Printing long on one side

D

Deleted member 16349

Guest
It is a strange industry. You have engineers, who know virtually knowing nothing about lithography, designing all the advancements in presses for the last hundred years.

On the other hand, you have experienced press operators, who think they know all about lithography, but have never designed any technology of significance telling everyone that the road to the future is only to keep to the knowledge of the past.

Unfortunately, they can't accept that the knowledge of the past resulted in higher waste and lower capacity. Today, trying to run a printing business with the knowledge of the past would quickly make it go broke.

I would add that there are many different skills needed to solve process problems. No one type can do it all.
 
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discountprinting

Active member
If with running metal plates (polyester plates can and do stretch) the other units all print the same except the Magenta that rules out paper stretch or fan out in the corners. Not 100% sure on your particular press, but most multi color presses have an adjustment on each tower for parallel alignment at the factory and/or installation adjustments...this is in addition to and separate adjustment from cylinder pressures adjustments but it works with it also. The adjustment usually consists of several locking bolts on the frame that ties to the plate cylinder and an adjustment screw on each side of the press (OS/NOS). You have to loosen these locking bolts to adjust and by turning the adjustment screw you either push the cylinder towards the feeder or the delivery on one side of the press or the other. It only takes a very small amount of adjustment to lengthen or shorten the image on one side of the press or the other. After you make the adjustment and re-tighten the bolts you ABSOLUTELY MUST reset you pressure (OS/NOS) as the move will change the pressure as it changes the parallel alignment of plate cylinder to the blanket cylinder. Then test print and adjust again as needed. Consult with you press mechanic and/or service manual for more specifics on this adjustment to your specific press. If the mechanic is not familiar with the adjustment find one that is. Some service manuals don't even refer to these adjustments as they are usually only done at the factory, but depending on wear, press relocations, etc. etc. sometimes this adjustment needs to be done for all units to print perfectly in register. Hope this helps.
 

discountprinting

Active member
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.

The solid print test is a good indicator of the problem I just mentioned in my previous post.
 

Alois Senefelder

Well-known member
Gentlemen,


I can't believe it was seriously suggested that the average USA pressman should start

Tinkering with the mechanics of a multimillion dollar, precision made Heidelberg Press.

Most of us are aware that the people posting on this forum requiring answers, are " Struggling"

just to put ink on paper. If I was the said employer, the problem would be rectified by the

press manufacturer, just think of the downtime and chaos, if this suggestion was allowed.


I await the "Outcry" from this post

Regards, Alois
 
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Ret Heidelberg Instructor

Well-known member
From my past experiences in the field, I met shop owners that wouldn't let their operators adjust rollers much less let them have a go at what discountprinting has suggested. Alois is correct, the manufacturer should correct and stand by the product to resolve the situation. There are various tools that the manufacturers have that can pinpoint the problems much better than a wrench happy operator. Mind you i knew some great press operators that missed there calling and should have been technicians.
 
There are a few different ways to check for print length problems. Alois and Erik are both correct. Remove the blanket and check the plate to blanket cylinder bearer pressures by tapping a thin film of ink on the plate cylinder bearer and put the unit on impression. Thin ink film should transfer evenly to the blanket cylinder bearer. put the blanket back on and be sure to pack to factory specs. Overpacking is a weak crutch and is not needed. Set the back pressure to the thickness of the stock you are running. NO more and No less. Run dry solids on 10+ sheets and check for even pressure across the sheet. Back to impression pressure off .004" and run 10 mores sheets with a dry solid. You should be able to see a slight breakaway. Back of the pressure"004" again. Breakaway should now be very noticeable and even across the sheet. If the breakaway is not even there is an obvious mechanical problem with that unit. All units should be the same and do the same thing (exactly) Remember that the number on the console showing back cylinder pressure is "only a number" Breakaways confirm the accuracy of the number. I also suggest "soft packing" the blankets!!! Putting a .016 packing sheet under a SM102 blanket is foolish!! Try (3) .004 sheets and (1) .003 sheet. Should get to acceptable Heidelberg standards? Blankets should also be tightened with a torque wrench!! If all the above was done and the print length is still off, Check the plate clamps. Especially if the clamp is a "SPEED" clamp. The clamp is adjustable on many presses and an incorrect setting will tight the plate more on 1 side than the other.
 
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Pressmanscooter

Well-known member
Thank you gentleman for the healthy debate that is raging due to my problem. To answer some questions brought up:

Contact test with ink transfer, bearer to bearer was good.
The unit in question has never had any cylinder repair work.
The plate clamps are speed clamps and I will check the bite evenness on those asap.

Since the subject of packing has been brought up, while it may not be related to the longer one side issue, I would like to ask, is there a magic number for blanket over/under bearer? Two different repairman say I should be .002 over plate and .004 over on the blanket. I am currently packed the exact opposite of this, 4 over plate, 2 over blanket. I just looked this up in the operators manual and Heidelberg is saying .0059 above on plate, 2 below on blanket. While there are many possible combinations I have to believe that one will yield optimum sharpness by eliminating any drag from different surface speeds between blanket and impression cylinders.

Thank you all.
 
If the packing behind the blanket is not at factory specifications, the impression pressure setting will not be accurate. If the blanket is over-packed, the impression pressure must be adjusted accordingly. Heidelberg like most manufacturers is looking for a .006"-.008" squeeze between plate and blanket cylinders. If the blanket is over-packed by .002" the impression pressure should also be backed off .002" For example, 10Pt cover stock should have the impression pressure set at .012". Most pressman on modern presses will preset the impression pressure to match the stock being run. What I have seen a lot of Heidelberg shops do is "NOT" pack behind the plate and make up the pressure with blanket packing. This practice will bring the blanket "over bearer". For those looking at the Heidelberg manual, The German word "foil" is referring to a plastic perma-pak sheet behind the plate. The manual says that "foil" should be behind the plate. For those that don't know how to install perma pak behind the plate without wrinkling it, Ask and I will tell.
 

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