windmill vacuum timing

Hi,
I’m having some paper pickup problems. It just happened when I was going from one job to another.

Every second sheet is not gripped properly and as a consequence it is delivered too far to the right, gets pinched by the side guide ans does not register properly.

I recorded a slow motion video ans by the looks of things one gripper just catches the paper pretty much exactly when vacuum gets released and it grips it about 4mm deep. The other gripper though does not close fast enough and when vacuum is released the paper moves a few mm forward so it is gripped about 3mm deeper into the sheet. And so it is taken too far and overshoots the side guide.

I was suggested to adjust gripper bite point by extending the mechanism one or a few half turns. Did not help however.

Is it possible to adjust vacuum release point? Perhaps by adjusting it to release a bit later perhaps I could make it hold long enough for the gripper to catch it. But not so long to allow the other (fast) gripper to not yet move with the sheet until vacuum gets released.

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First take a marker and mark the grippers 1 and 2. This way you can see if the same gripper is causing the problem each time. It sounds like you are making the correct adjustment but maybe went the wrong way and opened to much. If you are running with rubber suckers on take them off and retry the adjustment. The grippers also have springs on them. I ran for 3-4 years with broken springs on all the grippers. I finally bought new grippers and it was night and day difference to the closure speed, pressure and feeding control.

Is it worth going back to the previous job that ran ok to see if it will run now? Did you go from lays to no lays and you forgot to change something like the feed standard? Western411 came up with some good ideas, may be even checking the gripper hinges have been lightly lubed.

I switched back to previous job at some point, just to see if it would run OK. It ran flawlessly. Switched to the new one again and got the same problem again.

Yes, my grippers are marked and it’s the same one that’s causing the problem. To make it close sooner you need to extend T 1314 to make the link longer, right? I went as far as 3 full turns and it did not help. Then I just set it back to what it was.

I managed to get around the problem by removing sheet steadiers and only using one spring at the back. Suddenly it was feeding the same accross both grippers and registered flawlessly even if I printed the same sheet 5 times - it was spot on and you could never tell.

I did check those springs and one is broken on the gripper in question. Not sure if just 1 spring can make such a difference but I’m a bit reluctant to have it taken apart to replace it.

So yeah, I can print, but my setup still has this flaw and perhaps at some point it will just not be possible to get around it.

I think GT 1660 is the part that’s releasing vacuum. Unscrewing it and moving it slightly up should delay vacuum release. But for both grippers so I will not go there.

Thanks for your suggestions.

How to tell just Which one is out? probably have to have very extensive backround with this machine, and it’s factory settings. I f you can get the one to adjust to the other, maybe switch your approach and adjust the “Right one” to the “Wrong One” and see if that puts your image in the same spot with consistency between the 2.
Seeing as how your vacuum is good on the other job i doubt it is the problem. it would seem your grippers are not the same.

You mention sheet steadiers and I am wondering what you are talking about. With the back spring since I run to guides I don’t give it a lot of tension, I just want to keep the sheet from sliding back but I don’t want to pinch it against the front lay at the same time. I want to sheet to sit nice have freedom of movement. On heavier stocks I run a wedge shim at the back to raise the back of the sheet. As the front is picked up the back is already elevated and it feed better by cutting the drag effect. Since you switched back to the other job and it ran fine you may be fixing what is not broken. Run a sheet onto the platten with the gripper in question and stop it. Turn off the power and slowing turn the press by hand until you see the sheet drop into the guides. I am wondering if you lay fence in the feed table is all the way out to the left and the sheet is actually being pushed by the lay guides before it is completely released by the gripper. I run my feed pickup left side rail a little in at times to give the stock a chance to free itself from the gripper and drop to the guide. The same is true if the guide is to far in and the sheet has to drop to far. It is a gripper dance of grip, let go , drop to the guide, push the head stop, regrip and print. ( Oh also make sure the head stop is not all the way in - it may pinch or bounce the sheet ) I found with heavy stocks I am also careful with my packing to make sure I don’t over pack. That all I got tonight, my root beer float and Netflicks is calling my name.

P.S. first ericm makes a good point. One thing thing that was never touched on is the condition of the rubber on the grippers. Feed a sheet in and stop it past mid way and test for even gripper strength. If the good gripper feels stronger than the problem one it may also be part of the issue. Since even gripper strength of grab is also a factor of pickup it can cause a sheet to sort slip a little at pickup and slip out more as it slides over the typan and miss register at the guides.

Lastly, you said the one job worked fine and other job did not. Were the two job on different thickness of paper and what works the ticker or the thinner

The two jobs were exactly the same paper, only cut to a slightly different format.

I made a video in slow motion and you can clearly see that with the gripper I was trying to fix the sheet slides forward and is gripped more. It looks like the vacuum releases too early for this gripper and when it’s released the sheet slides forward by about 3mm before the gripper closes. Anyway, here’s the link

https://youtu.be/c9oiTX7EAQ8

It was never a problem before, I have absolutely no idea why it was a problem this time. I’ll start a new job in a day or two and record another video because it now seems to me that this particular problem largely solved itself or something.

But I’m noticing now a slight variation from one gripper to the other, it almost looks like the paper is left too far to the left and it never really reaches my side guide unless it’s pretty much all the way to the left. So I went from gripping it too much and carying it too far so the side guide pinched it to not carying it far enough so the side guide misses it. Or something. The difference with the side guide somewhere in the middle is about 0.25mm.

Will check by manualy turning the press like you suggested when I start my next job in a day or two. To see if I can spot anything.

Will also check if moving side guide all the way to the left makes it register spot on every time and moving it to the right at some point stops registering correctly Which would suggest that paper doesn’t reach it anymore I think.

Will also check rubber but last time I checked it it seemed fine.

Maybe I’m wrong, to me it sounds as the sheet is ripped from the sucker on the right side as you have the sheet separators a tad to far in. The sheet should come up parallel

cool video. Next time you shoot one put a mark on the end of the grippers so we can see it in the video. I can see the grippers seam to pick up differently but I was not sure which one was the issue. You could have a bent gripper bar which would cause the issue you are having. typenut might be correct. I see tripping spring looks look like they don’t flex and the sheet tends to fight to get to the gripper. The tripping spring might be pulling it away and causing it to then re suck to the sucker changing the position. I am not sure how heavy the stock is. On a heavy stock I don’t need the side trip spring, if fact I use very few front trips also. You may also turn every other sucker off and see if that helps. If you are running to guides make sure the front fence is in the center. Since it can be tilted for not running to guide, basically running paper in crooked , that can cause a problem when you return to using guides. From what I saw the guides should bring the sheet back to register even though they pick up a little different. I could not tell what you are doing but I guess the packing on the platten was for foil. Just watch the lip of the packing to make sure the sheet slides over it and watch how much packing is there so the sheet has an even service to slide against as the gripper releases and then the registers. Keep trying let us know how it is going.

I see what looks like shift when the gripper takes the sheet. It is hard to tell if it drag on the sucker bar or not. I can see what you mean about adjusting the sucker release to cure it. I cannot tell for sure if you have rubber suckers feet on or not. If yes, try taking those off. If not try adding them and see if it helps. I found the rubber suckers made it easier to pickup since the are pliable and will compensate for the paper. At the same time rubber suckers may alter your contact point into the grippers and make the problem worse. It was hard to tell how your sucker bar tilt is set but changing it may help. You may try altering that to change the contact point of the sheet pickup to see if it helps. Clean off both the rubber pad which is under the sheet when it feeds and the metal part of the grippers which is on top of the sheet when it feed. The grippers they can develop build up over time form press powder and paper coatings.