Registration issues

Greetings,

I am new to the site, and also to the printing industry.
This is the issue I’m facing:
The imprints from my two-color offset machine do not match. One is slightly wider than the other, in the direction parallel (not perpendicular) to the plate-cylinder. Does anyone have any ideas as to what might be the issue, and how to fix it? It is a very old machine, I must say.

Thanks in advance!

 

Do you have a picture of the marks, and show the direction of sheet travel. If it's as you say not perpendicular to the plate cylinder, you can fix it it by either adding or removing up to 0.004" from the plate cylinder and placing what you removed to the blanket cylinder and vice versa. If it's going out from side to side, there's is not much you can do but you can mitigate it by making sure the paper you are using is long grain. Good luck.

 

I could send some pictures in Monday, when I go to the printing house.
I’tried to draw something, and I’m sending you the drawing. It represents a paper of B2 format, with enlarged registration marks.
(Some time ago I had a problem with misregistration in the other direction, but this I menaged to solve roughly in the way you described; I put some paper behind the plate that made a wider impression.)

Now, I think it is important to say that I noticed that two things tended to improve this current issue: printing on thicker paper gave smaller misregistration (up to almost no misregistration), as did printing on long grain paper (but to a much lesser degree).

So, I suppose it is side-to-side misregistration. There is really nothing to be done?

 

You could try to switch paper from long grain to short grain

 

No, but I’ve tried both possibilities. Long grain seems to be slighly better, but it’s still not enough.

 

If you have ctp you can adjust size to one plate being smaller buy you are certain that your packing plate/blanket is correct?

 

I do use a ctp technology. I thought of this possibility, but it seemed somewhat outlandish to me. The shrinking factor would have to be different for every job; different paper-weighs would require different prepress solutions. E.g. thicker paper would require a smaller shrinking factor that a less thick paper. But I suppose it is a reasonable possibility. You've heard of people doing this? Prepress compensation for misregistration?

As for the plate/blanket relations, I'm not 100% sure my packings are correct. How could I know that? On the machine it is written that blanket + blanket-packing should be 3.2mm thick. However, it does not say anything about plate + plate-packing thickness.

P.S. Excuse me if at some point I write something unreasonable; I consider myself a beginner in this work.

 

Put paper back to press again to check on which unit the registration is bad, my experience, either your plate or blanket moves, or you need to readjust gripper pressure

 

The first unit gives a wider impression than the second unit. Now, it's hard to say which unit is out of order. I tried everything concerning gripper pressure, but nothing seemed to work. So, that would leave the possibility of loose plate or blanket?

 

Which brand model of press? 3,2 blanket sounds like Roland (1,9 blanket+1,3 packing). Plate i presume is 0,3 so undercut is 0,2.
Usually plate blanket squeeze should be 0,1. So if your blanket is even bearer with then plate should be 0,1 over.

I did use a template of KC/M/Y for coated/uncoated paper at ctp with different sizing. (yes lots of hotfolders hehe)

Also check your impression dial gauge if they match -PU1 and PU2- meaning if they stop at the same indication -eg from 0 to 0,5-.
I think you can check this with impression on and dial at 0, blanket/impression bearer should have a gap of 0,5 check with feeler. (these values with a pinch of salt) But clean bearers THOROUGHLY before attempting.

 

Start from plate clamp bar first, refer to service manual, tighten to correct pressure to see any improvement, what I said before is you only use unit 1 or unit 2, day print 50 sheets, then use that unit again repeat print these 50 sheets, the middle 30 sheets should be dead on spot

here is Komori tech video for your reference, basically, no matter 2 color or 4 color machine, the cause is the same.

 

The problem you have is a level of the direction of the fibers you have to cut the shape of the paper to be printed so that it is in the right direction of printing.
The direction of the fibers of the paper must be correct to eliminate this type of problem
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Look at what you are seeing. Your description suggests an obvious indeed problem. Imagine the sheet being bunch up in the middle before printing on the first unit. As it travels through more grippers, it flattens out. The image will appear wider. It reaches unit 2 which then prints as per the plate. To reinforce this….you say heavy stocks don’t give this issue. Because they are less affected by what ever is causing the buckling. Similar to long grain stock. Get someone to check your in feed. From presenting the sheet flat to gripper settings.

 

If there is a creasing of the paper at the level of the first group it will be clear in the print quality and it will find creasing at the level of the sheet due to the printing pressure which is not the case.
You must check the direction of the fibers of the print medium
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If you read the thread, the gentleman has tried both long and short grain stock and informs that long is slightly better. If the registration is slightly better at the tail of the sheet, then this would reinforce my suggestion. If you don’t understand why, then find a good printer and have him explain.

 

If the sheet is folded before passing to the first group, the print quality of the first group will not be good and the sheet will have creases because of the printing pressure, I have already had this problem quite a few times but it is not the case now with him. (It remains to be confirmed on his part)
The problem is an elongation of the support and it varies from one support to another according to the thickness, something that he cannot control with an adjustment on the machine or at the level of the dressing because the elongation and in the direction parallel with the impression cylinder

 

If this is an older Heidelberg with a ranger drum infeed you will want to consider the compensator. It's a common problem that compensators get worn out when press operators set the compensator off of its zero position to get a job as you describe to register from one unit to another. Forgetting to put the compensator upon completion of the job back to its zero position will over time wear it out to the point of needing service. This is not a job for the average press operator to replace and would suggest a press mechanic thats familiar with the older Heidelberg ranger drum equipped presses. If that turns out to be the problem and you get it repaired you MUST remember to set it back to its zero position when not needed!!!