making moulds

[Aliengod3]

Hey everyone,

I am trying to make molds of rocks and I wanted to know if anyone knew of any good casting mould materials that is flexible. That way I can mould it around the contours of the rock and not have the mould stick to the rock without being able to peel it off. Thanks

 

[hestan101]

you can buy cheap rock moulds. ive got some

 

[Legacy Account]

RTV silicon or silicon putty.

 

[Dragon Forge Design]

there are lots of materils you can use.. question is

- how much do you want to spend?

- how many copies do you want to cast once you have your mold?

- What are you wanting to cast your copies out of?

-is your rock loose, or is it fixed..as in like a big rock outside you want the texture from?

Answer these and I can better point you towards materials.

 

[Dragonsreach]

Plenty of materials availible, however one big thing to think about:-
Don\'t try to cast a mould of something which has a huge undercut as all you are asking for is a place for air bubbles to congregate and it\'s damn difficult to get the casting material out of the mould.
It\'s also why GW figures have so many thread lines coming off them, they are air channels from point where air would collect and ruin the cast.

 

[mickc22]

use the woodland scenic rock moulds, they are reasonably cheap, if you use Herculite to cast from them they make great rocks. You can break up the bigger castings easily enough. Tomps is where I got my silicone from BTW
I got my big bag of Herculite from Clayman Pottery Supplies, but that was because I was going down that way anyway

 

[freakinacage]

this stuff is pretty good:

silly/silli gum

not cheap (but ain\'t expensive) but it has good detail retention, sets in less than 10mins and is pretty flexible
you can get it in hobby craft in the uk but not sure where in the usa, but i think it is available

 

[mickc22]

oh yeah, I\'ve seen that too
that would be quite handy actually if you where going out to find some interesting rocks or textures to take a mould of

 

[freakinacage]

Originally posted by mickc22
oh yeah, I\'ve seen that too
that would be quite handy actually if you where going out to find some interesting rocks or textures to take a mould of

yeah it\'s great for textures. i always have some so if i find a texture i like, i can take an impression and use it on a base etc later. got a big bag of bits like that

 

[matty1001]

I\'v just managed to find that stuff in Newcastle Tim after you showed me it at yours last year. I am very tempted, although I\'v no use for it lol

Peace and love...

 

[Bigdennis52]

how much you want to spend is probabily one of the biggest factors in my opinion.

 

[RuneBrush]

I did the first half of a 2-part mold the other day using 2 part silicon rubber. It required 5% by weight of the catalyst, I discovered (more by luck than anything) that my kitchen scales didn\'t like weighing the 8g of catalyst being added to the silicon. I also worked out that 1ml is roughly equal to 1g of said catalyst. Finally you need something more solid than a plastic knife to mix it and need to get right down to the bottom to mix the elements together, else you\'ll end up with the mold taking twice the length of time to set or parts that never set.

What I currently have a problem on, is in future what material to use to set my master in, as plastercene is very tough to push delicate components into and difficult to remove for doing the other half of the mold.

Pete

 

[Baz]

Originally posted by RuneBrush
I did the first half of a 2-part mold the other day using 2 part silicon rubber. It required 5% by weight of the catalyst, I discovered (more by luck than anything) that my kitchen scales didn\'t like weighing the 8g of catalyst being added to the silicon. I also worked out that 1ml is roughly equal to 1g of said catalyst. Finally you need something more solid than a plastic knife to mix it and need to get right down to the bottom to mix the elements together, else you\'ll end up with the mold taking twice the length of time to set or parts that never set.

Pete

I found that if you transfer the silicone from the cup you are mixing it in to a second cup after mixing and then mix a little more before pouring it eliminates any unmixed parts and stops you having issues with the setting of the rubber. These videos should help too -

Mouldmaking 2Mouldmaking 1

 

[mickc22]

Originally posted by Baz

Originally posted by RuneBrush
I did the first half of a 2-part mold the other day using 2 part silicon rubber. It required 5% by weight of the catalyst, I discovered (more by luck than anything) that my kitchen scales didn\'t like weighing the 8g of catalyst being added to the silicon. I also worked out that 1ml is roughly equal to 1g of said catalyst. Finally you need something more solid than a plastic knife to mix it and need to get right down to the bottom to mix the elements together, else you\'ll end up with the mold taking twice the length of time to set or parts that never set.

Pete

I found that if you transfer the silicone from the cup you are mixing it in to a second cup after mixing and then mix a little more before pouring it eliminates any unmixed parts and stops you having issues with the setting of the rubber. These videos should help too -

Mouldmaking 2Mouldmaking 1

I was gonna say that too

another vid by Tap Plastics

 

[Legacy Account]

Top casting tips:

Use a syringe to measure out silicon catalyst :duh:

Buy a box of wooden mixing sticks (like big lollipop sticks) from Tiranti. Essential for mixing rubber and resin. You can reuse the ones you mix resin with. A box lasts years!

I found silicon easiest to mix properly in a wide and shallow container.

I used to mix resin in 100g batches in plastic cups. I weighed out the correct amount of part A into a cup using digital scales and marked it on the side of the cup. I added the right amount of part B and marked the level again. Keep that cup and use it as visual reference for pouring by eye. If you get the cups with rings around the outside they help loads. A stick marked with the correct levels is useful too. This saves lots of time. And scales.

If you leave your mixing sticks to set in the dregs of resin in your plastic cups the whole lot will pull away from the plastic when the resin sets, leaving perfectly clean cups for you to reuse. You also get cup-shaped castings to throw at your spouse

Dust your plasticine (and masters!) with talcum powder or French chalk before you press your masters into it. Use proper mould release spray before pouring your silicon.

Acquire a vacuum chamber if you want to cast resin properly.

HTH!

 

[Legacy Account]

Oh, health and safety.

If you\'re casting resins, get a SHIT HOT mask that blocks out fumes and make sure you do it in the garage or shed. Wear gloves.

You may not notice the fumes, but polyurethane contains isocyanates and these can trigger severe allergic reactions to the respiratory system and skin. Once you become sensitised, you will continue to have these reactions. I had an episode after using the stuff heavily for a year (with a mask and gloves...) and it scared the shit out of me!

Careful if you sand the stuff when it\'s set as well.

 

[Aliengod3]

I wish to spend less than $100 for everything. I found a site called smooth-on.com and they have nice starter kits with instructional videos on how to use their products but I am kind of scared to use all this stuff because I have no idea what the hell I am doing lol

 

[Legacy Account]

Go for the Pour On Silicon Starter Kit. That\'ll get you going. Silicon for moulds and polyurethane for casting. The only other stuff that you\'ll need: Lego, plasticine and a sheet of glass is useful.

What exactly are you trying to cast? Bear in mind that single-part moulds are much easier to produce and use than two-part moulds.

This chap has some useful tutes and advice:

Sogni Di Gundam

Check out his mould making tutes. Have a look at his galleries while you\'re there. Top stuff

Have a look at this too:

Robot Resource