rtv mold

Some secrets to RTV molds for polyester resin are to have considerable height to mold to increase hydraulic pressure, and to use a J-shaped sprue shape to make resin enter mold cavity from bottom.  That way it doesn't fight air trying to escape cavity. Of course, you must have vent tubes from top of mold cavity, at least one at every local highspot.  The real secret of mold design is to think like an air bubble. If you were trapped in the mold cavity and wanted a way to get out, where would you like to see a vent tube?

That's great! Thanks for the info. I'm looking forward to starting work on a master! I can't wait to try this!

if you let the rtv fill in the holes on the master it should work out to make the pockets hallow might have a bit of flash.if you use the resin I said the detail is very great

Let me ask-- What level of detail can be achieved? Would it be possible, for instance, to mold a flat car side sill with stake pockets and not have the stake pockets turn out as solid lumps? I could do a flat sill without pockets and attach them individually, but that would be a royal pain considering how many are on each car.

it turned out great have made 7 c630 bodies for cp rail units. only started casting this year tried many different brands the best I found were rubber mold was by chembar 2 part mixed by weight and the resin was from speciality resin both are found on ebay. found both items produced a great mold and resin casting. with the luck I have had with it not sure why I did not start along time ago.

Interesting! So, how'd it turn out? I'm considering making a mold to cast HO flat cars, as I have need for a great many. Have you ever done anything like that? I've never done any casting at all, so I'd appreciate any pointers.