Heidelberg gripper issue
Running a job today on Lettra 220. At first the press starts out printing fine, but after 10 or 20 sheets, it starts misprinting every other sheet. The misprinted sheet isn’t aligned correctly (so it’s not just a pure bounce) and has a mark from the side guide. I took a pencil and marked where each gripped picked up the sheet and it seems to be about 1/2 pica off between the two. One gripper is taking the sheet in an extra 1/2 pica. (It’s also taking it at an angle, which I assume is standard, so the 1/2 pica difference is at the bottom of the sheet.) Doesn’t seem like much but it’s causing hell with my job.
What do I need to adjust? Is it the angle of the gripper? Neither looks bent. I really only seem to have trouble running the heavy stocks (Lettra 220 or Savoy 236). I ran thousands of Strathmore Labels the other day and had no bounce or misalignment issues.
Help, please! I need to get this job printed today.
are you using gauges?? sounds like the pile height might be too high, run some stock thru without impression and see if it is hitting the gripper and going crooked, it could be a couple of different things, the joy of running a press!!
On one of our windmills we used to see lots of register issues depending on when the gripper releases the paper and the thickness of the paper. Duplexed stocks around 280#C and 220#C Lettra in particular were a nightmare.
We’ve found the issue to be a matter of when the gripper releases the paper, or basically how tight a grip it has on the paper when it hits the guides.
If the gripper has too tight of a grip, meaning not fully released, on a thick sheet the paper will contact the side guide and rather than gently moving into place, will load against the side guide and kind of pop up and out when the gripper finally loses grip. We’ll get some weird side to side register as well as up and down movement on the left side of the sheet (the delivery side guide) giving it an inconsistently angled print.
My guess is that we run way heavier stocks than these machines were designed or setup around. Lettra 220#C is in particular, a very thick stock physically as it’s uncalendared.
Our fix has been to adjust the length of the arm that actuates the gripper slightly so the gripper opens a bit earlier. If I remember correctly we shortened the length. This really helped with thicker stock like 220#C lettra. Be aware, and be careful with the adjustment as it’s a balance between too loose/early, and too tight/late. Adjust too early/loose and you’ll see thinner sheets like text weight register poorly as the grippers release too early to bring the sheet to fully contact the side guide.
As we run mostly heavy cover stock, our grippers are adjusted a bit loose. When we need to run a thin text weight stock if we have an issue with the grippers releasing before the sheet hits the side guide, we’ll add a few electrical tape layers to the gripper to get a better hold on the sheet.
Hopefully that makes sense and helps you. We wrestled with the issue for months before we figured this out as a fix. Good luck!
After some helpful emails and tinkering around for over an hour, I finally figured it out and fixed the issue. The parallel paper margin adjuster was angled out beyond parallel. I don’t know why, and I’m sure I’ve never adjusted it in the 6+ years I’ve had the press. I set it back to parallel, thinking it would keep the gripper from picking up too much of the paper and that did it. This is also probably why I’ve had a lot of paper bounce issues over the past couple years, particularly with the heavier stocks. I’m sure something will go wrong next month!
I’ve never had an issue with running thick paper. It’s usually something holding it back.