You can make a parabolic mirror from an old satellite TV dish, or a bathroom vanity mirror but that’s not fun. Making your own mirror allows you to get the exact curvature you need for whatever you might be burning, cooking or heating. It’s a fair amount of work, but the resulting energy the mirror produces is amazing.
Part 2: Making the mirror
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11 thoughts on “DIY: Parabolic mirror”
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A beautiful result but *way* too much work. It would have been faster, cheaper and less wasteful to create a fiberglass plug mold rather than casting concrete, then creating the concave surface from that. They’ve only been building boats this way for half a century now.
There’s a good basic description at:
http://www.valsparcomposites.com/moldmakerepair/moldmaking&repair.pdf
As an aside, it’s always amusing how much dirty technology (polyester fiberglass resin, self-adhesive metalized polyester film etc.) goes into “green” products.
I skimmed that document, previous commenter, and it describes making the plug from wood. I don’t have the skills or tools to make a parabola or anything close out of wood, but cement is pretty easy, given a mold. I could imagine suspending a flexible material to create a catenary shape with a simple rig, and then fiberglass or something over that. But the cement round still seems the easiest and most long-lasting.
(And by long-lasting, I meant reusable. If you’re going to make the mirrors that small, you’re probably going to need a lot of them. And then you could sell the mold or pass it around a village in need of such contraptions for cooking etc.)
Keep it simple… why not just polish the drum?
Fiberglass is nasty, and concrete creates like 1000 tons of CO2 from burning natural gas for every ton on concrete.
My god, what a LOT of work for such mediocre results! If it’s for solar heating/cooking, why not just bulid a multi-panel fold up model that so many people make out of mylar backed plastic mirrors?
Just stretch mylar across one end of a cylinder, seal around the edges and begin to evacuate the cylinder.
hey presto! An adjustable parabolic mirror.
Or like Dax said just polish the drum end.
Interestingly you can polish the domed base end of a coke can using chocolate (works as a v. fine abrasive!) and use that to start a fire :-)
Don’t they make highly reflective paint that would be suitable to, say take the drum base and spray coat it?
Or what about spinning the fiberglass backer while applying a lightweight urethane or epoxy to create a uniform and smooth finished surface before using the same approach with the paint on the fiberglass?
As far as finishing the edge, I was initially thinking metallic sheet metal tape, the high grade stuff steam fitters use, but something a little more elastic would probably be better suited to conform to the curve.
Martin has a pretty good idea with the suction style but I can’t imagine the mylar being as reflective…
Also you should probably attach a backing support prior to adding the reflective surface: like using flare-headed countersunk screws into a wood block; or something that can later be used to attach some kind of ball joint or support point to make the mirror more versatile rather than propping it against something.
Wouldn’t a magnifying lens be more effective for creating a sun powered boiler though?
I have to agree with what most of the previous commenters have said. The video is great, very detailed, and informative, but it seems like an awful lot of energy and material expense. There has got to be ways to making such a mirrored surface that don’t involve so much energy-intensive material. I mean, you could have even used that bowl you were using to scoop the concrete as a parabolic mirror…
I guess I could understand making a concrete mold like this if you were planning on making lots and lots of parabolic mirrors from it, but I also agree that simply salvaging the bottom of drums (treated reflectively) seems much more efficient and “green”.
i am in the process of building a parabolic mirror right now…first i acquired a satellite dish from a satellite dude.. he even gave me the mounting hardware…lol…next im buying some self adhesive acrylic mirror tiles from the internet, then im going to stick them on and heat them with a heat gun. that should work. i also just acquired a fresnel lens out of a old projector tv i saw in the trash.. along with that was a sheet of mylar ..a huge trapezoidal mirror.. i would use that for the dish, but im afraid of going through the effort just to find it dosent weather well…
Questions of efficiency remain for any solution, given technological alternatives.
I think the video was very good. It was clear, simple and easy to follow – with frequent comments on things to be careful of along the way. Best of all, it could be imitated in any part of the world (except the polar regions) if they had access to the materials. Given that those are light-weight, the logistics aren’t much of a problem.
The creativity of it got all of us thinking too, didn’t it?
That’s probably the best acheivement.
That’s pretty cool, the only problem is your trapped into using the parabolic dimensions of the water heater tank. . .you really can’t control the desired focal length