Silicone rubber and resin delivered from http://www.topmark.co.nz/ in Auckland. May as well knock out a tutorial about what to do with it then.
The rubber is a 2 part mix with a 10:1 ratio between parts A (the big white one) and B (the blue one). I could give you a detailed discussion on catalysis etc but I can't be stuffed, so just accept that its fine as long as you don't stuff up the ratio.
To prepare your masters for casting, you will have to attach them to a piece of plasticard.
On the left is the Lc top, and on the right is the casting for the headstocks, handbrake and brake cylinder. Build a plastic box around then to contain the rubber, (note that the Lc top will be a 2 part mould so there should be a 1cm gap arround the master so that the mould will be strong enough for casting). Finally, you will need to cover the masters with a thin coat of oil. This is to help release the master after the Silicone has cured. I've had problems extracting masters after forgetting this step. However take care as some oils may prevent the rubber from curing next to the master surface. I've used Vaseline before, and today's is using a lubricating oil. I'll report back if it goes wrong.
This is what the Rubber looks like during the mixing process. to work out how much you need you will have to calculate the volume of your mould box in cubic centimetres, which will give you the mass of rubber that you will have to mix up. mine came out at 50g. use a set of kitchen scales to weight everything out. Don't get the rubber components on anything as its a bastard to clean off. Stirr it until the colour is uniform. At this point you should degas the rubber to get rid of trapped air bubbles which can lead to imperfections in your mould. Unfortunately, I've got plenty of hot air but no vacuum. We'll just have to solve this another way in a later step.
The sharp end. I pour in a small amount of rubber into the mould, and then use an old paintbrush ( it will be useless for anything else after this) to give the master a good coat. The plan is to have a layer of rubber over the master and no air bubbles next to the surface. After you have done this then pour the rest of the rubber into the mould boxes.
The final step is to remove any trapped air bubbles. Do this by gently tapping the mould on a hard surface for 10 minutes. I have also used an electric razor to vibrate the mould as well.
Now just put aside to cure overnight somewhere warm.
Update: the moulds were cured after about 4 hrs, and the oil does not affect the curing of the rubber. the 10 minutes spent getting all the air out seems to have worked, there are no large visible flaws in the mould surface.
5 comments:
This is a very forgiving moulding silicon, but don't take anything for granted!
I haven't used a lubricant as yet, the silicon has an almost greasy surface, and as long as you let it dry at room temp, and don't leave it in the mould for too long, you should be ok.
Bang the mould as you pour, this I have found is enough to disperse the air bubbles
I'm wanting to know if it comes in something other than blue.....mauve, perchance??
I don't think i could pour and bang the mould at the same time. It was challenging enough to take a picture while pouring.
And a mould is a mould. The colour is irrelevent. I've still got green ones, and a red one somewhere.
What! only one pair of hands!
Put your camera on a tripod and timer or better still use a video cam, then we'll get sound effects as well! :-)
Ha, real men don't need tripods. They look like an expensive toy that always breaks (well, according to darryl)
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