Moulding and Resins

Moulding

Silicon Rubber – temperature vulcanise rubber (sets at room temp)

Leave 10mm space between the object you are casting and the container you are going to build up. And apple for example would be put on the base, supported by a piece of dowel and then you would work out how far around it you need to cut.

The dowel is to elevate the object so that the mould will be of the entire object.

To make the container, use styrene sheet bonded together using dichloromethane or use Lego.

The dowel should be about 10mm tall this way it has elevated the object and is not so long that it will bend.
You can attach the dowel to the object using hot glue gun. This will come off easily and will not damage the apple/object. You could use super glue, however this is sometimes very brittle and will damage the objects surface when you remove it. If using super glue, use activator as well. This will strengthen the bond and help it set quicker

To make a mould, use silicon rubber. It comes as a 2 part product, and needs to be mixed with the ratio of 1:10, for example 100g of silicon and 10g of hardener.
Hardener can be QC or SC, standing for Quick cure and Slow Cure.
Slow cure is sometimes considered better as it gives time for any air bubbles to rise up.

Mix it well so that there is no marbling effect. Remember to scrape the sides and bottom of the tub so that no hardener, or silicon stays there unmixed.
Put in the vacuum-degasser and remove air. The mixture will rise up and the collapse. Make sure to mix silicon in a large enough tub to prevent overflowing.

Pour into the container. Try to pour the mix onto a wall, this will let the mixture run down and fill the mould leaving no air bubbles on the surface of the apple.

Resin

Polyurethane resin – resin and fastener should be mixed in a ration of 1:1 proportions.
Pot life – 5 mins once mixed in a pot before it sets.
De-mould I about 20 – 30 mins. May be best to leave it longer to ensure its set.

To make things hollow, pour in about a 3rd of the resin required (once mixed of course) and then rotate the mould so that it covers all the surfaces of the mould. It should start to pour out of the air holes and pour hole.
Keep rotating for 5 mins. (Rotational moulding)
Through practise of this I have found it is best to rotate the mould for as long as possible, as this will allow the resin to set across the entire inside surface of the object, not just at the bottom.