FDanB@aol.com
Date: 02/08/03-09:45:26 AM Z
Judy said in her message...
>Then, I generally put a gallon jug or two of water on the top -- which
>takes all of two seconds... contact is excellent. And quiet.
First off, I don't question for a moment that Judy and others have had
great results getting good negative/paper contact with the glass-sandwich
type frame. If your printing paper is fairly immune from curl after
coating, you might get by just fine with a glass-sandwich frame. My
personal experience is different.
Ten years ago when I started making 12x18 platinums, I constructed one of
those glass honkers, feeling confident that such a heavy sheet of glass
could tame any marriage of paper and negative. Boy was I wrong!
Do the math on the water jug example: water is approx 8 lb/gal so with
two jugs you have 16 lbs. If your glass is really beefy, it might weigh
10 lbs. Now you have a total of 26 lbs. or 416 ounces of glass and jugs.
Now say you're using 16x20 glass for your frame, which makes a total of
320 square inches (though if you've designed your glass frame with enough
space for two gallon jugs, you probably have much more than that in
surface area).
Assuming the conservative 16x20 size, you do the math (dividing 416 oz.
by 320 in-sq and you find that you are really only getting 1.3 ounces per
square inch. That's nothing when it comes to flattening wavy paper
products. Of course with larger frames your weight per inch goes down
even further.
A vacuum frame creates 14.7 POUNDS of force per square inch. There aren't
many materials that can argue with that (in fact, you'd have to pile
nearly 600 gallon jugs on the glass to equal that figure).
Vacuum frames can be had very cheaply on the used market. The pumps are
noisy but the noise can be reduced by placing the pump in an adjacent
room (the frame, after all, is silent) or by insulating the pump from the
floor with vibration reducing material, like carpet padding. Much of the
noise is caused by the pump's vibration feeding into floors or cabinets,
acting much like a not-so-sub woofer.
You could try the two sheets of glass method first to see if it works for
your process. If it doesn't (and you don't want to buy new or build
yourself) check the "printing supplies" section of the yellow pages and
start asking about used vacuum frames.
Just don't ask me why on this beautiful praying-for-snow-in-Texas morning
I'm doing math about gallon jugs and vacuum!
Hope this helps,
Dan
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