From an engineering standpoint, the holes through the sides of mold
frames are of no benefit at all, except perhaps to the manufacturer
of the mold rubber, as we get to make a little more rubber.
I wish to caution you about one of the responses to your question.
If you are using separate sprue formers and buttons, the holes cannot
be used to locate the sprue, as once the sprue former is in the hole,
and particularly if it moves outward, deeper into the frame, you will
be unable to remove the mold from the frame. If you have sprue
formers in which the button and sprue are one piece, so that the
sprue former cannot move deeper into the hole, you will not have a
Hardness, flexibility and shrink cannot be affected by the jeweler's
handling of the vulcanizer.
When we make the rubber, the chemistry is what determines the shrink
and hardness. No man has the strength to place so much pressure on
the rubber that he might affect the hardness or the shrink. Our flex
grade is 35 shore A hardness, and the shrink is 2.3%--period!
If you feel comfortable with the movement of rubber through the
frame, it will generally do no harm. Keep in mind though, that
reducing the pressure within the mold frame, by permitting rubber to
leak through holes, can create non-fill situations.
Zero-D Products, Inc.