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Thread: Maximum Laminating Radius?

  1. #1

    Maximum Laminating Radius?

    Hello Everyone,
    I am planning to build a large square parabolic sun reflector. After a lot of thinking and researching an economical way to accomplish this I've decided on using strip laminate bending to create the parabolic ribs of a grid to mount an array of square mirrors on. I have never done this type of thing before and my woodworking experience consists of building tree houses and skateboard ramps as a kid.

    Based on what I understand, my plan so far is this is this: Lay up a bunch of long, thin wood strips and adhesive in a large parabola-shaped form, clamp them there, let them dry, and reapeat many many times.

    I know I can handle building the form. My main concern is the wood springing back at all after I take it out of the form. In all the pictures I've seen of laminates this curve radii are much smaller that what I am going to attempt. ( My parabola will be around 8 feet wide and 1.5 feet deep) It needs to be as perfect a parabola as possible or the efficiency will go way down.

    Do you guys have any tips on how to reduce or eleminate springback on such a shallow curve?

    Thanks a lot.

  2. #2
    Join Date
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    As far as I understand it, there is no need to remove the profile ribs once made the parabola.

    You are interested in the interior par not the exterior, aren't you? In this way you could have some sort of torsion box with a parabola on one of its sides.

    Besides, you would get plenty of flat surfaces ( four sides + bottom) to fix whatever support or base needed.
    Best regards,
    Toni

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  3. #3
    Thats true, but the problem with that is it would take a lot of material and would be extremely heavy and hard to erect on a sun-tracking mount. I just want to make a whole buch of identical ribs that I can bolt together parrallel and perpendicular to eachother and have a nice lightweight frame. (wireframe-like)

  4. #4
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    What about using urethane foam of medium density, it is easy to shape and very rigid and lightweight
    Best regards,
    Toni

    __________________________________________________ __________________________________________________ _________________
    web site:http://www.toniciuraneta.com
    I also dream of a shop with north light where my hands can be busy, my soul rest and my mind wander...

  5. #5
    Yeah that's a possibility but I don't know if it would be strong enough to hold sixty four square feet of glass mirrors. Especially in the wind. Ideally I would make the whole thing out of carbon fiber but that is way beyond my resources and ability.

  6. #6
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    how `bout an old satellite dish? bending wood to an exact radius isn`t usually something a novice jumps on (at least with success).....
    if you`re dead set on trying holler back with a few more specifics besides depth/diameter and being able to support lotsa weight.
    as a general rule metal is more cost effective than wood in stressed applications.
    welcome to family wood workin`!
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  7. #7
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    Quote Originally Posted by tod evans View Post
    how `bout an old satellite dish? ............
    welcome to family wood workin`!
    Dang, beat me to both of these!
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


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  8. #8
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    Do the ribs have to be an exact parabola curve or do they just all have to be exactly the same? Can you laminate up something long enough to cut all the ribs from (so they're at least all the same with or without springback) rather than try to get identical curves from glue-up to glue-up??
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  9. #9
    I figured metal would be more cost effective but wouldnt that me even more difficult to bend into a precise shape without expensive equipment? If you know a good way to get a curved metal shape I would love to hear it. Yeah an old c-band style dish would also work but I want something bigger than the common sizes. I also think it would look pretty cool to have mirrors on wood with a nice finish on it.

    As for specifics of my design, basically all I need is to make sections of a parabola having the equation y=(x^2)/16 in cartesian coordinates on the interval (-4',4'). I think a 1"x1" cross section on the sections would be good.

    All together I need 16 ribs.

    thanks for the help by the way.

  10. #10
    Quote Originally Posted by Doug Shepard View Post
    Do the ribs have to be an exact parabola curve or do they just all have to be exactly the same? Can you laminate up something long enough to cut all the ribs from (so they're at least all the same with or without springback) rather than try to get identical curves from glue-up to glue-up??

    Yes it needs to be an exact parabola due to the fact that nothing but a parabola will focus all light from a distant source to one single point. They also all need to be exactly the same.

    Is there anything I can do to totaly get rid of springback? So the layup will come out in exaclty the same shape as the form?

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