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  1. #1

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    hydrocal molds - finishing

    Hello everyone.

    Iยดm making hydrocal molds to produce my airplanes fuselages

    After having finished the hydrocal mold and demoulding the pink foam piece I seal the hycrocal with 3 or 4 layers of epoxy resin.

    Anyhow when taking out of each layer the excess of epoxy, it tends to leave some marks on the epoxy finishing which of course does nont allow a perfect surface.

    Any recommendation on how can I seal all this imperfection for achivieng a better finishing surface for my molds would by very much appreciated.

    Kind Regards
    Oddy
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  2. #2
    soarrich's Avatar
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    RE: hydrocal molds - finishing


    ORIGINAL: oddy

    Anyhow when taking out of each layer the excess of epoxy, it tends to leave some marks on the epoxy finishing which of course does nont allow a perfect surface.
    What do you mean by taking out each layer of excess epoxy?
    When I put the epoxy onto the Hydrocal I just brush it in, then let it set for a minute, then wipe it out, the only epoxy left in the mold is in the hydrocal. If after 3 applications of epoxy there is any excess, I guess you should sand it with 1000 grit, paper, then maybe buff it with a polishing compound. The molds I made where smooth after the epoxy though.
    Rich Border AMA 77727
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  3. #3

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    RE: hydrocal molds - finishing

    Thanks a lot for your help.

    Probably whats going on is that Iยดm not wiping out all the excess and marks of the paper im using to wipe out are being left of the surface.

    Ill be trying with the 1000 grid.

    Thanks

    Oddy
    If I say that the Burra is Prieta is because I have the pelos in my hand.

  4. #4

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    RE: hydrocal molds - finishing

    Have you guy heard of ES-221? Instead of sealing the plaster after the mold is made, you brush this onto the plug and then pour your plaster on top of it. It's call a PFP mold....plastic faced plaster. The downside it that you can't do the "pour straight onto foam" trick.
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  5. #5
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    RE: hydrocal molds - finishing

    Ultracal 30
    will work also , in place of your Hydrocal.
    It is not quite as brittle as the one your using
    and has a tad more compressive strength.

    Also,(and MOST importantly)
    The % expansion rate at setting for the
    Ultracal-30 is only 0.08;
    where-as the Hydrocal is 0.12 %.
    Ultracal-60 is only 0.07 %-but i Never have the patience to wait !

    -Hydrocal will work just Fine though.-

    Are you using Manila fibers for strengthening, or some other suitable fiber ?

    By the way PFP molds ARE the way to go. I did a post on how to make them over
    on rcgroups and had a 66.6%. "Negative reaction", from people wondering WHY
    a mold that can be heated to 300 degrees with near O distortion rate would be suitable. ...
    so i Deleted the post on topic.


    Bille
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  6. #6

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    RE: hydrocal molds - finishing

    Back in my boat building days, used to be handed a vac-u-formed plastic hull and told to make X copies of them. Would mount the half model to a big formica covered board, then seal the edges with free common old Bee's wax from a local paper cup place, and then lay on the Plaster of Paris (as it was cheap at less then $1 per bag) which stayed cool and then would not heat up and warp the thin plastic.

    Sanding? Well that went rather quickly, and details? I did not notice the scratch in the plastic there before.....

    Wm.
    Thousands of Laser Cut parts, thousands
    And plans too

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    RE: hydrocal molds - finishing

    Billie,

    I'd be interested in hearing about the ultracal molds. Process to make them, are they as good and tough as epoxy molds? Is it a wax prep for release? etc....


    Thanks
    Paul

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    RE: hydrocal molds - finishing

    The process for making an ultracal 30 mold will be pretty much the same, ultracal is a much harder stone and can be baked but takes much longer to cure or set up. Do release these as well as you would any other mold. can't compair them to epoxy molds.
    I'm suprised to see no one has drilled keys into their molds so they line up and close tight, i found this forum while searching for a troubleshooting issue with a cast i'm making for a prosthetic piece. How do you guys go about making your stone molds and what do you build the molds off of?


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