"Newbie advise! Mold making" Topic

Hi all

I'm going to have a go a making my own two part mold tommorow for my 6mm sculpted figure and I have a couple of questions, im using rtv/hd , is there are particular size the mold should be ? I was thinking of around 45mm square and 30mm deep, is this to small? I do not have access to a vulcaniser is this a major problem ? Will it effect the strength of the mold?

Thankyou in advance for any tips and answers

Richard

RTV rubbers don't need a vulcaniser – the rubber is cured using a chemical catalst. However, make sure it is a high temperature silicone rubber that can withstand the temperatue of the hot metal.

How big is really a matter of trial and error to a certain extent. The mould needs to be big enough and deep enough so that it doesn't deform too much when you pour the metal in or clamp it, plus you need a deep enough pouring aperature to allow the weight of molten metal to fill all of the mould.

I suggest that you look at a few Price August moulds first then make yours a bit bigger – RTV cured rubbers tend to be softer than vulcanised. After curing, may be an idea to heat them up in an oven for a while or just leave in a warm room for a few days to post cure.

Thankyou for you help, I will make a bit bigger as suggested , I was going to wait a full 7 days before casting to allow the mold to cure , another question do I leave the figure in the mold wile it's curing or should it be removed ?

Richard

Yes, leave it in while it cures. And make sure you coat it with a thin coat of mold release before you pour your RTV to make it easier to remove.

Ok so I have poured the first half waiting for it to set so I can pour the second half noticed lots of bubble coming to the surface wich I presume is a good thing , f

Richard

When you mix the rubber with the catalyst you will be mixing in air. Likewise, as the rubber heats up during curing trapped in the rubber will be released. Actually I did try to get rid of air bubbles by vibrating moulds as they set by turning on a drill and holding it against the sides of the mould! The warmer the uncured rubber when you use it the less chance of getting air bubbles trapped in the mould.

Mould release agent is a must – don't use it and life gets awkward.

Oh… don't remove the figure ever until you have done both sides of the mould. They never sit properly if you try and put them back. Likewise, small/thin bits like spears can 'spring' out of place and uncured rubber will seep underneath.

Ok guys second half poured now the first half came out very well , I did coat the figure with release agent suppose I will have to wait 4 days before I can see how it came out, this won't be easy I really want to see if it worked so I can make molds of my better sculpts and start casting, it's not easy being patient , :)

Richard

Hi Richard,

Glad to hear how its going. I too based the size of my moulds on Prince August ones. As I'm drop-casting I thought that they would have a good depth of mould to be successful.
Now that you have got your mould together I would like to say that when I started I had to experiment with making vents. I do this as I'm casting because I can then see where the mould is not filling with molten metal. I score a line with a sharp craft knife to the side of the mould and this allows for the gasses to escape. Here is a link to my blog about when I made scorpions. It shows where I needed to make the vents, but generally speaking you will not need as many vents if you are casting soldiers.Hope it helps.

link

Thankyou kropotkin very helpful indeed

Richard