In this instructable I will show how to make a simple silicone matrix/cavity mould, single piece, the simplest form of matrix mould, it is possible to do multipart matrix moulds but I wont be covering that in this instructable.
I needed to make a silicone mould of a part and I didn't want to use a load of silicone by doing a block mould for such a large part so I thought I would give matrix moulding a go.
there are a few methods for creating a thin silicone mould with a fibreglass jacket, one method is to add a thickener to the silicone paint it on until you think its thick enough then let it set, and build a fibreglass jacket on it. problem with this method is that you can end up with thin spots on silicone mould which would be prone to tearing.
A matrix mould allows a uniform thickness of mould over the whole part you want to cast and it uses significantly less silicone than a block mould so it works out slightly cheaper. the down side is that it requires a little more time for the setup.
This kind of mould is also referred to as a cavity mould as you are creating a cavity between the master (the part you want to mould) and the jacket.
you will need the following materials and equipment, some are optional and are noted as such. and a suitable master to make a mould of, I used a MDF elbow gimble master from my life size ED-209 project
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Condensation Cure Silicone - You could use and mold making silicone but I am using condensation cure Shore 25
Polyester laminating resin - for fibre glassing
Fibreglass Matt - I used 450 gsm its cheaper but you use more resin, you could use 300 gsm matt
Foil Tape - optional
M6 Bolts - 6mm bolts
M6 Penny Washers
M6 Wing Nuts
A thick disposable board
Equipment and consumables
Tongue depressors - for mixing resin
2" GRP Brush - this is a brush that can be used with the fibre glassing resin, normally its a natural fibre brush as they wont melt with the resin.
Paint mixing cups 600ml
Counter top food mixer - Optional, I used it to mix the silicone but you can mix it by hand.
Vacuum Chamber with Pump - Optional, I used this to degas the silicone to help prevent surface bubbles.
Saran wrap / Cling Film / Pallet wrap
WED Clay or Oil Based Modeling clay
Blue PVA Mould Release.
Vaseline / Petroleum Jelly
Silicone mould release
Old clothes / overalls - you don't want to get resin on good clothes
A drill bit the same size as the bolts.
A drill bit the same size as the straws, this happened to be the same size as my bolts so I only needed one.