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How can I Mold & Cast parts like these?

Discussion in 'Molding and Casting' started by KJShunk, May 31, 2018.

  1. KJShunk

    KJShunk New Member

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    Hello everyone!

    I am making an articulated action figure of a character in ZBrush & SpaceClaim(For Engineering). I was going to cast his main torso out of hard plastic(similar to ABS) and his limbs out of a polymer resin where its like hard rubber and semi flexible. I'm trying to figure out how to cast the polymer resin around a hard plastic hinge disk for the shoulders so his arms can swivel outward. When I cast around the disk, the polymer will go through the disk hole in the middle creating a "Hidden Pin". I know I have to mold and cast the hinge disk first and then insert it into the other mold to cast around it, but I'm not sure how to set the shoulder mold first so there is a spot to insert the disk hinge into the mold to cast around it. The two part casting for the shoulder is what I'm talking about. I'm also having trouble figure out how to mold the inside mushroom hole inside the bicep so the shoulder can pop into it.Help would be much appreciated! Thanks a lot!


    untitled.png dcc_anatomy_action_figure_final_580_538fb52ae8d975_00434518.jpg untitled4.png untitled2.png untitled3.png
     
  2. Cory

    Cory Keep an eye on quality!

    If i understand correctly; I would disect the piece like they do deer noses (see Ohio Taxidermy Supply for replacment noses. Once the piece is exactly how you would like it, you may need to make a block mold of the piece and do an injection mold. There are more experienced mold makers on here, but try and do things as simply as possible, working your way to complex. Even if it means making several molds that will need to fit together to make the correct one piece mold.
     

  3. Frank E. Kotula

    Frank E. Kotula master, judge, instructor

    go to smooth on and watch their videos that will aid you
     
  4. KJShunk

    KJShunk New Member

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    That's actually one of the first things I did haha but there's nothing on there showing molding and casting parts like these with holes inside that have undercuts and two part casts.
     
  5. fishmaster

    fishmaster Well-Known Member

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    Making molds like that you need pins that go into the holes. You would slide the pins into the hard parts, and make the mold. One of those pics showed an interior hole that had a step down. The pin would have to emulate that.
    Then when you demold the part the pin slides out first. Then before pouring the part the pin is slid back into the rubber. Obviously the pins have to be waxed and lubed so they don't stick in the plastic. Usually you would have a sprue area for the pouring and a second hole for venting the air. There is a mold maker in Kansas City Kansas that makes a lot of action figures but I cannot remember the name. As I remember they had some pics on the website (if they are still in business). Most of their molds used a plastic cup like a red solo cup for a mother mold to support the rubber.
     
  6. KJShunk

    KJShunk New Member

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    Would you be able to explain each part I talked about? The Bicep with the disk at the end with the hole going through it is for a pin to hold it to the forearm for the elbow joints. The "two part cast" is for the shoulders to swivel outward and the mushroom shape at the end of it needs to pop into the bicep. Am I confusing you at all? Hopefully not. I'm having trouble visualizing it a bit. I need to 3D model the parts in a way too where I can mold these successfully. If you have more help, it would be highly appreciated! Thanks man!
     
  7. fishmaster

    fishmaster Well-Known Member

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    If I was going to try to mold the piece you have pictured above in your fingers I would get a piece of brass rod the diameter of the hole in the disc. Then I would get a rod and create the step down ledge that comes in from the other direction. You could chuck a piece of brass stock in a drill and use a file to turn down the smaller diameter. Anyway, whatever it takes to make a rod that will slide into that socket.
    Then stick those rods into the holes, support it in a cup or tray and either make a two part mold or a solid block mold that is then cut open enough to remove the part. Smooth on makes translucent rubbers so that you can see the part as you are cutting it open. It would be made in a way that you could insert the pins into the mold, pour the part, remove the rods and then remove the part.
    Search some of the action figure and star wars related forums and you can probably find a tutorial that will better describe how to set it up and mold it. There are some really good mold makers and fabricators out there just doing this stuff for a hobby. Also model train forums have a lot of info. Good luck.
     
  8. jigginjim

    jigginjim Active Member

    I would say you could do it with a two part mold. then you just drill out the thru hole. Coming from a machinist mold building back ground the part your marking would be done in a injection mold with a minimum three separate parts to do mass manufacturing. I could be done as a one piece mold. but you are still the thru hole.