
piaferre made it!(author)2010-12-10

this is GREAT!

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renuka made it!(author)2010-05-05

this info needs to be more helpfull its lame lame lame

author
godofal made it!(author)2010-03-13

how about using this with a regular 12 volt solar panel?
would that couse any damage to the panel?

author
Sam+Grove made it!(author)2010-03-13

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.

author
Kiteman made it!(author)2007-05-19

Nice. I wonder if it would work with tougher plastic film, sprayed silver? That would last longer before you accidentally crush it.

author
Sam+Grove made it!(author)2007-05-19

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

author
macrumpton made it!(author)2009-08-10

http://www.Mirrorsheeting.com has mirrored vinyl and mylar up to 52" wide for a reasonable price.

author
regularbasscase made it!(author)2007-07-26

I'm thinking emergency blanket and a childs wading pool.

author
Sam+Grove made it!(author)2007-07-27

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.

author
macrumpton made it!(author)2009-08-10

Snow disks! Perfect! Now I wonder who carries them in Miami?

author
macrumpton made it!(author)2009-08-10

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.

author
macrumpton made it!(author)2009-06-06

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/

author
ehudwill made it!(author)2008-01-02

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?

author
toogood made it!(author)2007-06-26

would the bottom of a coke can work if it polised?

author
Sam+Grove made it!(author)2007-06-26

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.

author
toogood made it!(author)2007-07-02

cool i'll try it

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meddler made it!(author)2007-05-19

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.

author
Sam+Grove made it!(author)2007-05-19

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.

author
lemonie made it!(author)2007-05-19

This looks good, but I don't see the wood busting into flames. Do you know why your previous build worked better? L

author
Sam+Grove made it!(author)2007-05-19

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.

author
lemonie made it!(author)2007-05-19

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

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HOMEPIE64 made it!(author)2007-05-19

dude i love this

author
Sam+Grove made it!(author)2007-05-19

Thanks. This demo was so easy to make, I did a rebuild this morning which took about 20 minutes.

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