Two part mold registration

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Nov 28, 2022.

  1. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    What are some ways to register the two parts after I put the fiberglass in over the flange on both halves?

    I have the 4 registration tabs, however with the fiberglass about 1/8" thick (I cut out the fiberglass around the tabs) they have some movement, the top and bottom joint is not square because they no longer line up.

    I am thinking of using a hinge mechanism somehow, I'll have to cover with tape so the gelcoat does not get in the way...it's a flange type mold, both halves are flush, NOT shoebox type

    Also any ideas on how to grind the flange off the boat without disturbing the gelcoat. That is almost the hardest part of making these boats...

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  2. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Have you considered masking the flange and at a suitable stage,green trimming the laminate so that the flanges don't meet any obstruction?
     
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  3. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Full size boats use a "rub rail" over the joint. Some full size boats apply gelcoat along the joint after grinding the joint smooth, and then "hand" finish the applied gelcoat so that it is smooth and blends into the surrounding gelcoat. With two colors masking would be needed.
     
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  4. TANSL
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    TANSL Senior Member

    I see you finally got your body lines plan. Perhaps, for a small additional fee, you would have gotten help on how to build the moulds. Good luck with your project, I see that you are going to need it.
     
  5. aaronhl
    Joined: Aug 2012
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    aaronhl Senior Member

    No i havent gotten the body lines plans yet - this is for an rc boat project it's about 48" long - the ones you helped with are for a full size boat about 18 ft, but yes you can see I am still learning and what you are doing for me is a long term goal I have to one day build my own full size boat, these models are to learn
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Excuse me, I thought you were making a scale model of the big boat, to learn. You already know how to find me if you need to complete the help.
    Cheers.
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    It looks like you are using multiple layers of fabric between the pieces to join them together?
    There are some really strong adhesives that will work well for that, and much easier to use.
    Why is the hull laminate so lumpy?
     
  8. aaronhl
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    aaronhl Senior Member

    I think it's because I am not suing a fabric rolling, just dabbing my chip brush into the fabric to get the air bubbles out
    Yea the fabric is like 1/16" thick on both halves about 4 layers of 6oz, fabric, if I was using a different type of hull joint Id consider an adhesive...
     
  9. aaronhl
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    aaronhl Senior Member

    I need to have some fabric "curl" over onto the flange, maybe only curling over 1/8" would make trimming the seam easier after its out of the mold??...otherwise I feel cutting-trimming before I put them together without curling over the flange would make the seam even harder to fill later as there could be gaps??
     
  10. aaronhl
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    aaronhl Senior Member

    Similar question: So how do boat makers coordinate the top and bottom of the plug when building the mold? If the bottom half is built with bulkheads upside-down, how they make sure the top deck will fit on the bottom piece with a shoebox style seam?
     
  11. kapnD
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    kapnD Senior Member

    Those who are clever with the computer could design the cap to fit over the bulkheads, but I’d simply build the mold over top of the bulkheads with an appropriate sized filler to compensate for thickness of the piece.
     
  12. wet feet
    Joined: Nov 2004
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    wet feet Senior Member


    Depending on the integrity of the plug,it is sometimes possible to use the upper couple of feet of it as the basis of the deck plug.I know one instance where the entire hull plug was designed and constructed with a break line throughout the support structure so that only the outer skin needed to be cut through.It wasn't too difficult to add cross braces and to very carefully turn it over.At which point some very careful measuring was done to ensure that the plug hadn't distorted and it was levelled.Then the deck plug was built over it.Image attached of the cutting taking place.

    If it is a case of adding a revised deck to an existing hull,the usual thing is to lay up the upper portion of the hull and to bond in bulkheads to the depth required.Sufficient diagonal bracing is added to hold the shape and again,after careful measuring to ensure squareness,a plug can be built.For a smaller boat that has had a plug CNC machined,I would take a few measurements to verify fidelity and use the designer's data to prepare the components of the plug for cutting on a CNC router if the budget won't run to machining an entire deck plug.

    Much depends on the designer and the information he/she provides.An old stager who provides a few sections on a print and a 3D sketch of his vision for the boat will give the plug builder more of the traditional sort of work than the fellow who provides a solid model from which surfaces can be machined.With the modern model but no large 5 axis machine it becomes an exercise in offsetting surfaces and creating a structure that can have it's parts cut on a CNC router.Which is a lot faster than lofting the whole thing on one's knees.
     

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  13. aaronhl
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    aaronhl Senior Member

    Seems like the parting flange to the lower half would need to be added after making the top deck fit the bulkheads??
     
  14. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Can you provide a sketch of the situation you envisage?The generalised answer is that the details depend on the type of joint and the amount of planning that went into the construction of the plug.
     

  15. aaronhl
    Joined: Aug 2012
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    aaronhl Senior Member

    yes i agree with the type of planning, computers can help, however i am thinking without computers how would you fit a top deck to the finished bottom plug ? do you make the bottom plug so you can flip it right side up, make the top deck, then flip it over again to add the parting flange? here's a picture of an example , how are these two guys going to make a top deck to fit what they have already made for the bottom, fitting as a "shoe box design"?...Would it help to make a floor jig for the bulkheads that allows you full access to the outside rim of the plug after it's flipped??
    [​IMG]
     
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