need some advice on casting

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Lflank

Well-Known Member
As some of us know, I've recently ventured to dip my toe into the ocean of casting, and made some casts of a pred laser mine thingie using the beginner's kit from Smooth-On (I also did a test cast using a mold I made from Home Depot silicone too, which also turned out pretty good).

So now I'm ready to move to the next level of difficulty--casting an object that has two sides to it, instead of being flat on one side. What I'm thinking of doing is making a somewhat larger and more detailed version of my custom smart disk out of clay (which will force me to improve my currently-rudimentary sculpting skills), then casting it in resin. Since the only materials I know how to use are Smooth-On Oomoo 30 and Smooth-Cast 300, that's what I'm planning on using.

My dumb newbie question is how to physically cast both sides. It was easy enough with the flat-sided object--I just placed the object flat side down and then poured the Oomoo over it as thick as I needed it to be. But how do I do that with a two-sided object? I assume I need to somehow place the object in a casting box, make some sort of clay dam or something to cover the bottom half, then pour casting rubber onto the top half, let it dry, then flip it over and pour rubber on the other side. So my first question is: if I let the casting rubber on one side dry completely and then cast the other side, will the sealer and releaser prevent the new layer of casting rubber from sticking to the old one, so I end up with a two-part mold? I'm assuming so, but would rather ask and be sure.

The other thing I'm having trouble conceptualizing is how then to pour the resin into the finished mold. Somehow or another I'll need some sort of hole to the outside so I can pour the resin inside the mold. Can I assume that this will leave a little tube of resin in the finished cast which I would then have to remove (unless I can integrate the little tube into the design of the object itself)? I get that when casting a mask, you just pour the latex into the big hole at the bottom--but what happens when the object one is casting doesn't have any such hole?

Forgive me if this question sounds dumb, but this is all new to me.
 

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Lflank

Well-Known Member
you actually answered all of your own questions.

I kinda sorta have half a vague nebulous idea what I'm doing, but I just wanted to ask and be sure. :cry:


Many thanks. I'll go ahead and sculpt a new disc in clay, and after a dozen failed tries when I squash it and start over again until I finally get something decent, I'll go ahead and cast it.
 

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Darth Pinhead

Active Member
Yeah, definitely check out the smooth-on site, as well as YouTube. There are PLENTY of great videos out there. Best of luck!
 

Lflank

Well-Known Member
Sent you a PM

Got it. Let me go ahead and finish sculpting the model (that'll take me long enough all by itself). Then I'll be ready to do the details of casting it.

As I understand it, "keys" are little pegs that I put into both halves of the mold so that when I put the two halves of the mold together they line up properly the way they are supposed to?
 

Darth Pinhead

Active Member
Have you thought about coating the foamie version in resin and cleaning it up with bondo, maybe add some more detail with clay, and then casting that? Just an idea...

Whatever you decide, have faith in your skills brother and enjoy the learning process!
 

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Lflank

Well-Known Member
Have you thought about coating the foamie version in resin and cleaning it up with bondo, maybe add some more detail with clay, and then casting that? Just an idea...

Whatever you decide, have faith in your skills brother and enjoy the learning process!

I want to completely remake it. I want to change the size, and probably change the detailing.

Partly because I want to force myself to get better at working with clay.
 

VaderDave

New Member
As I understand it, "keys" are little pegs that I put into both halves of the mold so that when I put the two halves of the mold together they line up properly the way they are supposed to?
Close. If you look at the pics they show the guy using a pen to make indentations into the clay. These create bumps in one half and dips in the other that match up and lock the 2 halves in places when the mold is put together. These are the "keys" you are referring to.
 

Darth Pinhead

Active Member
Close. If you look at the pics they show the guy using a pen to make indentations into the clay. These create bumps in one half and dips in the other that match up and lock the 2 halves in places when the mold is put together. These are the "keys" you are referring to.
I've seen people press marbles into the clay wall, as well...
 

Lflank

Well-Known Member
Close. If you look at the pics they show the guy using a pen to make indentations into the clay. These create bumps in one half and dips in the other that match up and lock the 2 halves in places when the mold is put together. These are the "keys" you are referring to. ;)

Ahhh, I get it.
 

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Darth Pinhead

Active Member
That's where the mother mold and straps, rope, clamps, etc., come into play, to hold the form of the . Plenty of methods. On the bigger molds made of fiberglass or Plastipaste, you can drill holes through both pieces of the mother mold and use bolts, washers and wing nuts. Check out the rope aisle at Home Depot or cheaper yet, Harbor Freight for the tie down straps. Though, they may be a little large for this project and rope may suffice. Here's a great Smooth-On video...
 

Lflank

Well-Known Member
After several unsuccessful attempts, I finally have a basic clay shape that I like:

5673482166_ae7d73eaf7.jpg


I cut out a template from posterboard and used that to keep checking the shape. It's about 10.5 inches across.

I'm using air-dry clay. I didn't want to use sculpy or anything that stays soft because it's a thin flat shape and I didn't want it constantly warping as I work on it. So once it's bone dry, I'll start building up the center parts.
 

Lflank

Well-Known Member
I'm using air-dry clay. I didn't want to use sculpy or anything that stays soft because it's a thin flat shape and I didn't want it constantly warping as I work on it. So once it's bone dry, I'll start building up the center parts.


Arrrggghhhh, my first hard-learned lesson---using air-drying clay for thin flat shapes is, uh, not a good idea. Large cracks have appeared all over the place as it dries. If pieces end up breaking off completely, I'll have to superglue them back on or something. :(

I'm thinking my best option now is to let the piece finish drying, then fill in the cracks, let that dry, and then coat the whole thing with some mixed resin to strengthen it and hold it together.

Or is there a better option that I don't know about . . . ?
 

Eaglewood

Sr Member
Arrrggghhhh, my first hard-learned lesson---using air-drying clay for thin flat shapes is, uh, not a good idea. Large cracks have appeared all over the place as it dries. If pieces end up breaking off completely, I'll have to superglue them back on or something. :(

I'm thinking my best option now is to let the piece finish drying, then fill in the cracks, let that dry, and then coat the whole thing with some mixed resin to strengthen it and hold it together.

Or is there a better option that I don't know about . . . ?

You have to go slowly-- we all get anxious to get the mold done and pour that resin in-- just take your time and do it right. You will be more satisfied with the results.
 

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Don't want to see this ad? Sign up for anRPF Premium Membershiptoday. Support the community. Stop the ads.

Top