"Help!" for: Casting

[23Magnum]

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.

[23Magnum]

FAQ Section:

[23Magnum]

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:

[Hugh Holder]

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?

[twistedxknights]

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..

[Chantelle]

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)...

[this is haji]

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

[Hugh Holder]

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.

[hollywood]

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.

[ShadoKat]

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.