Split mold for hull

Discussion in 'Fiberglass and Composite Boat Building' started by Sam III, Apr 22, 2008.

  1. Sam III
    Joined: Sep 2007
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    Location: League City, TX USA

    Sam III Junior Member

    I am working on the design of a center line split mold for a sail boat.

    Mold will have normal flange on the centerline.

    How do you build the 'seam/joint' so that a large parting line of gel coat does not build up when you spray it in?

    Thanks

    Sam
     
  2. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    No big deal, but you do normally get a line from the split, it is however a built up line so it is easy to just sand off. If you made the mould very carefully the sand off line would of course be smaller, but in reality it simply just does not matter.

    Sometimes we put tape over the seam line, but for a hull, we just sand it off.
     
  3. ratrace2
    Joined: Dec 2007
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    Location: NJ USA

    ratrace2 Senior Member

    Fill it in with modeling clay, chavant, or something like that.....just firm enough and non-reactive to mold-release and Gel....
     
  4. Sam III
    Joined: Sep 2007
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    Sam III Junior Member

    Any suggestions for 'parting board'? Thinking of using particle board and putting a couple of coats of primer on it before release agent.

    Thoughts?
     
  5. ratrace2
    Joined: Dec 2007
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    Location: NJ USA

    ratrace2 Senior Member

    Sam,
    na, that will never work, too rough. It, the resin, will just pull it apart.
    Only if you wrapped 6Mil poly around plywood could you use it as a parting plane. You have to have a smooth, non-pourous surface. Something like metal tape, like they use to repair trucks, with the sticky tar on one side and the aluminium, thick, foil on the other..If you coulg get some plexyglass that would work and spray it with PVA, Mold release. :)
     
  6. Sam III
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    Sam III Junior Member

    What about 'Melamine faced' board?

    Sam
     
  7. ratrace2
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    ratrace2 Senior Member

    Sam,
    Sure, just test a little first. Use a good smooth coat of PVA sprayed on it.
    Remember, test, test, test everything a little bit.
     
  8. ratrace2
    Joined: Dec 2007
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    ratrace2 Senior Member

    I think there is a better way:
    Listen, build your plug and then glass it. OK, now you have your mold.
    Now, build up a flange from bow to stern, then cut the mold in half.
    The kerf of a sawzall is approx. 1/16th inch. No one will notice the size reduction in your boat. Or, just put a formica shim between the mold haves to restore the dimensions.
    _________________________________________________
    THE FLANGE: I like to use hardwood like Rock maple, or oak. Make the flange approx 4 inches high and about 2 inches wide. Drill holes through your flange 1/4" dia. every 12 inches should do it. :cool:
     
  9. juiceclark

    juiceclark Previous Member

    We're using the back, very smooth side of vinyl siding. You can buy it for nothing at Home Depot or Lowes and nothing sticks to it...especially with quick release on it.

    I'll try to find a pic or two of how we did it for our 50'.
    Tony in Sw FL
     
  10. ratrace2
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    Location: NJ USA

    ratrace2 Senior Member

    Juice,
    where did you find that vinyl siding? Years ago, I looked all over HD for the same applications, couldn't find "that".
    Need "Pics'....bad.:) :)
     
  11. Sam III
    Joined: Sep 2007
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    Location: League City, TX USA

    Sam III Junior Member

    I was also thinking about the smooth finished 4' x 8' Thrifty White Tileboard

    Model 346428
    SKU 346428

    http://contractorservices.homedepot...4437&pid=a13859ae-4382-403a-9c0c-7147640e84bb

    from Home Depot as well. As it is only 1/8" hardboard was planning to glue to 1/4" luan ply for some stiffness.

    Sam
     
  12. ratrace2
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    ratrace2 Senior Member

    Well, if that is the case, why don't you just use some "flashing" and 3M it to the Luan....
     
  13. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Sam, I use melamine faced particle board succeessfully- attach to brackets of same using "hot melt" glue - it shaves off with razor blade easily later. Regards from Jeff.
     
  14. juiceclark

    juiceclark Previous Member

    I was out at the mold today. They have it split in two because they're polishing the tooling gel on the mold. So, the little piece in the middle was removed and I forgot to ask exactly what it was and where they got it. I'm pretty sure it was from Lowes and was a piece of flat, white and smooth vinyl(very thin)...could be flashing but looked like siding without the flange along the edge. I'll ask tomorrow and give you an update.
     

  15. ratrace2
    Joined: Dec 2007
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    Location: NJ USA

    ratrace2 Senior Member

    Juice,
    Problem, I think this guy is working with a plug, not a "female" mold. Sure, you just slam the mold halves shut against the "vinyl siding/parting plane".
    Maybe we should find out what this guy is working with???

    _________SamIII, Question:______________________
    are you working with a plug....what kind of "stuff" are you doing. Care to lay some "context", background for your efforts?
     
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