Grippers loosing paper

Hello,
I’m having this problem with our Heidelberg windmill where the paper grippers are loosing every second or third paper in the middle of the run when I am not using the impression. The same thing happens also whenever I put the impression on, but only for the first paper that goes through the press!
I first thought the problem was a tacky form that causes this but now that I noticed that the problem occures also when not using the impression, it seems to be something else?
I saw this older discussion about this same thing (http://www.briarpress.org/32201) and have checked the grippers and they seem to be straight/parallel. I also checked the other Windmill we have and that works perfectly and the grippers looks just the same.
Please note that there is no such problem with impression on as soon as I get over the first paper that drops… UNTIL there is a need to take the impression off and put it back on… then again the first paper drops out in the middle.
This problem came now that I’m using a little bit thinner paper than before (thickness 0,02756inch so not actually thin at all).
If the gripper happens to take two papers instead of one, they go through with no problem (= thicker load).
So it has something to do with this thin/thick paper thing?
With this machine we are running with the Guides on and the paper feed table is moved to the left as it should.
What should I do to get rid of this problem? Any help?
Thank you!

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Ramblings from afar! completely irrelevant maybe, but who knows.?
Re the second line of Your post, i.e. *every second or third* sheet/paper, perhaps every ALTERNATE sheet from one gripper out of Sync. and/or one opposing gripper (of the two) with the Fingers Mal-adjusted, contact pads under the springs *beat up*?? etc.

probably complete rubbish, but elimination may help. Mick.

probably too much bother to swap over the grippers on machines to see if problem is which press or which set grippers?

Try putting some tape on the inside of the gripper. That might provide the thickness you need to correctly grab the sheet. Make sure the feedboard is completely parallel to the grippers. I had some issues for awhile and realized the feedboard was off parallel. Once I reset it, my feeding issues went away.

j

Hi, have you checked the rubber pads in the grippers? I often print on paper stock, about 0.005 - 0.007” without trouble, have you tried stock that thin? You could with the help of a friend turn the power off and turn the press by hand and feed a thin sheet into the gripper and see if it holds if you gently pull the sheet. I have seen on Briar Press somebody suggest checking the gripper springs to see if any are broken. Another thing ,on the grippers hinge side are some very small holes, they are not coloured for lubrication but I keep them clean from anti-set off powder and give them a tiny drop of oil. Just a few thoughts.

Thank you all for your replys!
Masking tape did not help (I maybe have to try again with more layers of it to get better result).
The grip is good with both grippers and they both seem to do this same thing (so it’s not about only one gripper). But I will have to try this with even thinner paper like Frank suggested.
The grippers in this machine are more worn out than in the other (the lower parts are like blades with small scratches). There is about 0,19inch strip of metal before the rubberparts begin while in the other machine the rubbeparts comes all the way to the edge of the grippers (I assume the rubber has worn out from there).
And we do give some oil also to those small holes regularily.
I will doublecheck the feedboard and yes, swapping those other grippers to this machine is a great idea (if it is something that can be done without doing any harm for the machines).

I’ll let you know as soon as I get some results.

Swapping over the Grippers? - - - Might be like opening a *Can of Worms* i.e. over the course of time (usually) they are adjusted individually for the Grip, via the double ended adjusters for each gripper arm, but the opposing pair are actuated from a common cam on the Head/Hub.
If it is decided to experiment and swap, the very least would be to mark (A) to (A) and (B) to (B) for correct replacement BUT then the independent/individual adjusters will probably have to be disturbed for snychoronisation, which is difficult enough in itself and not lightly taken on.!

Perhaps look up page 110 in the *On LIne* operations manual for replacement of the Contact Strip(s) and *Grip* test method,s.
One tip which may not be in the manual (for safety reasons possibly)? with the M/c. switched OFF and the grippers in the horizontal mode, with the *HEEL* of the palm of the hand, depressing the transverse operating rod for the pair of grippers, they can be opened, for test Grips and fitting Rubber strips, without removing the Arms.!

TEST GRIPS, with *Slivers* of thinnest stock as Feeler Gauges, we have in the past, (when all else has failed) resorted to using double sided, >Manicure< Emery boards, to fine tune the GRIP along the length of the gripper, of course, masking out the coarse side, of the Emery Board,!!!

Again, swapping over for experiments, try to make sure there is the means to resort to original configuration, as in (A) to (A) etc., and *Tippex* or Red/Yellow printing ink marks for the amount of movements on the adjuster links.

Good Luck. Mick.

Yeah, I’m just a new guy with these machines so I’m not gonna make any big experiments and/or adjustments for these. No worries:)

I have now tested the grippers with really thin paper and both grippers held the paper just as well as they do with thicker paper. I also put some more masking tape to the grippers and have now printed abt 2000 cards and here’s what I know.
The problem is in the moment where the paper should get back to the gripping arm after the arm opens for a short moment and paper drops to the guides. BUT now the problem occurs only when the impression is not on. That’s when the paper stays on the guiding bar and the gripper continues its way empty.
When I have the impression on, all goes smoothly, except that the first paper gets always wrongly placed so that the printed figure is not where it should be (ther’s abt 1inch mispositioning). AND these papers (the first ones to go through the press when the impression has put on) all gets a small dent/notch, that comes from the sideguide to the (front)end of the sheet. From the second card on, everything is just fine until I take the impression off.

I have had the denting issue and by moving the side guide a fraction out has overcome the problem. It seems as if the sheet is too far forward in the feeder stack. By landing on the side guide when not on impression the sheet just falls out when not held by the gripper.

Have you tried turning over the press by hand, slowly, once the paper is in the gripper- to see where your issues may be in the chain of operations? Or inching the press at a really low speed, just to observe the register guides in relation to the paper?

As had been mentioned- if you open the side guide all the way you may find the paper lays better w/r/t the slot in the gripper, and small adjustments in by trial allow you to find the point at which it would stop laying correctly against the side guide.

What kind of speed are you operating the machine at?
I always found that the higher the speed, the more difficult it is to get the paper to do what it ‘should’, but the trade-off is that the ink works better (for me) at higher speeds.
I’m always trying new tricks to get the sheet to lay correctly, avoid bounce, etc.

Good thoughts Frank and Haven,not sure that is the problem. I have what sounds like the same problem. On start up the first sheet feed thru the press with impression on will not be in location, it will be towards the flywheel. After that every sheet in the feeder will be dead on. I think is has something to do with the air some how. If I shut down the press without a sheet in the gripper the next to pick up will not be in location, but if I stop it with a sheet in the gripper I can let it sit for hours and it will locate.

Thanks to Frank, my problem seems to be solved now.
I moved the sideguide a little bit more out and after that everything went just fine (at least today). Simple as that.
Thanks everyone!

Valterri- glad you found the solution to this problem. Have you noted that you can still make some small lateral adjustment, or are you stuck with the side-guide in the same position? I guess you could always pull the chase and move the form small amounts if so.

JFeltz- this is interesting knowledge to acquire! If I am understanding you correctly…

So one could turn the press on, and with the flywheel up to speed- feed the press, potentially, with the impression lever off- wait for a sheet to be fed proper into the gripper- and then turn the impression on, in order to get past this hiccup?