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9488Re: platemaking issues

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  • parallel_imp
    Mar 12, 2008
      --- In PPLetterpress@yahoogroups.com, typetom@... wrote:
      > (I'm not clear what you mean by: "Proper use of relief valve will
      > leave no air between glass, neg, and plate, and full vacuum is
      > indicated by appearance of Newton's Rings." I'm not aware of a
      > "relief valve" in my system.

      Tom, the vacuum frames made by NuArc that are designed specifically
      for platemaking (fliptops, 26-1K etc.) have a relief valve or bleed
      valve. You leave it open until the blanket is pulled up to the glass,
      then slowly close it. That slower draw allows all the air to be
      removed without any remaining pockets.
      The NuArc contact frames designed for general contact printing
      (with no integral light source) don't have the relief valve in the
      stock vacuum system, which draws down in a few seconds. I suppose
      that's because only a few layers of film were normally placed in the
      contact unit, while the platemaker might have to support heavier
      contents such as a step-and-repeat board.
      Other than the valve, the frames function identically. It wouldn't
      be hard to add a valve, just cut the hose leading to the frame and
      insert a needle valve the appropriate size. It might simplify your
      process, if I'm right. But cardboard is cheap, and if a system works,
      it works.
      --Eric Holub, SF
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