Molding and casting-the right way?

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Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 7:58 pm

Okay, I know I already have a (tiny) bit of experience in this but my previous attempts were lacking. Apshalt has given me countless tips and info on this and I'm hugely gratefull for his assistance, its unfortunate that I seem to be the worlds worst pupil.
I'm throwing this topic up because I'm getting some cash soon for new supplies, bit with christmas right around ze corner, I cant afford to waste a penny.

I know about smooth on but I cant find a UK distributor for their stuff so It looks like ebay is my only choice.

Silicone: I previously used a 100:10 ratio silicone and had issues mixing it. Couldnt get the mesurements quite right and the silicone liked to bond to the plasticine i used, even after I coated it with mold release.
I'm thinking an equal 1:1 ratio mix would work better for me. Im thinking this one would be good for me, what do we think?
http://www.ebay.co.uk/itm/RTV-Silicone-ZA-40-Thixo-Skin-Safe-Mould-Making-500g-/320441993158?pt=UK_Crafts_Other_Crafts_EH&hash=item4a9bd4c7c6

Plasticine: Is there any particular type clay i need to embed the part in or was I just unlucky.
(This may end up irrelevant since I need to try Asphalt's method.)

Resin: Specifficaly getting it into the mold. My first attempt, the resin missed the mold entirely and only ended up with a small bit in the bottom of it. My second attempt I used a syringe and had more success apart from the unsighlty hole left were the syringe had been. Whats the best way of making sure it goes all the way into the mold?

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 8:22 pm

Rubber is just personal preference. You want long pot life and LOW viscosity.

That sounds like the two problems with your resin. Is it getting thick before you can fill your molds? If your materials have a short pot life (the amount of time they are liquid after mixing) then you will always have problems. The resin I use has a 15 -20 minute pot life. I can fill a ton of molds before it starts to set up and it has a viscosity only slightly higher than water.

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 8:35 pm

"Viscosity of the mix pre-catalisation
20000 cP"

What is Viscosity? Im hearing that word and it would be helpful to know its meaning.
Im guessing this is HIGH? What would be low?

Yeah, the resin I used hardened in around 5 mins. Looks like i need to look around some more.

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 8:42 pm

That is your biggest problem. And that is a high viscosity. Viscosity is a fluids ability to flow. You hear it a lot in engine oil adds. The lower the viscosity the closer the material is to water. The high the viscosity the closer the material is to cold honey. Low V good for casting. High V, very bad.

Pot life is the amount of time you have to work with it. I wouldn't recomend anything with a pot life under 15 minutes. That is the time from part A touches part B until it begins to harden. With yours having only a 3-5 minutes you are barely getting beyond the stir point.

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 9:01 pm

Ah ha. This would have been very useful to know a month ago! So what would be a good number for low viscosity? I'm looking around but without know how low it goes its hard to judge.

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 9:26 pm

The resin I use has a viscosity of 100cps.

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 9:42 pm

when I said 20000, I was talking about the rubber. My bad. How low should the silicone viscosity be. (dam thats a b**** to spell!)

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Re: Molding and casting-the right way?

Post  Guest on Wed Nov 28, 2012 10:06 pm

The closer to zero the better. 100 is like generic robitussin in thickness.

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Re: Molding and casting-the right way?

Post  Guest on Thu Nov 29, 2012 8:29 pm

Well this is the lowest viscosity I can find. Its a dam sight better than 20000 but is this a good buy for what Im trying to do with it?
http://www.ebay.co.uk/itm/221047663087?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

And is This a good resin to go with it?
http://www.ebay.co.uk/itm/250g-Polylite-Water-Clear-Casting-Resin-Hardener-/230498995666?pt=UK_Crafts_Other_Crafts_EH&hash=item35aacf8dd2

All this choice is maddening!!

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Re: Molding and casting-the right way?

Post  Guest on Thu Nov 29, 2012 9:55 pm

Sorry man I can't tell you anything about any of those. That rubber looks like something I would stay away from. It sounds like it is a little over reactive. Mixing it up in the wrong container with the wrong stirrer might screw up everything. Unless you have glass beakers and stir rods, then you are golden.

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