Post by only87 on Apr 15, 2007 22:11:27 GMT 1
Basically all the advice has already been written in the various threads. Use the forum search for naphtha.
But I'll give a short here again:
First thing is you need to know is casting with room temperatutre vulcanizing (RTV) silicone and resin. This is essential, there's no way around it. If you know already how it's done it's only a small step to shrink your silicone mold. This is where the naptha comes into the game. When making your RTV mold by mixing the viscid components, just add the naptha to the whole mix. Let the mold cure until the silicone has hardened out, unmold the master model and let the mold sit for a few days. The naphtha will diffuse into the air causing the mold to shrink. The mold will shrink unevenly at first but to the end everything will even out. Now the mold is ready for casting your scaled down model.
Naphtha is raw oil. It is commercially available as lighter fluid or cleaning benzine (cleaner's solvent). I use the Zippo brand lighter fluid, it's a little expensive compared to the other solutions but it doesn't have that penetrative odor of the benzine.
As for the silicone. I use a 1:1 mix that hardens out in under 45 minutes. You shouldn't use a silicone that takes much longer to vulcanize because the naphtha will eventually sink down in the fluid mix causing an unevenness in the shrinkage of the molds. You'd get "banana molds" I got my RTV off Ebay, it's called Hinrisil, another suitable brand I used so far is Silimint.
For the mixing ratio. For shrinking 1/72 models I found a ratio of 1:1 perfect for shrinking them to 1/87. For 1/76 use a little less naphtha. You'll figure out the right ratio very fast, I work by eye estimation, so I can't give you any figures. For bigger models you'll have to do a second shrinking run. I shrunk one 1/43 model so far, I needed four shrinking runs to bring it down to 1/87, still the final model is very clean with crisp detail. But 1/43 is nothing for starters, there's a little more to it, I'd adise you back to the Hydroshrink again for that. At least for the moment.
There aren't any more tips I can give you for the moment, that's basically everything you need to know to get started. If you have any questions, I'm here. But you'll se it's really easy once you got started.
Have fun,
Peter
But I'll give a short here again:
First thing is you need to know is casting with room temperatutre vulcanizing (RTV) silicone and resin. This is essential, there's no way around it. If you know already how it's done it's only a small step to shrink your silicone mold. This is where the naptha comes into the game. When making your RTV mold by mixing the viscid components, just add the naptha to the whole mix. Let the mold cure until the silicone has hardened out, unmold the master model and let the mold sit for a few days. The naphtha will diffuse into the air causing the mold to shrink. The mold will shrink unevenly at first but to the end everything will even out. Now the mold is ready for casting your scaled down model.
Naphtha is raw oil. It is commercially available as lighter fluid or cleaning benzine (cleaner's solvent). I use the Zippo brand lighter fluid, it's a little expensive compared to the other solutions but it doesn't have that penetrative odor of the benzine.
As for the silicone. I use a 1:1 mix that hardens out in under 45 minutes. You shouldn't use a silicone that takes much longer to vulcanize because the naphtha will eventually sink down in the fluid mix causing an unevenness in the shrinkage of the molds. You'd get "banana molds" I got my RTV off Ebay, it's called Hinrisil, another suitable brand I used so far is Silimint.
For the mixing ratio. For shrinking 1/72 models I found a ratio of 1:1 perfect for shrinking them to 1/87. For 1/76 use a little less naphtha. You'll figure out the right ratio very fast, I work by eye estimation, so I can't give you any figures. For bigger models you'll have to do a second shrinking run. I shrunk one 1/43 model so far, I needed four shrinking runs to bring it down to 1/87, still the final model is very clean with crisp detail. But 1/43 is nothing for starters, there's a little more to it, I'd adise you back to the Hydroshrink again for that. At least for the moment.
There aren't any more tips I can give you for the moment, that's basically everything you need to know to get started. If you have any questions, I'm here. But you'll se it's really easy once you got started.
Have fun,
Peter