Frustrating as it is, I need to make 2 copies of a small part:

I have some of these parts still on sprue too.

I have tried making a mould in milliput but it just broke apart on demould and stuck to the part even after leaving it for a day (requiring tedious cleaning afterwards). Then I tried making a mould in Polymorph, which I think worked fine but the milliput I used for the actual part also stuck to the mould. I am fairly sure I've had some success with this polymorph+milliput combination in the past (not the best detail but it worked at least), but now I have doubts milliput will ever work with the very thin barrel on these parts.

Is my milliput just gone bad? It seems to stay slightly flexible even after 24 hours, and goes a bit flaky which means it sticks to other surfaces and pulls apart easily. I threw out some air-drying clay (DAS) that had clearly gone bad, is the same true of the milliput? The one I have is the grey & green sticks, it has been kept airtight but the green stick has gone brown on the surface.

Is green stuff any better? Would liquid green stuff work? Any other alternative materials & methods anyone would suggest? So far I am hoping to avoid cracking out the silicone and resin as it's really messy, needs gloves etc and is generally not nice with kids around - especially resin. Presumably resin also has a shelf life too.

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I've had reasonable success with a GS-Milliput mix, about 70-30 GS-MP ratio, also I'll recommend gedeo siligum (available from hobbycraft stores) for mould making, I use it for all my casting purposes and it's ace, it also works with resin and metal up to 300 celsius, unlike that junk oyumaru....

I'd suggest a very light brush with baby oil as a mould release might help

you can also try GS with different mix ratios, apparently using less yellow (the hardener) makes it softer to work, yet it cures harder, I'd recommend letting GS cure for at least a week as it gets harder and harder over time, also a little flex is handy at 6mm scale

hope this helps!

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Great thanks. So do you think my milliput is knackered?

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Milliput is Great stuff, but not for casting in (o:

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Oh and for siligum, do you mean to make a mould with siligum and then press GS+milliput in? I've found my silicone moulds not so good for this because they are too flexible, i.e. you can't push the putty into the detail without deforming the shape. But then, the moulds I was trying were much larger.

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Yes I mean make the mould with siligum, then press the GS/milliput in, I find putting it in a bit at a time and working it into the detail with a cocktail stick or similar, then adding more and more generally works quite well, try to keep the GS flush with the mould (ie. don't overfill) repeat with the other half of the mould, then push together, helps if the mould is flat on both sides, then you can stick a plate on top and lean on it to squeeze the excess out (a few strategically placed vents can help here)

the siligum is pretty stiff, also the milliput/GS mix should be quite soft so you don't need vast amouts of force in my experience, make sure you've rolled it in your hands and it's warm, it makes a big difference

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So what do you use instead?

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OK great thanks, might take a look at siligum then.

Went to buy some green stuff, and am discovering the vast array of different modelling putties...

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don't forget to add keyways to the mould so both halves line up!! I generally poke the round end of a paintbrush into one half, then push the other on top so the two halves are keyed to each other

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Yeah with a traditional silicone 2 part mould I generally set the master in plasticine, poke some holes in the plasticine around it and pour over the silicone. Seems even easier with siligum.

Though not sure how well a 2 part mould is going to work with this piece - the barrel is detailed on all sides but only about 1.5mm thick.

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you may need to form the siligum around it with the round end of a paintbrush, alternatively cast it point down (eg. push the barrel into the putty....)

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It's getting it out again that I'm anticipating problems with, certainly barrel down. Just have to cut it out very carefully I expect.

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brush it with baby oil before pushing it in and it should slide out of the mould easily enough.... cutting the mould will mean more chance of deforming when you put the GS in....

I should add, whenever I use siligum, I always brush the part being moulded with either baby oil or vaseline mixed with white spirit to act as a release agent

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I mean getting the cast part out. With milliput it just breaks apart when pulling the two halves of the mould apart, leaving it stuck in the mould. With the barrel buried lengthways there'd be basically zero chance of getting it out without cutting the mould. With green stuff I'm not sure how it will be, but if it's softer than milliput then I would still expect problems.

OK ta. And what about the mould itself before pushing in the GS/milliput?

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seriously a little brush with some kind of lubricant and you'll be fine, GS doesn't stick to siligum anyway, I've cast a LOT of stuff (like dethkopta rotors to replace lost ones) and never had any issues, just give it at least 12 hours, preferably 24, to cure before pulling it out, I find making several moulds helps if you need to reproduce a part many times

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