Making Curves - is this one way?

Discussion in 'Fiberglass and Composite Boat Building' started by kach22i, Aug 9, 2007.

  1. kach22i
    Joined: Feb 2005
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    kach22i Architect

    I'm not sure how boat hulls are made, but I don't think it's as odd looking as this aircraft method. It's not a composite sandwich, it's a sheetrock plug mold for making a fiberglass part.

    What do you think?

    Would you ever do this for a boat?

    Carving the foam
    http://www.canardaviation.com/cozy/cowl.htm
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  2. JRL
    Joined: May 2007
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    JRL Im with stupid

    Thats the "really frustrating" way to do it.

    Another way would be to cut out graduated shapes from ply wood that narrow down to a specific shape. You would put foam between each cutout.

    Or buy a perfectly smooth block of polysytrene foam. Shape it. And then spray a heavy coat of surfacing primer on it. I made a cable guide plug for a buoy this way. Worked perfect.

    Also made a 7ft tall golf ball useing the same method.

    In the picture above he used Bondo with foam. Thats a nightmare. One sands easy, one doesnt. Creates lots of highs and lows.
     
  3. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    Whatever works is how it's done. The easier it is to get the shape you want, the better. There are easier ways than shown, with ready made products, but apparently the guy didn't know about them. Sometimes people can't afford them. The purpose is to get a smooth, preferably shiny shape that will support a barrier coat of wax, PVA, etc. and won't be melted or distorted by the resins solvents. It also has to be able to withstand whatever working has to be done on the glass with rollers, etc. but that sort of takes care of itself as you apply more layers. The first layer applied very carefully and allowed to set forms a base for the next layer which can be worked more vigorously, etc.

    On the project shown, which was also a process of discovery, the foam chunks were rough shaped approx. 1/2" below the finished shape. Plaster of Paris was first applied but was found to be too hard to sand or work, but it did form a solid coat over the foam and helped give a harder, more uniform surface to work with. The third experimental layer was quickset sheetrock mud from Home Depot that set in 20 minutes. It didn't set enough to sand in that time, but it did set enough to scrape and slice off to a still rough but closer to finish shape. Another coat of quickset mud allowed to dry long enough to easily sand finished that part of the project.

    As JRL says, there are other, better ways to get the foam shape, and if there are two textures that have to be worked, like foam and bondo, it's almost impossible to get a fair shape. (Bondo does have a small window of time where it can be shaped with a surfoam blade, which is almost fun.)

    With experience, the method shown could be fairly fast and cheap and accurate. He sealed the mud with latex paint, then wax etc. If it was to be a plug for a mold, an easy sanding hi build sealer/primer, like for autos, could be spray applied, followed by finish sanding, followed by a sprayed gloss finish, and then waxed, etc. to end with a production mold that would only take a final buffing to have a glasslike shine.
     
  4. kach22i
    Joined: Feb 2005
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    kach22i Architect

    I know all about that method, I'm still making a foam cone.:D

    http://www.hoverclubofamerica.org/forum/index.php?showtopic=1279&st=0
    I'm trying to figure out how to make my own tail cone for my ducted fan. I've stacked some foam "wedding cake" style with construction adhesive, weighted it and let it setup. Taking cheese gratter/body work type tools shaped it from square blocks. Put a center hole in it, which a sanding cyliner fit, put it in my lap and formed a wobbly cone.

    I need to fill in some gaps, undercut some of the the plates/blocks by accident. Micro bubbles or spay foam? Maybe just cut and glue foam wedges?

    Problems:

    1. Need something to get to final form with.

    2. Need to make a form fitting hub base plate so that I get good attachment and airtight seal to the hub.

    If I use the hub and engine as my lathe, I still need to secure to the hub. Any ideas on how to do this?

    I think the whole with when done gets a thin coat of glass and resin, any tips on how to do this without folds (and thick spots) which may throw it all out of balance?

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  5. kach22i
    Joined: Feb 2005
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    kach22i Architect

    I'm still waiting for the adhesive to dry after several weeks!

    [quote name='kach22i' date='Jul 30 2007, 11:43 AM' post='11893']
    UPDATE: 07/30/2007

    It's been very difficult to get the cone shape without a lathe, and without putting a layer of fiberglass to the flat part first (that I could find something to secure to) it's been tough going.

    If you can learn from my mistakes, bless you. I'm just waiting for the weak as caulk adhesive to dry. Had the thing working for a couple of minutes, but the glue not exposed to the outside was not curing inside of the plastic dish.

    I know this does not look safe, but it's got to be safer than using the hovercraft engine/fan/hub as a lathe.

    VIDEO:
    http://s184.photobucket.com/albums/x295/ka...nt=e3139e36.flv

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  6. kach22i
    Joined: Feb 2005
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    kach22i Architect

  7. Go-Man
    Joined: Aug 2007
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    Go-Man Trusts In Thrust

    what about making stringers and then rap 7/32 plywood over it then apply fiberglass
     
    Last edited: Aug 10, 2007
  8. SamSam
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    Location: Coastal Georgia

    SamSam Senior Member

    That's good. I don't suppose any of the neighbors have ever asked what you're doing. ;)

    It almost looks like a shape you could get from a plastic bowl. Or maybe a stainless bowl.Either use the bowl itself or layup a cone on the inside of the bowl and you would end up with a smooth on the outside cone. If you have overlaps of the same size evenly spaced around the perimeter with the layup as even as possible, the balance should be good, especially as the cone is in the center and won't get much centrifical force put on it.

    Sometimes people will need to turn something on a lathe (wood) but don't need holes in the piece from a faceplate so they will use two sided carpet tape to attach to the faceplate and then carefully pry the piece off when done.

    If you get caught up in your car/lathe setup by a loose shirtsleeve or something, you do realize you're screwed, don't you? Even idling it probably won't stop until you're so wound up in it, it kills from sheer overload and lugs itself to a stop, with you being the luggee. Or maybe your arm will come off first. Those farmers back home were always pretty surprised and regretful when they got snatched up by a power take off.

    Maybe find someone with a potters wheel or something. Maybe a local school will let you use their lathe or potters wheel for a few minutes.
     
  9. Go-Man
    Joined: Aug 2007
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    Go-Man Trusts In Thrust

    coudnt you use machinable wax or something on a lathe then use it as a mold?
     
  10. nero
    Joined: Aug 2003
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    nero Senior Member

    Perhaps it would be simpler to mount the cone to the hub or your craft. Have someone rotate the hub by hand. Use an orbital sander, disc sander, or finish sander with 60 to 36 grit paper. Rig up some way of supporting the sander or something to steady your hand with.

    Wrap the results in glass and epoxy. Then fair it with epoxy, silica, microbulbel dope. Sand again on hub when it is rotating.

    To shape the ring around the prop, mount a sander to the prop or remove one of the prop blades and make a holder for the sander. Rotate it by hand and this should sweep out a rough profile. Then make the exact profile you want and fix it to the prop holder. Add dope and rotate. By doing this you could get a close fit to the ends of the prop blades.

    Don't forget to wrap and cover everything with plastic and duct tape before doping and coating. smile
     
  11. kach22i
    Joined: Feb 2005
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    kach22i Architect

    Not a perfect cone but close enough to be fixed on top of the splitter.

    http://s184.photobucket.com/albums/x295/kach22i/
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    No injuries in the making of it, I'm happy so far.

    NOTE: I looked into using plastic flower pots before. The problem was I am very cheap and went to the 1-Dollar Store when the stuff from China cracked in my hands by droping it once and picking it up. Perhaps a nice metal mixing bowl from a garage sale would be better.
     
  12. Go-Man
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    Go-Man Trusts In Thrust

    Have a bycicle blocked up and the tire touching the hub of like a trailer or something? good exersize:D
     
  13. kach22i
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    kach22i Architect

  14. boonbeest
    Joined: May 2008
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    boonbeest Junior Member

    nice work but two much work

    when you have to make a form you beter use a stretch cotton .
    you make a lil form in wood just the contours.

    than you put over a stretch cotton.

    and that you cover with glassfiber.

    something like this

    (small example )

    this is with an old T-shirt
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    en this is what you can make with it
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    i use it a lot

    and its simple

    when youre contours are 100% and then you put over the cotton
    its very simple

    you can gleu the cotton are with small nails

    grtz
    BB
     
    1 person likes this.

  15. DanishBagger
    Joined: Feb 2006
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    DanishBagger Never Again

    Oh, haha, I can't help but laugh every time I see cars that like. But noone can say you're a crap fibreglass-boy. And the car-thingy? I guess it comes down to taste and interests (and age, I presume?).

    I really like the geeky gullwings shouting out "LOOK AT ME", they're great! :)
     
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