Help with Blue Stuff and Silicon Putty

[Bahir]

Hi all, I find myself once again asking for the collective wisdom of my fellow LAFers.

I have some OOP plastic weapons (snub pistols, hand flamers, eldar power fists, etc.) that I am trying to replicate to use in some conversions and I am having some difficulties with the double sided blue stuff molds. The two halfs of the weapons are not lining up. This could be that:
 

• I am not lining up my molds.
• I'm using too much green stuff and this is causing the mold to misalign
• I'm putting too much pressure on the mold and this is causing the misalignment.
• My mold is bad

Can anyone offer some tips on how to create two sided press molds for small fiddly bits?

I also recently procured some silicone putty from Green Stuff World (http://www.greenstuffworld.com/en/inicio/545-silicone-putty-300gr.html). Would this be a better option for trying to make double sided molds? I haven't seen much online on how to use this product, so any hints, tips, or tutorials would be most welcome.

Thank you in advance for your help!

[joroas]

I, too, have tried the blue stuff with similar results.  Would love some advice too.

[nic-e]

Are you putting keys on your moulds? And if so, how many?

Cutting the edges of your mould in a zig zag pattern alongside your keys will help stop slippage.

blue stuff and the reusable moulding putty aren't amazing materials, They tend to have shrinkage and be a bit too rigid for really good two part moulds. (ymmv of course, But i would always just use good quality rubber or silicone.)

Also bare in mind that you're trying to cast a material not designed for casting.Green stuff is a set material as far as casting is concerned, It's not viscous enough to flow into gaps in amould and will just get pushed out into the body of the mould and cause gaps and slippage.

have you got a picture of your mould? If so that could help?

[Connectamabob]

I agree with Nice-E: pics would help enormously in diagnosing the issue, but is does sound like a problem of not enough keys + the casting material is too stiff so it's pushing the mold out of whack while you're closing it.

I've never used Blue Stuff, but I've used silicone moldmaking putty, and found it awkward and unsuitable for most stuff. I suspect Blue Stuff would be a little bit better, but would still share a lot of the same problems. If you're looking to trade up from Blue Stuff, skip the putty and go straight to pourable mold rubbers. Contrary to what you'd think, the putty is actually way more awkward to use, so to my mind it's a product without a niche. IMO its market consists entirely of people who aren't experienced enough to know better yet.

If you really want to keep it cheap, the best thing you can do (apart from making sure your mold is well keyed) is stop casting with epoxy putties. Go to the hardware store and get some two part epoxy glue instead. It's a resin with a pourable consistency, and yes, you can cast with it. The end product is as good as GS. You'll get castings that have better detail, less distortion, and less flashing.

Powdering the mold with talc or cornstarch also helps, as it breaks surface tension and allows the casting material to get into crevices and displace air bubbles better.

[nic-e]

Following on from what connectamabob said, You can also use silicone caulk as a rought and ready casting silicone, just prepare your mould as you would for casting rubber and squirt the silicone over your desired object, spreading it gently with a brush before covering it to a decent depth.

Casting in two parts is something you really don't want to cheap out on. Blue stuff is useful for making sprig moulds and open cavity moulds, but silicone it is not.

Instamould or heat shaped casting putty is the same, useful for copying surface detail and shallow moulds, But not very good for two part moulds because of its tendency to catch air/warp ect ect ect

[Bahir]

Thank you for the advice, there is a lot of info here that I wasn't aware of. I'm in London for the next few days, but I will post some photos when I get home.

Thank you!