Resin shrinkage

[Bobster]

I am carving a master in basswood. My goal is to make a silicone mould of the basswood master and make a resin cast. Some of the parts will have more intricate fits. Do I need to allow for shrinkage of the resin in the master parts? (i.e. make it oversize some.)

Bobby

 

[exoray]

With decent quality silicone and resin the shrinkage will be very minimal, mot likely nothing you will ever notice...

 

[TheSt.LouisKid]

Depending on what resin you use you have a different percent of shrinkage. Speak to your resin supplier and ask how much their resin shrinks.

Also, a smalland/or flat part may shrink differently that a chunkier part. As we speak I am working on a resin part using a resin with a shrink rate of 3%. A large part of the piece has shrunk more than a plaque part that has to be installed to the side of the large part. The large part was made with an inset for the plaque and now the inset is smaller despite my trying to account for the shrink rate- resin shrinkage isn't an exact science. It means i'll file/sand a bit from the edge of the plaque. On another part I have countersunk holes for screws that I worked out fine for the shrinkrate.

If you need your resin copy to be exactly 8 inches in lenth then yes, you need to make your original pattern larger depending on the resin you use.

 

[xeno]

if all the parts that should fit together get cast in resin, then you probably won't see any difference, but if only one part gets casted then it could cause trouble.

also the silicone can shrink quit a bit, some shrink different if you put to much hardener in it.

small parts will have a smaller percentage of shrink then large parts.

 

[Bobster]

Thank you Flynn, St.LouisKid and Xeno for the great info. You have answered my question.

Best Regards,

Bobby