Printing long on one side

P

Pressmanscooter

Well-known member
I have a '92 CD 102 with new gripper pads that prints really nice except that the magenta unit prints long on the gear side. On the operator side, it prints with the rest of my process. If I register everything on the center marks (front to back) my red prints 1 line before other colors at the lead and 1 line after at tail. Had a mechanic in and the only thing we could find was that the blanket to impression squeeze was a little weak on the operator side. Corrected that, but made no difference. With new pads and no slur we eliminated sheet slipping out of the grippers as a possibility. Any thoughts or suggestions greatly appreciated. Thanks in advance.

Scooter
 
Too much squeeze can increase the print length. Maybe on your press you have too much squeeze on the gear side. Even if the squeeze looks right on the gear side, maybe try reducing it to see what happens.

I wrote a TAGA paper in 1997 related to this kind of issue which was primarily an analysis of a web press but some of the same analysis can be applied to sheetfed.

Just a thought. Hope you find the solution.
 
Check your plate packing if there is any and also check blanket packing with a packing guage. Do you have any problem in dampening system in problematic unit or the unit before the magenta.
There may be other issues too but as you said your grippers are good.
 
If this happens after changed new gripper pads. I suggest checking height between gripper pads and surface of impression cylinder in both sides OS and DS. If that height in OS is too much different compared to in DS, it could cause this problem.
Hope this helps!
Delta E
 
Pressmanscooter said:
The gear side printed long since I've been running it. The increased sharpness form the new pads is making it more noticeable.
Click to expand...

Maybe you have a mechanical problem in that unit. This reminds me of a some what similar issue I had with a web press in about 1985.

The operators set the impression squeeze by using feeler gauges by placing the gauges in the nip and putting the unit impression on. They would set the operator side and the gear side to the same values. Even if they did this correctly, it still indicated that there was too much squeeze on the gear side.

What seemed to happen is that by just putting the unit impression on, when the press was not running, did not fully move the impression cylinder into the proper position on the gear side. It was assumed that the gear engagement itself was preventing the full movement to happen. The final positioning of the impression cylinder would take place when the press actually ran, resulting in the higher squeeze.

This was a specific issue with the design of that press, which was a Chambon press. Anyhow, I designed a special gauge to measure the impression cylinder to bearer height at the point of nip contact and with that it was possible to set the press to get an even running squeeze on both the operator side and the gear side. I was happy to see that the operators continue to use that gauge for years after that time.

I don't know your press design in any detail, but maybe you have a similar problem in just that one unit. Your squeeze measurement when the press is not running might not be what it actually is when the press runs.

Hope this gives you some ideas.
 
You could also try another thing but it may or may not be the issue. Make sure the blanket is square and not cut on a bias. Run a test and then turn the blanket around and check the result. Other than that you could have all the cylinders (plate, blanket and impression cylinders) in that unit dialed in and measured with a gauge. The CD has a double impression cylinder. Check the fit from consecutive sheets and see if the problem is consistent. These are just some suggestions and I am sure there are other things that can be tried such as Break Away solids to check for cylinder damage. Start with correct printing pressure on a solid and then start backing off the pressure gradually to see if there are any low spots.
 
Quick Bearer to Bearer Impression Check.


1) ALL the plate/blanket cylinder bearers (G.S/W.S.) must be clean and dry.

2) On the Plate Cyl. -- place 3 DABS of ink (Cyan) the 1st dab 25mm in from the Lead Edge of the plate

2nd about halfway round, 3rd at the leave edge of the plate cyl.

3) Important that these "Dabs" be thinly rubbed down with your finger.

4) Next with the Cylinders on impression, rotate the press 3/6 revolutions.

5) Off impression, are the INK DABS evenly transferred ????


Regards, Alois
 
Alois Senefelder said:
Gentlemen,

Printing Press Cylinder Pre- Load Setting, Erilk's method is not the Correct Way.


Regards, Alois
Click to expand...

You make an assumption about a press and printing conditions you surely are not knowledgeable about. My method using a specially designed gauge provided the very qualified press crews with a way to set the impression squeeze to within a thou (0.001").

The press in question had impression cylinders that were not the same diameter as the blanket cylinder and the impression cylinders were free wheeling. They were not driven.

The impression cylinder to bearer height had a mechanical adjustment on both the gear side and the operator side.

Also, we were running thick coated board in this press for packaging material and when the web is not in the press, there was no contact between the blanket and the impression cylinder with the impression on.

Maybe you are really smart and have a better way. I don't think globs of ink would be one of them for the press I was talking about.
 
Last edited by a moderator:
Dabs of INK # 3029.jpg Dabs of INK # 1027.jpg Dabs of INK # 2028.jpg Gentlemen,

My Assumption - I say knowledge

Dabs of Ink ............ my reply



Regards, Alois
 
Alois Senefelder said:
Gentlemen,

My Assumption - I say knowledge

Dabs of Ink ............ my reply



Regards, Alois
Click to expand...

The discussion I was talking about was regarding setting the squeeze of the blanket to substrate on the impression cylinder. You seem to be talking about the contact of the bearers. Different thing as you should know. Your dab of ink test does nothing to lead to setting the squeeze of the blanket in the impression nip. I think you are confused and I don't really want to discuss things with someone who is so confused.

Maybe your imaginary name also means imaginary knowledge and imaginary experience of the kind that can not actually solve problems that are not addressed in a PDF or some very old manuals.
 
Stupid question, have you had any cylinder work done on that print unit in the past. Maybe some damage happened and one of the cylinders had to be built up. Try putting a dial guage on the operator side and the gearside bare cylinders and also the bearers and check the runout.
 
Last edited:
Stochastically speaking, should the dots be round or elliptical? Sorry I couldn't resist. I think it is time for me to go and find a paper stretcher and some color bars. Those who apprenticed in the good old days, and were had by their mentors will appreciate this.:D
 
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