Quote:
Originally Posted by dedyplay
The last build is the stuff of legends!
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Thanks! I've got lots of interesting plans for this next one, I'm hoping to speed the development of the carbon parts a bit so I can share something that's of more interest, especially if pondering the minutia of resin shrinkage isn't as fascinating as watching paint dry or grass growing!
Back to the minutia: Like I mentioned I took quite a while to come to terms with this and even did some testing. I made a mold of a steel ruler to see what would happen:
And sure enough, once the ruler "popped" from the mold, it would no longer go back in the mold:
This mold was made under the ideal conditions for low shrinkage, with a relatively slow cure under a tightly controlled 20 deg C temperature. The shrinkage isn't massive, but it also isn't nothing. Over the 12" ruler it's somewhere in the neighborhood of .5mm. Still enough to allow the dimension of the decklid mold to end up with a dimension 1.5mm "off" of the pattern part.
I have not yet tested the shrinkage of the composite carbon/resin matrix when cured, but I suspect it will be very slight (if again nearly undetectable).
With all that, I decided to very slightly increase the size of the pattern part. More on that soon!