Atmospherie assisted casting

Sometime ago, I thought that everything that has been said about
casting and vacuum casting in particular and that everything
that could be said had been said. I hate to be a bore. I do
occaisionally like to set myself up as flame bait, but you all
seem way too polite. Vacuum is not a force. In fact it is just
nothing. Metal is never sucked into a flask. Not with ordinary
flasks nor with a perforated flask. “What? I hear air being
sucked into the machine!”, you say. While it is true that you
migfht hear rushing air, even the air is not being “sucked”.
What is happening is that weight of a column of air more than
100,000 feet high is pushing the air into the void. This air has
a weight about equal to a column of mercury 29" tall. This is
what the dial numbering 0-30 relates to. As anyone that vacuum
casts knows the full 29" is never achieved in a vacuum caster
during the casting phase, but my experience has been that 26"
seems to be suficient. I have done both centrifugal and vacuum
casting with my best results coming from the vacuum variety.
Justa personal preference. It just seems to me that a little
adjustment in the way that we think about these things will allow
us to better visualize what is happening.

Bruce D. Holmgrain
Maryland’s first JA Certified Master Bench Jeweler