Return tapes buckling trailing edge of sheet

We have a Uni 1 PAB with the automatic tape sheet delivery tower. When using the return tapes, particularly with short sheets, the sheets get buckled on the trailing edge and can hang up or get mangled by the form. The pdf Uni 1 manual states:

Caution

When using the Automatic Tape Sheet Delivery, the cylinder sheet fingers are not required and they must be adjusted to the positions nearest the cylinder be<missing> sheet fingers are left in the printing area when using Automatic Tape Sheet Delivery, they may buckle the sheet on its return travel, which may cause it to hit the form.

Sounds like this may be our problem but I have no idea what they are talking about. Might someone enlighten me?

Thanks in advance for any advice.

6 thoughts on “Return tapes buckling trailing edge of sheet

  1. John Henry - December 18, 2021

    Check to see that the tapes are slightly wider on the upper drum than the front attachment to the bar at the printing cylinder. This may help to pull out the edges of the sheet. If the tapes are narrower on the upper cylinder, they can pull in the edges of the sheet and cause the slight pucker you are seeing.

    Do you have enough border to run the tapes further in on the sheet? That might assist a bit. You also could attach a sheet to the tapes and cut out the areas for the image to print through. This will act as a frisket to hold the sheet down on all sides (keep the frisket back from the grippers a bit or cut out the gripper area so the sheet doesn’t wrinkle).

    John Henry
    Cedar creek Press

  2. tomcolson - December 17, 2021

    Sorry it took me so long to post this. The pin and spring are installed, the ratchet pawl is engaged, and there is sufficient tension on the tapes to hold the sheet tight against the cylinder at the edges of the sheet. Still seeing this amount of bulging up in the center of the trailing edge of the sheet.

    I also checked that the tapes were wound properly around the drum in line with the positioning clamp. Moving them in and out on the sheet had no effect.

    Still stumped!

    https://vandercookpress.info/wp-content/uploads/2021/12/Automatic.mp4

  3. The Arm NYC - November 29, 2021

    Is this a heavy paper stock, or heavy ink coverage on a lighter one?

    Have you tried cranking a bit more tension on the tower ratchet? The tapes need to keep the sheet smooth to the cylinder. It sounds like they are failing to do this. It can be from the paper fighting to conform to the curvature of the cylinder, or it can be from ink tack not releasing it from the forme.

    DGM

  4. Paul Moxon, Moderator - November 21, 2021

    The tower is probably not rotating during carriage travel.
    Is the ratchet and pawl engaged?
    Check that the U-shaped spring and pin is in place (operator’s side of spoll)

    A video would help.

  5. tomcolson - November 20, 2021

    Thanks Paul. Our tapes appear to be installed correctly. Still mystified as to what’s going on.

  6. Paul Moxon, Moderator - November 20, 2021

    …. they must be adjusted to the positions nearest the cylinder bearers. If sheet fingers …

    The tapes may not be wound around the cylinder correctly. On the Universal I the tapes wind counterclockwise around the tower cylinder while the Universal III tapes wind clockwise. See attached image.

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