presstek 34di Reistration Problem. Any ideas?

Every time i go to back up a job when it is a print and tumble it never backs up properly . I dont know if it graphic work or if there is something i can move on my press?... The press is presstek 34di and the paper gets gripped at the short edge . Any suggestions on how i can fix this ? .. Thanx

 

How far off is the registration from front to back?
You have a about 2mm movement at the front lay to adjust for tumble printing. They are the dials on each side of the feed that have +1 to -1 adjustments. This adjusts how far into the grippers the paper is set.
If you registration is off more than 2mm, you will need for the registration to be adjusted to the file before imaging.

 

Adjusting the file is that the graphic people do that? its bout 3 mill . i tried once to move the front lays but that didn't make any difference

 

Yes, the graphic people would need to adjust further movement than 2mm.
If you turn both dials all the way clockwise and print a few sheets...then turn the dials all the way counterclockwise and print a few sheets...
You should see a 2mm difference in the alignment of the sheets. When tumble printing, this gives you a total adjustment area of 4mm.
If the first side was printed too far in either direction, no amount of adjustment on the second side can correct for proper alignment.

 

Yeah i just measure it from the grip edge it 13mm and from teh tail edge it 10 mm before image. See also can u help me with, when i put a color bar on a job on the tail it is never straight mainly the blue is just little bit higher. I dont know if this is down to my packin or pressure but i do have to put my pressure on a bit more or i completely lose the yellow. I measure the packin and its theright thickness .

 

Is the blue skewed from left to right...when it is closer to the edge on one side more than the other?? or is it just the blue is higher than the other colors?
If it is higher than the others, the image length for blue will need to be adjusted via the console...The directions for this are in the Operation Manual for the Operations Stand. I have a few of the manuals in PDF I can send you when I get access to the computer they are located.
Your packing may not be long enough to cover the end of the printed sheet. I use 490mm length packing that completely cover entire image area and beyond.

 

No it is just higher . i will read operation manual tomorrow and try follow the instructions there. The packin is the correct size as well i followed the book. Do you have any suggestions on why the yellow disapears as i bring back the pressure ?

 

Has the yellow always done that or is it a new issue?
When that occurs, stop the press, look at the blanket in that area where the image drops off. Is there ink in that area?
It may be possible that your blanket is crushed. It is easy to tell if you wipe the blanket down wish wash.

 

The blankets not bashed , its only when i stop the press there like 3 sheets in the press and as they come out the yellow gets lighter and by last one out its gone.

 

That is normal, as the press is releasing form rollers from the plate during a stop. The yellow form gets released before the sheet makes it fully through the impression cycle.
Always trash the last few sheets in a run, just as you would the first few start up sheets, as they will normally have some toning and roller marks that appear.

 

it is vital the graphic is in the correct position to start with. When we used this press we would place the graphic slightly into the grip edge then you can trim a little off of the back edge of the sheet until you get it to fit when backing up.