Image short on press

[djs222]

Guys,

im not looking for a definite answer, just pointing in the right direction.
We have a web press (imer 6 colour) and sometimes when we change a plate during the run (scratch, wear etc) we notice that the image is shorter from the new plate. If we change the whole set of plates then the fit is fine. Im from the plate area and my press knowledge is limited but wont accept the printers response that the ctp (ffei-alinte) is exposing plates around 1mm shorter every now and then. We make spare plates for our other presses and dont experience this fit issue. Like i said, all i would like is a few areas to explore. Every time this happens i would like to be able to measure the plate to confirm plate short or correct....but they always go missing.
Any advice would be gratefully received

[HPC]

If I understand this correctly, the only variable that is changing is the plate(s)? If you have a plate problem and only change one plate, then its out of register, I'd have to say its a plate problem. If all plates from the same plate run register, its in the plates. Only way to stretch or shrink an image on press is to change packing, or blankets.

[Kaoticor]

Are the other plates you make for the other press the exact same size plate as the press that has the problem???

If they are not the same size plate, you could check to see if that size of plate has some variance in the cut or squareness.

[GazKL440]

Rather an interesting problem this one, and I'll be interested to see what the issue is and how it's resolved...

Coming from the pressman's POV, it's very easy with a fairly left field problem such as this to blame pre-press. I mean all the other plates fit so why would a replacement plate not simply bolt up and present identical properties as the one it replaced with regards to print length? However, in my experience with modern CTP's is that plate reproduction is generally spot on with regards to fit/register. Occasionally if the rest of the set have been leaned on a little or stretched to get the corner to corner fit juuuust right, the new plate will also require the same tensioning...

FWIW, we run a lot of long run jobs that are common CMY with multiple black plate changes, and every single time I change a black plate it prints fractionally short for about 200 odd sheets before settling in and coming into a perfect fit. On higher quality jobs generally the couple of hundred run up sheets I use to nail the profile are sufficient to settle the print length, on campaign runs I juggle the circumferential a few thou till it comes in.

Have a chat with your pressmen: be nice, we are usually grumpy before coffee/smoke etc.... Ask if they've changed anything recently?? Especially in the blanket and packing area as changing packing under blankets or plates is really the only mechanical way on a press to alter print length.

For your own peace of mind, run a ruler over a few sets of plates and keep a log, even if you have to use your phone and photograph your measurements to prove your point!!! This way, when a replacement plate is required, a quick and simple measure will prove you correct or incorrect: then you can work out wether to call in some press techs, or CTP techs.

Good luck and let us know how it pans out!!

[Cornishpastythighs]

So if nothing else has changed and the print is now shorter when you install a new plate, maybe and I just say maybe your blankets have compressed enough during the run that when the new plate is installed it prints shorter on one unit. I assume it never prints longer. As for a remedy well changing all the plates at once or maybe doing some research into a different blanket. I know its a longshot but!!!

[kimberfanton]

Simple fact is; plates will stretch on the press especially on long runs!

[mike carlisle]

I have had the same problem of K plate changes and it print short for 200/300 impressions, then it seems to pull into registration. I think the plate is simply settling down on cylinder or the trapped air is farting/burping out. It is possiable the CtP; if made at extream temp changes can expand/contract a bit. However that plate would never fit correctly.

[SHELBY]

Guys,

im not looking for a definite answer, just pointing in the right direction.
We have a web press (imer 6 colour) and sometimes when we change a plate during the run (scratch, wear etc) we notice that the image is shorter from the new plate. If we change the whole set of plates then the fit is fine. Im from the plate area and my press knowledge is limited but wont accept the printers response that the ctp (ffei-alinte) is exposing plates around 1mm shorter every now and then. We make spare plates for our other presses and dont experience this fit issue. Like i said, all i would like is a few areas to explore. Every time this happens i would like to be able to measure the plate to confirm plate short or correct....but they always go missing.
Any advice would be gratefully received

I run a 20 unit goss and if we need to change a plate most times it never fits with the rest, so we output them all and change them all! It may have something to do with the output on the ctp. Although sometimes a one plate change will work but not always.Great thread by the way, I thought it was only us with this problem. Now I cant pick on the prepress guys anymore Damit!