Windmill Horizontal Bouncing

Is Your Packing and Tympan drawn tight and without little high spots or crooked, holding the stock off occasionally/intermittently,?

Are your grippers level? You can remove all your packing and look at how they sit over the platen. You should be able to slide a 6pt spacer underneath them, I believe.

Mine are old and little out of whack so I was struggling with registration like you describe. The gripper was sitting too close to the platen and it wouldn’t let go of the paper like it should..and sometimes the paper would pop out at the last minute, bouncing like you described.

Have you checked the front stand of the feed pile to make sure it hasn’t moved?

Sorry duplication

Sorry duplication

Thank you for your input, really appreciate that!

Dear @mick Tympan is really tight and even, I have changed it and even tried to add little printing powder on the top. That not helps.

Dear @AnnieW I checked grippers, they seems are even too far from the platen. How did you aligned them to place in proper distance? Just by bending? I have changed grippers, took pair of them from the press which has perfect registration, but that does not helped.

Dear @frank how front stand of the feed pile possible to be migrated? No it was not moved, and I would be happy to move it forward, but there are no space for such adjustment.

Thank you
Viktorija

Does it do it with all types of paper? Try using more gripper tilt, that will move the sheet back. You already have the side guide all the way out? Has the press run backward at all? (like when you come to a stop…that can throw the timing off.)

Make sure your your head guide is not all the way forward as the sheet can be forced into it causing a bounce back. At times I move my tray side guide in a little. If the stock comes into the lay guide to tight and gets pushed before the gripper lets go it will swim. The same is true about being to far away as the sheet has to drop into place from to far out. Frank is right about the front lay it must be square. If the front lay was tilted off center and you used the cheatters the stock may be to far out of position to register. The lay and head guide cant always fix the an untrue sheet feed. I found I have a hard time feeding a square sheet with guides. I use 1 to 1.5 ratio and it works fine. I cant feed a 4 x 4 but I can feed a 4 x 6 fine gripping the short side. Good luck you have some very smart folks that have answered your question already with good info and I am not one of those. I have learned that when things go wrong it is not always the press, it is generally me trying to make it do something it dont want to do.

One other thought, recently when printing heavy stock, the stock was being creased by the side lay and that was due to the sheets having a slight wave rather than being perfectly flat. Because of the wave the sheet was riding over the lay .
If you have the attachments and enough space in the non printing area you might be able to use the frisket which is really intended to help release the sheet after printng but might help before as well. Also I have found it better to have the side lay set to the centre position rather than too close to the platen. Hope this helps.

I have always wondered when the frisket makes contact. Is it after the sheet registers or before. If before, will it effective the ability of the sheets to drop into the guides. The issue you describe I have happen mainly on shorter sheet 3 - 4 inches but not longer ones. The bend in the sheet gets amplified when the gripper tilts away -especially on short sheets-at registration. My sheet tends to ride over the guide lay pin at times and mis- register. I made some shorter pins and it works bit like your idea also. We thought about using a frisket with soft mylar tip to act as a guide but not affect the sheet register just help it sit flat at the right time. I don’t know enough about the frisket

Thank you guys for the input, really appreciate that!

Will try to add thinner cheaters on the front lay (glue some polymer strips), will test and let you know about progress.

BTW miss-registration happens on different weights of stock.

Hi Victoria Please try to upload photos many times that helps to understand the situation

Hi,

Seems that I have moved forward in solving this bouncing problem.
Gripper tilt didn’t helped.

I have glued thin “cheaters” on the front lay and moved left paper support to right side, check out attached image (bigger image you can see here https://cl.ly/ac6726a1553c).
I didn’t print work with really tight registration, but I tried foil one color and seems that every impression goes in same place.

Anyway my question leaves unanswered - why, why one day that happens? Why grippers suddenly, without any reason, started to pick up paper too deep? And perfect, almost new, press stopped work like it should work.

@bppayne how you do gripper tilt? Maybe you mean suction unit tilt?

Is it any possibility to tilt front lay to front side?

solving_windmill_bouncing_problem.png

You say picking up to deep which does not make sense . Make sure your suction bar is not bent and the tension nob is tight. If running using rubber suckers try taking them off. Try adjusting your paper height to the point where it just picks up and no higher and then control it with the sucker tilt. If the paper is to high at the point of pickup it can cause a problem. There is a knob in the bottom photo showing the support. Make sure that nob is all the way clockwise and stays tight. My nob can move on it’s own which affects suction and I have to check it always. I don’t use cheaters with registration as the sheet arrives in the wrong spot. Feed a sheet part way into the press with each gripper bar and test pull it to make sure it is evenly tight on both bars. If they feel different the sheets may be slipping to much as they feed and the registration systems cannot correct it.

Watch to see that the feeder sheets are not drawn up and held by the sheet seperators. While that may cause the feeder to misread and stop, it may also continue and place the sheet forward of where it otherwise might go “biting deep”. Ensure, as you have already checked no doubt, that the paper curl all goes one way.

Hi,

Problem still persist. Seems that each second sheet bounce (check out this image https://cl.ly/0dd37f153338).

I found that each gripper picks up paper sheets differently (check out this image https://cl.ly/28fd983d0c71)
But I doubt that such small difference can be a reason of bouncing problem.

Any idea?

pick-up-gripper.jpg

I don’t see a guide on the right side of the stack. That may cause your sheets to kick a little. You dont need to run the right guide to tight but I always still put one in place to hold my sheets in a ready position. Try working with a very minimum amount of the strippers showing. You should be able to get by with 2. With a heavy stock you may not need them at all. Run at the slowest speed possible and watch your paper stack. You want to see if the sheet are ready to be picked up and at times speed can disrupt the next sheet to be fed and put it in a poor position for pickup and may cause it to misfeed. Try putting a paper wedge behind the stack. The idea is to lift the back of the sheet so as the suckers picks up the stock it makes it easier for sheet to level out before going into the press gripper. It may just be me, but I run a wedge or 2 behind every stack. You should see less drag as the stock pulls into the gripper and the stock is less likely to try to drop back off the suckers. Make sure your back springs are not to tight as it can fight the stock as it picks up. I always use 2 to hold the sheet square. I set an angle with the springs guides facing away from the top of pile as it is picked up. Make sure your spring guides don’t face into the pile above the pickup point as they might cause tension to the sheet to pull of the sucker after if has been pick it and try to knock it back off or release momentarily from the sucker.

I took of guide from right side of the stock to take better picture.

Looks like that on higher speed less bouncing.

Author - Worked hand in glove, with Heidelberg Platen & Cylinder Minder (machine manager) since early 60,s.

Picked up a few tips on the way, the following may be worth a try;-

When He is loading His stock, he not only >knocks it up<, prior to loading, but with blocks of less than 3/4” taps them gently with the Heels of the palm(s) into perfect contact with the forward Stanchion. of course with both side stanchions and usually as many as possible/practical Pen Steel separators.

Occasionally (with tricky stock) in the process of loading, He takes small blocks of stock 3/4” (ish) or 1/2 a ream and between both hands, (like a croupier bridging the deck of cards before dealing) puts some *AIR* into and between the sheets, appears to give better separation and aids the blast under. ??

Plus (once in a Blue Moon ?) have seen a fine braided, Copper Tail, hanging over the back edge of the stock to conduct the static away to earth, exactly as occasionally happens with small Litho press,s Multilith, Gestalith, Hamada, etc., etc.

1. Since You work with lay gauges registration on - there shouldn’t be a big problem if grippers pick sheets differently.
From what I see You need to check “flying Dutchman” to make every sheet stay at side guide.

2. Another quick hint I’m using to solve “bouncing back sheet” problem is applying some fine sandpaper on both front gauges. I mostly use P100 grit size but You need to test it individually. On thin paper I’m using higher grid size cause with P100 side guide smashes (more or less) the edge of the sheet due to high friction force between front guide and the edge of the sheet.

Still above methods will not answer what’s the origin of this sudden shift.

3. You’ve told that every second sheet bounces back off the side guide. From the picture above there is almost 3 mm difference on how deep the gripper picks each second sheet.
Not many reasons why it happens.
3.1. The gripper is bent. This can be tested with both of them when they are in the middle of delivering a sheet to delivery table (after press). Try manually open them and look whether the end of fixed part of gripper change it’s position. Mine were bent in such way that the gripper in the opening mode was kind of parabola.
3.2. The gripper is offset relative to its two fixing bolts. I’m not good in technical language but to make it easy both grippers have to be parallel to each other. Otherwise they will have different depth of sheet gripping.
Checking is easy - pick wide sheet (so that full gripper is used), draw a line when the gripper is closed after being picked. Open it. Correct gripper have the same depth on both sides of gripper.
3.3 The worst one. Read this (http://www.briarpress.org/44698#comment-66348)
3.4. The worst second. Gripper locking disc (T1406) can be overworn. Positioning of grippers is determined by the grooves in this disc. If the working side of groove is worn then the gripper will slightly change it’s position in space. Due to big arm it can be a 3 mm difference on the end of gripper.
This can be fixed by rotating that disc by 90 degrees. There are 4 grooves and only two are used. The remained ones are intact.

Why the sheet bounces? It might be that the gripping depth is so high (+ solid cardboard) that on a faulty gripper the edge of sheet actually hits side guide from above making it bounce back. If it were thin paper the side guide will just tear it when the guide pops up. But it’s only a guess.
In normal situation the edge of the sheet is 3-4 mm away from popping side guide.

windmill_locking_disc.png

windmill_gripper.png

This is not specific to your issue, however I have been able to figure out some very obscure issues in the past, especially when they are happening at speeds to fast to see. Take a video with your phone in slow motion. On my iPhone it is called “slo-mo” or something similar. When you play back, you may be amazed at the detail you are able to see, things that are impossible to see at full speed. It is obvious your problem is something very subtle. This may or may not help, but it can’t hurt, and it may help with future issues. Good Luck
Gil

Thank you guys, really useful info. Will check your suggestions @mick Hopper and @Gilman.

Yes, I meant the sucker bar tilt, not the gripper. Make sure both grippers are picking up the same amount of stock. That has been the cause of bouncing on my machine. Good luck.

I am not sure if you fixed this or not but here is something new to check. We thought our lay bar was bent so we have worked around that for some time. Sometimes it works sometimes not so good. The problem came back yesterday and I set out to fix it. I took both lay guides off and moved them to the far side so I could put them side by side. When laying a sheet into the guides I noticed it could not lay flat there was a little rock rather than a flat contact. One of my lay guides was dinged and a little twisted out of form. This gave one of the guides a high spot. I had an extra front lay guide and put it along side the other front guide and the sheet layed flat like it should. So I ran the job using 2 front lay guides and the problem went away. All this time my issue was a untrue lay guide. This is easy to check and not something we generally think of but makes a big difference.