Resin casting and bubbles: would this work?

Discussion in 'Replica Props' started by adamata, Apr 17, 2012.

  1. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    So, I am casting a set of parts for the training remote and the last piece is a small round part with a very thin post.

    When I pour the resin, the post is so thin that air gets trapped in the post. I have tried several different ways to get the air out, but I am getting mixed results and its a real PITA.

    So, here is my question.

    Could I pour the resin and then put these molds in a vacuum chamber to suck out the air bubbles trapped in the thin areas?

    Would that work?
     
  2. Leigh

    Leigh Sr Member RPF PREMIUM MEMBER

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    I'm no expert & I'm learning myself but can you not make a hole/chanel in the mould to let the trapped air out???
    I guess you would end up with a bit extra on your cast but you could just cut that off :confused Maybe
     
  3. Finhead

    Finhead Sr Member

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    Leigh is correct if your able to I would put another vent hole. If that is not an option you normally want to pressure cast not vac. The main issue with that is you would want to pressure mold as well.
     
  4. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    ok, so what I didn't explain is that this piece is about 5mm in diameter and the post in the center of it is about 2 mm thick and about 4mm tall.

    it is VERY SMALL :)

    like I said, the post diameter is the same as the smallest air bubble.

    crazy small.
     
  5. Etewaf

    Etewaf Active Member

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    I personally have not had any luck with vacuum degassing resin. You could get a resin that takes longer to cure and maybe get away with it. I made a similar thread a while back and the piece of advice that I got was to powder the mold, and that worked for my purposes, but your piece sounds quite intricate.
     
  6. Finhead

    Finhead Sr Member

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    Pressure casting will work fine then, but you will most likely need to redo the mold as a pressure mold or you will get surface imperfections as the resin pressures against the mold.

     
  7. trooper

    trooper Sr Member RPF PREMIUM MEMBER

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    have you tried the baby powder trick? just dust the mold with it and knock out the rest, i laughed the first time i heard it, but it works great :)
    if that does not work, pm me, I would be glad to help in this project :) maybe i can make a pressure mold and cast these for every one :) lmk
     
  8. Sith_Lord_Hritz

    Sith_Lord_Hritz Well-Known Member RPF PREMIUM MEMBER

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    what if you used a syringe/needle to inject a small amount of resin into the mold after you fill it like normal. Then it would push out the air and leave resin in its place. you can get needles from the drug store i think.
     
  9. Sith_Lord_Hritz

    Sith_Lord_Hritz Well-Known Member RPF PREMIUM MEMBER

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    Also i think i read someware that if you plan to vac resin in a mold then you will first need to use a vac when you make the mold as well.
     
  10. Alan Castillo

    Alan Castillo Master Member RPF PREMIUM MEMBER

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    A toothpick or an upside-down needle to slowly mix/move the resin before it cures could also release any air trapped in pesky corners.
     
  11. Dewback_Rider

    Dewback_Rider Active Member

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  12. Superkrates

    Superkrates Active Member

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    Venting is the best solution, but this may be the same problem I had with air getting trapped at the bottom when pouring resin into a mold for heat-sink fins - no amount of pressure would eliminate the bubble totally (venting was not an option) and I couldn't get powder into the small opening to eliminate the wall adhesion while pouring resin.

    Two things that can be done:
    Pour resin, then 'drag' the problem area (for this application you'll need a thin, stiff wire with it's end rounded as to not damage the mold) to break the wall adhesion and let the air rise out.
    -or-
    insert a plastic tipped syringe near the lowest point and inject resin into the area (the cavitation of the injected resin aids in venting the cavity.
     
  13. trooper

    trooper Sr Member RPF PREMIUM MEMBER

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    i think what you are referring to is pressure casting, if you want to pressure cast resin, the silicone mold needs to be pressure cast as well. Ive not heard of vacu casting, but doesn't mean anything :)
     
  14. franz bolo

    franz bolo Sr Member

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    You can pour the posts first and use a toothpick to get the bubble out, Then continue pouring. All depends on how you made the molds.

    You can even let the posts harden and then come back and pour the rest. Resin sticks to resin.

    FB
     
  15. Jumpergal

    Jumpergal Member

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    if it's that small and will be painted, is there any other way of getting the look without the casting? If it's the size of a wire, I mean, can you use a wire on a ball of Milliput or something? Sorry if this is off base, I was just trying to visualize what you're referring to.
     
  16. Rebelscum

    Rebelscum Sr Member

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    A couple things...

    Bubbles get bigger in a vacuum, so that's not good for resin.

    Vacuum silicone to remove bubbles as they expand and pop. If you don't do that, the rubber will have tiny holes just under the surface you can't even see, but when you then pressure the resin it will PUSH the resin into those bubbles and make tiny pimples on your cast.

    Pressue makes bubbles in the resin smaller.

    If you have a tiny piece, probably you gotta figure out how to get the bubble to escape during the pour as it sounds too big for even pressure to make it disappear. Sometimes I'll pour a tiny bit, squeeze the mold, rotate it, etc, to see if I can get it to work its way out. On a larger mold you would probably even see it come up, though this sounds so small, you may not see it.
     
  17. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    Ok, so here is the piece. Bottom row, center. Mind you, that stem is about 2mm thick. I might have another solution, but thanks for all the advice so far. I might try a few things before i resort to plan B

    [​IMG]
     
  18. trooper

    trooper Sr Member RPF PREMIUM MEMBER

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    i think i have that kit, is it from the same tank as the parts above it?

    if so i'll cast em up :)
     
  19. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    No, its from a 1:71 scale Panzer IV kit. the only part *not* from that kit.
     
  20. trooper

    trooper Sr Member RPF PREMIUM MEMBER

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    :lol crap, i thought it was an easy fix :)
    lmk if i can help

    jerry
     
    Last edited: Apr 17, 2012
  21. BrundelFly

    BrundelFly Sr Member RPF PREMIUM MEMBER

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    DEGASS RTV...

    PRESSURE CAST..resin (cured mold for casting)....

    Glue a TINY strip of styrene strip to the part..or...USE a TOOTH Pick to POP bubbles as you pour.
     
  22. micdavis

    micdavis Master Member

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    A monkey could do it. ;) Right?
     
  23. trooper

    trooper Sr Member RPF PREMIUM MEMBER

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    ive never realy had problems with resin, been doing it for years, the only problem ive had was with clear resin, trust me i now all about tooth picks lol i find trying to cast 2mm size windows the resin does not like to kick off for a looooong time, and will make new bubbles when your not looking !!!! :lol
     
  24. Jedifather

    Jedifather Sr Member RPF PREMIUM MEMBER

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    I have the same problem trying to cast "Graflex" style recharge pins. Still can't get the to come out right.



     
  25. 88reaper88

    88reaper88 Active Member

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    Could you not just use a bit of metal rod???
     
  26. Alaneye

    Alaneye Well-Known Member

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    When I was casting the jaw piston for my Terminator I had the same worry as it's a very thin part (about 1mm, maybe a bit less at the thinnest part).

    [​IMG]

    I used the single stem as the pouring end and I vented the ends of the twin stems into little 'bubble' air spaces. But when I poured the resin it still didn't run in as it is too viscous, but I found that when I squeezed the mould where the 'bubbles' are, it forced out the air which rose into the pouring spout and when I released it, the resin was sucked back into the 'bubbles', completely filling every part of the thin casing. Up to now it has worked for every one I have cast. I also dust the mould with talc.

    I'm at work at the moment, but if you like, I'll take a pic of you mould in case the description is a bit hard to imagine?

    Al
     
    Last edited: Apr 18, 2012
  27. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    I don't get the joke.

    So, I will try the squeeze method (Thanks Alaneye) or maybe trying to add a *very* little amount and then going back an adding more after the bubble has risen out (Thanks Franz Bolo).

    We'll see how that works :)
     
  28. Alan Castillo

    Alan Castillo Master Member RPF PREMIUM MEMBER

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    No love for the toothpicks ? :lol
     
  29. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    already tried them :-(
    same results as using a dental tool
     
  30. pfillery

    pfillery Active Member

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    Not a solution but a related question. I'm thinking about casting a replacement Exactra calculator bubble strip out of clear resin as I can't afford or justify the real thing and I'm not 100% happy with the blastech one. Is this prone to failure? It is also quite thin and clear and any bubbles are bad. Any ideas? Was just going to mould using clay and pour in clear resin.
     
  31. Ozymandius

    Ozymandius Sr Member RPF PREMIUM MEMBER

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    I cast thinner pieces up to .5 mm all the time without pressurizing, so it can be done if you know the tricks and how to combine them.

    1. Talc the mold. (already been said, but still good advice.
    2. Pour the resin.
    3. Cap the pour spout with your finger (you should be wearing gloves for this), and then tilt the mold to the side about 30 degrees and gently tap it on the table to dislodge the air. Tilt it to the other side and repeat as necessary.
    4. Take your finger off the pour spout and top off the level if it needs it.

    Adding extra vent tubes to the mold definately helps (especially for more complex parts or two piece molds, but I'm assuming here that you are using a one piece open top mold with the pin facing down, in which case there would be nowhere to put a vent.
     
  32. Ozymandius

    Ozymandius Sr Member RPF PREMIUM MEMBER

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    Pressing your part into clay for a temp mold almost never works because the clay will stick to your part and wreck the mold. However, if you lay a piece of cling wrap over the clay and push your part down into that, then you can pull on the cling wrap to cleanly remove your part and have a usable mold. You should also talc the clay mold as well for the best results.
     

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