TL;DR
Sheet misregister causes color-to-color misalignment. Check the front and side lays, sheet transfer timing, and gripper condition before adjusting register from the control panel.
What you might see
- color misregister visible at print edges
- register variation increasing through the run
- print shifted consistently in one direction
- fan-out in the sheet delivery section
Likely causes
Front lay stop wear allowing sheets to arrive at a varying MD position
Side guide not seating correctly, causing CD position variation
Gripper timing or force inconsistent, releasing the sheet early in the transfer
Feeder pile height variation causing sheet arrival timing to shift
Required tools
- Loupe or register measurement tool
- Replacement front lays (if worn)
- Feeler gauge for gripper force check
Safety first
- Keep hands clear of the feeder and impression cylinder area during test runs. The press runs at high sheet speed.
- Lock out the press before replacing lay stops or adjusting grippers inside the press.
Procedure
- 1
Pull 20 sheets from the delivery and measure color-to-color register deviation in both MD and CD. Determine if the deviation is systematic or random.[1]
- 2
Inspect the front lay stop surfaces for wear. Worn lays allow sheets to skid and over-travel. Replace worn lays.
- 3
Check the side guide adjustment. Confirm the guide seats the sheet against the fence with consistent force.
- 4
Inspect the gripper bars and gripper fingers for uniform closing force. Open and close the grippers manually at low speed and confirm uniform contact.[1]
- 5
Check the feeder pile height automatic control. An incorrect pile height changes the sheet arrival angle at the front lays.
- 6
Use the register fine-adjustment on the control panel to center the initial register.
- 7
Run 50 sheets after all mechanical corrections and measure register. Consistent register within specification confirms the root cause was mechanical, not print-related.
Sources
Heidelberg Heidelberg Speedmaster XL 106 / CX 102 Offset Press (Sheetfed / Web) general technical documentation, Heidelberg
Offset press sheet registration and feeder maintenance, general offset printing practice (general)
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