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Image Assembly on a Carrier Base

(January 2001) posted on Fri Oct 19, 2001

Coudray points out useful applications for carrier-based positives and tells how to put them together for accurate results in screenmaking.

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By Mark A. Coudray

Another reason for using a carrier base is if you rely on a pin-registration system that uses master carrier sheets. Such systems are based on the premise that smaller elements will be taped to the carrier sheets for precise transfer and registration to screens. This is usually a two-step process, with the carrier sheet being positioned on pins, followed by the screen being positioned onto its own set of registration locator points (either pins or three-point set stops) relative to the film. The carrier sheet, complete with the assembled images and registered accurately to the other carrier sheets in the job, is then transferred to the screen for exposure.


Using carrier sheets


The use of carrier sheets begins with some type of common registration system for the master carrier sheets. Typically, printers use the lay stops of the press or the gripper edge of the press sheet as the registration guides. You will need both a head stop and side guide so that all of the carrier sheets will have at least two common edges to align with.


From this fixed set of coordinates, a master press sheet (sometimes called a dummy) is laid out on conventional paper. The layout should include an allowance for a sheet gripper (if you are using a press with a take-off unit), color bars, and top, bottom, and side trim marks. The press sheet should also be bisected for head-to-tail and side-to-side centerlines.


The amount of time you spend on carrier-sheet layout is determined by how precise the final product needs to be. If it requires a high degree of precision, you need to check each flat for parallel and squareness. Don't assume the layout table is accurate--verify the position of design elements yourself. The few minutes it takes to double check this can prevent a huge amount of grief later.


If you have access to a large-format inkjet printer, you could create the entire dummy electronically and print it to paper. This print then becomes the composited press sheet, with all elements in position. If you are careful in the scaling, the final random elements can be very quickly assembled using the printed sheet as your guide. It is much faster than manually laying out the sheet.



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