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Making the Most of Pin Registration

(May 2003) posted on Tue Jun 03, 2003

Discover how to refine each step of the prepress workflow so you can realize the benefits of pin registration.

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By Mark A. Coudray

Progressing from the imaged film to a carrier base is typically the next step. Regular film is usually 0.004 in. thick, compared to the carrier base, which is 0.007 in. thick and more stable than conventional film. The carrier base is much less sensitive to changes in size caused by heat and pressure, both of which are quite common during screen exposure. Most carrier bases come prepunched to correspond with the pin-registration system you are using, which is helpful if you don't own a film punch.


In the ongoing quest to save money, you may be inclined to strip images off the carrier sheets and use the carrier sheets over and over. But remember that each time you mount the carrier on the pin bar, you slightly enlarge the punched holes. While the enlargement isn't too much of a problem at the top of the sheet, where the pins are, it is at the bottom because very small errors magnified over a distance create what is known as a <I>radial error</I>.


Picture a slice of pie. The error at the pointed end of the pie is minimal. However, by the time you get out to the edge, there is a huge transmitted error on either side of the fixed point. This flex means that you will see all kinds of variation at the tail end of the sheet.


Trapped air under the carrier is another common source of image-placement errors. To reduce the potential for trapped air, position the film on the pins and then carefully squeeze the air out, moving from the pins to the tail end of the sheet. A good tool for this is a 1-in. diameter hardwood round dowel, available at a hardware store. Wrap the dowel in several layers of cheesecloth to prevent damage to the carrier base or the film. After you force the air out, place a small strip of tape at the tail end of the carrier to keep it from moving.


Image application


Now is the time to apply the imaged film to the carrier. Those thin registration marks come in handy here.



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