"Glenn Ashmore" wrote in message
newsMQkb.80431$sp2.38130@lakeread04...
I see that mistake so often that I just automatically think inches Hg.
Any decent vacuum pump should be able to reach 25 to 28" Hg in a really
well sealed bag but a perfect seal is very hard to get. While
laminating plywood requires as much vacuum as you can get most glass
bagging is done below 15" so pump volume is usually a lot more important
than ultimate pressure.


true. the mercury thing can confuse people. i'm living in SI-land so a
unit like psi is already wierd enough. if you started talking about inches
of mercury here people would start looking up the address and phone number
of the nearest loony-bin. 'twould be like using a unit like a furlong per
fortnight or a slug/acre or something.... just unbelievably arcane and
difficult. ah well. us SI people owe the french for something....

still, every time i see that mistake i laugh because our engineering profs
did have a habit of trying it out on students and if you went for it you
were in BIG trouble.

hugh

p.s. i also always wonder if maybe people are vacuum bagging composites on
venus or half way down the atmosphere of jupiter.