"Help!" for: Casting

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  1. #1
    405th Staff 23Magnum's Avatar
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    "Help!" for: Casting

    This thread will contain general first hand knowledge of casting such as materials, methods, and techniques to get a workable model out of your molds.

    People who don't know: Post questions.

    People who know: Answer those questions.

    Please be as clear and detailed as possible with your questions and/or answers. Repeated questions or variations of certain questions may be consolidated over time into an FAQ section in the post following this one.

    Always ask and answer questions as if you were asking/answering your mother or grandmother. In other words, politely.

    Rudeness and/or impatience will be met with an infraction. You don't want too many of those.

    These threads are meant to reduce and hopefully eliminated the need for the numerous 'I need help threads' that seem to generate endlessly in this section of the forum.

    They are not a be all, end all to all questions that could ever be asked though. Some questions will be project specific and you may need to ask those IN the project's thread itself. However, some may not see your questions there so you may post a link to said project thread in the appropriate "Help!" thread when you need the attention of a few extra eyes.
    Last edited by 23Magnum; Aug 20, 2010 at 8:33 AM.

  2. #2
    405th Staff 23Magnum's Avatar
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    FAQ Section:

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    405th Staff 23Magnum's Avatar
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    Tutorials that involve this thread's subject matter and are approved by the site staff will be linked in this post. Please review them as they may already contain the answers you seek.

    Tutorial Section:

  4. #4
    When you finish your pull and have a piece made from smooth cast 320, roto, etc. how well do the parts take to sanding? I know ideally you should aim for a perfect buck before molding, but is ok to try to continue smoothing on a casted part?

  5. #5
    as i have never used smooth cast products i'll try and answer the second part of your question. It would depend on how much sanding you have to do and what the reason is. if it because of a flaw from the molding process.. then yeah a bit of sanding is alright.. if its a flaw with the master then more work is needed on the master..

  6. #6
    New Recruit Chantelle's Avatar
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    Quote Originally Posted by Hugh Holder View Post
    When you finish your pull and have a piece made from smooth cast 320, roto, etc. how well do the parts take to sanding? I know ideally you should aim for a perfect buck before molding, but is ok to try to continue smoothing on a casted part?
    I agree with twistedxknights. If it's because of the master mold, then you should aim to have that mold sorted out.
    As for Smooth-cast 320, it's a dense enough plastic resin to be sanded but I would suggest using a fine grit (probably anything #100 upwards) followed by buffing blocks. The thing with Smooth-Cast 320 is that it's meant to be pigmented when it's first used - it's pretty much impossible to paint directly, as the smallest, softest scratch will cause the paint to lift straight off (I've seen this with a variety of paints, too)...

  7. #7
    Its not a good idea to mold a incomplete piece, but if you find with some issue in your cast ( i keep getting two noticable wrinkles on the left side of my helmet mold everytime )

    It is sandable but it sure feels like it takes longer to sand compared to body filler.

    I also concur with chantelle about painting a raw cast. I thought i would be clever to primer first then mold. End results: most paints did not work very well on the casts.

    You can either primer it or roughen the surface with a fine grit sanding sponge
    Last edited by this is haji; Sep 21, 2010 at 6:47 AM.

  8. #8
    Well, my question was leaning more towards the pre-painting aspect of the piece but thanks guys.

    I used Roto-65 and the stuff takes well to paint and sanding. It's actually easier to sand than the bondo imo, simply because I can get in the tight areas and sand by hand instead of relying on a mouse. I seem to get things accomplished quicker ^_^

    There is no issue with major details or symmetry, everything is good to go. Just minor surface issues that, when working with bondo and it's pitting habbit, seem to take forever to fix - which actually adds more refining time. Sanding on Roto seems faster and gets me where I want to be in the long run without all of the hassle.

    Thanks again for the advice guys.

  9. #9
    hollywood's Avatar
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    I dont know if this is helpful or not, and since I havent started molding just yet I dont know this from experience. On several of Ithicas videos he talks about doing several "generations of molds". Gen 1 is from your master, as good as you can get it. Then he modifies and further refines, sands, and details his cast to perfection and makes a second generation mold. Gathering from this it sounds like the casts take well to modification and sanding, but I imagine this process can get expensive with the mold materials.

  10. #10
    ShadoKat's Avatar
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    I'm using SmoothCast 321, and finding that sands pretty nicely with coarser grits and, after doing that, takes smoothing with finer grits pretty well, also. Like everyone else said, you should work your master as much as possible, but some things are not as easy to do with clay because it is so very sensitive, and sometimes you need something a bit less malleable to finish. That's where transition molding comes in (the "generations of molds" that hollywood mentioned). You make a mold, do a cast with a more forgiving material, finish the cast, then make another mold. Voila!! Now, if you do a good enough job with the original master, you may only need a little bit of work, and you may find it's not worth the trouble to do a second round of molding. For my project, I ended up having to do a good deal of shaping with the sandpaper, leveling out some uneven spots that I couldn't fix in the clay, and it's been turning out all right so far... Except for one small problem, which I'm hoping someone here can help me with...

    After sanding, I'm getting a lot of little pinhole pits, likely caused by tiny air bubbles in the liquid plastic. Is there some way to minimize this problem during the slush casting process, or should I just resign myself to trying to fix it with body filler later?

    As for paint, the 321 seems to be taking paint just fine, as long as you use a coat of primer first.

  11. #11
    Quote Originally Posted by ShadoKat View Post

    After sanding, I'm getting a lot of little pinhole pits, likely caused by tiny air bubbles in the liquid plastic. Is there some way to minimize this problem during the slush casting process, or should I just resign myself to trying to fix it with body filler later?

    As for paint, the 321 seems to be taking paint just fine, as long as you use a coat of primer first.
    only thing i could suggest is to use small batches when your slush casting instead of one larger batch

  12. #12
    New Recruit Chantelle's Avatar
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    SK: Some products release vapours in heat and humidity that cause that, and other times it can be caused by dust in the mould. Not sure what would have caused yours, though!

  13. #13
    New Recruit Destructo Pup's Avatar
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    To help eliminate the tiny air bubbles your resin really should be degassed before the pour. If it is a fast cast resin that you wouldn't have time to degas before it kicks off, you can degas both parts (A & B) seperately then 'gently' mix them together with a stir stick before pouring into your mold. A couple other ways to help eliminate air bubbles in your casted parts... especially if you don't have a degassing station... is to be careful 'how' you pour your resin into the mold. A careful pour that doesn't allow a lot of bubbles to foam up will help eliminate bubbles in your casted part.

    Another trick I use a lot was to dust the inside of the silicone mold with baby powder and then bang out all the excess so your left with a nice even LIGHT dusting. It helps the resin flow throughout the mold and helps eliminate air bubbles especially in detail areas.

  14. #14
    ventrue's Avatar
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    Quote Originally Posted by Destructo Pup View Post
    A couple other ways to help eliminate air bubbles in your casted parts...
    I have also seen additives that are supposed to have that effect. They were simply called "degassing agent" (rough translation), so I'm afraid have no idea what they actually consist of, but they might be worth looking into.

  15. #15

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    thanks for this it really helps

  16. #16
    is really useful information

  17. #17
    New Recruit saint ignatious's Avatar
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    oes anyone have a general shopping list for a guy who wants to start the moulding process? im not new to the concept (pretty much how dentures are made and i been doing that for a while) so anything you would suggest i buy before i start up?

  18. #18
    009-SPA's Avatar
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    Has anyone on this site or otherwise casted with epoxy resin and Kevlar before? I'm going to do it the same way as with fibreglass, putting down a gelcoat first. Thanks in advance.

  19. #19
    sik1276's Avatar
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    Does Smoothcast require a respirator to work with?

    Also, the only store around my area that sells Smooth Cast is way too far; the closest store is TAP Plastics and they sell something called Tap QuikCast. Does anyone know how this compares to SmoothCast, notably the 300/320 series?

  20. #20
    ventrue's Avatar
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    Quote Originally Posted by sik1276 View Post
    Does Smoothcast require a respirator to work with?
    Some will say no, but I'd say yes, definitely wear one.

  21. #21
    Liamthedevastator's Avatar
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    I read somewhere that Roto urethanes tend to be rather flexible and can collapse in heat. Is Roto-65 strong enough to do detailed pieces such as the beak of a doctors mask from Assassin's Creed? (not to give too much away here...)

  22. #22
    Hey guys. About to cast out some stuff. How much smoothcast is required to cast 1 helmet? Would a trial kit be enough?

  23. #23
    Quote Originally Posted by Charlieiscool12 View Post
    Hey guys. About to cast out some stuff. How much smoothcast is required to cast 1 helmet? Would a trial kit be enough?
    Yes sir, a trial kit can get you a couple nice and sturdy helms (more if you use the material sparingly)

    Different types of plastic trial kits will give you different results. For instance, I noticed a trial kit of ONYX gave me a considerably less amount of material to make pulls from because it is thicker than 320.

  24. #24
    Alright cool. Just wanted t make sure before I bought some smoothcast. Whats the diff between smoothcast 320 and 300???

  25. #25
    sik1276's Avatar
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    I'm using TAP QuikCast for a mask I'm making. For the pep build, do we use Mod Podge or something to fill all the mini-holes left from the pepakura build?

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