Comments on: 219 Oldstyle Gripper Problem: too tight a grip

By: Fritz Klinke

Fritz Klinke — Fri, 17 Aug 2007 06:13:13 +0000

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.

By: Martha Chiplis

Martha Chiplis — Thu, 16 Aug 2007 17:15:52 +0000

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.

By: Eileen Callahan

Eileen Callahan — Sun, 12 Aug 2007 19:56:40 +0000

Hi Daniel:

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!

Eileen

By: The Arm NYC

The Arm NYC — Sun, 12 Aug 2007 14:09:32 +0000

Eileen,
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.

Daniel Morris
The Arm Letterpress
Brooklyn, NY