printlength issues. constantly.

[spigot]

yes i have had some alteration with the packing the plate option. Im leaning towards replacing the perma packing with thicker caliper stuff on the last unit so its plates on plates off still. it will be better but not perfect. i hate the variability, that cant be managed or contolled.
cheers all

 

[Frank R]

If you have some times put all new blankets on and pack them all with the proper packing. Pull break away solids to see if all of four impression cylinders are set correctly. Print the next job and if the last unit still prints long take 2 pts out of the blanket and add two under the plate. Remember to squeeze
The pressure on the BC 2 pts. You really should keep the pressures between all of the nip pts the same.
Make sure you torque the blankets the same. 45 to 50 Lbs

 

[spigot]

ive redone the lot, new blankets, packings, and run a whole lot of screen and solid plates.
With the overpacked last unit, its generally acceptable now, although this depends alot on the stock.
My calculations were like this, please add something if im off here!

blanket undercut 3.2
less blanket 1.95
less calibrated sheets 1.25
= 3.2

plate cyl undercut .5
less plate .27
less permapack .35

=.12 overpacked.

The only thing im not sure of is, is this level of overpacking enough to cause more dot gain?
Im told 0.05 is where you want to be in an ideal situation, but is 0.07 more going to do anything?

 

[pthielen]

Black print long

Black print long

It's the tack.

Most presses run K-C-M-Y. which is where the ink companies formulate their tack. Since you start out with Cyan, see if you can get the tack up.

Here is my suggestion:

Cyan - 15
Magenta-14
Yellow-13
Black-12

It might have to be reformulated at the ink company, but you might spend a lot more time over packing and under packing the press. Also, if you have an open unit, then run that one (preferably the first one) on impression to iron out the sheet.

Regard.
Paul
A.A.S Graphics Technology Dunwoody Industrial Institute
Pressman since 1979

 

[prasadhh]

Have u ever calculated the print length difference between paper and plate...? what is ur blanket + packing thickness? Have u checked ur recommended packings (check with operating manual)? Print length of the job should be calculated with the corresponding plate not with other unit.... If u correct the print length then u will have a correct register...

 

[penwrench]

Don't be afraid to pull that perma pak off and throw it in the trash... clean your plate cylinders. Get yourself some .003,.004 and .005 press pak and go old school. Perma pak is ok, IF you aren't having print length issues. Leave those impression cylinders alone, definitely! Also, slight corrections in print length can be achieved by changing blanket tension. Loosen a blanket slightly to print shorter, snug it down to increase print length.
Good Luck

 

[spigot]

Hi all

Thanks for great replies. Ive made some changes, and am seeing some good results. I have different packings and reducing some inks with preliminary success. Nothings ever going to be perfect though, but im happy if i can just keep it going and its 90% there.

thanks again

 

[vniehaus]

Just skipping through all this I read that you used film. We do to and sometimes our film is stretched. Sometimes we do add packing behind the plate to shorten the image but that's only on our web press and it's just .003. That's all I'll go. Our web press is old and I don't want to mess it up.

 

[Cornishpastythighs]

Here's an oldie but a goodie
Cylinder Packing for Changing Image Length