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DIY moulding techniques


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I'm trying to research sculpting and casting, and was wondering if anyone can help me with the mould making process.

There's two methods I'm interested in, pressure moulding and injection moulding.

It seems that pressure moulding is the most common among hobbyists, since they're generally casting in resin or silicone. I'm just wondering how to achieve the actual pressure, I mean I've seen some made with lego, but that's more of a basic frame.

Injection moulding is more complex, because if I want to cast different plastics I need to heat them at a very precise temperature and create a mechanism that, when heated injects the melted plastic into the mould where it will cool. The ones I've seen are all very big, metal and expensive, so I'm not sure how to go about making my own.

A point in the right direction would be appreciated.

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So the two types are actually very similiar in that they both invovle putting the casting material under pressure.

With pressure molding you put the mold into a container that can withstand the pressure you are casting at (not done it myself, but from what I've read typically 30-50 PSI). You then pressurize the container to the desired pressure and leave it there until the casting material has solidified. The trick is that you have to make sure the mold can handle the pressure. For example RTV silicone by default has enough small airbubbles in it that the pressure can cause the resin to get little pimples all over it. So you have to either put the RTV in a vacuum before you use it until it degasses (expands three or four times its size and then collapses) or you put it under similiar pressure while it cures.

For injection molding, instead of just putting the mold in a container, you put the casting material under pressure as it goes into the mold and keep it under pressure to it solidifies. If you have ever filled a water balloon, the technique is similiar. Once again you have to make sure that your mold can handle the pressure.

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I've been doing more research and am trying to figure the cheapest way to this.

One article I read mentioned melting sulpho-plastic over an even heat and pouring it into the mould, but not a lot of info about how to avoid air bubbles.

While I am trying to get my head around how to actually make a mould (two parts that can be bolted tight together while still being easy to split when the cast has hardened), it is achieving the pressure inside that my DIY brain is having trouble with. Most DIY moulds are clay or something, wrapped or coated in some form of lubricant - but the quality, at least for the silocne products I've seen, always seem subpar (lots of air bubbles).

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The binary liquid rubber molds do quite well, if you can get a hold of said rubber. There are plenty of tutorial videos on how to cast molds using such, and plenty of sites that sell it. What's been irking me is the inability to find any of it locally, considering my town used to be known as "Rubber City".

Here's a good video of mold making:


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That was pretty good (catchy song too). Would this method work with most materials? I'm just thinking about larger objects and such I may want to make using some form of plastic/hard resin or fibreglass. The casting material used here came as a liquid, would materials supplied as granuals, and melted down, work or would a would it be too hot?

I guess I'm mainly confused that the process seems so easy yet there's big, expensive machinery used to achieve the same result (though probably at a higher quality).

Time to go shopping =]

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I'm still a novice at casting molds. It's only been about a year since I decided to try to use Alumilite's mold putty (which I've dubbed purple stuff) to try to replicate existing models as one step along the road to making my own sculpts. It works fairly well on simple models and bases, but doesn't quite work well enough on most objects requiring a two-part mold. They do sell a simple kit for molding, but it only comes with mold mixture to make one or two small molds.

As far as what materials can be cast in which molds, I'm sure some are better than others, while others are an outright no-no. Read those warning labels! So far, the only modeling I've seen that uses the melted granules has been for terrain, but that's not to say that other models can't be made with it.

The casting resin works wonders, in a good mold. Tapping the table the mold is on can help remove air bubbles. An okay mold can be improved by sealing it with rubber cement before use, to prevent any leakage. After it's had a chance to set, just cut along the seam to separate it.

Spin molding is where we really want to head towards, if quantity and quality is our goal. I've seen quite a few good videos on how both Reaper and a DIY setup are nearly the same, except for the price / quality of the equipment.

I'm also looking into the wax-loss method of scupting, as it's supposed to be easier to work the wax into a final sculpt (anything has got to be better than sculpting with Green Stuff) and it dissolves as the mold is made from it.

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How Reaper Miniatures are made:[ame=http://www.youtube.com/watch?v=4hXxMY1JH8w]Part 1[/ame] and [ame=


Compare to [ame=

home set up[/ame] where we also would http://www.youtube.com/watch?NR=1&feature=endscreen&v=70QGqNMPZJw. Definitely farther from where I want to be at this time, but it's certainly something to keep in mind for the future.
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Skip the rollers and go directly towards injection, and this could work well for using pellet based plastics:



Note the part about shredding milk jugs. Talk about recycling / repurposing. I'd love to be able to boast that my line of miniatures was made from 100% recycled materials. That is assuming it gives a consistently good final product.

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