How to Part a Snake?

Discussion in 'Sand Casting' started by Melterskelter, Jul 15, 2021.

  1. Melterskelter

    Melterskelter Gold Banner Member

    As part of my ongoing FFA (Future Founders of America:)) project I have promised a 9-year-old that we will cast an aluminum snake. She has been interested in my foundry for the last year or so. (She is one of the girls I showed in a thread a while back casting an “R” in my foundry). She likes snakes and expressed an interest in casting one in aluminum.

    So, I found a rubber snake for not much on Amazon that she likes. It is about 6 x 8 inches in its coiled shape.

    006AE58D-29FE-4B09-90A9-46914AA3CDBC.jpeg

    I plan to cast it in sand using either petrobond or sodium silicate sand. The problem I have not yet figured out is how to part the cope and drag. The model does have a part line that is easily seen. But, laying flat on a surface the snakes part line varies from 1/4” to nearly 3/4” above the plane of the table.

    15BF3642-D482-4517-902B-F41E46C5922B.jpeg

    So, I thought of just placing the model on the molding table and packing the cope and then parting down to the parting line. That would be easy if the snake were not coiled, but there is not a lot of room between coils as is. Elevating the parts of the coils so the part line is in on plane would allow a poured in material like polyester resin that would make a follow board. But then the cast snake would not lay on a flat surface correctly. I could carefully pack sodium silicate/catalyst or epoxy sand around the snake beginning at the head and slowly packing and coiling the snake to make a follow board.

    I am posting here to get some better ideas. Help!

    Denis
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Hmmm,
    Not sure if you can pull it off in a sand cast unless you use a resin bonded sand.
    I think if you clayed it down to a table at the belly line then rammed one side might work. But not knowing how flexible the snake is its hard to say.
    Maybe she'll it up and burn it out??
     
  3. Melterskelter

    Melterskelter Gold Banner Member

    Yes, I think the top side will have to be a bound sand in some form as the scales must have negative draft near the part line. Plastolina may be the answer for the belly side. Or, maybe Bondo to a board.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Use a bunch of T-Pins/needles to pierce and stake the snake in place on a board with the parting line parallel and at a uniform height from the board. Level the board, frame in the snake with a drafted frame, and cast a follower with tooling resin or plaster..........

    Best,
    Kelly
     
  5. ESC

    ESC Silver Banner Member

    Piece of cake Melter, but labor intensive.
    What both Kelly and David said. But in order to pull the pattern it would need to be rigid in Petrobond. If you made a sodium silicate mold you would be able to pull a flexible pattern. The key is to have a small ledge at the parting line of the follower that is perpendicular to the pattern for strength. In one off castings I will ram up with the plasticine and then toss it when it is contaminated with the sand. For multiple castings I go through several POP steps to either end up with a Bondo follower or POP follower, and use them to cast a rigid pattern in Bondo to simplify the pattern draw. Each step loses some detail, so that needs to be considered.
    With the snake, think ahead to the gating since that would be a long run single gated. Think about having the coils touch in a couple of places to shorten the distance from the sprue.
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    As mentioned in my first post, the problem with the elevation of the parting line to a single level is that then the snake won’t lay level on the table once it’s cast. So I want to cast the snake so that it will be laying flat on the table and that probably will require some sort of puttied-up follow board system.

    I do plan on not trying to run aluminum the whole length of the snake but I actually think that I will make several gates across the base of the snake so that aluminum can enter each of the coil segments separately and hopefully fill that way. The problem with that method is that I may have a tendency to get cold shuts. Inclining the mold somewhat may help reduce the tendency toward cold shots if the aluminum is caused to flow from the lower level of the mold up the individual coils to the upper levels.

    Denis
     
  7. ESC

    ESC Silver Banner Member

    If you want the belly of the snake in a single plane then use the plasticine to form a follower that intersects with the parting line of your rubber snake.
    Any gate that is between coils will encroach on the body to the parting line unless it is a horn gate.
     
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    Going to be a fun project!!
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    Yes, I figure I’ll clean up the gates with my Foredom and some files. I’ll just cut a channel from one coil to the next for casting. This “simple” project may be challenging.

    Denis
     
  10. Jason

    Jason Gold

    You know this is coming.... Ceramic shell and burn his stinky ass out. At least it shouldn't expand and crack the shell.
    Only good snake is a dead snake!
     
  11. Melterskelter

    Melterskelter Gold Banner Member

    Yes, I figure I’ll clean up the gates with my Foredom and some files. I’ll just cut a channel from one coil to the next for casting. It may be “fun” as in challenging.

    On the other hand, I may learn how to make and use horn gates so that the gates can be on the less visible and more easily cleaned belly. The scale pattern on the belly is more of a cross-banding rather than the shingle pattern on the dorsum of the snake. That cross-banding will be more easily replicated than the shingle pattern.

    And after thinking more about the follow board and the various helpful comments above, I think I will pin the snake with its belly in contact with a plywood board and use somewhat softened Bondo to form a a sloping ridge to and slightly above the already-visible molding part line on the snake. Then, after the Bondo cures, I'll extract the snake. Since the snake is rubbery that will allow the snake pattern to flex some even if the Bondo mildly overarches the parting line. Once the snake is pulled out I can use a disc sander to lower the overarching Bondo border just to the part line which should be quite visible in the Bondo. That will establish the needed parting line which will vary by at least 1/2" in elevation from the board. Then I can use some sort of filler, if needed, to reduce the valleys in the areas between the Bondo follow board part lines.

    She better like this:).

    Denis
     
    Tobho Mott likes this.
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    Might be easier to stake it down, then pour pop up to the parting line...
    That's if the parting line is at the same height along the pattern...
     
  13. Melterskelter

    Melterskelter Gold Banner Member

    That’s the thing. It isn’t.

    Denis
     
  14. Can you completely bury the snake near the top of the drag and ram it up in petrobond then use a spoon to excavate to the snake's moulded parting line, dust with parting powder and ram the cope. The cope would partly extend into the drag a bit but should separate.
    Snake No2.JPG

    Big Snake No3.jpg

    Snaaaaaaake!!!!2.jpg
     
    Last edited: Jul 15, 2021
  15. Melterskelter

    Melterskelter Gold Banner Member

    Nice snake pics.

    Sure, I could cope down, but that would be tricky given the relatively close spacing of the coils. And then there is the need to repeat that work a few times until I get the gating and runners right. By pinning the snake and using bondo or POP, I can at least start at the head and spread the coils a bit to provide a bit more room for shaping the Bondo on the outside of the coil. Then as I progress I can place the next portion of the coil in position---nearer the prior coil and do the Bondo. Once I have a follow board it will be relatively easy to mold subsequent sand until I get it right. I will probably make more than one once I get it working. I will be using PBond---actually Kbond and Pbond mixed per a prior thread.

    Coping down was the first strategy I considered.

    Denis
     
  16. That's true: you can always cast it and bend the coils closer once it's cast.
     
    Melterskelter likes this.
  17. Melterskelter

    Melterskelter Gold Banner Member

    How flexible will the casting be? My impression so far is that cast 356 is fairly brittle and not inclined to bend much.

    Denis
     
  18. I was curious about that myself so I did the experiment (assuming alloy wheels are 356). In whatever finished state the wheel is, heat treated? it's as brittle as a fresh carrot and cracks with almost no bending at all. Once heated with a torch and allowed to cool it bends readily but I'd imagine only once or twice before cracking.

    wheel alloy heat treated 1.jpg

    wheel alloy annealed.jpg
     
  19. ESC

    ESC Silver Banner Member

    Mark, you're going to need a bigger flask;).
     
    Mark's castings likes this.
  20. Melterskelter

    Melterskelter Gold Banner Member

    So, this is like the heating and bending of 6061 T6 perhaps. That alloy also is pretty brittle. The method I learned not too long ago was to mark it with a Sharpie and heat until the ink faded. Then allow to cool. After that treatment it was indeeed pretty willing ot bend---once. Is that the method or something else that you used for heating? I'm feeling a little silly for not thinking of this. But I figured maybe this was more specific to 6061.

    Like this:



    Denis
     
    Last edited: Jul 15, 2021

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