The 219 OS I’ve been using has developed a terrible problem, which started about 6 months ago, and nothing I do seems to help. The grippers raise fine, but when depressed into the paper to HOLD the paper,the grippers clamp down very hard, MUCH harder than is needed to just hold the paper in position – and the pressure of this then creates a mark on the paper under each gripper. The mark most resembles a series of angled parallel lines indented into the paper at the exact position of each gripper. I’ve never seen this before. The problem does NOT come and go, but seems to be steady-state.
I tried to find some adjustment for the tension of the grippers’ “chomp down hold” on the paper, but couldn’t find anything that would ease off the tension of the gripper when released to come down on the paper to hold it in place.
I removed all the packing, put on new tympan paper, cleaned the bar, unloosened the screws at the top of the gripper bar on the backside (internal press) of the bar itself (which seemed NOT a good thing to do â€” those screws want to be kept tight) BUT NOTHING worked.
Any ideas? (Tried to take picture, but the indentations don’t show up on the paper.)
There should be only the top tympan sheet, be it the paper or Mylar, that is held in place by the gripper bar. A second sheet can be placed there as well if it is used under the tympan makeready to keep that sheet from moving. The tympan should have a sharp crease on the edge where it bends into the gripper bar–no rolled or curved edge, and the best crease you can do with Mylar. Sometimes there is some play in the positioning of the gripper bar, and it should be even with the leading edge of the tympan. It could be that Letra, at something like .021/.022″ thick is more than the design built into the grippers of the press that was designed for proofing paper at the .003/.005″ thick range. But in terms of spring strength, I would think .015″ or so variation in paper thickness would be negligible in terms of spring strength. My hunch is the tympan to gripper bar relationship is where the problem is.
I hope you figured out your problem by now.
I print on a 219AB, which I realize is different from your press. I have had to take the ‘tympan clamp bar assembly’ off to oil it and work the moving parts back and forth before putting it back on because of a severe stiffness such as you describe. The other thing I did was tape a little piece of Japanese paper to the problem gripper to soften the mark.
This is a teaching press, so sometimes things happen without my knowing. The grippers mark the papers exceptionally using a thicker paper, to be sure, but we have used fine papers before with no problem.
So to trouble shoot, I did try to take everything out and build it back up to a neutral position, as it should be “by the book.”
BUT not sure what I did is built up to the depth of the cylindar undercut. Will check that.)
We DO do the make-ready for each specific sheet on the top of the mylar. Could that be affecting this?
And, in desperation, as I wrote before,
I did loosen the six screws that sit in the bar directly over the spring/latch mechanism on the backside of the grippers proper that engage the spring to move the grippers up and down. This had some effect on the marks, but one or two would remain. And those screws obviously should NOT be unloosened, so THAT’s not it.
I’ll report back when I have re-checked the packing.
Thanks a lot!
This could be caused by a number of things so the easiest way to pinpoint the culprit is to think about what changes you made (if any) when you started to notice the problem. I read that you have changed the packing. When you replaced it did you build it back up to the depth of the cylinder undercut as marked on the cylinder? If the cylinder is over-packed then this will cause the sheet’s approach to the gripper bar to be akward and that can cause the marks you are describing.
Did you change to a different paper? If you are using Lettra and had previously been using a stock with properties more similar to the proofing stock the press was set up for then you could be noticing this while there has been no mechanical change in the press.
A thing to remember — the grippers are actually mechanically opened, but the mechanism is at rest when they are closed. So the likelihood that the problem is mechanical and has occured on all of the grippers seems, to me, quite unlikely.
If you can eliminate the possiblity that the issue is related to packing then we can look at what can be done to take some pressure off those grippers.
The Arm Letterpress