[Jewelry making - Article 00106] - Re: [Orchid] CNC cutting

[T R. Hawkinson, Ltd.]

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    Dear Jesse & All, I made metal molds commercially from 1978 through
    1985 or so. The price back then started at about $450.00. I can still
    make them but the price would have to be over $700.00. They take a
    good day to make. With care they will last forever. The material is a
    lead like product that has some safety concerns. One style of mold
    requires a master pattern to pour the molten metal around. This part
    is the blank or model for all production. Another option is to tool
    blank metal parts, creating a cavity for the wax or plastic to inject
    into. Both methods produce an excellent product that holds a lot of
    detail. The ring mold blanks are usually one or two styles  that have
    the design tooled into the side. Class rings are the example.
    Josten's and ArtCarved make their class rings this way. The master
    rings are still hand made in many cases. 

    The down side of metal molds is the COST! Plenty expensive to set up
    between the blank material cost or mold frames (usually custom made).
    Tooling machinery is expensive. Holding fixtures also usually have to
    be custom made to tool the parts. A metal mold will usually make just
    one design. Although I have made hollow ring molds from one outer
    master design allowing solid back, hollow back and hollow shoulder
    waxes from the same mold. Care must be maintained because if you drop
    a part it may not fit back together again. A metal mold is like a
    small metal puzzle that actually pulls of the injected wax or
    plastic. No undercut off the model will work. 

    High pressure injection is also required for the best injection and
    detail. The Muller Phipps vacuum wax injector is the industry
    standard. 

>         I'd like to know more about the differences between silicone
>     and metal molds, as well as the limitations and benefits of. each
>     method. 

    With my method the silicone injects a part I feel superior to the
    metal for several reasons. First is the cost. A silicone insert in my
    mold shell system cost about $4.00. The shell is reusable for any
    design the size of the finger hole. I make the finger holes in whole
    and half sizes. The blank plastics are also very affordable. 

    Second for detail, the mold injects everything on the model.
    Injection is also done under about 25 psi to deliver the best detail.
    I usually clamp the mold onto a Yasui wax injector and leave it on
    for about 25 seconds. The part dries with no shrink. In fact if I
    were to measure I would bet because of the pressure my parts may even
    be one or two percentages larger. Tooling small raised letters may
    work better being reversed if possible on some design. But I am happy
    with my results. 

    I usually tool a model for molding with my process so I have blank
    plastic parts with surface files that are imported to any surfacing
    software and detailed. I use ARTCAM as well as Cimigraphy. I'm hoping
    with the Gem Vision folks now selling a CNC mill, my surfacing ideas
    will work with 3d design & Matrix. 

>         What's your take on how metal molds compare with silicone in
>     terms of fineness of detail and repeatable successful casting of
>     signet, logo and medallion styles?  Accordingly, when designing
>     these styles intended for silicone molding, does one have to
>     compromise a bit on small raised features in general?  Besides high
>     production runs, in what other circumstances would it be favorable
>     to use a metal mold? 

    The detail tooled in plastic is impressive. The last time I saw
    samples cut by the Model Master folks they had a lot of highly
    detailed plastic masters as sample models. My molding process would
    reproduce these plastics exactly. The manufacturing process that
    follows would require experience also. Even Josten's doesn't polish
    the detailed sides of their rings anymore. They steel shot burnish
    them. 

    I also prefer to inject wax and not plastic. Plastic is harder to
    burn out and cast. The shrink on most plastics is unacceptable also.
    It all depends on the model and what you are trying to make. Metal
    molds are required for many products. Silicone, for me is more
    affordable and allows me a quicker turn around time for product. 

    Again, I would love to see anything finished from a CAD origin. 

Best Regards,
Todd Hawkinson
www.ajt-online.com



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