22" Didde Web Press - Inconsistent trim length

Discussion in 'Web-Presses' started by kgardner, Sep 30, 2009.

  1. kgardner

    kgardner New Member

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    Sep 2009
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    Location:
    H.O.T. Printing and Graphics - NW Ohio, USA
    I'm trying to help our press room manager troubleshoot an issue we have been having for a long time with our 22" Didde web press. If any other info is needed to help troubleshoot just let me know and I'll update with the info needed. That being said....here's the problem.

    We run 8.5"x11" statement shells on an 11" and 22" Didde press. When running on the 22" press if the pressmen turn the speed up on the press we are getting inconsistent trims (1 set of 2 forms would be trimmed long and the other set would be trimmed short). If we run the press at a slower speed everything is okay and the trims are consistent. Just wanted to see if we could troubleshoot before having to call in a Didde press tech.

    Any suggestions??

    Thanks,
    KG
     
  2. francisco delizo

    francisco delizo New Member

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    Oct 2009
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    Location:
    edmonton alberta
    suggestion

    hi i think theres a few things you could check to remedy your problem you should look into your web tension, check how tight your pull wheels are pulling by the delivery before the delivery blades or if worn out
    replace it to keep a consistent pull of your web and check on the gear side by the delivery sheeter if your main delivery drive belt is not worn out :)
     
  3. kgardner

    kgardner New Member

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    Location:
    H.O.T. Printing and Graphics - NW Ohio, USA
    Hi Francisco,

    Thanks for the reply. I checked with our pressmen and he said that they have checked the web tension and pull wheels and also the blades. He also said that the drive belt is not worn out but said that there IS some play in the gears of the delivery sheeter. Could the play in gears be causing this problem?

    Thanks,
    KG
     
  4. nosefo

    nosefo Member

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    Location:
    Norway,Stavanger
    Can you please answer my questions below. Then I can get a better picture of your problem.
    Are you using a cut off cylinder with one knife or two knifes?
    Do you have a fixed under knife?

    I Have a couple of solutions but it depends on your answers above.

    But here are some ideas so far:
    As Francisco wrote to you earlier, I do also belive that your problem are the pulling wheels in front of the sheeter. We have the same "problem" in our press if we feed the pullingwheels with to much air pressure. You should try to use as little pressure on these wheels as possible. Just enought to transport the paper.

    Why the pulling wheels are the problem?
    They are often fixed over a overfeeding roller/cylinder to avoid low web tension. These overfeeding rollers should not drag the paper with full torque, but they are capable to do that if you "lock" the paper aginst it. If you use to much pressure on the pullingwheels you do lock the paper and you will have a problem with the cut of lenght. You then drag the paper like a rubberband until the web tension are so tight that it overcome the force of the pullingwheels. Then your web will bounce/jump backwards some 1/10 of a mm (I have seen as much as 1mm when running thick and strong paper). This will cause differnet cutting lenght of the paper.

    Why the cut off lenght are constant when running on low speed?
    Then the web tension have more "time"to correct itself. The slippery effect between the pulling wheels and the roller do have a better effect then.

    Be awere that the backslip can be triggered by a "hard" knife. Put a light hand on the web just in front of the sheeter (30-50cm). If you can feel a vibration (dropping web) when the knife cut, you should adjust your knifes. We have just resharpened our knifes and now we can almost not hear when the knife cut the paper, and the vibration (dropping web) is gone. Good investment and a much better cutting edge on the paper.
     
  5. JOHN RADMILOVIC

    JOHN RADMILOVIC New Member

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    May 2010
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    Location:
    wales uk
    I don`t agree with pull wheel theory, knife setting is critical you should hear a small tick when set correctly,also check drive gears they are of a split
    design which enables operator to compensate for play or wear in gear train, having said that, the previous owner of our press sold it because of this
    very issue ,with care and correct settings the problem is almost eliminated.
     
  6. graphix emporium

    graphix emporium Member

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    Location:
    sydney
    crock of ****, its probably a stuffed clutch in your variation drive gearbox sunshine, that's what gives you drive tension on those old farts before the pull wheels are even brought into to it. use to kill with my eyes closed when i was an apprentice 30 years ago :) they never changed.... go old school milwaukee litho blues! I still love the piece of craps though, you can't kill em! :)
     
  7. graphix emporium

    graphix emporium Member

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    Location:
    sydney
    the 11" ones come out first and they where the base model for the 22's. they didn't change too much for as much as up scaled everything for the 22's and the variation clutches are pretty much the same on both. It mainly shows it's face when your fan folding or cutting off. They have about a 8 year turn around on the clutches from stock but most bodz don't know that so it causes hell for everyone for ever after until they eventually get done by chance years down the track.... :) good luck finding a local that can re-skin too!
     
  8. controlgraphics

    controlgraphics Senior Member

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    Apr 2011
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    160
    Location:
    Chicago,USA
    It may have to do with your feedback tach generator, the item that maintains a selected speed constant. We are controlgraphicsUSA, a provider of technical services and parts for the printing and convertiing industry. You can contact us with any technical questions or parts requests at controlgraphics@sbcglobal.net
     

  9. HPC

    HPC Senior Member

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    Apr 2011
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    Location:
    Illinois
    Did the pressman check per the manual? 20# 1 inch strip to pull but not break to set pulls. I'd also check to see if its sheeting off crooked, you can cut a sheet crooked, just take two sheets face to face, if not squared its cutting crooked. Your snaps may be worn or springs broken. Typically, a didde will have slop in the gears, this will get better the faster ya run her. As said earlier, sharp blades are important. If they bang your bending the edge of the paper.

    Also, is the dancer in the rollstand holding steady? At higher speeds if it goes up and down due to a brake problem this will cause different size sheets.
     
    Last edited: Apr 21, 2011
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