I now know how to make rubber resin casts.

[xiombarg]

I accidentally figured out how to make rubber last night. The resin I use combines equal parts 'A' and 'B', but last night I wasn't paying attention and mixed 1/3 'A' which is the hardener and 2/3 'B' which is the plastic base. Two hours later I pull my cast from the mold and it's rubber! So I guess if you are worried about your resin being too brittle, just add a little less hardener and you will probably gain the same percentage of flexibility in the plastic. It makes perfect sense but I had never thought about it.

It makes me want to cast some custom rubber kaiju figures!

[Mr. Ginrai]

What resin are you using?

And if you take a hobby knife and cut a piece in half, is it porous inside or is it a nice firm fill with no air?

Do you think you can dye it, if not, is it paintable?

[xiombarg]

Nov 13, 2013 13:11:30 GMT -5 Mr. Ginrai said:

What resin are you using?

And if you take a hobby knife and cut a piece in half, is it porous inside or is it a nice firm fill with no air?

Do you think you can dye it, if not, is it paintable?

I use Smooth Cast 327 urethane resin made by Smooth-on which is made specifically for adding pigment. I pressure cast all my resin casts so that all my casts are completely firm and bubble free inside and out. But for just standard casting without pressure I wouldn't use 327, instead I would use Smooth Cast 320, 321, or 322 which will all accept pigment ok.
If you just want a good paintable resin the Smooth Cast 300, 305 or 310 are great.

The longer the set up time of resin the less problems I have had with bubbles when not pressure casting. The fast setup stuff often gets so hot that it seems to create a boiling kind of reaction and then sets up as the bubbles are still working their way to the surface, perhaps due to the heat? Single piece molds with a large pour area are the worst for bubbles, but Two part molds with smaller vent areas don't seem to have this problem as much. I think it has something to do with oxygen reacting with the exposed surface of the hot resin, so bigger areas exposed to oxygen equals more bubbles and smaller areas with less exposure equals fewer bubbles. Whether that's really what it is or not I don't know, I only know what I've seen with my casts.

[boma83]

i ve tried that but ended with the resin still like gell.

you can use Flexible resin type for elastic thing

[xiombarg]

That's true, they do sell urethane rubber.

I've had resin that stayed like gel a couple of times. If you pull out your cast and part of it is sort of solid and the rest is like goo, then the two parts weren't mixed together enough. But when the whole thing is gel I think the ratio of the AB mixture was lower than what I did last night. I also let my cast setup for longer than normal and it could have been sticky if I had pulled it out sooner. I don't think I would dare go any less on my mixture than what I did if I try it again. I might try a couple of experiments in plastic cups with this.

[magengar]

I use the Alumilite tan colored resin,
with the Alumilite HS3 Mold-making Silicone rubber.
My resin requires a 1:1 mixture; but I'll try the same
accidental ratio you used, to see if I get the same
"rubber" result as you got.

As for bubble-free castings, I gently tap the mold with
a pencil or touch it with a vibrating massage wand,
to get the air bubbles out of my resin before it cures.

The Smooth Cast products appear to be more professional in nature,
and more expensive; but I'll give that brand a try someday soon.
I'll also have top learn how to add the pigment colors,
or I'd learn how to use colored paint inside the mold.

Thanks for starting this thread!

zozo-mag

[Lejam]

Mmmmmh, interesting.
I have to find a way to create molds for all my SOCs rubber parts.
Caterpillars from Ideon and Getter 3 already cracked...
Best is to create a first mold to extract the resin version you can rework a bit.
Then you can store it to recreate the rubber version.

Or, madness version : get some real caterpillar from kit with the good width size
and go diecast after molding process. Best is to find existind diecast versions...

[xiombarg]

Magengar: I usually rock my mold back and forth a couple of times to release any bubbles that might be stuck to the side. When using fast setting resin and not pressure casting I sometimes get surface bubbles where the pour area is. I've always thought it had something to do with a heat and oxygen reaction because the bubbles always seem to form right when the resin is getting really hot and setting up.

Lejam: You should be able to make standard silicone molds for rubber pieces. BUT, you want to put some kind of temporary filler material into the cracks before you make the mold. Plastic repair epoxy would probably work or maybe even a high end adhesive caulk like Lexel or Titebond Metal Roofing repair caulk. Both of these will stick to just about anything.