Vacuumed Boat Mold from finished Plug

Discussion in 'Fiberglass and Composite Boat Building' started by Breakwater, Aug 15, 2008.

  1. Breakwater
    Joined: Dec 2007
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    Breakwater Junior Member

    Hi All,

    I have a few mold creating questions specific to my application. Sorry, I know the topic has been covered, but I wasn't able to find much info searching.

    My plug is finished, and I want to make a mold of it now. (see attached picture of my plug.) I will be vacuum bagging the mold, and I'm curious how to make a gunwale flange, so that when a hull is formed in the mold, it will have a clear crease where it should be trimmed.

    if I were to lay a sheet of thin ply across the gunwales I would create a flange on each side, but a giant cavity in the bilge (or back-side of the ply) for the vacuum to crush.

    So, do I attach a 2-inch wide strip running the length of the boat, and use that as a flange? or are there better ways. Any help is appreciated since I am totally new to bagging.


    Also:
    How much time should the unit be left under vacuum pressure? (I usually allow epoxy 2-3 days to cure before working with it again.) should it be under vacuum for that long?

    How much resin should be wetted on the composite before the vacuum is turned on? (So that it fully impregnates the composite, but doesn’t have an large amount of excess bleeding through, or not enough.)

    How many lbs Mercury or PSI should I be running inside the bag?

    THANKS!!!!!!
     

    Attached Files:

  2. JRL
    Joined: May 2007
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    Location: Palm Beach Gardens, FL

    JRL Im with stupid

    For bagging, weigh your cloth, and use the equal amount of resin per ply. So if 1 yard of cloth weighs 8.8 ounces. Use 8.8 ounces of catylized resin.

    -If your final layer of cloth is a little dry. Dont worry, when the lamenant compacts it will push resin up through the last layer.

    As far as a flange goes. I prefer a minimum of six inches all the way around. That way you have the option to infuse, bag, or hand layup the part with plenty of room to work.

    Another option you might want to try is once you have a finished part. Put it back into the mould and score a trim line into the gel. Then re wax. Works really well.

    Vacuum: Initially youll want to apply vacuum pretty slowly to make bag adjustments. After the bag is sealed, and shaped. Youll want to pull the max your pump can turn out. As someone else mentioned before (and I have yet to try, but it makes sense) is apply full vacuum a few minutes before the resin starts to gel.
     
  3. wet feet
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    wet feet Senior Member

    You really ought to practise on something other than your first mould.I doubt that you would get any vacuum on your mould layup unless you use an envelope bag.This may expose weaknesses in your plug construction and result in a local collapse.What do you believe would be the disadvantage of a hand laid laminate which incorporates a flange for vacuum bagging the component?
     
  4. Eagle Boats
    Joined: Nov 2003
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    Eagle Boats Senior Member

    Why do you want to vacuum bag the mold? I always was under the impression that you vacuum bag in order to get a better resin to glass ratio which will increase the strength and reduce the weight. Are those criteria really necessary for a mold? I would keep it simple and build the mold out of tooling resin and chopped mat to a thickness of approximately 5/8 inches. Once the mold is made, then you can vacuum bag the parts made in the mold.
     
  5. Breakwater
    Joined: Dec 2007
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    Breakwater Junior Member


    Thanks a ton for the tips JRL.

    The only remaining question is how should I go about making the 6 inch flange on each side of the plug?

    I attached a few more pictures to describe what's going on.
    I appreciate it.

    The white mould is a finished mould of some boat that I pulled from the internet, It shows what I'd like mine to look like.
    The second is another angle of my plug.
     

    Attached Files:

  6. the1much
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    the1much hippie dreams

    add the flange to your plug.
    is this for a R/C or a REAL boat,,hehe,,, sorry but im a bit confused most the time,,hehe ;)
     
  7. Breakwater
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    Breakwater Junior Member

    I'm asking what to use as a flange.
     
  8. the1much
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    the1much hippie dreams

    i'd use "door skin",,attach from the "inside" of your plug ,, but be sure to radius all your "corners" of the connection.you'll always have "finish" work to do at the flanges,, the only real place to worry is where the flange connects to the hull,, paying CLOSE attention to that area will save lots of work on the "mold" side.,,,,,,but i say door skin cause it looks like an R/C boat,,,,if its a bigger boat,, i would use ply.,,,so what is it?? r/c?
    looks nice :D
    after attaching the door skin,, then glass over.
     
  9. Breakwater
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    Breakwater Junior Member

    Thanks.

    It's a Marblehead Class.
     

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  10. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    You run a good chance of making your mold inseparable from your plug if you vacuum bag it. Until your mold is "broken in" you also run a good chance of the same happening between your mold and the part if you vacuum bag it.
     
  11. the1much
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    the1much hippie dreams

    thats pretty cool man,,,,making the big ones are easy compared to someone making one of those,,,AND making it work!!
    pretty bad@ss :D
     
  12. JRL
    Joined: May 2007
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    JRL Im with stupid

    If it were me, I would trace the outline of the boat onto a piece of 1/4" MDF. Cut that out and then cap off the top side of the plug. Then glue the plug, cap side down, onto a piece of Melamine. From their form a 1/4" plasticine fillet around the edges of the plug and Melamine.

    Youll obviously have to cap off the transom area. Maybe an MDF plug coated with aluminum tape, then plasticine the seams?

    I did notice there is a slight curve on the open side of your plug. You can do a quick layup of glass and poly to get the contour. Transfer that shape to poster board or MDF. Then use that shape to fill the gap between the plug and flange.
     

  13. SamSam
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    SamSam Senior Member

    I think JRL is talking about the sheerline. I got to looking at the plug and it looks like there might be some tumblehome in the aft end of the boat. If that is the case you have to be careful you can remove the hull from the mold. You MIGHT be able to lift the bow out and then be able to pull the hull out like a foot out of a shoe, but then again you might not. If not, then you need a 2 piece, split mold. (Nevermind, I just noticed the first picture of the thread, which shows the transom, which doesn't seem to have any tumblehome.)

    Also, if your plug is the size you need for the finished hull, as far as the height of the sides goes, you might have problems vacuum bagging unless you extend the sides. You can't trim the laminate before bagging and end up with a finished edge, and you can't let it run long and flop over on the flange, as it won't bend over the corner without air bubbles or some other problem.
     
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