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Fine Tuning for Fine Details

(December 2012) posted on Tue Dec 18, 2012

Use these pointers to start making the adjustments needed to produce high-quality work.

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Basic alignment of major press components is a consideration that’s often overlooked. That’s unfortunate, because it can have a major impact on your ability print graphics with halftones, fine lines, and small text.

Press alignment
Press-alignment problems cause squeegee pressure to vary along the print stroke. To gauge the severity of your alignment problem, just consider how much adjustment is normally required to go from not printing to a full print. The greater the amount of necessary adjustment, the more sever the problem, and the greater the benefits of correct it.

The issue stems from the press table—the bed or platen—and the mechanism that carries the squeegee assembly being out of parallel in the direct of squeegee travel. In the example shown in Figure 1, the space between the squeegee carriage rails and the press bed is greater at the front than at the back. In this case, the image will begin printing at the read of the press where the space is the least. As pressure increases, the printed area increases toward the front until the entire image appears.

Let’s accept that in the ideal printing situation, you use the minimum amount of squeegee pressure that will produce a print. Consider the setup adjustment for this situation. That ideal, minimum pressure is now occurring at the beginning of the stroke. The pressure increases as the stroke progresses and, to some degree, the squeegee is effectively overpressured at the end of the stroke (Figure 2).

Excessive pressure interferes with fine-detail imaging by inducing smear underneath the stencil, causing fine reverse text or high-percentage dot areas to fill in and blur. The variance in pressure can yield a smear across the print, making it impossible to get equal control of print quality for the entire image. Why is this problem so common? One is mechanical; the other is perceptual, on the part of the printer.

Mechanically speaking, with time and use, machinery moves and settles. It’s sometimes repaired for various reasons, and alignment is not checked after the repairs are made. Sometimes, wear simply takes it toll on the equipment. Perceptually, many printers are stuck on the notion that it’s more important to have the screen parallel to the press table than to have the squeegee-carriage mechanism parallel to the table. Of the three—the table, screen, or squeegee—the screen is the least critical for absolute alignment.


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