Working to build a parabolic solar cooker templates....

I have for some time tried to figure out how to draw a parabolic shape and get that transferred over to  solar cooker.

I found this program that gives me the shape -> 

http://www.w1ghz.org/10g/software.htm

But the bmp it exports I found to be very sloppy.....

But I played with it and found if I gave it a huge number 1000 of intersect points that I got a decent number of data points,  I put that into excel  and graphed it,   and exported a picture from that..

Now that I had that I found I could manipulate that  to give me a picture out which then I could use this program to make  a print out of the parabola with a standard laser printer.

Using this open source program -> 

https://posterazor.sourceforge.io

Attached is the results of this,     I have printed this out and I am planning on testing using this as a template for either making parabolas....

I have an idea of using paper mache for the shape,   I am thinking that I could make different templates make the shape with paper mache, then put the different parabolas on my Chinese cooker to give me shapes with various focal lengths away from the cooker so I don't drip oil on the cooker itself, but must be careful not to catch things on fire :-) 

I got info on how to make large parabolas much easier than I did it...

https://www.imaginary.org/film/mathlapse-constructions-by-pin-and-string-conics#:~:text=Parabola:,chalk%20draws%20a%20parabola%20arc



String  is the way to go...

suggest looking up the wikipedia article on parabolas and move down to the pin and string construction section.  That is what we did 50 years ago in grade school.

One other comment it sounds like you might be working towards to a higher resolution than needed.  You are not building a telescope with perfect focus.  You are building a reflector with about a 4 or 6 inch rough focus needed.

The ones built out of cardboard and aluminum foil are the ones I most familiar with  Rim circle with a series of ribs with quasi triangles stuck to them.  About a dozen pie sections stuck to the ribs on 4 to 5 foot diameter circle produces a good enough circle.

If I wanted to build a form to mold over I would use the concrete and clay techniques working off a central pipe spinning the half form.

Here is the first video I found on it.  You only need one parabola half form to build the positive to cast over.

C. Letellier wrote:suggest looking up the wikipedia article on parabolas and move down to the pin and string construction section.  That is what we did 50 years ago in grade school.

One other comment it sounds like you might be working towards to a higher resolution than needed.  You are not building a telescope with perfect focus.  You are building a reflector with about a 4 or 6 inch rough focus needed.

The ones built out of cardboard and aluminum foil are the ones I most familiar with  Rim circle with a series of ribs with quasi triangles stuck to them.  About a dozen pie sections stuck to the ribs on 4 to 5 foot diameter circle produces a good enough circle.

If I wanted to build a form to mold over I would use the concrete and clay techniques working off a central pipe spinning the half form.

Here is the first video I found on it.  You only need one parabola half form to build the positive to cast over.

RE: String...   right before your post I put up a post where someone showed me the string method,  thanks for pointing that out.

Thanks for the link about the video on concrete molds,    I had found a video on a guy who did this same construction method for his solar parabola cookers...



This why I started making the template, I have lots of sand here in Florida, so most of the raw materials are here.

I have deabated using  aircrete,    fiberglass,    for the form,    but I think for the first few I will use paper mache till I get the prototypes done, then i will move to the forms that cost to make.....

The final move will be to put glass mirrors into the finished form....      

I have another idea of using foam as the filler....    

I guess this is why it has taken me so long to get this far as I find several different ways to do this thus I get into a mental freeze that stops my progress.

I found yet another one.

Some other possible suggestions.

In the late 80's or early 90's I went on an engineering field trip from Laramie to CO.  One of the stops that day was at SERI.  Solar energy research institute in Golden CO.  One of the things they were working on was portable mirrors with adjustable focus.  It was snap together pipe frame work that they put in a fairly tight mylar bag.  The frame stretched the bag gently.  Sort of like a giant drum.  They then applied a light vacuum to the bag.  By adjusting the vacuum it gave them a large variable focus parabolic mirror as the plastic stretched in its elastic limit.  It eventually turned out they were too fragile for long term use.  But this might be a faster way to prototype to what you want.  Get your base measurements off something like this so you only need one base prototype.  They are now known as NREL.(National renewable energy labratory)

NREL

I had been looking at something similar.  One of the things I looked at was cast material.  American Science and Surplus used to have bulk boxes of the plaster impregnated cloth for casts fairly cheap.  Don't know if they still do.

Another suggestion would be to look for old satellite dishes.  My father as a side gig sold satellite dishes in the late 70's.  They came in household sizes up to 12 feet in diameter.  8 and 10 were common and as the electronics got better they shrunk down to 5 and 6.  There were stamped metal ones and and rigid fiber glass ones.  Big thing is they were designed to hold up out in the weather over the long haul.  Would still need to be mirrored.  The stamped metal ones were painted black to reduce what the reflected out to the LNA so they didn't cook the electronics.  So if you could find one of them in good shape you might be able to simply polish the paint off,

Then another mirror option.  Read down the list here.  One of these was an outdoor rated mirror surface with something like 95% reflectivity and something like a 25 year warranty.  Lighter weight and non breakable and no surface to peel off the back from weathering.  Mirror option  It is one my wishful thinking list for several potential projects.  A tad pricey but might be worth it for long term projects.  As 2 of mine are over head the added safety of not being breakable would be worth it probably.

Suggest looking at the information on metal sand casting as they have a number of fairly cheap and safe ways to glue sand together for casting.  Adding water glass aka sodium silicate is one.  Wood flour is another and there were probably a dozen others.  You will want something cheap and low waste while you make your positives to cast off from.

Lesson learned the hard way on paper mache done with flour if it has any moisture exposure(even just high humidity) it can draw bugs and make a mess over the longer haul.  Given what I know now if I expected to want it longer term I would borate treat it in some form.  Probably mixed with the water right to begin with.  But you can also get the powder to mix with water so you can spray lumber with it too for termite and fire resistance so that would be my second option.  Available at any good lumber yard.

Now I had been dreaming on other things and wanting to play with aircrete too.  My thinking had been to do a skim coat of concrete, fiber, sand and concrete dye over the mold and then while still wet to pour it full of aircrete mix with fiber.  That would likely work for you too giving a lighter weight rigid parabolic shape that should be durable.  Have never gotten around to testing as other projects have priority.  

As for ferrocrete many of the things I want to do there would be thin giving a high risk of it spalling over the time so the wishful thinking to try there is Basalt fiber instead of steel wire for the form material to put the concrete on.

PS forgot one other.

If an aluminum reflector is the goal I went by a you tube video out of India on casting huge aluminum metal bowls for cooking  that might be ideal for casting parabolic reflectors.  It went into great detail on how the bowls were made.

C. Letellier wrote:PS forgot one other.

If an aluminum reflector is the goal I went by a you tube video out of India on casting huge aluminum metal bowls for cooking  that might be ideal for casting parabolic reflectors.  It went into great detail on how the bowls were made.

Thank you for those suggestions...

I actually  am working on the concept of variable focus for the mirrors...

Here is my idea.....

For the first round I will use paper mache with strips of bamboo run thru for re-enforcement....  

Then after shape is made, I have this idea of glue segments of mirror on cloth , then this cloth will be placed on the paper mache, but the idea is the cloth is removeable...   if I want to change focus, I just put another  paper mache backing behind the segmented mirror cloth on top of the paper mache, and this goes into my Chinese parabolic cooker for angle adjustment,    Doing this I should be able to make custom backings to which I can flop out different designs at will.

My plan is to start with paper mache,  try out different concepts then finish with aircrete or fiberglass for the next design..

I have already purchased alumicut   to polish aluminum to mirror surface....    I was thinking pop cans could be used......    

I have collected mirrors for this project, and it is now starting to come to the first proto types...

Thanks for your input...

Mart

Progress!!

Using the first template I have started forming the first mould.

Now I need to find some cardboard to make the paper mache.

C. Letellier wrote:You are going to want to screen the debris out of the sand in your work area.

My thought was to cover the sand with plastic then use paper crete on top...

May take me a few time before I get what I want.

So,   I am now trying out making paper crete.     never done this before...       I decided to run the cardboard thru a garbage disposal.       I made a mess the first time around, but now I think I have the hang of this.

First wet the cardboard,    then tear into small chunks, run thru the garbage disposal,  then dump out on a bed sheet to capture the small cardboard fibers.

I now have the sand, cement, and now will process the cardboard and see what happens.

http://forum.driveonwood.com/t/working-to-build-a-parabolic-solar-cooker-template/8235/35?u=mart85

Finished putting the paper crete on the mold… going to give it 4 days and see what happens.

Not trying to derail the thread but can anyone enlighten me as to what a solar cooker is?

It looks like it uses mirrors to focus sunlight on a specific spot to raise temperatures enough to cook, is it effectively an oven then?

What are the tradeoffs with other alternatives, such as a rocket mass oven which is also powerless, or a solar powered induction stove?

Is there any benefit to these over traditional ovens other than being electricity free and low tech? Does it cook slower and work better for certain meals for example?

Klaus Wolfgang wrote:Not trying to derail the thread but can anyone enlighten me as to what a solar cooker is?

It looks like it uses mirrors to focus sunlight on a specific spot to raise temperatures enough to cook, is it effectively an oven then?

What are the tradeoffs with other alternatives, such as a rocket mass oven which is also powerless, or a solar powered induction stove?

Is there any benefit to these over traditional ovens other than being electricity free and low tech? Does it cook slower and work better for certain meals for example?

Solar cookers have various means of concentrating the energy of the sun to cook....

This link has a good description, and many links to various types of cookers...

https://en.wikipedia.org/wiki/Solar_cooker


The benefits can include reduction of energy use to cook on sunny days so one could save fuel  with propane / wood with solar cooking..  

Down sides is cloudy days,  cost of the device, cost to maintain device,  windy days that can extend the cooking time or disturb the cooker.

Some people prefer solar cooking taste,  but myself I believe this is a personal preference.

For the cost,   I believe   that going direct to solar panels to an  "electric lunch box "    is the better option because it allows you to cook inside,   having to go out and move the solar cooker to follow the sun is a pain....

Myself as a prepper,   I like to have several options so I have a "Sun Oven"  box cooker,   a Chinese parabolic cooker,   a vacuum solar cooker.      Each of these take time to learn how to cook with them and get them to do the cooking you want to do.

Preparing for EMP events having the ability to use solar for the cooking can save the fuel that you need for rainy days, so just another option.

I would like to make a solar cooker that I can just leave outside.     Part of this build is learning the longevity of the building materials I use.

I love open source projects where people share in design like this one..

Thanks for humoring me Mart.

That makes a lot of sense, I guess in addition to diversifying your cooking methods one thing I hadn't thought of was the ability to make it yourself, or fix it if it breaks. Assuming you have some tinfoil or other reflective material on hand as a backup.

A solar lunch box is only as good as long as the dog doesn't knock it off the counter and the solar panels/batteries haven't degraded/died.

By the way, you mentioned a "Chinese parabolic cooker," would that effectively be the same thing, just a manufactured version from China?

When  I get back to the states I'll try making one, I'm not a prepper but it seems like a fun project even if I won't get a ton of use out of it.

Although, maybe I become one, preparing for a rainy day is always smart. Even if it's not the end of the world, you can always lose your job...

So this is what it feels like dumping 6-8 hours of work only to get a broken end of project....

https://www.skool.com/the-survival-gardener/working-on-building-a-parabolic-solar-cooker?p=342821cd

This was a flop, but  painful lessons learned.


Think I will re-evaluate the next direction I want to go...     Learned tons in my mistakes...    but it is painful not getting the results I hoped for.

Well...    First round on making a parabolic solar cooker was a flop.



What I learned in using paper crete:



1)   The mixtures to be mixed well,   some of the mixture did not mix well and the cardboard did not setup with the rest making weak areas.



2)    This would of been much stronger if there was a mesh added to this.    Being so large when I lifted it broke the bottom sections.      Either this needs mesh,  or to be made up of multiple sections for this size that can be joined together.



3)   The method I used is a ton of work breaking up the cardboard about 6 hours of breaking the cardboard down, mixing  and smoothing out....    



4)    I first just used sand for the mold shape,   which lost form after I applied the paper crete on top...      This was a mistake as it did not keep form,     Better would be to make the mold out of plaster or cement then use the template I created to make the form, then let harden, then make my forms off of that...        



5)     Buying a 120$    5 foot metal parabolic cooker off ebay is very cheap compared to the work I put into this :-)    



After thoughts:



In doing this I believe that I want a different shape for the parabolic design, one that is much flatter and will throw the focus point further out.        



Paper crete  to be done right demands to have the right tools to make it work.     The thicker parts of this design do seem to be durable.      I do see potential here for other projects.