I’m having some issues with a print I’m working on today. It’s a long form (photopolymer) – approx 17” – that I’m running vertically.
I’m using photopolymer on a solid wood base that’s shimmed with chipboard up to type high. Printing on Lettra 110 with black ink. The initial couple of lines are very heavy, inkwise as well as impression, but then within an inch or two the ink becomes more consistent, although not dark enough. I tried rotating the plate and running it horizontal, but I just got very hard impression and overinking on the leading edges as well as the opposite edge of the type. I’ve adjusted my rollers to type high as well. I have a rider roller for the press, but I’ve never used it and am not sure how to attach it, in case that might help the situation.
Fritz posted on Briar Press that it’s an oscillator for a platen press, although he didn’t know which. It came with my SP20, which is odd.
I’m not certain this is a Vandercook part.
Here’s a photo of what I was assuming was an extra rider roller for the SP-20. I have no idea how to attach it, so maybe it isn’t.
Jonathan also posted on briar press (http://www.briarpress.org/36343) where Fritz Klinke, John Henry, Daniel Morris and I responded.
There, Jonathan said that his wood base is MDF. This, in addition to the chipboard, is the mostly likely source of the problem. It’s taken for granted by many letterpress printers that the dimensional stability of MDF is good enough, but this is not the case when printing photopolymer type. According to ANSI the tolerance for all thicknesses of MDF is +/-.005″. which is significant.(Source: http://www.flakeboard.com/specs/ANSI%20A208.2-2002%20MDF.pdf page 7)
Also, if the extra rider is identical to the one in use, it may just be a spare part.