How do i make moulds.

[ZR1cliff]

I want to scratch build my own models and make parts to my own dimensions..ime at home with making the part out of wood first as a guide,but then how do i make the mould and where can i buy the white metal to melt down to make the part.
Thanks.

[Nevin]

Making moulds is a pain in the arse and you have to ensure that there are no overhangs etc which will stop it from releasing.

Basically, you make a wood plug, which you then cover in release agent (wax) then several layers of fibre glass. When cured, you will be able to tap this out and will have your fg mould. You then lay up fibreglass and release agent on the inside to make your item and when cured, release an item the same shape as your original wood plug.

However, I have only used this method for boat hulls, made from fibreglass, so you may need a different more heatproof method for white metal castings.

[gopher]

It really depends on the scale, for larger scale stuff then as Nevin suggests is one option, vac forming over a wood\clay master is another.

For smaller stuff you can start by pushing a master(dusted with talc) into the silicon stuff you put around the kitchen and bathroom, let it dry and fill with modelling material (it does work!), for better quality, longer lasting more detailed moulds then Alec Tiranti is your friend - check the casting section, my friend uses this to produce his pewter models.



cheers

Paul

[Nevin]

Also, if you do want to have certain shapes which would not release from a full mould, you can of course do split moulds which you join together, pour your working material in at one end, and then split them in half again when done to release the mould.

[ZR1cliff]

Thats given me some great ideas,thanks chaps.

[gopher]

Nevin said:

Also, if you do want to have certain shapes which would not release from a full mould, you can of course do split moulds which you join together, pour your working material in at one end, and then split them in half again when done to release the mould.

Of course, good point Nevin.

Moulds can be more than one piece - my friend uses 2 and 3 piece moulds. Start with ring of plasticine type stuff into which you push master. Pour over RTV rubber. Once set pull off plasticine stuff and leave master in set rubber and turn over. Pour over more rubber . Once set the mould can be used, parts are removed by simply opening the mould.

It's very good fun but hard to get the hang off, espcially when using a centrifugal casting machine as it is important to get good flow and balance.

Cheers

Paul

[Nevin]

gopher said:

Nevin said: Also, if you do want to have certain shapes which would not release from a full mould, you can of course do split moulds which you join together, pour your working material in at one end, and then split them in half again when done to release the mould. Of course, good point Nevin. Moulds can be more than one piece - my friend uses 2 and 3 piece moulds. Start with ring of plasticine type stuff into which you push master. Pour over RTV rubber. Once set pull off plasticine stuff and leave master in set rubber and turn over. Pour over more rubber . Once set the mould can be used, parts are removed by simply opening the mould. It's very good fun but hard to get the hang off, espcially when using a centrifugal casting machine as it is important to get good flow and balance. Cheers Paul

And expect to waste A LOT of whatever material you are using in the moulds. You will get it wrong many times before you get something you are happy with.