[Jewelry making - Article 00039] - Re: [Orchid] Vent holes in rubber molds

[castaldo]

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Dear Andrew,

    You don't say what the inconsistent results are and use the
    confusing term "wax molds", so it's hard to give you any advice at
    this point. 

    Is the rubber not flowing in and around the model and making a
    complete mold? Or are you having trouble getting the wax to inject
    into the finished mold? Those are two very different issues with very
    different solutions. 

    But neither one of these problems is affected by drilling vent holes
    in the aluminum mold frame. 

    The subject of vented vs. unvented mold frames has some similarities
    to passionate discussions about religion: each side is immovably
    convinced of the correctness of its position and unwilling or unable
    to listen to the opposite point of view. 

    Molding technology throughout the rubber industry (non-jewelry, that
    is) holds that molds should be closed, without vents, in order to
    build up internal pressure in the mold cavity in order to force the
    rubber into all the nooks and crannies of the design. 

    Believers in vented jewelry mold frames seem comforted by the sight
    of rubber flowing out of the vent holes: to them this means that all
    is well inside the dark and unseen cavity of the frame. 

    Millions upon millions of molds have been made with vented mold
    frames and even more without them. Both styles seem to work. 

    There is a belief that rubber shrinkage is reduced by the use of
    vented mold frames, but there is no empirical proof of this. I
    remember attending an early Santa Fe conference in the 1980's at
    which Louis Sanchez, then at Rio Grande, presented research on this
    subject. He compared shrinkage rates for molds made from unvented
    mold frames with those made and mold frames with various size holes
    in various positions. 

    I remember well his conclusion: "In conclusion, I have no
    conclusion". 

    So -- whatever mold vent hole religion you belong to, you might as
    well continue as you are. 

Michael Knight
CASTALDO
www.castaldo.com
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