Moldless composite mold

Discussion in 'Composites' started by 4trade, Jul 7, 2012.

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  1. Jul 7, 2012 #1

    4trade

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    Funny title...anyhow, i have been thinking to make composite turtledeck and tail fuse skin to my Cassutt. I can use that additional weight for tail because i will turbocharged my engine, and it will help to keep W&B in a proper limit. It will keep future maintenance easy and it is good looking too.

    I have been bouncing around idea for moldless mold....composite work is one of a kind job, so i don´t need or want mold if i can avoid to build it.

    My idea is that i build my turtledeck and tail skin like Rutan moldless planes. When i am that stage, that first skin layer is laminated, squeegeed and dry....i build (MIG weld) loose cage of tubing around it and fill that skin/ tubing space with construction foam. Then i take of my skin/ mold combination out of plane and turn it upside down. Now i got rigid first skin that work like mold too. I just need to add core material and squeegee inner layer of carbon fiber, and bulkhead.....after that i take that construction foam off with chemical or sand paper and my turtledeck is done. All i need to do is trim lines.

    That kind of job cut to need mold. it is fast and It is cheap, just add few scrap tube and foam.

    Any thoughts that this don´t work?
     
  2. Jul 7, 2012 #2

    wsimpso1

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    The really good thing (and potentially bad thing too) about composites is that you can make almost any scheme work if you put enough effort into developing it. Tom Arnold's video on building th AR5 covers an idea similar to yours, but in a simpler way. He used it for the front half of his wings and for his fuselage.

    The canned foam is ugly to work with and remove.

    Here is my summary of his method:

    Foam to shape of outside of airplane;
    Slurry, glass, resin, squeegee, peel ply, let cure;
    Build a simple frame of MDF, wood, etc, and stick it to outside with dabs of bondo;
    Set assy on frame, hotwire or otherwise remove unwanted interior foam;
    Slurry, glass, resin, squeegee, peel ply, let cure;
    Pop loose the frame - its done.

    No steel, no welding, simpler tools for the frame. And no canned foam, which is the really evil part. Instead, you just cut the frame parts close to shape for the outside.

    Billski
     
    Last edited: Jul 7, 2012
  3. Jul 7, 2012 #3

    autoreply

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    Why not work from the inside out? Layup a flat panel of glass over glass (the massive stuff) plate. Very thin, a single layer is sufficient. Wrap this around your frame and use 2 wooden formers to give it the required shape if necessary. Now glass in some reinforcements, like a strip of polystyrene, covered with another layer of glass and stop when the part is rigid. That saves you a lot of sanding and manual shaping. Naturally, the above only works in 2D-shapes or with a very small 3D curvature. But compared to creating a "perfect" outer skin by hand, it's a zillion times easier to just use a flat, shiny surface to do that for you..
     
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  4. Jul 7, 2012 #4

    4trade

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    I really want to AR-6 type of great looking, smooth curve after canopy, and therefore i cannot do it with flat plate. I can build it aluminum too, but same problem. That turtledeck is anyhow so much work if build composite materials, that i can put some extra effort and time to have those fine, elegant line like AR-6 or Symmetry. Side of a Cassutt upper longerons is curved shape and bottom longerons are straight, because of that fuse shape i need to build 3D shape anyway. I got English wheel and i can do some complex curve with aluminum, but it is really time consuming, and that result is noisy skin of a plane....

    I build much longer canopy, because i want excellent all around visibility for aerobatics. AR-6 and Symmetry is the great ones...ill like to look of those two good looking jewels. I cannot achieve that smooth lines because i have shorter and more chubby fuse....but close to these looks anyhow.
     
  5. Jul 7, 2012 #5

    autoreply

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    Ok. Another thought. Can you turn a large male (foam) mold on a lathe? (The basic shape) Nothing fancy, just two fixed clamps and a large block of foam you sand in the desired shape?
     
  6. Jul 7, 2012 #6

    4trade

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    I don´t believe that i can find that big lathe here. There is boat company, and they can mill any shape. They do these boat hulls like that....but it´s too expensive for me at moment, so i must chance spending $$$ to sweating back...HA HA!

    Here is picture at last summer...after then i decide to add curve at turtledeck.....and i need to thank for this extra effort HBA topic Most beautiful aircraft.....and picture of Synergy....ARGH
    I just want to fly good looking aircraft in future, so little more sweat now will be years of joy in a future.
    013 (Large).jpg
     
  7. Jul 7, 2012 #7

    dshowalt

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    regarding Autoreply and working from the outside in. could you not create a flat panel on a waxed table top (glass, formica, etc). And then use the MDF cradle to form the exterior shape. Then add stiffener ribs or bulkheads. similar to this video. Building Your Zenair Floats Video by HomebuiltHELP - YouTube
     
  8. Jul 7, 2012 #8

    4trade

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    I can´t build it like that because i want to smooth curve at turtledeck, that start to canopy....flow following canopy line down and curve smoothly to tail fin. I add one picture at rear side. I want to add curve behind canopy instead that flat turtledeck now.
    014 (Large).jpg
     
  9. Jul 7, 2012 #9

    4trade

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    .....did you mean by lathe some kind of rotating stand that i can build? If so, i was thinking to build that kind of thing to work. Just upper longeron "waist line" and couple of fixed bulkhead to build that basic foam shape. Plywood thing....
     
  10. Jul 7, 2012 #10

    autoreply

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    Yes. Two Y-beams that stand up and insert some round tubing in both ends. You just need to find a nice girl to turn it for you, so you can sand. Just using a waist line as guidance and you can get a nice, smooth shape.

    Instead of going through great troubles for a perfect surface finish, you might also be able to cover the sanded foam directly in stretch-able plastic and directly lay up the fiberglass, like this:
    http://www.homebuiltairplanes.com/f...c-machined-foam-stretchelon-bagging-film.html
     
  11. Jul 7, 2012 #11

    wsimpso1

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    Hey, the method I cited was done by Tom Arnold, the guy who did the AR5 and AR6.
     
  12. Jul 7, 2012 #12

    4trade

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    Some good advise, thank´s!

    Now comes another idea, that came with Billski´s mention how nasty that canned foam is....How about that: When first skin layer is done at male foam plug (with plastic between foam and skin), and it is dry i glue regular, thick wallpaper (with ornament and colors HA HA!) on that skin with wallpaper glue. I let it dry and add canned foam that stick and dry on a wallpaper surface. I got really rigid mold/ skin...take it off that male plug and turn it over for core and inner layer. I don´t need any kind of extra stiffener when working like that...and when part is done, i just cut most of canned foam off and soaked off that wallpaper on outer skin.

    Skin comes off a plastic covered mold easy, and wallpaper stuff come off easy too. These just fill their purpose at that moment and save my time.

    It´s not very common way to do it....but i cant see why it not work. Ideas why not?
     
  13. Jul 7, 2012 #13

    autoreply

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    One of the problems of "curing foam" (canned foam?) is that it keeps expanding. I messed up a few plugs that way.

    You could do what you're describing, but instead just use some foam "fillers" (thin strips of polystyrene or other foam and glass over that. That'll give you a stable frame to keep your skin in shape until you've added the bulkheads.

    Of course, Billski's suggestion (once you have the skin, add wooden frame and simply glue it to your outer skin) might be a lot simpler.
     
  14. Jul 7, 2012 #14

    4trade

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    I ask dummy question here because i have never done any composite work. I have basic information studied, but that is far away from real wold and reasonable part building. I was thinking that i may need to build very rigid outer frame for my skin before take it off and that canned foam is rigid and easy.

    How rigid that really need to be to build reasonable good part? I don´t want to do it twice, so how close i need to build these outer bulkheads (Billski suggestion type) to keep skin at dimension it should be...some kind of approximate?
     
  15. Jul 7, 2012 #15

    George Sychrovsky

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  16. Jul 8, 2012 #16

    dviglierchio

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    Great link - thanks!
     
  17. Jul 8, 2012 #17

    autoreply

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    George,

    Being a non-native speaker, those specific definitions are sometimes where I get stuck. Is the "packaging tape" you're referring to the transparent approximately 0.2mm thick (0.008 inch) tape they use to tape carton boxes etc?

    If so, does it conform well to 3D surfaces, fillets or blends for example?
     
  18. Jul 8, 2012 #18

    dino

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    It is mylar that doesn't have much stretch and creases when formed around curves.

    Dino
     
  19. Jul 8, 2012 #19

    Hot Wings

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    Yes, it's the same tape you are thinking about.

    It is limited to very mild compound curves. It works well on the type of shapes such as the turtle deck shown on the web site.

    I've used the heat shrink film sold here in the US as cheap window insulation for more extreme compound curves. Cut it for a loose fit and tape it down with the packing tape, then heat with a hair blow dryer. Never tried it with polyester or vinyl ester resin.
     
  20. Jul 8, 2012 #20

    4trade

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    That taping is great idea if tape lines don´t affect final surface. How much i can tolerate uneven surface of plug when this skin is hand laminated and squeegee?
     

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