Hi Paul,
Thank you so much for your help earlier this year with replacing our Vandercook [SP20] trip switch [springs]. I have run into another issue that is raising some questions now and I thought you may be a good person to ask.
Our ink rollers work great some of the time and there are other projects where a line of text will have a varying ink impression from one word or letter to the next. This leads me believe that one side of the roller is not just higher/lower than the other but maybe the middle sections of both ink rollers are not in line — have you experienced this?
Secondly, on a recent project the monogram at the top of an invitation was inking inconsistently. It was appearing smudged or spotty, while the text of the invite was printing great. The monogram has this lettering but it was not some overly large surface area really. We thought it may be an issue with the ink, as it was a color we have never used before (watermelon pink, very bright and light, almost neon), but I also wonder if the ink rollers had something to do with it. We found that if we waited a full minute in between prints (letting the press run and the ink rollers spin ink) the issue resolved itself. I have not run into this before — after looking into it I have the idea that maybe the ink rollers are slurring instead of rolling over the plate or that again maybe our rollers are not aligned. This was happening over a series of days with intermittent heavy rain and we did think maybe the inconsistent moisture in the air maybe would affect the ink, but I still feel that there is a roller issue.
Do you have any tips on testing for these issues? Also, how often do you replace your ink rollers and how do you know that they are ready to be replaced?
Again, thank you so much for all of your help; we really really appreciate it!
Thank you in advance,
The rollers may be undersized. Measure with calipers. For an SP20, the diameter should be 3.0”. They might be flared on the ends compared to the middle. Roller durometer (hardness) is a secondary factor. They get harder over time, exposure to natural and fluorescent light, and harsh solvents. They should be 20 to 25 on the Shore “A” scale. You don’t need a durometer gauge— just see if you can squeeze them.
If the rollers are in spec, the roller height may be set too high, causing them to ink the form on forward carriage travel, but the ink may be wiped from the form on the return to the feed board. Always check the height with a roller setting gauge where the form is located, not at the end of the bed. Replace a worn gauge-especially for polymer plates.
If the roller height is correct, but they’re still wiping the form on the return, the carriage bearings may be out of adjustment. See this recent post: https://vandercookpress.info/sp20-roller-height-changing-as-carriage-travels-end-to-end/
The form roller support brackets may be bent, preventing the bearing block ring on the cores’ end from being seated. Photos of the brackets with the rollers removed would help. NA Graphics sell improved support brackets. http://nagraph.com/
The quoins may be over-tightened, causing the form or base to rise up on one side.
Thin ink can be stiffened with magnesium carbonate.
Cylinder packing may be loose, causing the paper to skip and yield slurs.
Paper fed with the grain running the length of the bed instead of across the bed prevents the paper from fully curving with the impression cylinder. Star wheels and sheet fingers may help. Taping the end of the sheet to the cylinder can help but is not always practical.
Steelpoints placed at the tail of the sheet can prevent slurs but are scarce. (I am investigating having some fabricated). An alternative to Steelpoints is to put clean 5 pica furniture on its side.
I may have left something out because it’s late in the evening, and I’m traveling. I will revisit this post when I return home. As always, anyone with better ideas is welcome to comment.