How to tell if a roller has a flat spot?

About two weeks ago I started getting small faded areas when printing with my Vandercook #4. Even impression, just non-inking. Roller height well-adjusted, everything clean, well-inked, fresh tympan, tried swapping bases, yet it happened with several different plates (I use photopolymer for the most part).

The way that the faded area sometimes shifts vertically on the page and sometime disappears altogether makes me think it’s the rollers. I have a sneaking and sinking suspicion that there is a soft spot on one or both of the rollers (maybe someone rolled over a piece of furniture without telling me?).

One roller is just over a year old, the other is older but until two weeks ago both printed excellently. I’ve taken the rollers off and they look true; I’ve poked and prodded and can’t feel anything different about one spot compared to another. Can anyone tell me if there’s a sure way to determine if the rollers have been damaged? I’d rather not replace either or both if not necessary.

Thanks!

-Shelley

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Shelley -

I’ve had a model 4 myself for 30 years. It’s a great press, but rollers - and roller settings can cause problems.

“The way that the faded area sometimes shifts vertically on the page and sometime disappears altogether makes me think it’s the rollers.”

Me, too. But the question is which roller.

My first questions would be:

1. How large is the faded area?
2. Does the faded area repeat?
3. Is the faded area on the edge of the roller?

If the faded area appears more than once, and if you can measure the distance between the repeats of the faded areas, it will show you the diameter of the roller causing the problem. If the faded area only appears once, it could be because the milling action of the idlers is moving - or re-moving the problem from the forms.

If the faded area is on the edge - and is triangluar - check your roller adjustments on that side. A slipping bushing or some gunk on the gear or gear track could cause the roller to lift slightly and cause the fading. And, don’t be fooled. Even some gunk in the gears can move around to make the high spot move with it.

But always in troubleshooting the first thing to check are those easiest to test.

Lift the idler rollers slightly from the forms while the inking unit is parked and rotating. See if you can spot any problem with the texture of the ink as it mills.

Since a greasy spot - even a single drop of oil - on either of the steel oscillating ink drums is a real possibility - and the easiest thing to check, inpect them - both while they are inked as well as when they are clean.

Although it’s a pretty heavy duty solvent - and to be used only with extreme care on soft rollers - acetone will remove any grease or residue from steel or rubber rollers.

The same problem - a greasy spot - or a damaged area as you suspect - on one of the form or idler rollers is also a possiblity.

Although the second thing in troubleshooting is to reproduce and attempt to control the problem, that would require removing and reversing your form rollers to see if you can make the problem area move laterally.

Before you go to that much trouble, simply remove the inked up forms as a unit and test them for a flat spot. Remove the steel idlers and set that unit aside. The remove the entire inked up form roller carriage from the press and simply roll them over a large sheet of white paper - with no load on them. Roll them first one way, then the other. Check the last 7” of the print - both the left end and the right end - the areas where only one roller inked the paper. If there is a flat spot or a damaged area on either roller, it may be readily apparent in the print you make this way.

There could also be some dirt in the drive gears, forcing one of the rollers out of position as they carriage rolls. Dried ink or gunk could also move from one spot to another, or from the gear track to the round gears as well, so that’s something to check on, too.

If I think of something else, I’ll be back…

Let us know what you find out.

- Alan