Smoothing / Correcting RTV Molds

[niart17]

I made a mold of a part for my shuttle built so I can make resin copies using the Alumilite Casting kit you get at Hobby Lobby. Is there anything you can use to fill small pits and or modify the shape of an RTV mold? The mold came out ok, but where there was putty on the original part the rubber stuck and tore just a little bit and left a few very small pits. I know I can sand them out on the resin part so I'm not terribly worried about it, but I thought if I could fix the mold, that would save a lot of sanding later on. Also it would be nice to know for the future if there is a way to add features to modify existing molds. For instance maybe drilling small holes to make raised rivets on the resin parts or adding raised features on the mold to make recesses on the resin etc...

So what's the consensus?

Thanks in advance,

Bill

[BOC262]

You should be making all of your corrections to the pattern (the part the RTV will solidify around to make the mold). All of your effort should be directed toward making the pattern as perfect as possible. If there were some puttied areas on the pattern that caused tear out in the RTV, go back and do whatever you need to do to smooth out the puttied areas on the pattern. Sometimes it is helpful to spray a smooth coat of primer over the pattern prior to making the mold--that way you can see any areas that need fixing and the primer will provide a uniform smooth surface for mold making.

Trying to fix an RTV mold is difficult to impossible--make your corrections to the pattern. Same goes for adding detail--add the detail to the pattern.

HTH!

Karl

Edited November 16, 2012 by BOC262

[bzn20]

Bill

Karl is right,the pattern is the master.If you need to use it again, if something goes wrong with the RTV mold you will have to alter the master or go the nause of changing the RTV mould again.One master many identical molds!RTV is good but hopeless to cut without stretching or shrinkage.it doesnt drill the stuff moves out of the way,goes back to where it was,tears and is just an iregular shaped gash.Even worse wrap itself 'round the drill bit and take a chunk out.