Rather suddenly my rollers decided to crap out by not inking the form evenly. I am using photopolymer plates.
The Problem
Form is not being inked evenly. Ink is heaviest at the beginning of the form (the area the form rollers hit first). Based on the image above, it appears that the rollers are not freely rolling across the top of the form, rather pushing/sliding the ink across. The 2nd example is the worst case scenario – many of the bad impressions made the form look as if it were only half inked.
Observations
First, I’ve tried adjusting the roller height and the amount of ink in addition to cleaning all moving parts (nyliners, etc.) – all to no avail. I tried rubber and oil based inks. I even moved the form around on the bed. All with the same result. However, please note that I haven’t tried cleaning the crescent or worm.
I have observed the following behaviors:
[1] The oscillating roller does not appear to move/roll during inking of the smaller form. With the larger form, it rolls inconsistently – it rolls over some areas and slides across others.
[2] I get better results when the oscillating roller is in the up position (ie. not touching the form rollers).
[3] Even with the oscillating roller up, the problem seems to persist with the front form roller.
[4] I get best results when using only the back form roller (ie. without the oscillating roller or the front form roller in use).
On Another Note
Sort of on the same topic but an entirely different issue, when things are working okay, my rollers are not able to ink the entire bed. It does fine on the first 7″-9″ but the form rollers cannot make contact with the form on the rest of the bed. Does this mean my bed is uneven? If so, how do I fix this?
Thanks to Sara who also gave me a very simple and straightforward fix – that WORKED! Yay!
Indeed, my form roller gear wheel had come very loose – so loose that it wasn’t doing much at all really.
I’m still having problems with my inking my entire bed but I’ll tackle that another day since I rarely take advantage of the full bed.
Thanks to all for their invaluable input. I still plan on getting new rollers but it’s not so urgent.
Shrink or swell within the expected life of the roller, and using the right solvents. Typically that is expressed in the manufacturer’s one year warranty against defects. Our main reference is that synthetic rubber rollers do not behave like composition, shrinking and swelling with heat and humidity–thus much more predictable in performance.
Ah ha!
I will try this and hopefully this will fix things in the interim.
I will let y’all know how it goes.
Thanks!!
Setting aside that the simplest explanation is often the best (rollers are outta whack): we had a similar problem with one of the SP-20′s at the University of Iowa. The set screw on the form roller gear wheel had come loose and was not making contact with the roller core–it was inconsistent, but would keep the roller from turning smoothly across the form. The resultant crappy inking looked pretty similar to yours, an inked area followed by a skid.
Tightening the screw helped for a while; we eventually used a slightly longer screw and the gear stayed put.
And when we had the money we replaced the ancient rollers.
Sara
Hi Fritz!
Thanks for your input.
On the NA Graphics site, it says that your rollers are “are made from a soft compound that will not shrink or swell.” Is that true for the lifetime of these rollers or should I still replace them after 2 years?
I will doublecheck diameter although I’m not sure if I will be able to check durometer.
Thanks!
Five years is well past the break point for good work–many printers recover their rollers within the first 2 years. I think all the indicators point to the rollers, and as Paul mentions, both durometer and diameter should be checked. If the rollers are less than 2.500″ in diameter, then they have shrunken and most likely not uniformly, so that’s where the problem is. Cleaning all the parts described is fine but doesn’t relate to the inking problem. Correct diameter of the rollers to work with the oscillating and rider roller is important, and the original tac and softness of the rollers, measured in part by durometer, is required for proper transfer of ink. Also check the front rider roller bearings (in each end of the steel roller are bronze bearings) and these should both be the same diameter–if not, get new ones from us and eliminate that possibility.
Well, it’s inconsistent. There are details I accidentally left out…
I started with rubber based ink and suspected that it was the culprit for the misprinting (it was also printing a little goopy) so I switched to oil based ink. Things seemed to be going smoothly but about 50 impressions later, I was back to square one.
My rollers are about 5 years old. But they seem to be in okay shape. What is the best way to ascertain if it is a problem with swelling/shrinking and durometer?
The ink is just reflex blue – no transparent white. I didn’t put on a heavy coat but I didn’t consider the viscosity.
I’ve tried double-inking but the rollers still won’t hit the tailend of the bed.
You say the rollers suddenly crapped out, but perhaps you’ve just reached a tipping point. You did not state how old your rollers are. The diameter of one core may be shrunken (undersized) and the other swelled (oversized). The durometer or hardness of the rubber increases over time and is also influenced by other factors (solvent, oxidized ink, light
Also it looks as if the viscosity of your ink is too thin. Is there a lot of transparence white in this color? You could add magnesium carbonate to the ink on your mixing plate.
The second image appears to be a fairly large form. You probably need to double ink it in trip mode before making impression.