13472Re: Jumping image on Flatbed press?
- Apr 29, 2013This all sounds to me like erratic feeding, especially when lateral movement is mentioned.
On a real production cylinder press there is a brush that holds the sheet against into the printing nip. The Vandercook just has a couple ineffective springs (the fact the cylinder reverses direction prevents more positive sheet controls) and so the operator has to hold the sheet against the guide points accurately, and also must hold the sheet against the cylinder in a consistant manner. Any change will affect register.
Another factor is open space on the bed. If the entire bed is filled with plate base ahead of the image, then the sheet will be supported consistantly, but if there is blank area that has lower furniture, then the sheet can sag and the print position will be lengthened and/or shifted sideways. In some jobs the tail can be taped to the topsheet for control. Personally I prefer to use high furniture in blank areas so the sheet can't sag.
Eric Holub, SF
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