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Fish fins

Discussion in 'Molding and Casting' started by jamie11, Mar 30, 2014.

  1. I know a lot of people use a pressure pot to gets it out if the castings. My question is can you do this if your mold is a bondo type mold. Only see people doing this with silicone molds
  2. Can it be done... Yes. But, there are a number of reasons for using silicone for the media on this. I'll mention a couple, but if I miss a couple advantages, I'm sure my fish friends shall jump in and help out as well.

    1. Silicone molds yield excellent, very fine detail. You may have difficulty pulling all the intricate details of your fin with a product like bondo. Although the viscosities are both thick (silicone and Bondo) silicone takes a while to set up, allowing it to ease it's way into all the pores. It will give you the closest simulation of your fin.

    2. With a Bondo mold, you must add a release agent or your solid fin material will stick to your solid Bondo mold. And if you add a release agent to your mold, it will create difficulty in paint bonding to the part. So if you do use this method as a mold, you'll have to wash your fin with soapy water and scrub to release----the release.

    3. With a Bondo mold, you'll have to make a two-cavity tool. This means you'll have a parting line. Even if it's along the seams, a parting-line is a parting-line and you'll have to spend some time working the flashing from the part. With silicone, you can pour one half, flip it over and pour the second half. Silicone bonds to silicone, so you'll have a one piece tool that has the flexibility to allow you to pull your urethane (IE 3080) fin from the tool. (Sorry, couldn't resist plugging Innovative products.)

    4. Bondo also is exotherm dependent. This means it will build heat when it cures. This could damage your fin.

    5. Your fin is going to contain water. The water molecule will react with the Bondo causing it to slightly foam on the surface you want to be plush. Tin based silicones love water and it helps it cure, not hindering the cure by creating foam.

    And as you alluded to, pressure pots work great to squash any small bubble to microscopic size after the material has been poured into it, so no one will ever see them.
    Hope this is useful info.

  3. amigo

    amigo No habla Espanol

    Depending on the species and amount of detail such as wrinkles and fat rolls I can agree that RTV is sometimes advantageous for molding but Bondo molds can produce high quality results as well. The viscosity of both are similar but the detail coat with bondo is thinned substantially and cure is slowed down to allow for fewer air bubbles and better details. I also have never experienced problems with moisture when using Bondo to mold fins or for that matter the entire fish. A pressure pot is a nice tool to eliminate air bubbles in the fin if your having troubles.
  4. Yeah I get great results with bondo molds. Just wasn't sure if I could use a pressure pot with bondo molds
  5. Sorry. Didn't mean to pee in anyones Cheerios! Just wanted to assist as to the potential "why" in regards to silicone as the choice for mold media. If you can make Bondo work, that's great because you'll probably get more mold life from that type of mold. So there's the advantage of Bondo. Silicone will eventually dry up and tear.
  6. Haha you didn't upset me polymer guy. To tell you the truth I just got a tub of GI1100 to try out. I'm always up for trying new things to better myself. I just wasn't sure if I could pour IE3025 into my bondo molds and then put them in a pressure pot that's all. Just trying to get into the more advanced part of molding and casting. Thank you for your help.
  7. amigo

    amigo No habla Espanol

    Me neither. I dont eat cheerios.
  8. amigo

    amigo No habla Espanol

    If we could just get the air bubbles to just line up along the fin rays creating natural opacity we would really have something.
  9. HAHA! I don't eat cheerios either... Unless they made them in the shape of fish!
  10. Something to keep in mind.

    If you are going to pressure cast from a mold, you will need to make the mold under pressure.

    This is my experience. I have found that molds made by hand pouring contain micro bubbles that you will never see if you hand cast without pressure. But, when you put these molds under pressure in a pressure casting situation, you will see the casting material forced into the micro bubbles causing the surface of the casting to have what I call the "Pin Head" effect. Lots of small dots or bubbles on the outside of the casting.

    As for bondo,,,,,,, I cant say. I only know what will happen with the silicone.
  11. Thanks Doug