4 ms·

Random Destructive Acts via Focused Solar Radiation

36 points by fezz 11y ago

ntumlin 11y ago
There's a lot of videos on YouTube of people using Fresnel lenses from old projection TV's and melting various things. https://www.youtube.com/watch?v=jrje73EyKag https://www.youtube.com/watch?v=jrje73EyKag
- ChuckMcM 11y ago
  That was where I got mine, I asked at a TV repair shop if they had one, and they gave me two! Setting the asphalt on fire was entertaining. We built a simple frame for it out of frame components at the craft store to make it easier to point. My goal was to build an aluminum can smelter. At the time I had this idea that I could crush a diet Dr. Pepper can with my hands (this I often do) and then slide it down into a crucible at the focal point of the lens, and have it melt and drip into a bucket of water below, creating aluminum bb's which would be much denser than even crushed cans. The problem however was that aluminum oxidizes before it melts, so in the ideal set up you really want it running in an oxygen free environment. Way more work than I wanted to invest. Later I discovered induction heating (which you can do with a windmill, some magnets and a coil of wire around a piece of steel (or aluminum).
  - nsajko 11y ago
    About the oxidation, have you tried using a reducing agent (Na is probably easiest to get). Did you watch those videos of guys melting aluminum in their backyards? :)
    - ChuckMcM 11y ago
      I did not try sodium. But to be clear, the picture of a place to throw my empty soda cans which turned them into melted bits was the attraction, all without hooking up to grid power. I'm not actually trying to smelt aluminum as some are. But watching folks melting alumninum is instructive.
- tomtoise 11y ago
  Oh lord, that kid getting so close to the beam to try some egg. I'm not even a father and I flinched.
awakeasleep 11y ago
In case anyone reads this and gets excited enough to buy one, realize fresnel lenses are actually dangerous. It's almost like keeping some turpentine soaked rags in a cardboard box. Sort of kidding. The point is, you can have the lense somewhere you think is safe, but the angle of the sun changes throughout the year and one day six months later rays of light hit it. Or you have kids that don't think that way, and they leave it somewhere. Even as a fully aware adult, it's counterintuitive, because you'll be trying to take it outside and accidentally burn yourself, or set it agains something while you're getting ready, not realizing the lens was born ready and doesn't care about your plans. You always have to carry them in a sheathing material. Your brain expects something like that to have an off switch. They're cool, but you should probably keep them in an opaque sheath in a gun safe, and leave it alone when you're drinking.
- Natsu 11y ago
  The article provides ample evidence to support your claims, given how many items on their list of things burned are people.
- userbinator 11y ago
  The power of the Sun is definitely something to be respected... and since it's basically free, makes you wonder how much more of it could be harnessed to do other useful things. https://en.wikipedia.org/wiki/Solar_furnace https://en.wikipedia.org/wiki/Solar_furnace
- superuser2 11y ago
  Interesting. I work I a campus theater that has a lot of fresnel lenses in storage. We're careful with them because they're expensive glass, but have never thought of them as hazardous. There's no (direct) natural light anywhere near where they're kept, though.
- trhway 11y ago
  if only somebody gave the same advice to the "death ray" buildings architect - Vinoly. > but the angle of the sun changes throughout the year and one day six months later rays of light hit it. almost exactly word for word :) http://www.theguardian.com/artanddesign/2013/sep/06/walkie-talkie-architect-predicted-reflection-sun-rays http://www.theguardian.com/artanddesign/2013/sep/06/walkie-t... "The developers have blamed the problem on "the current elevation of the sun in the sky," a position Viñoly seems inclined to share. "When I first came to London years ago, it wasn't like this," he said. "Now you have all these sunny days. So you should blame this thing on global warming too, right?""
danieltillett 11y ago
When I was a kid I used to have one of these huge lenses (it was made of glass and made to make your 12” TV look like it was 30”). I used to use it to go around setting various things on fire when I was being bad and kill weeds in the lawn when I was being good. It was amazing how quickly it would work - a few seconds and the weed was dead.
salgernon 11y ago
Haltec in Mountain View (not to be confused with Halted in Sunnyvale) used to have one on display; it was about a meter width I seem to recall. There was a sign on it: "Warning: Sets Fires Instantly". (Haltec is gone now, but I seem to recall some serious lasers still available at Halted.)
SamReidHughes 11y ago
The Explorabook ( http://www.amazon.com/dp/1591747996 http://www.amazon.com/dp/1591747996 ) came with a Fresnel lens as one of its pages. Yes, a children's book came with a Fresnel lens inside! A kid detached his and brought it to summer camp, and after a few days, he was asked to leave it at home.
- TeMPOraL 11y ago
  > A kid detached his and brought it to summer camp, and after a few days, he was asked to leave it at home. That's how we kill creativity and curiosity in people.
  - adrianN 11y ago
    It's also how we prevent forest fires...
  - SamReidHughes 11y ago
    It was just some stupid kid that went around cooking human flesh and being a general nuisance.
    - fit2rule 11y ago
      What a pity the opportunity to foster an interest in science and technology was not taken. Surely there would have been some value in integrating the interest with the camp activities .. unless of course, thats not the purpose of camp.
- ohazi 11y ago
  Wow, this brings back memories... This book was fucking awesome.
  - Synaesthesia 11y ago
    The diffraction grating is super rad, and the agar gel too.
jonah 11y ago
Markus Kayser made a "Solar Sinter" e.g. a sun-powered 3D printer. http://www.markuskayser.com/work/solarsinter/ http://www.markuskayser.com/work/solarsinter/
- TeMPOraL 11y ago
  That uses sand as printing material. I.e. you go with it to a desert and start reshaping the environment! Absolutely amazing!
  - Gravityloss 11y ago
    They're thinking of doing something similar on the moon. Or why not on asteroids or elsewhere? You can create dust free landing pads, tiles for building, roads... Maybe just harden a regolith berm surface to lessen dust problems.

36 points by fezz 11y ago

There's a lot of videos on YouTube of people using Fresnel lenses from old projection TV's and melting various things. https://www.youtube.com/watch?v=jrje73EyKag https://www.youtube.com/watch?v=jrje73EyKag

ChuckMcM 11y ago
That was where I got mine, I asked at a TV repair shop if they had one, and they gave me two! Setting the asphalt on fire was entertaining. We built a simple frame for it out of frame components at the craft store to make it easier to point. My goal was to build an aluminum can smelter. At the time I had this idea that I could crush a diet Dr. Pepper can with my hands (this I often do) and then slide it down into a crucible at the focal point of the lens, and have it melt and drip into a bucket of water below, creating aluminum bb's which would be much denser than even crushed cans. The problem however was that aluminum oxidizes before it melts, so in the ideal set up you really want it running in an oxygen free environment. Way more work than I wanted to invest. Later I discovered induction heating (which you can do with a windmill, some magnets and a coil of wire around a piece of steel (or aluminum).
- nsajko 11y ago
  About the oxidation, have you tried using a reducing agent (Na is probably easiest to get). Did you watch those videos of guys melting aluminum in their backyards? :)
  - ChuckMcM 11y ago
    I did not try sodium. But to be clear, the picture of a place to throw my empty soda cans which turned them into melted bits was the attraction, all without hooking up to grid power. I'm not actually trying to smelt aluminum as some are. But watching folks melting alumninum is instructive.
tomtoise 11y ago
Oh lord, that kid getting so close to the beam to try some egg. I'm not even a father and I flinched.

awakeasleep 11y ago

In case anyone reads this and gets excited enough to buy one, realize fresnel lenses are actually dangerous. It's almost like keeping some turpentine soaked rags in a cardboard box. Sort of kidding. The point is, you can have the lense somewhere you think is safe, but the angle of the sun changes throughout the year and one day six months later rays of light hit it. Or you have kids that don't think that way, and they leave it somewhere. Even as a fully aware adult, it's counterintuitive, because you'll be trying to take it outside and accidentally burn yourself, or set it agains something while you're getting ready, not realizing the lens was born ready and doesn't care about your plans. You always have to carry them in a sheathing material. Your brain expects something like that to have an off switch. They're cool, but you should probably keep them in an opaque sheath in a gun safe, and leave it alone when you're drinking.

Natsu 11y ago
The article provides ample evidence to support your claims, given how many items on their list of things burned are people.
userbinator 11y ago
The power of the Sun is definitely something to be respected... and since it's basically free, makes you wonder how much more of it could be harnessed to do other useful things. https://en.wikipedia.org/wiki/Solar_furnace https://en.wikipedia.org/wiki/Solar_furnace
superuser2 11y ago
Interesting. I work I a campus theater that has a lot of fresnel lenses in storage. We're careful with them because they're expensive glass, but have never thought of them as hazardous. There's no (direct) natural light anywhere near where they're kept, though.
trhway 11y ago
if only somebody gave the same advice to the "death ray" buildings architect - Vinoly. > but the angle of the sun changes throughout the year and one day six months later rays of light hit it. almost exactly word for word :) http://www.theguardian.com/artanddesign/2013/sep/06/walkie-talkie-architect-predicted-reflection-sun-rays http://www.theguardian.com/artanddesign/2013/sep/06/walkie-t... "The developers have blamed the problem on "the current elevation of the sun in the sky," a position Viñoly seems inclined to share. "When I first came to London years ago, it wasn't like this," he said. "Now you have all these sunny days. So you should blame this thing on global warming too, right?""

danieltillett 11y ago

When I was a kid I used to have one of these huge lenses (it was made of glass and made to make your 12” TV look like it was 30”). I used to use it to go around setting various things on fire when I was being bad and kill weeds in the lawn when I was being good. It was amazing how quickly it would work - a few seconds and the weed was dead.

salgernon 11y ago

Haltec in Mountain View (not to be confused with Halted in Sunnyvale) used to have one on display; it was about a meter width I seem to recall. There was a sign on it: "Warning: Sets Fires Instantly". (Haltec is gone now, but I seem to recall some serious lasers still available at Halted.)

SamReidHughes 11y ago

The Explorabook ( http://www.amazon.com/dp/1591747996 http://www.amazon.com/dp/1591747996 ) came with a Fresnel lens as one of its pages. Yes, a children's book came with a Fresnel lens inside! A kid detached his and brought it to summer camp, and after a few days, he was asked to leave it at home.

TeMPOraL 11y ago
> A kid detached his and brought it to summer camp, and after a few days, he was asked to leave it at home. That's how we kill creativity and curiosity in people.
- adrianN 11y ago
  It's also how we prevent forest fires...
- SamReidHughes 11y ago
  It was just some stupid kid that went around cooking human flesh and being a general nuisance.
  - fit2rule 11y ago
    What a pity the opportunity to foster an interest in science and technology was not taken. Surely there would have been some value in integrating the interest with the camp activities .. unless of course, thats not the purpose of camp.
ohazi 11y ago
Wow, this brings back memories... This book was fucking awesome.
- Synaesthesia 11y ago
  The diffraction grating is super rad, and the agar gel too.

jonah 11y ago

Markus Kayser made a "Solar Sinter" e.g. a sun-powered 3D printer. http://www.markuskayser.com/work/solarsinter/ http://www.markuskayser.com/work/solarsinter/

TeMPOraL 11y ago
That uses sand as printing material. I.e. you go with it to a desert and start reshaping the environment! Absolutely amazing!
- Gravityloss 11y ago
  They're thinking of doing something similar on the moon. Or why not on asteroids or elsewhere? You can create dust free landing pads, tiles for building, roads... Maybe just harden a regolith berm surface to lessen dust problems.