Wednesday, October 26, 2011

On-press stability and consistency

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5 comments:

  1. Really good post. Finally a display of how variation in density has an influence on dot gain.

    At first, I almost got a heart attack thinking the heart beat plot was density.

    The density variation is maybe natural for a particular press and image combination but it is also something that can be reduced via improved press design.

    Over twenty years ago, I had a computer simulation done on a roller train of an existing press and a concept roller train, to evaluate density variations. It was clear that the level of variations could be brought down with a different roller train design.

    Get the variation down to a low enough level and then it becomes a non issue.

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  2. Hello, We are using the Fujifilm Luxel v8 with the Pro-v brilla hd plates, we are having difficulty getting colour correct with our curves, we are using apogee7 workflow 210 line screen.
    What would the ideal dot gain be, we are measuring our plate at 44% before printing, after printing we are getting a 60%, these measurements are for 50% tint
    We are using a Roland R700

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  3. @Anonymous
    Your dot gain is not unusual.
    But dot gains are not targets. There is no ideal dot gain. Instead tone reproduction curves are targets. I.e. you want a certain tone reproduction in your presswork, therefore whatever dot gain gives you that tone curve on press is the dot gain you want.

    The steps are:
    1) Define a target tone reproduction curve for your presswork.
    2) Image plates with no curve applied.
    3) Run to your standard SIDS.
    4) Measure the dot areas
    5) Build compensation curves for the plate that will bring the presswork to your target
    6) Image plates with those curves
    7) Do a verification press run using those curved plates to confirm that the curves are correct.
    8) Adjust curves as needed

    The assumption is that these press runs are dedicated - i.e. not tacked on to a live job.

    gordo

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  4. You clearly identified that a certain amount of variation occurs but did not explain what causes this variance or whether different processes or presses result in different amounts of variation. Would a Heidelberg Speedmaster52 have more variance than a Speedmaster 102 due to its more complex roller train? What about flexographic printing?

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  5. IMHO, the variation seen is caused by the design of the press and the very tight tolerances that it must operate within (see this post: http://qualityinprint.blogspot.com/2008/12/older-manual-model-like-one-pictured-or.html ). Also, I would speculate that a larger press (like the SM 102) might have the potential for greater variation than a smaller press (like the SM 52) simply because there is a greater area within which variation can occur.

    Flexo is potentially more stable than offset because you eliminate issues related to mixing fountain solution and ink on press. You also eliminate one ink transfer point (plate to blanket).

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