Not sure if this is the correct section, but does anyone have any tips for starting out casting up some items?

I am toying with the idea of making some scenery, making 1-part or 2-part silicone moulds (depending on the piece) and using resin to make copies. I also am not sure about the legality of copying commercial products that are no longer in production or readily available on the second hand market. Can I do this as well? Obviously I do not want to sell them, they'd be for personal use only. I only want to do a few different items and only a few copies of each, so is it even worth the time and money investment?

In terms of advice, I'm thinking:
What viscosity of silicone should I use?
How thick does the mould need to be to rigid enough?
Are there any problems with making moulds from items made with specific materials?
Are mould release agents needed (either for silicone-silicone, or silicone-resin)? If so, will one product work for both, and are there any alternatives that I might already have?
Is a vacuum pump necessary (again for either the silicone or the resin)? Again, any tips for achieving this cheaply?
How much silicone would, say, an objective-sized piece need?

Also, are there other approaches I should consider? What about press moulds, materials like DAS etc?

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Random answer: the mold itself doesn't need to be very thick, if you use plates of some sort to hold it together. I use foamcore cut to fit, and three or four rubber bands.

Tin-cured RTC silicon (the most common type) doesn't seem to have material sensitivity, except for moisture. Platinum-cure supposedly hates sulfur. Just to be safe, I use Kleen-Klay, a sulfur free modelling clay.

You'll need rubber-to-rubber mold release. You can get some at MicroMark, along with aforementioned Kleen Klay.

My preferred silicon iis Smooth-On's Mold Max 10. I like their Smooth-Cast 321 resin.

I don't use a vacuum pump, using the slow-high pour technique, then setting the mold on a running clothes drier to help vibrate out air bubbles.

If you live in a part of the world where they are sold a Smooth-on starter kit is nice. They have two types, the brush on may be more appropriate for larger terrain pieces.

Smooth-on Oomoo silicones and Smooth Caste resins don't need vacuuming.

You probably will never need a vacuum rig. However, a pressure pot is a must if your seeking perfection, especially with the quick setting resins.

There's lots of info on the net, videos etc. that will show you how to do it.

A little tip I could share is, I hold my two part molds together with rubber bands and after I pour the casting resin in I just real quickly 'spread' the halves apart while keeping the rubber bands on. That helps the resin get in all the nooks and crannies. Even if you do that a pressure pot is a good thing to have (you will need an air compressor).

On the whole, I find casting in resin to be very time consuming, expensive, fiddly, and I personally wouldn't recommend it on a whim, or for something that's available.

As to the legality, in my informal opinion, technically it's probably as illegal for you to copy a mini as it is to make copies of a record album. (although I believe the law views the two items differently).
Conversationally, how I interpret the law is: after 20 years a specific design of a sculptured object that is no longer produced has an expired trade mark/copy right and can be reproduced by others.
However, if you attempted to sell said minis, I am pretty confident you would find that not all Courts or lawyers would enjoy such a liberal interpretation of the law.
If you wanted actual legal advice on the matter you probably would need to contact an attorney.

Sorry I should have said, I am based in the UK. Thanks for the answers so far, very informative!

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I am having trouble visualising the "slow high" method, and haven't seen this mentioned elsewhere. Can you elaborate?

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Slow high is how you pour the RTV from your mixing pot to the mould form. ie slowly and from a height, this basicly means the stream of RTV is very thin and bubbles in the RTV from mixing arent able to make it into the mould form as the stream of RTV is thinner than the diameter of the bubble, so they burst.

You can do similar with the resin pouring too.


EDIT: For moulding supplies in the UK try tomps.com I use ACC Silicones MM922 RTV and tomps ownbrand fastcast polyurethane resin (slow version), I find the combination works well and I can get a lot of casts from a mould as the resin seems much less nasty to the RTV, 100 pulls from a mould rather than 25.

I've just started serious moldmaking and casting, and I am using both a vacuum and pressure pot. I wasn't sure about the vacuum, but I found multiple sources saying that if you planned on using a pressure pot, you are better off with the vacuum. The reason being that if there are bubbles within the rubber mold, when you apply the pressure to compress the bubbles in your resin, you compress the bubbles in the rubber mold as well. This can cause strange things to happen to your mold, and deform your cast.

That being said, I think the long and slow method does remove *most* of the bubbles, and I don't know if my vacuum makes *that* much of a difference. I will tell you that there are a metric ton of bubbles created in the liquid rubber when I stir the component parts together. I know this because my vacuum chamber is clear and I see every single air pocket drawn up to the top of the goo - it's pretty crazy.

Bear in mind, the vacuum chamber and pressure pot aren't cheap tools (and resin and RTV aren't cheap either.) You'll need a good vacuum pump, some sort of chamber that can withstand the vacuum, an air compressor capable of putting out at least 40PSI, and a pressure pot capable of withstanding at least double that (you want to be safe.) Also, vacuum chambers and pressure pots are dangerous - vacuum chambers can implode, sending shards flying, and pressure pots are literally bombs waiting to go off. Side story: I bought my pressure pot at Harbor Freight. The cashier asked me if I wanted to buy the extended service plan, in case the pot failed. I declined, stating that if the pot failed, I would likely be dead. Seriously, this stuff can be dangerous if you use the wrong tools for the job.

So, in summation: if you are casting a couple of items, or just learning how to cast, and aren't too worried about flaws (like bubbles) in your final product, don't worry about the vacuum and pressure pot. If you're going to be casting more than a couple of items, want to get serious, and don't want those imperfections in your casts, and think your investment in the tools is worth the return your're going to get with your casts, consider the additional tools.

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Thanks for the clarification about the 'slow high' method. I guess painting a thin layer on will also help to keep any bubbles from coming into contact with the surface.

On materials, I don't imagine I'll be wanting 25+ casts for each mould but I'd rather use a recommendation so I will take a look.

I really don't think I'll be going for vacuum or pressure, I am on the edge whether it's worth the cost as it is and don't really want to explain to the wife why I am playing with dangerous tools just to make a few bits and bobs for what is essentially a casual hobby!

Overall I am a bit more put off doing it with the effort and expense involved than I was before, so will have a think about it, but I do find it difficult to constrain my curiosity and may be tempted to just "have a go". If nothing else it may give me a new appreciation of GW and its competitors' mass production efforts.

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Yeah, it is certainly a "serious" hobby when you push it. I spent the money because I felt that in the long run, it would be worth it. I also plan on doing some resin buildings (see the Terrain forum) and figured the extra expense would diminish over time as the returns increased.

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Bear in mind that you dont 'need' pressure/vac to get good casts, it just makes them easier/more reliable in intricate moulds. As an example, by using a very low viscosity resin (like the one I mentioned earlier) you can achieve basicly perfect casts without extra kit, my latest mould is 23/23 perfect casts (as in actually perfect, not a single surface bubble, though there are undoubtably ones inside) You can achieve that with some disposable cups, coffee stirrers and a set of digital scales if you want.

Domestic Vaseline (or similar) will work just fine as a rubber-rubber mold release if you're looking to save.

*edit: ok misunderstood the question on legality

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I should probably clarify a bit better than my original post, I am mainly thinking about casting my own creations not those of popular wargames hobby manufacturers Not that I don't want to do that too, but whether I do or not is on my own conscience I guess (and I don't imagine I will).

I know Games Workshop in particular gets a lot of stick for being very litigious, but the company has a business model that depends hugely on its intellectual property. They spend a lot on stores which exist to develop the market, so they need a) a unique product and b) control over how it's sold, to provide sufficient margin. Funnily enough in some countries companies are obliged to enforce their IP even where it doesn't make sense, otherwise they lose their entitlement to enforce it later (this being on the basis of "you didn't care then, so you can't say you care now").

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sorry to hijack someone else's thread, but how do you go about making two part moulds? I assume you pour the silicone into a former, then add the component and some pegs to align the other half, allow to dry, coat in a release agent and then add a second layer of silicone to create the other half. is this correct?

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Not how it is generally done, though might work.

The traditional way is to get some plasticine (that doesnt react/inhibit your RTV [check your RTV data sheet]) and roll it out into a sheet. Then pick out an indentation for your master so that it sits with ~half exposed, place the master in and push the plasticine in around it to seal. Also stick some key objects (ball bearings) in the plasticine around the edges to allow the 2 mould halves to allign correctly. Build your mould form walls. Pour RTV. Wait your set time. Remove walls. Remove plasticine, leaving master in the RTV mould half you have just poured. Rebuild you mould form walls, give the RTV a coat of RTV-RTV release agent (vaseline disolved in white spirit if you are cheap) let the release carrier evaporate (the white spirit). Pour RTV. Wait set time. Demould.

Remember that for a 2 part mould you will need somewhere for the resin to enter and air to exit, so factor these sprues/runners/risers into your master.