Mold frame material stability over time

Discussion in 'Boatbuilding' started by cmclaughlin, Jun 1, 2018.

  1. cmclaughlin
    Joined: Oct 2013
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    Location: NE USA

    cmclaughlin Junior Member


    I am starting a build of a 40’ sailboat in foam sandwich. I am CNC cutting as much of the boat as possible and wanted to start with smaller, non-structural items like seats and tables etc, before moving up to bulkheads and finally the hull. The hull will be built on a male mold. Proceeding in this way, would there be any issues if I cut out the mold frames now vs waiting until right before I start the hull? I planned on using OSB for these sections. They would be stored indoors but there are significant changes in temp & humidity here (Northeastern US) and I’m concerned the frames may change significantly from being cut to being used (could be a year or more). Access to the CNC cannot be assumed at a later time…

    If significant distortion of the frame is to be expected, are there other materials from which to cut them that would perform better, or is it unwise to make frames ahead of time in general?

    Thank you for your time!
  2. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    What kind of foam???

    And is it stable if kept flat and in a humidity controlled environment?

    If you cut them now you could put glass on them, even a single layer, but then you don't have as strong a bond between the tab and the bulkhead as you would if you laminated it all at once.
  3. cmclaughlin
    Joined: Oct 2013
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    cmclaughlin Junior Member

    Foam is H-80 divinycell. I assume it is stable. I understand that the bonds will not be as strong, but I anticipate bagging the inside hull skin in one shot and cannot visualize how I could avoid some secondary bonding. My question was more about the frames for the hull mold and their dimensional stability over time. I just re-read Gougeon's and found they both warn against using OSB, and recommend particle board for molds so I think I'm good. Should have read that before posting!
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you are concerned about moisture on the molds, paint them.

  5. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Particle board is very susceptible to humidity, although many shops use it (MDF) to CNC cut new shapes for plugs and molds, it will change shape quickly sometimes when stored in non climate controlled area. Sealers are used to stabilize the finished shape if it needs to sit for a period of time, or will be used multiple times. Painting it will help.
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