CNC parabolic dish.

[Prozacgod]

I was talking to a buddy about build a primestar dish solar cooker and we were debating on the merits of gluing 100's of small mirrors onto it, or finding some decent foil, something thin enough to mold, but thick enough you might be able to polish it.

I told him, well if it wasn't for the precise alignment of the mirrors I'd just build one from scratch that was flat - then I realized well heck I bet some people out there in CNC land could easily carve a wood panel to the correct depths, and gluing the mirrors would go more efficiently (less guess work) and uniformly.

Thoughts?

I could probably write the code to find the positions of each of the mirrors based on focal point. and mirror square size, but I don't know how this would turn into CNC gcode or something, would be glad to help out if someone thought it was a worthy project.

--
-Prozacgod

"Prozac may heal the mind, but friends can mend the soul"

[Scott Kovaleski]

I had the same thought to make cheap parabolic mirrors for a schlieren photography setup. I think a problem is aperture size, since most 3d printers and hobby mills/lathes are limited in size. Maybe in sections?

You also have optical quality being an issue, though focal spot size isn't as big a deal for a cooker.

The best idea I have seen is a guy who made a cylindrical parabolic mirror buy letting silvered Mylar hang under its own weight from two rails. I think that was on Hackady if you want to try to find it. That would be dead simple to make work.

Dr. Scott Kovaleski
Associate Professor
Electrical and Computer Engineering
University of Missouri
349 Engineering Building West
Columbia, MO 65211

Ph: 573-882-8377
Fx: 573-882-0397

koval...@missouri.edu

highvoltage.missouri.edu

[Chad LaFarge]

Just spit-ballin’, here. No experience.

 

I’ve considered a heavy-weight mylar roll (http://compare.ebay.com/like/400214138366?_lwgsi=y&ltyp=AllFixedPriceItemTypes&var=sbar ). I imagine one could find some high-temp spray adhesive (a quick Google yields http://www.yourautotrim.com/perhittrimad.html ).

 

Cutting a sheet of plywood to make a two parabolic curve templates and magically bending some surface to that shape, and using that as the substrate for the mylar might be a fun experiment to try.

 

I wonder how much the reflection would suffer if you simply pressed the mylar around an acrylic form, shiny-side in, and let the sun shine through the acrylic. It would be more likely to keep a smooth reflective surface, but refraction and diffusion could occur.

 

Hasn’t Dan Rojas done some videos on parabolic troughs/dishes?

 

Chad

[Prozacgod]

Talk about getting an idea that works quickly! The mylar idea lead me to this: I have a reflective piece of acrylic, that is thin and sturdy - it flexes into a very nice parabolic curve. I can set this up between two bars (similarly to the mylar) and it will be strong enough to be pointed towards the sun 

I happen to have a few sections of old unused old cast iron drain pipe clean em' up and BAM "instant" hot water heater ;) 

wonder how much heat would be lost off the surface of the cast iron pipe VS something thinner and more conductive to heat?  Painted black copper for instance?  I'm assuming the temperatures here might be to hot for ABS or similar right?

Originally we just wanted to make a hot dog cooker or "death ray" - but a legitimate project might come of this.

I started thinking of the code for making a flat surface that has many "ramps" to affix mirrors too, but - I'm no mathematician I brute force a lot.  I'm starting to think this is the kind of problem Prolog was made for, but I don't know it well enough to pull that off.

[Chad LaFarge]

Is this helpful?

 

http://phoenixnavigation.com/ptbc/articles/ptbc37.htm